Response of simple turbulence models to step changes of slip velocity

A numerical study was performed of two turbulent boundary layers with sudde n changes of the slip velocity at the mall, The first is the two-dimensiona l flow on a flat plate with a sudden increase of the wall velocity, The sec ond flow is a three-dimensional boundary layer along a cylinder whose upstr eam section is rotating with a constant circumferential velocity, while the downstream section remains still. Computations were carried out with a wid e range of simple eddy-viscosity models: an algebraic model, two one-equati on models, a two-equation k-epsilon model, and a zonal k-omega model. For t he two-dimensional how, it is shown that though all of the models somewhat overestimate the rate of relaxation of the inner region of the boundary lay er after its perturbation, they are quite capable of predicting the crucial reduction in skin friction over the moving mall. They also describe adequa tely the insensitivity of the outer region of the boundary layer to the rem oval of the inner region, found in the experiments, From the standpoint of accuracy of the major two-dimensional how characteristics, the zonal k-omeg a and two one-equation models appear to be close to each other and signific antly better than the two-equation k-epsilon and algebraic models. For the three-dimensional flow, all of the models perform approximately equally, wi th only a slight superiority of the differential models over the algebraic model. When one considers that these models cannot reproduce the significan t deviation between the Reynolds-stress vector and the shear vector observe d in the experiment, the agreement of the computations with the data on the mean flow characteristics is unexpectedly good.