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RE: [PSUBS-MAILIST] Thrust from a pump?
Yes, and in addition depending on the type of pump a thrust bearing
could be on the wrong end of the shaft in "reverse".
Lots of food for thought here...
Alec
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Dan H.
Sent: Thursday, January 04, 2007 9:45 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Thrust from a pump?
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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