energies Article Experimental and Numerical Studies on the Inﬂuence of Blade Number in a Small Water Turbine Grzegorz Peczkis 1, *, Piotr Wi´ sniewski 1 and Andriy Zahorulko 2   Citation: Peczkis, G.; Wi´ sniewski, P.; Zahorulko, A. Experimental and Numerical Studies on the Inﬂuence of Blade Number in a Small Water Turbine. Energies 2021, 14, 2604. https://doi.org/10.3390/en14092604 Academic Editor: Davide Astolﬁ Received: 23 March 2021 Accepted: 26 April 2021 Published: 2 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional afﬁl- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Power Engineering and Turbomachinery, The Silesian University of Technology, 44-100 Gliwice, Poland; piotr.wisniewski@polsl.pl 2 Volodymyr Martsynkovskyy Computational Mechanics Department, Sumy State University, 40007 Sumy, Ukraine; a.zagorulko@omdm.sumdu.edu.ua * Correspondence: grzegorz.peczkis@polsl.pl Abstract: This paper demonstrates the procedure of blade adjustment in a Kaplan-type water turbine, based on calculations of the ﬂow system. The geometrical adjustment of a twisted blade with varying chord length is described in the study. Computational ﬂuid dynamics (CFD) analysis was used to characterise aerofoil and turbine performance. Furthermore, two turbines, with a different number of blades, were designed, manufactured, and tested experimentally. The numerical model results were then compared with the experimental data. The studies were carried out with different rotational velocities and different stator blade incidence angles. The paper shows a comparison of the turbine efﬁciencies that were assessed, using numerical and experimental methods, of a ﬂow system with four- and ﬁve-bladed rotors. The numerical model results matched up well with those of the experimental study. The efﬁciency of the proposed turbines reached up to 72% and 84% for four- bladed and ﬁve-bladed designs, respectively. These efﬁciencies, when considered with the turbine’s simplicity, low production and maintenance costs, as well as their potential for harvesting energy from low energy ﬂows, mean that Kaplan turbines provide a promising technology for processing renewable energy. Keywords: small water turbines; renewable energy; Kaplan turbine; CFD 1. Introduction In recent times, there has been a strong interest in replacing conventional power plants, powered by fossil fuels, with renewable energy sources [1]. Individually, many European countries have pushed development in their energy sectors towards nuclear, wind, and solar power. The introduction of biomass and weather-fuelled power generation to the energy grid has increased expectations of emission-free energy systems. Hydropower technologies can help to fulﬁl these expectations. In well-developed countries, hydropower technologies are already commonly used to harvest power from high-energy water sources; however, lower-energy water sources are mostly not [2]. Consequently, small water turbines are experiencing a renaissance [3–5]. The need for harvesting energy from relatively small water ﬂows, which has been disregarded for years, creates challenges for engineers to design systems since ready- made algorithms are not available in the literature. New water turbine systems have to be designed since the operating conditions are very different than those used for large water ﬂows. Many innovative, small turbines are now being developed to ﬁll the previous void; one example of these is jet turbines. New prototypes are also being developed that combine new design concepts with tried and tested classical designs. Due to the ongoing improvement of numerical tools, it has become much easier to improve the efﬁciency of turbine designs. However, this has resulted in the temptation to continuously make small improvements, which, for relatively simple and cheap constructions, is not economically justiﬁed [6]. Energies 2021, 14, 2604. https://doi.org/10.3390/en14092604 https://www.mdpi.com/journal/energies