High speed water through an orfice question?

[allblowdup]

Trying to decide on a nozzle design. Right now we are using a 650 hp engine to move 4000 gal/min through an orfice that is 3.080 in Dia. Rough pressures are variable but are in the 200-250 area. The nozzle I have right now is 14" long and tapers down from the pump outlet od of 7" to the 3.080. It is in a racing jet boat so we are using the exhaust stream for propulsiom. My question is I can have the inside of the 14" long tapered nozzle smooth or I can cut rounded grooves in it with the direction of flow. The pump is a combination axial/centrifical design and does have a straightning ssytem on its outlet although the water is still spinning somewhat upon exit.


Mark

 

[LittleInch]

On the basis that no one else has had a go at this - I've never seen anything like it - it must be some racing boat if you've got a 650 hp engine.... I can't see the grooves having any real effect on either swirl or velocity at those sorts of flowrates and velocities and it looks a bit of a bitch to weld it to the circular nozzle or flange. At this sort of velocity you probably want to look into rocket engine / jet engine nozzles and ask some of the guys on the aerotech forums what they think. This is a smooth taper and that's probably what you need to avoid any sharp or very sudden changes in profile or diameter.

If water swirl is an issue for you then I would try a cross set of vanes in it and then just try it out or rig up a small test version.

Not sure what exactly you're trying to achieve or modify / improve though.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[allblowdup]

Thanks, Yes it is a racing boat and we us these on boats up to 1500 hp and 140+ mph. Up untill now all of them have been hand made and have had some sharper corners in them ( roughly make a change of 15 deg) I am cnc milling from a 3.5" piece of plate to get the curve as smooth as possible. The grooves are from milling the inside. Just trying ti figure out if they could be hindering or helping flow is all.

 

[LittleInch]

Avoiding sharp corners and changes in direction is much more important. They won't help the flow I don't think as you just get more surface area, but so long as they are relatively smooth then you probably won't notice the difference. A good shiny coating is more important that won't get ripped off by your enormous velocities.

Have you ever thought about using standard piping components? Type "pipe reducer 16.9" into google images - there isn't a 7" version but there is 8" and 6". Also you can buy formed elbows long radius and just cut to whatever angle you want. Weld it up then grind off the internal weld bead? They come in all sorts of metals.

Reducer is maybe a little short, but is smooth radius.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

Doesn't actually answer your question but well worth reading anyway.

http://services.eng.uts.edu.au/~phuoc/docs/writings/Swir-9i.pdf

The Ornel pump units were powering jet boats way back when Adam was a boy, worth doing some research on the Ornel jet pump boats, from memory the pump units may have been called "Squid"

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[tkall]

Damn...I'm in the wrong business.

 

[rtronics]

Try Hamilton Jets in New Zealand, they have been in that business the last 30-40 years.
Regards, Ray

 

[hydtools]

Looks like a job for a cnc lathe.

Ted

 

[allblowdup]

Well right now i am making them on a cnc mill.
I guess another way of looking at it would be.
Having a divergent cone 14" long with the large end 7" and the small end being 3.100" would the cone be more effecient at moving water through it at 200 psi inlet pressure with a smooth inner surface or with a grooved surface in the direction of flow. Both having a swirl factor to the flow.

 

[hydtools]

I do not think the difference in efficiency will be significant, smooth or grooved as you have.

Ted

 

[MintJulep]

Looks like a good candidate for a casting.