Effects of essential performance parameters on the starting transient of a straight cylindrical supersonic exhaust diffuser (SED) are numerically investigated. Diffuser starting and evacuation transients are examined in terms of SED lengths and pre-evacuation configuration. Preconditioned Favre-averaged Navier-Stokes equations incorporated with a low Reynolds number turbulence model and Sakar's method to treat turbulence compressibility is solved for strongly turbulent all-Mach diffuser flows. The numerical method is properly validated with the measurements with accuracy. Characteristic locus of diffuser-starting and diffuser-unstarting modes is constructed for the diffusers of three different lengths (L/D = 2, 5, and 20). Flow evolutions visualized in diffuser mode-transition regimes manifest a threshold L/D over which the SED starting transient is unique. An occurrence of plume blowback into the vacuum chamber due to lower initial pressure (PC,INIT/PA = 0.0027) expedites expansion of nozzle exhaust and diffuser choking, and causes faster chamber evacuation than the atmospheric starting.
|Number of pages||11|
|Journal||International Journal of Heat and Fluid Flow|
|Publication status||Published - 2008 Oct 1|
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Mechanical Engineering
- Fluid Flow and Transfer Processes