[Land-speed] [BULK]Re: Polar Moment

[joseph lance]

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 at 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