Velocity slip and interfacial momentum transfer in the transient section of supersonic gas-droplet two-phase flows

Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-phase (gas-droplet) flow in the transient section inside and outside a Laval jet (LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) X 10(4) Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090 ms for the two-phase flow formed inside the LJ and less than 0.5 ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number M-g from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocimeter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.