Cavitation Erosion Prediction on Francis Turbines-Part 3 Methodologies of Prediction

Abstract

Summary:In the frame of a joint research programme between EDF, HydroQuébec and IMHEF, different methods are investigated to predict cavitation erosion on Francis turbines from mode!. They are based on measurement of pitting, pressure fluctuations and acceleration. The measurement techniques have been detailed in Part I and Part 2. The present article describes essentially the theoretical and practical aspects of the methods and discusses the results obtained until now from the mode! and prototype tests. The first analysis shows that the methods proposed are suitable to measure cavitation aggressiveness on mode! and on prototype, and that the level on the mode! is several orders of magnitude smaller than on the prototype. To adjust transposition laws, a more complete set of data is needed.

Scaling study of cavitation pitting from cavitating jets and ultrasonic horns

“…Knapp [19][20][21] introduced the idea that the pits could be used to understand the intensity of the cavitation field. Similar ideas of observing pits to represent the cavitation field was used in hydraulic turbine cavitation erosion studies [22], where it was found that the cavitation aggressiveness in the full scale is more severe than that of the model scale. Recent studies using pitting tests includes the use of thin copper foil in order to capture relative small magnitude impacts [23], analysis of pitting to determine the impact loads for a modeling effort for ductile metals [24], evaluation of flow aggressiveness in the study of hydraulic turbine flows [25], and applications to the erosion studies of marine propellers [26,27].…”

Relationship between material pitting and cavitation field impulsive pressures

“…Cavitation pitting studies dates back to the early 1900's when Parsons and Cook [17] observed the depth and dimensions of the pitted areas on marine propellers. Since then, many researchers have tried to correlate the location of pitting with cavitation bubble clouds along with statistics of pit number and pit diameters and depths [2,[18][19][20][21][22][23][24]. More recently, pitting tests were also conducted using thin copper foil in order to capture relatively small magnitude impacts [25].…”