Numerical Assessment of Density Ratio and Mainstream Turbulence Effects on Leading-Edge Film Cooling: Heat and Mass Transfer Methods

Within the context of leading-edge film cooling in a high-pressure turbine vane, the present study is a step forward toward modeling showerhead performance for a baseline geometry (namely four staggered rows of cylindrical holes) at engine-like conditions, starting from a previous investigation, at low-speed flow (exit isentropic Mach number of Ma(2)(is) = 0.2), low inlet turbulence intensity of Tu(1) = 1.6%, and density ratio of DR similar to 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity, and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aerothermal features of the flow in the leading-edge region in the presence of a larger density ratio (DR similar to 1.5) and turbulent mainstream (Tu(1) = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness (eta), obtained by using the pressure-sensitive paint (PSP) technique. DDES predictions of eta were computed using the species transport model (i.e., mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e., heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I, and Tu(1) should be taken into account when the goal is matching engine-like conditions.