Hybrid RANS/LES Simulation Method Based On SEM

Turbulence plays a major role in many engineering application.In aeronautics for instance the flows around aircrafts are turbulent,the mixing of fuel and air in the engines takes place in a turbulent flow and noise is generated by turbulent vortices on the surface of the aircraft.Therefore, how to predict turbulence accurately and observe complex flow structure is very important.Based on the in-house RANS and LES CFD program,we give a research on hybrid RANS/LES computational method.First of all,by reading related document for reference,the advantage of hybrid RANS/LES method can be guaranteed;Then in this thesis we show the basic equation of SEM and give a further modification so that we can achieve anisotropic turbulence.Next,the Spalart-Allmaras turbulence model was added on the base of the origin edition,and verified the RANS program on a plate.The length-scale and time-scale is very important to the realisic of flow, in order to obtain all the parameters which SEM need,we found a feasible approach that can transform SST parameters into SA.After that,the RANS/LES program was verified on a plate,the RANS compultation is steady and the downstream LES domain is unsteady,SEM was applied on the interface,and all the mean parameters SEM need are captured from the steady S-A RANS computation.Finally,the T106 D low pressure turbine was simulated for both steady and unsteady state.In this simulation,LES domain is located near the wake,the rest domain is simulated by RANS;The pressure distribution has a good agreement with experiment value,,and so the friction coefficient on the pressure side is.But on the suction side, the friction coefficient is beyond experiment value.The unsteady case captured the downstream wake development clearly.Futhermore,campare to the pure LES simulation, hybrid RANS/LES simulation saved computation cost and shortened the time a lot.