Laboratory modeling of flow regimes in a draft tube of Francis hydro-turbine

Sergey Shtork,Kemal Hanjalic,Ivan Litvinov,Andrey Mitryakov,P Dančová

doi:10.1051/epjconf/201714302103

Sergey Shtork, Kemal Hanjalic + Show 3 more

Open Access

https://doi.org/10.1051/epjconf/201714302103

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Abstract

The paper reports on some results of the experimental study of flow and pressure pulsations in a laboratory model of the draft tube (DT) of Francis-99 hydro-turbine over a broad range of operating regimes. Velocity distributions at the model inlet varied within 866 modes of the turbine load conditions, including those with maximum coherent pressure pulsations on the model walls. The contact and non-contact methods were used to measure pressure pulsations on the model walls using acoustic sensors and to measure the averaged velocity distribution with a laser Doppler anemometer “LAD-06i”. Analysis of the results have showed that in the model cone there are flow modes with forming of precessing vortex cores, accompanied by a sharp increase in the amplitude of coherent pressure pulsations on the wall and the velocity field rearrangement. It is shown that the vortex core starts forming with an increase in the integral parameter of swirl up to S>0.5. A novelty of the work is the combination of the rapid prototyping (3-d printing) of the inflow swirl generators and computerized measurement techniques that makes it possible to acquire rapidly a large amount of experimental data for a variety of designs and operating conditions. The results can provide insight into the effect of various design and operating parameters on the flow physics, as well as serve for verification of the numerical simulations.

Highlights

The growing energy consumption nowadays imposes high requirements to the hydroelectric power plants
It is seen that the dominant peak in the spectra, which is associated with the rotation frequency of the precessing vortex, first increases in its level, and starting from the flow rate 0.39Qc reaches maximum at the flow rate of 0.49Qc, and at 0.79Qc disappears completely from the spectrum
These pulsations are most likely caused by the precessing vortex core, which is formed in the cone of the draft tube at nonoptimal operation modes

Summary

Introduction

The growing energy consumption nowadays imposes high requirements to the hydroelectric power plants. Varying the generator load results in short-term changes in rotation frequency of the turbine impeller, thereby the flow behind it becomes swirling This leads to the formation of unsteady flow regimes under which the vortex instability of the swirling flow behind the impeller is formed. The work [11,12] presents a method that using a combination of fixed and rotating vane swirlers allows reproducing velocity distributions at the inlet of the draft tube model, which are very close to those behind the full-scale Francis turbine. A clear relationship between the velocity distribution behind the impeller and the level of pressure pulsations caused by the PVC are not fully understood either It is in this context, the present work investigates the flow regimes with strong pressure pulsations in the model draft tube of hydraulic turbine, the vortex nature of these pulsations and relation to the PVC effect. Analysis of the velocity distributions allowed identifying indicators of the PVC formation by varying the input parameters of the test stand

Experimental techniques

Results

Conclusions