Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E18: Flow Control: Actuator Design and Analysis |
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Chair: Nathan Webb, Ohio State University Room: 206 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E18.00001: Supersonic cavity flow control using plasma actuators Nathan Webb, Dennis Omari, Mo Samimy Flow over cavities with a length to depth ratio of order 1 undergo so called ``Rossiter'' resonance for certain combinations of free stream Mach number, upstream boundary layer characteristics, and cavity length. This is caused by the amplification of natural perturbations in the cavity shear layer by the Kelvin-Helmholtz instability. The amplified perturbations in the shear layer grow and roll up into large-scale structures, which interact with the trailing edge of the cavity. This interaction produces acoustic waves that travel upstream and further perturb the shear layer. If the timing/phase is correct, a feedback loop is formed. Artificial perturbations can be used to alter the resonance condition and thus the flow characteristics. In the past we used Localized Arc Filament Plasma Actuators (LAFPAs) to perturb the shear layer of a subsonic cavity and demonstrated significant control authority to suppress or excite resonance. This work seeks to examine control authority of the LAFPAs in the supersonic regime. Experiments conducted with a supersonic cavity demonstrated the LAFPAs retain the ability to suppress or excite resonance. The ability to either excite or suppress resonance, as needed, is required in some applications. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E18.00002: LES-based characterization of a suction and oscillatory blowing fluidic actuator Jeonglae Kim, Parviz Moin Recently, a novel fluidic actuator using steady suction and oscillatory blowing was developed for control of turbulent flows [1]. The suction and oscillatory blowing (SaOB) actuator combines steady suction and pulsed oscillatory blowing into a single device. The actuation is based upon a self-sustained mechanism of confined jets and does not require any moving parts. The control output is determined by a pressure source and the geometric details, and no additional input is needed. While its basic mechanisms have been investigated to some extent, detailed characteristics of internal turbulent flows are not well understood. In this study, internal flows of the SaOB actuator are simulated using large-eddy simulation (LES). Flow characteristics within the actuator are described in detail for a better understanding of the physical mechanisms and improving the actuator design. LES predicts the self-sustained oscillations of the turbulent jet. Switching frequency, maximum velocity at the actuator outlets, and wall pressure distribution are in good agreement with the experimental measurements. The computational results are used to develop simplified boundary conditions for numerical experiments of active flow control. \\ $[1]$ Arwatz \textit{et al.}, \textit{AIAA J.} \textbf{46}(5) 2008. [Preview Abstract] |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E18.00003: Modeling of a zero-net mass flux actuator for aqueous media Bradley Ayers, Charles Henoch, Hamid Johari A zero-net mass flux actuator was designed to maximize the jet thrust with a 3-in size constraint. The actuator was driven by a solenoid moving a piston in a cavity and when the solenoid circuit was opened, a return spring pulled the piston until the de-energized position was reached. Using the solenoid characteristics, a model was developed to assist in determining the optimal design parameters such as the piston diameter and stroke length, orifice diameter, and the spring constant. The model consisted of three separate elements: the solenoid and return spring forces; the fluid inertia within the cavity as well as the mass of moving parts; and the pressure loss associated with the orifice. The actuator model was used to determine the piston motion through one cycle. A piston stroke length of 4 mm and a cylinder bore of 45 mm was chosen resulting in a slug stroke ratio of 3.9. For the shortest possible waveform and the chosen actuator parameters, the model predicted the piston reaching its maximum stroke of 4 mm in 10 ms, and then returning to its resting position in 31 ms. Thus, a maximum frequency of 32 Hz was found for the shortest waveform in an ideal setup. The model predictions were compared with PIV measurements. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E18.00004: Vectoring of parallel synthetic jets Tim Berk, Bharathram Ganapathisubramani, Guillaume Gomit A pair of parallel synthetic jets can be vectored by applying a phase difference between the two driving signals. The resulting jet can be merged or bifurcated and either vectored towards the actuator leading in phase or the actuator lagging in phase. In the present study, the influence of phase difference and Strouhal number on the vectoring behaviour is examined experimentally. Phase-locked vorticity fields, measured using Particle Image Velocimetry (PIV), are used to track vortex pairs. The physical mechanisms that explain the diversity in vectoring behaviour are observed based on the vortex trajectories. For a fixed phase difference, the vectoring behaviour is shown to be primarily influenced by pinch-off time of vortex rings generated by the synthetic jets. Beyond a certain formation number, the pinch-off timescale becomes invariant. In this region, the vectoring behaviour is determined by the distance between subsequent vortex rings. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E18.00005: Manipulation of Turbulent Boundary Layers Using Synthetic Jets Zachary Berger, Guillaume Gomit, Philippe Lavoie, Bharath Ganapathisubramani This work focuses on the application of active flow control, in the form of synthetic jet actuators, of turbulent boundary layers. An array of 2 synthetic jets are oriented in the spanwise direction and located approximately 2.7 meters downstream from the leading edge of a flat plate. Actuation is applied perpendicular to the surface of the flat plate with varying blowing ratios and reduced frequencies (open-loop). Two-component large window particle image velocimetry (PIV) was performed at the University of Southampton, in the streamwise-wall-normal plane. Complementary stereo PIV measurements were performed at the University of Toronto Institute for Aerospace Studies (UTIAS), in the spanwise-wall-normal plane. The freestream Reynolds number is 3x10$^{\mathrm{4}}$, based on the boundary layer thickness. The skin friction Reynolds number is 1,200 based on the skin friction velocity. The experiments at Southampton allow for the observation of the control effects as the flow propagates downstream. The experiments at UTIAS allow for the observation of the streamwise vorticity induced from the actuation. Overall the two experiments provide a 3D representation of the flow field with respect to actuation effects. The current work focuses on the comparison of the two experiments, as well as the effects of varying blowing ratios and reduced frequencies on the turbulent boundary layer. [Preview Abstract] |
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