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.
Inlet conditions for a turbulent jet are known to affect the near field behavior but eventually lose their significance downstream. Metrics of importance are often derived from mean and fluctuating velocity components, but little has been done to explore inlet effects on transport of a scalar quantity (e.g., temperature). This paper aims to provide fundamental understanding in this regard and employs large eddy simulations (LES) of a nonisothermal round turbulent jet (Reynolds number of 16,000) with geometry and boundary conditions mimicked after a well-known experimental study. The jet inlet is first modeled with a standard Blasius profile and next by performing a simulation of the upstream flow modeled with either detached eddy simulations (DES) or LES for the second and third approaches, respectively. Only the model employing LES for both upstream nozzle and downstream jet is found to completely capture the root-mean-square (RMS) temperature behavior, namely, a distinct hump when normalized by the local mean centerline temperature at roughly five diameters downstream. Regarding the far field conditions, all three inlet conditions converge for the centerline values, but the radial distributions still portray non-negligible differences. Not surprisingly, the complete LES modeling approach agrees the best with experimental data for mean and RMS distributions, suggesting that the inlet condition plays a vital role in both the near and far field of the jet. The current effort is the very first LES study to successfully capture flow physics for a nonisothermal round turbulent jet in near and far field locations.
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