This study investigates the use of X-ray microtomography (XMT) to reveal the structure of complex porous biological tissues and the fluid flow through them during wetting. It also evaluates fluid dynamical simulations based on XMT data to reproduce and analyse these flows, with a final aim of revealing fluid transport and void formation in such tissues. To fulfil the objectives, the wetting flow of a polymer liquid through an initially dry conditioned Norway spruce wood sample is visualised using XMT at the MAX IV synchrotron. The liquid flow front progression captured after 24 s and 48 s reveals uneven filling of longitudinal tracheids and flow between them via the tiny pits which connect tracheids. Most tracheids fill between 24 and 48 s, possibly due to removal of air inclusions. Large density gradients near cell walls suggest that the fluid followed and deposited along wall structures. Computational fluid dynamics simulations (CFD) of saturated flow through the tomography-based geometry indicate velocity profiles that resemble pipe flow in longitudinal tracheids and flow rate differences among them. The latter indicates that the geometry itself may cause the experimentally observed uneven flow. Streamlines show intra-tracheid flow development and clear flow direction change at the pits. Additionally, wetting simulations, using a constant contact angle, capture initial uneven filling between the tracheids on shorter time scales than could be capture by the experiments. These simulations furthermore show air entrapment during filling, consistent with experimental observations. Combining XMT with CFD enables detailed studies of flow in biological porous media. Faster X-ray scanning, incorporating dynamic contact angles and accounting for diffusion in simulations could further refine insights into fluid progression during capillary-driven flow into complex structures of porous biological tissues.

Downstream migration of salmonid smolts through regulated rivers remains a major ecological and engineering challenge, with high mortality and delay rates despite mitigation measures like bypasses and guidance systems. This study integrates Computational Fluid Dynamics (CFD) with fish telemetry to analyze how salmon smolts respond to local hydraulic conditions in a real riverine environment. By coupling detailed CFD flow models with two-dimensional smolt track data from a hydropower facility in northern Sweden, we identified behavioral tendencies linked to specific flow velocities. The analysis of fish movement patterns indicates a general tendency to follow the main current during migration, with occasional variations influenced by initial velocity and local flow conditions. This behaviorally informed CFD–telemetry approach provides a method for identifying behavioral patterns based on velocities and demonstrates its potential to improve fish passage models, supporting more ecologically effective hydropower design. This study highlights the need for broader datasets to fully capture smolt behavior and to develop standardized, transferable modeling frameworks for fish–flow interactions.

Hydropower and dam structures worldwide are facing evolving requirements due to changes in climate, better methods for flood estimates, combined with the needs of surrounding interests. Improved understanding of the hydraulic behavior of spillways, and the approach flow leading up to them, is important for evaluation of existing spillways and considering potential redesigns. There is limited research on the distribution of flow across a multiple outlet spillway, therefore a purpose built experimental setup is utilized to examine the impact of various geometrical changes on the flow distribution across a spillway with three outlets. The maximum difference measured between the different outlets were as much as 10%. While small changes to abutment and pier corners were found to reduce total discharge capacity up to 8%, with increased discharge and overflow height causing greater reduction in the capacity of the spillway. To further investigate the flow behavior leading up to the spillway outlets, ADV measurements were conducted to capture flow velocities. The measured flow cross sections indicate a stable flow field leading away from the inlet, stagnation zones and recirculation zones leading up to the spillway, with minor variations occurring for increasing inlet flow rates.

This work examines the relationships between flow restoration, natural flow regimes and riparian vegetation utilizing a case study in northern Sweden. The riparian zone is one of the most species-rich ecosystems and forms an important link between aquatic and terrestrial systems. The integrity of the riparian zone and its vegetation is harmed by flow alteration in numerous rivers, which calls for enhancing riparian management and ecological mitigation measures. Here, we take an ecohydraulic approach, combining a hydraulic model and data on inundation tolerance of riparian vegetation to evaluate the effects of reintroducing seasonal flow variation in a bypassed reach with minimum discharge. The results show that implementing the seasonal flow variation is projected to benefit riparian vegetation by extending the riparian zone and to lead to the development of distinct vegetation belts similar to riparian vegetation along free-flowing rivers. Additional simulations demonstrated that a further increase in riparian area could be achieved by increasing the magnitude of the minimum flow release. While the method assumes the riparian vegetation to be in equilibrium with the flow regime, continued monitoring is needed to assess how fast the riparian vegetation adjusts to new flow conditions.

