Assessment of Various Flow Solvers Used to Predict the Thermal Environment Inside Space Shuttle Solid Rocket Motor Joints

Qunzhen Wang §ATK Thiokol Propulsion Corp., Brigham City, UTINTRODUCTIONIt is very important to accurately predict the gaspressure, gas and solid temperature, as well as theamount of O-ring erosion inside the space shuttleReusable Solid Rocket Motor (RSRM) joints in theevent of a leak path. The scenarios considered aretypically hot combustion gas rapid pressurization eventsof small volumes through narrow and restricted flowpaths. The ideal method for this prediction is a transientthree-dimensional computational fluid dynamics (CFD)simulation with a computational domain including bothcombustion gas and surrounding solid regions.However, this has not yet been demonstrated to beeconomical for this application due to the enormousamount of CPU time and memory resulting from therelatively long fill time as well as the large pressure andtemperature rising rate. Consequently, all CFDapplications in RSRM joints so far 1'2 are steady-statesimulations with solid regions being excluded from thecomputational domain by assuming either a constantwall temperature or no heat transfer between the hotcombustion gas and cool solid walls.The complicated gas dynamics, heat transfer, and O-ring erosion phenomena in the RSRM jointpressurization process are currently modeled by twowidely used computer codes. One is SFLOW 3'4, whichwas recently developed at ATK Thiokol Propulsion, andthe other is JPR 5'6, which was developed by NASAMarshall Space Flight Center. While both codes applySINDA/G 7, a commercial thermal analyzer, to calculatethe solid temperature for a given heat flux, the flowsolvers used to model the transient compressible flowsare very different. Before SFLOW was developed, acode called ORING2 8 and its previous version ORINGhad been widely used at ATK Thiokol Propulsion topredict the thermal-flow environment at various RSRMjoints. The major difference between these codes is alsothe flow solver used to calculate the pressure,temperature, and Mach number of the gas as well as theheat flux from the hot combustion gas to thesurrounding cold solid parts.The flow of high pressure and high temperaturecombustion gas from the RSRM combustion chamber tothe O-ring grove inside various joints is a highlytransient compressible process involving flow areachange, friction, heat transfer from the hot gas to coldsolid walls, as well as the mass addition due to the flowpath and O-ring erosion. The main objective of thispaper is to assess the capability of various flow solvers,which have been used in simulating the thermalenvironments of RSRM joints, to accurately predicttransient compressible flow phenomena with areachange, friction, heat transfer, and mass addition.Besides the flow solvers used in SFLOW, ORING2,ORING and JPR, another flow solver is studied wherethe governing equation is the generalized one-dimensional steady flow equation taking into accountthe effects of area change, friction, heat transfer andmass addition 9. Specifically, the following five flowsolvers have been incorporated into SFLOW to studytheir capability in accurately predicting the transientcompressible flows with area change, friction, heattransfer and mass addition: (1) isentropic method, (2)ORING2 method, (3) Lapple 1° method, (4) generalizedmethod, and (5) SHARP 1H3 method. Note that,although SHARP can perform two-dimensional as wellas three-dimensional CFD simulations, only the one-dimensional part is considered in this paper. The otherfour solvers are for one-dimensional flows only.The following test cases with exact solutions are used toassess the above flow solvers: (1) steady flow with areachange, (2) steady flow with friction, (3) steady flowwith heat transfer, (4) steady flow with mass addition,02002, ATK Thiokol Propulsion Corp.Published by American Institute of Aeronautics and Astronautics, Inc., with permission_Sr. Principal Engineer, Gas Dynamics, AIAA member1American Institute of Aeronautics and Astronautics