Experimental investigation of the mass flow gain factor in a draft tube with cavitation vortex rope

HYPERBOLE Symposium 2017 (HYdropower plants PERformance and flexiBle Operation towards Lean integration of new renewable Energies)

Landry, C.^1 ; Favrel, A.^2 ; Müller, A.^2 ; Yamamoto, K.^2 ; Alligné, S.^1 ; Avellan, F.^2

Power Vision Engineering Sàrl, Chemin des Champs Courbes 1, Ecublens

1024, Switzerland^1

EPFL Laboratory for Hydraulic Machines, Avenue de Cour 33bis, Lausanne

1007, Switzerland^2

关键词: Cavitation compliance;    Cavitation vortex ropes;    Experimental identification;    Experimental investigations;    Mass flow gain factor;    Operating condition;    Quasi-static methods;    System stability analysis;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/813/1/012022/pdf
DOI  :  10.1088/1742-6596/813/1/012022

来源: IOP

【 摘 要 】

At off-design operating operations, cavitating flow is often observed in hydraulic machines. The presence of a cavitation vortex rope may induce draft tube surge and electrical power swings at part load and full load operations. The stability analysis of these operating conditions requires a numerical pipe model taking into account the complexity of the two-phase flow. Among the hydroacoustic parameters describing the cavitating draft tube flow in the numerical model, the mass flow gain factor, representing the mass excitation source expressed as the rate of change of the cavitation volume as a function of the discharge, remains difficult to model. This paper presents a quasi-static method to estimate the mass flow gain factor in the draft tube for a given cavitation vortex rope volume in the case of a reduced scale physical model of a ν = 0.27 Francis turbine. The methodology is based on an experimental identification of the natural frequency of the test rig hydraulic system for different Thoma numbers. With the identification of the natural frequency, it is possible to model the wave speed, the cavitation compliance and the volume of the cavitation vortex rope. By applying this new methodology for different discharge values, it becomes possible to identify the mass flow gain factor and improve the accuracy of the system stability analysis.