Convex Turbulent Boundary Layers With Zero and Favorable Pressure Gradients

Abstract

A turbulent boundary layer subjected to multiple, additional strain rates, namely convex curvature coupled with streamwise pressure gradients (zero and favorable, ZPG and FPG) was investigated experimentally using laser Doppler velocimetry. The inapplicability of the universal flat-plate log-law to curved flows is discussed. However, a logarithmic region is found in the curved and accelerated turbulent boundary layer examined here. Similarity of the mean velocity and Reynolds stress profiles was achieved by 45 deg of curvature even in the presence of the strongest FPG investigated (k = 1.01 × 10−6 ). The Reynolds stresses were suppressed (with respect to flat plate values) due primarily to the effects of strong convex curvature (δo /R ≈ 0.10). In curved boundary layers subjected to different favorable pressure gradients, the mean velocity and normal Reynolds stress profiles collapsed in the inner region, but deviated in the outer region (y+ ≥ 100). Thus, inner scaling accounted for the impact of the extra strain rates on these profiles in the near-wall region. Combined with curvature, the FPG reduced the strength of the wake component, resulted in a greater suppression of the fluctuating velocity components and a reduction of the primary Reynolds shear stress throughout almost the entire boundary layer relative to the ZPG curved case.