Wake Flow Analysis of a Vortex Shedder Situated Downstream of Double Elbows Out-of-Plane

本研究使用一50 mm管流進行實驗，渦流流量計放置於不同平面雙彎管下游。為了感測渦流溢放信號，在渦流產生器上放置微機電感測器。分析微機電感測器的信號可得到渦流溢放頻率，及所對應的量測不確度值及信號品質值。由結果顯示，當渦流產生器在雙彎管下游18D位置，ReD=6.25×10^4，渦流溢放頻率的量測不確度值最小，為0.319%。當渦流產生器在雙彎管下游16D位置，ReD=6.25×10^4，渦流溢放信號品質最佳，其對應值為9.645；這此情況下，吾人進一步使用X型熱線探針在渦流產生器下游3D與1D截面量測尾流場流速，配合條件取樣方法及參考微機電感測器渦流溢放信號，而得到在這兩個截面的流場結構資訊，在1D截面可明顯地看見渦流溢放結構，但是在3D截面因擴散作用而不明顯。

關鍵字

無資料

並列摘要

Experiments were made in a 50 mm pipe system, with a vortex flowmeter situated downstream of double elbows out-of-plane. A Micro-Electro-Mechanical- -System (MEMS) sensor was installed on the vortex shedder for sensing the flow motions associated with vortex shedding. Analysis of the MEMS sensor signals was carried out to obtain the quantitative information concerning the vortex shedding frequency, its uncertainty and the signal quality defined. As found, the lowest measurement uncertainty reduced was 0.319%, due to the case of the vortex shedder situated 18 D downstream of the double elbows for ReD=6.25×10^4. On the other hand, the best signal quality in terms of the signal to noise ratio defined was 9.645, for the vortex shedder situated at 16 D downstream of the double elbows at ReD=6.25×10^4. Further, under this flow condition, an X-type hotwire probe was positioned at 3D and 1D, respectively, downstream of the vortex shedder for surveying the velocity distributions in these cross-sectional planes. By applying a conditional sampling technique referring to the MEMS sensor signals obtained simultaneously, the hot-wire signals were analyzed and reduced for the ensemble-averaged flow structures in these two cross-sectional planes. The results indicate that the vortex shedding structures could be clearly identified at 1 D downstream of the vortex shedder, but had diffused greatly at 3 D downstream.

並列關鍵字

wake flow ； MEMS sensor ； vortex flowmeter

國際替代計量

Wake Flow Analysis of a Vortex Shedder Situated Downstream of Double Elbows Out-of-Plane

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