Nonpremixed Combustion in an Accelerating Transonic Flow Undergoing Transition

Mixing layers composed of gaseous fuel and oxidizer streams passing through curved channels with or without chemical reactions are studied by performing two-dimensional numerical simulations. The flows are subjected to either transverse acceleration or both transverse and streamwise accelerations; the flow accelerates from low subsonic speed to low supersonic speed in the case with the streamwise acceleration. We focus on the development of the mixing layers from laminar flow to the transition regime. The full Navier–Stokes equations coupled with multiple-species equations and the energy equations with chemical reactions are solved using a finite-difference numerical scheme. The effects of turning are investigated on two different flow configurations; one has a faster and lighterairstreamontheoutsideofthecurveandaslowerandheavierfuelstreamontheinsideofthecurve,theother onehasaslowerandheavierfuelstreamontheoutsideofthecurveandafasterandlighterairstreamontheinsideof the curve. Because of the turning, the flow profiles are significantly altered, and the instability mechanisms are modified.Inmostcases,themixinglayerswiththefasterandlighterairstreamontheoutsidearemoreunstablethan themixinglayerswiththeheavierandslowerfuelstreamontheoutside. Thereactingmixinglayersarealwaysmore unstable than the corresponding nonreacting cases in terms of the turbulent kinetic energy. Positive and negative vorticities aregenerated inthe reacting casebythe barocliniceffect associated with the largedensity gradient across the combustion zone. The mixing layers with imposed streamwise accelerations show stabilizing effects, and the chemical conversion rates decrease due to the acceleration.