A simple method for deducing properties of laminar wall jets in uniform pressure fields, with undetermined far-field conditions

Abstract

A simple method is proposed in order to draw various information concerning boundary layers that develop axisymmetrically on a flat plate, when the outer pressure field is uniform, and when the far-field conditions, perpendicularly to the plate, are unknown. It is shown that if, at an arbitrary radial coordinate r0, one measures both the value of the maximum radial velocity (i.e., Um) and the height (i.e., δ) where the radial velocity reaches its maximum value, one can build a nondimensional number, which we shall call A. This number is an invariant in this study. It also allows us to calculate several parameters, such as, for instance, the local shear rate on the plate or the power laws for the radial velocity decrease and the boundary layer thickness increase, according to the downstream distance, corresponding here to the radial coordinate r.