利用直接模擬蒙地卡羅法於螺旋曳引式幫浦參數研究

Abstract

利用三維非結構直接蒙地卡羅法模擬稀薄氣體於螺旋曳引式幫浦的流場，並且在模擬中使用VHS(Variable Hard Sphere)分子模型、NTC(No Time Counter)碰撞取樣、VTS(Variable Time-Step)及利用Cell-By-Cell 的粒子追蹤法來完成分子的移動。根據1991年 Nanbu 的實驗條件，直接模擬真實三維螺旋曳引式幫浦的幾何參數(包括螺旋溝槽深度、靜子與轉子的間隙、螺旋角)和轉速，利用幫浦性能參數體積流率、質量流率、壓縮比、進出口壓差，進行在幫浦管道中的流場的分析。結果顯示溝槽深度、分子重、螺旋角和轉速的增加可以提高抽氣速率和質量流率；當轉子與靜子間隙加大，抽氣速率和質量流率將會下降。

Numerical simulations of rarefied gas flows in spiral drag pump (SDP) channel are carried out by using the three-dimensional unstructured direct simulation Monte Carlo (DSMC) method. Using Variable Hard Sphere (VHS) molecular model, No Time Counter (NTC) collision sample and variable time-step method (VTS) to simulate the molecular collision kinetics and use Cell-By-Cell particle tracing method complete the part of molecular move. According to Nanbu et al. (1991) experiment condition, to simulate a real three-dimension model on SDP geometry parameter (include depth of groove, gap size, screw angle) and rotation speed directly, use the pump performance parameter are volumetric flow rate (pumping speed), mass flow rate (throughput), compression ratio, and pressure different (between discharge and inlet) to analysis the flow field in the pump channel. The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Results show that to increase the depth of groove, molecules mass, screw angle and rotation speed can raise the pumping speed and the mass flow rate. As the gap value increases, pumping speed and the mass flow rate will be decreased.