Okay,

 

Monty thinks the emphasis is on the BL.

I believe (don't know), the main-problem is the upper ductwall shape. Even if you have perfect BL flow, the upper wall shape is still not good and will stall the flow.

At the end of the game you want good flow at all speeds and be able to close any ducts to limit excess cooling (when you hopefully get there).

Obviously BL will play a role in your installation as the intake is rather narrow.

However BL or not - BL does not mean there is no flow, just slower and more turbulent, but still generally going towards the cooler.

Aerodynamics in the duct should be much the same for laminar, turbulent, any flow, as long as there is flow.

When things stall is when flow pretty much ceases (in the stalled area ....), no matter how well things where at the entrance.

The stall in this case is rather "easy" to get, as the speed seems rather low already. Still may be good enough if you can do away with the stall.

So I suggest to work on the duct wall first and optimize it.

 

As suggested, with some kind of sheet, alu, fiberglass, etc. You can curve it more and more until you peak.

Maybe pinched ducts (copyright Ed!!) are not working here, but it may as well - if they work a Ed's theory explains (energizes the flow...)

 

If this works, modify according to the best shape found.

Then try to improve with VGs or sanding or turbolator tape.

Then go for the exit - after all it is a differential pressure game....

 

TJ

 

On 7/18/07, M Roberts <montyr2157@alltel.net> wrote:

Al,

 

I think you need to do something to energize the boundary layer. If you can't divert it you need to put some energy into it. It is probably getting slow and separating from the face of the duct. That is what your data seems to indicate to me.

 

I like the shape that Thomas proposes better than what you have now, however, I still think you will need some VG's in front of the inlet.

 

I know it may seem counter intuitive, but turbulence may actually help in this case. You will not get very efficient internal diffusion, but it will be a lot better than what you have now. I don't think that putting a turning vane will help too much without doing something to energize the boundary layer first. You'll just have a slow thick low energy layer, and a high energy layer separated by a turning vane.

 

It is really easy to duct tape some aluminum VG's in front of the inlet and see what it does.

 

You may need a combination of Thomas' contour, VG's and a turning vane. Go with the easy fix and work your way up in complexity.

 

Monty