Diffusor design

[es335]

Hi.

Does anyone have any references to how a diffusor should be designed, i.e. angles vs. velocity.
My "diffusor problem" has air as fluid and an inlet/outlet velocity approx. 20m/s - 5m/s. I would like to avoid any detachment.

And, does anyone know if a diffusor flow is inherently unsteady?

Any references to papers or books are welcome.

 

[m777182]

I have some 20 years old papers mainly in German language about the design of injectors.If acceptable,send me a mail to dixie.m@email.si
regards m777182

 

[BarryEng]

Check out 'internal flow systems' by D S Miller (BHRA) British hydraulic research assoc. (24 pages on diffusers).
In the days of venturi flumes, to minimise the head loss (& energy recovery), the angles were about 25 degrees (included angle) for reducers & 4 to 7 degrees for diffusers.
If you check out Daugherty & Ingersol (fluid mechanics) 5th edition p 194, the head loss drops down to a min (0.13 v2/2g) at about 4 to 7 degrees, rises to a max (1.15 v2/2g)at about 60, then drops to about v2/2g from 120 to 180 degrees.
Start with Miller.