Alok Majumdar

Numerical Modeling of Pressurization of a Propellant Tank

An unsteady finite volume procedure has been developed to predict the history of pressure, temperature and mass flow rate of the pressurant and propellant during the expulsion of the propellant from a tank. The time dependent mass, momentum and energy conservation equations are solved at the ullage space. The model accounts for the change in the ullage volume due to expulsion of the propellant. It also accounts for the heat transfer from the tank wall and propellant to the ullage gas. The procedure was incorporated in the Generalized Fluid System Simulation Program (GFSSP). The results of several test cases were then compared with a published correlation of pressurant requirements for a given displacement of propellant. The agreement between the predictions and the correlation was found to be satisfactory.

Numerical Modeling and Test Data Comparison of Propulsion Test Article Helium Pressurization System

A transient model of the propulsion test article (PTA) helium pressurization system was developed using the generalized fluid system simulation program (GFSSP). The model included pressurization lines from the facility interface to the engine purge interface and liquid oxygen (lox) and rocket propellant-1 (RP-1) tanks, the propellant tanks themselves including ullage space, and propellant feed lines to their respective pump interfaces. GFSSPs capability was extended to model a control valve to maintain ullage pressure within a specified limit and pressurization processes such as heat transfer between ullage gas, propellant, and the tank wall as well as conduction in the tank wall. The purpose of the model is to predict the flow system characteristics in the entire pressurization system during 80 sec of lower feed system priming, 420 sec of fuel and lox pump priming, and 150 sec of engine firing.

Numerical Prediction of Conjugate Heat Transfer in Fluid Network

An unsteady finite volume procedure for conjugate heat transfer in flow network that takes into account the longitudinal conduction through the solid is presented. It uses a fully coupled approach in which the governing equations for solid and fluid are coupled through solid to fluid heat transfer that is expressed as a function of flow properties and temperature of solid. As an evaluation of the proposed technique, a chilldown problem for a cryogenic transfer line is formulated and solved. Test cases modeling transient flow of liquid hydrogen (LH2) and liquid nitrogen (LN2) under saturated and subcooled liquid conditions are presented. The effects of varying the inlet driving pressure on the chilldown time and flow rates have been evaluated. Increasing the driving pressure decreased the chilldown time and increased the flow rate. Subcooling the inlet cryogen further reduced the chilldown time. Numerical predictions are compared with available experimental data and are found to be in good agreement. The proposed model captures the essential features of conjugate heat transfer and provides an efficient and robust way for predicting chilldown of transfer line at a low computational cost.

Effect of idealized asymmetric inhibitor stubs on circumferential flow in the Space Shuttle SRM

Computational fluid dynamic analyses have been performed to calculate circumferential pressure and velocity gradients in the vicinity of an asymmetric inhibitor stub in the port of the Space Shuttle solid rocket motor. The three-dimensional Navier-Stokes equations were solved by an iterative finite volume algorithm, SIMPLE, incorporated in a general purpose computer code, FLUENT. Turbulence was represented by way of effective viscosity, which was calculated from local turbulence energy and its dissipation rate (K-e model). The numerical predictions were compared with the measurements from a 1.5% scale, cold-flow model of the redesigned solid rocket motor. The calculated circumferential pressure distribution upstream of the inhibitor stub compares well with the measured data.

Network Flow Simulation of Fluid Transients in Rocket Propulsion Systems

This paper presents a numerical study of fluid transients in a pipeline with the sudden opening of a valve. A network flow simulation software (Generalized Fluid System Simulation Program) based on the finite volume method has been used to predict the pressure surges in a pipeline that has entrapped air at one end of the pipe. The mathematical model is formulated by involving the flow equations in the liquid (water) zone and compressibility of the entrapped air. The numerical results are compared with the experimental data available in the literature. The study is conducted for a range of the reservoir pressure and for different amounts of initial air present in the pipeline. The numerical results compare well within reasonable accuracy (less than 8%) for a range of inlet-to-initial pressure ratios when the amount of air present is relatively high (α≈0.45). A fast Fourier transform is performed on the pressure oscillations to predict the various modal frequencies of the pressure wave.

