Ryan Wallace

Boundary Feedback Flow Control: Proportional Control with Potential Application to Aero-Optics

A large percentage of the losses in performance and effectiveness of airborne optical systems are caused by turbulence. In an effort to reduce these adverse effects in airborne optical systems, we are exploring the use of both openand closed-loop flow control over a cylindrical turret. A series of experiments were performed at a Reynolds number of 2 10, based on the turret’s diameter and freestream velocity, which corresponds to aMach number of 0.3. The three-dimensional turret contained an actuation system that consists of 17 synthetic jets placed upstream from the leading edge of the aperture. Initially, a large database containing no control and open-loop control was obtained. These data sets provide a rich ensemble for the development and application of a simple proportional closed-loop control with the use of proper orthogonal decomposition. Surface pressuremeasurements were acquired across the aperture region for all cases studied. Results from the open-loop test demonstrate a reduction of 19.6% in the root-mean-square values when compared to the baseline case. The closed-loop flow control results show that the root-mean-square pressure fluctuations are reduced by 25.7%, the integral scales are significantly reduced, and the flow is driven toward homogeneity.

Flow and Aero-Optics Around a Turret Part II: Surface Pressure Based Proportional Closed Loop Flow Control

As focused light passes through turbulent ∞ow the light is distorted and the intensity is reduced. An extended study using active ∞ow control to afiect the turbulent region over the a ∞at aperture of a 3-D hemispheric turret was conducted in the Air Force Research Laboratory’s Subsonic Aerodynamic Research Laboratory (SARL) wind tunnel at WrightPatterson Air Force Base. The SARL experiments were performed at a Mach number of :3, which gives Reynolds number on the order of 2;000;000. At these Reynolds numbers the ∞ow becomes highly complex and more challenging to study. A large database from previous work containing no control and open loop control cases provided a rich ensemble for plant model development based on low dimensional techniques such as the split-POD method of Camphouse (2007). PIV velocity data was acquired along with simultaneously sampled surface pressure data at various planes across the turret with and without control. Control authority was acquire by actuators mounted upstream of the aperture that generated a momentum ∞ux in the ∞ow around the turret. Simple proportional closed-loop control was performed using the bandpass flltered temporal POD mode coe‐cients of the surface pressure as the feedback signal. This paper shows that the active control reduced the root mean squared of the pressure ∞uctuations, shrunk the integral scales, and drove the ∞ow towards homogeneity.

A SNAPSHOT DECOMPOSITION METHOD FOR REDUCED ORDER MODELING AND BOUNDARY FEEDBACK CONTROL.

Abstract : In this paper, we develop a reduced basis construction method that allows for separate consideration of baseline and actuated dynamics in the reduced modeling process. A prototype initial boundary value problem, governed by the two-dimensional Burgers equation, is formulated to demonstrate the utility of the method in a boundary control setting. Comparisons are done between reduced and full order solutions under open-loop boundary actuation to illustrate advantages gained by separate consideration of actuated dynamics. A tracking control problem is specified using a linear quadratic regulator formulation. Comparisons of feedback control effectiveness are done to demonstrate benefits in control effectiveness obtained from separate consideration of actuated dynamics during model reduction.

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.

Flow characteristics of active control around a 3D turret

At high speeds the wake of a hemisphere turret is completely separated and fully turbulent. Within this region of separated flow large density fluctuations develop. The problem comes in with attempting to propagate light through the turbulent wake of the turret. As the a light beam passes through the wake and the shear layer of the turret, the beam becomes distorted. Distortion of the beam causes the intensity of the light to be reduced making a laser less effective. By manipulating the flow around the turret, in particular the region just over the laser aperture, the loss of light intensity can be minimized. Active flow control has been shown in pervious work to alter the flow characteristics around an object. In the effort to delay the onset of stall around an airfoil at high angles of attack Glauser et al (2004) and Ausseur et al (2005) were successful at showing that utilizing an active flow control system was a very effective means of control. The active flow control included open and closed loop control. For the closed loop control, a low dimensional analysis of the velocity field around the airfoil and the surface pressure along the airfoil, was fed back into a simple proportional controller. Closed loop flow control reduced the onset of stall as the angle of attack was increased. and the system also consumed less power to prevent stall than the open loop control. A pervious experiment perform under similar conditions and procedures was performed in the Syracuse University windtunnel. In this experiment open loop flow control was test on a quarter sized turret at a low freestream speed. After a large database of surface pressure and velocity measurements where obtain it was seen that there was a reduction in the unsteady fluctuating characteristics. In an effort to take this a step further and improve on the open loop control, the next step was to investigate the effects of open loop and closed loop control upon the flow and aero-optics of the system at a much higher Reynolds number. Like the pervious work before, the surface pressure based proportional closed loop control was found to have a positive effect upon the wake of the turret.

Flow and aero-optics around a turret. Part 1. Open loop flow control

A large percentage of the losses in performance and eectiveness of airborne optical systems are caused by turbulence. In particular, separated turbulent flow phenomena is present in several aero-optics applications. In an eort to reduce the adverse eects of turbulence in airborne optical systems, we are exploring the use of both open and closedloop flow control over a cylindrical turret. A series of experiments were performed at Reynolds number of 2;000;000 that corresponds to a Mach number of 0:3 using a half scale test model. The 3D turret contained an actuation system that consists of 17 synthetic jets placed upstream from the leading edge of the aperture. Multiple actuation cases were tested to evaluate the eects of active flow control over the aperture area and their control authority. Simultaneous surface pressure and velocity measurements were acquired in the separated region for both with and without flow control. Pressure results from the open loop test presents reduction of 10 percent in the root-mean-square values when compare to the baseline case. Two-point statistics showed that the forcing is driving the flow towards homogeneity across the surface of turret.

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.

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.