Re: CONTROLLED TURBULENCE
http://www.bwspeakers.com/index.cfm.../ObjectID/3A7554F4-4779-11D4-A67F00D0B7473B37LineSource said:
Re: Re: CONTROLLED TURBULENCE
We were doing that to the intake and exhaust ports of racing engines back in the 80's. In some cases it worked, in some it didn't.454Casull said:
Honestly, I think the laminar vs. turbulent discussion is mostly a red herring for speaker ports. It takes several diameters of flow distance to be able to classify the flow as fully developed even when the flow is just in one direction and steady.
In the case of ports you have unsteady flow and the boundary layer hasn't developed enough to round off the velocity profile - you can hardy call that anything but "turbulent". I havent run any numbers, but I bet you find that there are large losses from re-entrant flow (sudden expansion from a pipe into the world or into the box). The flares allow flow separation and vortex formation to occur further from the main jet and this reduces chuffing.
My $0.02
In the case of ports you have unsteady flow and the boundary layer hasn't developed enough to round off the velocity profile - you can hardy call that anything but "turbulent". I havent run any numbers, but I bet you find that there are large losses from re-entrant flow (sudden expansion from a pipe into the world or into the box). The flares allow flow separation and vortex formation to occur further from the main jet and this reduces chuffing.
My $0.02
Sinc this is a huge education for me, I decided to look at this further. High excursion subs generally are putting out port air at 20-100 mph that reverses direction 20 times per second.
The reynolds number to support laminar flow is around 2000. The port never sees flow that slow. In fact at 1 m/s in a 4" port, the Re is 7000. At 17 m/s, a number unibox uses for port noise, the Reynolds number is a gazillion.
And the one article mentions port compression beginning around 50000, graphically visible at only 7 m/s. Someone check my math.
So ron, thumbs up baby. dimple gimmicks? I don't know. But to be cute I put some golfballs in my ports, half with dimples and half without, using a 10 HZ sin wave, and only the ones without dimples flew out. It looked like the bingo machine in there.
Just kidding about the golf balls, but if someone can tell me the RE number for a golfball cruising at 150 mph, I'd take another look. That much I am sure about, dimples give golfballs less resistance and more distance. You can quote me.😉
The reynolds number to support laminar flow is around 2000. The port never sees flow that slow. In fact at 1 m/s in a 4" port, the Re is 7000. At 17 m/s, a number unibox uses for port noise, the Reynolds number is a gazillion.
And the one article mentions port compression beginning around 50000, graphically visible at only 7 m/s. Someone check my math.
So ron, thumbs up baby. dimple gimmicks? I don't know. But to be cute I put some golfballs in my ports, half with dimples and half without, using a 10 HZ sin wave, and only the ones without dimples flew out. It looked like the bingo machine in there.
Just kidding about the golf balls, but if someone can tell me the RE number for a golfball cruising at 150 mph, I'd take another look. That much I am sure about, dimples give golfballs less resistance and more distance. You can quote me.😉
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