Nonlinear stability and structure of compressible reacting mixing layers

The parabolized stability equations (PSE) are used to investigate issues of nonlinear flow development and mixing in compressible reacting shear layer s, which are modelled with an infinitely fast-chemistry assumption. Particu lar emphasis is placed on investigating the change in flow structure that o ccurs when compressibility and heat release are added to the flow. These co nditions allow the 'outer' instability modes-one associated with each of th e fast and slow streams-to dominate over the 'central', Kelvin-Helmholtz mo de that exists unaccompanied in incompressible non-reacting mixing layers. Analysis of scalar probability density functions in flows with dominant out er modes demonstrates the ineffective, one-sided nature of mixing that acco mpanies these flow structures. Colayer conditions, where two modes have equ al growth rate and the mixing layer is formed by two sets of vortices, offe r some opportunity for mixing enhancement. Their extent, however, is found to be limited in the mixing layer's parameter space. Extensive validation o f the PSE technique also provides a unique perspective on central-mode vort ex pairing, further supporting the view that pairing is primarily governed by instability growth rates; mutual induction appears to be a secondary pro cess. This perspective sheds light on how linear stability theory is able t o provide such an accurate prediction of experimentally observed, fully non linear flow phenomenon.