Steady and Unsteady Heat Transfer in a Transonic Film Cooled Turbine Cascade

Abstract

This paper reports on an investigation of the heat transfer on the suction side of a transonic film cooled turbine rotor blade in a linear cascade. Heat transfer coefficient and film effectiveness are first determined for steady conditions. The unsteady effects of a passing shock on the heat transfer are then investigated. The film cooling pattern used is a showerhead design with three rows on the suction side, one row at the stagnation point and two rows on the pressure side. The experiments were performed at engine representative temperature and pressure ratios using air as coolant. Heat transfer measurements are obtained using a Heat Flux Microsensor, and surface temperature is monitored with a surface thermocouple. Static pressure is monitored with a Kulite pressure transducer. The shock emerging from the trailing edge of the NGV and impinging on the rotor blades is modeled by passing a shock wave along the leading edges of the cascade blades. The steady-state heat transfer coefficient is 8% higher with film cooling than without film cooling. Shock heating of the freestream flow is determined to be the major contribution to the unsteady variation of heat flux, leading to an increase of about 30°C to 35°C in recovery temperature and adiabatic wall temperature.

Unsteady Strong Shock Interactions in a Transonic Turbine: Experimental and Numerical Analysis

“…Dunn et al [10], followed by Abhari et al [11], have performed time-averaged and time-resolved measurements of a transonic single-stage research turbine in a short duration facility. More recently, Popp et al [12] and Nix et al [13,14] reported the progression effect of shock waves on film-cooled blades through a transonic turbine linear cascade.…”

Effect of Variable Properties Within a Boundary Layer With Large Freestream-to-Wall Temperature Differences

“…Thus, it is often advantageous to examine a given film-cooling scheme by analyzing its convective heat flux, q, governed by q = -T") (1) where h is the convective heat-transfer coefficient, Taw is the adiabatic wall temperature, and T" is the temperature of the wall. (2) where Tr is the recovery temperature. If this were the only parameter to vary in Eq.…”

“…Film cooling is known to increase mixing, which in turn increases h [1]. Popp et al [2] showed that, for no fibn cooling present, Eq. (1), the heat flux to the wall would increase with film cooling, causing an undesired effect.…”

“…Then, they created a transient convective heat-transfer case and measured the walltemperature profile at two time steps of the transient. However, as with Popp et al [2], their method also assumes he / hc{T") and n f n{Tw), which are both valid for the low temperatures they considered. Then, he and n distributions were calculated from a conduction analysis of the transient response.…”

“…He utilized a method similar to that proposed by Popp et al [2] to determine heat-transfer coefficients and adiabatic effectivenesses. Rather than the method of continuous measurement and modification of freestream condition proposed by Popp et al [2], DeLallo [8] took two steady-state measurements with constant freestream conditions and different wall temperatures. The resulting two data points were used to form a line of which the slope was he and the q = 0 intercept was Taw.…”