Ivan Božić

To determine the performance of a large-scale hydraulic turbine, it is common to conduct model tests in laboratory conditions and to recalculate the obtained results to the corresponding prototype. For this purpose, a large number of scale-up formulas have been developed and considered so far, and only the ones standardized by IEC 60193 and IEC 62097 are used. In these expressions, the prototype water temperature plays a role, however, in many cases its effect is neglected. In this paper, an analysis of the influence of water temperature on prototype characteristics (hydraulic efficiency) is presented. Moreover, a sensitivity analysis was carried out in order to assess the importance of a precisely defined prototype water temperature.

Reliable and stable operations of hydropower units are among the main priorities in the functioning of hydropower plants in extremely dynamic and demanding contemporary electric power systems. Everything that causes deviation from the stated priorities needs to be properly analyzed and, if possible, eliminated. Pressure pulsations that appear in a hydraulic turbine can have an impact on an increase in hydraulic oscillations and mechanical vibrations, structural damage, instability of the power transmitted to the generator, and resonance, as well as on a decrease in the efficiency of the hydropower unit. Numerous phenomena that occur during the exchange of energy in the hydraulic turbine flow domain cause pressure pulsations. Understanding fluid flow dynamics around an isolated hydro profile is the first and essential stage for optimizing the performance and the design of all types of hydraulic turbines. This paper provides an additional contribution to the unsteady water flow numerical analysis of the isolated NACA0009 hydro profile, truncated to 90% of its original length, in order to check and confirm the induced pressure pulsations. The simulations were conducted for different attack angles of the profile under constant outlet pressure and inlet flow velocity. Some of the numerical results were verified by the available experimental data and compared with other published results.

Understanding cavitation phenomena is fundamental for improving the design and efficiency of all types of hydraulic machinery and fluid-mechanical systems. This research provides an additional contribution to the unsteady numerical simulation of the NACA0009 hydroprofile, truncated to 90% of its original length, in order to check and confirm its various hydrodynamic characteristics in cavitating conditions, including pressure pulsations. Numerous simulations were performed for different attack angles of the profile under constant cavitation number and constant flow velocity, thus expanding the scope of analysis of pressure, lift, and drag coefficients. Some of the numerical results were verified by the available experimental data and compared with other published results. In addition to quantitative indicators for each flow condition, a visualization of cavitation cloud is also provided, showing better insight into the interaction of fluid and structure.

Small hydropower plants (SHPPs) have evolved in a sustainable way, providing clean, renewable and reliable electricity with minimal impact on the environment. This paper looks at the methodology for planning SHPPs, with a detailed case study of the Bistrica Majstorovina SHPP. The study outlines the technical, environmental and economic aspects of SHPP development, including site selection, design optimization and integration into local energy grids. It also examines the socio-economic benefits of SHPPs, such as improving the living conditions of the local population and promoting local economic growth. The Bistrica Majstorovina SHPP case study demonstrates the practical implementation of sustainable energy solutions and highlights best practices and lessons learned from project implementation. This paper provides a comprehensive framework for future SHPP projects, contributing to the wider adoption of sustainable energy practices.

To meet the growing demand for electricity generation, the use of renewable energy sources represents an ideal alternative to traditional resources. Compared to individual systems utilizing renewable energy sources, hybrid renewable energy systems (HRES) for electricity generation combine renewable energy sources and/or fossil fuels, providing more reliable electricity supply while achieving environmental and economic sustainability. It is crucial to optimally model all components of hybrid energy systems to meet overall electricity demands with minimal investment and operational costs. This paper provides an overview of currently available commercial software for optimizing hybrid renewable energy systems, with a specific focus on the software Homer (Hybrid Optimization of Multiple Electric Renewables). Approaches and phases of the optimization process for these systems are presented, as well as key parameters that must be considered during analysis.

Adopting adequate operational and safety measures is a significant part of the investigation of transient processes of hydropower plants (HPPs), both throughout the design stage of prospective plants and throughout the planning stage of the HPPs envisaged for refurbishment/uprating. One of the surge tank (ST) types, insufficiently researched so far, with a potential positive techno-economical influence, is the semi-pneumatic surge tank (SPST). Since the detailed analyses of SPST have never been performed or published before, the SPSTs have been examined here by presenting theoretical considerations, a newly developed mathematical model and comprehensive numerical simulations. The aim is to improve the performance of the open-air variations of STs. Multiple numerical simulations for a specific case-study HPP have been performed with the conclusions about the peculiarities and benefits of the SPST implementation. Firstly, numerical results for the existing as-built surge tank and corresponding alternative SPST have been compared, in order to verify the developed model. Variations of the main SPST constructive parameters have been analyzed, with the aim to determine the sensitivity of particular influences on transient processes versus its geometry alterations. The conducted analyses show that the SPST application brings HPP transient behaviour improvement compared to open-air ST. Dimensions of the new surge tank with specific aeration orifice could be smaller than the ones previously defined: both the diameter of the optimized upper and lower chamber and the core could be decreased by 20% and 12.5%, respectively.

Designing a small hydropower plant (SHPP) necessitates fulfillment of energy and ecological constraints, so a well-defined design flow is of the utmost significance. The main parameters of each SHPP are determined by appropriate techno-economic studies, whereas an improved approach to defining more precise SHPP installed parameter is presented in this paper. The SHPP installed parameter is the ratio of the design flow and averaged perennial flow obtained from the flow duration curve at the planned water intake location. Previous experiences in the design of SHPPs have shown that the SHPP installed parameter has a value in a wide range without the existence of an unambiguous equation for its determination. Therefore, with this aim, the thirty-eight (38) small watercources in the territory of Montenegro, denominated for the construction of SHPPs, have been investigated. SHPPs are divided into two groups depending on the installed capacity and the method of calculating the purchase price of electricity. For both groups, the range of SHPP installed parameter is determined according to the technical and economic criteria: the highest electricity production, the highest income, net present value (NPV), internal rate of return (IRR), and payback period (PB).

It is sometimes economically unreasonable to develop specific turbines, but rather to use a well-known concept of a pump in the turbine mode – PAT (Pump As Turbine). Inspired by PAT, the scope of this paper covers the assessments of the possibility to use marine propellers as runners for the hydrokinetic turbines. Numerical analyses are conducted for selected propeller geometry with the aim of evaluating its energy characteristics in the turbine regime. The chosen propeller belongs to the conventional, thoroughly experimentally tested, Wageningen B-screw series. The experimental data were used for validation of the numerical results in propeller regimes. Based on the obtained results, the researched non-optimized turbine in its optimum regime achieves a satisfactory power coefficient which is close to the value of other types of contemporary hydrokinetic turbines efficiencies.

Staining procedures in virtual H&E ex vivo microscopy is non-standardized, and image quality can be tuned by systematic parameter optimization. We are using structured illumination microscopy and image processing for an objective assessment of staining procedure. Bovine muscle tiles of 2x2 cm are used as experimental tissue. In these experiments we differ staining procedure by varying stain and rinse solvent, dye concentration, and immersion time. Quantitative measures of staining quality were compared. Our findings confirm the profound impact of the confluence of multiple factors in staining quality, and suggest general strategies for successful protocol development.