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bw65vw
Samba Member
Joined: August 04, 2020
Posts: 149
Location: Tennessee
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 Posted: Wed Aug 11, 2021 8:21 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| vamram wrote: |
| UK Luke 72 wrote: |
Who's gonna test a venturi ring with Andrigs fan then?  |
I will...eventually. I just got the Andrig's fan last week and have a venturi ring on my '73. But...it's my daily driver and am not keen on dropping the engine for this at the moment. |
I was thinking the exact same thing while reading this! |
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mark tucker
Samba Member
Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Thu Aug 12, 2021 8:13 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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1st, arguing with engineers or college graduates is like  
2nd. the foam seal may not stay
3 the foam seal may not increase the air flow.
4 that seal ring may lessen the air flow.5 fan to shroud clearance can change things too...5 what we may think or were schooled to think/KNOW may not always be correct.
6 think about what the wing does...increases air speed on one side (top or bottom)and...if you block off 1 side .(top or bottom)..will it still fly. 
personaly I see the ring as 2 serfaces like a wing but diferent.it has 2 sides to redirect the incomming air. block off one side and....only real testing with real testing equipment in the right testing environment will tell. |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Thu Aug 12, 2021 6:16 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Seeing as we are sharing in theories here I will add mine. The venturi ring in my view is not like an airplane wing, it like the leading edge slats on an airplane wing. The purpose of those are to delay the turbulence above the wing that causes stalls. They do thier best work at low air speeds and high angles of attack.
The wing here I would argue is the curved inlet side of the fan and the ring is the leading edge slat. Any air going into the fan is low speed and yes tend to be turbulent or partially stalled if you will. The job of the ring then, like the slats on the wing is to straighten out that turbulent (stalled) pocket of air just inside and close to the fan wall. Help the fan grab it and move it on.
By blocking that gap you do two things, first is that you reduce air flow to the fan. It may not appear so because the air now has to speed up because the fan is trying to pull the same amount of air through a smaller hole. So velocity goes up but total volume goes down. The second thing that will happen is the turbulent (stalled air) pocket becomes larger decreasing the efficiency of the fan.
I will try to draw it out later this evening but don't expect it as pretty as the last one!
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Floating VW
Samba Member
Joined: April 28, 2015
Posts: 1597
Location: The South Zone
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| Posted: Thu Aug 12, 2021 7:24 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| chrisflstf wrote: |
| I like sealing the venturi ring, but any chance the foam could get sucked into the fan? |
No chance, whatsoever. The foam seal is laminated to the venturi ring, and also clamped between the ring and the shroud. You couldn't force that seal into the fan even if you tried to shove it in with a screwdriver!
I've been driving around with the venturi ring sealed like that for about a year now, and all I can say is that whatever I did, it's working. Some back-to-back testing with hard data for comparison would be nice, but I doubt I'll ever do any. For myself, I don't need to. The amount of air blowing out the bottom of the engine is so noticeably greater (and carrying more heat) than it was before I installed the venturi ring and seal, I don't need any more proof than what's already in the pudding. Now, is that because of the foam seal, or in spite of it? I honestly don't know. But it's working spectacularly! Too well, in fact. The engine runs too cold most of the time, and now it's even worse. Today I even began to wonder if it's possible to damage the cylinder heads by running them too cold.
| vamram wrote: |
| UK Luke 72 wrote: |
| Who's gonna test a venturi ring with Andrigs fan then? |
I will...eventually. I just got the Andrig's fan last week and have a venturi ring on my '73. But...it's my daily driver and am not keen on dropping the engine for this at the moment. |
Keep us posted, man! And don't make us wait too long!
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works." |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Thu Aug 12, 2021 7:37 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Not the heads, the pistons and cylinders will wear faster than normal and your oil may get contaminated sooner.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Fri Aug 13, 2021 4:13 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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I told you it wouldn't be pretty!
