Coefficient of drag and lift of a car

[sickman]

car with spoiler | Automotive | SimScale

I need some help with the coefficient of drag and lift in simscale.
How to set the values of drag and lift in forces and moments coefficients for a given design?
and is anything wrong with the simulation in the above link?

[jousefm]

Thanks for your question!

Tagging @yosukegb4, @Get_Barried as well as @Retsam and @DaleKramer here. Yosuke created a post regarding that a while ago, but maybe he can give you some tips specific to your project now.

Best,

Jousef

[yosukegb4]

Hi @sickman ,

I checked your model a bit.

• No boundary condition on the car surfaces - set them as no slip walls for sure
• “Center of rotation” is on the half of your car wheel base and it may be [ 0, ?, 0 ] in your coordinate system
• “Lift direction” is [ 0, 1, 0 ] in your coordinate system
• “Drag direction” is [ 0, 0, -1 ] in your coordinate system
• “Pitch axis” is [ 1, 0, 0 ] in your corrdinate sysytem
• “Reference length” is the wheelbase length of your car
• “Reference area value” is the frontal projection area of your car

Please check them again by yourself.

Best,
Yosuke

[sickman]

Thanks for the help.
Now I got some clarity about" Lift and Drag direction" but about" Center of rotation" and “Pitch axis”, I’m still confused.
Can you explain what exactly Center of rotation and Pitch axis means in this simulation and on what basis should we assign the coordinates for both of them.

[yosukegb4]

Hi @sickman !

The pitch axis is needed to calculate Clf and Clr. Clf and Clr are very important for a car aerodynamics.

I hope my post and the capture image in it help you. The post explains about the pitch axis settings and so on.
The coordinate system is different from yours, but the concept of setting is the same.

Please click the link below and see my post.

Newbie. Forces and moments Help

Hi @gcanfield, I also think it is the best way to calculate the forces of car from the coefficients. These coefficients are distributed to the front Cl(f) and rear Cl(r), not to each wheels. I calculated the coefficeints in the setting as in the figure below. [image] I do not have conclusive evidence of the setting because it was judged only by myself, but I was determined that they are probable from the following points. The coefficients calculated in Result Control matched the coeffici…

Feel free to post any questions you may have.

Best,
Yosuke

[cbocaoco]

When getting for the lift coefficient do is still need to change the reference area? Or the frontal projection of the car is as it is?

[yosukegb4]

Hi @cbocaoco ,

Generally, you set a value of your car frontal projection area as the reference area.

'fp-023b_Test-C' simulation project by yosukegb4

Hi @Takumi ! Reference Length Value : Wheel Base (in the case of car CFD simulations) [image] Reference Area Value : Frontal Projected Area of a Car [image] If you have further questions, please do not hesitate to ask questions. Best, Yosuke

If the value of the frontal projection area is unknown when executing your simulations, you can calculate the coefficients with a setting of 1.0 [m^2] tempolally, and later correct the coefficients by using the correct value of your car frontal projecttion area by yourself.

Best,
Yosuke

[cbocaoco]

So does that mean upon getting the drag and lift coefficient they have the same area which is the frontal area of the car?

[yosukegb4]

Yes, the same reference area should be set for the lift and the drag.

[cbocaoco]

Thank you