Patrick Shea

Simulation-Guided, Model-Based Feedback Flow Control for a Pitching Turret

Closed-loop systems have been developed for controlling the flow above a three-dimensional turret while the hemispherical top of the turret rotates about the pitch axis. Separation and concomitant turbulence levels incurred through the pitching cycle were altered by suction jet slots circumscribing the aperture, which served as control input; an array of pressure sensors on the turret surface provided the controller with information about the state of the flow above the surface. The control objective was to minimize the separation and turbulence in the dynamic environment created by the articulating turret. The closed-loop control systems included dynamical and measurement-based estimators, regulators, filters, and compensators. These components were developed using both computational and experimental data, and the control systemswere evaluated through a series of control-in-the-loop computation-fluid-dynamics simulations and wind-tunnel runs. The implementation of this suction flow-control system resulted in a decrease of fluctuating velocity over the flat optical aperture. Initial simple proportional and the advanced proportional-integral closed-loop control systems were able to decrease the fluctuating velocity more efficiently than the steady suction of open-loop control. The more-advanced closed-loop controllers showed a better ability to track the trends of the separation and turbulence levels as the hemisphere of the turret pitched. The development of the controller design and numerical demonstration of the closed-loop feedback system is described in a companion paper.

Model-Based Feedback Flow Control Development and Simulation for a Pitching Turret

The closed-loop control systems include dynamical and measurement-based estimators, controllers, filters, and compensators. These components are developed using both computational data from computational fluid dynamics simulations and experimental data from wind-tunnel runs within the common framework of SMARTFLOW: engineering software for flow control system design. The control systems are evaluated through a series of controlin-the-loop computational fluid dynamics simulations, demonstrating the merits of feedback control through robustness in the presence of measurement noise, modeling errors, and highly unsteady conditions. The computational fluid dynamics simulations also demonstrate reductions in actuation energy below levels required by open-loop systems.

Analysis of high speed jet flow physics with time-resolved PIV

This work focuses on a Mach 0.6 turbulent, compressible jet flow field with simultaneously sampled near and far-field pressure, as well as 10 kHz time-resolved PIV. Experiments have been conducted in the fully anechoic chamber and jet facility at Syracuse University. The PIV measurements were taken in the streamwise plane of the jet along the center plane at various downstream locations. In addition, measurements were taken off of the center plane to obtain a three-dimensional view of the jet flow. Active flow control (both open and closed-loop) was performed in order to see the effects on the potential core length and overall sound pressure levels. Various reduced-order models have been used to analyze previous experimental data sets at Syracuse University. This paper will focus on the analysis of the flow physics, using the time-resolved velocity field coupled with the simultaneously sampled pressure. Novel modeling approaches such as observable inferred decomposition and cluster-based reduced-order modeling have been implemented in an effort to link the near-field velocity with the far-field acoustics.

Comparison of spatial and temporal resolution on high speed axisymmetric jets

The current investigation examines a 2 inch, circular, high-speed jet with two separate PIV setups simultaneously sampled with far-field pressure. Subsonic and supersonic velocity measurements are performed in the streamwise (r-z) plane of the jet with both time-resolved PIV and large window PIV configurations, taken at different times. The 10 kHz time-resolved PIV captures 1.5 streamwise diameter windows at several downstream locations. The large window PIV utilizes 3 simultaneously captured cameras stitched together to view a single interrogation window of the flow field approximately 2.5-9 streamwise diameters from the nozzle lip. Both PIV setups have an approximately 1.5 diameter spatial window in the radial direction. In this paper, we will focus on the Mach 0.6 flow in the region of the potential core collapse (z/D = 6 7.5). Low-dimensional modeling techniques in the form of proper orthogonal decomposition, Lumley (1967) and Sirovich (1987), are implemented in order to help us understand the large scale, energetic events within the flow. In previous work, the time-dependent POD modes from the TRPIV have been correlated with the far-field acoustics to determine which low-dimensional structures best relate to the noise. These correlated events are deemed as “loud” modes, Low et al. (2013). One issue is that this approach is greatly influenced by the temporal and spatial nature of the PIV. By utilizing the differences in our PIV setups, we map the convergence of POD modes based on their spatial and temporal resolution.

Suction Flow Control at High Reynolds Number

Flow control has been shown to reduce the aero-optic distortion due to density ∞uctuations within a wake of an airborne turret. By manipulating the ∞ow over the turret directly afiects the density ∞uctuation that incur aero-optic distortions. This paper focuses on suction ∞ow control over a three-dimensional turret at a freestream velocity of Mach 0.3. Aero-optic measurement were taken over the ∞at aperture of the turret with and without open loop suction control clearly showed a decrease in the distortions as the amount of suction increased. Fluctuating surface pressure simultaneously sampled with the aero-optic measurements showed the inverse where as the suction increased the surface pressure rms decreased. Another set of tests were taken as the hemisphere dynamically pitching with open-loop and closed-loop suction ∞ow control. The closed-loop control system employed a low dimensional measurement based proportional controller. Both the open-loop and closed loop control test showed a change in ∞ow over the aperture as compared to the baseline case.

