Re: [PSUBS-MAILIST] Thrust from a pump?

["Dan H." <jmachine@adelphia.net>]

But Alec,
Wouldn't using a reversible pump as a thruster require you to use two small 
output nozzles instead of a larger suction input and ported down output 
nozzle.  I'm not sure if the pump would like that. Sounds like a cavation 
problem.

Maybe a single direction pump and a Y valve to two separate output 
nozzles?????

Dan H.
----- Original Message ----- 
From: "Smyth, Alec" <Alec.Smyth@compuware.com>
To: <personal_submersibles@psubs.org>
Sent: Thursday, January 04, 2007 9:16 AM
Subject: RE: [PSUBS-MAILIST] Thrust from a pump?


Wow, what an A+ response! Thanks Brian for yours as well. With this 
information I can now go out and do some virtual shopping to see how much 
I'd have to spend to accomplish the same thrust with the two approaches. Off 
hand I'd say the well pump solution would likely be cheaper, but mating 
trolling motors to pump heads makes use of two brand new trolling motors I 
happen to have sitting in the garage.

thanks,

Alec

________________________________

From: owner-personal_submersibles@psubs.org on behalf of Cliff Redus
Sent: Wed 1/3/2007 8:58 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Thrust from a pump?



Alec,



Below is a derivation of thrust that can be developed from a axial flow pump 
in terms of volumetric flowrate.



The thrust due to accelerating fluid through a pump can be written as



F=M(V1-V0)



Where M is the mass flow rate, V0 is the free stream velocity upstream of 
the pump and V1 is the velocity exiting the pump.



But the mass flow rate M can be related to the volumetric flow rate Q as



M=Density*Q



Substituting, the thrust in terms of volumetric flow rate is



F=Density*Q(V1-V0)



But the volumetric flow rate Q is related to velocity in the pump duct ID as



Q=V1*A=V1*Pi*D^2/4



Where D is the duct ID.



Solving for V1, and substituting, the thrust can be written as



F=Density*Q(Q/(Pi*D^2)-V0)



For a thruster oriented approximately normal to the direction of flow, the 
inlet velocity can be assumed to be zero.  The thrust then reduces to



F = 4*Density*Q^2/(Pi*D^2)



Or



F= 0.001766*(q/d)^2



for freshwater where,



F = Thrust, lbf

q =  pump volumetric flow rate in gpm

d = pump outlet duct inside diameter in inches



As an example, a pump with a capacity of 200 gpm flowing through a 2" duct 
would develop 17.7 lbf of thrust.

Cliff


----- Original Message ----
From: "Smyth, Alec" <Alec.Smyth@compuware.com>
To: personal_submersibles@psubs.org
Sent: Wednesday, January 3, 2007 4:20:48 PM
Subject: [PSUBS-MAILIST] Thrust from a pump?



I'm contemplating using water pumps as maneuvering thrusters (NOT for main 
propulsion). Cousteau's socoupe used a hydraulic pump for the jets, but I'd 
like to avoid that route if possible due to the excessive noise. DC 
submersible pumps are convenient but I haven't found anything beefy. I could 
try mating a trolling motor to a pump head. Submersible well pumps look 
promising because they're very powerful yet compact, but they require AC, 
and I don't think I can reverse them so I'd need four pumps instead of two. 
I could of course hang trolling motors off the boat font and back, but it 
really messes up the hydrodynamics of what can otherwise be a quite clean 
design, and the props on my trolling motors make them too large to duct into 
the MBTs.

Assuming I do settle on some kind of pump, the next question is how strong 
it needs to be. Does anyone know how to translate GPM (or LPM) into static 
thrust?

Any ideas or experiences would be much appreciated.


Thanks,

Alec

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