Date:         Sat, 24 Aug 2002 10:53:01 +0100
Reply-To:     Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject:      Re: Custom Scoop Update - Should you care!
Content-Type: text/plain; charset="iso-8859-1"

Alistair,

I just said, be aware of Reynolds No...... and don't jump to conclusions...

...and if I spent my time sitting on my duff, I wouldn't know what you obviously don't:- that to a fly, the air's like treacle, which is why they can change direction and accelerate away from your swat quicker than you can swing it. And why to a Pterordactyl or a hang glider the air appears somewhat less sticky, and less thick too if you can imagine being an airliner at 500 mph and 7 miles up. Thats what Reynolds No is about... Speed x Length /Viscosity - no units.

and yes, no relation, unless you run the tunnel at something close to (scaled) Re Nos.
 and if you want to
>... at least visualise the flow around the van in a gross way...

.. find a big smoky fire near a roadside and drive through it while someone on the roadside videos it. (that'd be fun).
...or drive behind aVanagon thats burning oil or smoking bad (or use a smoke cannister up front), and watch those Karman vortex wakes (even more fun) - most flat backed vehicles have a very predictable flow pattern, the key thing being when the flow suddenly changes its overall character, maybe 20, maybe 60 mph - that's what Re No. quantifies.
.. but I won't go on and explain further, as it appears you know what you know and don't much want to know what you don't.

Clive
'88 Syncro Transporter

----- Original Message -----
From: "Alistair Bell" <albell@uvic.ca>
To: "Clive Smith" <clive.harman-smith@ntlworld.com>; "vanagon"
<vanagon@gerry.vanagon.com>
Sent: Friday, August 23, 2002 5:39 PM
Subject: Re: Custom Scoop Update - Should you care!


> on 8/22/02 3:29 PM, Clive Smith wrote:
>
> > Just be aware that as :
> > a) Water has a different visosity than air;
>
> yes, of course
>
> > b) the Reynolds No. (non-dimensional number controlling viscous flow
> > behaviour)
> > of a model in water bears no relation to that of a full sized vehicle in
> > air -
>
> really? *no* relation? Of course the Reynolds # will be different but you
> can at least visualise the flow around the van in a gross way - we are
> talking fun here, not a detailed examination.
>
> >
> > ------- you are unlikley to come to any useful conclusions using your
flume
> > tunnel.
>
> yes, the idea was not to come up with data but to visualise flow in a
> general way.
>
> > However, tufting your van and using mirrors or a camera to observe the
flow
> > might
> > be more worthwhile- but your conclusions from what you see - again -
might
> > not.
>
> sure you might come to a false conclusion but if you see the tufts waving
> vertically or moving in a confused manner near and around the vents you
> might, just might, discover something. Its a whole lot better than sitting
> on your duff talking about it :)
>
>
> Alistair
>
>