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Bo B. B. Jensen January 27, 2000 06:31

Wall Shear Force
Hello Everyone

I have a qeustion regarding the measurement of wall shear force in geometries with water flow.

Is there anyone who has any experience with measuring the wall shear force on walls in complex geometries with water flow??



kang January 28, 2000 16:46

Re: Wall Shear Force
not a direct measurements, but could be interoplated from the velocity measurements close to the wall, though

COBOK January 28, 2000 18:07

Re: Wall Shear Force
Hi, there. Although it is not the right forum to post the "experimental" question, but people may have different background, as life is not straightforward. I used to measure wall shear stress directly using a custom made hot-wire probe mounted on the wall. It was almost 15 years ago, and I have not been able to engage in novel experimental techniques since then. I'd like to add that: (i) it is possible to use a hot film probe to measure a wall shear stress for water flows, even on walls with non-trivial geometries. However, limitations are quite severe and you'd need to make sure results are acceptable. (ii) Even though modern techniques as PIV are good for the core flow region, no proper results could be obtained for the regions close to wall. So PIVs cannot be used for measuring the velocity at the proximity to wall in order to get a wall shear stress. Accuracy will be way too low... Even for trubulent flows.

My suggestion: look for the papers in Journal of Fluid Mechnaics, and Experiments in Fluids (?). My best

John C. Chien January 28, 2000 18:48

Re: Wall Shear Force
(1). The direct measurement of the wall shear force can be done with a small round balance unit. This type of mechanical device has been used for large model in the air. Since it is mechanical, I think, it can also be used in the water. (2). Recently, I have seen the development of micro devices designed for the surface shear stress measurement in the journal paper. But I have no idea whether it is available for routine usage. It is likely that the micro device is still in the development stage. This type can be used for more complex surfaces because of it's surface mount and it is small. But I don't have any references in these areas.

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