[carlos_cfx]

Hi CFX specialists,

I am simulating an external flow over a vehicle using CFX.

Is there any possibility in extracting the resulting forces at the wheels?

I have tried functions like
force()_x@wheel
but you will only receive the resulting forces created on the wheel surface and summed up into the pressure point.

Does anybody have an idea?

Due to the overdetermined situation (4 wheels) this issue can't be solved by calculations. It can only be roughly approximated.

Cheers
Carlos

[ghorrocks]

but you will only receive the resulting forces created on the wheel surface and summed up into the pressure point.

I do not know what this sentence means.

If you are saying the force is for the 4 wheels rather than individual wheels - if you have a mesh primitive for each wheel you can get the force per wheel there, otherwise you will need to edit your mesh so each wheel is a different boundary. Both of these methods will give you the force on each wheel.

[carlos_cfx]

Hey ghorrocks,

thanks for your reply!

well what I mean is the resulting force distribution of the negative lift force on the whole body. This lift results in down forces at each of the four wheels at the contact area to the road.

Having separated components for the wheels I will receive only the force created by the wheel geometry and not the whole body. Having asymmetric aerodynamics on the vehicle (left/right side) I will need to figure out the created side forces at the wheels as well.

I once read something like:
"torqueX()@location"
But I am not sure how to use it cause I have four wheels in my model and differing down forces at each side.

Cheers
Carlos

[ghorrocks]

My previous post said what your options are - use mesh primitives if they exist, otherwise you will need to define a different boundary pathc for each wall.

Then it is a trivial matter to get the forces and moments of each tyre individually.

[kacjak256]

Hi Carlos


Have you managed to find the solution of your problem? I also try to calculate the force on each wheel of a car.

[ghorrocks]

This post is 8 years old. You are lucky I am really old as well because normally people from posts that old are long since dead.

But I repeat what I said 8 years ago - as long as you have defined a surface for the wheel then you just need force_x/y/z()@wheel and you get the forces. If you have not defined the wheels as separate surfaces then go back to your solid modelling or mesh software and change your mesh so the wheels are separately surfaces.

[kacjak256]

Originally Posted by ghorrocks

This post is 8 years old. You are lucky I am really old as well because normally people from posts that old are long since dead.

But I repeat what I said 8 years ago - as long as you have defined a surface for the wheel then you just need force_x/y/z()@wheel and you get the forces. If you have not defined the wheels as separate surfaces then go back to your solid modelling or mesh software and change your mesh so the wheels are separately surfaces.

Hi ghorrocks


Thank you for your reply


I see this post is 8 years old, but I didnt want to create new thread about the same problem.


Anyway, by defining a surface of the wheel, you mean the whole wheel or just the contact surface with the ground?

Also, how the model of airflow space should be made to achieve the proper result? I was importing CAD file of the car in geometry section and then I created the cube around it. The ground of that cube is also a plane of contact with the wheels. After that I was using boolean operation to create an airflow space. Should I draw the cube a bit lower, so the wheel will not have a contact with the ground wall or maybe the problem is somewhere else?

[ghorrocks]

The force_x/y/z function returns the force on the surface you apply it to. As simple as that.

I do not understand your final paragraph.

[kacjak256]

And it gives the total force from car body distributed to each wheel?


In final paragraph I was trying to describe how I modelled the geometry to carry out the simulation.

[ghorrocks]

CFD gives you the forces the fluid acts on the surface. What happens to those forces when it is applied to the body depends on stiffness, inertia, loading conditions and so on - that is more of a FEA question, or a free body diagram at least.