Current Search: Cattafesta, Louis N. (x)
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 Title
 Unsteady Characteristics Of A Slatcove Flow Field.
 Creator

Pascioni, Kyle A., Cattafesta, Louis N.
 Abstract/Description

The leadingedge slat of a multielement wing is a significant contributor to the acoustic signature of an aircraft during the approach phase of the flight path. An experimental study of the twodimensional 30P30N geometry is undertaken to further understand the flow physics and specific noise source mechanisms. The mean statistics from particle image velocimetry (PIV) shows the differences in the flow field with angle of attack, including the interaction between the cove and trailingedge...
Show moreThe leadingedge slat of a multielement wing is a significant contributor to the acoustic signature of an aircraft during the approach phase of the flight path. An experimental study of the twodimensional 30P30N geometry is undertaken to further understand the flow physics and specific noise source mechanisms. The mean statistics from particle image velocimetry (PIV) shows the differences in the flow field with angle of attack, including the interaction between the cove and trailingedge flow. Phaselocked PIV successfully links narrowband peaks found in the surface pressure spectrum to shear layer instabilities and also reveals that a bulk cove oscillation at a Strouhal number based on a slat chord of 0.15 exists, indicative of shear layer flapping. Unsteady surface pressure measurements are documented and used to estimate spanwise coherence length scales. A narrowband frequency prediction scheme is also tested and found to agree well with the data. Furthermore, higherorder spectral analysis suggests that nonlinear effects cause additional peaks to arise in the power spectrum, particularly at low angles of attack.
Show less  Date Issued
 20180329
 Identifier
 FSU_libsubv1_wos_000428659900002, 10.1103/PhysRevFluids.3.034607
 Format
 Citation
 Title
 Characterization of Supersonic Flow Around a Hemispherical Model.
 Creator

Carnrike, Daniel Andrew, Kumar, Rajan, Cattafesta, Louis N., Collins, E. (Emmanuel), Florida State University, College of Engineering, Department of Mechanical Engineering
 Abstract/Description

Propagation of laser beams through complex flow field caused by radar system housing has been an important topic for many years dating back to the mid 1960s. Applications for radar systems range from missile defense, directed energy to target designation and tracking. Complications are introduced when laser systems are no longer stationed on the ground, but instead mounted on airplanes traveling at subsonic, transonic and supersonic speeds. Housing systems have been developed with a variety...
Show morePropagation of laser beams through complex flow field caused by radar system housing has been an important topic for many years dating back to the mid 1960s. Applications for radar systems range from missile defense, directed energy to target designation and tracking. Complications are introduced when laser systems are no longer stationed on the ground, but instead mounted on airplanes traveling at subsonic, transonic and supersonic speeds. Housing systems have been developed with a variety of different designs with some designs more optimal for decreasing laser aberrations than others. The work presented strives to characterize flow around a hemispherical configuration (D = 10.16 cm) for a turret housing system in the supersonic flow regime. Multiple diagnostic tests were conducted at the Florida Center for Advanced AeroPropulsion in the Polysonic Wind Tunnel Facility. Shadowgraph visualization, surface oil flow visualization, static pressure and unsteady pressure data characterized the complicated supersonic flow field around a hemisphere. Observations were conducted at Mach 2 while Reynolds number changed, ReD = 1.8 ∗ 106 and ReD = 3.6 ∗ 106. Complex shock system consisting of a lambda shock and detached bow shock were observed upstream of the hemisphere center through shadowgraph images. While a shocklet system was developed between the foot of the lambda shock and the detached bow shock from the unsteady boundary layer shockwave interaction. Surface oil flow visualization accented the development of an axisymmetric horseshoe vortex and the presence of a secondary shock location upstream of the hemisphere. A centerline static pressure distribution quantified the visualization techniques. A stagnation point of 30◦ was observed on the body for both ReD case. While, flow separation occurred at slightly different locations on the hemisphere; flow separated at 103◦ for ReD = 1.8∗106 and 107◦ for the ReD = 3.6 ∗ 106. Location of flow separation is further strengthen by the unsteady pressure data as the energy fluctuations are less on the separation line for the different Re cases. The study found that flow structures for different ReD cases were similar, except for the strength of the different flow features; as the flow feature magnitudes were greater for ReD = 3.6 ∗ 106 case. Also observed from the unsteady pressure measurement data, the wake structure behind the hemisphere were different in nature as the wake structure for the ReD = 1.8 ∗ 106 case was larger than the ReD = 3.6 ∗ 106 case. Planar Particle Image Velocimetry was conducted in the Pilot Wind Tunnel Facility at the Florida Center for Advanced AeroPropulsion on a dynamically similar flow (M = 2,ReD = 1.8∗106). Planar PIV for different Z/D planes were also measured on a D = 19.05 mm hemisphere, which highlighted the presence of an expansion fan at the apex of the hemisphere with decreasing effects on the external flow field as flow moved further away from the centerline of the hemisphere. The results presented in this work characterized supersonic flow around a hemisphere and has laid the groundwork for the development of active or passive flow control techniques in order to minimize flow structures, which ultimately lead to less aerooptical aberrations.
Show less  Date Issued
 2017
 Identifier
 FSU_FALL2017_Carnrike_fsu_0071N_14262
 Format
 Thesis
 Title
 Global Stability Analysis and Control of Compressible Flows over Rectangular Cavities.
 Creator

