Quote:
Originally Posted by tasdrouille
So, I've been reading a bit about wind tunnels lately, secretly dreaming of someday building my own.
So I'm reading about all this stuff, closed or open jet, corner vanes, contractions ratios, screens, honeycombs and what not to get the cleanest flow possible, and for a 200 square feet test area I'm ending up with something over 150 feet long and so tall that even if I had the money I would never get the permit to build it.
But what if someone was to make a garage sized tunnel? Something 24 feet long by 12 feet wide and 10 feet tall. Make one end with a bellmouth lip and the other end with what would be needed to move 600000 CFM. How dirty would the flow be? How meaningful would the measurements made in such a tunnel be for a common midsize car? What would be needed to move 600000 CFM?
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The big boys say do not exceed 5% blockage or buoyancy will destroy any chance of meaningful data.That would require a test section of 400 square feet for a car with 20-square feet frontal area.To get a turbulent boundary layer,at a minimum 20-mph would require 704,000 cubic feet per minute fan capacity.Typically,you need 6-pipe diameters length of tunnel to kill vorticity and get nice even laminar flow into the test section.If yo do circulation,you can save on power but you have to do alot of full area turning-vanes at every corner and then maybe flow-straighteners before the test section.If you do smoke,you have to do purge and makeup air.Just operating the tunnel heats the air because of friction,so unless you have a climatic tunnel,you have to do continuous "weather" monitoring within the tunnel to properly reduce your data at the end of the run.I want to say that GM's tunnel has a 60,000-hp electric motor to turn the 80-ft dia. fan.Fixed stator blades are typically used at the fan to help the air on and off the fan blades with minimum vorticity.----------------- NASA Ames uses a "wall" of fans,each with bell-mouth openings,and boattail stingers after the motors feeding a common duct as a draw-through configuration.Nice San Francisco Bay Area weather to go with it!------------------------ I'll have to brush up on physics to calculate the fan HP.-------------------------- You might want to play with tufts while you ponder the tunnel.I get a friend and daughter to drive chase car and photograph the tufts.Its more valid than a tunnel.Not as sexy though!-------------- If you stare at a teardrop long enough you'll develop an "eye" for the air.If what you do ,is as occurs on the teardrop,you're there!