LES of an Isothermal High Reynolds Number Turbulent Round Jet

Abstract

Round turbulent jets have fundamental relevance in various engineering applications and are also of practical interest in the lower plenum of the High Temperature Gas-Cooled Reactors (HTGR). In the direction of developing an experimentally validated computational model for the lower plenum flow, a Large Eddy Simulation (LES) of an isothermal high Reynolds number confined jet has been studied. The enclosure within which the jet is confined has been selected large enough so that the results can be compared with well-known experimental studies available in the literature. The Sub-Grid Scale (SGS) model chosen within the LES framework is a variant of the dynamic Smagorinsky model. The effect of inlet flow profile and turbulent fluctuations on the evolution of the jet have been analyzed in detail. The mesh distribution was found to play a vital role in the magnitude and profile of the Reynolds stresses throughout the computational domain. Additionally, it is critically important to properly specify the turbulent fluctuations at the jet inlet in order to accurately predict key near field characteristics such as the potential core length. We perform a separate discrete eddy simulation of the flow in the nozzle upstream of the jet inlet to accurately determine the inlet turbulent fluctuations. The LES results of this study include both first order statistics (mean velocity field) and second order statistics (components of the Reynolds stresses). For each of these quantities, excellent agreement is obtained between our LES predictions and experimental measurements. This research lays the groundwork needed to develop a high-fidelity computational model of the complex mixing flow in the HTGR lower plenum.