R/C Naval Combat

Alright folks, I have been playing, on and off again, with some cfd code durring my lunch break here... there is a link to a dxf and a picture... I just did a little parametric work, starting with the BC style as a baseline and a 5 psi drop across the nozzle... then I worked on tweaking the geometry to maximize flowrate (meaning more efficient, less losses.

To put this in perspective, the worst design that was checked out sat at ~1.2 gpm and the best at 1.9... that variation indicates to me that we can do a lot better on pump outlets, be it for efficiency or for raw power...

There are some unrealistic features, as I can not deal with multiple different fluids, so it is modeled as simply a restriction... The picture below is one of the best I have found (predicted, it remains to be seen how it does in reality) and it appeared that the continuous curvature spline curve resulted in lower losses than a straight section... the curvy part is on the pump side of the orifice... the minimum diameter is 1/8"...

anyways, I am just throwing this out there to start a discussion...

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I should note that the capped ends are used to facilitate the cfd boundary setup...

I don't know how many fluid engineers we have on the site.... I certainly don't understand what you are presenting.

basically, that would be a better (theoretically, if my assumptions are not flawed) pump outlet than the one you and I are currently using

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Originally posted by JustinScott

I don't know how many fluid engineers we have on the site.... I certainly don't understand what you are presenting.

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Hey I resemble that remark...

Greg what code are you using for your Color Filled Drawings?

flowworks... not terribly impressed but it is easy on the "I've got it at work and use it for other stuff so lunch time here I come" front..

I simply set it up as a fixed pressure at the two boundaries with no slip on the walls , with smooth walls. I know there is some roughness but until I figure out how to actually make it I won't be able to figure out what that value is... although I could ballpark it.

Incompressable flow, STP conditions for fluid properties. I set the pressure drop low enough that I wouldn't have to deal with cavitation issues at the sharp edges in the original model.

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Originally posted by Greg McFadden

basically, that would be a better (theoretically, if my assumptions are not flawed) pump outlet than the one you and I are currently using

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"Better" in what way? What are you trying to achieve?

JM

I suspect Greg is trying to increase output through a restricted outlet. IRCWWC and MWC restrict outlet size to 1/8" or less diameter. A brass rod with a 1/8" hole drilled through it would pass around 1 to 1.5 gallons a minute.

Greg's tapered design going from a wide inlet and tapering to a legal 1/8" opening will allow more flow.

For a comparison, Dave Ranier's tapered outlets can boost flow on a stock BC motor and pump by 1 gpm or more to 2 - 3 gpm total. Change to a high rpm motor and his outlet/BC pump combination can pump over 4 gpm. That combo was directly responsible for keeping my Richelieu floating on top of the water during the last sortie of the MWC 2008 NATs.

Greg's drawing is a lot like Dave's outlet design.

I actually tried a straight line inlet and saw a significant increase in flowrate by going from the straight inlet to the curvy inlet (continuous curvature curve), although the curve is more difficult to make. The difference was on the order of 10% for that change so it may actually be useful.

The tapered outlet also helps, but I have not checked into more curvy crap for it.

When I was still making pumps, I found that counterboring the outlet also improved flow a bit... but it would be a crude approximation of the taper...

the goal was to make the restrictor more efficient... you either get more flow with the same pumping power (e.g. less battery usage) or more top end flow possible with the same setup.

So how do we get one built? Unless we actually have one on hand, we won't know. Looks like it should be done with a CNC lathe, but a mill should be able to do it right? ...albeit slowly.

mill would be difficult. even lathe difficult due to depths. it may have to be a turned 2 piece mold insert and then molded out of plastic...

-Greg

I got to find the article I wrote for hull busters and then I'll post the way I did it. (Not that I don't remember, just it's all written down).
Danny

Yep my outlet looks allot like Greg's. I took his picture and made a few changes to it, like the length, retaining ring, and 7 deg taper that I use. But the rest of it is just about the same.

My next try will be with a 3 deg internal taper, when I get around to trying it. I think it will improve it a couple of percent, but not really sure if it will or not. I make mine on my lathe.

actually, you have it backwards from mine. the straight taper on mine is on the outlet.

I was playing with lead in tapers and it seemed that the short curvy part worked better than the long shallow taper. (at least in the cfd results)

If you get a chance, run what I have done thru your program, and see how it does if you would.

Thanks

no problemo. I can just reverse the boundary conditions on monday.

-Greg

Sorry for the long delay folks. Christmas and all that. I had to tweak the model with longer and symmetric inlet/outlet lengths to be able to the reverse condition.

Same run, as before, new model.

Water flows from left to right per the first picture in the first thread: 1.75gpm
Water flows from right to left per teh first picture in the first thread: 1.40 gpm

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Originally posted by Greg McFadden

mill would be difficult. even lathe difficult due to depths. it may have to be a turned 2 piece mold insert and then molded out of plastic...

-Greg

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Have you thought about cutting a ream out of tool steel to make these? You might be able to use a standard tapered ream for the outlet. If you have (or can make) a tool post grinder for your lathe you could modify an existing ream/counterbore for the inlet side.

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Originally posted by Greg McFadden



Same run, as before, new model.

Water flows from left to right per the first picture in the first thread: 1.75gpm
Water flows from right to left per teh first picture in the first thread: 1.40 gpm

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Holy macaroni!!!! Thanks Greg you made my day.
Danny