From: "Smyth, Alec" <Alec.Smyth@compuware.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] Thrust from a pump?
Date: Thu, 4 Jan 2007 11:50:42 -0500
>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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