An experimental investigation was performed to understand the development andsuppression of the secondary flow structures within a compact, serpentine jet engineinlet duct. By employing a variety of flow diagnostic techniques, the formation of a pairof counter-rotating vortices was revealed. A modular fluidic actuator system that wouldapply several different methods of flow control was then designed and manufactured toimprove duct performance. At the two bends of the inlet, conformal flow controldevices were installed to deliver varying degrees of boundary layer suction, suction andsteady fluid injection, and suction and oscillatory injection. Testing showed that suctionalone could delay flow separation and improve the pressure recovery of the duct by asmuch as 70%. However, this technique was not able to rid the duct completely of thenonuniformities that exist at the engine face plane. Suction with steady blowing,however, increased pressure recovery by 37% and reduced distortion by 41% at theengine face. Suction with pulsed injection had the least degree of success in suppressingthe secondary flow structures, with improvements in pressure recovery of only 16.5%and a detrimental impact on distortion. The potential for gains in the aerodynamicefficiency of serpentine inlets by active flow control was demonstrated in this study.
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