Received: from opus.hpl.hp.com (opus-fddi.hpl.hp.com) by jr.hpl.hp.com with ESMTP (1.37.109.24/15.5+ECS 3.3+HPL1.1) id AA293427882; Fri, 5 Feb 1999 12:51:23 -0800 Return-Path: <fjouaux@scv1.apple.com-DeleteThis> Received: from hplms26.hpl.hp.com by opus.hpl.hp.com with ESMTP (1.37.109.24/15.5+ECS 3.3+HPL1.1) id AA281947881; Fri, 5 Feb 1999 12:51:21 -0800 Received: from mail-out1.apple.com (mail-out1.apple.com [17.254.0.52]) by hplms26.hpl.hp.com (8.9.1a/HPL-PA Relay) with ESMTP id MAA13821 for <wind_talk@opus.hpl.hp.com-DeleteThis>; Fri, 5 Feb 1999 12:51:20 -0800 (PST) Received: from mailgate1.apple.com (A17-128-100-225.apple.com [17.128.100.225]) by mail-out1.apple.com (8.8.5/8.8.5) with ESMTP id MAA31700 for <wind_talk@opus.hpl.hp.com-DeleteThis>; Fri, 5 Feb 1999 12:42:39 -0800 Received: from scv1.apple.com (scv1.apple.com) by mailgate1.apple.com (mailgate1.apple.com- SMTPRS 2.0.15) with ESMTP id <B0005130855@mailgate1.apple.com-DeleteThis> for <wind_talk@opus.hpl.hp.com-DeleteThis>; Fri, 05 Feb 1999 12:42:31 -0800 Received: from hookipa (hookipa.apple.com [17.205.40.238]) by scv1.apple.com (8.8.5/8.8.5) with SMTP id MAA19434 for <wind_talk@opus.hpl.hp.com-DeleteThis>; Fri, 5 Feb 1999 12:42:32 -0800 Message-Id: <199902052042.MAA19434@scv1.apple.com-DeleteThis> To: wind_talk@opus.hpl.hp.com-DeleteThis Subject: Re: Coyote Wind Block Calcs / Fishermans Park Date: Fri, 5 Feb 1999 12:42:32 -0800 From: Francois Jouaux <fjouaux@apple.com-DeleteThis> X-Mailer: by Apple MailViewer (2.100)
Matt,
Typically, winds in a tunnel have no relation to reality. Testers
scale down the real site and have to scale down the wind as well. The
Reynolds number, which has no unit, is what allows the
correspondance between the models and reality. Fluid temperature,
fluid viscosity, but especially the models' dimension are in the
equation (you don't even need to use air as the fluid).
Let's say they increase the wind in the wind tunnel. At one point
they start seeing turbulences along the buildings. They note the
model wind speed, compute the Reynold number from the size of the
model buildings, temperature, etc...
What does this mean in reality ? If they put in the same Reynold
number equation the size of the real buildings, the temperature,
etc... it gives them back the speed of the real winds that would have
the same turbulent effects. At any scale, this is the only constant
and is the key to fluid flows modelling.
This natural consistency explains why the eddies in your sink, the
rollers on the coast and the low pressures on a satellite image
basically look the same, even though they have much different sizes.
-Francois and what is left of his fluid mechanics classes.
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