Re: [PSUBS-MAILIST] hydrodynamics question

[CARRO@wans.net]

I have been designing around scoops also (because they 
are sexy) and I figured the intakes to be larger than 
the prop diameter. If not, the increased velocity of 
the exhaust would pull a vacuum on the front side of 
the prop and reduce your thrust.
--- Original Message ---
From: Michael Holt <mholt@richmond.edu>
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] hydrodynamics question

>Alec Smyth wrote:
>> 
>> My design has twin props astern, in tunnels fed by 
side-scoops (a la fighter
>> jet). I'm currently making the mold for the stern 
fairing, and I'm
>> contemplating the best size and shape for the 
scoops. Given that water is
>> essentially incompressible, am I correct to assume 
the frontal area of the
>> scoops should be the same as the area of the prop 
tunnels? Another
>> possibility would be to eliminate the scoops 
altogether and go with NACA
>> intakes or such. But the scoops are definitely 
sexier.
>
>Keep in mind that NACA intakes or scoops will ingest 
all sorts
>of floating stuff.  You're gonna have to find a way 
to screen
>them -- probably with bars parallel to the flow, 
because real
>screens would add significant drag.
>
>I have here a paper on pumpjet design.  It's 
from "Underwater
>Missle Propulsion," editied by Leornard Greiner and 
published
>in the 60s by Compass Publications.    If you're 
interested,
>I can try to have it scanned.
>
>I'd like to see pictures of what you're doing, too.
>
>
>
>
>
>Mike H.