Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session L17: Flow Control: Plasma Actuators & ApplicationsControl
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Chair: Thomas Corke, University of Notre Dame Room: 605 |
Monday, November 20, 2017 4:05PM - 4:18PM |
L17.00001: Pulsed-DC DBD Plasma Actuators Alan Duong, Thomas Corke, Flint Thomas A power system for dielectric barrier discharge (DBD) plasma actuators that utilizes a pulsed-DC waveform is presented. The plasma actuator arrangement is identical to most typical AC-DBD designs with staggered electrodes that are separated by a dielectric insulator. A key difference is that the pulsed-DC actuator utilizes a DC voltage source to drive the actuator instead of an AC voltage input. The DC source is supplied to both electrodes. The exposed electrode remains constant in time while the encapsulated electrode is periodically grounded for short instances then is allowed to rise to the source DC level. Further investigation of the pulsed-DC plasma actuator was conducted. Time-resolved velocity measurements were done to characterize the induced velocity field generated by the pulsed-DC plasma actuator. A model of the pulsed-DC plasma actuator is developed in LTspice for further study. The work presented are intended in developing a model to be used in CFD flow control simulations. [Preview Abstract] |
Monday, November 20, 2017 4:18PM - 4:31PM |
L17.00002: Investigation of Scaling Effects in Surface Dielectric Barrier Discharge Actuators Alvin Ngo, Jamey Jacob, Kedar Pai Scaling effects on the plasma induced flow field of a surface dielectric barrier discharge (SDBD) actuator is investigated experimentally. The SDBD actuator consists of two asymmetrically arranged electrodes, one exposed to atmospheric air with the other encapsulated, separated by a dielectric material. Application of high voltage in ambient conditions causes a self-limiting plasma to form along the edges of the exposed electrode. An entrainment of flow near the plasma region is observed as momentum is transferred into the quiescent atmospheric air. The impact of varied dielectric material, dielectric thickness, and electrode gap distance is evaluated using PIV and optical techniques to observe the induced flow and plasma intensity, respectively. The induced flow outputs are found to be affected significantly by the dielectric material changes and moderately by the thickness and gap distance changes. The induced flow from various actuator types are compared and their overall effectiveness at transferring momentum into the flow is examined. [Preview Abstract] |
Monday, November 20, 2017 4:31PM - 4:44PM |
L17.00003: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 4:44PM - 4:57PM |
L17.00004: Close-loop Dynamic Stall Control on a Pitching Airfoil Ian Giles, Thomas Corke A closed-loop control scheme utilizing a plasma actuator to control dynamic stall is presented. The plasma actuator is located at the leading-edge of a pitching airfoil. It initially pulses at an unsteady frequency that perturbs the boundary layer flow over the suction surface of the airfoil. As the airfoil approaches and enters stall, the amplification of the unsteady disturbance is detected by an onboard pressure sensor also located near the leading edge. Once detected, the actuator is switched to a higher voltage control state that in static airfoil experiments would reattach the flow. The threshold level of the detection is a parameter in the control scheme. Three stall regimes were examined: light, medium, and deep stall, that were defined by their stall penetration angles. The results showed that in general, the closed-loop control scheme was effective at controlling dynamic stall. The cycle-integrated lift improved in all cases, and increased by as much as 15\% at the lowest stall penetration angle. As important, the cycle-integrated aerodynamic damping coefficient also increased in all cases, and was made to be positive at the light stall regime where it traditionally is negative. The latter is important in applications where negative damping can lead to stall flutter. [Preview Abstract] |
Monday, November 20, 2017 4:57PM - 5:10PM |
L17.00005: Dynamic Stall Control Using Plasma Actuators Nathan Webb, Achal Singhal, David Castaneda, Mo Samimy Dynamic stall occurs in many applications, including sharp maneuvers of fixed wing aircraft, wind turbines, and rotorcraft and produces large unsteady aerodynamic loads that can lead to flutter and mechanical failure. This work uses flow control to reduce the unsteady loads by excitation of instabilities in the shear layer over the separated region using nanosecond pulse driven dielectric barrier discharge (NS-DBD) plasma actuators. These actuators have been shown to effectively delay or mitigate static stall. A wide range of flow parameters were explored in the current work: Reynolds number (Re $=$ 167,000 to 500,000), reduced frequency (k $=$ 0.025 to 0.075), and excitation Strouhal number (Ste $=$ 0 to 10). Based on the results, three major conclusions were drawn: (a) Low Strouhal number excitation (Ste \textless 0.5) results in oscillatory aerodynamic loads in the stalled stage of dynamic stall; (b) All excitation resulted in earlier flow reattachment; and (c) Excitation at progressively higher Ste weakened and eventually eliminated the dynamic stall vortex (DSV), thereby dramatically reducing the unsteady loading. The decrease in the strength of the DSV is achieved by the formation of shear layer coherent structures that bleed the leading-edge vorticity prior to the ejection of the DSV. [Preview Abstract] |
Monday, November 20, 2017 5:10PM - 5:23PM |
