[DHarston]

Hi all,
I want to be able to display pressure areas contributing to downforce similar to the way Toet does in the attached image (Pressure as oppose to Cp is fine), but cannot find anything on the subject here

I understand iso-clip to get the deadband region, but struggling how to get the pressure component at a surface in Z to be displayed

Thanks in advance for any help that can be offered

[AtoHM]

You can show force components on a surface. Its all there in CFD Post already.


Edit: Excuse me please I did not check your reference thoroughly. I must read through to get what he is really showing there. I guess somebody else will give you a quicker answer

[DHarston]

Originally Posted by AtoHM

You can show force components on a surface. Its all there in CFD Post already.

Hi, thanks for the reply
I understand, is there a way to have units in pressure (Pa) instead of Newtons?

[Opaque]

What are you looking for?

There is no way that downforce is given [Pa], either it is a force or it is a pressure or stress, but it cannot be both

[DHarston]

Maybe I am not expressing myself well.
I think the image I attached to the original post explains what I am looking for best. As close as possible to the outcome in the image is preferable
Thanks

[Opaque]

Be careful. Images do not mean anything if it is not clear what we are plotting.

Units are provided to be very explicit about the meaning of quantities, not about colors.

To convert fron force to pressure/stress, we need an area. The main question is what area? and what is the intended use downstream.

[ghorrocks]

If you define a variable pressure * Normal Vector_x/y/z (where x/y/z is replaced with the direction you want) and plot that on the surface you will get the pressure acting in the direction you indicate, which appears to be equivalent to the plot you show.

Note: This does not include wall shear, so it is not the total force on the surface. You can add wall shear if you add some terms to the variable.

Note2: If you plot force on the elements then it will show the force acting on the element, which will be a function of the size of the elements. This is not going to be very useful as the mesh size changes everywhere.

Note3: This all just goes to show you need to be very careful defining exactly what you want to show and carefully choosing the method of showing it, as Opaque says.

[AtoHM]

Glenn is right of course. I want to add, indeed you can also just define the cd value in this variable. The key part will be using only the wall normal vector component you need. If you want to go all the way, you can also include your deadband region by setting small values to zero within the variable definition. Then it should look identical to what your reference shows.
As your reference says "cd-plots" I assume the shear components mentioned are not included there. He also gives a good hint to use normalized plots like cd instead of actual pressure to make it way easier to compare results of different configurations which you should go for as well.


Btw nice to see, that these guys also use open source postprocessing tools instead of the commercial packages only.

[DHarston]

Hi all, sorry for the delay,
I was able to do it in the end - I tried Glenn's method, but it didn't recognise "Normal Z".
I did however find a solution by using the expression ForceZ/Area to achieve the result I needed. I can now adapt this to get Cd and CL plots should I need to

Apologies for the simple questions; I'm 'relatively' new to CFD and specifically analysing in Post in as much detail