[jon g]

Have got far enough to model the flow round a hill climb race car all very informative But

having issues getting out real values for drag and downforce and working out the centre of pressure to work out front rear balance

has anyone got some pointers on how to tackle this ?

If one uses the overall study goals for force etc does that include the ground plane as well ?

Do I have to select each surface?

can you name a set of surfaces? cant see how yet.

any advice would be most welcome.

Objective is to improve what we have a bit no going to the F1 chase the last little bit.

Many thanks

[Boris_M]

Hi Jon,

The global goals are all valid for everything within the computational domain, so also the road.
If you use a surface goal (as forces act on surfaces) and select the parts in the assembly of which you want the forces, you can get them directly on these parts.
If you use local coordinate systems you can get the values of forces and torque relative to that coordinate system instead of the global coordinate system.
This way you can, for example, use a coordinate system that sits in the CG of the front wing and ask for the forces on the front wing only relative to that local coordinate system.
If you select the part or parts, it will automatically take all surfaces of those parts.

No, you cannot name the surfaces, that's defined by the CAD system as the geometry is created. You can name the goals, but not the CAD surfaces.

As for finding the center of pressure, you'll have to work with the torque on the coordinate systems and the forces to find the center of pressure with the help of math. So leverage etc.

Regards,
Boris

[jon g]

First of all Many thanks for the clear and concise reply it is good to know i am going the right way

I have another query: I noticed in the general settings initial and ambient conditions that for air at normal temp/pressure when i changed to pressure density that the value is 1kg/m^3 I was expecting to see 1.225.
did a study on a cube to verify the drag co-efficient and the value of air density in results was better am I right that this changes as the flow is calculated. ( ran it as pressure and temp specified. )

Also been reading up how the meshing works in the technical manual understand the refinement rules ( the auto seems to work well )
don't understand what the initial mesh level control 0-3 red then 3-7
is this just the initial level ? the tutorials imply it is more complicated

on the whole car it is refining cells round the wing profiles and tyres ok
slot gaps look like they could use a finer mesh assume i will have to go manual and set higher level for channel refinement.

have added a png file of the mesh at a slot

Many Thanks Jon

[Boris_M]

For external simulations these are the parameter of the air coming into the computational domain. In an internal simulations they are starting conditions for all cells and if you have a different inflow then they will adjust as the flow develops.

The automatic settings has some automation behind it which considers geometry to some degree as well as boundary conditions. In aerodynamics I would advise to use manual settings and local settings for exactly such slots and airfoils. You need to resolve the flow better than in complex flow problems with a lot of mixing etc. Here the streamlined form is very important.
I put a document about best practice in external aerodynamics. It was done for airplanes but the meshing advice are good for automotive as well. Of course the wing detail I would use strongly for wing anaysis only, in a whole car the mesh can get big quickly so it is a little bit of playing with the settings to resolve it good enough but not super fine. Airplanes are highly aerodynamic. Cars too but much more blunt considering the separation behind them.

http://www.floefd.com/download/BPG_E...rodynamics.zip

Hope this helps.
Boris

[jon g]

Thanks that looks just the ticket got some serious reading and testing to do. now
seem to be making progress.

Thanks Jon