Numerical Investigation of Three-Dimensional Separation in Twisted Turbine Blade: The Influence of Endwall Boundary Layer State

The substantial adverse pressure gradient experienced by a turbulent boundary layer while approaching an endwall-mounted twisted turbine blade and caused the impending flow to separate three-dimensionally to form a dynamically active horseshoe vortex (HSV) system in the junction of the turbine blade with endwall. The large eddy simulations (LES) of the flow past a twisted turbine blade mounted on a curved endwall with periodic boundary condition in pitchwise direction is carried out for Re = 50000 to methodically investigate the HSV dynamics. The significant variations with Re in terms of mean flow quantities, heat transfer distribution, and coherent dynamics of turbulent HSV are shown in computed results. The HSV system consists of a multiple number of necklace-type vortices that are shed periodically at maximal frequencies. For high Re, we show that outburst of wall govern the instantaneous flow field, averaged vorticity affiliate with the growth of hairpin vortices that enclose around and dislocate the primary HSV. The time-mean endwall heat transfer is prevailed by two bands of high heat transfer which encircle the leading edge of the blade. The band of maximal heat transfer, occurs in the corner region of the juncture, while the secondary high heat transfer band (thin as compare to primary) develops upstream of primary band, in between primary and secondary bands a relatively low heat transfer region is identified.