Sun, Yiyang, Taira, Kunihiko, Yu, Weikuan, Cattafesta, Louis N., Ukeiley, Lawrence S., Lin, Shangchao, Florida State University, College of Engineering, Department of Mechanical...
Show moreSun, Yiyang, Taira, Kunihiko, Yu, Weikuan, Cattafesta, Louis N., Ukeiley, Lawrence S., Lin, Shangchao, Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

The present numerical investigation aims to uncover the inherent instability in compressible cavity flows and aid designs of effective flow control to alter undesirable flow features. Twodimensional (2D) and threedimensional (3D) global stabilities of compressible opencavity flows are examined in detail, which provides insights into designs of active flow control to reduce the pressure fluctuations over the cavity. The stability characteristics of compressible spanwiseperiodic opencavity...
Show moreThe present numerical investigation aims to uncover the inherent instability in compressible cavity flows and aid designs of effective flow control to alter undesirable flow features. Twodimensional (2D) and threedimensional (3D) global stabilities of compressible opencavity flows are examined in detail, which provides insights into designs of active flow control to reduce the pressure fluctuations over the cavity. The stability characteristics of compressible spanwiseperiodic opencavity flows are investigated with direct numerical simulation (DNS) and biglobal stability analysis for rectangular cavities with lengthtodepth ratios of $L/D=2$ and 6. This study examines the behavior of instabilities with respect to stable and unstable steady states in the laminar regimes for subsonic as well as transonic conditions where compressibility plays an important role. It is observed that an increase in Mach number destabilizes the flow in the subsonic regime and stabilizes the flow in the transonic regime. Biglobal stability analysis for spanwiseperiodic flows over rectangular cavities with large aspect ratio is closely examined in this study due to its importance in aerodynamic applications. Moreover, biglobal stability analysis is conducted to extract 2D and 3D eigenmodes for prescribed spanwise wavelengths $\lambda/D$ about the 2D steady state. The properties of 2D eigenmodes agree well with those observed in the 2D DNS. In the analysis of 3D eigenmodes, it is found that an increase of Mach number stabilizes dominant 3D eigenmodes. For a short cavity with $L/D=2$, the 3D eigenmodes primarily stem from centrifugal instabilities. For a long cavity with $L/D=6$, other types of eigenmodes appear whose structures extend from the aftregion to the midregion of the cavity, in addition to the centrifugal stability mode located in the rear part of the cavity. A selected number of 3D DNS are performed at $M_\infty=0.6$ for cavities with $L/D=2$ and 6. For $L/D=2$, the properties of 3D structures present in the 3D nonlinear flow correspond closely to those obtained from linear stability analysis. However, for $L/D=6$, the 3D eigenmodes cannot be clearly observed in the 3D DNS, due to the strong nonlinearity that develops over the length of the cavity. In addition, it is noted that threedimensionality in the flow helps alleviate violent oscillations for the long cavity. The analysis performed in this paper can provide valuable insights for designing effective flow control strategies to suppress undesirable aerodynamic and pressure fluctuations in compressible opencavity flows. Threedimensional nonlinear simulations (DNS and LES) are also conducted to examine influence of cavity width, sidewall boundary conditions, free stream Mach numbers, and Reynolds numbers on opencavity flows. DNS and large eddy simulations (LES) are performed with $L/D=6$, widthtodepth ratios of $W/D$=1 and 2 for Reynolds number of $Re_D = 502$ and $10^4$. To numerically study the effects of cavity width on the flows, we consider (1) 2D cavities with spanwise periodicity and (2) finitespan cavities with noslip adiabatic walls. Furthermore, the analyses are conducted for subsonic ($M_\infty=0.6$) and supersonic ($M_\infty=1.4$) speeds to reveal compressibility effects. It is found that, at low $Re_D=502$, widening the cavity can decrease the velocity fluctuations of the flow by introducing spanwise variations in the shear layer to reduce the kinetic energy from spanwise vortices associated with Rossiter modes. Both velocity and pressure fluctuations decrease in the finitespan cavity compared to those with spanwise periodic boundary conditions. With the characteristics of base flows revealed, flow control is implemented for turbulent cavity flows where steady blowing is introduced along the leading edge of the cavity for both subsonic ($M_\infty=0.6$) and supersonic ($M_\infty=1.4$) flows. We examine how the actuations interact with the flows and reduce the velocity and pressure fluctuations with and without sidewalls. From the control study, we find that pressure reduction on the cavity surfaces can be achieved in an effective manner by taking advantage of 3D flow physics.
Show less  Date Issued
 2017
 Identifier
 FSU_FALL2017_Sun_fsu_0071E_14244
 Format
 Thesis
 Title
 Three Dimensional Control of HighSpeed Cavity Flow Oscillations.
 Creator

