Abstract
The mixing processes in an accelerated duct flow from subsonic to supersonic flow speed with blunt-body wakes were investigated experimentally. Four different injectors, all with their trailing edges located in the subsonic part of the flow and designed as wing bodies, were compared. A toluene/nitrogen mixture was added into the flow through the injectors, and the flow structures behind the injector trailing edges were visualized applying laser-induced fluorescence imaging. The injector flow was parallel to the duct flow and at angles of 45 deg and 90 deg to the ambient air flow. Furthermore, one injector was designed with ramps on the upper and lower surface. Instantaneous images showed that the mixing process was dominated by separated shear layers behind the injectors, which rolled up to vortices being shed from the blunt trailing edge. The injector flow spread out more with increasing injection angle and the edges of the vortices were frayed. In the case of the ramp injector, additional streamwise vortices were generated, and thus the mixing took place in the core region of the flow for a longer distance. Scaling properties such as the half-width, the gradient of the growing wake, and the virtual origin were calculated. This showed that the half-width of the intensity profiles followed the -power-law. Furthermore, the intensity at the duct centerline decreased asymptotically, and the wake showed a self-preserving state.
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