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-   -   a couple printed ideas (https://vansairforce.net/community/showthread.php?t=147771)

Chkaharyer99 07-12-2018 07:07 PM

Quote:

Originally Posted by Steve Melton (Post 1273068)
a short vane inside has better distribution. should not be too difficult to construct.










no vane version, same mass flow


Looks great Steve.

Steve Melton 07-12-2018 08:50 PM

I hit the button before I went to the airport tonight.

1/2 scale

and BTW, these always need a bulb at the hose connection end or they WILL become loose. I'll add that feature. this is now planned to be an internal layup first. then bond the internal vane secondly. seems that we are getting a plan together.


Paragon 07-13-2018 12:07 PM

Steve,

I would not put too much effort into designing internal vanes and such, unless you are prepared to very carefully design a lot of them.

Your transition is so abrupt, I doubt you can fill the exit plane with a solid, unseparated flowfield. More likely, with a vane, you will move the separated areas around.

Several things to note:
1. The inlet will have a Pt (or Velocity) profile, the details of which depend on upstream duct shape, inlet conditions, etc. This profile would affect the results substantially.
2. If there is a heat exchanger at the exit plane, that represents a flow restriction that will be felt upstream, so the results of a CFD analysis could be affected by it's presence or lack thereof.

In order to obtain an unseparated profile at the exit of this transition, you would probably need a very carefully designed array of vanes in both directions, like a thrust reverser cascade in concept. Even there, if not well designed, taking into account the inlet profile, the result could be worse than no vanes at all.

I personally would leave out the vane.

Just my $0.02 worth.

-Paragon (CFD Guy)
Cincinnati, OH

Steve Melton 07-13-2018 03:51 PM

Quote:

Originally Posted by Paragon (Post 1273244)
Steve,

I would not put too much effort into designing internal vanes and such, unless you are prepared to very carefully design a lot of them.

Your transition is so abrupt, I doubt you can fill the exit plane with a solid, unseparated flowfield. More likely, with a vane, you will move the separated areas around.

Several things to note:
1. The inlet will have a Pt (or Velocity) profile, the details of which depend on upstream duct shape, inlet conditions, etc. This profile would affect the results substantially.
2. If there is a heat exchanger at the exit plane, that represents a flow restriction that will be felt upstream, so the results of a CFD analysis could be affected by it's presence or lack thereof.

In order to obtain an unseparated profile at the exit of this transition, you would probably need a very carefully designed array of vanes in both directions, like a thrust reverser cascade in concept. Even there, if not well designed, taking into account the inlet profile, the result could be worse than no vanes at all.

I personally would leave out the vane.

Just my $0.02 worth.

-Paragon (CFD Guy)
Cincinnati, OH


I am not a CFD expert. I don't want an array of vanes. I am attempting to spread the flow and minimize the dead zone at the abrupt transition. the transition is to clear a prop cable, so it is needed. HX is mounted long side against the firewall, so a guide vane perpendicular to that direction should help even if the air profile is skewed to the backside of the inlet area.

Airflow Systems also uses a guide vane. they have experience with these.


Steve Melton 07-13-2018 09:27 PM

mold for internal layup
 
well, we will see if this works. outside mark lines are vane location option. when complete, cut mold off and throw it in the trash.

3 inch scat tube version

duct mold







vane mold







4 inch scat tube version





4 inch scat tube version flow. I like it.




Steve Melton 07-14-2018 06:21 AM

3 inch duct first print. looks good.


Chkaharyer99 07-14-2018 10:23 AM

Steve,

I see you added an exterior bump hump just below the inlet. On the inside there is a groove.

Pretty cleaver. I think I understand your thinking with that addition. Correct me if I?m wrong.

When the inside of the plenum gets taped off the groove gets taped over to prevent it from being filled with fiberglass Resin. After taping the interior a suitable fiberglass resin release agent gets applied over the tape followed by fiberglass layups. After the process cures, the hump/bump can be cut but only deeply enough to slice through the 3D printer plug but not the fiberglass beneath it. The inlet portion can then be removed exposing an appropriately sized OD inlet for the selected inlet tube (scat/sceet/other) to be attached.

A metal band could even be added to the inside prior to the fiberglass lay up to strengthen the inlet and prevent distortion or crushing when a the inlet tube clamp is applied and tightened.

With fiberglass on the interior, the remaining 3D plug can remain or be removed.

Was this what you were thinking with the hump/bump and groove?

Snowflake 07-14-2018 10:51 AM

Quote:

Originally Posted by Paragon (Post 1273244)
I would not put too much effort into designing internal vanes and such, unless you are prepared to very carefully design a lot of them.

I think the important thing to note here is that Steve isn't going for a "perfect" solution, which I agree would require a lot more vanes and a lot more CFD analysis to get it "right". He's going for a "best solution that can be achieved with reasonable effort," and I think he's getting pretty close.

Even Steve's basic transition shape without the vane would be better than many of the folded aluminium ones, as at least Steve's shape has rounded transitions which will carry the air further before separation occurs. Adding a single vane will help distribute more of that air across more of the cooler, and is definitely an improvement, so the effort is probably worth it. A side benefit is that it provides additional structural rigidity, which probably isn't a bad idea either.

A perfect solution probably exists, but you'd need to 3D print the final part using a high-temperature stable plastic, possibly one of the heat-treatable ABS plastics or something even more exotic.

Steve Melton 07-14-2018 12:35 PM

Quote:

Originally Posted by Snowflake (Post 1273424)
I think the important thing to note here is that Steve isn't going for a "perfect" solution, which I agree would require a lot more vanes and a lot more CFD analysis to get it "right". He's going for a "best solution that can be achieved with reasonable effort," and I think he's getting pretty close.

Even Steve's basic transition shape without the vane would be better than many of the folded aluminium ones, as at least Steve's shape has rounded transitions which will carry the air further before separation occurs. Adding a single vane will help distribute more of that air across more of the cooler, and is definitely an improvement, so the effort is probably worth it. A side benefit is that it provides additional structural rigidity, which probably isn't a bad idea either.

A perfect solution probably exists, but you'd need to 3D print the final part using a high-temperature stable plastic, possibly one of the heat-treatable ABS plastics or something even more exotic.

my thoughts:

1. no metal band needed. add an extra ply of material if needed. maybe just layup the groove firstly with small plies to make flush.

2. layup the interior with 3 to 4 plies of material

3. layup all surfaces, push material into groove. maybe use some wax paper and foam or something at the groove to hold in place.

4. after cure, remove ABS plastic. may destroy to the mold but that's OK.

you may work out other ideas once you get into it.

there may be others with more experience with fiberglass layups that could add better directions.

Chkaharyer99 07-14-2018 01:19 PM

Steve,

1. Agreed.

2. Copy. Would you use 6 ounce cloth or something else? I have West Systems Epoxy.

3. Copy.

4. Agreed.


Thank you,


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