Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session G05: Flow Control: Actuator Design and Analysis (5:00pm - 5:45pm CST)Interactive On Demand
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G05.00001: Internal flow properties of a Sweeping Jet actuator for different Coanda surface geometries Vladimir Parezanovi\'c, Mariam Amer, Abdul Raouf Tajik We investigate the internal flow dynamics of a Sweeping Jet (SWJ) actuator with different Coanda surface shapes, using time-resolved pressure and PIV measurements. The performance of each design is assessed in terms of the jet oscillation frequency, the static pressure drop, and the spectral distribution quality. Three different Coanda surface profiles are tested: (i) a diverging straight line, (ii) a curved elliptical profile, and (iii) a backward-facing step profile. High-frequency Kulite pressure sensors are used to record the temporal flow dynamics at key points inside the actuator. It is observed that a straight-line surface yields the best oscillation frequency peak definition. An elliptical profile is causing a lower pressure drop by around 10\%, which makes it the most energy-efficient design. The Coanda surface with a backward-facing step profile increases the jet oscillation frequency by up to 30\% for the higher actuator mass flow rates. However, this increase in maximum frequency is accompanied by an inferior oscillation frequency peak definition. Time-resolved PIV measurements of the internal flow will be presented to discuss the physical mechanisms specific to each of the different Coanda surface geometries, which are responsible for these performance improvement. [Preview Abstract] |
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G05.00002: Actuator Waveform Design using Nonlinear Adjoint Looping on the Acoustic Flow in an Inkjet Printhead Matthew Juniper, Petr Kungurtsev In inkjet print heads, piezo-electric actuators along one side of a 100 micron channel eject pico-litre droplets from a nozzle on the other side of the channel. After ejection, the acoustic reverberations in the channel must die away before a new droplet can be ejected. It takes several hundred microseconds for the reverberations to die away naturally so, instead, open loop control of the actuator is used to eliminate the reverberations. The current state of the art is to design this waveform with trial and error on several thousand experiments. In this study we instead use nonlinear adjoint looping of a numerical simulation of the acoustic flow in the channel in order to converge to the optimal actuator waveform. In doing so, we identify the physical mechanism through which the reverberations are eliminated and find the minimum time required for this. [Preview Abstract] |
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G05.00003: Toward Understanding Sparse Sweeping Jet Configurations on Aircraft Control Surfaces Emile Oshima, Oliver Wild, Stephanie Rider, David Jeon, Israel Wygnanski, Morteza Gharib Many aerospace research institutions are looking to integrate active flow control (AFC) devices into the design process of next-generation commercial and military aircraft. Sweeping jet actuator (SWJ) arrays are attractive for their reliable design and demonstrated flow control efficacy. Many previous efforts have focused on uniform array designs that cover the entire wingspan. Still, we expect the interaction between the jets and the complex 3D flow over a wing to vary significantly with spanwise location. Experiments are conducted on a short aspect-ratio swept-back wing model in the Lucas Wind Tunnel at Caltech. A spanwise array of twelve SWJ is installed at 80{\%} chord, and each jet is equipped with an on-off mechanism to enable testing of various sparsity levels and distributions. Force measurements, surface tuft visualization, and particle image velocimetry data are combined to understand the different flow physics involved. We show that jets can be grouped mainly into three categories based on spanwise position, providing useful insight for driving future AFC design and optimization processes. [Preview Abstract] |
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G05.00004: Active control strategy for the vortex-induced vibration of sphere via near-wake jet flow Amir Chizfahm, Rajeev Jaiman We present an active base bleed flow control strategy for the unsteady wake flow and the vortex-induced vibration (VIV) of spheres at low Reynolds number. For the proposed control strategy, a reduced-order model (ROM) is developed by the eigensystem realization (ERA) algorithm, which provides a low-order representation of the unsteady flow dynamics in the neighborhood of the equilibrium steady state. The actuation is considered via near-wake jet at the base side of the bluff body. The resulting controller designed by linear low-order approximation can suppress the nonlinear saturated state, which further confirms our earlier hypothesis about the linear mechanism in a nonlinear self-sustained VIV phenomenon. A systematic linear ROM-based stability analysis is performed to understand the eigenvalue distributions of elastically mounted spheres. Results from the ERA-ROM analysis are consistent with those obtained from fully nonlinear fluid-structure interaction simulations. A sensitivity study on the bleed coefficient has been performed to obtain the optimum actuation effort. Overall, the proposed control is found to be effective in suppressing the vortex shedding and the VIV for a range of reduced velocities and mass ratios. [Preview Abstract] |
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G05.00005: Vortex Dynamics of Pitched Orifice Synthetic Jets in Quiescent Fluid John Farnsworth, Matthew Knickerbocker, Joseph Straccia The influence that the orifice pitch angle and downstream lip radius have on the vortex dynamics of an aspect ratio, $AR = 20$, rectangular synthetic jet actuator issuing into quiescent fluid are investigated experimentally using particle image velocimetry measurements. Comparisons are made for an orifice pitch angle of $\alpha = 45^\circ$ and dimensionless downstream lip radii of $R^* = 0$, 5.1, and 7.8 at conditions of $Re = 910$ with $St = 0.097$. The time- and phase-averaged velocity fields were recorded on the centerline of the orifice major axis in addition to two off-centerline spanwise positions. Analysis of the phase-averaged vorticity field showed that the vortex formation is strongly influenced by the lip radius, which noticeably alters the flow field development. Specifically, increasing the downstream lip radius increases the asymmetry in the strength of the elongated vortex that is formed. This in turn increases the momentum near the wall aligned in the direction tangential to the wall. Additionally, all geometries exhibited a highly three-dimensional jet development which is the result of vortex dynamics associated with: 1) spatial variability in self-induction, 2) circulation asymmetry, and 3) possibly interactions with the wall image vortex system. [Preview Abstract] |
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G05.00006: Experimental Investigations Of A Pressure Anomaly In The Operation Of A Synthetic Jet Actuator. Rick Cressall, Tim Persoons, Kenneth Christensen Synthetic Jet Actuators (SJA) are used in a growing number of flow control applications ranging from flow separation, thermal management, to noise control in aviation. An SJA operates by oscillating a flexible membrane inside a cavity connected to a nozzle. This yields a steady train of vortices that produces momentum transfer that mimics a turbulent jet produced from a nominal nozzle. Due to the complex physics involved in the interaction between an SJA and its surroundings, a reduced-order model can be used to reliably operate an SJA independent of external disturbances or minor changes in the driver characteristics. Development of these reduced order models are an active area of research. Recent work has identified a pressure anomaly that is unexplained and unaccounted for by current models. This work attempts to understand and explain the physics of the pressure anomaly using experimental methods to better improve the reduced order models. Phase-locked displacement measurements of the flexible membrane are acquired at multiple locations using a laser displacement sensor [Preview Abstract] |
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