ASSESSMENT OF 2-SCALE AND 3-SCALE K-EPSILON MODELS FOR ROTATING CAVITY FLOWS

A three-scale k-epsilon turbulence model was recently developed for co mplex flows such as rite rotor-rotor and rotor-stator cavities found i n gas turbine engines. The three-scale is a logical extension of the p revious two-scale k-epsilon model of Ko and Rhode (1990). Both multisc ale turbulence models are presented and assessed via comparison with m easurements for possible adoption in future cavity computations. A sin gle computer code solving the two-dimensional axisymmetric Navier-Stok es equations with a ''switch'' for selecting among the various turbule nce models being compared was used. It was found for both cavity cases that the three-scale model gives a marginal improvement over the two- scale model. Further, both multiscale models give a substantial improv ement over the standard k-epsilon model for the rotor-stator case, esp ecially in the near-wall region where different eddy sizes are found. However; the feasibility of using a multiscale model for the rotor-rot or case is unclear since it gives improved values over the standard hi gh-Re model in some regions but worse values in other regions. In addi tion, the solutions provide enhanced insight concerning the large chan ges in flow pattern previously photographed in the rotor-rotor case as rotation increases. In particular it is shown how: (a) the number of recirculation zones increase with increasing rotation rate and (b) the recirculation zones decrease lit size with a decreasing G ratio.