L17.00006: Plasma-based Compressor Stall Control Ryan McGowan, Thomas Corke The use of dielectric barrier discharge (DBD) plasma actuator casing treatment to prevent or delay stall inception in an axial fan is examined. The actuators are powered by a pulsed-DC waveform which induces a larger peak velocity than a purely AC waveform such as a sine or sawtooth wave. With this system, a high-voltage DC source is supplied to both electrodes, remaining constant in time for the exposed electrode. Meanwhile, the covered electrode is periodically grounded for several microseconds and allowed to rise back to the source DC level. To test the actuators' ability to interact with and modify the formation of stall cells, a facility has been designed and constructed around nonconductive fan blades. The actuators are installed in the fan casing near the blade tips. The instrumentation allows for the measurement of rotating pressure disturbances (traveling stall cells) in this tip gap region as well as fan performance characteristics including pressure rise and flow rate. The casing plasma actuation is found to reduce the correlation of the rotating stall cells, thereby extending the stall margin of the fan. Various azimuthal arrangements of the plasma actuator casing treatment is explored, as well as input voltage levels to the actuator to determine optimum conditions. [Preview Abstract] |
Monday, November 20, 2017 5:23PM - 5:36PM |
L17.00007: ABSTRACT WITHDRAWN |
Monday, November 20, 2017 5:36PM - 5:49PM |
L17.00008: Turbulence growth and its dependency of wake vortices on excitation frequency by local body-force around two-dimensional hump Aiko Yakeno, Yoshiaki Abe, Taku Nonomura, Soshi Kawai, Kozo Fujii We investigated details of wake vortex dynamics to cause turbulence increase and early flow-reattachment under excitation forcing by a plasma actuator setting around a 2D hump numerically. The local body-force was homogeneous in the spanwise direction and bursting temporally. That actuation generates two-dimensional roll vortices and other turbulence motions such like three-dimensional rib structure in downstream. These dynamics depended on the excitation frequency. We tried to discuss multi-scaled vortices separately with considering the temporal phaseaveraged statistics of the excitation frequency and others, those are related to roll vortices and others with rib structure between rolls. It was found that the maximum value of non-periodic fluctuation in downstream correlated with flow-reattachment performance more than that of periodic fluctuation of roll vortices. The amplitude becomes large around separation position in early reattachment cases. The spacial growth rates of peak values in the wall-normal direction are same for high frequency cases, K-H instability modes, however not true for low frequency cases. In high frequency cases, amplitude in the early state of separation plays a significant rule to increase it in downstream. [Preview Abstract] |
Monday, November 20, 2017 5:49PM - 6:02PM |
L17.00009: Wake behind circular cylinder excited by spanwise periodic disturbances Yudai Sasaki, Iwami Uchida, Jun Sakakibara We experimentally investigated the influence of flow control of the wake behind a circular cylinder excited by temporal periodic disturbances with spanwise phase variations using plasma actuators, motivated by reducing drag forces by suppressing development of large scale vortices. Plasma actuators were segmented in the spanwise direction, phase differences were given to adjacent electrodes. This experiment was conducted at \textit{Re}$\simeq $8000 and the wake was visualized by PIV. Compared to without forcing, when the phase difference is 180° and non-dimensional forcing frequency$_{\mathrm{\thinspace }}$is higher than approximately 1.0, small vortices induced by periodic disturbance emerged in the free shear layer and the drag forces decreased. [Preview Abstract] |
Monday, November 20, 2017 6:02PM - 6:15PM |
L17.00010: Influence of ion transport on discharge propagation of nanosecond dielectric barrier discharge plasma actuator Weizhuo Hua, Fukagata Koji A numerical study has been conducted to understand the streamer formation and propagation of nanosecond pulsed surface dielectric barrier discharge of positive polarity. First we compared the result of different grid configuration to investigate the influence of x and y direction grid spacing on the streamer propagation. The streamer propagation is sensitive to y grid spacing especially at the dielectric surface. The streamer propagation velocity can reach 0.2 cm/ns when the voltage magnitude is 12 kV. A narrow gap was found between the streamer and dielectric barrier, where the plasma density is several orders of magnitude smaller than the streamer region. Analyses on the ion transport in the gap and streamer regions show the different ion transport mechanisms in the two different region. In the gap region, the diffusion of electron toward the dielectric layer decreases the seed electron in the beginning of voltage pulse, resulting that ionization avalanche does not occur. The streamer region is not significantly affected by the diffusion flux toward the dielectric layer, so that ionization avalanche takes place and leads to dramatic increase of plasma density. [Preview Abstract] |
Monday, November 20, 2017 6:15PM - 6:28PM |
L17.00011: Separation control of NACA0015 airfoil using plasma actuators Daisuke Harada, Jun Sakakibara Separation control of NACA0015 airfoil by means of plasma actuators was investigated. Plasma actuators in spanwise intermittent layout on the suction surface of the airfoil were activated with spanwise phase difference $\varphi =0$ or $\varphi =\pi $ in the case of dimensionless burst frequency$F^{+}=6$ and $F^{+}=0.5$ at $Re=6.3\times 10^{4}$. The lift and drag of the airfoil were measured using a two component force balance. The flow around the airfoil was measured by PIV analysis. In the condition of $F^{+}=6$ and $\varphi =\pi $ at around stall angle, which is 10 degrees, the lift-to-drag ratio was higher than that of$F^{+}=6$ and $\varphi =0$. Therefore, it was confirmed that aerodynamic characteristics of the airfoil improved by disturbances with temporal and spatial phase difference. [Preview Abstract] |
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