Zhang, Yang, Cattafesta, Louis N., Tam, Christopher K. W., Taira, Kunihiko, Collins, E. (Emmanuel), Florida State University, College of Engineering, Department of Mechanical...
Show moreZhang, Yang, Cattafesta, Louis N., Tam, Christopher K. W., Taira, Kunihiko, Collins, E. (Emmanuel), Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Cavity structures, like weapons bays and landing gear wells on aircraft, suffer from severe oscillations under high speed flow conditions. These oscillations are associated with intense surface pressure/velocity fluctuations inside the cavity which can radiate strong acoustic waves and cause structural damage. The physics of cavity flows have been studied for several decades with much of the effort put towards flow controls to reduce these oscillations. Geometric modifications of the cavity...
Show moreCavity structures, like weapons bays and landing gear wells on aircraft, suffer from severe oscillations under high speed flow conditions. These oscillations are associated with intense surface pressure/velocity fluctuations inside the cavity which can radiate strong acoustic waves and cause structural damage. The physics of cavity flows have been studied for several decades with much of the effort put towards flow controls to reduce these oscillations. Geometric modifications of the cavity structure are usually only effective for suppressing the oscillations within the designed flow conditions. Therefore, active flow control is more attractive for a wider application range. Previous research have proven that mass/momentum injection at the cavity leading edge can effectively suppress the pressure/velocity fluctuations. Due to the limited control authorities of current actuators, a steady actuation which introduces threedimensional disturbances is studied to reduce the energy requirements of the actuator and improve the suppression of the oscillations over a wide range of freestream Mach numbers. Surface fluctuating pressure measurements are acquired to determine the control performances of a number of 3D actuation configurations. Flow fields, including velocity fields and density gradient fields, are measured to reveal the flow features with and without the flow control. Mathematical methods, including modal decomposition analysis, are further applied to study the dynamics of the flow field. All of these analyses together elucidate the effective 3D actuation mechanism in the cavity flow control. The suppression of pressure fluctuations are obtained in both fullspan and finitespan cavities. The successful flow control is found to be the redistribution of the energy in the shear layer by the counterrotatingvortex pairs, which are introduced by the 3D actuation in the crossflow. In addition, a design guide for the actuator geometry is given based on the observations.
Show less  Date Issued
 2017
 Identifier
 FSU_FALL2017_ZHANG_fsu_0071E_14127
 Format
 Thesis
 Title
 Flow Physics and Nonlinear Dynamics of Separated Flows Subject to ZNMFBased Control.
 Creator

Deem, Eric Anthony, Cattafesta, Louis N., Sussman, Mark, Taira, Kunihiko, Collins, E., Moore, Matthew Nicholas J., Hemati, Maziar, Florida State University, College of...
Show moreDeem, Eric Anthony, Cattafesta, Louis N., Sussman, Mark, Taira, Kunihiko, Collins, E., Moore, Matthew Nicholas J., Hemati, Maziar, Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Aircraft, turbomachinery, wind turbines, and other systems that generate or rely on aerodynamic forces are designed to operate most efficiently when flows are fully attached. However, especially due to increasing offdesign performance requirements, there is significant risk of inefficient operation or failure due to flow separation. This work formulates a procedure for extending the performance envelope of many fluidic systems by delaying flow separation through real time separated flow...
Show moreAircraft, turbomachinery, wind turbines, and other systems that generate or rely on aerodynamic forces are designed to operate most efficiently when flows are fully attached. However, especially due to increasing offdesign performance requirements, there is significant risk of inefficient operation or failure due to flow separation. This work formulates a procedure for extending the performance envelope of many fluidic systems by delaying flow separation through real time separated flow state estimation and control. The history of active separation control is rich; however the approach presented here is novel in that it employs "real time" dynamical system updates to track nonlinear variations in the flow and provide robustness to flow state conditions. First, the dynamics of the canonical laminar separated flow over a flat plate at Rec=10⁵ are characterized by employing fullfield, timeresolved PIV and unsteady surface pressure measurements. Dynamic Mode Decomposition (DMD) is employed on the high dimensional PIV velocity fields to identify the dynamically relevant spatial structure and temporal characteristics of the separated flow. Then, results of various cases of openloop control using a zeronet mass flux actuator slot located just upstream of separation are presented that show separation reduction occurs for the employed actuation method. Real time estimates of the dynamical characteristics are provided by performing online DMD on measurements from a linear array of unsteady surface pressure transducers. The results show that online DMD of the pressure measurements provides reliable estimates of the modal characteristics of the separated flow subject to forcing. Furthermore, the dynamical estimates are updated at a rate commensurate with the characteristic time scales of the flow. Therefore, as the separated flow reacts to the applied forcing, online DMD applied to the surface pressure measurements provides a timevarying linear estimate of the evolution of the flow. Building upon these results, methods for adaptive control of flow separation based on the model provided by online DMD are formulated and implemented on the separated flow. Feedback control is implemented in which Linear Quadratic Regulator gains are computed recursively as the model provided by online DMD is updated. This physicsmotivated, autonomous approach results in more efficient flow reattachment, requiring approximately 30% less actuator effort as compared with the commensurate open loop forcing case. Since this approach relies solely on observations of the separated flow, it is robust to variable flow conditions. Additionally, this approach does not require prior knowledge of the characteristics of the separated flow.
Show less  Date Issued
 2018
 Identifier
 2018_Su_Deem_fsu_0071E_14530
 Format
 Thesis
 Title
 NetworkTheoretic and DataBased Analysis and Control of Unsteady Fluid Flows.
 Creator

