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 mike March 14, 2004 09:49

Help with symmetry

I'm modelling a car mockup in a wind tunnel, and I'm defining a symmetry plane along the longitudinal axis of both. I'm interested in the Cd an Cl of the car buy I've a doubt: In the turbulence specification method (in hidraulic diameter) and in the area of reference values, I've to introduce the total front surface of the car mockup or only the half value of this surface due to the symmetry used? Thanks a lot.

 Jun March 15, 2004 13:10

Re: Help with symmetry

Hi, Are you specifying the inlet or outlet condition of the wind tunnel? if it's so, there is no need to consider the hydraulic diameter of the car mockup.

 mike March 15, 2004 13:36

Re: Help with symmetry

Hi. Thanks for your response. I'm specifying the inlet as "velocity inlet" and the outlet as "outflow". In the "velocity intel" dialog box I'm specifiying the turbulence by the turbulence intensity of the wind tunnel and the hydraulic diameter of the car, introducing the half of frontal surface of this one. I've constated that this value isn't really relevant for the drag coefficient (the variable that I'm interested in), the fundamental value is the area used for adimensionalize the force and introduced in the "Reference values..." dialog box, and I don't know what I've to introduce: the total frontal surface of the car or only the half of this surface. Thanks.

 Jun March 15, 2004 16:28

Re: Help with symmetry

hi, if I understand you correctly, you should use the hydraulik diameter of the wind tunnel inlet for the turbulence specification at the inlet other than the one of the car. To calculate the normalized forces, you need to input the half surface area. The symmetry condition only provide kind of boundary condition. You are not supposed to get the forces acting on the whole car by using the symmetry boundary. Hope it helps.

 mike March 15, 2004 17:41

Re: Help with symmetry

Thanks a lot, Jun.

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