Direct numerical simulation of the entrainment coefficient and turbulence properties for compressible spatially evolving axisymmetric jets

Abstract

In order to gain a better insight in the entrainment coefficient and turbulence properties of a spatial evolving round jet flow in the jet development from the near-field region to the far-field region, we performed Direct Numerical Simulation (DNS) of a round jet with Reynolds number equal to 5000. A computational grid consisting of about 500million is used in present DNS simulation, which is the largest grid used in round jet simulation by DNS method. The computational domain extends up to about 100 jet radii in the streamwise direction, which is found to be large enough for the jet to reach a truly self-similar state. Inflow buffer zone is used in our DNS simulation in order to efficiently simulate the fluid entrainment process. The entrainment coefficient, Reynolds stress and turbulent kinetic energy are plotted with a high resolution and sufficient DNS database to understand the evolution of the jet development. The DNS grid resolution is tested by the wave-number spectrum and Kolmogorov length scale. The DNS results are compared explicitly with the experimental data, and some inconsistencies between DNS and experimental data are explained in our research.We found that the inflow buffer region can significantly affect the jet development in the near-field region, but it takes a mild effect on the entrainment process in the transitional and far-field region. By the inspecting of contours of kinetic energy at plane (Z=0), it reveals that main turbulence production takes place in the high-shear regions. After the high-shear regions, the turbulent kinetic energy begins to decrease along the streamwise direction. The strong growth of kinetic energy along the jet axial direction means that inadequate resolution in the steep growth region of kinetic energy will lead to inaccurate results for the DNS of a spatially evolving round jet.