The flow control in twin air-intakes is necessary to improve the performance characteristics, since the flow traveling through curved and diffused paths becomes complex, especially after merging. The paper presents a comparison between two well-known techniques of flow control: active and passive. It presents an effective design of a vortex generator jet (VGJ) and a vane-type passive vortex generator (VG) and uses them in twin air-intake duct in different combinations to establish their effectiveness in improving the performance characteristics. The VGJ is designed to insert flow from side wall at pitch angle of 90 degrees and 45 degrees. Corotating (parallel) and counterrotating (V-shape) are the configuration of vane type VG. It is observed that VGJ has the potential to change the flow pattern drastically as compared to vane-type VG. While the VGJ is directed perpendicular to the side walls of the air-intake at a pitch angle of 90 degree, static pressure recovery is increased by 7.8% and total pressure loss is reduced by 40.7%, which is the best among all other cases tested for VGJ. For bigger-sized VG attached to the side walls of the air-intake, static pressure recovery is increased by 5.3%, but total pressure loss is reduced by only 4.5% as compared to all other cases of VG.

Pylon-blowing systems provide an effective way of minimizing the interaction effects due to pylon-wake impingement experienced by pusher propellers. This paper presents a numerical study of the uniformity of the blown pylon wake as a function of blowing-slot geometry and blowing momentum coefficient. The flow around the pylon was simulated by solving the steady-state Reynolds-averaged Navier-Stokes equations. The numerical setup was validated using experimental data for both trailing-edge blowing and chordwise blowing configurations. If experimental error is neglected, the model error for the chordwise blowing layout was 15-17%. It was shown that maximal wake uniformity was achieved for a chordwise blowing configuration with the blowing slots positioned at x/c = 0.7. This location provided the best compromise between boundary-layer thickness upstream of the blowing slot, available mixing length, and boundary-layer development downstream of the slot. The corresponding optimal blowing coefficient resulted in a slight velocity overshoot in the boundary layer at the pylon trailing edge. This overshoot then mixed with the deficit associated with the boundary layer formed downstream of the blowing slot to arrive at a nearly uniform velocity profile in the pylon wake. Under asymmetric inflow conditions, the chordwise blowing approach provided effective wake filling if the blowing coefficients on upper and lower surfaces were separately matched with the local boundary-layer thickness at the blowing slot. A linear relation between required blowing rate and boundary-layer thickness was found. Following this approach, the resulting wake was made nearly uniform at an angle of attack of 9 • .

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