| AVS 56th International Symposium & Exhibition | |
| Vacuum Technology | Wednesday Sessions |
| Session VT-WeM |
| Session: | Partical and Theoretical Aspects of Gas Dynamics |
| Presenter: | R. Versluis, TNO Science and Industry, The Netherlands |
| Authors: | R. Versluis, TNO Science and Industry, The Netherlands R. Dorsman, TNO Science and Industry, The Netherlands |
| Correspondent: | Click to Email |
Last year we presented a new method to model moving surfaces in DSMC. The method was validated by modelling a single rotor of a turbomolecular pump and comparison with experimental results. We have now applied the method to model the gas dynamics inside a 25 stage turbomolecular pump (13 rotors and 12 stators) under various discharge pressures and for various gases and gas mixtures. The turbo pump consists of two sections with different number of blades and different angles. The compression of the turbopump is about 6 orders of magnitude and the flow regime insode the pump goes from free molecular conditions at the inlet side to transitional flow on the discharge side. Interesting phenomena inside the pump are shown, such as a non-linear pressure profile inside he pump, with the non-linearity taking place at a position that would not be expected based on the geometry. Details of the gas flow inside the turbopump are visualized such as the concentration profile of gas mixtures inside the pump, temperature effects and the pressure contours inside the pump. All of these things can also be visualized as a function of time showing the pressure increase at the blade edges ahen a rotor passes a stator and the pressure decrease when the rotor has passed the stator, followed by the backflow of molecules in the wake of the blade.
The method allows a completely new look inside the turbopump and offers possibilities for simulation of new prototypes, optimisation of blade geometry, spacing etc. The current algorithm that calculates the interactions between molecules and rotors is limited to linear blade motions. The rotational motion of the blade is therefore linearized to a straight motion, but the method itself is general. The algorithm can easily be replaced for non-linear velocities although the calculation of collisions between blade and molecules becomes more tedious.
By running the calculations a large cluster of dedicated computers (up to 100 parallel nodes) the calculation time for discharge pressures around 1 Pa is still reasonably small (around 1 day).
The attached document shows an example of the results of a calculation for nitrogen.