Nair, Aditya Gopimohan, Taira, Kunihiko, Sussman, Mark, Cattafesta, Louis N., Oates, William, Alvi, Farrukh S., Brunton, Steven L. (Steven Lee), Florida State University,...
Show moreNair, Aditya Gopimohan, Taira, Kunihiko, Sussman, Mark, Cattafesta, Louis N., Oates, William, Alvi, Farrukh S., Brunton, Steven L. (Steven Lee), Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Unsteady fluid flows have complex dynamics due to the nonlinear interactions amongst vortical elements. In this thesis, a networktheoretic framework is developed to describe vortical and modal (coherent structure) interactions in unsteady fluid flows. A sparsifieddynamics model and a networkedoscillator model describe the complex dynamics in fluid flows in terms of vortical and modal networks, respectively. Based on the characterized network interactions, modelbased feedback control laws...
Show moreUnsteady fluid flows have complex dynamics due to the nonlinear interactions amongst vortical elements. In this thesis, a networktheoretic framework is developed to describe vortical and modal (coherent structure) interactions in unsteady fluid flows. A sparsifieddynamics model and a networkedoscillator model describe the complex dynamics in fluid flows in terms of vortical and modal networks, respectively. Based on the characterized network interactions, modelbased feedback control laws are established, particularly for controlling the flow unsteadiness. Furthermore, to characterize modelfree feedback control laws for suppressing flow separation in turbulent flows, a datadriven approach leveraging unsupervised clustering is developed. This approach alters the Markov transition dynamics of fluid flow trajectories in an optimal manner using a clusterbased control strategy. To describe vortical interactions, dense fluid flow graphs are constructed using discrete point vortices as nodes and induced velocity as edge weights. Sparsification techniques are then employed on these graph representations based on spectral graph theory to construct sparse graphs of the overall vortical interactions which maintain similar spectral properties as the original setup. Utilizing the sparse vortical graphs, a sparsifieddynamics model is developed which drastically reduces the computational cost to predict the dynamical behavior of vortices, sharing characteristics of reducedorder models. The model retains the nonlinearity of the interactions and also conserves the invariants of discrete vortex dynamics. The network structure of vortical interactions in twodimensional incompressible homogeneous turbulence is then characterized. The strength distribution of the turbulence network reveals an underlying scalefree structure that describes how vortical structures are interconnected. Strong vortices serve as network hubs with smaller and weaker eddies predominantly influenced by the neighboring hubs. The time evolution of the fluid flow network informs us that the scalefree property is sustained until dissipation overtakes the flow physics. The types of perturbations that turbulence network is resilient against is also examined. To describe modal interactions in fluid flows, a networkedoscillatorbased analysis is performed. The analysis examines and controls the transfer of kinetic energy for periodic bluff body flows. The dynamics of energy fluctuations in the flow field are described by a set of oscillators defined by conjugate pairs of spatial POD modes. To extract the network of interactions among oscillators, impulse responses of the oscillators to amplitude and phase perturbations are tracked. Using linear regression techniques, a networked oscillator model is constructed that reveals energy exchanges among the modes. In particular, a large collection of system responses are aggregated to capture the general network structure of oscillator interactions. The present networked oscillator model describes the modal perturbation dynamics more accurately than the empirical Galerkin reducedorder model. The linear network model for nonlinear dynamics is subsequently utilized to design a modelbased feedback controller. The controller suppresses the modal fluctuations and amplitudes that result in wake unsteadiness leading to drag reduction. The strength of the approach is demonstrated for a canonical example of twodimensional unsteady flow over a circular cylinder. The networkbased formulation enables the characterization and control of modal interactions to control fundamental energy transfers in unsteady bluff body flows. Finally, unsupervised clustering and datadriven optimization of coarsegrained control laws is leveraged to manipulate poststall separated flows. Optimized feedback control laws are deduced in highfidelity simulations in an automated, modelfree manner. The approach partitions the baseline flow trajectories into clusters, which corresponds to a characteristic coarsegrained phase in a lowdimensional feature space constituted by feature variables (sensor measurements). The feedback control law is then sought for each and every cluster state which is iteratively evaluated and optimized to minimize aerodynamic power and actuation power input. The control optimally transforms the Markov transition network associated with the baseline trajectories to achieve desired performance objectives. The approach is applied to two and threedimensional separated flows over a NACA 0012 airfoil at an angle of attack of 9° Reynolds number Re = 23000 and freestream Mach number M∞ = 0.3. The optimized control law minimizes power consumption for flight enabling flow to reach a lowdrag state. The analysis provides insights for feedback flow control of complex systems characterizing global clusterbased control laws based on a datadriven, lowdimensional characterization of fluid flow trajectories. In summary, this thesis develops a novel networktheoretic and databased framework for analyzing and controlling fluid flows. The framework incorporates advanced mathematical principles from network science, graph theory and dynamical systems to extract fundamental interactions in fluid flows. On manipulating these interactions, wake unsteadiness in bluff body flow is reduced leading to drag reduction. Finally, databased methods are developed to deduce optimal feedback control laws for poststall separated flows. The networktheoretic and databased approaches provides insights on fundamental interactions in fluid flows which paves the way for design of novel flow control strategies.
Show less  Date Issued
 2018
 Identifier
 2018_Su_Nair_fsu_0071E_14745
 Format
 Thesis
 Title
 Use of Resolvent Analysis for Design of Active Separation Control with ThermalBased Actuators.
 Creator

Yeh, ChiAn, Taira, Kunihiko, Tam, Christopher K. W., Cattafesta, Louis N., Alvi, Farrukh S., Oates, William, Florida State University, College of Engineering, Department of...
Show moreYeh, ChiAn, Taira, Kunihiko, Tam, Christopher K. W., Cattafesta, Louis N., Alvi, Farrukh S., Oates, William, Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

