Influence of the choice of the inlet turbulence intensity on the performance of numerically simulated moderate Reynolds jet flows – Part 1 – the near exit region of the jet

Abstract

A real problem when trying to develop a numerical model reproducing the flow through an orifice is the choice of a correct value for the turbulence intensity at the inlet of the numerical domain in order to obtain at the exit plane of the jet the same values of the turbulence intensity as in the experimental evaluation. There are few indications in the literature concerning this issue, and the imposed boundary conditions are usually taken into consideration by usage without any physical fundament. In this article we tried to check the influence of the variation of the inlet turbulence intensity on the jet flow behavior. This article is focusing only on the near exit region of the jet. Five values of the inlet turbulence intensity Tu were imposed at the inlet of the computational domain, from 1.5% to 30%. One of these values, Tu= 2% was the one measured with a hot wire anemometer at the jet exit plane, and another one Tu= 8.8% was issued from the recommendation of Jaramillo (1). The choice of the mesh-grid and of the turbulence model which was the SST k-ω model were previously established (2). We found that in the initial region of the jet flow, the mean streamwise velocity profiles and the volumetric flow rate do not seem to be sensitive at all at the variation of the inlet turbulence intensity. On the opposite, for the vorticity and the turbulent kinetic energy (TKE) distributions we found a difference between the maximum values as high as 30%. The closest values to the experimental case were found for the lowest value of Tu, on the same order of magnitude as the measurement at the exit plane of the jet flow. Mean streamwise velocity is not affected by these differences of the TKE distributions. Contrary, the transverse field is modified as it was displayed by the vorticity distributions. This observation allows us to predict a possible modification of the entire mean flow field in the far region of the jet flow.