Onboard Measurements of Pressure and Strain Fluctuations in a Model of low Head Francis Turbine. Part 1 : Instrumentation

In this first part of a 2 papers series, we present the experimental procedure for onboard measurement of pressure and strain fluctuation in a model of low head Francis turbine. 28 miniature pressure sensors are fitted in the pressure and suction sides of two consecutive blades. A specific technique for sensors mounting has been developed allowing a direct manufacturing of the pressure sensors in the runner blades. This prevents from any geometry alteration of the hydraulic profile. Furthermore, miniature piezo electric strain gauges, 70 times more sensitive than conventional gauges, are embedded in pressure and suction side of 2 runner blades. Data acquisition is ensured by 32 channels onboard digitiser, having 12 bits resolution, 64 K-samples memory depth and 20 kHz maximum sampling frequency. Both static and dynamic calibration procedures of the pressure transducers are described. Analysis of experimental results and comparison with CFD calculation are presented in the second part (Ref. 7).