Air Force Builds Quiet Mach 6 Wind Tunnel

An anonymous reader writes "To help design 'scramjets' -- vehicles that'll travel thousands of miles per hour as they leave the atmosphere and zip around the globe -- the U.S. Air Force has just funded a wind tunnel that operates quietly at Mach 6. To get a quiet flow, the throat of the Mach 6 nozzle must be polished to a near-perfect mirror finish, eliminating roughness that would trip the flow."

"Quiet"?

[timeOday]

From reading the article, I gather "quiet" is being used here as a technical term which is roughly synonymous with laminar, or lack of turbulence (rather than "gee I wish my vacuum cleaner were quiet").

Can anybody with the right background tell me whether that's the case?

Re:Another old one...

[james_shoemaker]

Grad student 1: This job sucks.
Grad student 2 (turning on wind tunnel): No, it blows!

      All wind tunnels suck, the flow off of a fan is to turbulent to get good readings.

James

Re:Some further comments

[Moofie]

Columbia broke up somewhere north of Mach 12, I believe.

I'd be much, MUCH more concerned about an engine unstart than about a mechanical problem with the heat shielding system. So much so, that I'd be totally unwilling to fly aboard a scramjet-powered aircraft that had a pilot with a joystick in his hand.

Re:Super Smooth vs. Dimples...

[penguin121]

The reason that dimples work for a golf ball is exactly the same reason they would be counter productive for the wind tunnel. Basically the dimples induce a turbulent flow around the golf ball, which reduces the flow seperation at the rear of the ball as compared to that resulting from laminar flow over a smooth ball. By reducing the size of the flow separation region, the pressure drag on the ball is significantly reduced, allowing the ball to travel farther. Now in the case of the wind tunnel turbulent flow along the walls would generate noise that would interfere with the experiments, so they want as smooth a surface as possible to minimize turbulence at the tunnel walls, thereby minimizing the background noise.

Re:Some further comments

[Darth_brooks]

Indeed, unstarts were a huge problem with the early SR-71's. They never really "solved" the problem of unstarts, they just mitigated the problem by having the flight control system control engine restarts at high speed.

Re:Cultural Reference

[afidel]

No, something needed to be done, the valve that stuck open needed to be closed. They were incorrectly acting because the system was not responding as they expected based on their inputs. Btw TMI pisses me off. People whine about the dangers of nuclear power, yet TMI which was about the worst possible scenario for a US nuclear power plant released less radiation than a MUCH smaller coal plant would in a year.