Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session LD: Flow Control VI |
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Chair: Mark Glauser, Syracuse University Room: 101D |
Monday, November 23, 2009 3:35PM - 3:48PM |
LD.00001: Assessment of Closed-Loop Control Using Multi-Mode Sensor Fusion For a High Reynolds Number Transonic Jet Kerwin Low, Basman Elhadidi, Mark Glauser Understanding the different noise production mechanisms caused by the free shear flows in a turbulent jet flow provides insight to improve ``intelligent'' feedback mechanisms to control the noise. Towards this effort, a control scheme is based on feedback of azimuthal pressure measurements in the near field of the jet at two streamwise locations. Previous studies suggested that noise reduction can be achieved by azimuthal actuators perturbing the shear layer at the jet lip. The closed-loop actuation will be based on a low-dimensional Fourier representation of the hydrodynamic pressure measurements. Preliminary results show that control authority and reduction in the overall sound pressure level was possible. These results provide motivation to move forward with the overall vision of developing innovative multi-mode sensing methods to improve state estimation and derive dynamical systems. It is envisioned that estimating velocity-field and dynamic pressure information from various locations both local and in the far-field regions, sensor fusion techniques can be utilized to ascertain greater overall control authority. [Preview Abstract] |
Monday, November 23, 2009 3:48PM - 4:01PM |
LD.00002: An Adjoint Solver for Unsteady Navier-Stokes Flows and Application in Uncertainty Quantification Qiqi Wang, Frank Ham, Gianluca Iaccarino, Parviz Moin We present a parallel adjoint solver for unsteady incompressible Navier-Stokes equation. Backward time-stepping for the time-dependent adjoint equation is achieved using the dynamic checkpointing scheme. This adjoint solver is suitable for very long time integration without knowing the number of time steps a priori. The required computational time and memory is only three to five time the solution of the forward Navier-Stokes equation for tens of thousands of time steps. The adjoint solver is tested on a laminar cylinder vortex shedding calculation at Reynolds number 100. Application of the adjoint solver in propagating uncertainties with large number of random variables is also presented. [Preview Abstract] |
Monday, November 23, 2009 4:01PM - 4:14PM |
LD.00003: Direct Numerical Simulation of Forced Round Jets Muralidhar Krishnamurthy, Trushar Gohil, Arun Saha Jet control leading to noise reduction and efficient combustion can be achieved by manipulating its coherent structures. In the present study, direct numerical simulation of free circular (round) jets has been performed for two types of forcing, namely, flapping (FLP) and dual-mode excitation (DME). A Reynolds number of 1000 based on average jet velocity and nozzle diameter is considered. A small scale perturbation of 5{\%} rms velocity is initially added to the three velocity components. DME perturbation is obtained by combining an axisymmetric excitation at the preferred mode frequency and helical excitation at a frequency fixed by the disturbance frequency ratio. For both contexts, the amplitude of the large scale excitation is 15{\%} of the base velocity. The finite difference representations are second order accurate in time, fourth order in the advection term and sixth order in diffusion. With small-scale perturbation, well-defined vortex rings are shed at the preferred mode frequency. With DME, a spectacular increase of jet spreading is seen on one of the orthogonal planes. On the other hand, for the FLP perturbation, the circular jet shows a bifurcation pattern that is practically a $\Psi $-shape. [Preview Abstract] |
Monday, November 23, 2009 4:14PM - 4:27PM |
LD.00004: The interaction of an array of circumferentially varying stators with a uniform crossflow John Farnsworth, Michael Amitay A propuslor capable of producing maneuvering forces in all directions effectively eliminates the need for additional control surfaces. Side forces can be generated by the propeller through the variation of the inflow swirl velocity to a conventional propeller. These control forces are generated based on the same geometric principles as a helicopter swash-plate. Instead of cyclically adjusting the propeller blade pitch angle, the relative pitch angle of a fixed pitch propeller is cyclically altered through a preswirled inflow generated by an upstream stator row. Wind tunnel experiments were conducted where global and detailed flow measurements were acquired through surface static pressure, and stereoscopic PIV on a simplified propulsor model. From these measurements a better understanding of the fluidic interactions associated with the non-uniform upstream stator row and the flow field was achieved. [Preview Abstract] |
Monday, November 23, 2009 4:27PM - 4:40PM |
LD.00005: Controlled Transitory Flow Attachment over a Stalled Airfoil George Woo, Ari Glezer Controlled attachment of transitory stall over a pitching airfoil is investigated in wind tunnel experiments using an array of surface-integrated pulsed jet actuators. The actuation has a characteristic time scale that is an order of magnitude shorter than the convective time scale of the base flow and results in momentary flow attachment with significant temporal changes in circulation and consequently in the aerodynamic forces and moments. The flow field in the cross stream plane above the pitching airfoil and in its near wake is investigated using high-resolution PIV phase-locked to the actuation. A single actuation pulse results in transitory flow attachment that is manifested by rapid increase in the global circulation and aerodynamic forces and persists for about ten convective time scales before the flow becomes fully stalled again. Large-scale changes in vorticity accumulation that are associated with repetitive, burst-modulated actuation pulses are exploited for significant extension of the streamwise domain and duration of the attached flow that is coupled with an increase in the peak circulation. Measurements of the interaction between the pulsed jets and the cross flow reveal details of the severing and collapse of the separated flow domain, and the dynamics of vorticity accumulation within the attaching boundary layer. [Preview Abstract] |
Monday, November 23, 2009 4:40PM - 4:53PM |
