Boundary layer analysis of ventilated partial cavity for friction drag reduction

摘要

This paper describes the use of water tunnel plate experiments and large eddy simulations to understand ventilated partial cavity (VPC) flow, especially the mechanism of friction drag reduction. The different flow behaviors along the flow direction indicate that VPC can be divided into three regions: continuous cavity, transitional cavity, and mixing cavity. Specifically, in the continuous cavity region, the flow state can be regarded as laminar; the density and dynamic viscosity are close to those of the strictly gas phase; and the resulting wall shear stress reaches minimum level along the flow direction. In the transitional cavity region, the flow state is similar to the transition state of single-phase flow with density, viscosity, and wall shear stress along the flow direction all exhibiting exponential growth. In the mixing cavity region, the flow state is analogous to turbulence. The flow is in a phase mixed state. The dynamic viscosity is close to that of the strictly water phase. The resulting wall shear stress is stable with small fluctuations. Importantly, the analytical boundary layer equation for wall shear stress derived from the momentum equation remains applicable to the continuous cavity and the mixing cavity regions.