# Quantification expérimentale et numérique de l'agressivité de cavitation

Abstract : Cavitation is a major issue in hydraulic machinery, due to its negative consequences: performance drop, vibrations increase and damage.This PhD is dedicated to cavitation erosion and aims to propose tools in order to quantify the erosive potential of a cavitating flow.Experiments were carried out on a symmetrical hydrofoil based on a NACA0015 with a flat area between 27% and 70% of the chord length for an easy instrumentation with pressure sensors.The study is focused on partial cavitation that detaches from the leading edge of the hydrofoil and periodically sheds vapor clouds.All experiments are conducted in the LEGI cavitation tunnel, partly renovated for the new purposes of this PhD.Meanwhile, numerical calculations are performed with the in-house 2D cavitating unsteady code IZ developed at LEGI.Flow analyses are based on high-speed videos and numerical simulations.These analyses give the cavity dynamics, the maximum cavity length and the shedding frequency.The influence of the hydrodynamic parameters (flow velocity, hydrofoil angle of attack, cavitation number) on the cavity behavior is studied.Strong 3D effects observed experimentally make it difficult to predict the cavity dynamics with the two-dimensional code. Nevertheless the maximum cavity length and the shedding frequency are well predicted numerically.A matrix of eight sensors, with an active area of 2x2~mm$^2$, was made and flush mounted on the hydrofoil between 30% and 67% of the chord length.These sensors allow measuring pressure peaks due to the collapse of vapor structures on the hydrofoil surface. Acquisitions are made simultaneously on the eight sensors at a sampling rate of 10 MHz.The flow aggressiveness is estimated experimentally from the peak frequency distribution as a function of the peak amplitude.Numerically an aggressiveness parameter is defined from a model developed previously at LEGI. This parameter allows estimating an instantaneous and mean aggressiveness at the surface of the hydrofoil.The origins of the most aggressive areas are identified from local studies.Comparison between experimental and numerical results shows that the numerical approach overestimates the aggressiveness close to the hydrofoil leading edge.Globally, the experimental and numerical results are in pretty good agreement for low incidence.The most aggressive area is localized at the cavity closure and the flow velocity has a huge influence on the aggressiveness level.
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Submitted on : Tuesday, September 11, 2018 - 11:19:07 AM
Last modification on : Thursday, January 3, 2019 - 4:30:09 PM
Document(s) archivé(s) le : Wednesday, December 12, 2018 - 2:31:00 PM

### File

CARRAT_2018_archivage.pdf
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### Identifiers

• HAL Id : tel-01871731, version 1

### Citation

Jean-Bastien Carrat. Quantification expérimentale et numérique de l'agressivité de cavitation. Matériaux. Université Grenoble Alpes, 2018. Français. ⟨NNT : 2018GREAI044⟩. ⟨tel-01871731⟩

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