Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G26: Flow Control: Plasma Actuation |
Hide Abstracts |
Chair: Thomas Corke, Notre Dame Room: 608 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G26.00001: Vorticity Generation in a Single Nanosecond Spark Discharge Due to Shock Curvature Bhavini Singh, Lalit Rajendran, Pavlos Vlachos, Sally Bane Spark plasma discharges are generated by raising the voltage difference between two electrodes, until breakdown voltage is reached, resulting in ionization of gas in the electrode gap. This rapid release of energy results in the formation of a shock wave as well as a region of hot gas that expands and cools with time. At later times, vortex rings are formed near each electrode that entrain ambient gas into the electrode gap to cool the hot gas kernel. However, the mechanism(s) responsible for the generation of vorticity in the flow field, and the effect of electrical energy deposited in the gap on this vorticity is unclear. We hypothesize that the shock wave formed at the time of the discharge generates the vorticity by means of baroclinic effects due to shock curvature, and this vorticity field then develops into the pair of vortex rings observed at later times. In this work we develop a detailed analytical framework to relate the vorticity generation to the shock curvature and energy deposited in the electrode gap, and test this framework using 700 kHz shadowgraph and 100 kHz pulse-burst Particle Image Velocimetry (PIV) measurements. We extract the shock curvature from the shadowgraph images and compare the predicted vorticity field from the framework with the measured vorticity field from PIV. These measurements along with the framework will help ascertain the role of shock curvature and energy deposited on the vorticity generation. [Preview Abstract] |
(Author Not Attending)
|
G26.00002: Design of a zero-net-mass-flux actuator based on a DBD jet in a partially enclosed cavity. Anood Alkatheeri, Abdul Raouf Tajik, Abdulla Aljaberi, Vladimir Parezanovic Recently, Lucas et al. [1] have shown that a shallow cavity at the base of a 3D bluff body can significantly stabilize the symmetry breaking mode of its wake. A natural recirculation of the flow near the base opposes the selection of an asymmetric state, which symmetrizes the wake and yields a higher base pressure (reduced drag). Our work investigates the possibility of recreating this effect, using a partially enclosed cavity with a Dielectric Barrier Discharge (DBD) jet inside. When the DBD jet is activated it produces suction and blowing action at the two lateral slits of the cavity which can hopefully yield a similar effect on the bluff body wake. Current work focuses on the optimal design of such a cavity, using 2D URANS-based simulations in conjunction with the electrodynamic force model of a DBD jet [2]. The dynamics of the DBD jet inside a several different cavity shapes are simulated for steady and periodically pulsed actuation, and the velocity profiles are analyzed. The goal is to establish the most important geometric properties of the cavity for a desired balance between suction and blowing action from the two slits using a single DBD jet. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G26.00003: Laminar boundary layer response to impulse forcing by an array of plasma actuator vortex generators Hossein Khanjari, Ronald Hanson In this computational and experimental study the response of the Blasius boundary layer to an impulse force is examined. The array of actuators are arranged to act as vortex generators. This arrangement of actuators has previously been used to control steady and quasi-steady streaks occurring in the boundary layer. In the experimental portion of the study, hot-wire velocity measurements are performed. Using the actuator input as reference, the dynamic response of the streamwise velocity in the boundary layer to the pulsed plasma actuation is reconstructed by a phase-averaging technique. Several experimental cases are used to calibrate a momentum source distribution to model the effect of the actuator numerically. The forcing model is applied in conjunction with a commercial computational fluid dynamics code to simulate the boundary layer flow and the response to forcing. Following validation of the computed flow it is shown that the key aspects related to the dynamics response, such as a non-minimal phase behavior of the wall shear stress can be explained by a secondary vortex structure that depends on the streamwise extent of the actuator. The results have important implications to the overarching motivation of a dynamic control system. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G26.00004: On The Physical Mechanism of Turbulent Boundary Layer Drag Reduction Under AC-DBD Plasma Actuation Samaresh Midya, Alan Duong, Thomas Corke, Flint Thomas The results of a series of experiments are reported which use near-wall active flow control designed to intervene in the process of streamwise vortex (SWV) generation, which is primarily responsible for turbulence production in wall-bounded flows. The flow control method utilizes an array of flush mounted AC-DBD plasma actuators in a ZPG TBL over the range of Re$_{\mathrm{\tau }}=$550-1750. The control flow consists of a series of near-wall, span-wise oriented unidirectional wall jets with velocity comparable to the friction velocity and has been shown to produce significant reductions (around 20{\%}) in drag. The control flow is fully characterized using PIV. The span-wise wall jets inhibit the formation of near-wall SWVs {\&} thus reduce the turbulence production. This manifests itself in the reduction of near wall turbulent Reynolds stress producing events. The focus of the reported experiments is to further clarify the~mechanism of drag reduction. X-wire measurements utilizing the quadrant splitting technique are performed downstream of the actuator. These are used to characterize {\&} contrast both the duration of {\&}~time interval between quadrant 2 {\&} 4 events in the actuated {\&} non-actuated flows. The quadrant contributions to the Reynolds stress are compared for natural {\&} actuated cases. Effort has been made to correlate the observed drag reduction {\&} the change in Reynolds stress profile. The turbulence statistics have also been compared to similar statistics obtained from a ZPG TBL under pulsed-DC plasma actuation where even higher drag reduction was achieved. