Effect of Periodic Blowing on Attached and Separated Supersonic Turbulent Boundary Layers

Effect of Periodic Blowing on Attached and Separated Supersonic Turbulent Boundary Layers

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VOL. 29. NO. 10. OCTOBER 1991 AIAA JOURNAL 1651 Effect of Periodic Blowing on Attached and Separated Supersonic Turbulent Boundary Layers Michael S. Selig* and Alexander J. Smitst Princeton University, Princeton, New Jersey 08544 Periodic blowing at frequencies up to 5 kHz was used to control the unsteadiness of two-dimensional shock- wave/turbulent boundary-layer interactions. Two separate experiments were performed. In the first case, pe- riodic blowing was introduced through a spanwise slot in the wall to produce an unsteady shock-wave/boundary- layer interaction boundary layer on the tunnel wall. In the second case, periodic blowing was introduced into the shock-induced separation bubble formed by a 24-deg compression comer interaction. The incoming flow conditions for both experiments were M, = 2.84, Re)l = 6.5 x IO'/m, and 0 0 = 26 mm. Measurements of the fluctuating mass flux and wall pressure were made, and the unsteady flowlield was visualized through stroboscopic schlieren videography. The measurements were conditionally sampled based on the phase of the blowing cycle. The results suggest that (at least in this case) the naturally unsteady shock motion in the compression ramp interaction does not contribute significandy to the turbulence amplification, as had been previously thought. Instead, there is strong evidence to suggest that large-scale motions associated with the maxima in the angular momentum profiles in the downstream boundary layer are responsible for the large mixing observed. I. Introduction T HE characteristic unsteadiness of shock-wave/boundary- layer interactions was first documented by Kistler I in a study of a supersonic separated flow produced by a forward- facing step. It has since been observed in attached and sep- arated compression comer flows,~·3 blunt fin interactions,4-" and oblique shock interactions produced by a sharp fin at different angles of attack. 7 K Despite this extensive experi- mental work, the effects of the unsteadiness on the boundary layer, and the mechanisms that cause the unsteadiness, are not well unJerstood. The turbulence levels typically display a large amplification downstream of the shock, and shock unsteadiness has been suggested as an important mechanism for transferring mean flow energy into the turbulence. Y.III It seems reasonable to suppose that the instantaneous shock position i~ affected by the incoming boundary-layer turbu- lence, and Debieve and Lacharme" confirmed that free- stream turbulence can cause the deformation and oscillation of an oblique shock. Furthermore, when the flow is separated, large-scale "breathing" of the separated zone may induce an unsteady shock motion,Y and since the frequency of the shock motion in a compression ramp interaction depends on the ramp angle,6 the unsteadiness may also depend on the shock strength.
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This note was uploaded on 10/20/2010 for the course AERONAUTIC A.E. taught by Professor Allwyn during the Spring '10 term at Anna University Chennai - Regional Office, Coimbatore.

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Effect of Periodic Blowing on Attached and Separated Supersonic Turbulent Boundary Layers

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