Procedia Engineering 39 ( 2012 ) 68 – 75

1877-7058 © 2012 Published by Elsevier Ltd.doi: 10.1016/j.proeng.2012.07.009

XIIIth International Scientific and Engineering Conference “HERVICON-2011”

The Francis Pump Turbine With Stochastic Blades

František Pochylýa, Miloslav Haluzab, Jind ich Veselýc, c*

abBrno University of Technology, Institut of Power Engineering, Technická 2896/2, CZ - 616 69 Brno, eská republika c KD Blansko Engineering, a.s., apkova 2357/5, CZ - 678 01 Blansko, eská republika

Abstract

In the article are introduced a special hydraulic designs of pump Francis turbines. There are compared characteristics of classical pump Francis turbine and stochastic blade pumps Francis turbine. There are introduced pump Francis turbines with inserted splitter blades in the runner and pump Francis turbines with stochastic blade cascade.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Sumy State University

Keywords: Pressure oscillation; pump turbine; stochastic; inserted splitter blades; characteristics.

1. Introduction

It is known, that in the work of pump turbine - high frequencies of pressure pulsation can occur. This pressure pulsations are generated by interaction between the runner and distributor. Thereby an

inception of pressure pulsations on frequencies depending on rotor rotation and combination of blades and vanes can occur.

The pressure pulsations can cause the oscillation of discs of the runner. This phenomenon is often present in the runners with a small number of blades, mainly in the Francis pump turbines. The prevention of the undesirable oscillations is possible in the stage of hydraulic design of the machine by tuning the system this way to prevent the turbine against frequency of resonance and on the real machine by retuning the system by inserting splitter blades.

* Corresponding author. Tel.: +420-541-14-2348. E-mail address: haluza.m@fme.vutbr.cz.

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69 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

2. Retuning of the runner by splitter blades

In the runners with small number of blades, coincidence of natural frequency with excitation frequency is possible. If this happens, it is necessary to retune the runner.

The easiest way is inserting splitter blades into the interblade channel of the runner, see fig.1. This splitter blade must be designed so that it alignes with streamlines of relative velocities. The spectrum of excitation is possible to affect by method by unequal wrap angle , ( the distance a is

not equal to the distance b) (see fig.1). This reconstruction can cause retuning and the change of excitation. From the point of view of hydraulic efficiency it is necessary to design the leading edge without the

shock. It is possible to set Angle M the same as angle . This way it is possible to obtain the splitter blade with different M angle as well as to obtain the same hydraulic efficiency.

Fig. 1. Inserted splitter blades

Fig. 2. Flow in the channel

In the fig. 2 , there is possible to see the actual design of the runner of Francis pump turbine .

70 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

In the next figures (fig.3,4,5) it is possible to see the comparison of pressure pulsations of both designs (with and without splitter blades).

Fig. 3. Pump mode (7 blades, 9 blades, 7+splitter blades)

Fig. 4. Pump turbine (7 blades)-turbine

71 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

Fig. 5. Pump turbine with splitter blades

Fig. 6. Pressure pulsation – draft tube

72 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

Fig. 7. Pressure pulsation –spiral case

In the figure 8, there is an illustration of an amplitude-frequency characteristic. If we look on the different variants of solution, it is necessary to aim our attention on comparison of

the hydraulic design with 7 blades (original runner) and on the runner with 14 blades (7 splitter blades included).

The aim was only retuning the runner (characteristic fig. 8), the hydraulic characteristic is not deteriorated.

Fig. 8. Amplitude – frequency characteristic

The modification of M angle can improve the hydraulic relations.

73 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

But this modification was not realized, on this experience the design of 9 bladed runner had been done, see figure 3.

3. The runner with non-uniform blade cascade

3.1. Francis pump turbine

Nowadays pump turbines are requested (besides pressure pulsations restriction and undesirable resonance frequency elimination) to operate in extended range of regimes, but still with good efficiency..

It is possible to reach this aim by hydraulic design of Francis pump turbine runner with stochastic blades.

This runner is depicted in the fig.4.

Fig. 9. Runner blade cascade with 9 blades of the heterogeneous runner

The number of blades is 9, there are three same blades, it means there are three groups of three different blades.The aim was to change the spectrum of frequency excitation and to reach high hydraulic efficiency.

Comparison of runners with uniform blades and stochastic blades is introduced in following figures,see fig.10,11,12.

74 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

Fig. 10. Measurement of pressure pulsation

f=142Hz=142Hz

Harmonic Response Characteristic

0

0.2

0.4

0.6

0.8

1

1.2

1.4

100 125 150 175 200 225 250 275 300 325

Excitation frequency [Hz]

Rel

ativ

e D

evia

tio

n [

1]

9 Blades Homogenous9 Blades - New Design

f=227Hz

f=208Hz

f=265Hz

Fig. 11. Harmonic response characteristic

75 František Pochylý et al. / Procedia Engineering 39 ( 2012 ) 68 – 75

Pump Mode - Wicket Gate Opening a0/a0opt=1.0

90

92

94

96

98

100

102

104

60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135

Q/Qopt [%]

ηη ηηre

l[%

]

9Blades-Homogeneous-Model Test

9 Blades-Homogeneous-CFD

9 Blades-Heterogeneous-CFD

9 Blades-Heterogeneous-Model Test

Turbine Mode - Wicket Gate Opening a0/a0opt=1

90

92

94

96

98

100

102

104

75 80 85 90 95 100 105 110 115 120

n11/n11opt [%]

ηη ηηre

l[%

]

9 Blades-Homogeneous-Model Test

9 Blades-Homogeneous-CFD

9 Blades-Heterogeneous-CFD

9 Blades-Heterogeneous-Model Test

Fig. 12. Comparison of efficiency between model test and CFD simulation

It is possible to find conclusions:

• Mechanical design is comparable to classical design with homogenous blade passages. • Efficiency level of the heterogeneous runner is high. • Pump turbine can be operated in wide operating range with higher efficiency level. • Pressure pulsations in pump turbine are supressed in case of application heterogeneous blade

passage. • Pressure field in vaneless area is shifted to lower frequencies in turbine mode. • Pressure pulsations in pump mode are considerably decreased especially in unstable areas. • Cavitation features are affected by different blade shape at turbine trailing edge • The concept is suitable for pump turbines which operate with high unit speed.

Acknowledgement

This work was gratefully acknowledged by grant projects: GA101/09/1715, GA101/09/1716

References

[1] Pochylý F.: Persistence extending of the runner of pump Francis turbines (in Czech language). Research Report n. VUT-

EU13303-QR-08-06, Brno, May, 2006.

[2] Veselý J., Obrovský J., Mikulášek J.: Theoretical and practical results of hydraulic research of stochastic blade passage

application in hydrodynamic machines. Conference Hydro – 2010, Lisbon, Portugal, 2010.

[3] Veselý J., Pochylý F., Obrovský J., Mikulášek J.: A New Concept of Hydraulic Design of Water Turbine Runners. IAHR

24th Symposium on Hydraulic Machinery and Systems, October 27-31, Foz do Iguassu, Brasil, 2008

[4] Veselý J., Mikulášek J., Obrovský J.: Stochastic Hydraulic Design for Low Specific Speed Pump Turbine Runner.

Waterpower XVI, Spokane, USA, 2009.