Évolution récente de la technique des jaugeages industriels aux moulinets dans les écoulements en charge

Abstract

Current meters have been in use for flow gauging purposes for a very long time. They are subject of stringent requirements, especially when used as a check on hydraulic machine performance. The very principle of their operation, however, is a source of uncertainty, consisting as it does in the use of a current meter calibrated in calm water in a flume to measure discharge in turbulent flow in an enclosed space. Methods of use based on sound experience have managed to keep this margin of error within reasonab1y close limits. The increasingly wide range of use of these instruments and the wish to achieve greater accuracy have been followed by intensified research, which has centred around the two most important effects discovered in previous research, namely (i) an 'interference' effect between the current meters and their supports and (ii) the effect of flow turbulence. This research has now progressed so far that it should soon be possible to reduce these effects, for example by a careful reappraisal and choice among existing equipment. On the current meter data output side, improvements have been made to the impulse emission system and to velocity and discharge calculation methods. Technological progress has also been made with ball-bearing and propeller manufacture, with the result that it should now be possible to cut down considerably on calibration operations, which would be replaced by simple propeller geometry and bearing opposing torque checks. Finally, two gauging methods for convergent streamline flow are mentioned, which tend to improve measurement accuracy in this field and which have recently been compared.