高攻角彈體之動力及尾流引致振動之研究

Flow Induced Unsteady Vibrations of Sharp-Nosed Circular Cylinders

陳智杰(F. B. Hsiao) ； 蕭飛賓(C. C. Chen) ； 梁勝明(S. M. Liang) ； 金麟聖(L. S. King)

《中華民國振動與噪音工程學會論文集》 1994 (1994/06) Pp. 9-20

https://doi.org/10.30028/CSSVANNUAL.199406.0009

摘要

在本量測實驗中，我們採用五分量平衡儀配合熱線測速儀來量測彈體在高攻角時的動態／靜態受力趨努。研究發現，量測尾流渦流釋放的適當位置為(平均值 X)=2D，(平均值 Y)=0.68L，(平均值 Z)=D/2，雷諾數低較易量測到渦流釋放情形，極高攻角時渦流釋放情形近似二維圓柱，史綽荷數介於0.17-0.19之間。在動態受力之頻域分析中，我們發現幾個主要的頻率－流場的頻率（不穩定之剪流層及尾流渦流釋放）、結構的自然頻率、流場與結構耦合之頻率。而由不穩定之剪流層隨鼻端側滾角改變的現象，我們可得存在鼻端幾何外形上微小不對稱之證據。為維持穩定的飛行姿勢，須避免尾流渦流釋放接近結構之自然頻率，以減少嵌入效應發生的可能性，進而降低擾動量。

並列摘要

A uniform flow passing over sharp-nosed circular cylinder models at high angles of attack (AOA) is experimentally studied in a low speed wind tunnel. The unsteady flow induced vibration characteristics of models in conjuction with their downstream wake behaviors are carefully investigated by means of measurements from a force/moment balance and a hot-wire anemometer. Results indicate that flow respectively passing over the models behaves quite the same as it passing over a conventional 2-D circular cylinder for AOA approaching 90°. After normalization, the Strouhal numbers of the shedding vortices vary between 0.17 and 0.19 for all AOA's used. When a model is positioned at a moderate AOA, say around 70°, several peaked frequencies are clearly noted in the dynamic force/moment measurements. Data show that this is comprised of the effects among the flow properties (shear-layer and vortex shedding instabilities), model structure (natural frequency), and the flow-structure coupling. It also indicates that the side force is dependent on the model roll angle, which acts as a fashion like a stepwise variation, due to some degrees of flow microasymmetry acting on the model inducing unsteady behavior. The locked-in phenomenon is also found when the vortex shedding frequency is close to the natural vibration frequency of the model, which causing strong self-excitation and inducing high-amplitute vibration in the model and the wake flow.