Prediction and analysis of the cavitating performance of a Francis turbine under different loads

ABSTRACT

The variations in the operating conditions of Francis turbines may lead to cavitation due to pressure pulsations in vanless space. In order to combat the fluctuations in power demand and input flow conditions such as net head and discharge, the turbine needs to be operated at off-design conditions. Due to the higher demand of medium-specific speed Francis turbine at most of the hydropower plants, it is necessary to predict the low-pressure zone and vapor bubbles formation on the surface of turbine runner blades. Under the present study, it is proposed to investigate the cavitation and performance characteristics of a medium-specific speed Francis turbine. In order to resemble the fluctuations in load, three different operating regimes, i.e. part-load, rated load and over-load, were considered to especially highlight the performance under cavitation and without cavitation conditions of the turbine. Based on investigations, it has been revealed that turbine experiences a minimum drop in hydraulic efficiency corresponding to rated-load operation and the maximum drop in efficiency was observed during the over-load operation. The pressure variations across the runner blades were observed at mid-span of the blade in stream-wise direction. The cavitation characteristics of the turbine were derived by using the sigma curve and the vapor volume fraction. The critical values of sigma for part-load, rated-load, and over-load regimes were obtained as 0.18, 0.12, and 0.16, respectively. The results obtained under the present investigation were verified by the experimental model testing results of the turbine.

KEYWORDS:

• Renewable energy
• hydropower
• Francis Turbine
• cavitation
• hydraulic efficiency

Nomenclature

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Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Mustafa Kamal

Md. Mustafa Kamal is pursuing Ph.D. from the Department of Hydro and Renewable Energy at IIT Roorkee, Roorkee, India. His work mainly focuses on hydro turbines and hydrokinetic turbines. He received his Masters from Maulana Azad National Institute of Technology, Bhopal, India in the field of hydropower engineering.

Gaurav Saini

Dr. Gaurav Saini is presently working as Assistant Professor in the School of Advanced Materials, Green Energy and Sensor Systems, Indian Institute of Engineering Science and Technology (IIEST) Shibpur India. He received his Ph.D. in Renewable Energy (Hydrokinetic Turbines) in the year 2020 and M. Tech, (Fluid Machinery and Energy Systems) in the year 2014 from Indian Institute of Technology Roorkee, Uttarakhand India. His research areas include Renewable Energy (Hydrokinetic Energy, Wind Power, and Biomass), Computational Fluid Dynamics (CFD), and Fluid Mechanics and Fluid Power. Dr. Saini is skilled in Computational Fluid Dynamics (CFD) - numerical modeling and roto-dynamics analysis, Multiphase flow analysis, Modeling of various renewable energy resources viz. wind, marine, solar and hydrokinetic energy for rural applications, wind and hydrokinetic- Technology selection and design, Installation strategies, Performance evaluation, and O&M issues.

Ali Abbas

Dr. Ali Abbas earned his Ph.D. from the Department of Hydro and Renewable Energy at IIT Roorkee, Roorkee, India. His work mainly focuses on the transient phenomena in the draft tubes of hydro turbines. He is currently working at Flovel Energy Pvt. Ltd., Faridabad, India, as a manager – Design and Engineering.

Vishnu Prasad

Dr. Vishnu Prasad is a Professor in the Department of Civil Engineering at Maulana Azad National Institute of Technology, Bhopal, India. He earned his Ph.D. in the field of hydropower. His work mainly focuses on fluid mechanics, hydropower, and CFD.