Detection of cavitation vortex in hydraulic turbines using acoustic techniques

27th IAHR Symposium on Hydraulic Machinery and Systems

Candel, I.^1 ; Bunea, F.^2 ; Dunca, G.^3 ; Bucur, D.M.^3 ; Ioana, C.^1 ; Reeb, B.^4 ; Ciocan, G.D.^5

Gipsa-lab, Grenoble Institute of Technology, France^1

National Institute for R and D in Electrical Engineering ICPE-CA, Bucharest, Romania^2

Power Engineering Faculty, Politehnica University of Bucharest, Romania^3

Electricité de France, Division Technique Générale, Grenoble, France^4

Laboratoire de Machines Hydraulique, Université de Laval, Québec, Canada^5

关键词: Acoustic techniques;    Adverse pressure gradient;    High order statistics;    Low-frequency response;    Mechanical elements;    Resonance phenomena;    Vortex interactions;    Vortex-detection techniques;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/22/5/052007/pdf
DOI  :  10.1088/1755-1315/22/5/052007

来源: IOP

【 摘 要 】

Cavitation phenomena are known for their destructive capacity in hydraulic machineries and are caused by the pressure decrease followed by an implosion when the cavitation bubbles find an adverse pressure gradient. A helical vortex appears in the turbine diffuser cone at partial flow rate operation and can be cavitating in its core. Cavity volumes and vortex frequencies vary with the under-pressure level. If the vortex frequency comes close to one of the eigen frequencies of the turbine, a resonance phenomenon may occur, the unsteady fluctuations can be amplified and lead to important turbine and hydraulic circuit damage. Conventional cavitation vortex detection techniques are based on passive devices (pressure sensors or accelerometers). Limited sensor bandwidths and low frequency response limit the vortex detection and characterization information provided by the passive techniques. In order to go beyond these techniques and develop a new active one that will remove these drawbacks, previous work in the field has shown that techniques based on acoustic signals using adapted signal content to a particular hydraulic situation, can be more robust and accurate. The cavitation vortex effects in the water flow profile downstream hydraulic turbines runner are responsible for signal content modifications. Basic signal techniques use narrow band signals traveling inside the flow from an emitting transducer to a receiving one (active sensors). Emissions of wide band signals in the flow during the apparition and development of the vortex embeds changes in the received signals. Signal processing methods are used to estimate the cavitation apparition and evolution. Tests done in a reduced scale facility showed that due to the increasing flow rate, the signal - vortex interaction is seen as modifications on the received signal's high order statistics and bandwidth. Wide band acoustic transducers have a higher dynamic range over mechanical elements; the system's reaction time is reduced, resulting in a faster detection of the unwanted effects. The paper will present an example of this new investigation technique on a vortex generator in the test facility that belongs to ICPE- CA.