穿音速截面法則(transonic Area Rule)呢?我在網路上找很久都是零
- TonyLv 71 decade agoFavorite Answer
親愛的 Rmax ,
(1) Kutta Condition: 對於一個翼形而言，在特定攻角時，旋流(circulation)Γ的值會使氣流平順地離開後緣；若後緣是有限角，則後緣就是停滯點(V1=V2=0)；若後緣是尖角，則翼形上下表面離開後緣的氣流速度大小相同、方向相同(V1=V2)；在此V1是翼形上表面離開後緣的氣流速度，V2是翼形下表面離開後緣的氣流速度。以數學式來說，氣流的渦流強度(strength of vortex sheet)在後緣為零，即γ(TE)=0。這是因為γ(TE)=V1-V2，且在後緣V1=V2，故γ(TE)=0。
(2) Transonic Area Rule: 為了減小跨音速震波的影響，NASA物理學家Richard Whitcombe於1955年提出穿音速截面法則，也就是飛機在穿音速飛行時，前緣和後緣的震波不可避免，但如果飛機沿前進軸線上的截面積急劇改變，將產生額外的震波，增加阻力。為了避免這額外的阻力，飛機沿縱軸的截面積應該均勻改變（或者說截面積沿縱軸的二階導數或曲率應該恆定），而截面的形狀倒是無關緊要，這就是著名的跨音速面積率，也是超音速飛機"蜂腰"的來源。
2008-07-04 16:52:51 補充：
快考試了, 加油!Source(s): 張三+李四
- shamejudgeLv 71 decade ago
The Kutta condition is a principle in steady flow fluid dynamics, especially aerodynamics, that is applicable to solid bodies which have sharp corners such as the trailing edges of airfoils. It is named for German mathematician and aerodynamicist Martin Wilhelm Kutta.
Kuethe and Schetzer state the Kutta condition as follows:
A body with a sharp trailing edge which is moving through a fluid will create about itself a circulation of sufficient strength to hold the rear stagnation point at the trailing edge.
In fluid flow around a body with a sharp corner the Kutta condition refers to the flow pattern in which fluid approaches the corner from both directions, meets at the corner, and then flows away from the body. None of the fluid flows around the corner and remains attached to the body.
The Kutta condition is significant when using the Kutta–Joukowski theorem to calculate the lift generated by an airfoil. The value of circulation of the flow around the airfoil must be that value which would cause the Kutta condition to exist.
The Whitcomb area rule, also called the transonic area rule, is a design technique used to reduce an aircraft's drag at transonic and supersonic speeds, particularly between Mach 0.8 and 1.2. This is the operating speed range of the vast majority of commercial and military fixed-wing aircraft today.