Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E25: Flow Control: Jets |
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Chair: Dan Henningson, KTH Room: 31A |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E25.00001: Modeling Forced Jets with Parabolized Stability Equations Aniruddha Sinha, Tim Colonius The theory of parabolized stability equations (PSE) is employed to model the forcing response of high-speed and high Reynolds number round jets. Recently, this theory has been successfully applied to unforced subsonic and supersonic jets to predict the dynamics of the wavepackets implicated in noise radiation to aft angles. The effect of some unsteady actuation mechanisms (e.g. those based on plasma, fluidic injection, etc.) may be practically considered to be impulsive in nature rather than sinusoidal. As a first approximation, linear PSE modes, computed as instabilities of the unforced jet, are suitably combined to simulate the impulse response. The predictions from this procedure compare reasonably well with experimentally determined phase-averaged near-field pressure in subsonic jets forced with localized arc filament plasma actuators. The model can be improved by incorporating the nonlinear interactions between the excited modes in the jet. Such a model is being applied to predict the changes to the dynamics of a supersonic jet actuated by pulsed air injection. The end goal is to use the validated PSE model to understand noise source mechanisms, and propose novel actuation strategies for their mitigation. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E25.00002: Effect of Orifice Angle on Synthetic Jet Actuators Pooya Kabiri, Doug Bohl Synthetic Jet Actuators (SJA's) are commonly used in flow control experiments. It has been shown that in many applications the direction of the jet with respect to the flow direction and surface geometry is important. For example, when controlling separation on an airfoil, the maximum control is obtained when the exit jet is directed parallel, rather than perpendicular to the surface. Typically, the SJA itself must be rotated to direct the flow. In some cases this may not be possible and the orifice must be oriented to direct the flow. This work investigates the flow field induced by a SJA's with the exit orifice located on the surface opposite of the membrane and differing exit angles. The orifices investigated are oriented straight (i.e. 90\r{ }) or angled (60\r{ }, 30\r{ }) with respect to the membrane surface. The entrances to the orifices are contoured to inhibit flow separation within the orifice. The results show that the peak exit velocity is found when the orifice is straight and systematically reduces as the angle becomes smaller. The results also show that the external flow field is greatly affected by the orifice angle. When the orifice is straight a pair of vortices are formed that convect away from the slot. As the angle is reduced a boundary layer is formed on the external surface of the SJA. This boundary layer changes the formation of the vortex pair and inhibits convection of the vortices away from the slot. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E25.00003: Spatio-Temporal Flow Structure over a NACA-0015 Airfoil under the influence of ZNMF Jet Flow Control Callum Atkinson, Nicolas Buchmann, Julio Soria The spatio-temporal flow structure associated with Zero Net Mass Flux (ZNMF) jet forcing at the leading edge of a NACA-0015 airfoil (Re = 30000, AoA = 18 deg) is investigated using high-repetition rate Particle Image Velocimetry (HR-PIV). In the absence of forcing, flow separation occurs at the leading edge, while ZNMF jet forcing at a frequency of f+ = 1.3 leads to a nearly complete reattachment with a 45\% lift increase. The structure and dynamics associated with both the forced and unforced case are considered and the dominant frequencies are identified. A triple-decomposition of the velocity field is performed to identify the spatio-temporal perturbations produced by the ZNMF jet forcing. This forcing results in a reattachment of the flow, which is caused by the generation of large-scale vortices that entrain high momentum fluid from the freestream. Forcing produces a series of vortices that are advected parallel to the airfoil surface. Potential mechanisms by which these vortices affect the flow reattachment are discussed. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E25.00004: Using a wall-normal jet to modify the large-scale structures in a turbulent boundary layer Murali Krishna Talluru, Brett Bishop, Nicholas Hutchins, Chris Manzie, Ivan Marusic We report on attempts to use a wall-normal jet to modify the large-scale structures (``super structures'') that are known to populate the logarithmic regions of high Reynolds number turbulent boundary layers. An upstream spanwise array of surface mounted shear-stress sensors detects the passage of the large-scale events. A rectangular wall-normal jet, located downstream of this array targets the identified event and a second spanwise array downstream of the jet monitors any alterations to the large-scale structure. A traversing hot wire probe is mounted above the downstream array to look for modifications across the depth of the boundary layer. As a first step, an off-line control strategy is investigated. In this case, there is no active controller, the jet is periodically fired with fixed parameters and during post-processing, the ``control'' strategy is emulated in a conditional sense to understand the interactions of an actuated jet with the larger turbulent structures. The results from off-line control scheme are used to develop a real-time control scheme to systematically target the large-scale high skin friction events. The outcome of this control approach on both the instantaneous coherent structures and also the time-averaged quantities is investigated. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E25.00005: Synthetic Jet Control of a Yawing Axisymmetric Body Thomas Lambert, Bojan Vukasinovic, Ari Glezer The global aerodynamic forces and moments on an axisymmetric yawing body are controlled in wind tunnel experiments by exploiting the interaction of an array of synthetic jet actuators with the cross flow over the tail section of the body. The model is supported by a vertical wire through its aerodynamic center and is free to move in yaw. The baseline motion of the model is a yaw oscillation with amplitude and frequency that both monotonously increase with free stream velocity, characteristic of vortex shedding. The aft-facing control jet actuators emanate from narrow, azimuthally segmented slots around the perimeter of the tail section, and activation of the control jets effects the model's path through localized flow attachment on integrated Coanda surfaces. The control jets are used to control the yaw trajectory of the model using a closed loop PID controller. The baseline and controlled model motion is monitored using a laser vibrometer, and the flow evolution near the body and in its near wake is investigated using PIV. The coupled, time dependent response of the model to the actuation is investigated with emphasis on controlling its unstable modes. [Preview Abstract] |
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