Active Flow Control of a Pitching Turret Flow Field Using Closed-Loop Feedback Control

Experimental testing of an active ow control system on a three-dimensional, nonconformal turret has been performed at a diameter based Reynolds number of 2:0 10. Active ow control was achieved using dynamic suction and various open and closed-loop feedback control algorithms in an e ort to determine the most e ective and e cient control scheme for reducing aero-optic distortions in the vicinity of the turret aperture. Dynamic surface pressure and PIV measurements have been used to better characterize and understand the ow eld in order to evaluate the active control system. From this research, it has been shown that dynamic suction has the ability to manipulate the separated ow above the turret aperture and can signi cantly alter the characteristics of the aperture ow eld. Open-loop control was shown to be the most e cient form of control when set to the proper suction levels, but the merit of closed-loop feedback control has also been shown, especially for cases where the aperture of the turret is dynamically pitching. Generally, open-loop control systems require scheduling of the active control system during pitching where a closed-loop control system would not due to the sensing capabilities.

Closed-Loop Flow Control for an Articulating Turret

A series of wind tunnel tests were performed to evaluate systems for controlling the flow over a three-dimensional, articulating turret. The turret has two rotational degrees of freedom: pitch and yaw. The yaw angle is modulated sinusoidally in time at three fixed pitch angles, creating asymmetric (and fully turbulent) flow over the turret. Control actuation consists of suction jets located on the top of the turret, using the duty cycle of valves in the suction lines to change suction velocities. One valve controls suction velocity in jet slots located on the left side of the turret, and another valve controls velocity in jet slots on the right. Each valve is controlled by an independent, proportional regulator that receives signals from a separate measurement-based state estimator—utilizing two groups of surface pressure sensors located on the top of the turret (left and right). The multipleinput-multiple-output (MIMO) controller is twice as effective as an open-loop controller in reducing average levels of fluctuating velocity. The closed-loop system is also three times more efficient as measured by the ratio of control effectiveness to required input.

Feedback Flow Control for a Pitching Turret (Part I)

Abstract : Closed-loop systems have been developed for controlling the flow above a three-dimensional turret. The top of the turret is hemispherical, houses a flat optical aperture, and can rotate about two axes (pitch and yaw). The extent of separation and concomitant turbulence levels in the flow above the aperture change as the turret rotates. The control objective is to minimize the separation and turbulence in the dynamic environment created by the articulating turret. The closed-loop control systems include dynamical and measurement-based estimators, regulators, filters, and compensators. These components are developed using both computational data from CFD simulations and experimental data from wind tunnel runs within the common framework of SMARTflow - engineering software for flow control system design. The control systems are evaluated through a series of control-in-the-loop CFD simulations and wind tunnel runs, demonstrating the merits of feedback control through robustness in the presence of measurement noise, modeling errors, and highly unsteady conditions and through reductions in actuation energy below levels required by open-loop systems. Controller designs and computational tests are described here; wind tunnel tests are described in the companion paper.

Aerodynamic Control of a Rectangular Wing Using Gurney Flaps and Synthetic Jets

An experimental investigation was performed on a rectangular wing section at low angles of attack to determine the aerodynamic flow control eectiveness of pairing a near-trailing-edge Gurney flap with an array of synthetic jet actuators. In this investigation, a Gurney flap was placed a small distance upstream of the synthetic jet actuator orifice with the goal of using the synthetic jet actuators to augment the eects of the Gurney flap. The main advantage of the Gurney flap was a lift increase that was accompanied by a separated region downstream of the flap which the synthetic actuators were able to manipulate for additional lift increments. Sectional lift and quarter-chord pitching moment data were acquired at Rec = 1.57 ◊ 10 5 and angles of attack ranging from = 0 - 12 for dierent configurations of the Gurney flap and synthetic jet array. For configurations where significant aerodynamic control was observed, the flow physics in the vicinity of the flap and actuators were investigated with ensemble-averaged PIV measurements. These measurements showed that the control scheme could either augment or reduce the lift on the wing section depending on the location of the synthetic jet actuators. When the synthetic jets were placed on the pressure surface, the control scheme had a lift increase on the order of 10% and a corresponding decrease in the pitching moment for the range of angles of attack investigated. When the synthetic jets were placed on the suction surface, the control scheme had the opposite eect with percent decreases in lift of 10% or greater. These changes in the lift and pitching moment were the result of a change in the circulation around the wing section by a modification of the trailing edge flow in the wake of the Gurney flap. Thus it was shown that the synthetic jet actuators were able to manipulate the wake of the Gurney flap and augment the eects of the Gurney flap.

Investigation of "Loud" Modes in a High-Speed Jet to Identify Noise-Producing Events

The current investigation focuses on a fully compressible, axisymmetric jet operating at high subsonic conditions. The test bed of interest includes 10 kHz time-resolved particle image velocimetry coupled with simultaneously sampled near and far-field pressure measurements. The experimental results to be presented have been conducted in the Syracuse University anechoic chamber at the Skytop campus. This study focuses on identifying possible noise-producing events in the flow field by implementing reduced-order modeling techniques to extract “loud” modes in the flow. These concepts are coupled with waveletbased diagnostic tracking techniques to examine the spatial and temporal nature of the “loud” modes. For this work, Mach 0.6 and Mach 0.85 will be the focus, in an effort to understand the noise-producing structures in a subsonic jet. The overall goal of this work is to efficiently link near-field velocity with far-field acoustics to identify the interactions of the flow field responsible for far-field noise generation. Low-dimensional “loud” modes can then be implemented into closed-loop control algorithms in real-time for far-field noise suppression. This paper will focus on these “loud” modes, primarily linking the flow physics directly to the acoustics.