Loading...

Developing a Hybrid Molecular-Continuum Algorithm to Simulate Gas Flow in Micro-Nano Propulsion Systems

Roohi Golkhatmi, Ehsan | 2010

1569 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40821 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Darbandi, Masoud
  7. Abstract:
  8. With the rapid development in the application of nano-micro systems in space propulsion systems, it is necessary to obtain accurate analysis of flow field in these devices. New generation of space missions are usually performed by using a network of small-scale satellites. The mission control of such small-scale satellites requires specialized propulsion systems than produce small propulsive forces of about 1 micro-Newton. The main purpose of the current PhD thesis is analysing the flow field in different nano/micro propulsion systems by using a hybrid Navier-Stokes (NS)-direct simulation Monte Carlo (DSMC) method. Nano/micro propulsion systems experience different rarefaction regimes from continuum to transition and free molecular ones. Simulation of nano/micro propulsion systems with pure molecular or continuum solver is not accurate and efficient due to this widespread change of flow regimes. The current study aims to increase accuracy and efficiency of a hybrid DSMC-NS software which simulate nano/micro propulsion systems. To achieve this goal, we first develop and extend required components for a hybrid solver including a 2-D DSMC code for simulating subsonic-supersonic flows with different wall heat flux boundary conditions. We extensively validate the results obtained from our code with the literature and analytical solutions of NS equations subject to slip boundary conditions. We extend our DSMC solver to Information Preservation (IP) formulation to reduce statistical scatter of solution in low speed flow in long channels. We use our IP code to derive a new analytical expression for dynamic viscosity, mass flow rate, and pressure drop in transition regime in order to extend the Navier-Stokes equations to higher Knudsen number flows. We extend our molecular solver to 3-D application in arbitrary geometries and unstructured meshes under the framework of OpenFOAM. In this process, we use existing algorithms in OpenFOAM such particle tracking in general geometries. After developing our 3-D code, we extensively validate it by solving high speed flows over different geometries such as flat plate, cylinder, and 3-D corner at different Knudsen number regimes. The key stage of our study focuses on developing and validating hybrid molecular-continuum algorithm. We use the NS solver of OpenFOAM as a continuum solver for our hybrid algorithm. The molecular solver is the developed 3-D DSMC solver. We use our hybrid algorithm to simulate flow in different nano/micro propulsion systems suggested in the literature. We calculate key parameters of nano/micro propulsion systems such as thrust, propulsive efficiency, discharge coefficient, and specific impulse. We also study the dependency of these parameters to the nozzle geometry and inlet gas conditions. We show that use of hybrid algorithm decreases computational expanses while accuracy is preserved.

  9. Keywords:
  10. Direct Simulation Monte Carlo (DSMC)Method ; Hybrid Algorithm ; Navier-Stokes Equation ; Micro/Nano Propulsion System

 Digital Object List

  • محتواي پايان نامه
  •   view

 Bookmark