Developing a Parallel DSMC Algorithm for Simulating Flow in Micro-Nano Propulsion Systems

Mirjalili, Vahid | 2009

723 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39305 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. With the rapid development of mico-nano propulsion systems in micro-spacecrafts and micro-sattelites, precise investigation of flow field in these devices has become necessary. Micro propulsion systems usually have a thrust in order of mili Newton, and they can be used for maneuvers of spacecrafts with mass of less than 10 kg. Micro propulsion systems are usually classified according to their thrust generation mechanism to different classes like cold gas, and chemical propulsion systems. Cold gas micro propulsion systems obtain their energy from thermodynamic expansion of gas and not by combustion. If the flow fiel dimensionare comparable to mean free path, rarefaction effects are observed in flow behavior. According to rarefaction of different flow regimes from continuum to free molecular regime are observed. Propelant expansion aontains different flow regimes including free molecular. So, for flow modeling in micro-nano propulsion systems, it is necessary to use particle-based methods like DSMC. In this thesis, a numerical code based on the DSMC method using unstructured grid and parallel computing ability has been developed. Since the convergent-divergent nozzle is the most important part of a cold gas propulsion system, flow modeling in theses device leads to the investigation of flow behavior in micro-nozzles. For optimization and increasing the efficiency of numerical code, the appropriate number of subcells according to unstructured grid geometry is chosen and Chen-Piera algorithm is used for particle locating in computational domain. The results of unstructured grids are compatred with structured results and also with valid refrences. Subsonic boundary condition in nozzle inlet using method of characteristics has benn implemented. Because of high gradient in outlet section of the nozzle, implementing the pressure boundary condition at the outlet leads to inequlibrium condition in inlet-oulet mass flow rate. Numerical experience, showed that for correct physical simulation of flow a buffer section at he outlet of nozzle is required. In addition to studying the efficiency and exit thrst of nozzles, interesting physical phenomenas are observed. For instance, because of the increase of viscous effects and boundary layer thickness growth in high Knudsen numbers, it is not possible to have supersonic flow. Back pressure implementation leads to separation in the divergent. Effect of viscosity in small dimensions avoid strong shock waves and instead we will have Mach cores, and multiple expansion-compression waves in the divergent part. The DSMC code is transformed into C++ language and is revised in linux operating system, and parallel computing is implemented by using OpenMPI library. The parallel code is used in a cluster and the speedup is compared with linear ideal case
  9. Keywords:
  10. Monte Carlo Method ; Parallel Processing ; Microchannel ; Micronozzle

 Digital Object List