可壓縮管流的理論與數值分析比較

Numerical Analysis of Compressible Channel Flows and Comparison with Theoretical Prediction

陳威銘(Wei-Ming Chen)

指導教授 ： 許文震

國立清華大學/工學院/動力機械工程學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00688

摘要

本文之研究乃是利用泛用型計算流體力學軟體STAR-CD作可壓縮管流的模擬，將其結果與一維假設下(Quasi-One-Dimensional Assumption)的可壓縮流理論做比較，藉此希望能對其物理真實現象做深入的了解，並提供日後在應用可壓縮流理論時，作為參考的依據。分析模型共分為低長寬比約13的直流道、L型、U型流道，並且探討截面漸縮效應，及高長寬比為1000的微直流道、U型微流道。模擬結果顯示，在低長寬比的漸縮流道中，摩擦效應可以忽略，且與理論不同的是，在真實流場中摩擦是會造成流體平均流速減少，而熱傳效應僅能使近壁面的流體加熱，截面均溫性甚差；L型及U型流道部分，由模擬結果顯示，在彎道入口時，流體會在外側形成最大壓力區，內側速度高於外側；反之當流體通過彎道後，外側的流速高於內側，溫度也較內側為低。此外，模擬結果亦可發現彎道會造成流體加速，於進出口前後壓差較漸縮流道為小的情況下，管道出口的馬赫數可以達到超音速流的狀態。在高長寬比微流道的模擬中可以發現真實流場與理論預測十分吻合，相同長度的彎管流場現象，溫度部分與直微流道近似，其餘結果也與理論相符合。藉此本研究可知，當流道為高長寬比的微流道時，可以使用理論來計算與預測流場現象，進而節省數值模擬所花費的時間。

關鍵字

可壓縮流 ； 管流 ； 微流道

並列摘要

The purposes of this study are to simulate compressible channel flows by a CFD commercial software (STAR-CD) and to compare the numerical results with those predicted by the conventional theory based on a quasi-one-dimensional assumption. We expect to obtain the real physical phenomena of channel flows encountered in practical applications. The physical models in the present study include the low-aspect-ratio channels (L/W=13), L-type and U-type channels with a converging effect on the cross sectional area, the high-aspect-ratio microchannels (L/W=1000) and U-type microchannels. Unlike the theory which shows a reduction in the average flow velocity by wall friction, the results reveal that the friction effect for low-aspect-ratio channels is negligible, the fluid is heated only near the wall and the temperature distribution is quite non-uniform across the cross section of channels. For the L-type and U-type channels, a high pressure region is formed at the entry in the outer region of the curved section and the flow velocity in the inner region is higher than that in the outer one. The behavior of flow after the curved section is reversed and the fluid temperature at the outer region is lower than the inner one. In addition, the simulation results also reveal that the fluid is accelerated in the curved section. The Mach number at the channel exit can reach a supersonic state if the pressure difference between the inlet and outlet is lower than that in a converging channel. It is also found that for high-aspect-ratio microchannels the numerical results are in good agreement with those according to the theoretical prediction. With an identical channel length, both the straight and the U-type microchannels have similar velocity and temperature fields. This fact indicates that, for high-aspect-ratio microchannels, one can simply utilize the theory based on a quasi-one-dimensional assumption to predict the phenomena of channel flows.

並列關鍵字

compressible flow ； channel flow ； microchannel flow

參考文獻

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