Anyway that is my theory as to how it works.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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sled
Samba Member
Joined: February 16, 2005
Posts: 6179
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| Posted: Fri Aug 13, 2021 6:55 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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yes, the outside of the venturi ring should be open.
...but it still works when sealed as well.
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FreeBug
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Joined: March 12, 2012
Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Fri Aug 13, 2021 7:18 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| oprn wrote: |
I told you it wouldn't be pretty!
Anyway that is my theory as to how it works.
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That's how I see it too. I wonder if the issue wasn't that not all of the fan was being used. It is really easy to see how the flow to the entry is improved, with eyeballs and some smoke. You'll also see how far the fan can suck air from...it's far. |
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mark tucker
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Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Fri Aug 13, 2021 7:42 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| oprn wrote: |
I told you it wouldn't be pretty!
Anyway that is my theory as to how it works.
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I thingk dats what i said.... |
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Floating VW
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Joined: April 28, 2015
Posts: 1597
Location: The South Zone
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| Posted: Sun Aug 15, 2021 3:26 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Ok, so I was up until 4 in the morn' doing a little research on centrifugal fans (since I'm kinda bored and I'm enjoying this discussion), and I learned a few things.
First off . . .
| oprn wrote: |
I told you it wouldn't be pretty!
Anyway that is my theory as to how it works.
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That's a good drawing and a solid theory! There is a good chance you may be right with this one.
The only problem I have with it is in the proportions. The inlet of the fan is actually much deeper and trumpet shaped, which gives the incoming air a better chance of making the turn before it hits the front leading edges of the blades. And also, the angle of incidence in the blades changes from the front to the back, which should further help deal with the problem you described in your theory (thereby negating the need for a gap behind the venturi ring). If you look closely at the pictures I took, you can even see how the back edge of the venturi ring doesn't quite go as deep as the front edge of the blades:
And here, you can see by the curved appearance of the blades how the angle of incidence changes from the front to the back:
Something else that is being overlooked is the fact that there is not one, but two gaps affecting the flow of air into the impeller. The one everybody is focusing on is the gap between the venturi ring and the impeller. But the second, and perhaps the more important one, is the gap between the shroud and the impeller.
Now, I did come across a few research articles that did actually show there is some benefit to having a gap between the inlet duct (in this case, the venturi ring and shroud) and the impeller opening, but only in a low-mass air flow situation. Air returning from inside the volute, or shroud, to the impeller inlet can create a sort of "low momentum jet" which "could prevent local flow from separation, reducing the local flow turning losses," according to the article. However, according to the same article, "this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow," which has "a higher impact on flow losses than the blade leading edge separation." In other words, the gap allows you pay Paul, but you are robbing twice as much from Peter to do so. This is from, Impact of Fan Gap Flow on the Centrifugal Impeller Aerodynamics.
And this excerpt from the conclusion of Effect of Inlet Clearance Gap on the Performance of an Industrial Centrifugal Blower with Parallel Wall Volute: "The effect of clearance between the suction duct and impeller inlet in a centrifugal fan with parallel wall volute is studied in the present investigations. The clearance produces a positive effect on the pressure rise and the efficiency at lower mass flow rates when compared to the design mass flow rate conditions, and negative effect at higher mass flow rates."
This diagram from the article Effect of Axial Gap between Inlet Nozzle and Impeller on Efficiency and Flow Pattern in Centrifugal Fans shows the clearance gap they are referring to (ahem, notice the foam seal at the base of the venturi ring):
But my favorite part from the conclusion of that same research paper, was the discovery that, even though a larger air gap was beneficial when the flow rate was low, and a smaller gap was better when flow was high (which is the category the fan in an ACVW belongs to), a gap of ZERO was better in both situations! In their words: "Even though zero clearance case produces a higher pressure rise and efficiency in the impeller for all cases;"
If you look again at my crude diagram showing the foam seal, you can see that I also closed this gap:
Ok, sorry for the long-winded rebuke. Like I said, I'm bored. But I still maintain the foam seal is a good idea!
