Effect of Approaching Boundary-Layer Thickness on Turbulent Cavity Flow

摘要

The effect of approaching boundary-layer thickness on turbulent cav-ity ow properties is investigated. First, an experimental study is carriedout using a designated wind-tunnel apparatus, which enabled a system-atically change of the boundary-layer thickness. Second, in order togain deeper understanding and to delve into the detailed oweld prop-erties, numerical simulations (based on hybrid RANS/LES turbulencemodelling) for several approaching boundary-layer thicknesses were con-ducted. The examined cavity conguration has a length-to-depth ratio ofL=H = 6.25, and a width-to-depth ratio of W/H = 2. The work focuses atsubsonic ow conditions (a free-stream Mach number of M_∞ = 0.40 and aReynolds number of Re_H = 1.6×10~6), however little data regarding highertransonic Mach numbers is also analyzed. Application of linear hydro-dynamic stability theory, together with examining the measurements ofthe mean and uctuating pressure along cavity ceiling, revealed that asthe approaching boundary-layer gets thicker, the shear-layer has lowergrowth rates (that are related to lower frequencies), and the shear-layergrowth saturates at a more upstream position. In other words, thickerincoming boundary-layer can stabilize the shear-layer uctuations, whichin-turn causes lower pressure gradients along the cavity.