Numerical Investigation of turbulent coupling boundary layer of air-water interaction flow

Abstract

Air-water interaction flow between two parallel flat plates, known as Couette flow, is simulated by direct numerical simulation. The two flowing fluids are coupled through continuity of velocity and shear stress condition across the interface. Pseudo-spectral method is used in each flow subdomain with Fourier expansion in streamwise and spanwise directions and finite difference in vertical direction. Statistically quasi-steady flow properties, such as mean velocity profiles, turbulent intensities, Reynolds stress and turbulent kinetic energy (TKE) budget terms show significant differences between air-water interface turbulence near the water side (IntT-w) and wall-bounded turbulence(WT) while there are some similarities between IntT-w and free surface turbulence (FST). Due to the velocity fluctuation at the interface, water side near interface turbulence flow (IntT-w) is characterized with a thinner viscous sub-layer and decreased intercept parameter B in log-law layer, strengthened Reynolds stress and eddy viscosity, together with a stronger production term, decreasing-then-increasing dissipation term and negative turbulent diffusion term in TKE budget.

(cont.) Abundant physical phenomena exist on the water side turbulent flow with four major types of three-dimensional vortex structures identified near the interface by variable-interval spacing averaging (VISA) techniques. Each type of vortex structures is found to play an essential role in the turbulent energy balance and passive scalar transport.