2 cm hole - Small, cheap flowbench for restriction

[taphonomist]

Hey all,
I've read around a bit, but am very new to this. I'm a grad student at University of Cincinnati in mechanical engineering (fluids), but don't really have any flowbench experience. We are in the process of designing an intake for a FSAE car, which involves crushing air down a 2 cm restriction. This is not a flat plate restriction, and we're looking to do some very cheap, qualitative testing of various designs for the restriction and compare to our CFD data.

I'm thinking of a simple orifice style setup made from PVC pipe with a shop-vac and a variac. If anyone has any advice, I'd appreciate it.

Thanks much,
Dustin Lindley

[hollywood63]

Welcome and check out the Pitot Tube section. Lots of info and help from everyone on the site.
Art

[86rocco]

I agree with Hollywood, because you'll be dealing with a fairly tight range of flow values, that seems like a particularly good application for a pitot tube type set-up, a long pipe with the variac controlled shop vac at one end, your 2cm hole at the other and a pitot tube somewhere in the middle

[Thomas Vaught]

At one time I ran some of the Formula SAE events
in Detroit through the SCCA (Sports Car Club of
America).

At that time you guys were using around 600 cc engines. What are you using today and is that really the size of the restriction? I though it was bigger.

Several people on the board have equipment of the electronic variety that would be fairly reasonable in price that would allow you to test your ideas.

The Board Owner, "Bruce" does a lot of small engine testing.

Ask away.

Tom V.

[larrycavan]

[larrycavan]

Orifice test setup suggestion [working blind on what the restrictor looks like]

20mm = .7874" [shooting for 1.0Cd]

.7874" diameter with 1.0 Cd = 46.9CFM @ 12" DP

1.0" orifice with .62 Cd @ 12" DP = 46.9CFM [make your test orifice that size]

12" Rise with 30" inclined leg gives a nice extended scale to work with.

25.4 mm [1"] orifice is small enough to give you acres of room inside a relatively small settling chamber [ results should be quite accurate]

[1] used vacuum cleaner motor
[1] 4 x 8 sheet of plywood [painted boths sides]
[1] 5" control valve [should allow accurate adjustments]

minature version of MSD bench with intake hole off to one side and orifice plate as far away as possible toward the other side but not so close to the outer wall that it interferes with flow.

build it in on weekend...

Larry C

[taphonomist]

Wow! Thanks much for all the replies! I'll post tonight with some screenshots of the initial design.

20 mm is the diameter, and we're working with 600 cc engines. 20 mm is a painfully tiny hole, and the idea is to maximize the flow mostly by playing with the inlet. We are curently looking at using involutes on both sides of the restrictor, on the front leading up to the throttle body diameter, and on the back out to a 7 degree cone (to prevent separation). Most of the work will be in the base diameter for the inlet involute and how that meets up with the throttle body.

This site is the best resource for this type of info that I've found, and I have alot to learn! More to come...

Dustin

[Thomas Vaught]

Larry,
In the past, the Formula SAE people measured the orifice with pin gages to make sure it was the right size but the actual shape/ profile was up to the students.

A lot of the students would build an "Optimized Venturi" which would have several diameters larger inlet area and then a proper transition after the venturi to regain as much pressure recovery (flow) as possible.

Tom V.

[larrycavan]

With 600cc as the engine size, would I be right to conclude they are motorcycle engines?

Where is the restrictor located?

If it is indeed motorcycle engines I'd have to think the restrictor is upstream from the carbs.

If that's the case, I'd make the air box enormous!

Larry C

[bruce]

12* is a magical number on the inlet, my work has been with 1" venturi dia on my carbs. Venturi location in relation to your fuel nozzle will have alot of play in how the carb works. I have been playing with an annular discharge setup and that has showed some promise. No dyno numbers just yet but they are coming soon.

[taphonomist]

The engine is a honda f4i, 600 cc. We'll be using a fuel injection system, and the restriction has to be after the throttle. We had talked about using a slide type throttle, which I think would be best for flow, but is more difficult from a design and construction point of view. We need to put a throttle position sensor on, and also have to have 2 throttle return springs, all of which is much easier with a butterfly. My current idea is that a large butterfly some distance away from the restriction may be the best comprimise. The question then becomes how best to blend the cylinder of the throttle body into the curve for the restriction.

I'm in the process of cleaning up the casting marks on the ports, but we don't expect to get too much out of that, given the restriction. I'm not sure what airbox volume we'll go for, but I gather that we need some settling volume to keep the pulses out of the restriction to whatever extent we can.

A friend of mine back home has a nice homemade flow bench, so I'll be checking that out over Christmas, and probably doing a bit more reading around here.

Dustin

[Thomas Vaught]

I would do like some turbo cars do and have the throttle body several inches like 12" away from the restriction. This will allow a larger volume to be present at the restriction with minimal restriction up stream of the piece. I would make a very smooth transition from the large diameter to the restriction and then go into a large volume plenum before going to the runners.

The large volume will help with proper air distribution AFTER the restriction which sometimes people miss. A lot of air to 2 runners and very little to the other two is really bad for power.

JMO

Tom V.

[Mouse]

This is an illustration of a simple test jig I set up to test a check valve in front of a vacuum motor using a Flow Performance FE2.0m flow element.

By connecting a shop vac to the back end of the floe element and removing the vacuum motor, you would have a miniture test setup for your restrictor.

Or, leave the vacuum motor for an even more compact test setup (forget the shop vac).

John

[larrycavan]

[larrycavan]

Tom,

I missed your reply on this....I agree with what you're saying. Get the restriction in between large volumes where it will have the least effect on the overall flow pattern.

Those restrictors have got to absolutely kill the output on a high revving 600cc motorcycle engine. I would think that a high volume plenum after the restictor and before the port entrance would be a must have.

Are they using a single throttle body or the OEM setup of 1 per cylinder?

If it's one per, then after the throttle bodies, the runners would have to converge to a point where the restrictor is located...rather like a 4-1 exhaust in reverse fashion with a puny little hole at the collector...YUK!

Larry C