| 摘要: | 某些對飛行安全有害的諸如氣象現象風切、雷雨、冰或雪相對其他危險因子而言是大家所了解的。而大雨對飛機所造成的氣動力損失則是正在進行中的研究主題且需要長遠的進行研究。本研究首先對前人所做的因大雨效應而使得飛機性能減低的研究進行重新探討，再來用解析方法去計算二維機翼遭遇大雨時的狀況並且討論一些初步得到的結果，最後以典型的飛行動力學方程式去解飛機接近落地或落地到煞車時大雨的影響。經由天氣預測、雷達技術、資料傳達、飛行員訓練的體認，因天氣因子所造成的航空事故在近十年間大大的減少。另一方面因為大雨所造成的飛機性能及空氣動力係數依然稍微的不清楚甚至矛盾，航空研究學會及學校持續的發表新的研究結果。而對於飛機積冰的問題，吾人嘗試以計算流體力學來解決，大致上可以分為三個步驟，第一步是網格點之生成，之後是流場解，最後是水滴軌跡方程式。根據流場解結果，以線性分析求解控制體積內流場之速度分佈狀況，而水滴軌跡運動方程式是一時間與速度的函數，因此可以預測若干時間後， 水滴行進的方向與位置，並以此判斷出水滴是否撞擊機翼，俟積冰形成後，吾人再重新生成網格點、流場解與積冰，如此疊代運算，直到吾人所要求的時間為止。吾人之研究結果，積冰之成長趨勢相當符合，但是在部分區域，其積冰分佈與積冰厚度上有所誤差，而提出了改善之方法。
此研究之目的著重於回顧此地區最新的發現以及利用新的解析方法去計算當飛機遭遇大雨或積冰時空氣動力減少的結果，期望能達到一般的結論。最重要的是此科學上的結果能提出於航空界中，以期在決定性關鍵中能扮演好它的角色。經由本工作將會得到一些資料並能對航空公司運作上有所助益，長遠來說，以期使得飛機飛的更安全些。
The detrimental effects of some meteorological phenomenon such as wind shear, thunderstorm, ice/snow etc, to aviation safety are relatively well known. But aerodynamic influences due to heavy rain are still the on-going research subject, and needs further investigation. This research first review some research finding of heavy rain effects on aerodynamic performance degradation. Then an analytical method to compute the two-dimensional heavy rain condition is introduced and some preliminary results are discussed. Finally, the classical flight dynamics equations are solved with rain and rain/gust influences in the approach to land and the touch down to brake phases. It is felt that the quantitative information gained in this work could be useful to the operational airline industry, and greater effort should put in this direction to further improve aviation safety. Through the combining efforts in weather forecast, radar technology, data communication, and pilot training awareness, aviation accidents due to these phenomena have decrease drastically in last decade. On the other hand, the adverse efforts of gust wind and heavy rain on aircraft performance and aerodynamic efficiency remain somewhat unclear and even contradictory, and new research results are still reporting from aviation research institutes or universities.
The three causes lead to Airplane crash that include human, mechanism, and the weather. Ice accretion, the topic we want to discuss in this article, categorized into the weather. Broadly speaking, the reason of ice accretion was that temperature of air lower than freezing point, and droplet exist in supercooled water. When droplet impact on airfoil, it accretes. Bowyer's unstructured grids scheme is useful to generated grids. It will generate grids automatically only by some inner or outer boundary points. It's easier to add or eliminate specific grid, and thus more suitable for complex geometry, just like ice accretion shapes. The numerical scheme employed is the typical Roe's scheme on Euler equations, and the 4 th order Runge-Kutta time stepping method is also used to accelerate the convergence rate. Droplet motion equation and tell droplet if impact the airfoil or not, based on the results of solver. Apply ice accretion analysis, the ice accretion shape come out. After that, the grids regenerate, so do flowfield and ice accretion. It lasted repeatJy until the time we set. The ice accretion results show that the trend of ice accretion is correct, but ice accretion profile and ice accretion thickness is not as good as we expected. Several improvements have been presented.
The purpose of this project is first to review the latest findings in this area, and through a new analytical method to compute the aerodynamic degradation effects in heavy rain and ice accretion conditions, it is hoped that a general conclusion can be reached. Most important is that these scientific results should pass on to the aviation community, and plays its role at some decisive moments. |
