Effects of unequal injections on a laminar swirling flow in a pipe with dual-tangential-entries
Other Title
非等量入流對雙切型渦漩層流之影響分析
Journal
Transactions of the Aeronautical and Astronautical Society of the Republic of China
Journal Volume
32
Journal Issue
3
Start Page
193
End Page
201
Date Issued
2000
Author(s)
Abstract
本文主要目的在分析雙管切型渦漩流非等量入流對流場大結構之影響效應，重點特別放在流場中最具代表性的過漩流中心迴流區上。在過去雙切型渦遊流之入相關研究均只探討等量放流下之流動情形，但在實際使用上常多少會有完全等量的情形，是故此常被直覺的接受為計算模擬與實驗結果有所差異時的一個「合理」歸因所在，但其是耶？非耶？則在文獻中未見探討。本文首先以實驗驗讓證計算結果之可靠性；而後由數種不同程度之非等量入流之數值計算結果發現，雙管切型渦漩流之各流場變數中，以徑向速度對入流非等量性之敏感性最高；對於其他流場變數而言，若切向入流之非等量程度不大於10%時，非等量因素對渦漩流場的影響太小可直接予以忽略！在10%~20%間只有在渦漩流場上游局部區域有些微影響，至於非等量程度超過20%後，非等量因素的影響方值得重視。綜合而言之，非等量入流使得渦漩流上游之壓力降低、上游中心圓錐區縮小、中心迴流區增大、促進流體混合，其對渦漩流近場結構之影響遠大於其對渦漩流遠場之影響。
This paper concerns mainly the effects caused by two unequal inlet injections on the flow structure of a laminar swirling pipe flow with double tangential entries, especially on the central recirculation region. All the past studies are based on the assumption of equal inlet injections for the reason of simplicity. This symmetric inlet condition is however more or less deviated in practical use and it is therefore often quoted in the literature as the reasonable and main reason for the case when numerical and experimental results are not matching. None has been discussed for the effects of unequal injections. Numerical computations have been firstly verified through the LDA experimental data. Effects of various "asymmetry level", defined as the dimensionless inequality of two injections, are then numerically studied in this paper. Present results show that the radial velocity component is the most sensitive to the asymmetry levels among all flow quantities. Effects of unequal injections on other flow quantities are negligible if the asymmetry level is not larger than 10%. The flow changes slightly in the near field for the level between 10% and 20%. The unequal injections are only important for still higher asymmetry cases. As the asymmetry level increases, the upstream pressure decrease, the central recirculation region expands towards both upstream and downstream directions. Overall speaking the effects of the asymmetry on the swirling flow are important in the near field, but not in the far field.
Subjects
渦漩層流
雙切型管
非等量入流效應
實驗
數值計算
laminar swirling flow
dual-tangential-entry tube
unequal injections
experiment
numerical calculation
Publisher
Aeron Astron Soc Rep China, Taipei, Taiwan
Type
journal article