Investigation of laminar sublayer on permeable surfaces with injection

Abstract

The thin-wall region — the laminar (or viscous) sublayer, in which the molecular mechanism of transfer predominates — plays an important role in friction and heat-transfer processes in a turbulent boundary layer. In particular, the relation between the sublayer thickness and the height of the surface roughness determines the nature of the flow — hydrodynamically smooth or rough — over the surface. This is of great practical importance and, hence, the roughness criterion has become the subject of numerous and systematic investigations. There are exhaustive data for the majority of the commonest cases encountered in practice [1]. The velocity on the boundary of the laminar sublayer appears as an important parameter in two-layer calculation schemes (e.g., [2–4], etc.). Although the theoretical analysis of a turbulent boundary layer with injection started several decades ago, there are at present hardly any reliable experimental data which can be used to determine the variation of the parameters within and at the boundary of the sublayer in relation to the injection rate. In this work we used interferometric diagnostics for precision experimental investigations of the parameters of the laminar sublayer on permeable surfaces with injection.