Simultaneous wall shear rate measurements by a three segmented electrodiffusion probe and laser-Doppler-anemometry |
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| Authors: | H-W Bewersdorff A Gyr K Hoyer V Sobolik |
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| Institution: | (1) Department of Chemical Engineering, FH Lausitz, D-01968 Senftenberg, Germany, DE;(2) Institute of Hydromechanics and Water Resources Management, Swiss Federal Institute of Technology, CH-8093 Zürich, Switzerland, CH;(3) Department of Mech. Engin., University of California, Santa Barbara, CA 93106, USA, US;(4) Institute of Chemical Process Fundamentals, AS CR, CZ-16502 Prague, Czech Republic, XX |
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| Abstract: | In a fully developed turbulent channel flow, the instantaneous wall shear gradient was measured simultaneously by an electrodiffusion
(ED) probe and by laser-Doppler anemometry (LDA). The LDA measurements were done in the viscous sublayer and the linear velocity
profile was used to calculate the instantaneous shear gradient at the wall. The electrodiffusion probe requires presence of
a suitable electrolyte (e.g. an iodine and potassium-iodine aqueous solution) for reduction of the species on the working
electrode (cathode). This results in a concentration gradient of the ions due to the convective diffusion of the I3]- to the cathode.
Due to the limited molecular diffusion rate and due to the dimension of the electrodiffusion probe its frequency resolution
is limited. It is shown in which limits the correction of the signal on the concentration boundary layer inertia is not necessary
and the probe can be used for measuring instantaneous wall shear gradients in turbulent flows. The results are compared with
those obtained by LDA and elucidate the capability of the ED probe for measuring instantaneous shear rates at low Reynolds
numbers.
Received: 25 October 1995/Accepted: 16 July 1996 |
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