An Experimental Study of the Turbulent-Flow Boundary-Layer Development in Smooth Annuli

Abstract

This investigation was concerned with the turbulent flow with negligible heat transfer of a Newtonian fluid in the inlet region of smooth, concentric, constant-area annuli. Experimental mean-velocity profiles, static-pressure gradients, boundary-layer thickness parameters, and local friction factors were determined for airflow in annuli with radius ratios of 0.344 and 0.531. Each annulus was studied with both square-edged and rounded entrances. Flow separation caused by the abrupt change in area of the square-edged entrance resulted in skewed velocity profiles near the inlet. Consequently, no conventional boundary-layer growth occurred in the square-edged-entrance annuli. Further downstream, the skewness disappeared, and typical fully developed mean-velocity profiles were obtained. The turbulent mixing of fluid near the square-edged entrance appeared to have a stabilizing influence on the flow downstream. Conventional boundary-layer growth occurred in the rounded-entrance annuli since the gradual inlet produced a flat velocity profile at the beginning of the constant-area section. Velocity profiles, shape factors, displacement thicknesses, and local friction factors were appreciably affected by the transition from laminar to turbulent flow that occurred in the boundary layers. Further, fully developed velocity profiles were not obtained in the lengths tested.