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Résumé :
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This report presents the results of research into the development of a modified Preston tube fot the measurement of boundary shear stresses in hydraulically smooth channels. Modifications made to the conventionnal tube comprise the adddition of a "wake" pressure tube to which Preston , which relies on static pressure measurements from wall tappings. Initial development and calibration of the modified Preston tube, was experimentally undertaken using air in a closed circular conduit . this work confirmed the applicability of revised Preston tube calibration relationships by Patel and produced a new relationship between Roving Preston tube and equivalent Preston tube differential pressures. Verification and furthe development of the RPT concept was undertaken using water in an open channel. Shear stresses were measured whithin the range 0.2 to 1.8 Nm2. Average boundary shear stresses, derived from integration of measured distributions within the channel, were in good agreement with those estimated from energy grade line slopes associatedwith flow within the channel. Research undertaken by others has investigated the use of the Preston tube under a variety of flow conditions, and concluded it to be well suited to the measurement of boundary shear stresses in both closed and open conduits. Development and calibration of the RPT essentially comprised extensions to Preston's original technique . In view of the good experimental correlations obtained between average RPT and energy grade line sloope derived shear stresses, it is concluded that the RPT technique may e reliably applied to the measurement of boundary shear stresses.
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