Three-Dimensional Boundary Layers Over an Infinite Swept Bump and Free Wing

摘要

Three-dimensional laminar boundary layers past an infinite swept bump and free wing were investigated numerically using the fractional step method. The objective of the work was to study the effect of surface curvature induced changes in pressure gradient and changes in the freestream flow on boundary layer skewness and growth. Simulation results demonstrate that for flows over the bump the first transition from adverse to favorable pressure gradient occurs at the front concave/convex inflexion and the second transition from favorable to adverse pressure gradient occurs at the summit. For flows past a free wing, the only transition from favorable to adverse pressure gradient occurs in front of the summit and the subsequent adverse pressure gradient is larger than the corresponding value for the bump. For both the bump and wing, the increase of initial skewing angle from 0 to 30 deg causes a 10 percent reduction in the length of the wake; the wake behind the wing is about 12 percent longer in streamwise extent than the corresponding wake behind the bump. Integral parameters in the flows over the bump display a wavy trend due to the two transitions of the pressure gradient. On the other hand, the single transition from favorable to adverse pressure gradient brings about a monotonic increase of the integral parameters for flows past the wing. Near separation and reattachment, surface-streamlines are skewed strongly in the spanwise direction. Conditions of flow detachment for the bump and wing are in good agreement with correlations for laminar separating flows with power-law velocity profiles as well as correlations for wall-curvature-induced turbulent separating flows.