Large-eddy simulation of unsteady flows past a spiked body

Abstract

Unsteady flows past a spiked body are investigated numerically with wall-resolved large-eddy simulation (LES). The inflow features a Mach number of Ma=2.21 and a Reynolds number of Re=1.2×105. The ratio of the spike length to the blunt body diameter is L/D=1.0. A comparative study of three meshes of different grid resolutions has been conducted by assessing their predictive accuracies and associated subgrid-scale effects. The LES results obtained based on three meshes are compared with the experimental and numerical data found in the literature. A proper orthogonal decomposition (POD) analysis has been conducted based on the pressure and axial velocity fluctuations to investigate turbulence structures. It is observed that the turbulence structures corresponding to the first four POD modes are the most energetic. Furthermore, it is seen that the dominant recirculation zone along the spike in a pulsation cycle can be reconstructed based on the first two POD modes of axial velocity fluctuations. The physical mechanisms of the collapse and inflation processes of the pulsation cycle are investigated based on a detailed transient analysis of fine-resolution LES data. The temporal evolution of vortices and shock waves are investigated. An interesting characteristic Z-shaped trajectory of the instantaneous flow pattern is observed. It is discovered that the pulsation cycle is dominated by the pressure differences between the recirculation zone and two high-pressure regions immediately in front of the cylinder face and near the spike tip.