I've no data on diffusers other than what Hucho published,or the original sources he used.These all have just a simple angle,although I was given to understand that 4-degrees was the maximum upward slope angle which would guarantee attached flow.
Since the tufts are 'flying' a bit,rather than attempting to polish the surface of the diffuser,it would appear that the boundary layer is somewhat compromised under there with eddy flow underway.The tufts do mostly point to the rear so there's no apparent recirculation,so she's helping.
Love the camera work! These images are as good as anything coming out of a world-class wind tunnel.Thanks!
