Intake/outlet ratio in venturi tunnel/diffuser

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Tom888
Tom888
1
Joined: Thu Mar 17, 2022 10:29 pm

Intake/outlet ratio in venturi tunnel/diffuser

Post

I notice that all F1 cars has very high intake of venturi tunnel.
Is this set by regulation or this improve function of venturi tunnel?

If there is no regulation, will you design high intake or very low/close to ground intake if your goal is to maximum downforce?
Is there best ratio for intake/outlet?


high intake,I think at least 30cm
Image

very low "intake" , maybe 5cm, VW IDR,
I think they dont have rules in peaks peek, so does that mean that low intake is best for high downforce?
Image

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Stu
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Joined: Sat Nov 02, 2019 9:05 am
Location: Norfolk, UK

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Tom888 wrote:
Thu Mar 17, 2022 10:51 pm
I notice that all F1 cars has very high intake of venturi tunnel.
Is this set by regulation or this improve function of venturi tunnel?

If there is no regulation, will you design high intake or very low/close to ground intake if your goal is to maximum downforce?
Is there best ratio for intake/outlet?


high intake,I think at least 30cm
https://i.imgur.com/1yNyWmA.jpg

very low "intake" , maybe 5cm, VW IDR,
I think they dont have rules in peaks peek, so does that mean that low intake is best for high downforce?
https://media.autoexpress.co.uk/image/p ... wood-1.jpg
The VW has two sets of ground effect.
There is a short front section that outlets behind the front wheels (effectively a front wing), the second one is located under the body and is ‘fed’ by the flow between the splitter and ‘nose’.

The new F1 floors look to have a HUGE inlet, but the inlet strakes tend to divert a large amount of that sideways out of the floor before the ‘throat’. There is an ideal range for the ratio between inlet CSA and throat CSA, somewhere in the region of 1.2-1.4:1. If you try to be too greedy the floor can choke, if you are not greedy enough you give up download. Hence, porpoising….. because they are all seeing how greedy they need to be!!
Perspective - Understanding that sometimes the truths we cling to depend greatly on our own point of view.

scheffers
scheffers
12
Joined: Fri Feb 22, 2019 9:37 am

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Tom888 wrote:
Thu Mar 17, 2022 10:51 pm
I notice that all F1 cars has very high intake of venturi tunnel.
Is this set by regulation or this improve function of venturi tunnel?

If there is no regulation, will you design high intake or very low/close to ground intake if your goal is to maximum downforce?
Is there best ratio for intake/outlet?


high intake,I think at least 30cm
https://i.imgur.com/1yNyWmA.jpg

very low "intake" , maybe 5cm, VW IDR,
I think they dont have rules in peaks peek, so does that mean that low intake is best for high downforce?
https://media.autoexpress.co.uk/image/p ... wood-1.jpg
All but one 'upright stakes' lead to the outer edge of the floor, at least the cars we have seen underneath so far; to create a sealing vortex on the outside edge of the floor. So they would naturally need some height in the one remaining 'stake' that leads to the tunnel to get in enough air. Correct me if i'm wrong on this.

Tom888
Tom888
1
Joined: Thu Mar 17, 2022 10:29 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Stu wrote:
Fri Mar 18, 2022 8:02 am
Tom888 wrote:
Thu Mar 17, 2022 10:51 pm
I notice that all F1 cars has very high intake of venturi tunnel.
Is this set by regulation or this improve function of venturi tunnel?

If there is no regulation, will you design high intake or very low/close to ground intake if your goal is to maximum downforce?
Is there best ratio for intake/outlet?


high intake,I think at least 30cm
https://i.imgur.com/1yNyWmA.jpg

very low "intake" , maybe 5cm, VW IDR,
I think they dont have rules in peaks peek, so does that mean that low intake is best for high downforce?
https://media.autoexpress.co.uk/image/p ... wood-1.jpg
The VW has two sets of ground effect.
There is a short front section that outlets behind the front wheels (effectively a front wing), the second one is located under the body and is ‘fed’ by the flow between the splitter and ‘nose’.

The new F1 floors look to have a HUGE inlet, but the inlet strakes tend to divert a large amount of that sideways out of the floor before the ‘throat’. There is an ideal range for the ratio between inlet CSA and throat CSA, somewhere in the region of 1.2-1.4:1. If you try to be too greedy the floor can choke, if you are not greedy enough you give up download. Hence, porpoising….. because they are all seeing how greedy they need to be!!
What will happend if you exceed 1.4:1(too big inlet) ?
And what with outlet(diffuser), design maximum without flow separation(stall),can I force diffuser at 25AoA with vortex generators without stall?

