Abstract
Abstract This paper explores the computation of a turbulent jet discharged parallel to and immediately below the free surface of an expanse of the same fluid at rest. The turbulence is modelled using second-moment closures, and results are reported for both the linear return-to-isotropy model, and the newer two-component limit (TCL) model developed at UMIST. Computations of the first 40 inlet jet diameters downstream have been obtained using a 3D solver, and results are compared with experimental data. The TCL model is shown to be the more successful in predicting the flow, although it is also concluded that the treatment of the dissipation rate at the free surface requires further consideration. The fully self-similar state is not achieved until considerably greater downstream distances that either these 3D computations, or experiments, have explored, due to the gradual growth of streamwise vorticity driven by gradients of the Reynolds stresses in the cross-stream plane. This asymptotic state has also been calculated, using a separate 2D calculation scheme which employs a suitable similarity transformation. Both models tested predict a very large asymptotic lateral spreading rate, even greater than that found in the corresponding 3D wall jet.
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