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Author: Subject: Rules for attached flow
pigeondave

posted on 24/7/21 at 08:32 AM Reply With Quote
Rules for attached flow

Hi all,

I've been thinking about flow through the radiator for a while now and after watching this video https://youtu.be/YLtTl4wrO_A even more so.

They talk about the transition and not to have the angle too steep otherwise the flow becomes detached.

My question is, does anyone know a safe rule of thumb for ensuring attached flow.

My thinking is, when looking side on, if I know the height of the rad (navy line), and the distance away from the opening (lime line), I can draw a right angled triangle.

The angle of the hypotenuse (red line) should not be greater than XX degrees. Does anyone know what this should be?

I could then draw a radius to join the two ends of the triangle (radius is the card template which they're using indicated with black arrow).

But should this be a radius or an ellipse or a clothoid?



My thinking is that its a bit like designing mountain bike jumps, you can put a bit of maths into it and get something predictable and safe. Safe in this case is keeping the attached flow and having the intake work efficiently.

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PAULD

posted on 24/7/21 at 01:49 PM Reply With Quote
Look up a Clark y aerofoil and use the upper surface. These stall at about 16 degrees, but with such a small aspect ratio I think you might be worrying too much.
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pigeondave

posted on 24/7/21 at 03:34 PM Reply With Quote
quote:
Originally posted by PAULD
Look up a Clark y aerofoil and use the upper surface. These stall at about 16 degrees, but with such a small aspect ratio I think you might be worrying too much.


Thanks for that.

Not worrying, just bored and thought of something to look up.

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coyoteboy

posted on 25/7/21 at 08:47 AM Reply With Quote
If you're bored, play with OpenFOAM

[Edited on 25/7/21 by coyoteboy]





Report your local potholes, it actually works!

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Mr Whippy

posted on 25/7/21 at 02:14 PM Reply With Quote
So you have this huge radiator but an inlet that looks about a quarter of the area. Air is going to rush in and slam the brakes on as the volume increases and resulting in a pathetic breeze through the core, even if the air remains attached.
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pigeondave

posted on 25/7/21 at 03:30 PM Reply With Quote
quote:
Originally posted by Mr Whippy
So you have this huge radiator but an inlet that looks about a quarter of the area. Air is going to rush in and slam the brakes on as the volume increases and resulting in a pathetic breeze through the core, even if the air remains attached.


That's why I'm interested in the science of it.
From what I've read (and not really understood) so far is that its about the change is static pressure across the core and not the dynamic pressure of the air.

The total pressure = dynamic pressure + static pressure.

There's a conservation of energy thing going on, so for you to increase the static pressure you need to reduce the dynamic pressure. I believe that the expansion does this.

If you read the youtube comments, someone has linked to a forumla SAE paper which shows that the sweet spot for openings might be 0.7 of the area of the rad.

Like I say, I'm still reading about it as its an area which interests me.

@MR Whippy maybe you could explain what the ideal radiator set up is. That way I could look at ideal, and work back to see what can be incorporated on the Fury?

I have my engine as far back as it can go so I could get the same bar across the rockers as what the BEC have. This has given me quite a bot of room to play with.

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pigeondave

posted on 25/7/21 at 03:36 PM Reply With Quote
quote:
Originally posted by coyoteboy
If you're bored, play with OpenFOAM

[Edited on 25/7/21 by coyoteboy]


Thanks for the link.
That looks like another level of complicated, I struggle enough with AutoCAD 360.
But one for the list if I get seriously bored and have time to do some modelling.

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indykid

posted on 25/7/21 at 09:00 PM Reply With Quote
7 degrees per surface

You might be ok on the bottom surface, but you won't maintain attached flow on the top





me? ambivalent? well, yes and no

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