Do you maybe have pictures of IDR undertray?
I cant find it...

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Stu
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Joined: Sat Nov 02, 2019 9:05 am
Location: Norfolk, UK

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Tom888 wrote:
Fri Mar 18, 2022 4:32 pm
Stu wrote:
Fri Mar 18, 2022 8:02 am
Tom888 wrote:
Thu Mar 17, 2022 10:51 pm
I notice that all F1 cars has very high intake of venturi tunnel.
Is this set by regulation or this improve function of venturi tunnel?

If there is no regulation, will you design high intake or very low/close to ground intake if your goal is to maximum downforce?
Is there best ratio for intake/outlet?


high intake,I think at least 30cm
https://i.imgur.com/1yNyWmA.jpg

very low "intake" , maybe 5cm, VW IDR,
I think they dont have rules in peaks peek, so does that mean that low intake is best for high downforce?
https://media.autoexpress.co.uk/image/p ... wood-1.jpg
The VW has two sets of ground effect.
There is a short front section that outlets behind the front wheels (effectively a front wing), the second one is located under the body and is ‘fed’ by the flow between the splitter and ‘nose’.

The new F1 floors look to have a HUGE inlet, but the inlet strakes tend to divert a large amount of that sideways out of the floor before the ‘throat’. There is an ideal range for the ratio between inlet CSA and throat CSA, somewhere in the region of 1.2-1.4:1. If you try to be too greedy the floor can choke, if you are not greedy enough you give up download. Hence, porpoising….. because they are all seeing how greedy they need to be!!
What will happend if you exceed 1.4:1(too big inlet) ?
And what with outlet(diffuser), design maximum without flow separation(stall),can I force diffuser at 25AoA with vortex generators without stall?

Do you maybe have pictures of IDR undertray?
I cant find it...
If you have too big an inlet you risk choking, because all of that air has to go through the throat. As far as I understand it there is no real limitation on the diffuser side (other than minimising turning flow).
I will see if I can find anything on the VW, although it is very similar in ideology to the last LMP1 cars (Porsche 919, Audi R18 & Toyota TS050)
Perspective - Understanding that sometimes the truths we cling to depend greatly on our own point of view.

Hoffman900
Hoffman900
137
Joined: Sun Oct 13, 2019 2:02 am

Re: Intake/outlet ratio in venturi tunnel/diffuser

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The complication in all this is the venturi tunnel is only half a duct, with the road surface being the other half and it potentially have leakages. Add in variable ride heights, and this further complicates it.

Also! Where the min pressure center occurs matters for balancing purposes.

Tom888
Tom888
1
Joined: Thu Mar 17, 2022 10:29 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Stu wrote:
Fri Mar 18, 2022 6:39 pm
Tom888 wrote:
Fri Mar 18, 2022 4:32 pm
Stu wrote:
Fri Mar 18, 2022 8:02 am


The VW has two sets of ground effect.
There is a short front section that outlets behind the front wheels (effectively a front wing), the second one is located under the body and is ‘fed’ by the flow between the splitter and ‘nose’.

The new F1 floors look to have a HUGE inlet, but the inlet strakes tend to divert a large amount of that sideways out of the floor before the ‘throat’. There is an ideal range for the ratio between inlet CSA and throat CSA, somewhere in the region of 1.2-1.4:1. If you try to be too greedy the floor can choke, if you are not greedy enough you give up download. Hence, porpoising….. because they are all seeing how greedy they need to be!!
What will happend if you exceed 1.4:1(too big inlet) ?
And what with outlet(diffuser), design maximum without flow separation(stall),can I force diffuser at 25AoA with vortex generators without stall?

Do you maybe have pictures of IDR undertray?
I cant find it...
If you have too big an inlet you risk choking, because all of that air has to go through the throat. As far as I understand it there is no real limitation on the diffuser side (other than minimising turning flow).
I will see if I can find anything on the VW, although it is very similar in ideology to the last LMP1 cars (Porsche 919, Audi R18 & Toyota TS050)
What happend with airflow when is choked? velocity drop instead rise?

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Stu
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Joined: Sat Nov 02, 2019 9:05 am
Location: Norfolk, UK

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Tom888 wrote:
Fri Mar 18, 2022 7:48 pm
Stu wrote:
Fri Mar 18, 2022 6:39 pm
Tom888 wrote:
Fri Mar 18, 2022 4:32 pm


What will happend if you exceed 1.4:1(too big inlet) ?
And what with outlet(diffuser), design maximum without flow separation(stall),can I force diffuser at 25AoA with vortex generators without stall?

