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PostPosted: Sun Oct 03, 2010 2:04 pm 
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I managed to prang my C-One undertray quite badly the other week whilst 'giving it some' on a rather rough stretch of road in North Wales (the rear section has bent the brackets and formed a 'v' around the exhaust....:oops: ), so yesterday I took it off to try and beat it back into something approximating the correct shape.

However whilst looking at it I think I've spotted that the cooling slots are actually located in the wrong place, as you need pressure differential across the radiator/FMIC etc to actually draw air through them, the greater the delta P the more air will pass through.

The current slots are located on the downward facing slope:

Image

Image

So I loaded up a model I've already made for the front end of the ST205 into Catia, and measured up the C-One tray and added it on. I fired up Ansys the CFD software I use and created a steady state speed of 70mph and left it to run overnight. Looking at the results this morning sure enough the slots would be better moved back about 6" to the section of the undertray that is parallel to the road:

Image

I'm going to be modifying the tray next weekend anyway as I want it to add on side-plates to fill the space between the wheels and pulleys/gearbox as a lot of crap gets thrown up into there. I intend to use the existing tray to make a mould that I can then layup carbon/kevlar hybrid cloth to produce something similar to this:

Image

I intend to set up instruments in the engine bay; one in front of the rad and one behind to measure the pressure difference with the different slot locations prior to creating the composite one. After a baseline run, I will fill in the current cooling slots and make some new ones on the rear flat section of the tray just in front of the axles and see what difference it makes, and then another run with the side plates added.


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PostPosted: Sun Oct 03, 2010 6:39 pm 
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Hi,

WOW, nice :)

it is also good to see that there is high pressure at area between bonnet and front windscreen
but i why should the c-one slots bad located, they lower the engine bay pressure to become a higher delta P

i just saw that TTE also placed a air escape in the shroud at the backside of the intercooler pre rad

Image


greetz

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PostPosted: Sun Oct 03, 2010 6:56 pm 
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Dan wrote:
So I loaded up a model I've already made for the front end of the ST205 into Catia, and measured up the C-One tray and added it on. I fired up Ansys the CFD software I use and created a steady state speed of 70mph and left it to run overnight. Looking at the results this morning sure enough the slots would be better moved back about 6" to the section of the undertray that is parallel to the road:

Image



Very impressive Mate!

But... would it be possible for you to add GT-four lips at the model?

PS: I installed screw inserts on the C-one plate, and then I screwed #3 teflon slits to avoid damaging the plate against the ground.. ;)

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PostPosted: Sun Oct 03, 2010 7:03 pm 
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Sunny wrote:

it is also good to see that there is high pressure at area between bonnet and front windscreen



A theorical model can't describe all that happen in the real world...
only wool yarn can! ;)
In fact there is an high pressure spot in the middle of the cowl, but not in the sides.



Quote:
but i why should the c-one slots bad located, they lower the engine bay pressure to become a higher delta P



I suspect they put there the slots because in the place suggested by Dan they can easily hit the ground...

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Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
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PostPosted: Sun Oct 03, 2010 8:33 pm 
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Hi,

i think he can leave the lips as the slotes are side by side to them

no i never will remove the gasket or raise the bonnet
i was counting the minuetes until you comment it :lol:

for sure, especially on gravel stages the risc of hiting becomes high

greetz

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PostPosted: Sun Oct 03, 2010 8:39 pm 
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Wolf_Tm wrote:
But... would it be possible for you to add GT-four lips at the model?


Yeah sure, give me the height of it and how far back along the nose they are and I'll add them.

Be aware though that the section that this model is generated on is straight along the centreline of the car, so if what you're talking about are the chin spoilers fitted to the front lip of UK cars then they won't be visible.

Sunny wrote:
but i why should the c-one slots bad located, they lower the engine bay pressure to become a higher delta P


They aren't bad, but could be better, if that makes sense?!! As Wolf says, they were probably put there to protect them to an extent, however with making them out of Kevlar I don't know if that will be such a problem? I was thinking of perhaps not making them as slots, but mould in 'bump' strips on the bottom of the tray as a lot of the rally ones seem to have, but cut the back of them off to let the air out.

Image

Say 4 of these things on the tray, about 75mm wide and 20mm high. Solid Kevlar with the back cut open to provide the air outlet?
Image


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PostPosted: Sun Oct 03, 2010 8:48 pm 
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with all the flow diagrams can you work out the drag coeficient of a gtfour then chap?

im interested to see how it compares to a car of todays day and ages seen as the car looks wise seems fairly well flowed


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PostPosted: Sun Oct 03, 2010 8:50 pm 
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Sunny wrote:
Hi,

no i never will remove the gasket or raise the bonnet
i was counting the minuetes until you comment it :lol:



Wool cords never lie!
But hey, it's not mandatory to believe them... :lol:

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Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
http://www.facebook.com/wolf.tm


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PostPosted: Sun Oct 03, 2010 8:55 pm 
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Dan wrote:

Be aware though that the section that this model is generated on is straight along the centreline of the car



SUUUNNNYYYYY ???? :lol: :lol: :lol:



Quote:
so if what you're talking about are the chin spoilers fitted to the front lip of UK cars then they won't be visible.



