Active flow control based on surface dielectric barrier discharge (SDBD) has become a focus of research in recent years, due to its unique advantages and diverse potential applications. Compared with the conventional SDBD with straight electrodes, the serrated electrode-based SDBD has a great advantage due to its 3D flow topology. It is believed that the boundary layer separation of moving objects can be controlled more effectively with this new type of SDBD. In SDBD with a serrated electrode, the R (tip sharpness) and N (tip number per unit length) have a great influence on the discharge and induced airflow characteristics. In this paper, a parametric study of the characteristics of SDBD with a serrated electrode has been conducted with different ranges of R and N. Aspects of the power consumption, the steady medium temperature distribution, and the maximum induced airflow velocity have been investigated. The results indicate that there is a critical value of R and N where the maximum power consumption and induced airflow velocity are achieved. The uniformity of the steady temperature distribution of the medium surface is found to be more dependent on N. We found that the accelerating effects of the induced airflow can be evaluated with the Schlieren technique, which agree well with the results from the pitot tube.

Currently, great interests are paid to the surface dielectric barrier discharge due to the diverse and interesting application. In this paper, the influences of the electrode gap on the discharge characteristics have been studied. Aspects of the electrical parameters, the optical emission, and the discharge induced gas flow were considered. The electrode gap varied from 0 mm to 21 mm, while the applied AC voltage was studied in the range of 17 kV–27 kV. Results indicate that with the increase of the electrode gap, the variation of discharge voltage exhibits an increasing trend, while the other parameters (i.e., the current, power, and induced flow velocity) increase first, and then decrease once the gap exceeded the critical value. Mechanisms of the electrode gap influencing these key parameters were discussed from the point of equivalent circuit. The experimental results reveal that an optimal discharge gap can be obtained, which is closely related to the applied voltage. Visualization of the induced flow with different electrode gaps was realized by the Schlieren diagnostic technique. Finally, the velocities of induced gas flow determined by the pitot tube were compared with the results of intensity-integral method, and good agreements were found.

Three-dimensional flow simulation and blade tip high-response static pressure measurements were performed on an isolated subsonic compressor rotor to gain more insight into the stall inception mechanism of the compressors. The Navier—Stokes solver, EURANUS, was used for computation. The steady-state flow solution was achieved at the convergence of a four-stage explicit Runge—Kutta integration scheme. The time-dependent calculation was implemented in the implicit dual time stepping scheme, which allowed for the solution of a steady-state problem at each physical time step. The high-response static pressure was measured using five Kulite sensors installed on the casing. The data acquisition frequency was 100 kHz. The recorded data were later analysed using wavelet analysis method. Correlating the simulation result and the measurement result, it was shown that as the compressor was approaching the near stall (NS) condition, the tip leakage vortex dissipation and shedding became violent. The shedding or dissipated flow structures would consequently scatter around the blade tip passage, which formed the initial onset of stall disturbances. These scattered vortexes would finally lead to compressor stall as they hit and merge with each other into low-frequency disturbance of significant size and energy. A stall pre-alarming method based on the monitoring of the low-frequency spectrum power at the NS condition was also suggested by this study.

High-speed railway today has become an indispensable means of transportation due to its remarkable advantages, including comfortability, convenience and less pollution. The increase in velocity makes the air drag become the main source of energy consumption, leading to receiving more and more concerns. The surface dielectric barrier discharge has shown some unique characteristics in terms of active airflow control. In this paper, the influences of surface dielectric barrier discharge on the aerodynamic characteristics of a scaled train model have been studied. Aspects of the discharge power consumption, the temperature distribution, the velocity of induced flow and the airflow field around the train model were considered. The applied AC voltage was set in the range of 20 kV to 28 kV, with a fixed frequency of 9 kHz. Results indicated that the discharge power consumption, the maximum temperature and the induced flow velocity increased with increasing applied voltage. Mechanisms of applied voltage influencing these key parameters were discussed from the point of the equivalent circuit. The airflow field around the train model with different applied voltages was observed by the smoke visualization experiment. Finally, the effects of surface dielectric barrier discharge on the train drag reduction with different applied voltages were analyzed.

This work experimentally investigates plasma actuator (PA) forcing effects on the base flow and developing crossflow (CF) instabilities in a swept wing boundary layer. Spanwise-invariant plasma forcing near the leading edge is configured according to the Base Flow Modification (BFM) strategy. A simplified predictive model is constructed by coupling an experimentally-derived plasma body force and Linear Stability Theory and is used to infer the stability characteristics of the boundary layer subject to BFM. The base flow velocity is measured by stereo-PIV at various PA operating conditions. Similarly, the developing CF instabilities, triggered through Discrete Roughness Elements, are quantified by planar-PIV. The results demonstrate that a PA can reduce the boundary layer CF component, whereas the control authority shows a high dependence on the momentum coefficient. The dissimilar reduction between the streamline-aligned velocity and CF component leads to a local re-orientation of the base flow. Spanwise spectral analysis of the time-averaged flow indicates that stationary CF instabilities can be favourably manipulated whereas the BFM reduction effects depend on the corresponding initial amplitudes of stationary instabilities. An evident spanwise shift in the trajectory of stationary CF vortices is observed, which appears to result from the local alteration of the boundary layer stability due to the PA forcing. Despite the overall reduction in amplitude of stationary CF instabilities, unsteady disturbances are found to be enhanced by the PA forcing. The current results shed light into the underlying principles of BFM-based PA operation, in the context of laminar flow control.