Turbulence Measurements in a Two-Dimensional Wall-Jet

Paper i proceeding, 1991

The high capacity of todays computers has enabled the extension of turbulence models to strongly anisotropic flow fields, i.e. the interest has been focused on the use of the models based on the transport equations for the Reynolds stresses (RST models). To improve these turbulence models well-defined, simple and fundamental experiments are needed, in which gradients of the different turbulence parameters are determined. Together with direct simulations of the Navier-Stokes equations these experiments yield a good base for the improvement of the modelling of different terms in the Reynolds equations. An excellent presentation of the closure problem and the terms of interest for the development of turbulence models has recently been published by Groth (1991). A fundamental, well-defined and simple flow case is the wall-jet, where an interaction between a wall boundary layer and a free shear layer forms the anisotropy as well as the inhomogeneous character of the flow field. A comprehensive literature survey of wall-jets was carried out already in the beginning of the eighties by Launder and Rodi (1980), who studied a large number of more or less well-defined wall-jet experiments. The main conclusion of this survey was a lack of well-defined experiments in simple and fundamental geometries. If the study is limited to the two-dimensional case, a further conclusion from the work of Launder and Rodi was that many of the studied flow cases did not fulfil the condition of two-dimensionality. Although more than ten years have passed since the work of Laundry and Rodi was presented, very few investigations have been reported in which fundamental wall-jets have been studied. Especially well-defined turbulence measurements are needed, since anisotropy of the two-dimensional wall-jet yields a case well suited for the evaluation of e.g. new dissipation models, see Hallbäck et al. (1990). The purpose of the present work was to determine the turbulence field of a two-dimensional wall-jet in a simple and also well-defined geometry without influence of an outer disturbing flow field. To accomplish these measurements was a wall-jet rig used. All turbulence measurements were carried out using hot-wire techniques, single- and cross wires. The measurements presented here were performed at a Reynolds number of ___, based on the slot height and the extensions of the measurements in the flow direction was in the range of x/h=25 through x/h=156 (x-coordinate in the main flow direction and h-slot height).