Measurement and Analysis on the Instability of the Swirling Wake Flow at Low Reynolds Number

本文主要針對渦漩流體通過鈍體所形成之不穩定流場結構作作量測及分析。渦漩流體通過鈍體會在鈍體後方形成一複雜之迴流泡尾流，隨著旋流數的增加。在較大旋流數時，流場下游會形成渦旋回流，利用雷射光頁觀察可以發現具迴流泡、渦漩回流、渦漩破裂三種模態；隨著諾數增加時，在圓盤周緣衍生形成剪流層會產生渦漩流逸，形成不穩定性結構；利用頻譜設備量測剪流層與渦旋回流在渦漩流逸時所具有之不穩定性，配合流場結構可以發現速度擾動具有不穩定波、層流波、次臨界波三種模態。

關鍵字

渦漩；鈍體；剪流層；渦漩流逸

並列摘要

This study is aimed at the observation and measurement of the unstable flow structure when swirling fluids pass through a bluff-body at low Reynolds number. The flow field combining the swirling flow with wake flow will form complicated recirculation structures behind the circular disc. It will bring unstable phenomenon with the increment of the swirl number. Flow structures observed with laser-light sheet at different swirl strength show three characteristic modes: recirculation-bubble mode, vortex breakdown mode, and vortex breakup mode. Eddy shedding appears in shear layer derived from the outer rim of the disc even at the low Reynolds number. Hot-wire anemometry is used to measure the instability frequency of this eddy shedding. Three types of velocity fluctuations at different extent of swirl strength are identified with instability wave, laminar wave, and subcritical wave.

並列關鍵字

swirl ； bluff-body ； shear layer ； vortex shedding

國際替代計量

Measurement and Analysis on the Instability of the Swirling Wake Flow at Low Reynolds Number

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