Effect of Coolant Inlet Conditions on Supersonic Film Cooling

Abstract

The influence of the coolant gas inlet height and Mach number on supersonic film cooling were analyzed numerically while keeping the mainstream inlet conditions and coolant mass flow rate unchanged for a given coolant gas. The results indicate that, for the same coolant gas without a shock wave or with a weak shock wave, the supersonic film cooling mainly depends on the coolant gas flow rate and has little relationship to the coolant inlet height or the Mach number. For the cases with a strong shock wave, reducing the coolant inlet height (i.e., increasing the Mach number) improved the supersonic film cooling. The main reason is that the coolant gas velocity increases when the coolant inlet height is reduced for a given coolant mass flow rate, which increases the coolant flow momentum, and so the coolant gas more effectively resists the interference of the shock wave. The results also show that helium is more easily affected by the coolant inlet conditions than methane or nitrogen when the inlet Mach number is the same for the same inlet height. Nomenclature c = mass concentration, kg∕m 3 c p = specific heat, J∕kg · K D = diffusion coefficient, m 2 ∕s E t = total energy, J∕kg e = internal energy, J∕kg k = turbulent kinetic energy, m 2 ∕s 2 Ma = Mach number m = flow rate, kg∕s Pr = Prandtl number p = pressure, Pa r = recovery factor T = temperature, K u, v = velocity, m∕s x = distance from the slot along the surface, m y = coordinate normal to the surface, m Sc = Schmidt number s = coolant stream inlet height, mm γ = specific heat ratio η = adiabatic effectiveness μ = dynamic viscosity, Pa · s ρ = density, kg∕m 3 ω = dissipation of turbulent kinetic energy, 1∕s τ = shear stress, kg∕m · s 2 Subscripts aw = adiabatic c = coolant stream r = recovery condition ∞ = freestream

Numerical simulation of supersonic film cooling in a rearward-facing slot

“…The turbulence model of Menter's shear stress transport (SST) k À v model 27 was also used, which effectively blended the robust and accurate formulation of the k À v model in the near-wall region with the freestream independence of the k À e model in the far field. Peng et al 21 also proved the availability of the SST k À v model.…”

“…26 O'Connor and Haji-Sheikh 19 and Maqbool et al 20 modeled film cooling in supersonic nozzle to develop an experimentally validated tool. Peng et al 21 analyzed the effects of coolant inlet conditions on supersonic film cooling to improve the cooling effectiveness using the minimum amount of coolant. Konopka et al 22 investigated film cooling with favorable and adverse pressure gradients, analyzed the effects of shock wave on film cooling 23 and later they extended their work to consider the conditions of film coolant using helium and hydrogen.…”

“…Although the semi-models made a distinction before and after the turning point, structural changes in the flowfield were not inspected because of the limitation associated with the one dimension nature of the models. The detailed structures of flowfield at this turning point can be obtained using computational fluid dynamic (CFD) method, but so far, there is rare CFD work concentrating on the flowfield changes at this point, including the Reynolds-averaged Navier-Stokes (RANS) based works of O'Connor and Haji-Sheikh, 19 Maqbool et al, 20 Peng et al, 21 large eddy simulation (LES) by Konopka et al, [22][23][24] and direct numerical simulation (DNS) by Keller et al 25 and Keller and Kloker. 26 O'Connor and Haji-Sheikh 19 and Maqbool et al 20 modeled film cooling in supersonic nozzle to develop an experimentally validated tool.…”

Effects of feeding pressures on the flowfield structures of three-dimensional film cooling

“…Opposing jet is a hot spot of research in recent years (Shen et al 2019), but it is mainly used for cooling at stagnation areas, and its corresponding cooling length is shorter compared with tangential cooling jet. Increasing the slot height can also improve the cooling effectiveness (Peng et al 2015), who's essence is to increase the mass flow rate and the thickness of the cooling film. Regarding the cooling gas, it is generally believed that gases with higher specific heat ratio have higher cooling efficiency (Eckert et al 1966), such as hydrogen and helium, and in real engineering applications, helium is safer and more reliable than hydrogen.…”

Experimental Studies of Film Cooling in Supersonic Combustors

“…7 Wei Peng et al numerically studied the effect of coolant inlet conditions on supersonic film cooling and the results indicate that, for the same coolant gas without a shock wave or with a weak shock wave, the supersonic film cooling mainly depends on the coolant gas flow rate and has little relationship to the coolant inlet height or the Mach number. 10 All the studies above are conducted in the condition of ideal model, and not consider the shape of the combustors and the combustion in the internal of combustor. Therefore, the present experiments are conducted under the condition of a practical combustor.…”