Frequency of Unsteady Motions in Wake of a Wing

機翼尾流區非穩態流體結構的頻率探討

毛世威(Shih-Wei Mao) ； 黃榮芳(Rong-Fung Huang)

《中國航空太空學會學刊》 33卷3期 (2001/09) Pp. 155-162

https://doi.org/10.6124/TAASRC.200109_33(3).02

摘要

本文以實驗方法探討NACA0012機翼尾流區非穩態結構的頻率特性，並以簡易的相似理論與因次分析法辯證在極限狀況時之無因次函數關係與物理機制。熱線風速儀實驗探測到五種非穩定結構的特徵模態：不穩定波及層流、次臨界、過渡、超臨界四種渦旋流逸。在不同的雷諾數／攻角的區域存在著不同的非穩定結構特徵模態以及頻率特性。發生在低雷諾數及低攻角區域的不穩定波主要是由黏滯力主宰，因此Roshko數維持近乎常數。然而在大雷諾數及低攻角區域的超臨界渦旋流逸是由慣性力所主宰，因此Strouhal數維持近乎常數。介於兩極限狀況之間，層流渦旋流逸的Strouhal數隨著雷諾數的增加而增大。在雷諾數增加到次臨界渦旋流逸發生時，Strouhal數突降至一個低值，然後又開始隨著雷諾數的增加而增大。Strouhal數跨越層流與次臨界渦旋流逸區域時的突降是由於在轉換成次臨界渦旋流逸時，渦旋的紊流度突增，捲入效應增強，剪流層突張而導致的。

關鍵字

尾流 ； 渦旋流逸 ； 不穩定性

並列摘要

The frequency of unsteady motions in the wake behind a NACA0012 wing model was studied experimentally and justified analytically. Five characteristic instability modes: instability wave as well as laminar, subcritical, transitional, and supercritical vortex shedding were experimentally detected in the wake by using a hot wire anemometer. Different instability modes observed in different regimes of Reynolds number present different frequency characteristics. The Roshko number of the instability wave that occurs at low Reynolds numbers remains constant. However, the Strouhal number of the supercritical vortex shedding that observed at large Reynolds numbers remains almost constant. In the regime between two limiting cases, the Strouhal number increases with the increase of Reynolds number in the regime of laminar vortex shedding and decreases suddenly to a lower value as the shed vortices change to the subcritical mode. The analysis by employing the similarity theory and dimensional analysis technique to the limiting ranges of Reynolds number justifies the mechanisms of the instabilities in the viscous dominated and inertial dominated regimes.

並列關鍵字

Wake ； Vortex shedding ； Instability