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.

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.

Ducts with rectangular cross-section are widely used in HVAC distribution systems applied to residential, commercial and industrial buildings where round elements cannot be used. Usual practical problem is calculating the required pressure drop to drive the air-flow for a given duct geometry at a certain flow rate, for which the total hydraulic losses should be obtained. Friction losses in ducts depend on their size, flow capacity and construction material, while minor losses are caused by changes in flow stream direction, expansions or contractions, fittings and valves. The installation of elbow in a channel can induce larger losses due to local flow separation and swirling secondary flow. Viscous incompressible flow of air in the ducts was modelled and simulated. Hydraulic losses in cascade connected straight rectangular sections by three elbows are evaluated with the application of CFD. Rectangular ducts which have the same hydraulic diameter but differ according to the lengths of their straight sections were being analysed. The numerically obtained loss coefficients were compared with available theoretical data and show good agreement especially in a selected range of Reynolds number. A conclusion is drawn from the comparative analysis that the lengths of the straight sections between the elbows significantly influence the duct hydraulic resistance because of the contribution the velocity profile uniformity. Moreover, during the separate analysis of the elbows, it is detected that the elbow position in the system is an influencing parameter on the elbow loss coefficient.

Besides the purification process in the wastewater treatment plant that includes mechanical, biological, and chemical approaches, analysis of hydraulic behavior is also fundamental. This means developing a digital replica of the physical process by simulating the hydraulic parameters. Studying fluid behavior in the plant enables process optimization, improves plant behavior, prevents equipment malfunctions, and more. This paper focuses on defining the concept of a wastewater treatment plant prototype, simulating it, and identifying the available and most suitable software that enables efficient process simulation and validation. The hydraulic parameters, as per the literature review and the proposed concept, that will be simulated are pressure, flow, pressure drop, and water level. MATLAB/Simulink and Python programming languages are considered the most suitable software/programming languages for hydraulic parameters simulation.

Tandem airfoils, used in the fields of aerodynamics for race cars and aircraft designs, are a key part of current research due to the aerodynamic complexity they introduce, while offering performance benefits.A numerical 2D CFD analysis of a tandem airfoil system was performed in this paper to determine their optimal positioning for achieving maximum aerodynamic efficiency and analyzing the resulting flow field. Simulations were conducted in Ansys Fluent using a high quality mesh and refined boundary layer conditions, targeting y+<1. Key parameters analyzed include the lift coefficient CL, drag coefficient CD, theCL/CD ratio, and flow visualizations such as pressure, velocity, streamlines, velocity vectors, and turbulent kinetic energy. Results indicate that the optimal angle of attack for the variable airfoil is -25°, where the highes CL/CD ratio is obtained. However, flow visualizations show wake formation at this angle, highlighting the need for further aerodynamic optimization to balance efficiency and wake reduction.

A T-junction of a hydraulic system is the point where hydraulic parameters (which are defined by variable pressure and discharge) join or separate. The transmission of the hydraulic conditions distributed by the T-junction connection are numerically analyzed in different conditions which provide insight into the distribution – transfer of hydraulic parameters through the T-junction. Numerical calculations were performed for defining the transient modes and the interaction between the hydraulic parameters in the case of a T-junction with the application of the AFT Impulse software package. The software was chosen as suitable based on previous experience with good alignment between numerical calculations and field measurements. The results from the numerical prediction of the occurrences for different conditions in the T-junction construction showed the influence of simultaneity (interaction and dissipation) of the fluid flow parameters, time delay or parallel flow and counter-flow in the transient modes, which contribute to the technical opinion on the phenomena occurring in a T-junction.