Some Effects of Coolant Density on Film Cooling Effectiveness

Abstract

Experiments have been conducted on a large wind tunnel model of the leading edge region of a turbine blade. The model had a semi-circular leading edge in which four rows of holes were symmetrically placed about the stagnation line, two at ±15° and two at ±44°. Air and alternatively CO2 were injected from the coolant holes after contamination with a known small percentage of propane. Using a flame ionization detector and the mass transfer analogy, the film cooling effectiveness was measured at various overall mass flow ratios and at various streamwise locations for each coolant type. The division of coolant flow rate from the two rows of holes was found to be more unequal for CO2 than for air, an effect which is predicted from a simple analysis of the coolant/free stream interaction and the hole discharge coefficient. This has practical implications for actual turbine operation since earlier cut-off of the coolant from the front row of holes, due to density differences, could have disastrous effects on the blade. This effect also further complicates any attempt to identify overall trends of coolant density on performance. It is not possible to conclude that air or CO2 coolant has a higher film cooling effectiveness, although, in general, air appears better close to the first row of holes, and CO2 better at some distance downstream of both rows. Based on the measurements, the effects of mass flow ratio, momentum flux ratio, relative hole placement in each row, and spanwise versus streamwise injection are discussed in the paper.

Film cooling on a turbine guide vane: A numerical analysis with a multigrid technique

“…The overall conclusion was that lm cooling provides better cooling effectiveness on the suction surface compared with that on the pressure surface. Several investigations (by Gartshore et al [8], Ou et al [9] and Mehendale et al [10]) have been made to resolve the effect of different parameters on lm-cooling effectiveness. It was observed that the lm-cooling effectiveness is a complex function of blowing ratio, density ratio, injection angle, blade geometry and the injection hole con guration.…”

Aspects of Vane Film Cooling With High Turbulence: Part I — Heat Transfer

“…Mehendale and Han (1992) have shown that leading edge (or showerhead) film cooling can produce substantial levels of heat transfer augmentation, with increasing blowing ratio, even when high levels of inlet turbulence are present. Additionally, Gartshore (a al, 1993) in an experiment and Garg and Gaugler (1995) in a calculation have shown the heat flux in the showerhead region may not be uniform in either the spanwise or streamwise directions due to the joining of coolant jets from different rows leaving regions of good and poor coverage. In addition to showerhead configurations which typically have spanwise inclined holes, studies with spanwise and compound angle holes on flat plates such as Ligrani and Ramsey (1995), Sea, Schmidt, andBogard (1994), andEkkad, Zapata, andHan (1995) have also documented high levels of augmentation for turbulent boundary layers.…”