科研之友
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摘要
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 How 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 lighter air stream on the outside of the curve and a slower and heavier fuel stream on the inside of the curve, the other one has a slower and heavier fuel stream on the outside of the curve and a faster and lighter air stream on the inside of the curve. Because of the turning, the How profiles are significantly altered, and the instability mechanisms are modified. In most cases, the mixing layers with the faster and lighter air stream on the outside are more unstable than the mixing layers with the heavier and slower fuel stream on the outside. The reacting mixing layers are always more unstable than the corresponding nonreacting cases in terms of the turbulent kinetic energy. Positive and negative vorticities are generated in the reacting case by the baroclinic effect associated with the large density 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.
- 出版日期2008-5
