Best Practice Advice AC6-15

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Key Fluid Physics

The runner rotation leads to fluctuations due to the interaction of runner blades with guide vanes (rotor?stator interaction). An balance of the runner or an asymmetry of the stator also leads to pulsations. These pulsations propagate to the spiral case and can interfere with each other. Rotor–stator interaction is determined by a combination of the numbers of guide vanes and runner blades. Different modes are excited depending on their ratio. The intensity of these pulsations is strongly influenced by the radial clearance between the guide vanes and the runner. The frequency of these pulsations is usually high and it is of the order of several tens of the runner rotation frequency. Karman vortices can be formed on the vanes of the stator, guide vanes or runner blades. Fluctuations associated with Karman vortices can resonate with the vane body. If the body is sufficiently flexible, its vibrations may have the opposite effect on the vortex street. The profile of the vane trailing edge has a significant impact on the intensity of these pulsations. Thus, this requires a high precision when manufacturing the trailing edge. The fluctuations associated with the Karman vortices have an even higher frequency, exceeding the runner rotation frequency by a factor of 100 or even more. However, the greatest problems are caused by low-frequency pulsations in the draft tube. There are different vibration – generating mechanisms, some of them are associated with the precession of the vortex core (PVC). Precession of the vortex core occurs under partial load (at a discharge rate of 0.5–0.85 of the optimal value), where the flow has a considerable residual swirl.

REFERENCES

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• Kuibin P. A., Litvinov I. V., Sonin V. I., Ustimenko A. S., & Shtork S. I. (2016). Modelling inlet flow in draft tube for different regimes of hydro turbine operation. Vestnik Novosibirsk State University. Series: Physics. 11(1), 56-65.
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• Minakov, A. V., Platonov, D. V., Dekterev, A. A., Sentyabov, A. V., & Zakharov, A. V. (2015a). The numerical simulation of low frequency pressure pulsations in the high-head Francis turbine. Computers & Fluids, 111, 97-205.
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• Minakov A., Platonov D., Litvinov I., Shtork S., Hanjalić K. (2017) Vortex ropes in draft tube of a laboratory Kaplan hydroturbine at low load: An experimental and LES scrutiny of RANS and DES computational models. Journal of Hydraulic Research 55(3), 668-685
• Nicoud, F., & Ducros, F. (1999). Subgrid-scale stress modelling based on the square of the velocity gradient tensor. Flow, Turbulence and Combustion, 62(3), 183-200.
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• Skripkin, S., Tsoy, M., Shtork, S., & Hanjalić, K. (2016). Comparative analysis of twin vortex ropes in laboratory models of two hydro-turbine draft-tubes. Journal of Hydraulic Research, 54(4), 1-11. http://dx.doi.org/10.1080/00221686.2016.1168325.
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Contributed by: A. Minakov [1,2], D. Platonov [1,2], I. Litvinov [2], S. Shtork [2], K. Hanjalić [3] — 

[1] Institute of Thermophysics SB RAS, Novosibirsk, Russia,

[2] Siberian Federal University, Krasnoyarsk, Russia,

[3] Delft University of Technology, Chem. Eng. Dept., Holland.

Front Page

Description

Test Data

CFD Simulations

Evaluation

Best Practice Advice