This paper is focused on the guide vane cascade as one of the most crucial stationary sub-systems of the hydraulic turbine, which needs to provide efficient inflow hydraulic conditions to the runner. The guide vanes direct the flow from the spiral casing and the stay vanes towards the runner, regulating the desired discharge. A parametric design tool with normalized geometrical constraints was created in MATLAB, suitable for generating guide vane cascade geometries for Francis turbines. The goal is to determine the limits of these constraints, which will lead to future faster prediction of initial guide vane configurations in the turbine optimal operating region. Several geometries are developed using preliminary design data of the turbine and are investigated using CFD simulations close to the best efficiency point (BEP) of the turbine. This research is part of the Horizon-2020—HydroFlex project led by the Norwegian University of Science and Technology (NTNU), focusing on the development of a flexible hydropower generation.

The frequencies with predominant amplitudes in low specific speed Francis turbines are related to rotor-stator interaction and they are calculated on the basis of the runner rotational speed and the number of guide vanes and runner blades. Pressure pulsations in the blade channels can be a reason for noise and vibration in the turbine above allowed level. High pressure pulsations can be caused by certain combination of runner blades and guide vanes number and/or resonance with one of the runner’s natural frequencies. The stress parameters of the Francis-99 turbine guide vanes and their modifications are analysed in this paper. The main aim is to determine the impact of the geometry modification (thinner for increased efficiency) of the guide vanes on the Francis turbine stresses by performing numerical simulations. The original Francis-99 turbine guide vane geometry and three modifications consisting of new guide vane shapes are being considered. The numerical investigation of the flow field is based on the k-ω SST turbulence model with ‘frozen rotor’ approach selected, constituting a quasi-steady state analysis, without taking into account the physical rotation of the runner to obtain Rotor-Stator Interaction (RSI). Pressure distribution on one guide vane determined by a Computational Fluid Dynamics (CFD) simulation of the turbine is coupled to a Finite Element Method (FEM) simulation in order to analyse the stresses. The results from the one-way fluid-structure interaction analysis give the stresses distribution and deformations of the guide vanes. Moreover, modal-acoustics analysis is conducted to obtain the natural frequencies of the guide vanes in water and comparison is made with the calculated vortex shedding frequencies to estimate the risk of resonance.

The high head Pelton turbines operate with extreme conditions. In case to need a sudden stop of operation, one of the important parts is jet deflector, which can be in push-out, or cut-of options. The paper presents the optimisation procedure of Pelton Turbine push-out jet deflector shape using numerical simulation of three-dimensional turbulent flow in order to minimize the forces, stresses, deformations and torque of jet deflector servomotor. The calculations are performed using the CFD package Ansys CFX. The steps for flow modelling, 3-D geometry definition, mesh generation, pre-processing and post-processing, as well as the optimised results obtained from the numerical simulation of the flow in the jet-deflector are presented. The work corresponds with the actual approach of methods development for flow simulation and calculations of Pelton Turbines. The kinematic and dynamic flow parameters are calculated based on CFD simulations. The results of the calculations represents reliable tool in the procedure of development and construction of Pelton Turbines parts.

Urban air pollution during winter is a major challenge in many cities, where emissions from residential heating lead to elevated particulate matter levels. Atmospheric dispersion modelling supports the understanding of spatial and temporal pollution behavior and enables the assessment of source contributions relevant for targeted mitigation. In this study, the ADMS-Urban dispersion model was applied to simulate hourly PM_2.5 and PM₁₀ concentrations across the city of Skopje, North Macedonia. Residential heating was the focus of the analysis, while emissions from road traffic and industrial activities were also included to ensure a realistic representation of the urban emission environment. A representative winter day was analyzed to examine the influence of wind patterns and diurnal boundary-layer height variability on particulate matter dispersion. Modelled concentrations were evaluated against measurements from urban air quality monitoring stations and showed good agreement in reproducing both night-time accumulation and daytime dispersion. The results indicate that household heating using biomass is the dominant contributor to wintertime particulate matter emissions, with PM₁₀ prevailing over PM_2.5. These findings underline the need for targeted emission reduction measures in the residential heating sector and demonstrate the usefulness of short-term dispersion modelling for supporting air quality management strategies in Skopje.