Numerical Simulation of Liquid Nitrogen Chilldown of a Vertical Tube

This paper presents the results of a one-dimensional numerical simulation of the transient chilldown of a vertical stainless steel tube with liquid nitrogen. The direction of flow is downward (with gravity) through the tube. Heat transfer correlations for film, transition, and nucleate boiling, as well as critical heat flux, rewetting temperature, and the temperature at the onset of nucleate boiling were used to model the convection to the tube wall. Chilldown curves from the simulations were compared with data from 55 recent liquid nitrogen chilldown experiments. With these new correlations the simulation is able to predict the time to rewetting temperature and time to onset of nucleate boiling to within 25% for mass fluxes ranging from 61.2 to 1150 kg/(sq m s), inlet pressures from 175 to 817 kPa, and subcooled inlet temperatures from 0 to 14 K below the saturation temperature.

Computational Model of the Chilldown and Propellant Loading of the Space Shuttle External Tank

This paper describes a computational model of the chilldown and propellant loading of the Space Shuttle External Tank liquid oxygen and hydrogen tanks at Launch Complex 39B at Kennedy Space Center. The purpose of the computational model is to predict the time required to chilldown the entire assembly consisting of the ground system transfer line and propellant tanks in order to compare with observed loading times, to evaluate the feasibility of similar models developed for the Ares I Upper Stage. The model also predicts the history of inflow and outflow from the tank, pressure and temperature inside the tank, and heat leak through the walls. The Generalized Fluid System Simulation Program (GFSSP), a general purpose network flow analysis code, has been used to develop this computational model. The paper describes the simulation of the loading process for both tanks and compares the resulting predictions to measurements.

Numerical Modeling of Thermofluid Transients During Chilldown of Cryogenic Transfer Lines

This paper describes the application of a finite volume procedure for a fluid network to predict thermofluid transients during chilldown of cryogenic transfer lines. The conservation equations of mass, momentum, and energy and the equation of state for real fluids are solved in a fluid network consisting of nodes and branches. The numerical procedure is capable of modeling phase change and heat transfer between solid and fluid. This paper also presents the numerical solution of pressure surges during rapid valve opening without heat transfer. The numerical predictions of the chilldown process have been compared with experimental data.

NUMERICAL PREDICTION OF TRANSIENT AXIAL THRUST AND INTERNAL FLOWS IN A ROCKET ENGINE TURBOPUMP

This paper presents the application of the Generalized Fluid System Simulation Program (GFSSP) to model the time-dependent flow in a complex secondary flow circuit of the turbopump of the Fastrac engine currently under development at Marshall Space Flight Center. GFSSP is a general purpose computer program for analyzing steady-state and time-dependant flowrates, pressures, temperatures, and concentrations in a complex flow network. The program employs a finite volume formulation of mass, momentum and energy conservation equations in conjunction with the thermodynamic equation of state of real fluids. GFSSP was used to calculate the axial thrust and internal flow distribution of the Fastrac engine turbopump during the start and shut down transients. The models discussed in this paper use boundary conditions that were extracted from turbopump test data. The GFSSP predicted turbopump secondary flow passage pressures and temperatures were compared with actual measured values.

Numerical Modeling of Fluid Transients by a Finite Volume Procedure for Rocket Propulsion Systems

This paper describes the application of a finite volume procedure for a fluid network to predict fluid transients following a rapid valve closure in a long cryogenic pipeline. The conservation equations of mass, momentum, energy, and the equation of state for real fluids are solved in the fluid network consisting of nodes and branches. In the present formulation, the speed of sound does not appear explicitly in the governing equations. Instead, the equation of state for a real fluid is solved in conjunction with the conservation equations to calculate the compressibility factor for modeling the wave propagation phenomenon. The numerical procedure is also capable of modeling the wave propagation due to phase change and gas-liquid mixture. The predicted history of pressure and velocity variation in a single pipe has been compared to the solution by the method of characteristics (MOC) for liquid oxygen (LO2 ), liquid hydrogen (LH2 ), and water (H2 O). The paper also presents the numerical solution of pressure surges for a gas-liquid mixture, condensation of vapor, and flow circuit with parallel branches and tailpipe.Copyright