二維機翼穿越渦流層之力元分析

Abstract

流場結構與物體受力之間的關係一直是相當受關注的研究議題，在這之中多重物體間尾流相互影響的複雜問題，常以渦流與機翼的交互作用之現象作為研究基本型態。了解尾流導致的受力震盪為結構安全課題中的重要一環。 本研究將模擬在二維流場中，機翼穿越另一機翼的尾流渦漩形成的渦流層之情形，探討重點為流場狀況及機翼的受力變化。研究中採用的機翼型號為NACA0010，在雷諾數1000的流場下使用工程軟體Ansys Fluent來取得流場資訊，並嵌入使用者自訂方程式做進一步的力元分析。本研究使用Chang(1992) 提出的力元理論方法獲得物體之受力，與一般表面壓力積分法不同，力元方法將力做拆解來區別個流體元素對力的貢獻，首先將力元所得的結果與Fluent用壓力積分法計算的結果做比較，兩者相當吻合，故本研究能夠準確地利用力元方法探討流場內個別渦漩對升、阻力的貢獻與影響。除了有助於深入了解流場性質外，並且能用來分析、預測、設計有利於實際應用的流場。

Flows around multiple bodies are common in aerodynamics, each body disturbs the free-stream and the disturbances interact with other bodies. Vortex–airfoil interaction is studied as a prototype of such problems. In order to know the vortex structure of the flow and forces applied on the airfoil, we simulate the case of airfoil intersecting a vorticity layer which is formed by the airfoil’s wake in a two-dimensional flow field. In our cases, Reynolds number is 1000 and airfoil type is NACA0010. We use Ansys Fluent to compute the basic flow information. Combining these flow info with Force Element Decomposition. It turns out to be a useful method to decompose total force into separated elements, which yields us a better view of the flow structure and interactions of vortices. It also helps us to quantify the contribution of a specific vortex in lift or drag force. Our research is focused on forces applied to the airfoil in different vortex strength and different angle of attack. The results show that the vortex strength is linear to the force change, and angle of attack has a lot to do with the distribution of force element.