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This study investigates the characteristics of the shedding vortex around the Coanda surface and its impacts on the circulation control (CC) performance. Delay detach-eddy simulation based on the two-equation k-ω shear stress transport (SST) turbulence model performed to solve the flow field. The simulation results show that near the Coanda trailing edge, large vortices periodically shed from the lip above the jet slot and the shedding vortex is surrounded by a series of strip vortices during its downstream movement. The shedding vortex transfers the disturbance to the jet boundary layer and affects the near-wall velocity. Dynamic mode decomposition shows that the shedding vortex and its high-order harmonic flow structures attenuate very slowly and dominate the flow field. The mode with a sub-harmonic frequency of the shedding vortex displays the strip vortices dragged out by the shedding vortex. A larger shedding vortex can intensify the mixing of the jet shear and boundary layers, making the jet velocity decay faster. The size of the shedding vortex can be reduced by decreasing the lip height, thus slowing down the attenuation of the jet velocity and improving the CC performance.

Pulsed Surface Arc Discharge (PSAD) is one of the essential techniques in flow control. In this paper, the effects of electrode configuration on the heat transfer characteristics of PSAD and the disturbance characteristics of PSAD on the flow field were investigated by thermal imaging and high-speed photography technology. By defining the Curvature of Curve (COC) of the electrode, we investigated the physical mechanism of the electrode configuration affecting the PSAD disturbed flow field. The results show COC has the optimal solution COCopt. When COC{less than or equal to}COCopt, the smaller the COC, the more concentrated the PSAD disturbances to the flow field. When COC>COCopt, the electrode configuration will have an endpoint effect, resulting in a deviation between theoretical COC and real COC. The larger the COC, the stronger the endpoint effect, and the more concentrated the PSAD disturbances to the flow field. COC affects the disturbance degree of PSAD to the flow field by distorting electric field intensity distribution. The change in electric field intensity causes the fluctuation frequency of the flow field to be inconsistent with the discharge frequency of the PSAD. The stronger the distortion degree of the electric field intensity, the stronger the high-frequency characteristics of the fluctuating frequency of the flow field, and the stronger the high-frequency characteristics of the flow mode of the flow field. In addition, we obtained the value range of COCopt within 0.5~0.7 through theoretical derivation and established a mathematical model of electrode structure's effect on the flow field's flow structure.

Circulation control (CC) is used extensively to control the attitude of rudderless aircraft experiencing ground effect in take-off and landing phases. The investigation of ground effect on airfoil CC is necessary to improve flight performance and quality in proximity to the ground. The aerodynamics and flow field of a modified NACA0012 airfoil with CC in ground effect are investigated with numerical simulations. The compressible Reynolds-averaged Navier–Stokes equations with the shear-stress transport k − ω turbulence model equations are solved using the Finite Volume Method (FVM). Simulation results show that the ground effect changes the lift increment per unit jet momentum coefficient, and CC can reverse the polarity ground effect. The effective angle of attack α E and the downwash space downstream airfoil are altered by the ground effect resulting in variations of airfoil surface pressure and lift. Unlike the unbounded flow field, the jet attachment distance is not only determined by the jet momentum coefficient but it can change with the ride height, which is the distance from the ground to the center of the semicircular Coanda surface, for the same jet momentum coefficient.