This study aims to examine the use of a fundamental thermal input for separation control and provide a design guideline via resolvent analysis. The use of the thermal actuator is motivated by the interest in the use of thermalenergybased actuators from the active flow control community. We conduct a series of numerical investigations to uncover the underlying control mechanism of thermalenergybased actuators and examine their control effectiveness when a fundamental thermal energy source...
Show moreThis study aims to examine the use of a fundamental thermal input for separation control and provide a design guideline via resolvent analysis. The use of the thermal actuator is motivated by the interest in the use of thermalenergybased actuators from the active flow control community. We conduct a series of numerical investigations to uncover the underlying control mechanism of thermalenergybased actuators and examine their control effectiveness when a fundamental thermal energy source is introduced as the only external perturbation. We consider a thermal actuator model that introduces localized boundary actuation in the form of unsteady heat flux. This external thermal actuation is added to the righthandside of the energy equation in the compressible NavierStokes equations. We study how the localized thermal forcing affects the farfield and nearfield of the surrounding flow. To provide design guidelines to active separation control, we perform resolvent analysis on the mean baseline flows and use it as a linear model to examine the energy amplification and flow response to different actuation frequencies and wavenumbers. Since the key to suppressing flow separation lies in the excitation of the instabilities in the shear layer that forms over the airfoil, we consider a free shear layer and perturb it with a fundamental thermal input in the first part of this study. In this model problem, local periodic heating is introduced at the trailing edge of a finitethickness splitter plate. Twodimensional direct numerical simulations are performed at the platethicknessbased Reynolds number of 1000. We find that thermal actuation introduces low level of oscillatory surface vorticity flux and baroclinic torque at the actuation frequency in the vicinity of the trailing edge. The produced vortical perturbations can independently excite the fundamental instability that accounts for shear layer rollup as well as the subharmonic instability that encourages the vortex pairing process farther downstream. We demonstrate that the nonlinear dynamics of a spatially developing shear layer can be modified by the local oscillatory heat flux as a control input. Next, we leverage the findings from the thermally perturbed free shear layer and extend the employment of the thermal actuation technique to the control of flow separation over an airfoil. The separated flows over a NACA 0012 airfoil at two poststall angles of attack 6° and 9° and chordbased Reynolds number ReLc = 23,000 are considered. The thermal actuator is placed near the leading edge to introduce unsteady thermal forcing. Threedimensional largeeddy simulations (LES) are employed in this investigation. Of particular interest is the influence of the frequency and spanwise wavelength of the thermal actuator introduced at the natural separation point. We observe that the thermal forcing is capable of reattaching the flow by encouraging the rollup of the vortex sheet emanating from the leading edge. Discrete coherent spanwise vortices are formed and leads to the generation of lowpressure region over the top surface enabling lift enhancement. Under certain 2D actuation cases, the turbulent flow is completely laminarized and turns into a 2D flow. To further enhance the aerodynamic performance of the wing, we consider the trigger of vortex breakdown by introducing spanwise perturbation in the thermal forcing. It is found that spanwise variation in the forcing can enhance mixing past the mid chord and entrains freestream momentum, benefitting from both the lowpressure core of the spanwise vortices and the recovery of the flow momentum in the aft portion of the wing. For the successful controlled case that achieves reattachment, we observe a significant reduction in drag by up to 49% and an increase in lift by up to 54%. The fluctuations in aerodynamic forces are also reduced by up to 84% with the unsteady thermal actuation. We also find that the excitation of shearlayer rollup over the airfoil and the turbulentlaminar transition after the rollup both play important roles to achieve effective separation control. Complementary to the parametric study using LES, we perform resolvent analysis on the baseline flows to obtain further physicsbased guidance for the effective choice of these control input parameters. The global resolvent analysis is conducted on the baseline turbulent mean flows to identify the actuation frequency and wavenumber that provide high energy amplification. The present analysis also considers the use of a temporal filter to limit the time horizon for assessing the energy amplification to extend resolvent analysis to unstable base flows. We incorporate the amplification and response mode from resolvent analysis to provide a metric that quantifies momentum mixing associated with the modal structure. By comparing this metric from resolvent analysis and the LES results of controlled flows, we demonstrate that resolvent analysis can predict the effective range of actuation frequency as well as the global response to the actuation input. We demonstrated the effectiveness of the thermal actuation to suppress flow separation over the airfoil. Supported by the agreements between the results from resolvent analysis and LES, we believe that this study provides insights for the use of resolvent analysis in guiding future active flow control.
Show less  Date Issued
 2018
 Identifier
 2018_Su_Yeh_fsu_0071E_14631
 Format
 Thesis
 Title
 A Graph Based Approach to Nonlinear Model Predictive Control with Application to Combustion Control and Flow Control.
 Creator

Reese, Brandon M., Collins, E. (Emmanuel), Alvi, Farrukh S., Foo, Simon Y., Cattafesta, Louis N., Oates, William S., Florida State University, College of Engineering, Department...
Show moreReese, Brandon M., Collins, E. (Emmanuel), Alvi, Farrukh S., Foo, Simon Y., Cattafesta, Louis N., Oates, William S., Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Systems with a priori unknown, and timevarying dynamic behavior pose a significant challenge in the field of Nonlinear Model Predictive Control (NMPC). When both the identification of the nonlinear system and the optimization of control inputs are done robustly and efficiently, NMPC may be applied to control such systems. This dissertation presents a novel method for adaptive NMPC, called Adaptive Sampling Based Model Predictive Control (SBMPC), that combines a radial basis function neural...
Show moreSystems with a priori unknown, and timevarying dynamic behavior pose a significant challenge in the field of Nonlinear Model Predictive Control (NMPC). When both the identification of the nonlinear system and the optimization of control inputs are done robustly and efficiently, NMPC may be applied to control such systems. This dissertation presents a novel method for adaptive NMPC, called Adaptive Sampling Based Model Predictive Control (SBMPC), that combines a radial basis function neural network identification algorithm with a nonlinear optimization method based on graph search. Unlike other NMPC methods, it does not rely on linearizing the system or gradient based optimization. Instead, it discretizes the input space to the model via pseudorandom sampling and feeds the sampled inputs through the nonlinear model, producing a searchable graph. An optimal path is found using an efficient graph search method. Adaptive SBMPC is used in simulation to identify and control a simple plant with clearly visualized nonlinear dynamics. In these simulations, both fixed and timevarying dynamic systems are considered. Next, a power plant combustion simulation demonstrates successful control of a more realistic MultipleInput MultipleOutput system. The simulated results are compared with an adaptive version of Neural GPC, an existing NMPC algorithm based on NetwonRaphson optimization and a back propagation neural network model. When the cost function exhibits many local minima, Adaptive SBMPC is successful in finding a globally optimal solution while Neural GPC converges to a solution that is only locally optimal. Finally, an application to flow separation control is presented with experimental wind tunnel results. These results demonstrate real time feasibility, as the control updates are computed at 100 Hz, and highlight the robustness of Adaptive SBMPC to plant changes and the ability to adapt online. The experiments demonstrate separation control for a NACA 0025 airfoil with Reynolds Numbers ranging from 90,000 to 150,000 for both fixed and pitching (.33 deg/s) angles of attack.
Show less  Date Issued
 2015
 Identifier
 FSU_migr_etd9435
 Format
 Thesis
 Title
 A Method to Predict Circulation Control Noise.
 Creator

