Baffle to reduce airflow noise in a scroll housing

G

Guitarman

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Here is a patent application to be found in_ http://www.pat[URL="http://www.patentsonline.com/5120193"]entsonline.com/5120193[/URL]. It is my understanding that a baffle 12/14% of the blade width, located up to 90 degrees past the cut off point/exit point of the housing, unloads the blade turbulence after the blades pass the exit point. I intend to incorporate the baffle since I think that most of the noise comes from this area of the impeller/scroll housing. Comments welcome. Guitarman.:)
 
An interesting idea. Here's a couple thoughts on it, for what they are worth(!) Since it projects into the outlet airflow, I wonder if it'll reduce the overall system performance somewhat. Second, the patent was awarded to GM and speaks to reducing the fan noise in automotive heating and cooling systems. The mechanics of the airflow in these systems may be quite different from ours. Third, if it works I want to put one in my shop vac!

FYI I could not access the patent thru the site in your link. It was some kind of psuedo-spam site. I was able to locate it by searching on the patent number 5120193 at the USPO site: http://patft.uspto.gov/netahtml/PTO/srchnum.htm but I could not view the images.

Dan
 
Guitarman said:
Here is a patent application to be found in_ http://www.pat[URL="http://www.patentsonline.com/5120193"]entsonline.com/5120193[/URL]. It is my understanding that a baffle 12/14% of the blade width, located up to 90 degrees past the cut off point/exit point of the housing, unloads the blade turbulence after the blades pass the exit point. I intend to incorporate the baffle since I think that most of the noise comes from this area of the impeller/scroll housing. Comments welcome. Guitarman.:)
Click to expand...
Guitarman,
I found about the same information a few months ago and had an email exchange with Bill Pentz about this topic. He explained to me that he knows about the possible modifications to the blade and the possible advantages it might have. The reason why he did not implement these adjustments is that he found it would clog the blade if you accedently let the bin overflow into the cyclone and filters. It would be very had to clear the blade of chips because you would have to take the cyclone appart.
The whole setup was over-dimensioned to take care of the lower efficientcy to compensate for a system that would need next to no intervention once set-up.
The noise factor is something to look into and as far as I can tell (and emails from me to Ed) he got some ideas he wants to work on(?).
Up to now the best idea is to add a (small) fin to the bottom of the blade. The best comparason is the tip of an airpanewing that has this small fin at 90° to the wing at the end of the wing to reduce the drag after the plane.

There is still some work that can be done. I found a different approuch but I will explain it in a different post You can see my solution in the Gallery: Erik's ClearVue in Gent, Belgium

Erik
 
Noise controle application

Noise controle application

In my search for a beter sound reduction for the noise that comes out of the cyclone I found the following two ducuments:
http://www.grc.nasa.gov/WWW/AcousticalTest/Documents/PDF/Vibration_Control_Principles.pdf
and
http://www.cincinnatifan.com/catalog...3-internet.pdf
In the second document on page 10 you can read "Air flow is also reduced when the elbow is too close to the fan discharge. A minimum length of 4 times the wheeldiameter of straight duct should be installed between the fan discharge and an elbow."
So I removed the elbo from my system (see Gallery: Erik's Clearvue in Gent, Belgium) and made the air flow straight into my filterbox.
Because the dimentions change from a narrow 'duct' to a wider 'box' I added pannels at 45° and an extention of the bottom of the 'duct to reach half way into the box. Against the back og the box is a pannel at 45° to defelct the air down. I got some of the principles out of the booklet, first on my list above.
Putting the whole thing to the real-life test in my system I found that the noise comming from the transistion and box are a very low rumble and not very irretating.

The most noise is still comming from the blade in perticular the point where the blade comes closest to the wheelhouse.

In an email, I got from Bill Pentz, he mentions the noise problem and writes that the fact that the bottom corner of each blade has a small radius reduced the noise considerably.
The noise is comming from the turbulance of the the 'back' of the blades. Making the air come beter of the blade will improove things BUT at the same time it might cause the fan to cloge-up with chips if the bin overflows. So difficult choices: ease of use or less noise.....

The 'Vibrations' pdf also helps to understand how you can reduce noise. The difference between noise isolation and noise absorbsion is very important and should both be tackled.

Just my 2 cents

Erik
 
Noise control

Noise control

Thanks Erik, I appreciate the links, I will check them out. I also read the one on the outlet distance and I am also enclosing my filters in a box and will extend the scroll outlet at least as far as recommended (four times the fan diameter) I think was the recommendation in the link you listed. It was listed in a thread previously on this site but I lost track of where. I am attempting to design a back flush provision on my filters but haven't figured it out yet. (I am also trying to learn Google Sketchup at the same time to do the design, so it's a little slow in coming.) I am not afraid of fan clogs since I am incorporating a photo sensor on the sawdust collection bin which will shut off the fan when it senses an overfill condition. Regards, Guitarman.
 
Guitarman,

If you look at page 3 on the left in the middle there is a drawing of a wheel labeled 'backward inclined'. That is about the simplest solution to the blade turbulace you can find. A simple ring on the bottom of the blades. Bill wrote to me that he tried this and stop using it because of the clogging. But in your situation it might just be the best solution.
An other thing I noticed in the design of the blowers on the cincinnati website is that the 'inlet' of the wheel, where the vertical tube meets the wheel, is more like the shape of the front of a trumpet. The air get directed closer to the center of the wheel so that the 'pushed' into the blades. Again this would normally create the clogging problem.
Something to try?
Keep me posted
Erik
 
It's Coming!

It's Coming!

It will be here soon, don't miss it. :D
Thanks to all whose ideas I have used. Regards Guitarman.
 
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