Contribution of wind shear to the entrainment process of the atmospheric convective boundary layer

  • Entrainment flux ratio indicates the promotive effect of shear on entrainment
  • The fraction of the shear-generated TKE available for entrainment is defined
  • The averaged fraction reveals 38.5% of shear-generated TKE used for entrainment
Abstract

Wind shear induced by the velocity difference has an important effect on the stably stratified turbulent flow in the atmospheric convective boundary layer (CBL). Cases with different velocity difference are conducted by Large-eddy simulation (LES) to reveal the contribution of shear effect to entrainment. The result shows that the shear-generated turbulent kinetic energy (TKE) in the entrainment layer is partially consumed by the negative buoyancy, which increases the entrainment flux minimum and enhances the entrainment flux ratio in the range of 0.188 - 0.352. Based on the hypothesis of the independence of the shear-generated TKE and buoyancygenerated TKE, an approach for the fraction of the shear-generated TKE available for entrainment is proposed, and the averaged fraction reaches 38.5%, but the evolution tends to increase with the enlargement of velocity difference.

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