The turbulent wall jet

The present article has arisen from an invitation by the Organizing Committee of the AFOSR-Stanford Conferences on Complex Turbulent Shear Flows (1980/81) to make a critical review of the experimental literature on turbulent wall jets. The desired outcome of the enquiry was the identification of one or more experiments on wall jets that were demonstrably of good accuracy and would serve to test the reliability of the new crop of calculation methods for turbulent flows that has emerged since the 1968 Stanford Conference on Turbulent Boundary Layers. A summary of our enquiry is to be published in the Proceedings of the 1980 Conference but, to comply with space limitations, that document provides only the barest summary of the recommended test cases. The publication of this more complete documentation of our survey will, we hope, be of interest not only to those who are concerned with wall jets and their application in Aeronautics but more widely to those working on different aspects of turbulent shear flow phenomena. A wall jet may be defined as a shear flow directed along a wall where, by virtue of the initially supplied momentum, at any station, the strcamwise velocity over some region within the shear flow exceeds that in the external stream. Within this broad definition a very wide range of flows and phenomena has been examined. Indeed, there have been well over two hundred experimental studies published on the turbulent wall jet. Of these about one half has been prompted by heat transfer considerations and in most of these cases the flow field has been insufficiently well documented to merit close attention for the present purpose. Even where detailed data exist, these experiments have commonly employed sufficiently large temperature differences (or gas mixtures of sufficiently different molecular weights) that one could not be certain that the flow field evolution was strictly independent of that of the thermal or species fields. The present enquiry has in fact firmly limited attention to flows where the thermophysical properties of the wall jet could be regarded as uniform. If we had not imposed such a limit on the breadth of flows considered, time would have imposed its own limitation on the depth to which our enquiry could have been taken. It may be said, moreover, that for the majority of situations in external aerodynamics involving wall jets, the uniform-property idealization is not far from the truth. Among the seventy or so aerodynamic studies that our survey has examined, attention is here given to situations with relatively simple flow topography that would allow certain intrinsic and unambiguous truths about the turbulence structure to emerge either by direct measurement or by inference from the mean flow's evolution. Within each subclass of experiments the following broad criteria have guided our assessment: