伴隨噴流之超音速飛行體阻力分析

在21世紀的今天飛行器減阻的課題越來越重要，在軍事用途上，它可以使戰鬥機或飛彈變得更省油，飛的更快；民用方面則可發展出更省油更環保的飛行器。在此我們試圖使用噴流方法達到減阻效果，我們於超音速彈體的前後方，分別加上逆向噴流及順向噴流，並分析其物理現象，利用逆向噴流衝擊相對氣流來改變外部流場並達到減阻效果；利用順向噴流補足彈體後方因分離流或膨脹波所形成的低壓區塊，以減少壓差阻力。　　我們利用Gambit產生網格，並使用CFD求解軟體Fluent中內建的LES及κ-ε 模組求解驗證案例及新案例，新的案例中包含半球形及喇叭狀的機鼻外型之局部逆向噴流、數個局部順向噴流、以及細長比為14.5的全彈體於飛行速度2.5馬赫時兩種噴流的搭配結果。另外我們還嘗試計算噴流所需的耗能量及其效率的基本推算：逆向噴流因為動量損失而使減阻效果變差，順向噴流則可製造出一個淨推力的效果，且似乎不需花費太多能量，所以整體效果優於逆向噴流。就結果而言，噴流概念將來也許可以實際應用於真實的超音速飛行器或彈體設計上。

關鍵字

超音速；鈍體；逆向噴流；順向噴流；減阻； LES模組； κ-ε模組；空氣動力學

並列摘要

Drag reduction is an important objective for aircraft operation, and become even more vital in the twenty-first century. In military usage, fighters or missiles can therefore save fuel consumption and attain higher flying speed; and in civil practice, the goal of more efficient and environmental concerned flights can be achieved. Here we try some approaches to accomplish the purpose of drag reduction. The physical phenomenon of supersonic projectile aerodynamics with counter-flow and rear end jets are analyzed in current effort. Using counter-flow jet to impinge upon the opposite free stream flow in order to change the flow field and thus in the hope of reducing drag force. On the other hand, we could also employ rear end jets to fill the domain which is after the projectile rear end so as to decrease the base drag and the drag from supersonic expansion waves. In addition to the grid construction and flow solver routine, LES model and k-epsilon model of CFD Fluent code are also employed in our studies for verification and case studies. Investigated problems include local counter-flow jet situations with hemispherical nose and trumpet-like nose configurations, several local rear end jet cases, and the combination of both nose counter-flow and rear end jets for a real missile-like projectile with a fineness ratio of 14.5 and Mach number of 2.5. With the newly defined drag reduction efficiency parameter; the drag reduction of counter-flow jet is not so good because of loss momentum of the reverse thrust. The rear end jet flow can be considered a big thrust there, and comparisons are also made. After the simulations of the energy consumption of the jets and efficiency of all different cases, it appears that we do not need to spend too much energy to transform the total drag to become net thrust, and it is believed that the jet conception considered in this work can found their practical application in future supersonic projectile operation.

並列關鍵字

Supersonic ； Blunt body ； Counter-flow jet ； Rear end jet ； Drag reduction ； LES model ； κ-ε model ； Aerodynamics

參考文獻

[2] Finley, P.J., “The Flow of a Jet from a Body Opposing a Supersonic Free Stream,” Journal of Fluid Mechanics, Vol. 26, 1966, pp. 337-368.

[3] Shang, J.S., “Plasma Injection for Hypersonic Blunt-Body Drag Reduction,” AIAA Journal, Vol. 40, No. 6, June 2002, pp. 1178-1186.

[4] Shang, J.S., “Plasma Injection for Hypersonic Blunt-Body Drag Reduction,” AIAA Journal, Vol. 40, No. 6, June 2002, pp. 1178-1186.

[5] Gauer, M. and A. Paull, “Numerical Investigation of a Spiked Blunt Nose Cone at Hypersonic Speeds,” Journal of Spacecraft and Rockets, Vol. 45, No. 3, May-June 2008.

[6] Ahmed, M.Y.M. and N. Qin, “Drag Reduction Using Aerodisks for Hypersonic Hemispherical Bodies,” Journal of Spacecraft and Rockets, Vol. 47, No. 1, January-February 2010, pp. 62-80.

國際替代計量

伴隨噴流之超音速飛行體阻力分析

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