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G26.00005: High-speed Schlieren visualizations of plasma pulsed jet in subsonic and supersonic regimes Nicolas Benard, Yang Zhang, Haohua Zong, Marios Kotsonis, Lou Cattafesta, Eric Moreau A novel type of pulsed jet using a spark discharge has been developed in recent years at PPRIME Institute. The device combines a cavity continuously fed by an external pressure source and a plasma discharge propagating from a small needle aligned with the jet orifice. The electric circuit uses a pre-ionization wave to trigger the ignition of the spark discharge. This system has been developed for flow control applications where high-frequency forcing and high momentum injection are both required. The cavity is supplied by constant air pressure at 2.4 bar, producing supersonic jet from the 1-mm diameter orifice. Subsonic conditions can also be achieved by adding a neck extension including a sudden expansion from 1 to 2 mm. In the present investigation high-speed schlieren visualizations have been conducted at a repetition rate of 100 kHz for both supersonic and subsonic operating modes. The energy released is 100 mJ/pulse, and the visualizations clearly demonstrate the strong modulation of the flow conditions from the jet orifice to the surrounding flow region. Precursor and secondary shock waves are visualized as well as the structure of the pulsed jet with a vortex ring formed in front of the jet. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G26.00006: Ac-DBD vs Ns-DBD Plasma Actuation on a Turbulent Mixing Layer Ashish Singh, Jesse Little A parametric study is undertaken to compare ac-DBD (momentum) and ns-DBD (thermal) plasma actuators in a low speed turbulent mixing layer using an identical load. The mean flow response to each actuation technique is matched at a fixed downstream location. The imposed equivalence in local control authority between the two actuators extends to the global flow, both in the mean and fluctuating components. The ns-DBD plasma actuator requires six times more energy to achieve the same control as the ac-DBD in this specific flow. By studying the flow field very near the splitter plate trailing edge, the difference in momentum versus thermal actuation mechanisms is revealed. A velocity deficit is observed for both actuators, but a thermal bump-like mechanism is responsible in the ns-DBD case while a near surface jet redirecting momentum is found in the ac-DBD case. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G26.00007: Vortex Development in a Laminar Separation Bubble measured via Tomographic Particle Image Velocimetry John Kurelek, Serhiy Yarusevych, Marios Kotsonis The development of shear layer vortices in a laminar separation bubble is investigated experimentally using Planar and Tomographic Particle Image Velocimetry. The experiments are carried out in a series of wind tunnel tests, with the bubble formed on a flat plate subjected to an adverse pressure gradient. Sensitivity to spanwise uniform (2D) and small-amplitude spanwise modulated disturbances (3D) is explored, with disturbances produced using surface mounted dielectric barrier discharge plasma actuators. Compared to the natural case, both types of forcing lead to earlier vortex formation that is rendered essentially two-dimensional at roll-up. While the vortex filaments remain largely two-dimensional until breakdown when subjected to the 2D forcing, deformations rapidly develop within the separation bubble at the spanwise wavelength that matches the input wavelength when 3D forcing is applied. The results elucidate the mechanism responsible for the observed rapid vortex deformations from the initially weak spanwise component of the input disturbances and the associated impact on the mean bubble characteristics. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G26.00008: Phase-resolved Body-force Determination of an AC-DBD Plasma Actuator in Laminar Flow Marc Tobias Hehner, Goncalo Coutinho, Ricardo Pereira, Nicolas Benard, Jochen Kriegseis In continuation of earlier efforts (Kriegseis et al., 2013, JPhysD, Benard et al., 2013, JPhysD, Pereira et al., 2014, JApplPhys, D\"{o}rr\&Kloker, 2015, JPhysD) the present study revolves around the PIV-based characterisation of plasma-induced body-force fields in laminar boundary layers ($U_\infty \leq 30$ m/s). Both common approaches, Navier-Stokes equation (NSE) and vorticity equation (VE), are applied to the obtained phase-resolved velocity data (24 phases). The extracted forces are compared in terms of time-averaged and phase-resolved force distributions. Additional force-magnitude information is determined to evaluate the impact of the airflow on the actuator performance. The plasma actuator exerts a co-flow force (along mean flow) in a flat-plate laminar boundary-layer flow. The power consumption of the actuator was found constant for $U_\infty \leq 30$ m/s. Interestingly, the determined force from NSE changes significantly with increasing airflow velocity, whereas the calculated force from VE budgets a constant integral force magnitude. Consequently, the implied assumptions of either approach are revisited and limits of the formerly consider suitable simplifications -- at least for quiescent air -- are discussed on the basis of the obtained data. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700