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

Abstract

Within the context of leading edge film cooling in a high-pressure turbine vane, the present study is a step forward towards modelling showerhead performance for a baseline geometry (namely 4 staggered rows of cylindrical holes) at engine like conditions, starting from a previous investigation, at low speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6% and density ratio of DR ∼ 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 aero-thermal features of the flow in the leading edge region at larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness obtained by using the pressure sensitive paint (PSP) technique. DDES predictions were computed by means of 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 Tu1 should be taken into account when the goal is matching engine-like conditions.

Large Eddy Simulation of Film Cooling with Forward Expansion Hole: Comparative Study with LES and RANS Simulations

“…The 6.25 × 10 −6 s time step means that the mainstream convects the hole diameter after 400-time steps [23,24]. The maximum Courant-Friedrichs-Lewy (CFL) number was less than one (U∆t/∆x = 0.3125) [25]. After the solution had reached a statistical steady state, the statistics of the solution were collected for about 20 flow-through times for the main flow (about 0.5 s).…”

Particle Deposition in the Vicinity of Multiple Film Cooling Holes

“…This so-called film cooling technology has been widely used for decades in turbomachinery for its high reliability in turbine blade cooling. Numerous studies have been carried out to reveal the mechanism of film cooling, optimize the design of hole, and improve cooling efficiency [1][2][3][4][5][6].…”