Reger, Robert, Cattafesta, Louis N., Tam, Christopher K. W., Taira, Kunihiko, Oates, William S., Florida State University, College of Engineering, Department of Mechanical...
Show moreReger, Robert, Cattafesta, Louis N., Tam, Christopher K. W., Taira, Kunihiko, Oates, William S., Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Underwater vehicles suffer from reduced maneuverability with conventional lifting appendages due to the low velocity of operation. Circulation control offers a method to increase maneuverability independent of vehicle speed. However, with circulation control comes additional noise sources, which are not well understood. To better understand these noise sources, a modalbased prediction method is developed, potentially offering a quantitative connection between flow structures and farfield...
Show moreUnderwater vehicles suffer from reduced maneuverability with conventional lifting appendages due to the low velocity of operation. Circulation control offers a method to increase maneuverability independent of vehicle speed. However, with circulation control comes additional noise sources, which are not well understood. To better understand these noise sources, a modalbased prediction method is developed, potentially offering a quantitative connection between flow structures and farfield noise. This method involves estimation of the velocity field, surface pressure field, and farfield noise, using only nontimeresolved velocity fields and timeresolved probe measurements. Proper orthogonal decomposition, linear stochastic estimation and Kalman smoothing are employed to estimate timeresolved velocity fields. Poisson's equation is used to calculate timeresolved pressure fields from velocity. Curle's analogy is then used to propagate the surface pressure forces to the far field. This method is developed on a direct numerical simulation of a twodimensional cylinder at a low Reynolds number (150). Since each of the fields to be estimated are also known from the simulation, a means of obtaining the error from using the methodology is provided. The velocity estimation and the simulated velocity match well when the simulated additive measurement noise is low. The pressure field suffers due to a small domain size; however, the surface pressures estimates fare much better. The farfield estimation contains similar frequency content with reduced magnitudes, attributed to the exclusion of the viscous forces in Curle's analogy. In the absence of added noise, the estimation procedure performs quite nicely for this model problem. The method is tested experimentally on a 650,000 chordReynoldsnumber flow over a 2D, 20% thick, elliptic circulation control airfoil. Slot jet momentum coefficients of 0 and 0.10 are investigated. Particle image velocimetry, unsteady pressure and phasedacousticarray data are acquired simultaneously in an aeroacoustic windtunnel facility. The velocity field estimation suffers due to poor correlation with the unsteady pressure data, especially in the 0.10 momentum coefficient case. The prediction without slot jet blowing matches single microphone measurements within 010 dB over the frequency range of interest while the prediction with the jet active is quite poor and differ from measurements by as much as 35 dB. Suggestions for improvement of the proposed method are offered. Data from the acoustic array are then investigated. Single microphone spectra are obtained, and it is shown that background noise is significant. In order to circumvent this problem, beamforming is employed. The primary sources of background noise are from the tunnel collector and jet/sidewall interaction. DAMAS is employed to remove the effects of the array point spread function. Spectra are acquired by integrating the DAMAS result over the source region. The resulting DAMAS spectral levels are significantly below single microphone levels. A scaling analysis is performed on the processed array data. With a constant freestream velocity and a varying jet velocity the data scale as M6. If momentum coefficient is held constant and freestream velocity is varied the data scale as M7.
Show less  Date Issued
 2016
 Identifier
 FSU_2016SP_Reger_fsu_0071E_13109
 Format
 Thesis
 Title
 On the Stability and Control of a Trailing Vortex.
 Creator

Edstrand, Adam, Cattafesta, Louis N., Hussaini, M. Yousuff, Schmid, Peter J., Taira, Kunihiko, Oates, William S., Florida State University, College of Engineering, Department of...
Show moreEdstrand, Adam, Cattafesta, Louis N., Hussaini, M. Yousuff, Schmid, Peter J., Taira, Kunihiko, Oates, William S., Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