Do you maybe have pictures of IDR undertray?
I cant find it...
If you have too big an inlet you risk choking, because all of that air has to go through the throat. As far as I understand it there is no real limitation on the diffuser side (other than minimising turning flow).
I will see if I can find anything on the VW, although it is very similar in ideology to the last LMP1 cars (Porsche 919, Audi R18 & Toyota TS050)
What happend with airflow when is choked? velocity drop instead rise?
Airflow stops (or reduces to a very low level), leading to an increase in pressure and the car ‘pops’ up; relieving the choke.
Perspective - Understanding that sometimes the truths we cling to depend greatly on our own point of view.

Tom888
Tom888
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Joined: Thu Mar 17, 2022 10:29 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Stu wrote:
Fri Mar 18, 2022 9:13 pm
Tom888 wrote:
Fri Mar 18, 2022 7:48 pm
Stu wrote:
Fri Mar 18, 2022 6:39 pm


If you have too big an inlet you risk choking, because all of that air has to go through the throat. As far as I understand it there is no real limitation on the diffuser side (other than minimising turning flow).
I will see if I can find anything on the VW, although it is very similar in ideology to the last LMP1 cars (Porsche 919, Audi R18 & Toyota TS050)
What happend with airflow when is choked? velocity drop instead rise?
Airflow stops (or reduces to a very low level), leading to an increase in pressure and the car ‘pops’ up; relieving the choke.
It is very unintuitive that flow can slow down, if take water hose and decrease outlet diameter with your finger, water is going faster and faster..
Last edited by Tom888 on Sat Mar 19, 2022 6:28 am, edited 1 time in total.

Greg Locock
Greg Locock
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Joined: Fri Jun 29, 2012 11:48 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

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It's called Mach choking and is the formation of shock waves due to incompressible flow. In a wind tunnel you can hear it with a surface mike, it sounds like tearing paper or a raspberry (I never have, it isn't an issue on solar cars).

Image.

https://en.wikipedia.org/wiki/Choked_flow

Hoffman900
Hoffman900
137
Joined: Sun Oct 13, 2019 2:02 am

Re: Intake/outlet ratio in venturi tunnel/diffuser

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What Greg said. Basically for a given pressure differential on either side of the minimum cross sectional area, at choke flow, additional mass cannot be realized.

This is how restrictors work on race engines. As the depression in the cylinder increases with rpm, additional mass cannot enter the cylinder once the restrictor has choked, so the engine “realizes” less atmospheric pressure with increasing rpm until pumping / frictional losses overcome things.

The hard part is you are trying to balance aerodynamic downforce balance, and the fact there are leakages out the sides of the floor , the ground isn’t entirely flat, and the car side is sprung with varying ride heights and not an infinite amount of stiffness.

I am not convinced Merc’s problem is entirely a choked flow issue and not an issue of vortex shedding causing resonance in the chassis.

Tom888
Tom888
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Joined: Thu Mar 17, 2022 10:29 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

Greg Locock wrote:
Fri Mar 18, 2022 10:29 pm
It's called Mach choking and is the formation of shock waves due to incompressible flow. In a wind tunnel you can hear it with a surface mike, it sounds like tearing paper or a raspberry (I never have, it isn't an issue on solar cars).

https://en.wikipedia.org/wiki/Choked_fl ... tterns.gif .

https://en.wikipedia.org/wiki/Choked_flow
You think that airflow reach speed of sound when flow is choked in throat?
I thnik that dont happend in auto racing.

So is flow speed up to 1 Mach or it is slow down in choke condition (in raceing)?

Tom888
Tom888
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Joined: Thu Mar 17, 2022 10:29 pm

Re: Intake/outlet ratio in venturi tunnel/diffuser

Post

The new F1 floors look to have a HUGE inlet, but the inlet strakes tend to divert a large amount of that sideways out of the floor before the ‘throat’.
You mean of this curves strakes at inlet that push air outwards?
Why they push this large amount of air outward instead direct it into tunnels?

If tunnels has skirts to the ground(forbiden by rules), then strakes dont need to go outwards?

Image
Last edited by Tom888 on Sat Mar 19, 2022 7:00 am, edited 1 time in total.

Tom888
Tom888
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Re: Red Bull RB18

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Where is inlet of venturi tunnels here, some picutre that show inlet?

Image

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Stu
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Location: Norfolk, UK

Re: Red Bull RB18

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Tom888 wrote:
Sat Mar 19, 2022 8:45 am
Where is inlet of venturi tunnels here, some picutre that show inlet?

https://f1tcdn.net/gallery/var/resizes ... /007.jpg
It is not visible in this shot, obscured by the tyre.
Perspective - Understanding that sometimes the truths we cling to depend greatly on our own point of view.