Research On The Flow, Heat Property And Subgrid Scale Model Of Rotating Turbulent Channel Flow

Turbulent channel flow subject to spanwise rotation is a prototype of coolingpassages in turbo-machinery and generator. In this thesis, the rotation effect on theturbulence and the heat transfer is investigated, and new subgrid scale models forrotating turbulent channel flow are proposed to capture the major rotating effect. Thenew models are examined in rotating channel at Re=7000, Ro=0.0,0.3,0.6, whereReynolds number Re=umh/ν and rotation number Ro=2h/umare based on the halfwidth of the channel h, the bulk mean velocity um, the molecular viscosity and therotating rate of the channel. The subgrid scale model for passive scalar is also examinedat Pr=0.1,0.3,0.7and1.0, with Prandtl number Pr=ν/κ, where κ is the moleculardiffusity. The major achievements of this thesis are as follows.The database of direct numerical simulation of rotating turbulent channelflow is established at parameters introduced above. The statistical results inrotating channel are given. The budget of the transport equations of theReynolds stress and turbulent kinetic energy is studied to discuss the majorrotating effect. The results indicate that the Reynolds shear stress, on which therotation has direct and strong effect, should be primarily considered to capturethe rotating effect in a subgrid scale model. The investigation on the passivescalar shows that the scalar fluctuation and the streamwise velocity fluctuationare in good similarity in non-rotating turbulent channel flow, but this similarityis violated in rotating channel.Based on characteristic of the rotating turbulent channel flow, newdynamic subgrid scale stress models are proposed. Unlike the conventional eddyviscosity model, the new models assume a nonlinear constitution between thesubgrid scale stress and the resolved strain rate tensor. New dynamic methodsare considered to determine the model coefficients for the nonlinear modelreasonably. The linear part of the new model, taking the same form and dynamicprocedure as the eddy viscosity model, could give sufficient subgrid scaledissipation. The nonlinear term is expected to captured the rotating effect, so thetransport equation of the Reynolds shear stress is used to derived the model coefficient of the nonlinear term.Various subgrid scale stress models, including3new models and4existingmodels, are examined in rotating turbulent channel flow. The statistics obtainedfrom the new dynamic nonlinear models are superior to the previous models.Especially, the globally-coefficient dynamic nonlinear model is able to predictthe evolution of the Taylor-G rtler vortices correctly. This is a significantprogress of subgrid scale models.The large eddy simulation of the passive scalar is also conducted. It isfound that the eddy diffusity model is able to capture the rotating effect, so thenonlinear form is not necessary for scalar subgrid scale model. Examined inrotating channel, the passive scalar obtained from large eddy simulation is foundto be in good agreement with the direct numerical simulation results, if the fluidmotion is correctly predicted by the subgrid stress model.