Computational studies of venting hydrogen flame impingement on the Space Shuttle external tank

Abstract

The hydrogen vent valve on the outside of the Space Shuttle External Tank is ordered to close right before launch and should remain closed during flight. However, there is an accepted risk that a small amount of leakage of hydrogen during flight may occur. There is a possibility that the mixing of the leaking hydrogen with the ambient air may form a combusting plume if ignited. The impingement of the burning plume on the External Tank may damage its Thermal Protection System. A series of computational studies were performed to predict the heating of the Thermal Protection System by the impingement of the hydrogen flame. -he calculations were based on solutions of the ,,ree-dimensional compressible Navier-Stokes equations together with a two-equation turbulence model and a two-reaction global hydrogen combustion model. Predicted heat fluxes compared well with available experimental data. The final results will be useful to help design a stronger Thermal Protection System to withstand such a flame impingement scenario. Introduction The External Tank (ET) on the Space Shuttle contains two internal tanks which hold liquid hydrogen and oxygen, as shown in Figure 1. A certain amount of the liquid hydrogen continually boils to gaseous hydrogen (GH2). While the vehicle is on the pad, the GH2 vents through a relief valve and duct located on the side of the ET and is transported away through an umbilical and burned in a burn stack. Just prior to lift-off, the GH2 vent valve is ordered to close. However, the valve could remain Senior Scientist, AIAA Senior Member Program Manager, AIAA Member * .* Qy’ighl American lastitutc d Aemnautics lad ArtroDautics, h., 1%. All rigs Mcrvcd. t Orbiier omitted for clarity N.B. These are approximate dimensions Fig. 1. Space Shuttle vehide slightly open, even though the valve sensors may indicate it is closed. The slowly leaking GH2 will mix with the ambient air as the vehicle flies along its t ra jectory, forming a transversely injected plume. The plume can ignite if an ignition source is present. The burning hydrogen flame can impinge on the ET and damage its Thermal Protection System (TPS). Computational analyses based on solutions of the three-dimensional compressible Navier-Stokes Equations were performed to predict the heating rates to the surface of the E T Thermal Protection System. The key physical phenomena that need to