Numerical simulation of the evolution of shock waves and plasma kernels of multi-point laser-induced plasma in supersonic flow

Abstract

Compared with single-point laser-induced plasma, multi-point laser-induced plasma shows some advantages in ignition and flameholding, but with little research. Therefore, numerical studies of multi-point laser-induced plasma in supersonic flow are conducted using an instantaneous energy deposition model. In the studies, the single-pulse laser energy of every laser focus is 50 mJ, the laser focus configuration is linear, the inflow velocities are from Ma 1.5 to Ma 2.5, and the distances between adjacent focal spots are from 2 to 4 mm. The evolution process of shock waves and plasma kernels in supersonic flow has been described in detail when the inflow velocity is Ma 2 and when the distance between adjacent focal spots is 2 mm. Besides, the evolution law of the velocity field, the streamline, and the plasma kernel position in the flow field have also been analyzed. The results reveal that the volume of the plasma kernel increases rapidly within 15 μs and that the initial shock wave has a strong deflection effect on the supersonic flow. Moreover, the effects of inflow velocities and distances between adjacent focal spots on multi-point laser-induced plasma are compared using the plasma kernel's average temperature, volume, and specific surface area. Under the conditions of the studies, the results show that the distance between adjacent focal spots is the main reason affecting the evolution. Thus, a distance longer than 4 mm between adjacent focal spots should be avoided for multi-point laser-induced plasma in supersonic flow because the plasma kernel could not be fused in a timely manner.