Trailing vortices are both a fundamental and practical problem of fluid mechanics. Fundamentally, they provide a canonical vortex flow that is pervasive in finite aspect ratio lifting bodies, practically producing many adverse effects across aeronautical and maritime applications. These adverse effects coupled with the broad range of applicability make their active control desirable; however, they remain robust to control efforts. Experimental baseline results provided an explanation of...
Show moreTrailing vortices are both a fundamental and practical problem of fluid mechanics. Fundamentally, they provide a canonical vortex flow that is pervasive in finite aspect ratio lifting bodies, practically producing many adverse effects across aeronautical and maritime applications. These adverse effects coupled with the broad range of applicability make their active control desirable; however, they remain robust to control efforts. Experimental baseline results provided an explanation of vortex wandering, the sidetoside motion often attributed to windtunnel unsteadiness or a vortex instability. We extracted the wandering motion and found striking similarities with the eigenmodes, growth rates, and frequencies from a stability analysis of the Batchelor vortex. After concluding that wandering is a result of a vortex instability, we applied control to the trailing vortex flow field through blowing from a slot at the wingtip. We experimentally obtained modest reductions in the metrics, but found the parameter space for optimization unwieldy. With the ultimate goal of designing control, we performed a physicsbased stability analysis in the wake of a NACA0012 wing with an aspect ratio of 1.25 positioned at a geometric angle of attack of 5 degrees. Numerically computing the base flow at a chord Reynolds number of 1000, we perform a parallel temporal and spatial stability analysis three chords downstream of the trailing edge finding seven instabilities: three temporal, four spatial. The three temporal contain a wake instability, a vortex instability, and a mixed instability, which is a higherorder wake instability. The primary instability localized to the wake results from the twodimensional wake, while the secondary instability is the mixed instability, containing higherorder spanwise structures in the wake. These instabilities imply that although it may be intuitive to place control at the wingtip, these results show that control may be more effective at the trailing edge, which would excite these instabilities that result with the eventual break up of the vortex. Further, by performing a wavepacket analysis, we found the wave packets contained directivity, coming inward toward the vortex above and below the wing, and traveling outward in the spanwise directions. We conjecture that this directivity can be translated to receptivity, with freestream disturbances above and below the wing being more receptive than spanwise disturbances. With this, we provide two methods for instability excitation: utilizing control devices on the wing to excite nearfield instabilities directly and utilizing freestream disturbances to such as a speaker to excite nearfield instabilities through receptivity.
Show less  Date Issued
 2016
 Identifier
 FSU_2016SP_Edstrand_fsu_0071E_13141
 Format
 Thesis
 Title
 An Aeroacoustic Characterization of a MultiElement HighLift Airfoil.
 Creator

Pascioni, Kyle A., Cattafesta, Louis N., Sussman, Mark, Alvi, Farrukh S., Xu, Cheryl, Choudhari, Meelan, Florida State University, College of Engineering, Department of...
Show morePascioni, Kyle A., Cattafesta, Louis N., Sussman, Mark, Alvi, Farrukh S., Xu, Cheryl, Choudhari, Meelan, Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

The leading edge slat of a highlift system is known to be a large contributor to the overall radiated acoustic field from an aircraft during the approach phase of the flight path. This is due to the unsteady flow field generated in the slatcove and near the leading edge of the main element. In an effort to understand the characteristics of the flowinduced source mechanisms, a suite of experimental measurements has been performed on a twodimensional multielement airfoil, namely, the MD...
Show moreThe leading edge slat of a highlift system is known to be a large contributor to the overall radiated acoustic field from an aircraft during the approach phase of the flight path. This is due to the unsteady flow field generated in the slatcove and near the leading edge of the main element. In an effort to understand the characteristics of the flowinduced source mechanisms, a suite of experimental measurements has been performed on a twodimensional multielement airfoil, namely, the MD30P30N. Particle image velocimetry provide mean flow field and turbulence statistics to illustrate the differences associated with a change in angle of attack. Phaseaveraged quantities prove shear layer instabilities to be linked to narrowband peaks found in the acoustic spectrum. Unsteady surface pressure are also acquired, displaying strong narrowband peaks and large spanwise coherence at low angles of attack, whereas the spectrum becomes predominately broadband at high angles. Nonlinear frequency interaction is found to occur at low angles of attack, while being negligible at high angles. To localize and quantify the noise sources, phased microphone array measurements are per formed on the two dimensional highlift configuration. A Kevlar wall test section is utilized to allow the mean aerodynamic flow field to approach distributions similar to a freeair configuration, while still capable of measuring the far field acoustic signature. However, the inclusion of elastic porous sidewalls alters both aerodynamic and acoustic characteristics. Such effects are considered and accounted for. Integrated spectra from Delay and Sum and DAMAS beamforming effectively suppress background facility noise and additional noise generated at the tunnel wall/airfoil junction. Finally, temporallyresolved estimates of a lowdimensional representation of the velocity vector fields are obtained through the use of proper orthogonal decomposition and spectral linear stochastic estimation. An estimate of the pressure field is then extracted by Poissons equation. From this, Curles analogy projects the timeresolved pressure forces on the airfoil surface to further establish the connection between the dominating unsteady flow structures and the propagated noise.
Show less  Date Issued
 2017
 Identifier
 FSU_2017SP_Pascioni_fsu_0071E_13776
 Format
 Thesis
 Title
 Active Flow Control and Global Stability Analysis of Separated Flow over a NACA 0012 Airfoil.
 Creator

Munday, Phillip M. (Phillip Michael), Taira, Kunihiko, Hussaini, M. Yousuff, Alvi, Farrukh S., Cattafesta, Louis N., Lin, Shangchao, Florida State University, College of...
Show moreMunday, Phillip M. (Phillip Michael), Taira, Kunihiko, Hussaini, M. Yousuff, Alvi, Farrukh S., Cattafesta, Louis N., Lin, Shangchao, Florida State University, College of Engineering, Department of Mechanical Engineering
Show less  Abstract/Description

