Disk/Cavity Wall Cooling Effectiveness Experiments With Air and CO₂ as Coolants Free

Experiments were conducted with a turbopump drive disk/cavity model to determine the effects of coolant density on the composition of the fluid within a disk cavity. The 3-D, large-scale model simulated the aft cavity of the Space Shuttle Main Engine (SSME) high-pressure-fuel turbopump including the flow through the blade shanks of the second stage turbine and the nuts and bolts on the rotor and cavity walls. Coolant was injected near the bore of the turbine disk and gas sampling measurements were made to determine the fraction of the gas from each fluid source. Air was used as the gas entering the cavity through the blade shanks and air or carbon dioxide (CO2) was used as the coolant injected axisymetrically near the rotor bore. CO2 was also used as a trace gas when air was used as the simulated coolant. All the flow exited the cavity through the rim seal. CO2 concentration measurements were made to deterime the composition of gas withdrawn through pressure taps at selected radii from the disk bore to the simulated airfoil platforms. Results were obtained and are presented for a range of coolant flow rates. When air was used as coolant, the rotor wall concentrations were approximately 100 percent coolant from the disk bore to radii where momentum integral models indicate all the coolant is entrained in the disk boundary layers. When the coolant was CO2, having a density of approximately 1.5 times that of air, the coolant concentrations were generally less on both the rotor and cavity walls, indicating that the higher density coolant produced increased mixing with the upstream flow, entering near the cavity OD through the blade shanks.