The intakes of Unmanned Ariel Vehicles (UAV) and Unmanned Combat Ariel Vehicles (UCAV) have complex serpentine geometries that include curvature, area increase and offsets. This is from the requirements of stealth features in such inlets. There is also a design requirement to keep the intake length short. Tight geometrical curvatures coupled with flow diffusion are known to generate secondary flows and many a time lead to flow separation. So flow at the exit may be quite distorted and total pressure losses may be high. Therefore some kind of flow control is required to ensure that the design goals of pressure recovery and flow quality are maintained.

Significant previous research has been carried out by one of the authors on flow control in S-Duct and serpentine duct geometries with various options of passive and active controls (1, 2, 3 and 4). In one of the latest of such studies (5), very encouraging results have been obtained in improving performance of S-duct diffusers using a zero net mass flow (ZNMF) active control. The present paper is a CFD study on modeling the flow in such a duct with and without flow control. As large amount of experimental data is available for both passive and active control on this geometry, it can be used to validate CFD predictions. The experimental results are available for improvement in pressure recovery and reduction of flow distortion using both passive and active flow controls including a combination of suction and blowing (vortex generator jets) for low-subsonic flow regime. Once the CFD model is proven to make good predictions for the present geometry, the same could be applied to more complex and realistic intake geometries.

The numerical (CFD) study carried out is a turbulent flow analysis in S-duct geometry to estimate pressure recovery and flow distortion with and without use of flow control techniques. The flow is modeled inside a rectangular section S-shaped duct with a Reynolds number of 1.479×105 based on the intake duct height. The diffusing duct has an area ratio of 1.25. The location of vortex generators and suction are based on the benchmarked experimental data (5) and is remodeled for CFD computations. The analysis is carried out for the low-subsonic (incompressible) flow and the CFD results are compared with the experimental results. The results obtained for bare duct and zero net mass flow (ZNMF) agree very well with the experimental data. As such, in future, work can be carried out at high subsonic, more complicated geometries and at various vortex generator jet angles to optimize the pressure recovery for high Mach number flows.

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