Volumetric Flowrate of a jet boat

[BigN8]

Anyone know what the volumetric flowrate of each engine is of out jet boats? I have searched a little and there is some discussions as it pertains to jet skis, and it seems most come up with around 4000 gpm. One of the key variables needed is the pressure at the nozzle. I have seen 40 psi from other posts, but that seems low to me.

Any physics masters out there care to figure this one out???

 

[GTBRMC]

While this seems like a fairly straightforward question, and it can be calculated, the complex geometry of the impeller (even if exact geometry is known) makes the calcs challenging.
Remembering that water is incompressible (neglecting any entrained gasses) simplifies the calcs of a waterjet pump vs. a similar gasjet pump (like an aircraft jet engine).

Having said that, the basic equation set to use, the Reynolds-averaged Navier–Stokes equations (or RANS equations) http://en.wikipedia.org/wiki/Reynolds-averaged_Navier–Stokes_equations, is intimidating:

Description of the method to use RANS:



This can be simplified by using a graphical approach as described here:
http://www.wseas.us/e-library/conferences/2006venice/papers/539-661.pdf

PS: Just kidding - these calcs are possible, but obviously not for most people.

A far better idea would be to go to Yamaha or other source that has empirically tested flow rate. Good luck in your quest, young Jedi.

Note: I did some work like this in engineering school but that was a long, long time ago in a galaxy far, far away.

Protip: Never take a course from a Thermodynamics II professor whose research area is shockwave modeling at the tip of a supersonic impeller.

 

[Volffas]

Sorry I can't answer your question, but I can provide a video of our jet nozzles in action if anyone is interested. I know the short answer is "a lot" but I wouldn't have anyway of guessing exactly what "a lot" means.

 

[Jim Robeson]

A Lot. I used some fuzzy math

 

[Britboater]

Wow....my head hurts

 

[BigN8]

While this seems like a fairly straightforward question, and it can be calculated, the complex geometry of the impeller (even if exact geometry is known) makes the calcs challenging.
Remembering that water is incompressible (neglecting any entrained gasses) simplifies the calcs of a waterjet pump vs. a similar gasjet pump (like an aircraft jet engine).

Having said that, the basic equation set to use, the Reynolds-averaged Navier–Stokes equations (or RANS equations) http://en.wikipedia.org/wiki/Reynolds-averaged_Navier–Stokes_equations, is intimidating:
View attachment 18591
Description of the method to use RANS:
View attachment 18592
View attachment 18593

This can be simplified by using a graphical approach as described here:
http://www.wseas.us/e-library/conferences/2006venice/papers/539-661.pdf

PS: Just kidding - these calcs are possible, but obviously not for most people.

A far better idea would be to go to Yamaha or other source that has empirically tested flow rate. Good luck in your quest, young Jedi.

Note: I did some work like this in engineering school but that was a long, long time ago in a galaxy far, far away.

Protip: Never take a course from a Thermodynamics II professor whose research area is shockwave modeling at the tip of a supersonic impeller.

Thanks for the research however I think These Reynolds equations apply more to jets and air being the fluid. Simply flow rate calcs use diameter of pipe or nozzle and pressure of the pump along with pump head and specific Gravity of water. All this is easy to factor except the pressure at the discharge of the nozzle which I assume is parabolic since it's an outlet.

 

[Julian]

Hold my beer...I got this!

I'll get a bucket and catch the flow....

 

[GTBRMC]

Thanks for the research however I think These Reynolds equations apply more to jets and air being the fluid. Simply flow rate calcs use diameter of pipe or nozzle and pressure of the pump along with pump head and specific Gravity of water. All this is easy to factor except the pressure at the discharge of the nozzle which I assume is parabolic since it's an outlet.

You missed my comment at the end, I was not completely serious. However, the RANS equations are for incompressible fluids...ie: liquids, not gasses.

You might reach out to this guy, he may have data. Had no idea there was such an animal out there as the "Adjust-A-Thrust" until I Googled this:
http://www.wetwolf.com/yam/

 

[sstegh]

Enough volume to be dangerous to rectal and vaginal cavaties.

 

[tdonoughue]

All I can contribute is that the area of the jets is about (my rough estimate) 6x6, or 36 inches^2. Two jets gives you 72 inches^2. If the output is 40 psi, that is 2880 pounds of thrust. Impresses me as possible...

 

[Scottintexas]

@cybuch does the flyboard require a certain flow rate ?

 

[BigN8]

Not for a fly board

 

[Ronnie]

After reviewing all of the above comments I think 40 psi sounds about right.

I am surprised nobody asked why the answer is important / what's it for.

 

[Speedling]

After reviewing all of the above comments I think 40 psi sounds about right.

I am surprised nobody asked why the answer is important / what's it for.

Mmmmmk, humor us?

And it all depends on horesepower, rpm (linked to current horsepower made) impeller pitch etc. Gonna have to lnow the psi at the tip, which is 80-85mm

 

[Ronnie]

@Speedling , I was just kidding. I have no idea what the answer is. I have degrees in business and law not engineering. However, The question reminded me of ones that my engineering room mates used to have to deal while in undergrad (e.g. How much water will pass through a pipe with X diameter and no pressure behind it?). That stated I'm not so much interested in the answer to the question as I am the reason the question was asked.

 

[txav8r]

Enough to move my boat 52mph. That is good enough for me, however, I am not certain that even in engineering that they don't calculate, design, build, and then come to find out it is close, but they have to redesign and build to account for all the variables they didn't consider. To reword that, grab a pump off the shelf, bolt it on, test...and adjust. That is the same as "get a bigger hammer" and "were going to need a bigger boat"!!!

 

[Evildwarf]

As my wise and aged father would have so sagely stated when confronted with such an intricate question:

Who the f#@k cares boy,
Mash the throttle and hang on!

love that guy....

 

[justason]

Sorry I can't answer your question, but I can provide a video of our jet nozzles in action if anyone is interested. I know the short answer is "a lot" but I wouldn't have anyway of guessing exactly what "a lot" means.

man, that's enough enough to destroy a rectum or vagina !!

 

[txav8r]

man, that's enough enough to destroy a rectum or vagina !!

That would be a helluva upgrade to my bidet!

 

[justason]

In simle math terms. Wouldnt the diameter of the impeller, the blade pitch and rpms define an approximate volume/displacement?