DIRECT NUMERICAL-SIMULATION OF NEAR-INTERFACE TURBULENCE IN COUPLED GAS-LIQUID FLOW

Turbulence structures near the interface between two flowing fluids ha ve been resolved by direct numerical simulation. As a first step the i nterface has been kept flat, corresponding closely to the recent gas-l iquid flow experiments of Rashidi and Banerjee [Phys. Fluids A 2, 1827 (1990)], with the fluids coupled through continuity of velocity and s hear stress boundary conditions. For density ratios between the fluids typical of air and water, the turbulence characteristics on the gas s ide are quite similar to that in wall regions. The liquid side shows l arger velocity fluctuations close to the interface and ejections origi nate closer to the interface. The mean velocity distribution, turbulen ce intensities, Reynolds stress and various other statistical measures are significantly altered compared to those in the wall region of cha nnel flows. Quasi-streamwise vortices form in the areas between high a nd low shear stress on both sides of the interface. At any given insta nt, about a fifth of these appear to be coupled across the interface. Whether the others are, but the coupling is too weak for the detection technique used, or were coupled previously remains an open question. In any case, sweeps usually occur on the high shear stress side of the se vortices and ejections on the low shear stress side. Significant co upling exists across the interface with over 60% of the Reynolds stres s in the region close to the interface being associated with coupled e vents -the main coupling coming through gas ejection-liquid ejection e vents over low shear stress regions, with a lesser but significant num ber of gas sweep-liquid sweep events over high shear stress regions. ( C) 1996 American Institute of Physics.