Experimental study of transition in a compressible free shear layer

The object of this work is the experimental determination of laminar-turbulent transition in shear layers separating adjacent compressible streams. An earlier theoretical determination of transition, based on a minimum Reynolds number condition, is reviewed as a possible asymptotic transition limit when the flow is either an equilibrium shear layer or an equilibrium wake. A theory for the laminar flow development in the non-equilibrium regime downstream of the trailing edge is also presented for the first time, and is found to agree very well with numerical methods. The transition and laminar flow theories are then joined to design an experiment aimed at producing non-equilibrium flows in a supersonic wind-tunnel, and at detecting the transition zone in such a flow. Flow and transition measurements done in this layer show that the shear-layer transition Reynolds number, based on the layer thickness and the fast-side unit Reynolds number, agrees with the corresponding number found by the equilibrium transition theory within 25%. It is concluded that the asymptotic transition theory utilized gives reasonable estimates even close to the trailing edge.