Lance;
You might be able to do this but just simple tests between two or more
shapes in the same medium (water) is more of what I had in mind.
Testing different ideas such as does a pointed nose have lower drag on my
car than a rounded one? Run the rounded model and then glue on a pointed
nose-- is it faster? Simple comparative tests that cost nearly nothing to
do-- if you have access to a pool.
Regards, Neil Tucson, AZ
-----Original Message-----
From: joseph lance [mailto:jolylance@earthlink.net]
Sent: Wednesday, January 16, 2008 12:17 PM
To: neil@dbelltech.com; 'Ed Weldon'; 'Don McMeekin'; 'Keith Turk'
Cc: 'land-speedsubmit'; 'Elon'; NT788@comcast.net
Subject: Re: [Land-speed] [BULK]Re: Polar Moment
Neil;
Interesting idea, you're talking about a "similitude" experiment--trying to
get comparable results with different fluids (air & water).
But it would require using the analytical aerodynamic characteristics of a
car, the air density and pressure, and calculating the Reynolds numbers,
etc. at various speeds. Then you would have to do the same thing for the
small model and calculate those Reynolds numbers and other parameters for
the motion in water and try to find conditions that give you the same
Reynolds number in both water and air. This is the only way to know if the
results would mean anything before doing all the work setting up the
experiment.
If the right data were available for the full size car some trail similitude
calculations for water could be done to see if it's at all feasible. Might
need consider liquids other than water. Maybe Mayf has some Reynolds numbers
that could be used as a starting point.
It's been a long, long time since I did any similitude calculations for
fluid flow---we seem to generate a lot of interesting ideas for engineering
student projects.
Lance
----- Original Message -----
From: <neil@dbelltech.com>
> Ed;
>
> I've often wondered if I could investigate the aerodynamics of a design by
> using a scale model in water instead of air. The drag effects, etc should
> show up at quite low speeds in water compared to air since its density is
> far higher. Granted, water isn't compressible like air but we're talking
> about subsonic vehicles so this may be practical-- what do you think?
>
> My idea is to do the drag measurements with a minimum of instrumentation.
> Simply build a smooth ramp and place it in a swimming pool at a known
> angle
> and let the model roll down the ramp for a measured distance. The faster
> it
> covers that distance, the lower the drag. The distance would need to be
> long
> enough for the model to reach its terminal velocity. Make the model fairly
> heavy to eliminate the buoyancy effects.
>
> Jon might have to chip a hole in the ice, though :)
>
> Regards, Neil Tucson, AZ
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