Francisco Pereira

Measurement and Modeling of Propeller Cavitation in Uniform Inflow

An experimental and theoretical investigation on a cavitating propeller in uniform inflow is presented. Flow field investigations by advanced imaging techniques are used to extract quantitative information on the cavity extension. A refined map of the propeller cavitating behavior is established. Measurements are compared to numerical results obtained using an inviscid flow boundary element method for the analysis of blade partial sheet cavitation and supercavitation. The effect of the trailing wake vorticity on the prediction of the cavitation pattern is analyzed via a wake alignment technique

Prediction of Cavitation Erosion : an Energy Approach

Note: Using Smart Source Parsing pp 3 Reference LMH-ARTICLE-1998-003View record in Web of Science Record created on 2005-11-04, modified on 2017-05-10

Dynamic calibration of transient sensors by spark generated cavity

The cavitation erosion in hydraulic machines is often due to repeated collapses of transient vortices shed by the main cavity attached to the leading edge of the blades. Vibratory approach in detection of cavitation erosion has shown that the cavitation induced noise may be used to measure the aggressiveness of a given cavity development. These measurements require the use of transient sensors such as pressure or acceleration sensors. Most of time, the frequency responses of such transducers are provided by the manufacturers but they are no longer valid because of their specific mounting. Thereby, one has to perform unsteady calibration on site. Thus, we propose to use an instrumented underwater spark generator which allows the generation of an exploding bubble. The resulting pressure impulse, similar to that induced by the cavitation collapse, is used to excite the transducers in a wide frequency band. Preliminary study of this new calibration system shows that the exploding bubble generates intense shock waves with resulting over pressure that may reach up to 1’700 MPa within a duration less than 5 μs. Validation of this new technique is performed in the IMHEF high speed cavitation tunnel. 30 piezoresistive pressure transducers mounted on a NACA009 hydrofoil are thus calibrated by introducing the spark generator in the test section.

Cavitation Erosion Prediction on Francis Turbines Part 1 : Measurements on the Prototype

In the process of developing tools for cavitation erosion prediction of prototypes from model tests, 4 on board aggressiveness evaluation methods were tested on a severely eroded blade of a 266 MW Francis turbine. These are pressure, pit counting, DECER electrochemical and vibration measurements. All methods provided coherent results on the blade mounted measurements. The test program provided understanding of the heterogeneous erosion distribution of the prototype blades and quantitative data for comparison in subsequent tests on the model of the machine.

Developments and Applications of PIVin Naval Hydrodynamics

In this chapter, particle image velocimetry (PIV) is introduced as an essential tool for flow diagnostics in the field of naval hydrodynamics. The needs and requirements that the PIV technique is expected to meet in this particular sector are examined in Sect. 2. In Sect. 3, we review some of the most recent applications of experimental naval hydrodynamics and the technological solutions chosen to address the scientific challenges involved therein.

A VERSATILE FULLY SUBMERSIBLE STEREO-PIV PROBE FOR TOW TANK APPLICATIONS

A unique, highly modular and flexible underwater system for stereoscopic particle image velocimetry (PIV) measurements has been designed, manufactured and tested. The instrument is intended for planar three-dimensional velocity measurements in large facilities such as water tow tanks and tunnels. The performance of the system is assessed in four major stereoscopic configurations. Errors under 2% for the inplane components and 4% for the out-of-plane components are found. The system is tested in the INSEAN large circulating water channel where the measurement of the flow around a model ship oriented at a moderate yaw angle is performed and puts into evidence the main features of the flow.

Velocity and Wall Pressure Correlations Over a Forward Facing Step

This work describes an experimental study of the flow field and wall pressure fluctuations induced by quasi-twodimensional incompressible turbulent boundary layers overflowing a forward-facing step (FFS). Pressure fluctuations are measured upstream and downstream an instrumented FFS step model installed inside a large-scale recirculation water tunnel while two dimensional velocity fields are measured close to the step via time-resolved PIV. The overall flow physics is studied in terms of averaged velocity and vorticity fields for different Reynolds number based on the step’s height. Pressure spectra and cross-correlations are measured as well, and the convection velocity characterizing the propagation of acoustic and hydrodynamic perturbations is computed as a function of the distance from the vertical side of the step. The evolution of the overall Sound Pressure Level measured at the wall shows that the most critical flow structure is the reattachment region downstream the step where an unsteady recirculation bubble is formed.