Turbulent Boundary Layer Formed by Spanwise Gaps between Roughness Elements. 2nd Report, Turbulence Quantities along the Centerline.

Abstract

In order to investigate the effect of gap size on the centerline development of a boundary layer flow through a gap in an isolated wall-mounted roughness element, the turbulence quantities for flow through four gap sizes have been measured. All measurements were made at a Reynolds number of 3300, based on obstacle height and free stream velocity. From the centerline features immediately downstream from the gap, the gap size can be classified into three cases, the S gap (G/δ0=1/8), M gap (G/δ0=1/4 and 1/2) and L gap (G/δ0=1). The magnitude of each turbulent quantity due to the distortion produced by the gap varies with gap size. However, the turbulent quantities show similar downstream tendencies independent of gap size. The turbulent properties show maximum distortions at x/G=4 to 10 downstream from the gap. The gap size effect on major flow features was also analyzed with both the appropriate velocity and length scales. Further downstream from the gap, it is shown that all four centerline turbulent flows are different from undisturbed flow.