LD.00006: 3-D Interactions of Synthetic Jets and Cross-Flows - Experiments Joshua Wood, Michael Amitay The interaction of synthetic jets with a cross-flow over a finite wing was studied experimentally at a low Reynolds number and low angles of attack using PIV. The focus of the work was to explore the details of the flow structures near the synthetic jets. The interaction of the synthetic jets with the flow resulted in an array of counter-rotating vortical structures. The pair of counter-rotating vortices formed at the jet orifice was found to be two-dimensional just downstream of the jet orifice; however, as it advected downstream, it developed three-dimensionalities. The effect of the momentum coefficient (or blowing ratio) on the 3-D interaction was also explored; at low momentum coefficient only a slight interaction between the vortices was observed; however, as the momentum coefficient increases, the vortices interacted with each other, causing them to lift off the surface. Furthermore, the spanwise extent of the coherent structures was reduced as they advected downstream. [Preview Abstract] |
Monday, November 23, 2009 4:53PM - 5:06PM |
LD.00007: The Lift Response of a Stalled Wing to Pulsatile Disturbances David Williams, Gilead Tadmor, Tim Colonius, Wesley Kerstens, Vien Quach, Seth Buntain The transient lift response of a low Reynolds number wing subjected to small amplitude pulsatile disturbances is investigated. The wing has a semi-circular planform, and is fully stalled at a 20$^{\circ}$ angle of attack. Micro-valve actuators distributed along the leading edge of the wing produce the transient disturbance. It is shown that the lift response to a single pulse increases with the square root of the increasing actuator supply pressure, and that the lift response curves are similar to each other when scaled by the total impulse. Furthermore, for fixed actuator supply pressure, the amplitude and total impulse of the transient lift response curve increases with increasing external flow speed. In this case the lift response curves are similar when scaled by the dynamic pressure. The lift response to a single pulse can be treated as a filter kernel, and can be used to predict the lift time history for arbitrary actuator input signals. Comparisons with multiple-pulse inputs and continuous actuation modulated at low frequencies show good agreement between the model predictions and the experiment. [Preview Abstract] |
Monday, November 23, 2009 5:06PM - 5:19PM |
LD.00008: A Moving Airfoil Controlled by Synthetic Jets Sol Keun Jee, Omar Lopez, Robert Moser, Ali Kutay, Jonathan Muse, Anthony Calise There is a growing interest in synthetic jets in flow controls. Here we consider the use of synthetic jet actuators in active control of an airfoil. An adaptive controller is integrated with a CFD model which includes details of the synthetic jet actuators and detached eddy simulation for turbulent flows at Re=900,000. This integration allows us to investigate a moving airfoil controlled by synthetic jets. Two synthetic jet actuators are mounted on the top and bottom of a NACA 4415 airfoil close to the trailing edge to generate bi-directional aerodynamic moment. Aerodynamic performance is explored using the closed-loop controller to regulate 2-degree-of-freedom motions of the airfoil. The coupled CFD/controller model simulates maneuverings of the airfoil as studied experimentally in wind tunnel tests. Modeling of unsteady aerodynamics with synthetic jets is validated against measurements in the wind tunnel including aerodynamic forces, surface pressure distributions and PIV velocity fields. The coupled model also demonstrates rapid maneuvers on the order of the convecting time scale. The characteristics of the unsteady aerodynamics coupled with the vehicle dynamics and the synthetic jets will be discussed. [Preview Abstract] |
Monday, November 23, 2009 5:19PM - 5:32PM |
LD.00009: Coanda-assisted Spray Manipulation Katie Mabey, Barton Smith, Reid Archibald, Brian West An overview of research on a flow control technique called Coanda-assisted Spray Manipulation (CSM) is presented. CSM uses a high-momentum control jet under the influence of the Coanda effect to vector a high volume-flow jet or spray. Actuators provide the capability of moving the location of applied control flow making rotary or arbitrary motion of the vectored flow possible. The presented work includes a fundamental isothermal study on the effects of rotation speed and Reynolds number on a vectored jet using a belt-driven CSM actuator. Three-component velocity data were acquired for three Reynolds numbers and three rotation speeds using timed resolved high-speed stereo Particle Image Velocimetry. A second CSM system with 16 pneumatically-driven control ports has been retrofitted to a flame spray gun. This combination provides the capability to rapidly alter the direction of applied metal powders. High speed video of this process will also be presented. Finally, a fundamental study on the pneumatic system's response to minor losses and connection lines of varying lengths is presented. [Preview Abstract] |
Monday, November 23, 2009 5:32PM - 5:45PM |
LD.00010: Active Vibration Control of an S809 Wind Turbine Blade Using Synthetic Jet Actuators Victor Maldonado, Matthew Boucher, Rebecca Ostman, Michael Amitay Active flow control via synthetic jet actuators was implemented to improve the aeroelastic performance of a small scale S809 airfoil wind turbine blade model in a wind tunnel. Blade vibration performance was explored for a range of steady post-stall angles of attack, as well as various unsteady pitching motions for a chord based Reynolds number range of 1.29x10$^{5}$ to 3.69x10$^{5}$. Blade tip deflection was measured using a pair of calibrated strain gauges mounted at the root of the model. Using flow control, significant vibration reduction was observed for some steady post-stall angles of attack, while for dynamic pitching motions, vibration reduction was more pronounced (for a given angle of attack) on the pitch up motion compared to the pitch down motion of the blade cycle. This effect was attributed to the phenomenon known as dynamic stall, where the shedding of a leading edge vortex during the pitch up motion contributes to elevated values of lift (compared to static angles of attack) and lower values of lift when the blade is pitched down. This effect was also quantified through the use of Particle Image Velocimetry. [Preview Abstract] |
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