Compressibility and variable inertia effects on heat transfer in turbulent impinging jets

Abstract

This article shows the importance of flow compressibility on the heat transfer in confined impinging jets, and how it is driven by both the Mach number and the wall heat-flux. Hence, we present a collection of cases at several Mach numbers with different heat-flux values applied at the impingement wall. The wall temperature scales linearly with the imposed heat-flux and the adiabatic wall temperature is found to be purely governed by the flow compression. Especially for high heat-flux values, the non-constant wall temperature induces considerable differences in the thermal conductivity of the fluid. This phenomenon has to date not been discussed and it strongly modulates the Nusselt number. In contrast, the heat transfer coefficient is independent of the varying thermal properties of the fluid and the wall heat-flux. Furthermore, we introduce the impingement efficiency, which highlights the areas of the wall where the temperature is influenced by compressibility effects. This parameter shows how the contribution of the flow compression to raising the wall temperature becomes more dominant as the heat-flux decreases. Thus, knowing the adiabatic wall temperature is indispensable for obtaining the correct heat transfer coefficient when low heat-flux values are used, even at low Mach numbers. Lastly, a detailed analysis of the dilatation field also shows how the compressibility effects only affect the heat transfer in the vicinity of the stagnation point. These compressibility effects decay rapidly further away from the flow impingement, and the density changes along the developing boundary layer are caused instead by variable inertia effects.

Large eddy simulation of a thermal impinging jet using the lattice Boltzmann method

“…16 can vary when using compressible solvers with variable viscosity. Otero-Pérez and Sandberg 41 , in their study of Mach number and temperature gradient effects on impinging jet heat transfer, noted that the variation of λ f has rarely been evoked in the literature (as this test case has mostly been done for incompressible flows). They state that either λ f (T ) or λ f constant can be used in the calculation of the Nusselt number.…”

Heat Transfer Investigation on Under-expanded Supersonic Impinging Jets by Large Eddy Simulation

“…The diffusivity of the sub-grid scales is solved by assuming a constant turbulent Prandtl number (Pr t ) of 0.9. The code has recently been validated by [8] for subsonic impinging jets.…”

Flow structure and heat transfer analysis of the floatation nozzle with a moving wall

“…Except for the differences between the floatation nozzle and slot nozzle, the effects of the Mach number on the flow and heat transfer of impinging jet are also widely studied. When the Mach number is relatively low, the compressibility of the fluid can be ignored; however, the influences of Mach number must be considered when it is larger than 0.3 (Fénot et al, 2019;Otero-Pérez and Sandberg, 2020). The effects of the nozzle type on the flow and heat transfer of impinging jet are investigated by many researchers.…”