Ok, no problem then!



Quote:

They aren't bad, but could be better, if that makes sense?!! As Wolf says, they were probably put there to protect them to an extent, however with making them out of Kevlar I don't know if that will be such a problem? I was thinking of perhaps not making them as slots, but mould in 'bump' strips on the bottom of the tray as a lot of the rally ones seem to have, but cut the back of them off to let the air out.



I think it was WAYYY easier my way...
I shortened the C-one plate and so, looking at your model, now mine ends were blue is a bit darker...

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Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
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PostPosted: Sun Oct 03, 2010 9:01 pm 
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Wolf_Tm wrote:
Sunny wrote:
Hi,

no i never will remove the gasket or raise the bonnet
i was counting the minuetes until you comment it :lol:



Wool cords never lie!
But hey, it's not mandatory to believe them... :lol:


PS: I think the model does not count the force of the air INSIDE the engine bay trying to escape out.
In fact you can see light pressure (yellow) over the central bonnet vent, but, in the real world, the air DOES escape from there... correct Sunny?
Same is for the cowl.

PS2: Wool cords NEVER lie... :)

_________________
Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
http://www.facebook.com/wolf.tm


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PostPosted: Sun Oct 03, 2010 9:15 pm 
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dale wrote:
with all the flow diagrams can you work out the drag coeficient of a gtfour then chap?

im interested to see how it compares to a car of todays day and ages seen as the car looks wise seems fairly well flowed


I honestly don't know, it quite probably is possible with this software as it's a world leader for CFD analysis, however I don't know how to do it! :lol: You'd have to have an extremely complex model featuring all gap lines etc to get an accurate figure. I'm fairly certain Toyota published a Cd figure for it though?

I was reading an article the other day with a report written by Volvo who reckon practically 1/2 of the drag on their cars comes from the revolving wheels, 1/3 from the air ducts into/out of the engine bay and the rest comes from the air flow around the body! :shock:


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PostPosted: Sun Oct 03, 2010 9:28 pm 
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Wolf_Tm wrote:
PS: I think the model does not count the force of the air INSIDE the engine bay trying to escape out.
In fact you can see light pressure (yellow) over the central bonnet vent, but, in the real world, the air DOES escape from there... correct Sunny?
Same is for the cowl.


Indeed, I was just interested to see what happened on the underbody around the undertray so ignored the flow through the engine bay itself. I do intend one day to model up the full engine bay interior with all vents etc.

Did you see this Red Bull F1 car with the flowpaint all over it's back end during one of the practise sessions at Monza a few weeks ago? Even with their CFD computing power they still find it easier to smear fluorescent paint on the car and driving around the track for 20 minutes to find out where the air actually goes to!
Image
Apparently at the next race they had modified their exhaust system so it blow on a slightly different piece of body work and knocks 0.0000001 seconds off a lap.... :lol:


Oh, and wool tufts NEVER lie! :wink:


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PostPosted: Sun Oct 03, 2010 10:32 pm 
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Dan wrote:
Wolf_Tm wrote:
PS: I think the model does not count the force of the air INSIDE the engine bay trying to escape out.
In fact you can see light pressure (yellow) over the central bonnet vent, but, in the real world, the air DOES escape from there... correct Sunny?
Same is for the cowl.


Indeed, I was just interested to see what happened on the underbody around the undertray so ignored the flow through the engine bay itself. I do intend one day to model up the full engine bay interior with all vents etc.



Waiting for it... :D


Quote:
Did you see this Red Bull F1 car with the flowpaint all over it's back end during one of the practise sessions at Monza a few weeks ago? Even with their CFD computing power they still find it easier to smear fluorescent paint on the car and driving around the track for 20 minutes to find out where the air actually goes to!
Image
Apparently at the next race they had modified their exhaust system so it blow on a slightly different piece of body work and knocks 0.0000001 seconds off a lap.... :lol:



:lol:


Quote:
Oh, and wool tufts NEVER lie! :wink:


AHahhahaAHa :lol:

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Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
http://www.facebook.com/wolf.tm


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PostPosted: Mon Oct 04, 2010 7:46 pm 
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Hi,

theoretical on a flat surface air should escape in the front 1/3 and enter the engine bay in 2/3 and 3/3
but depents on the angle of inclination of the car
(tear-off edge of the escape)

i think you should start the programm once again with engine bay flow to get a correct sight of things.......air is a hart to appraising medium

wolf, i'am sorry i don't understand this joking, my english is not good enought :oops: :lol:

greetz

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PostPosted: Mon Oct 04, 2010 8:35 pm 
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Sunny wrote:

wolf, i'am sorry i don't understand this joking, my english is not good enought :oops: :lol:


What joking Sunny ?!? :?:

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Wolf_Tm
TM 250 enduro 2 stroke
GT-four ST205 Snowy White with selfmade 3SGTE v4.1 - [2.34kg/bhp DynoDynamics]
http://www.youtube.com/WolfTm250
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