於過渡區之穩態可壓縮流流經圓柱體的流場及熱傳分析之研究

Abstract

本研究主要是應用平行化非結構性的直接蒙地卡羅法模擬在過渡區之穩態可壓縮流流經圓柱體的流場及熱傳分析。使用grid over-lapping method 來加速在回流區的sample數量。流場的設定條件Knudsen number＝0.02∼2，Reynolds number＝10∼75，Mach number=0.1∼3，圓柱表面溫度則為300K∼900K。數值模擬的結果顯示出在圓柱後的回流區會隨著Reynolds number增加而有增長的趨勢，隨著Knudsen number的增加，流場變的較稀薄，而有逐漸減小的趨勢。此外，圓柱表面的溫度也會影響回流區的存在與否。

Flow field and heat transfer for argon gas flows surrounding a circular cylinder at low Reynolds numbers in the transitional regime is simulated using the unstructured-mesh, parallel direct simulation Monte Carlo [DSMC] method. A grid-overlapping method is designed to speed up accumulating an appreciable number of samples within wake region. Flow conditions include free-stream Knudsen numbers in the range of 0.02-2, free-stream Reynolds numbers in the range of 10-75, free-stream Mach number in the range of 0.1-3, and surface temperature of the cylinder in the range of 300-900K. Numerical results show that the size of symmetric recirculating bubble behind the cylinder increases with increasing Reynolds numbers at constant Knudsen number, while it decreases with increasing Knudsen numbers at constant Reynolds numbers. In other words, rarefaction tends to destroy the formation of recirculating bubble behind the cylinder. In addition, heat transfer from the surface of the cylinder correlates strongly with the existence of the recirculating bubble behind the cylinder.