Thanks Ron! I couldn't remember the formula and I didn't have my
books/tables handy.
On the 2nd point, actually, laminar flow is not the same as "straightness".
Laminar flow refers to non-turbulent flow immediately adjacent to the
bodies' surface whereas the "straightness" I was referring to was for the
overall
airflow in the tunnel. You always want a smooth straight airflow in the
tunnel.
For low drag, you try to maintain laminar flow over the body, whereas for
high lift applications, you often need to artificially induce turbulent
airflow
immediately adjacent to the lifting body so as to avoid airflow separation.
For a car, you want laminar flow over the (upper) body, but you *may* want
non-laminar flow over the rear wing. Whether you do or not will depend on
the track - high speed (Spa) or high downforce (Monaco)
Mike
-----Original Message-----
From: Ron Soave <redlotus@spacey.net>
To: Mike Gigante <mikeg@vicnet.net.au>; Daniel1312@aol.com
<Daniel1312@aol.com>
Cc: spridgets@autox.team.net <spridgets@autox.team.net>
Date: Sunday, December 13, 1998 3:43 PM
Subject: Re: Wind tunnel access minor math ahead
>Last math for 1998, I promise.
>
>1) Mike's first point - The Reynolds Number is:
>
>Re = {(rho) * (v) * d} / (mu)
>
>where
>rho is density of the air ( = to 2.7 * P/T, with pressure in psia and temp
>in degrees rankine {deg R = deg F +460})
>v = velocity
>mu = kinematic viscosity of the air (varies slightly with temp)
>
>2) Mike's 2nd point - "Straightness" = laminar flow, which is typically
>considered to be Reynold's number less than 3,000.
>
>You really want to make sure your tunnel provides a repeatable source flow
>of air with evenly distributed lines in the flow field (representing a nice
>even pressure delivery).
>
>----------
>> From: Mike Gigante <mikeg@vicnet.net.au>
>> To: David Ramsey <dwramsey@worldnet.att.net>; Daniel1312@aol.com
>> Cc: spridgets@autox.team.net
>> Subject: Re: Wind tunnel access
>> Date: Monday, December 14, 1998 12:47 PM
>>
>> If you do decide to use scale models and a home built tunnel,
>> there are a couple of important things to take care of.
>>
>> 1) Reynolds Number (size, density, airspeed, viscosity all combine
>> to make a scale model act the same (aerodynamically) as the full
>> size.
>>
>> 2) "straightness" of the air. Baffles and honeycomb (in-line) are used to
>> reduce the turbulence and vorticity of the air.
>>
>> If you want to be *really* fancy, you could include a rolling road as
>part
>> of the tunnel.
>>
>> Of course if you just want a faster sprite, why not buy the sebring coupe
>> replica kit from Brian Archer. It's aerodynamics would be a lot better
>> than stock and it is a purdy little thing.
>>
>> Mike
>>
>
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