Study of Mixing Enhancement in Helium Jet/Shock Interaction by Laser Pulses

The mechanism of low-density jet mixing enhancement by a pulsed laser plasma is investigated through a combined numerical and experimental method. A helium jet is injected in parallel to a Mach 2.4 supersonic airstream, and interacts with an oblique shock generated by a compression ramp of 20 deg. The helium jet Mach numbers are set to be 1.01 and 1.80 for the sonic and supersonic fuel jets in the scramjet combustor, respectively. For jet mixing enhancement control, the laser pulses at frequencies ranging from 5 to 25 kHz are introduced inside the jet. The experimental results show that laser pulses significantly improve the jet mixing with jet width increased by 30% seen from the averaged schlieren images. Three-dimensional unsteady Reynolds-averaged Navier–Stokes equations are solved, and the numerical results further reveal that the jet mixing enhancement is strongly associated with large-scale vortex rings stimulated by the laser pulses interacting with shock waves. These large-scale vortices prompt the jet cross-sectional area and mixing efficiency two times larger. However, the total pressure recovery coefficient is reduced by 0.16% downstream. Meanwhile, the turbulent kinetic energy of jet flow is significantly increased and favorable for the jet mixing.