41 replies to this topic

[siztenboots]

if someone has an accurate scale model , we have several wind tunnels here

[alanoo]

That's the key, the CAD model So, accurate 3D Scan -> CAD model then open doors to CFD softs and accurate scale models...

[starlight]

Better pay for a full 3D Scan of a VX then stick it in a CFD software

Unfortunately you will also need to model the apertures, air intakes and what is behind them, and underside. Just modelling the closed top of the body from a scan is not sufficient for accurate CFD modelling.

[Winstar]

Better pay for a full 3D Scan of a VX then stick it in a CFD software

Unfortunately you will also need to model the apertures, air intakes and what is behind them, and underside. Just modelling the closed top of the body from a scan is not sufficient for accurate CFD modelling.

not quite true, to get an exact figure for things like cd and lift then yes you would need an accurate representation of the 'underhood' however what you can do with a less detailed model is assess the merits of different aerodynamic features against one another.

[siztenboots]

Better pay for a full 3D Scan of a VX then stick it in a CFD software

Unfortunately you will also need to model the apertures, air intakes and what is behind them, and underside. Just modelling the closed top of the body from a scan is not sufficient for accurate CFD modelling.

not quite true, to get an exact figure for things like cd and lift then yes you would need an accurate representation of the 'underhood' however what you can do with a less detailed model is assess the merits of different aerodynamic features against one another.

mixing drag and against frontal area

CdA , Lotus Elise 1999 = 6.35 sq ft (0.590 m2)

[starlight]

You would definately need an accurate front aperture and radiator model due to the significance of the flow going through there and up through the bonnet... Probably not so important for the engine bay area as you say, although the relative air bleed from the engine cover and through the rear wheel arches may play a significant role in the rear lift...

[Winstar]

You would definately need an accurate front aperture and radiator model due to the significance of the flow going through there and up through the bonnet...

Probably not so important for the engine bay area as you say, although the relative air bleed from the engine cover and through the rear wheel arches may play a significant role in the rear lift...

as long as you where comparing against a baseline case and assessing the design changes then a representative shapes and flow paths would do, the loss though the front apature region is dominated by the flow characteristics of the radiator.

[slindborg]

You would definately need an accurate front aperture and radiator model due to the significance of the flow going through there and up through the bonnet...

Probably not so important for the engine bay area as you say, although the relative air bleed from the engine cover and through the rear wheel arches may play a significant role in the rear lift...

as long as you where comparing against a baseline case and assessing the design changes then a representative shapes and flow paths would do, the loss though the front apature region is dominated by the flow characteristics of the radiator.

like going to a crappy/inaccruate RR.... aslong as you baseline it there and do subsequent runs with X mods there then its the difference you are after that matters, and not the exact figures

[starlight]

mixing drag and against frontal area

CdA , Lotus Elise 1999 = 6.35 sq ft (0.590 m2)

VX220 NA
Cd = 0.38, FA = 1.6 sq m, CdA = 0.61

VX220 Turbo / VXR
Cd = 0.41, FA = 1.6 sq m, CdA = 0.66

oh and MIRA wind tunnel works out around £500/hr

Edited by pjohn151, 24 November 2009 - 03:01 PM.

[siztenboots]

mixing drag and against frontal area

CdA , Lotus Elise 1999 = 6.35 sq ft (0.590 m2)

VX220 NA
Cd = 0.38, FA = 1.6 sq m, CdA = 0.61

VX220 Turbo / VXR
Cd = 0.41, FA = 1.6 sq m, CdA = 0.66

oh and MIRA wind tunnel works out around £500/hr

cool i was looking for those figures to plug in to the data logger

[alanoo]

You would definately need an accurate front aperture and radiator model due to the significance of the flow going through there and up through the bonnet...

Probably not so important for the engine bay area as you say, although the relative air bleed from the engine cover and through the rear wheel arches may play a significant role in the rear lift...

But you can do a model from a crashbox with simple hand tools
not possible for the whole car

[vxr36]

The non scientific approach... I found that the front of my car went light after fitting Nitrons and having a geo. Basically the effect of improving cornering performance meant that the back was left slightly lower than the front (proportionally speaking). I guess the top of the car must have been a wedge shape, producing some downforce, because it was definitely less as the 'angle of attack' was reduced. So it would make sense to lower the front or raise the rear to increase downforce at the front - Not a good solution as cornering would be compromised. Instead I put on the unsightly Astra G splitter, which is big and ugly but a little more forgiving than some on humps. It is a long time since I have had it fitted but I clearly remember that the stability was improved immensly.

Edited by vxr36, 25 November 2009 - 08:45 AM.

[Duncan VXR]

You def want some rack on our cars height setup imo Like the look of the tms race car front splitter , just need a bigger rear wing to be sure I did think a while back about the angled wind deflector things you can attach to the front corners to give downforce - see them on a lot of time attack cars. But figured it may just slow me down if not done correct

[Mangham54]

Just a matter of thought.... wasn't there a guy or team that were looking to use a VX for a project at Loughborough Uni? If so don't they have a pair of full-size wind tunnels and would they be any use... Might be time to make and then phone a friend?

Edited by Mangham54, 25 November 2009 - 12:41 PM.

[starlight]

if someone has an accurate scale model , we have several wind tunnels here

How about this one

[Mattias]

I'm working on a CAD model in Catia V5 at the moment but I'm not sure when it will be done. If anyone else want to have a go at it I'll post the bluprint needed here, and a picture of a car I made a few years ago Regars/ Mattias  speedster.gif   232.46KB   8 downloads  bild16.jpg   265.99KB   7 downloads

[Duncan VXR]

Well done looks really good

[Mattias]

Preview of work so far:

[Stefan_A]

The BADSTER boys are doing some serious rework, not very well suited for road use though...

[Exmantaa]

I'm working on a CAD model in Catia V5 at the moment but I'm not sure when it will be done.
If anyone else want to have a go at it I'll post the bluprint needed here, and a picture of a car I made a few years ago

Regars/ Mattias

Do you have that blueprint in another "editable" CAD format??