No abstract

Flow separation under crosswind conditions seriously jeopardizes the quality of the nacelle's ow eld. In this paper, microsecond pulsed surface dielectric barrier discharge (µSDBD) is used to suppress the ow separation and reduce the crosswind distortion of the nacelle. The ow structure induced by the µSDBD is rst explored by a high-speed schlieren system. The pressure waves composed of a cylindrical wave surrounding the electrodes and a at wave at the top of the cylindrical one can be perceived, which indicates the fast gas heating produced by the µSDBD. A set of wind tunnel tests are then conducted to verify the ability of µSDBD to suppress the nacelle ow separation and study the in uence laws of pulse frequency, coverage area, and the actuator layout on the ow control effects. Results show that plasma actuation can not only improve the total pressure at the exit of the nacelle but also suppress the ow distortion caused by the crosswind. The best ow control effect can be achieved at the pulse frequency of 500Hz, with the value of sectional distortion coe cient reduced by 57.76% compared with the baseline condition. The ow control effect with the plasma actuator covering 120° of the nacelle perimeter is better than that of 60° and 180° coverage, showing the highest ow control e ciency in the 120°c ondition. The µSDBD can improve mixing between the boundary layer and the main ow, enhancing the ability of the boundary layer to resist the adverse pressure gradient, which is bene cial to ow separation control.

Flow separation under crosswind conditions seriously jeopardizes the quality of the nacelle’s flow field. In this paper, microsecond pulsed surface dielectric barrier discharge (µSDBD) is used to suppress the flow separation and reduce the crosswind distortion of the nacelle. The flow structure induced by the µSDBD is first explored by a high-speed schlieren system. The pressure waves composed of a cylindrical wave surrounding the electrodes and a flat wave at the top of the cylindrical one can be perceived, which indicates the fast gas heating produced by the µSDBD. A set of wind tunnel tests are then conducted to verify the ability of µSDBD to suppress the nacelle flow separation and study the influence laws of pulse frequency, coverage area, and the actuator layout on the flow control effects. Results show that plasma actuation can not only improve the total pressure at the exit of the nacelle but also suppress the flow distortion caused by the crosswind. The best flow control effect can be achieved at the pulse frequency of 500Hz, with the value of sectional distortion coefficient reduced by 57.76% compared with the baseline condition. The flow control effect with the plasma actuator covering 120° of the nacelle perimeter is better than that of 60° and 180° coverage, showing the highest flow control efficiency in the 120° condition. The µSDBD can improve mixing between the boundary layer and the main flow, enhancing the ability of the boundary layer to resist the adverse pressure gradient, which is beneficial to flow separation control.

To develop active flow control technique which can suppress the nacelle intake flow separations caused by crosswind effectively, microsecond plasma actuation is used to control the flow separations of a typical nacelle intake model. Both experimental and numerical investigations have been implemented to uncover the corresponding flow control effects. The plasma actuation is installed near the inception point of the nacelle intake flow separations. According to the experimental and numerical results, the nacelle intake flow separations caused by crosswind are suppressed by the plasma actuation. The frequency of the plasma actuation as well as the scale of the flow separation are influential to the flow control effects. The compressive wave induced by the plasma actuation will act on the separated flow as well as the interface between the flow separation zone and the mainstream zone. This is the mechanism behind the suppression of nacelle intake flow separations using microsecond plasma actuation.

We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current (DC) voltage. The discharge tests show that sliding discharge and extended discharge are filamentary discharge. The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle, ultimately expands the discharge channel. The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge (DBD). The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge, which causes a bulge structure in the discharge channel. The bias DC electrode can deflect the direction of the induced jet, then modifying the properties of the boundary layer. Extended discharge can accelerate the velocity of the starting vortex, improving the horizontal velocity profile by 203%. The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate, compared with sliding discharge and DBD. However, the momentum growth of sliding discharge lasts longer in the whole pulsed cycle, indicating that sliding discharge can also inject more momentum.