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Question: 6 consider the variation of drag coefficient with reynolds number...

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6 Consider the variation of drag coefficient with Reynolds number for an infinitely-long circular cylinder, shown in the attached sheet. (a) Sketch flow patterns around a cylinder and discuss the formation of the von Kármán vortex street. [5 marks] (b) With reference to the boundary layer, explain the sudden reduction in drag coefficient for a smooth cylinder at Re 2 x 105. Explain the effect of roughness at Re 1 x 105. [5 marks] A typical first-world war biplane fighter, such as the Sopwith Camel F.1 shown in Figure Q6, had a number of vertical inter-wing struts and diagonal bracing wires. On the Camel, the total length of the vertical struts (summed together) was 15 feet (4.57 m); these struts were cylindrical in cross section with a diameter of 2 inches (50.8 mm). The total length of the bracing wires was 60 feet (18.3 m), each with a cylindrical diameter of 3/32 inches (2.29 mm). (c) Calculate the drag contributed by these struts and bracing wires when the Camel is flying at its maximum speed of 115 mph (51 m/s) at sea level Data at sea level: ρ 1.2 kgm-3, T 288 K and μ 1.8 x 10-5 kgm-1s-1 [10 marks] (d) In steady-level flight at 115 mph (51 m/s) at sea level, the Camel has a mass of 660 kg. Determine the drag coefficient of the aeroplane and the percentage of drag which is due to the struts and wires. Data for the Camel: lift-to-drag ratio, L/D 7.5; wing area, S 21.5 m2 [5 marks] Historical note: The prototype of the Sopwith Camel first flew on 22 December 1916. Approximately 5,490 aeroplanes were ultimately produced. A metal fairing over the gun breeches created a hump that led to the unusual name Figure Q6102 10 Infinitelyl plate 1 Infinitely long circular cylinder Finite circula cylinder eld 5 Effect of surface roughness or 102 Infinitely long circu 10.1 .2ls 12 s 102 s 10° 2 5 10,2 5 10.2 s 10% 2 5 1062 510,

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