Marlyn Y. Andino

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.

Innovative Flow Control Concepts for Drag Reduction

This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wings leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs. The ERA systems analysis studies performed by NASA indicated that AFC-enhanced vertical tail could produce approximately 0.9% drag reduction for a large twin aisle aircraft and IAM coatings could enable approximately 1.2% drag reduction recovery for a potential total drag reduction of approximately 3.3% for a single aisle aircraft with a natural laminar flow (NLF) wing design.

Investigation of different active flow control strategies for high speed jets using synthetic jet actuators

We present in this paper a set of experiments geared towards characterizing the system response of the near fleld jet shear layer to difierent modes of forcing. Several open and closed loop control tests were conducted. The open loop control cases included simple sinusoidal forcing (with varying coe‐cient of momentum and frequency), phased forcing and amplitude modulated forcing. The closed loop cases included feeding back the Fourier flltered signals from 3 diameters and 6 diameters downstream. The correlations between the near fleld Fourier flltered pressure modes and the far fleld noise are changed signiflcantly for all control cases; demonstrating the ability to efiect control authority in the near fleld region. An examination of the far fleld noise spectra, however, demonstrates only minor changes from the control.

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 Disturbance Measurements in the National Transonic Facility

Recent flow measurements have been acquired in the National Transonic Facility to assess the test-section unsteady flow environment. The primary purpose of the test is to determine the feasibility of the facility to conduct laminar-flow-control testing and boundary-layer transition-sensitive testing at flight-relevant operating conditions throughout the transonic Mach number range. The facility can operate in two modes, warm and cryogenic test conditions for testing full and semispan-scaled models. Data were acquired for Mach and unit Reynolds numbers ranging from 0.2≤M≤0.95 and 3.3×106<Re/m<220×106 collectively at air and cryogenic conditions. Measurements were made in the test section using a survey rake that was populated with 19 probes. Roll polar data at selected conditions were obtained to look at the uniformity of the flow disturbance field in the test section. Data acquired included mean total temperatures, mean and fluctuating static/total pressures, and mean and fluctuating hot-wire measurements...

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.

Flow Control Effects on Length Scales Over a Turret

Turbulence has an adverse effect on aero-optic applications when present in separated and inviscid flows, boundary and shear layers. A study of the flow physics around a cylindrical turret with the application of open-loop control has been performed. The evaluation of flow control performance is accomplished by analyzing the changes in the turbulent flow time/length scales across the turret surface for three cases: baseline, modulated sine wave and pure sine wave. Simultaneous velocity and unsteady pressure measurements were acquired at a Reynolds number of 300,000 based on turrets diameter. Turbulence intensity results present reduction of 20% on the u′ for the actuated cases. Results of the autocorrelations of the unsteady pressure sensors exhibit a more organized, almost periodic behavior. Flow control demonstrates the ability to organize the flow structures moving the flow towards homogeneity. Even when the measurements performed are not direct measures of the aero-optics, literature suggest that the...

Sweeping Jet Optimization Studies

Progress on experimental efforts to optimize sweeping jet actuators for active flow control (AFC) applications with large adverse pressure gradients is reported. Three sweeping jet actuator configurations, with the same orifice size but dierent internal geometries, were installed on the flap shoulder of an unswept, NACA 0015 semi-span wing to investigate how the output produced by a sweeping jet interacts with the separated flow and the mechanisms by which the flow separation is controlled. For this experiment, the flow separation was generated by deflecting the wings 30% chord trailing edge flap to produce an adverse pressure gradient. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the three actuator configurations. The actuator with the largest jet deflection angle, at the pressure ratios investigated, was the most efficient at controlling flow separation on the flap of the model. Oil flow visualization studies revealed that the flow field controlled by the sweeping jets was more three-dimensional than expected. The results presented also show that the actuator spacing was appropriate for the pressure ratios examined.