aircraft simulation

Vitali · December 18, 2011, 13:37

Hello!
I'm running simulation for external aerodynamics for a model aircraft (scale 1:33) previously tested in a wind tunnel. I'm using CFDesign with k-epsilon turb model. Conditions are the same as the wind tunnel conditions (scale, air speed,pressure) but results (lift and drag forces) are not according to the experiment...
what turbulance/laminar ratio and turbulance intensity have I to use?
thank you and sorry for my bad English

truffaldino · December 18, 2011, 13:42

k-e model is not good for this purpoce: Usually it gives garbage results when simulating aircraft, especially at low Reynolds numbers, when there are separations, transitions etc. For a model aircraft I would rather used non-PDE based software, such as XFLR5: It will give you much more better results.

Truffaldino

k_k · December 18, 2011, 15:40

what is the Reynolds Number of your flow? if the Re of your flow is greater than 10^6 you are free to use any turbulence model without low Re corrections assuming the flow is fully turbulent. For flows or Re of the order 10^5, you have to use turbulence schemes with low Re corrections and have a very fine grid, y+ of 1 should be adequate. Even though there exists no universal low Re, transitional turbulence model, turbulence models with low Re corrections turned on should give acceptable results.

The turbulence intensity of the wind tunnel in which it was tested should be documented in the report on the wind tunnel experiment, so read that document carefully. It should be between 3% to 5% in many cases.

You can use a turbulence viscosity of the ratio between 5 to 10, to start with. The sensitivity of the solution on this value has to be tested along with grid independence check to prove confidence on the simulation results.

December 18, 2011, 13:37	aircraft simulation	#1
Vitali New Member Join Date: Dec 2011 Posts: 1 Rep Power: 0	Hello! I'm running simulation for external aerodynamics for a model aircraft (scale 1:33) previously tested in a wind tunnel. I'm using CFDesign with k-epsilon turb model. Conditions are the same as the wind tunnel conditions (scale, air speed,pressure) but results (lift and drag forces) are not according to the experiment... what turbulance/laminar ratio and turbulance intensity have I to use? thank you and sorry for my bad English

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December 18, 2011, 13:42		#2
truffaldino Senior Member Join Date: Jan 2011 Posts: 249 Blog Entries: 5 Rep Power: 17	k-e model is not good for this purpoce: Usually it gives garbage results when simulating aircraft, especially at low Reynolds numbers, when there are separations, transitions etc. For a model aircraft I would rather used non-PDE based software, such as XFLR5: It will give you much more better results. Truffaldino

December 18, 2011, 15:40		#3
k_k Member Kailash Join Date: May 2011 Location: London, UK Posts: 45 Rep Power: 15	what is the Reynolds Number of your flow? if the Re of your flow is greater than 10^6 you are free to use any turbulence model without low Re corrections assuming the flow is fully turbulent. For flows or Re of the order 10^5, you have to use turbulence schemes with low Re corrections and have a very fine grid, y+ of 1 should be adequate. Even though there exists no universal low Re, transitional turbulence model, turbulence models with low Re corrections turned on should give acceptable results. The turbulence intensity of the wind tunnel in which it was tested should be documented in the report on the wind tunnel experiment, so read that document carefully. It should be between 3% to 5% in many cases. You can use a turbulence viscosity of the ratio between 5 to 10, to start with. The sensitivity of the solution on this value has to be tested along with grid independence check to prove confidence on the simulation results.