Enhancing the efficiency of an axial impulse turbine with a diffuser


  • Geetam Saha Virginia Tech https://orcid.org/0000-0003-0968-6806
  • Diogo Neves Ferreira Instituto Superior Técnico, Universidade de Lisboa
  • Narasimalu Srikanth Nanyang Technological University, Singapore
  • Lei Zuo University of Michigan, Ann Arbor




Oscillating Water Column, Wave Energy, Impulse turbine, Self-Rectifying Turbines


In oscillating water column wave energy converters, the aerodynamic losses caused by flow misalignment between the rotor outlet and the outlet guide vane of self-rectifying impulse turbines are a significant design problem. The symmetrical positioning of guiding vanes on both sides of the rotor is the reason for it. In comparison to the equivalent Wells turbine, the efficiency of impulse turbines is lower because of these losses in the outlet guide vane. This paper presents a strategy to develop an
improved design of an axial impulse turbine to reduce the losses in the outlet guide vane along with the residual kinetic energy loss by integrating a diffuser between the rotor and guide vanes. The proposed model was investigated numerically using RANS simulations. Multiple diffuser geometries were tested against the reference turbine for comparison of the performance characteristics. The results support the hypothesis behind the proposed design. The performance was compared extensively with the reference case in terms of the dimensionless loss coefficients for a better insight into the contribution of all the turbine sectors. The current work shows a possible design path for the performance improvement of the turbine. Results also support the fact that the guide vanes need to be
redesigned for obtaining maximizing efficiency with the proposed design. The losses in the outlet guide vane were reduced by approximately 50% with an overall efficiency rise of around 2%. 

Author Biographies

Geetam Saha, Virginia Tech

Geetam is a first-year Ph.D. student at Virginia Tech, Mechanical Engineering. His research interests include marine energy extraction devices, turbomachinery, and computational fluid dynamics. He got involved in a variety of research works during the course of his undergraduate studies such as the design of oscillating water column (OWC) wave energy converters for low wave heights, optimization of air turbines for OWC applications, the aerodynamic study of high-rise buildings under wind excitation.

Narasimalu Srikanth, Nanyang Technological University, Singapore

Dr. Narasimalu Srikanth joined Energy Research Institute @ NTU (ERI@N) as a Senior Scientist and Programme Director, leading the Wind & Marine research team. He has more than 25 years of Industrial experience and earlier he was with Vestas Wind systems as a senior specialist in the Technology department, leading some of the key research activities related to aeromechanics and condition monitoring specialization of wind turbines.

Prior to this appointments, he also served ASM Technology Singapore leading the research and development of semiconductor equipment and with Tata engineering (TELCO) at Pune (India) focusing on heavy machinery design. He received his first masters from Indian Institute of Technology, Bombay, India in machine design and his second masters in materials engineering and his first PhD in the area of mechanical engineering and a second PhD in Technology Management from National University of Singapore (NUS).

Dr. Narasimalu has published in more than 90 international journals and has more than 30 patents. His areas of technical research interests are wind & tidal resource mapping marine & turbine development, structural health monitoring and simulation methods. He is a member of OES, ASME, ASM, ASPE, IEEE and MRS(S). 

Lei Zuo, University of Michigan, Ann Arbor

Lei Zuo joined in the University of Michigan-Ann Arbor as an endowed professor in August 2022. Prior to that, he was the Robert E. Hord Jr. Endowed Professor at Virginia Tech and Director of NSF Industry-University Collaborative Research Center for Energy Harvesting Materials and Systems. He conducts research and teaching in the area of marine renewable energy, energy harvesting, mechatronics design, vibration control, vehicle dynamics, smart structures and sensors, and advanced manufacturing. He has authorized about 360 papers, including over 10 with best paper awards. His research has been supported with over US$25M by NSF, DOE, ONR, DOT, EPA, USAID, US Army, national labs, NY and VA state agencies and industry. He has advised 16 PhD and over 50 masters to competition of their degrees and over 10 postdocs. He has been a Fellow of ASME since 2016.

Lei Zuo was the sole recipient of the 2017 ASME Leonardo da Vinci Award and the 2015 ASME Thar Energy Design Award, for “eminent achievement in the design or invention of a product which is universally recognized as an important advance in machine design,” and the 2015 ASME Thar Energy Design Award for “pioneering research in energy engineering, especially at large energy scale.” He also received R&D 100 Awards in 2011 and 2015, recognizing the 100 most significant technology innovations worldwide for those years. Lei Zuo received a 2014 SAE Ralph R. Teetor Educational Award, a 2014 EPA P3 award and three DOE American-Made Challenges Prizes (2019 and 2020).



How to Cite

G. Saha, D. N. . Ferreira, N. Srikanth, and L. . Zuo, “Enhancing the efficiency of an axial impulse turbine with a diffuser”, Proc. EWTEC, vol. 15, Sep. 2023.