Upward Overshooting in Turbulent Compressible Convection. I.Effects of the relative stability parameter, the Prandtl number, and the P\'eclet number

TL;DR

This study uses 3D simulations to analyze upward overshooting in turbulent compressible convection, revealing a layered structure and how overshooting distance scales with key parameters, aligning with a turbulence model.

Contribution

It identifies a three-layer structure of overshooting zones and examines how overshooting distance scales with stability, Prandtl, and Péclet numbers, supported by simulation and model comparison.

Findings

Overshooting zone has three distinct layers.

Overshooting distance decreases with stability parameter S.

Overshooting distance increases with Prandtl number Pr.

Abstract

In this paper, we investigate the upward overshooting by three-dimensional numerical simulations. We find that the above convectively stable zone can be partitioned into three layers: the thermal adjustment layer (mixing both entropy and material), the turbulent dissipation layer (mixing material but not entropy), and the thermal dissipation layer (mixing neither entropy nor material). The turbulent dissipation layer is separated from the thermal adjustment layer and the thermal dissipation layer by the first and second zero points of the vertical velocity correlation. The simulation results are in good agreement with the prediction of the one-dimensional turbulent Reynolds stress model. First, the layer structure is similar. Second, the upper boundary of the thermal adjustment layer is close to the peak of the magnitude of the temperature perturbation. Third, the P\'eclet number at the upper boundary of the turbulent dissipation layer is close to 1. In addition, we have studied the scalings of the overshooting distance on the relative stability parameter $S$, the Prandtl number $\rm Pr$, and the P\'eclet number $\rm Pe$. The scaling on $S$ is not unique. The trend is that the overshooting distance decreases with $S$. Fitting on $\rm Pr$ shows that the overshooting distance increases with $\rm Pr$. Fitting on $\rm Pe$ shows that the overshooting distance decreases with $\rm Pe$. Finally, we calculate the ratio of the thickness of the turbulent dissipation layer to that of the thermal adjustment layer. The ratio remains almost constant, with an approximate value of 2.4.