Showing papers by "Vagesh D. Narasimhamurthy published in 2004"

Unsteady-RANS Simulation of Turbulent Trailing-Edge Flow

Abstract: Unsteady RANS (Reynolds Averaged Navier Stokes) computations of turbulent trailing-edge flow have been carried out at a Reynolds number of 1000 (based on the free-stream quantities and the trailing-edge thickness) using a 3D Finite Volume code, in which a Low Reynolds Number (LRN) model and model were implemented. The realizability constraints suggested by Durbin was also implemented in the models to study their effect on the unsteady vortex shedding. Central differencing scheme was used for all the computations, but van-Leer scheme was also tried in order to study the influence of numerical schemes on unsteady vortex shedding. Results from a Direct Numerical Simulation (DNS) of the same flow are available for comparison and assessment of turbulence models used in the URANS code. Two-dimensional URANS calculations are carried out with turbulence mean properties from the DNS used at the inlet; the inflow boundary-layer thickness is 6.42 times the trailing-edge thickness, close to typical turbine blade flow applications. The LRN model failed to capture unsteady vortex shedding, but when realizability constraint was implemented, the model captures flow unsteadiness. Many of the key flow features observed in DNS are also predicted by the modelling; the flow oscillates in a similar way to that found in bluff-body flow with a von Kármán vortex sheet produced downstream. The recirculation bubble predicted by unsteady RANS has a similar shape and a length close to DNS. It was found that the unsteadiness plays an important role in the near wake, comparable to the modelled turbulence. A spectral analysis applied to the lift and pressure drag coefficients show that a Strouhal number based on the trailingedge thickness is 0.104, very close to DNS value. It was found that van-Leer scheme being a bounded scheme and dissipative in nature, produces higher resolved kinetic energy compared to central difference scheme; the reason for which has to be investigated.