– Background

Flexible electricity demand and low profit margin have pushed hydro turbines to their extreme operating limit. The turbines are often operated at unfavourable load, which has raised significant concerns for the hydropower industry and has challenged the existing design criteria. In fact, the main requirement for modern turbines is high efficiency over the whole operating range. However, this is difficult to obtain.

Computational fluid dynamic (CFD) techniques have been extensively used in turbine design. There are significant challenges in the numerical modelling due to complex flow structure in the turbine. A particular technique applied to an operating load does not work for another operating load of the same turbine. This results in a time consuming process, which makes the numerical modeling of the hydraulic turbine expensive in terms of the requirement of computational power and time. In a competitive market higher cost is not affordable. Therefore, there is a need to optimize the CFD modelling applied to investigate the hydro turbines.

Moreover, due to confidentiality, none of the modern turbine designs are available in public domain. This makes it difficult for engineers/researchers to explore their skill and knowledge in evaluating hydro turbine designs. The academicians do not have access to the modern design techniques adopted by the industries except through collaborating work.

Francis-99 is a series of three workshops, which provides an open access of the complete design and data of a model Francis turbine. It provides an open platform to the hydropower researchers and it gives the possibility to explore their capabilities and enhance their skills. In fact, this is the main objective of the workshops. The researchers can use these data and perform numerical studies by applying different tools and techniques.

Three workshops have been planned. The first workshop concentrates on the steady state operating condition of the Francis turbine. The second workshop concentrates on the transient operating conditions such as load variation and start-stop. The third workshop concentrates on the fluid structure interaction in the Francis turbine. For more information, please visit the webpage for each workshop.

Waterpower Laboratory
Waterpower Laboratory
Photo: Chirag Trivedi, 02 July 2015.

The Waterpower laboratory is actively involved in research and development of hydro turbines since 1917. It consists of a flexible infrastructure, which gives the possibility to operate test rigs in open and close loop configurations. There are two turbine test rigs, Francis turbine/pump-turbine and Pelton turbine, and several piping loops for the investigations of water hammer, surging, pressure-time method, etc. Laboratory personnel conduct field measurements such as efficiency measurement, pressure pulsations, vibration, etc. The turbine testing is conducted according to IEC 60193 and IEC 60041.

The close loop piping system in the Waterpower laboratory can be pressurised to maximum of 100 m and the open loop system has a maximum head of 16 m. Available pumping power is 700 kW and the maximum flow rate is 1.1 m3 s-1. Achieved maximum hydraulic efficiency of the model Francis turbine is 93.4%. Pressure and velocity measurements are frequently conducted in the laboratory. An average of one PhD thesis, ten master thesis, and ten student projects are conducted per year. The laboratory is actively involved in research and development projects through industrial and academic collaborations, and it always encourages young researchers and welcomes to conduct research. Ongoing PhD level research work in the laboratory can be found here.

Francis turbine
Test rig of the model Francis turbine/pump-turbine. Complete view of spiral casing, draft tube cone, elbow, and draft turbine outlet connected to the downstream tank. Pressure and velocity (LDV and PIV) measurements can be conducted in the transparent section of the draft tube cone.
Photo: Chirag Trivedi 29 May 2012.
Francis turbine pumping system
Pumping system for Francis turbine test rig. Both pumps can develop head over 100m when they are operated in series.
Photo: Chirag Trivedi 29 May 2012.

The model Francis turbine utilized for Francis-99 is a scaled model of the turbines operating at Tokke power plant in Norway. The Francis turbine has a splitter blade runner, which includes 30 blades. The runner outlet diameter is 0.349 m. The obtained maximum hydraulic efficiency of the turbine is 93.4% at the best efficiency point and the uncertainty was +/- 0.16% [1]. The test rig is extensively used for the model testing and for specific investigations such as rotor stator interaction, vortex rope, rotating stall with pump-turbine runner, water hammer, cavitation, etc. The open loop hydraulic system is used to perform transient measurements such as load variation, start-stop, and total load rejection. Moreover, strict guidelines are used for the calibration of each instrument utilized during the measurements. Complete history of the calibrated instruments is maintained for reference study in order to observed any deviation of the characteristics over  time.

[1] Chirag Trivedi, 2014, Experimental and numerical investigations on steady state and transient characteristics of a high head model Francis turbine, Ph. D. thesis, Indian Institute of Technology Roorkee.

Francis runner
Francis turbine runner outlet
Photo: Chirag Trivedi 29 May 2012.

The model Francis turbine runner is scaled 1:5.1 to the prototypes operating at Tokke power plant. The leading edge profiles of the runner main blades and splitter blades are similar. The main blades are twisted around 180 degree from inlet to the outlet of the runner. The blade thickness at the trailing edge is 3 mm. Runner inlet and outlet diameters are 0.63 m and 0.349 m, respectively. The runner inlet height is 0.06 m and the specific speed is 0.27. Miniature pressure sensors are integrated in the runner to acquire pressure values during the measurements. Wireless telemetry system is used to transmit the pressure values from the runner to the stationary logging system. In Norway, the majority of the turbines are ranged from mid-head to high-head. This model turbine has played important role in the research and development of the high head turbines over the last decade.


Highlight of the first workshop

The first workshop was held 15th and 16th of December 2014 at the Norwegian University of Science and Technology. Various researchers have conducted extensive numerical studies on the high-head Francis turbine, and the obtained results were presented during the workshop. Approximately 50 researchers participated in the workshop, and 14 papers were presented. Almost all aspects of numerical studies were discussed during the workshop including numerical modelling, meshing, verification and validation, challenges in the numerical study, and how can numerical modelling be optimized. The detailed summary of the work is available here.

Group photograph (First workshop)
Group photograph of the first Francis-99 workshop
Photo: Chirag Trivedi 16 December 2014.

Mon, 18 Sep 2017 09:06:35 +0200