Under floor flow & diffusers

[chuckdanny]

F1 art

It seems that my bird is gaining feathers in there!



And like a swallow tail

[RicME85]

I do love this thread.
What software are you using for each stage? (Modelling, simulation, postprocessing)

[chuckdanny]

Hi, happy you like it, it's turning more into aesthetic than technical
I use solidworks for the modeling and star+ for all cfd.

[RicME85]

Would love to learn how to use Star CCM+
From the playing around I have done so far it looks complex. I have looked at Youtube for video tutorials but there seems to be nothing to actually get you going like most programmes.

[chuckdanny]

You should RTFM, its a very good manual, one of the best with plainty of recommendations and dedicated tutorial.

[MadMatt]

Star-CCM+ includes an immense help file with few tutorial in it as well as example files that you will need. Its enough to get you started! If you read the whole thing and understand it you will probably know more about CFD than most people here (including myself)

[RicME85]

Thats the problem Matt, I struggle learning from just reading a tutorial, especially with the morphine I use, thats why I like to watch videos of someone else.

[chuckdanny]

I don't know what's the effect of morphine but you could ask specific question on where you are stuck and if it's about just using the soft workflow i could help.
Basically you must use part based meshing with surface remesher in an operation instead of in the meshing continuum wizard.
Remesher is translating cad bad triangulation into more cfd appropriate triangulation, it is about having good control of leading edges and trailing edges, in between can be big size, use prismatic layer to capture boundary layer, physic models use spallart almeras or k omega, you still must have one region to which the mesh is bound and where you specify the boundary conditions (speed etc...). Part based meshing allow more control on specific surfaces like the bird.
There are 2 kind of solvers, coupled flow and segregated, i use coupled with which i control convergence with courant number.
It can be intimidating at 1st but concentrate on external aerodynamic don't go straight on the multiphase thing and particule transport to model the path of a tire piece of rubber

[MadMatt]

A scalar scene with a resampled volum render derived part

Could you be a bit more specific? I am interested in getting the same kind of renders. I found that iso surfaces are also nice to see the general shape of the wake from which you can draw how the vortices are formed, as well as streamlines, but I cannot make the smoke effect! I managed in Ansys, but not in Star-CCM+.

[chuckdanny]

Yes, in the derived part folder, right clic on it create a resampled volum part as you create streamlines, vortex cores etc...
Maybe you have an old version of the soft which didn't have it.
As part property select the whole region, cell to voxel ratio near to 1 get a better resolution while killing performance.
Just drag n drop this derived part on a new scalar scene and choose vorticity magnitude for example as field.
A volum rendrer part is just a box that you edit (snap to part to adjust) in place.
THere is a volum rendering settings item in the displayer where you can further control the quality and switch a local lighting on.
They introduced a new gizmo to play with, controllable color map (shift the red toward the blue etc...) with which you can precisely control the opacity per color range to see the core of a vortex through its periphery for exemple and color distribution, it's in the tools folder => colormaps. You can create "opacity flag" on the map and set specific opacity.
A global opacity exist also on the displayer level

[chuckdanny]

To go back to the topic of underfloor flow and diffusers a video that is necessary when being held away from the subject for a while, preventing me of saying weird things about aerodynamics. I never saw it before that's why...

https://www.youtube.com/watch?v=wMxK2Gt ... plpp_video

So the name of a diffuser => device that create a turbulent boundary layer that prevent adverse pressure gradient from creating flow separation by allowing a better vorticity diffusion in the boundary layer, no back flow.
That's the point i was confused about some years ago the question of separation. Is it the point between laminar shear less flow and boundary layer whether it is laminar or turbulent when above a certain threshold => wrong
Separation caracterise flow reversal. But of course in a rotating pattern some of the flow is going back if the general velocity is lower than the rotational one, it's a question of mean velocity profile across the boundary, i often make the confusion.
In the exemple the turbulent boundary layer is not separated despite being at quit a distance from the wall

[chuckdanny]

I'm not sure to be clear enough, flow reversal in a diffuser is establishing as a large spanwise vortex concentrating vorticity into this large structure. This affect the very working principle of the diffuser which pump and extract and accelerate flow.
To counteract this there are two solution that i can see :

1st : this turbulent boundary layer that diffuse (opposite of concentrate) vorticity efficiently preventing this big flow reversal structure.
2nd : streamwise vorticity which concentrate instead of diffuse but in a usefull manner as we have seen on my transat chair in ground effect and that is exactly what they are doing, streamwise vorticity concentration at the edge of diffuser and vorticity diffusion (Vortex generators) at the center with strakes bounding those regions.

[MadMatt]

Yes, in the derived part folder, right clic on it create a resampled volum part as you create streamlines, vortex cores etc...
Maybe you have an old version of the soft which didn't have it.
As part property select the whole region, cell to voxel ratio near to 1 get a better resolution while killing performance.
Just drag n drop this derived part on a new scalar scene and choose vorticity magnitude for example as field.
A volum rendrer part is just a box that you edit (snap to part to adjust) in place.
THere is a volum rendering settings item in the displayer where you can further control the quality and switch a local lighting on.
They introduced a new gizmo to play with, controllable color map (shift the red toward the blue etc...) with which you can precisely control the opacity per color range to see the core of a vortex through its periphery for exemple and color distribution, it's in the tools folder => colormaps. You can create "opacity flag" on the map and set specific opacity.
A global opacity exist also on the displayer level

Thanks I will take a look at if this is included in v7!

[chuckdanny]

Unfortunatly probably not.

I've gone off track on this thread and started too many thing (enthusiasm , spring i don't know). I didn't know the strict rules of f1 technical which make sense.
What about a return to my transat chair in ground effect, do you remember?
I could trust the numbers and evaluate upside and underside contributions to downforce, adding strakes, further shielding the sides, what result would you expect from the latter ?
I observed that the shielding create vortices like variante explain for the diffuser strakes that further improve donwforce of a raked transat chair in ground effect, so what would you expect from a complete watertight sideskirt ?

[Crucial_Xtreme]

This Flying bird under the nose of the merc seems powerfull, lets call it angry bird !

http://oi60.tinypic.com/zk0qs7.jpg

Speaking of under floor flow, diffusers & Merc...

Great W06 diffuser pics from Sochi