The attenuation and reduction of a simulated hot streak due to mainstream turbulence, hot streak pitch position and film cooling
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This study investigated the effects of the vane and mainstream turbulence level on a simulated hot streak in a simulated three vane cascade. The effect of film cooling on the reduction of the hot streak was investigated for a fully film-cooled vane. To determine how the showerhead, suction side and pressure side coolant regions contributed to hot streak reduction, these regions were tested individually with and without the hot streak activated. The effect of mainstream turbulence level and coolant density ratio on coolant profiles and hot streak reduction was also investigated. Finally, superposition of coolant profiles and hot streak profiles was compared with measured data to evaluate the capability of additive superposition in predicting hot streak reduction due to film cooling. The effects of mainstream turbulence on the attenuation of a hot streak were found to be significant, with changes in the shape and size of the hot streak. Comparisons between the hot streak impacting the vane at the stagnation line and passing through the mid-passage showed that the peak hot streak temperature was the same for an impinging and non-impinging hot streak. Interaction with the adiabatic vane caused very sharp temperature gradients in the hot streak at the trailing edge of the vane, resulting in an increase or decrease in hot streak peak strength depending on pitch position. Additional attenuation of the hot streak occurred in the stator/rotor axial gap. Results with film cooling indicated that, while full-coverage film cooling had a substantial effect on the hot streak, this effect was primarily due to the showerhead and suction side coolant with a much lesser effect due to the pressure side. It was discovered that coolant profiles at the trailing edge could be scaled by the coolant hole exit temperature, while reduction of the hot streak was less for film cooling at low density ratio. Measurements also showed a much higher degree of coolant spreading under conditions of high mainstream turbulence. Overall, downstream of the vane using high blowing ratios, the hot streak peak was reduced by 83% compared with the peak value upstream of the vane.