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Turbulent free-surface flows are encountered in several engineering applications and are typically characterized by the entrainment of air bubbles due to intense mixing and surface deformation. The resulting complex multiphase structure of the air–water interface presents a challenge in precise and reliable measurements of the free-water-surface topography. Conventional methods by manometers, wave probes, point gauges or electromagnetic/ultrasonic devices are proven and reliable, but also time-consuming, with limited accuracy and are mostly intrusive. Accurate spatial and temporal measurements of complex three-dimensional free-surface flows in natural and man-made hydraulic structures are only viable by high-resolution non-contact methods, namely, LIDAR-based laser scanning, photogrammetric reconstruction from cameras with overlapping field of view, or laser triangulation that combines laser ranging with high-speed imaging data. In the absence of seeding particles and optical calibration targets, sufficient flow aeration is essential for the operation of both laser- and photogrammetry-based methods, with local aeration properties significantly affecting the measurement uncertainty of laser-based methods.

This paper presents a photogrammetry-based system for capturing turbulent aerated flow topography in a laboratory environment, especially for complex hydraulic phenomena character-ised by turbulent, non-stationary, and non-homogeneous aerated flows. It consists of ten high-resolution cameras equipped with monochromatic sensors and custom-built LED lights, all synchronised for accurate data acquisition. Post processing involves Structure-from-Motion and Multi-View Stereo techniques to calculate exterior and interior orientation parameters that ensure accurate alignment within a desired coordinate system, and conversion to point clouds. The proposed method showed great potential for capturing free water surface topography of turbulent aerated flows with high spatial and temporal resolution over the entire field of view of the cameras. Due to the unique capabilities of this system, direct comparisons with existing benchmarks were not possible. Instead, average free water surface profiles were derived from selected control cross sections, using 2D LIDAR measurements for verification. Both the LIDAR and photogrammetry averaged profiles showed remarkably good agreement, with deviations within ±20 mm. Validation showed that photogrammetry can be used to measure the complex aerated turbulent free water surface. In this way, this approach, involving consecutive image dataset acquisition at predefined intervals, is proving to be a valuable tool for observing, visualising, analysing, investigating, and gaining a comprehensive understanding of the dynamics of the free water surface.

This study investigates the computational fluid dynamics (CFD) modeling of supercritical open channel junction flow using two different turbulence models: k-ω shear stress transport (SST) and k-ω SST scale-adaptive simulation (SAS), in conjunction with Volume of Fluid (VOF) and mixture multiphase models. The efficacy of these models in predicting the intricate free surface fluctuation and free surface elevation in a supercritical junction is evaluated through a comprehensive analysis of time-averaged free surface data obtained from CFD simulations and Light Detection and Ranging (LIDAR) measurements. The dimensionless Reynolds (Re) and Froude (Fr) numbers of the investigated scenario were Fr = 9 and Re = 5.1 × 104 for the main channel, and Fr = 6 and Re = 3.3 × 104 for the side channel. The results of the analysis demonstrated a satisfactory level of agreement with the experimental data. However, certain limitations associated with both CFD and LIDAR were identified. Specifically, the CFD performance was limited by the model’s incapacity to consider small-scale turbulent effects and to model air bubbles smaller than the cell size while the LIDAR measurements were limited by instrument range, inability to provide insight into what is happening below the water surface, and blind spots. Nonetheless, the k-ω SST turbulent model with the VOF multiphase model most closely matched the LIDAR results.

A developed methodology for determining the physical properties of mineral fibers prepared from different input mixtures under the same spinning wheel conditions is described and discussed. Energy dispersive X-ray fluorescence spectroscopy was combined with simultaneous thermal analysis and thermogravimetry to study the mineralogical composition and typical melting and crystallization temperatures. The mechanical properties measured with nanoindentation were related to the mineralogical properties and the results obtained are in agreement with the literature. The developed methodology shows reliable performance and demonstrates the ability to study the mechanical properties of mineral fibers, their mineralogical composition, and thermal properties. The presented experimental methodology opens up the possibility of researching the mechanical properties of mineral fibers for the purpose of defining production recipes in the field of mineral thermal insulation materials.

The issue of ever-increasing amounts of waste activated sludge (WAS) produced from biological wastewater treatment plants (WWTPs) is pointed out. WAS can be effectively reduced in the anaerobic digestion (AD) process, where methanogens break down organic matter and simultaneously produce biogas in the absence of oxygen, mainly methane and CO2. Biomethane can then be effectively used in gas turbines to produce electricity and power a part of WWTPs. Hydrodynamic cavitation (HC) has been identified as a potential technique that can improve the AD process and enhance biogas yield. Rotary generators of hydrodynamic cavitation (RGHCs) that have gained considerable popularity due to their promising results and scalability are presented. Operation, their underlying mechanisms, parameters for performance evaluation, and their division based on geometry of cavitation generation units (CGUs) are presented. Their current use in the field of wastewater treatment is presented, with the focus on WAS pre/treatment. In addition, comparison of achieved results with RGHCs relevant to the enhancement of AD process is presented.

The article presents an experimental and numerical study of vortex generation and shedding from a NACA 4421 airfoil at low Reynolds number. The experiment was conducted in a low speed wind tunnel by flow visualization. A high speed camera was used to record flow structures at the airfoil trailing edge. The recorded images were processed with an in-house developed software based on the advection-diffusion equation to compute instantaneous 2-D velocity fields. These results were compared with results of the CFD simulation which employed the scale-adaptive simulation (SAS) turbulence modelling. The SST-SAS model produced finer and less stable turbulent structures compared to an URANS simulation with the shear stress transport model. Time averaged velocities and frequency spectra for the both models are in good agreement, but variability of flow in both time and frequency domain is higher in case of the SST-SAS model. Velocity fields computed on the basis of visualization show generally acceptable agreement with the CFD results. Higher errors occur in areas of unperturbed smoke trails and areas of high velocity gradients, however, the vortex shedding frequency is captured with excellent agreement to the experiment.