simulating a radiator in CFX 17

[Anonymous No.1516325]

I recently joined a small german formular student team (20 members) and was assinged to the aerodynamics division. I noticed that the current simulation model of the car is faulty since the radiators are treated as solid objects that do not let air pass through. The values for the radiator were sourced from a test at which the air was moving at a very low speed. Not very representative for a simulation running at 30 miles per hour.
I tried looking up solutions to the problem but i could not figure out how to define a part as porrous or a filter. A description of the progress would be really appreciated. thanks in advance! (pic related is the current car)

[Anonymous No.1516400]

>>1516325
How much experience do you have with CFD software?

[Anonymous No.1516429]

>>1516400
this, and also what you'll be using is important
>representative at 30MPH
you are definitely on the correct track though, your AutoX and Endurance courses are gonna be at this range, with a possible max of 60-70 MPH.

also, judges don't care about results as much as they do the process, so to get max points, just make sure your process is right even if your CFD results are shitty, and then comment on what you'd change

[Anonymous No.1516438]

>>1516325
you do not need to make cfd for these amateur stuff, use linear model derived from the thermodynamic laws applied with the right boundary conditions....
>inb4 i cant into math

[Anonymous No.1516442]

>>1516438
the formula student event bridges the gap in between amateur and professional, the best student teams will absolutely have extensive CFD validation and test time for their vehicle or they'll get slammed during their design review

that being said, yeah definitely do hand calcs as a basis for where to start with a lot of this. if you can, make friends with your aero professor, come to him with a very particular problem you have, and see what he says

[Anonymous No.1516443]

>>1516325
is this the car ??
cause the front spoiler ruins the air for the side intake,
and why is the base surface of the front wing curved the other way ?

the wiglet on the front, the surface finish is odd, you should grind? (not sure about the terminology: maybe polish) them more ...

wtf

[Anonymous No.1516444]

>>1516442
>CFX 17
ok then why just make the porous media in your 3d structure and meshing it ...
>inb4 finer mesh need more time

[Anonymous No.1516445]

>>1516325
what a pos

[Anonymous No.1516448]

>>1516400
i myself have zero experience (started uni 2 months ago) however we noticed flow lines bunching up on front which is caused by the radiator model behaving like a solid wall or badly assinged preassure values for the front and rear facing side of the radiator. since posting i have been doing some reading and i know that i have to define the radiator as porous media fluid zone. that would require the darcy equation.

[Anonymous No.1516449]

>>1516429
but a bad model will negatively impact following decisions regarding aero

[Anonymous No.1516452]

>>1516444
actually someone in the team tried that before how ever he said intergrating that in to the car model would be a pain in the ass

[Anonymous No.1516468]

>>1516448
Personally i think the effect would be negliable to consider them rigid. And especially with CFD it's a good idea to keep it as simple as possible or you'll screw yourself over.

>>1516452
Can't you just get data from seperate simulations of the radiators and implement that as a function in your model? It's fairly easy to do with Fluent using UDF's.
Not 100% accurate but would be more than good enough.

[Anonymous No.1516493]

>>1516468
i might try that one once i get my head around the programm. also i was able to calculate the permeability of the radiator at a value of 2,123*10^-8 m^2. is that a possible value? it might be a little messed up since i used the viscosity of air at 40'c is 19.20^10-6 kg m-1 s-1 instead of 18.24

[Anonymous No.1516518]

>>1516493
Are you taking into account the changes in density and viscosity due to temperature differences in the radiator?
which is dependant on the power generated by the engine
which is dependant on the air resistance
which is dependant on the pressure drop over the radiator
which is dependant on the power generated by the engine
See what i mean when you should keep things simple?

[Anonymous No.1516539]

>>1516518
okay i get now :D anyway thanks for giving advice

[Anonymous No.1519217]

>>1516518
There's simple and there's spherical-horse-in-a-vacuum simple. Just measure temps in and out during testing and use that as an assumption. No need to iterate a bunch of times to determine the nearest tenth of a degree.