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"It's time you started treating people as individuals, rather than mathematically predictable members of an aggregate set, regardless of how well that works." |
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busdaddy
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Joined: February 12, 2004
Posts: 51156
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Aug 15, 2021 4:10 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Then why didn't that office tower full of well educated and highly paid VW engineers just re design the shroud inlet?, or make the ring with a formed lip that sealed up upon installation?. They were fiddling with this mod for years before it was introduced on production models, most factory doghouse shrouds have the dimples where the ring goes right from 71, lots of science and testing went into it.
Go ahead and use your foam seal, I'll leave mine open since I've seen great drops in temps when installing the ring as designed, YMMV. 
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12744
Location: Western Canada
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| Posted: Mon Aug 16, 2021 4:24 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Very interesting! What we really need at this point is "clinical trials", set up a shroud and fan and test it both ways and compare both with the bone stock set up over the range of RPMs that are real life. Me doing the testing in my climate using head temps and you doing the same in yours... far too many variables.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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FreeBug
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Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Mon Aug 16, 2021 7:11 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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What I think I see, looking at that image...is that the flow under the venturi ring wouldn't impede, the flow path curvature affects both sides, and it's just a sacrifice of the volume you could flow if the foam wasn't there. Just a thought. |
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Floating VW
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Joined: April 28, 2015
Posts: 1597
Location: The South Zone
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| Posted: Mon Aug 16, 2021 5:47 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| busdaddy wrote: |
| Then why didn't that office tower full of well educated and highly paid VW engineers just re design the shroud inlet? . . . |
Good question. Personally, I think it was a combination of not wanting to spend the money, and just not understanding the aerodynamics the way we do today. Hell, Formula 1 cars didn't even start using wings until the late 60's, 'cause no one really understood them. Fifty-some years later, the wings are one of the most complex parts on the car, and they keep finding ways to improve them every year!
| oprn wrote: |
| Very interesting! What we really need at this point is "clinical trials", set up a shroud and fan and test it both ways and compare both with the bone stock set up over the range of RPMs that are real life. Me doing the testing in my climate using head temps and you doing the same in yours... far too many variables. |
It would surely be nice, but honestly, I'd rather just concede that you guys are right and I am wrong, than bother with it. We're most likely only talking about a 1% or 2% difference in performance, either way. Probably less. I doubt we could even design a test that would be accurate enough to register such a minor difference.
Then again, I wish you guys could all experience first hand how much air is coming out the bottom of my engine now, with that sealed venturi ring. I'm not exaggerating when I say it's like a giant leaf blower. It's not normal!
| FreeBug wrote: |
| What I think I see, looking at that image...is that the flow under the venturi ring wouldn't impede, the flow path curvature affects both sides, and it's just a sacrifice of the volume you could flow if the foam wasn't there. Just a thought. |
Very possible. But I think the inside diameter of the venturi ring is already large enough to not create any restrictions, even with this small sacrifice in volume. I could be wrong, though.
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FreeBug
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Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Tue Aug 17, 2021 5:24 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| Floating VW wrote: |
| and just not understanding the aerodynamics the way we do today. Hell, Formula 1 cars didn't even start using wings until the late 60's, 'cause no one really understood them. |
Maybe. But let's not forget, these folks were building jet airplanes, ballistic missiles, and rocket-powered Messerschmitts, a quarter century earlier.
| Floating VW wrote: |
| Then again, I wish you guys could all experience first hand how much air is coming out the bottom of my engine now, with that sealed venturi ring. I'm not exaggerating when I say it's like a giant leaf blower. It's not normal! |
Could this be an increase in velocity, rather than volume? Fascinating stuff!
I'm with you. If this really works, I'll be the first to put foam on mine... |
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Wreck
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| Posted: Tue Aug 17, 2021 5:43 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Also the unlimited piston engine pylon racers are still using wings designed on a slide rule 
crazy that overhead cam , 4 valves a cylinder with fuel injection was flying around the skies in the 1930's .
