Michell v CFD and EFD: Round 2007

johnhazel said:

However, I could be just all dazed and confused about this.......

John H.

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An easier way would be to go to www.cyberiad.net/michlet_betas.htm and download the executable file on that page. The allowable viscosity range is now 0.5 to 2.0 centipoise.

Leo.

Leo
Thank you for the wider limits. I will have a look and see if it explains the slight difference we see.

John
I am surprised by the results for the sand paper. The comparison we had was with a vacuum layup of carbon fibre without out any finishing the difference in drag translated to a 0.1kph in 11.5kph. So on the face of it the friction factors for the 40 grit and 80 grit paper look much worse than I expect. No doubt the orientation of the surface has an impact but the cloth was similar to a fine mesh.

On the other hand riblets reduce drag so certainly shows smooth surface is not the best. I think there is some opportunity to work on surface damping methods like the animal world has developed but clearly random roughness is not beneficial.

Rick W.

Leo Lazauskas said:

An easier way would be to go to www.cyberiad.net/michlet_betas.htm and download the executable file on that page. The allowable viscosity range is now 0.5 to 2.0 centipoise.

Leo.

Click to expand...

Leo
I have tested it and the results from Michlet with viscosity at 1.6e-6 (4C) are now much closer to what we were measuring in Calgary. The increase in drag is up by 5% from the drag for 1.2e-6 (13C) - the value used previously. The water was cold because Greg had to wait for ice to melt before he could do testing.

Rick

Leo Lazauskas said:

An easier way would be to go to www.cyberiad.net/michlet_betas.htm and download the executable file on that page. The allowable viscosity range is now 0.5 to 2.0 centipoise.

Leo.

Click to expand...

Thanks. That's much easier.
John H.

Rick Willoughby said:

I am surprised by the results for the sand paper. The comparison we had was with a vacuum layup of carbon fibre without out any finishing the difference in drag translated to a 0.1kph in 11.5kph.

Click to expand...

Maybe there was a reduction in the total amount of detached flow which compensated for some of the drag from the roughness.

Rick Willoughby said:

On the other hand riblets reduce drag so certainly shows smooth surface is not the best. I think there is some opportunity to work on surface damping methods like the animal world has developed but clearly random roughness is not beneficial.

Click to expand...

Yes, worth looking into....

John H.