Particle dispersion in supersonic particle-laden jets

Particle-laden supersonic jets are often encountered in advanced engineering applications where a comprehensive control of particle dispersion is crucial. Although particle dispersion has been extensively studied in the past, the local mechanisms that cause the radial particle transport, such that particles leave the jet core, remain unclear in supersonic jets. To this end, we conduct a direct numerical simulation of a confined low Reynolds number, perfectly expanded supersonic jet carrying four different-sized particles. Here, particles and gas are simulated with Lagrangian and Eulerian approaches, and the fluid–particle energy and momentum exchange is modelled with two-way coupling. The initial Stokes number of these particles ranges between $1.5$ and $6.0$ . We found that each particle size has a specific axial location, $x_r$ , where they start travelling radially. This location is defined by a local Stokes number of approximately ${\textit{St}}^* \approx 0.6$ ; the delay in particles’ response to the local eddies in a supersonic flow causes their ${\textit{St}}^*$ to drop below unity. The local turbulent structures formed by the jet promote the radial transport of the particles that have similar characteristic time scales. Despite two-way momentum coupling, particles and gas influence each other via different mechanisms. For the considered range of ${\textit{St}}$ , particles dominantly influence the fluctuating velocity component of the gas, while gas mainly affects the mean velocity component of the particles. Moreover, the particles’ reaction to the compressibility effects is a direct function of particle inertia, where the probability of finding larger particles in a high-density gradient and dilatation region is higher.