Investigation of an optimal pulsed jet mixing and combustion in supersonic crossflow

The enhanced mixing and combustion mechanism of pulsed sonic jet with optimal frequency in supersonic crossflow with a 10° ramp has been investigated using Large Eddy Simulation (LES). The results show that the energetic structures from the barrel shock and shear vortex are further enlarged at the phase of 1/4T0 periodically due to the swing forward and backward effect of the bow shock. There coexists clockwise and counter-clockwise rotating shear layer vortex structures in the pulsed jet, while only counter-clockwise rotating shear layer vortex structure is found in the steady case. The mixing process and the flame distribution are significantly affected by these structures of different scales. The reflected shock waves in the transverse jet in supersonic crossflow have strong coupling effects with the heat release rate. The pulsed jet is also found to improve the non-premixed dominant heat release rate, but not the premixed one. The mechanism of enhanced mixing and combustion efficiency relevant to the optimal frequency of 50 kHz is studied with Power Spectral Density (PSD) and wavelet analysis, and it is interesting to notice that the optimal pulsed jet frequency has strong coupling effects with the bow shock swing back and forward frequency, the jet shear layer and barrel shock frequencies (i.e., 50 kHz). However, for the non-pulsed steady case, the bow shock characteristic frequency is found to be 40 kHz, which suggests the optimal pulsed jet frequency can be 40 kHz. In order to further validate it, Unsteady Reynolds Averaged Navier Stokes (URANS) simulations have been performed with the pulsed jet frequency of 40 kHz. It is optimising to see that the mixing and combustion efficiency are further improved.