Experimental Investigations on Transpiration Cooling for Scramjet Applications Using Different Coolants

Abstract

The extremely high heat loads within a scramjet combustor require the use of high-temperature materials combined with efficient cooling concepts. A promising technique is the application of transpiration cooling to ceramic matrix composite materials. A supersonic hot-gas-flow test facility is used to investigate this cooling method. The carbon/carbon samples tested have porosities of about e = 11%. The airflow is electrically heated up to 1120 K total temperature with a total pressure of ≈3 bar and is accelerated to a Mach number of 2.1 within the test channel. Air, argon, and helium are used as coolants for blowing ratios from 0 to 1 %. The surface temperature of the porous wall is measured via thermocouples and infrared thermography. Pressure and mass-flow measurements are used to analyze the throughflow characteristics of the porous materials at various temperature conditions. An approach based upon simplified analytical models is presented to analyze the experimental data of throughflow behavior and cooling efficiency. The simplified thermal model is used to analyze the effect of fluid property variations with temperature on pressure loss for different coolants and shows good agreement with the experimental data.