The heat and mass transfer in packed bed reactors (PBRs) are strongly influenced by the random packing of particles, making a thorough understanding of the packed bed structure crucial for optimal reactor design. This study investigates the impact of particle shape irregularities and size distributions on packing and transport properties using X-ray microtomography (XMT) imaging. Key morphological parameters, including void fraction and tortuosity, are extracted and analyzed. Two pore network models (PNMs)- one using cylindrical throats and another based on dense graph approach- are compared, with the dense graph model more accurately reflecting empirical tortuosity distributions. Results reveal that in monodispersed beds, void fraction decreases for particle diameters below 2 mm, nearing theoretical minimums for spherical packings, while tortuosity aligns with established models despite particle sphericity ranging between 0.6 and 0.8. In contrast, highly polydispersed beds exhibit lower void fractions compared to monodispersed beds, yet their tortuosity distributions remain similar. Visualization indicates small particles fill voids without blocking flow paths, preventing substantial tortuosity increases. These findings enhance understanding of packed bed behavior and provide valuable insights for designing biochar-based PBRs.

Climate change is projected to significantly alter hydrological conditions across the Northern Hemisphere, with increased precipitation variability, more intense rainfall events, and earlier, rain-driven spring floods in regions like northern Sweden. These changes will affect both natural ecosystems and hydropower-regulated rivers, particularly during ecologically sensitive periods such as the grayling spawning season in late spring. This study examines the impact of extreme spring flow conditions on grayling spawning habitats by analyzing historical runoff data and simulating high-flow events using a 2D hydraulic model in Delft3D FM. Results show that previously suitable spawning areas became too deep or experienced flow velocities beyond ecological thresholds, rendering them unsuitable. These hydrodynamic shifts could have cascading effects on aquatic vegetation and food availability, ultimately threatening the survival and reproductive success of grayling populations. The findings underscore the importance of integrating ecological considerations into future water management and hydropower operation strategies in the face of climate-driven flow variability.

In this study, a three-dimensional hydrodynamic model is developed to investigate diurnal thermal dynamics induced by pumped hydropower storage operations. At this stage, the focus is on thermal mixing in a generic reservoir, with the aim of providing a methodology that can be adapted to various reservoir scenarios. Key issues include enhancing the understanding of how numerical grid resolution impacts modeling results and demonstrating a method for conducting mesh studies in standing water bodies influenced by flow fields, such as those generated by pumping. The model, being implemented in Delft3D FM, is designed to simulate the upper reservoir of a pumped hydropower plant under initial conditions of thermal stratification. A systematic mesh study was conducted by varying cell sizes in different directions to evaluate their influence on the modeling results. A Richardson analysis shows that the longitudinal resolution, along the main reservoir direction, has minimal impact, while the vertical and the lateral resolutions are critical to avoid thin layers in the mesh and prevent oscillations and numerical inaccuracies. The research demonstrates that pumped hydropower operations alter the thermal regime in the upper reservoir, leading to thinning and temperature fluctuations in the epilimnion, as well as weakening the thickness and strength of the thermocline. Additionally, these operations promote the formation of a large-scale recirculation zone. The adaptable model framework allows for changes in bathymetry, initial stratification conditions, and pumping scenarios, enabling new insights into general temperature dynamics and mixing patterns. 

Renewable energy sources such as hydropower are important to reduce the global emissions. Hydropower, however, comes with other environmental challenges by altering the ecological conditions in the rivers. Hydraulic models connected with fish habitat models could be one tool to assess the environmental impacts and evaluate mitigation measures for fish habitats. This study examines the limitations of steady-state hydraulic simulations in a low-sloping river located between two hydropower plants, where downstream regulations significantly influence the river flow dynamics. A 2D hydrodynamic model in Delft3D FM was applied to compare steady-state and transient simulations, focusing on how hydraulic variables affect the spawning habitat. The results show that steady-state models fail to capture time-dependent damping and delayed water level responses, leading to systematic underestimation of hydraulic variability. Peak bed shear stress values were under-predicted by the steady-state interpolation, which may under-predict spawning ground stability. Additionally, the steady-state approach failed to capture daily habitat fluctuations, resulting in a mean absolute error of 2910 m2 in spawning habitat area per hour. This study demonstrates how errors in hydraulic calculations propagate into habitat assessments, potentially leading to misleading long-term evaluations of fish populations. This study highlights the importance of selecting appropriate hydraulic modelling approaches based on river-specific flow dynamics. Future studies should investigate the sensitivity of fish habitat models to hydraulic inputs from steady-state and transient simulations by integrating these approaches into advanced fish modelling tools, such as individual-based models. This will help determine the optimal balance between computational efficiency and accuracy in long-term habitat assessments.