The objective of this computational study is to examine and quantify the influence of fundamental flow control inputs in suppressing flow separation over a canonical airfoil. Most flow control studies to this date have relied on the development of actuator technology, and described the control input based on specific actuators. Taking advantage of a computational framework, we generalize the inputs to fundamental perturbations without restricting inputs to a particular actuator. Utilizing...
Show moreThe objective of this computational study is to examine and quantify the influence of fundamental flow control inputs in suppressing flow separation over a canonical airfoil. Most flow control studies to this date have relied on the development of actuator technology, and described the control input based on specific actuators. Taking advantage of a computational framework, we generalize the inputs to fundamental perturbations without restricting inputs to a particular actuator. Utilizing this viewpoint, generalized control inputs aim to aid in the quantification and support the design of separation control techniques. This study in particular independently introduces wallnormal momentum and angular momentum to the separated flow using swirling jets through model boundary conditions. The response of the flow field and the surface vorticity fluxes to various combinations of actuation inputs are examined in detail. By closely studying different variables, the influence of the wallnormal and angular momentum injections on separated flow is identified. As an example, openloop control of fully separated, incompressible flow over a NACA 0012 airfoil at α = 6° and $9° with Re = 23,000 is examined with largeeddy simulations. For the shallow angle of attack α = 6°, the small recirculation region is primarily affected by wallnormal momentum injection. For a larger separation region at α = 9°, it is observed that the addition of angular momentum input to wallnormal momentum injection enhances the suppression of flow separation. Reducing the size of the separated flow region significantly impacts the forces, and in particular reduces drag and increases lift on the airfoil. It was found that the influence of flow control on the small recirculation region (α = 6°) can be sufficiently quantified with the traditional coefficient of momentum. At α = 9°, the effects of wallnormal and angular momentum inputs are captured by modifying the standard definition of the coefficient of momentum, which successfully characterizes suppression of separation and lift enhancement. The effect of angular momentum is incorporated into the modified coefficient of momentum by introducing a characteristic swirling jet velocity based on the nondimensional swirl number. With the modified coefficient of momentum, this single value is able to categorize controlled flows into separated, transitional, and attached flows. With inadequate control input (separated flow regime), lift decreased compared to the baseline flow. Increasing the modified coefficient of momentum, flow transitions from separated to attached and accordingly results in improved aerodynamic forces. Modifying the spanwise spacing, it is shown that the minimum modified coefficient of momentum input required to begin transitioning the flow is dependent on actuator spacing. The growth (or decay) of perturbations can facilitate or inhibit the influence of flow control inputs. Biglobal stability analysis is considered to further analyze the behavior of control inputs on separated flow over a symmetric airfoil. Assuming a spanwise periodic waveform for the perturbations, the eigenvalues and eigenvectors about a base flow are solved to understand the influence of spanwise variation on the development of the flow. Two algorithms are developed and validated to solve for the eigenvalues of the flow: an algebraic eigenvalue solver (matrix based) and a timestepping algorithm. The matrix based approach is formulated without ever storing the matrices, creating a computationally memory efficient algorithm. Based on the matrix based solver, eigenvalues and eigenvectors are identified for flow over a NACA 0015 airfoil at Re = 200, $600, and $1,000. All three cases contain similar modes, although the growth rate of the leading eigenvalue is decreased with increasing Reynolds number. Three distinct types of modes are found, wake mode, steady mode, and modes of the continuous branch. While this method is limited in the range of Reynolds numbers, these results are used to validate the timestepper approach. Increasing the Reynolds number to Re = 23,000 over a NACA 0012 airfoil, the timestepper method is implemented due to rising computational cost of the matrixbased method. Stability analysis about the timeaveraged flow is performed for spanwise wavenumbers of β = 1$, $10π, and $20π, which the latter two wavenumbers are representative of the spanwise spacing between the actuators. The largest spanwise wavelength (β = 1$) contained unstable modes that ranged from low to high frequency, and a particular unstable lowfrequency mode corresponding to a frequency observed in the lift forces of the baseline largeeddy simulation. For the larger spanwise wavenumbers, β = 10π ($L_z/c = 0.2$) and $20π ($L_z/c = 0.1$), lowfrequency modes were damped and only modes with $f > 5$ were unstable. These results help us gain further insight into the influence of the flow control inputs. Flow control is not implemented in a manner to directly excite specific modes, but does dictate the spanwise wavelengths that can be generated. Comparing the unstable eigenmodes at these two spacings, the larger spanwise spacing ($\beta = 10\pi$) had a greater growth rate for the majority of the unstable modes. The smaller spanwise spacing ($\beta = 20\pi$) has only a single unstable mode with a growth rate an order of magnitude smaller than $\beta = 10\pi$. With the aid of the increased growth rate, perturbations to the flow with a wider spacing become more effective by interacting with natural modes of the flow. Taking advantage of these natural modes allows for decreased input for the wider spanwise spacing. In conclusion, it was shown that the influence of wallnormal and angular momentum inputs on fully separated flow can adequately be described by the modified coefficient of momentum. Through further analysis and the development of a biglobal stability solver, spanwise spacing effects observed in the flow control study can be explained. The findings from this study should aid in the development of more intelligently designed flow control strategies and provide guidance in the selection of flow control actuators.
Show less  Date Issued
 2017
 Identifier
 FSU_2017SP_Munday_fsu_0071E_13086
 Format
 Thesis