Within the context of leading edge film cooling in a high-pressure turbine vane, the present study represents a step toward modelling showerhead performance (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 *Ma~2is~* = 0.2), low inlet turbulence intensity of *Tu~1~* = 1.6% and low density ratio of *DR* \~ 1. Those operating conditions, dictated by constraints relating to Particle Image Velocimetry setup, 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* = 3.0.

Here, the potential of DDES is exploited to predict the aero-thermal features of the flow in the leading edge region in the presence of larger density ratio (*DR* \~ 1.5) and turbulent mainstream (*Tu~1~* = 13%), while matching either *BR* or *I*. DDES predictions of film cooling 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 experimental database contains surface measurements of film cooling adiabatic effectiveness (*fcae*), obtained by using the pressure sensitive paint (PSP) technique.

At matched BR, higher DR translates into lower coolant-to-mainstream momentum thus allowing for greater surface coverage on the pressure side of the vane. Conversely, film effectiveness distributions at low and high DR are almost the same along the suction side. Although the influence of high mainstream turbulence on showerhead performance is less relevant than that of high DR, an increase in the turbulent dispersion of the coolant jets causes a noteworthy reduction in adiabatic effectiveness levels on the pressure side.

From the numerical point of view, the most interesting finding is that DDES predictions are dependent on the approach used, under the same *DR*, *BR*, *I* and *Tu~1~*. The discrepancies between MT and HT results concern not only the contours of *fcae* but also the displacement of the jet cores above the leading edge surface. The coolant plume pertaining to the row#2-jet is the most affected by the simulation method, because of the interaction with the weak mainstream in the stagnation region.

Since ‘‘heat” and ‘‘mass” domains are not interchangeable despite matching *DR*, *BR,* *I* and *Tu~1~*, DDES has been exploited to reproduce engine-like conditions, thanks to the temperature difference between the coolant and the hot mainstream, so as to obtain the desired *DR* of 1.5. Compared to PSP data, in which room temperature carbon dioxide is used as the coolant stream, the simulation computed similar iso-contours of *fcae* but definitely higher effectiveness values downstream of the showerhead, along the pressure side. It follows that PSP laboratory testing does not ensure scaling to engine conditions, in the present scenario of complex interaction between the showerhead jets.


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

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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