Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session OO: Separated Flows III |
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Chair: Fady Najjar, University of Illinois at Urbana Champaign Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 11 |
Tuesday, November 21, 2006 12:15PM - 12:28PM |
OO.00001: Optimization of Zero Net-mass Flow Actuators for Aero-optics Applications Jonathan Mihaly, Moira DeNatale, Marlyn Andino, Mark Glauser We are working to optimize zero net-mass flow actuators to manipulate flow around an airborne laser turret in order to reduce destructive aero-optics effects. Synthetic jets are created by 50mm piezoelectric disk actuators. Our optimization process involves setting the actuator's cavity size, frequency, and amplitude to achieve the strongest, most consistent jet possible. We are also investigating the affects of driving a single actuator verses driving two actuators in or out of phase with one another. Hotwires are used to collect data and time series for the velocity profile of each actuator. Our approach in initially determining cavity depth has been to use a resonance frequency equation which estimates the cavity depth for a given frequency characteristic to the actuator. The length and area of our opening slot are being held constant throughout our optimization process; however, we are considering the effects of having a sloped opening slot at an angle of 30 degrees to the flow, thus changing the length and area of that particular opening slot. Results from our study will be applied to the actuators used in the turret of the airborne laser at high velocities. [Preview Abstract] |
Tuesday, November 21, 2006 12:28PM - 12:41PM |
OO.00002: Flow Prediction Using Low-Dimensional Methods Julie Ausseur, Jeremy Pinier, Mark Glauser, Henry Carlson Dynamical systems are developed and studied to be later integrated in an experimental flow-control algorithm. In this study, we focus our attention on the choice of the flow variable whose dynamics are modeled by the evolution equation. First we apply Proper Orthogonal Decomposition (POD) on the velocity variables, and a low-order dynamical system is obtained experimentally based on a Galerkin projection of the Navier-Stokes equation onto the POD eigenfunctions. We are then able to trace the evolution of the predicted POD modes and to compare them to original real-time data. Following a previous study, we also apply POD on the convection terms from the Navier-Stokes equations and compute a new POD basis along with eigenmodes from which an evolution equation is obtained using a curve fit method. A comparison between the prediction results of both variables will be established. [Preview Abstract] |
Tuesday, November 21, 2006 12:41PM - 12:54PM |
OO.00003: Time-Resolved PIV and Pressure Measurements of Oscillating and Pulsating Flow in a Rapid Expansion Barton Smith, Cameron King Separating oscillating flow in an internal expansion with a total angle of 30 degrees is studied experimentally. Time-Resolved PIV measurements and simultaneous pressure measurements reveal that during the accelerating portion of the cycle, the flow may remain attached in spite of a very large adverse pressure gradient. During the decelerating portion of the cycle, the flow is more prone to separation. The duration and extent of the separation depends on Reynolds number (based on stokes layer thickness) and more critically, the oscillation displacement amplitude relative to the cross-stream dimension. The time-varying pressure measurements are used to determine the resultant minor losses for the flow in each direction as well as the acoustic impedance. These are found to be a decreasing function of the Reynolds number and an increasing function of displacement amplitude. The impact of the addition of a steady-flow component in the direction of increasing flow area is also assessed. [Preview Abstract] |
Tuesday, November 21, 2006 12:54PM - 1:07PM |
OO.00004: Dynamics of Compliant Membranes Forced by Vortex Shedding Arnold Song, Ricardo Galvao, Kenneth Breuer Low-aspect-ratio wings composed of thin, compliant membranes are unique to flying and gliding mammals such as bats and flying squirrels. The distinct structure of the membrane wing is thought to be a major contributor to the extraordinary flight capabilities with respect to agility and maneuverability of these animals. We present wind tunnel measurements of the static deformation and unsteady vibrations of a thin, low aspect ratio membrane wing subject to forcing by vortex shedding from leading edge separation. The three-dimensional membrane dynamics are measured via high-speed stereo photogrammetric tracking of an array of discrete locations on the membrane. The dependence of the static deflection and aerodynamic forces on dynamic pressure, angle of attack and membrane elasticity are reported. In addition, at high angles of attack, unsteady vibrational modes in the membrane are measured, and connections with the leading edge vortex shedding are explored. The implications for animal flight behavior will also be discussed. [Preview Abstract] |
Tuesday, November 21, 2006 1:07PM - 1:20PM |
OO.00005: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2006 1:20PM - 1:33PM |
OO.00006: Scaling of Plasma Synthetic Jet Actuators Jamey Jacob, Arvind Santhanakrishnan The plasma synthetic jet actuator (PSJA) is a geometric variant of a plasma actuator, consisting of an annular electrode array that results in a circular region of dielectric barrier discharge plasma. Quiescent flow PIV measurements of the PSJA reveal that the flowfield on actuation resembles that of a zero-mass flux or synthetic jet that is useful for flow control, particularly separation reduction. Like synthetic jets, unsteady pulsed actuator operation results in formation of multiple vortex rings. The output jet momentum is found to be affected by the power input, actuator dimension and pulsing frequency. While increasing the input power increases the maximum jet velocity, an optimum range of pulsing frequencies and actuator dimensions are observed to exist in order to maximize jet momentum. This presentation examines scaling relations for PSJA operation in quiescent flow. Specifically, the relation between input power, actuator dimension, pulsing frequency, and output jet velocity is demonstrated analytically starting from fundamental fluid dynamics principles. The relations obtained from the scaling analysis are compared with experimental results for validation of the model. [Preview Abstract] |
Tuesday, November 21, 2006 1:33PM - 1:46PM |
OO.00007: Influence of upstream turbulence on self-sustained oscillations in an open cavity Sang Bong Lee, Hyung Jin Sung Main feature of an open cavity is a self-sustained oscillation which is caused by the interaction between the instability of shear layer and impingement. The presence of the self-sustained oscillation is well-known for incoming laminar boundary layer, not for turbulent boundary layer. In the present study, DNSs and LESs of turbulent flow over an open cavity are performed to investigate the influences of upstream turbulence and cavity length on the self-sustained oscillation (3,000$\le $Re$\le $12,000, 1$\le $L/D$\le $6). When the ratio of the cavity depth to the upstream momentum thickness is small (D/$\theta $=10), the separated shear layer has the energetic frequencies due to 3D vortical structures near the leading edge. The small vortices related to upstream high-speed streaky structures produce high pressure fluctuations on the trailing edge. The separated shear layer and 3D vortices undergo a complex transition as the cavity length increases. Meanwhile, if the depth ratio to the momentum thickness is large (D/$\theta $=40), turbulence statistics and frequency spectra show a development of 3D vortical structures which are related to the self-sustained oscillation. [Preview Abstract] |
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