Only way to test is back to back CHT readings on all cylinders on the same road on the same day . I wonder it a GoPro shooting 240fps and a small smoke bomb would be enough to photograph the airflow etc . |
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balljoint
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Posts: 166
Location: Tobago
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| Posted: Tue Aug 17, 2021 11:49 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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After lots experiments with speaker box ports/airflow and decibel levels i have no doubt the sealed path on the outside of the ring will promote smoother undisturbed airflow to the intake of the fan BUT....
The ultimate version of this would be to increase the diameter of the ring to match the intake diameter of the fan, get rid of the inner flare on the ring and butt it up as close as possible to the fan.
Same principle as a velocity stack....tried and proven.
The space between the outer diameter of the fan and shroud could be blocked but not absolutely necessary.
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swharris
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Location: N. Orange County
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| Posted: Tue Aug 17, 2021 6:49 pm Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Maybe I missed it, but I have seen nothing speaking to the OUTPUT side of this equation. You are stuffing more air in, but are people accommodating the exit of that air?? Much like a turbocharger system, you can add all the compressor speed and volume you want, but to get any real FLOW you need to have a GD big exit tube...otherwise you are just choking the flow with exhaust restriction.
Are people taking off the lower tin or getting rid of it all together? What about T3 cool tin? Keep it? Toss it? Also, the real metric of this mods success should be not flow, but better cooling. Where are the tests for that? Not trying to bag on this cool idea, just pointing out one data set for the inputside does not tell the entire story.
If I glossed over it reading this long thread I apologize. |
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Floating VW
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Joined: April 28, 2015
Posts: 1597
Location: The South Zone
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| Posted: Wed Aug 18, 2021 9:19 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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| FreeBug wrote: |
| Floating VW wrote: |
| Then again, I wish you guys could all experience first hand how much air is coming out the bottom of my engine now, with that sealed venturi ring. I'm not exaggerating when I say it's like a giant leaf blower. It's not normal! |
Could this be an increase in velocity, rather than volume? Fascinating stuff!
I'm with you. If this really works, I'll be the first to put foam on mine... |
Since the size and shape of the outlet hasn't change at all, nor has the size and relative RPM of the fan, I'd say any increase in the velocity of the air coming out of the bottom of the engine is a direct result of the increased volume of air being moved by the fan, right?
I know that I had to remove a shim from the fan pulley after installing the venturi ring, because the fan was moving so much more air that it caused the belt to start squealing at around 3000 RPM. And (you're going to laugh at this), I hate wearing shoes, even when I'm in the garage working on my car. But I have to put my boots on when I adjust my timing now, because the air is carrying so much more heat that it burns my toes!
| balljoint wrote: |
. . . The ultimate version of this would be to increase the diameter of the ring to match the intake diameter of the fan, get rid of the inner flare on the ring and butt it up as close as possible to the fan.
Same principle as a velocity stack....tried and proven. . .
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I agree 100% with this. A velocity stack mated as close as possible to the fan inlet would probably be ideal.
| swharris wrote: |
| Maybe I missed it, but I have seen nothing speaking to the OUTPUT side of this equation . . . Also, the real metric of this mods success should be not flow, but better cooling. Where are the tests for that? |
You're right, no one has really mentioned anything about the outlet side (well, until now, I guess). I just assumed the size of the outlets in the shroud were more than sufficient to handle any increase in flow provided by the venturi ring. Maybe they're not?
Also, I hesitate to provide any hard numbers related to the improvements in cooling I have noticed. I don't measure the temperature of my cylinder heads in the same place as everybody else, so the numbers might not really be relevant to anyone but myself. All I can say, is that they run scary cold.
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Frederik
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Location: Sweden
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| Posted: Wed Sep 22, 2021 5:58 am Post subject: Re: fan shroud air flow with and without ventuir ring (data heavy) |
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Thats basicly the Porsche design of the ring on a 36hp shroud.
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