一道波音空气动力学的考题 ？
有人对空气动力学精通吗.可以告诉我准确答案吗?[ 本帖最后由 FreddyMusic 于 2006-5-19 17:46 编辑 ]
Re:求准确答案,
同上 一道波音的考题挺有意思！谁做出来了，:@:@:@狠狠的加分！
[ 本帖最后由 FreddyMusic 于 2006-5-20 16:15 编辑 ] 哈哈 HH
[ 本帖最后由 nrist1981 于 2006-6-17 19:02 编辑 ] 好，做做看 好題目,但我不是航空系的,只是搞CFD一小段時日而以,弄錯了請指正!
原題目:
Question 1: Wind Tunnel
You are an aerodynamicist for The Boeing Company. The company has decided to enter the general aviation aircraft market. The new aircraft will be a smaller version of the blended wing-body design that Boeing has been developing. You have been tasked with developing a wind tunnel testing program to complement Computational Fluid Dynamics simulations of the flow about the aircraft in cruise conditions. The following baseline estimates are available:
1• Mean chord, 1.5 m
2• Wing span, 10 m
3• Cruise velocity, 60 m/s (about 220 km/hr)
4• Speed of sound at cruise altitude, 300 m/s
5• Density at cruise altitude, 0.4 kg/m3
6• Dynamic viscosity, 1.5 x 10-5 kg/(ms)
The wind tunnel targeted for the testing has the following properties:
1• An oval cross-section 3 m wide by 2 m high.
2• The tunnel can be pressurized such that the density can be set from 1 kg/m3 to 2 kg/m3.
3• Maximum tunnel velocity, 100 m/s.
4• Speed of sound, 340 m/s.
5• Dynamic viscosity, 1.8 x 10-5 kg/(ms)
Consider the following questions:
11. On the aircraft, what will be the dominant sources of drag during cruise?
主要還是viscous force,因為機翼都是採streamlined設計, 所以form drag 應該很小 (interference drag 因形狀未知,故目前不考慮)
22. Can the wind tunnel be used to produce reliable test data for cruise?
風洞比對最主要還是Reynolds Number, 所以
Re=Density*Velocity*L/visocosity
假設原機及模型的特徵長度分別為 Lo, Lm
Re,original=Re,model
則
0.4*60*Lo/1.5e-5=1*100 *Lm /1.8e-5 (上限)
0.4*60*Lo/1.5e-5=2*100 *Lm /1.8e-5 (下限)
Lm/Lo=0.144~0.288
所以模型縮小比例需 0.144到0.288 ,也就是模型的 wing span 長度需等於 1.44~2.88 meter
應該是可以測試的
33. If yes to (2), suggest a size for the wind tunnel model and the corresponding tunnel flow conditions for testing. If no to (2), suggest a possible modification to the tunnel that would allow for testing. Then, based on this modification, suggest a size for the wind tunnel model and the corresponding tunnel flow conditions for testing.
一般飛機的Frontal Area/風洞截面積 <=5%, 所以為減少壁面效應,採用 scale =0.144的模型進行吹試
speed=100 m/s, viscosity=1.8 e-5, density=2 kg/m3
[ 本帖最后由 Kiddosuper 于 2006-10-19 15:09 编辑 ] niu啊，佩服佩服:D，感觉自己还有很多需要学习啊
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