A combined CFD-DSMC method for numerical simulation of nozzle plume flows

Small rockets are used extensively for attitude control and other low thrust operations on trans-atmospheric vehicles and spacecraft. Low thrust electric thrusters and a variety of chemical thrusters are being developed for these applications. Several experimental and numerical studies have been directed towards the prediction and characterization of the fluid dynamics and kinetics of the nozzle and plume flows.; The objective of this dissertation is to develop a methodology for performing simulations of a complete nozzle plume system. The combined approach involves four steps. First, a continuum simulation of the nozzle plume system is performed. An unstructured Navier-Stokes solver for performing these simulations is developed. The next step involves predicting the breakdown of Navier-Stokes equations from the Computational Fluid Dynamics (CFD) simulations and dividing the domain into a CFD region and a Direct Simulation Monte Carlo (DSMC) region. Various parameters that could be used for this are investigated and a new parameter is proposed. The third step involves transferring information from the CFD simulation to the DSMC simulation. Different methods of transferring information are analyzed. The last step involves performing DSMC simulations. DSMC simulations are performed and the results are analyzed to investigate the breakdown of the Navier-Stokes equations.; This method is applied to the study of two nozzle systems for which experimental results were available. The first system involved is a hydrogen thruster. The results obtained from CFD simulations of the system are compared with experimental measurements. The next system analyzed is the expansion of carbon di-oxide into vacuum. The near plume region is simulated using a CFD approach. The results obtained are compared with experimental measurements. A breakdown parameter is used to split the domain by predicting the breakdown of the Navier-Stokes equations. DSMC simulations are performed of regions where CFD methods are not accurate. DSMC results are analyzed in detail in an attempt to investigate the failure of the CFD approach. DSMC simulations of the back flow region are performed and different methods of passing the information from the CFD simulations to the DSMC simulations are investigated.