Fully three dimensional modelling of the spilling from a reservoir with relatively complex geometry were performed and compared to experimental results from a physical scale model with the aim to advance the science of numerical modelling of free surface flow of real reservoirs. In the set-up in focus the water was spilled from the reservoir through three gates that could be manoeuvred separately. In the first case two of the gates were closed and the third gate was partly opened. In this experimental set-up the water surface in the reservoir was close to horizontal. Therefore it was here meaningful to compare a rigid lid modelling approximation to the more computational heavy method of Volume of Fluids. In the second case, all three gates were open, resulting in a nonhorizontal varied flow surface profile in the reservoir upstream critical sections at the spillway crests. This case was simulated with Volume of Fluids and the position of the air-water interface was derived for two turbulence models, the standard k-and SSG. Water levels, velocities and the shape of the water surface were compared to experiments.The simulation results capture qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments regardless of method used to simulate the free surface. In general, simulations with the standard k- and the more advanced SSG turbulence models give the same results with respect to the averaged quantities measured.

Simulation-driven design with computational fluid dynamics has been used to evaluate the flow downstream of a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed, and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations, and the tailrace jet from the turbines is stronger in the simulations. A fishway entrance was included in the simulations, and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed for further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.

Known as the "king of fishes," the Atlantic salmon (Salmo salar, Salmonidae) is an iconic freshwater species whose contribution to human well-being has long been recognized, as have widespread declines in its abundance, partly due to river regulation.To understand how salmon conservation has been addressed within the ecosystem services (ES) framework, we synthesized the peer-reviewed literature on ES provided by salmon in regulated rivers. We developed a search string to capture allusions to provisioning, regulating, supporting and cultural ES and assessed the results to identify knowledge gaps. The effects of hydropower on fisheries catches and on modelled populations were shown in several publications. Overall, few studies focused explicitly on ES from salmon and hydropower; this is surprising given the considerable body of literature on salmon in regulated rivers. Wild salmon as a food source and other provisioning services are less important today than historically. Because predators such as salmon are important for facilitating biodiversity by cycling nutrients and controlling food webs, there is a scope of work for future assessments of these regulating and supporting services. Few papers explicitly addressed cultural ES, despite the salmon's longstanding iconic status; this is a knowledge gap for future ES assessments in relation to hydropower. The influence of ES assessments for policy makers is growing through the Intergovernmental Panel for Biodiversity and Ecosystem Services (IPBES) and the post-2020 biodiversity strategy. Explicitly addressing ES poses an opportunity for river managers to raise awareness of aquatic conservation efforts and well-informed decision-making for sustaining ES.

Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structural upgrades. This has led to renewed laboratory model tests. For some dams, even computational fluid dynamics (CFD) simulations are performed. This provides the possibility to compare the spillway discharge data between the model tests performed a few decades apart. The paper presents the hydropower development, the needs for the ongoing dam rehabilitations and the history of physical hydraulic modeling in Sweden. More than 20 spillways, both surface and bottom types, are analyzed to evaluate their discharge modeling accuracy. The past and present model tests are compared with each other and with the CFD results if available. Discrepancies do exist in the discharges between the model tests made a few decades apart. The differences fall within the range −8.3%-+11.2%. The reasons for the discrepancies are sought from several aspects. The primary source of the errors is seemingly the model construction quality and flow measurement method. The machine milling technique and 3D printing reduce the source of construction errors and improve the model quality. Results of the CFD simulations differ, at the maximum, by 3.8% from the physical tests. They are conducted without knowledge of the physical model results in advance. Following the best practice guidelines, CFD should generate results of decent accuracy for discharge prediction.

The fluid dynamics within a water tunnel is investigated numerically using a RANS approach with the k-ε turbulence model. The computational model is based on a laser scan of a hydropower tunnel located in Gävunda, Sweden. The tunnel has a typical height of 6.9 m and a width of 7.2 m. While the average cross-sectional shape of the tunnel is smooth the local deviations are significant, where some roughness elements may be in the size of 5 m implying a large variation of the hydraulic radius. The results indicate that the Manning equation can successfully be used to study the localised pressure variations by taking into account the varying hydraulic radius and cross-sectional area of the tunnel. This indicates a dominant effect of the tunnel roughness in connection with the flow, which has the potential to be used in the future evaluation of tunnel durability. ANSYS-CFX was used for the simulations along with ICEM-CFD for building the mesh.

In urban areas in cold regions snow handling is a significant part of municipal activity. The snow is usually ploughed off the streets and then transported to a snow deposit. As a consequence the snow is mechanically blended, packed, polluted and piled up, giving it a characteristic texture, shape, and size. To predict snow deposit melt an energy budget model that uses general meteorological data has been derived. The model is a synthesis of available energy balance terms developed for natural snow covers, and general mass and heat transfer considerations. This approach was found applicable for estimating snow deposit melt. Only geometry, radiation, sensible and latent heat are included to the model. Radiation was found to be the major source of snow deposit melt. Very little difference was found between top and side energy fluxes. Model predictions were compared with measurements of two pilot snow deposits which were constructed with snow collected from the streets of Luleå, Sweden. The degree day approach also seems to be an applicable method to estimate snow deposit melt.

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A mathematical simulation of energy conversions in a fully developed channel flow Simulation mathématique des transformations d'énergie dans des écoulements turbulents pleinement développés en canal URBAN SVENSSON Ass. Prof., Water Resources Engineering, SUMMARY A detailed analysis of energy conversions in a fully developed channel flow on a sloping plane is provided. It is the lowering of the centre of mass that releases potential energy which, of course, ultimately will leave the domain as a boundary heat flux. A mathematical model, based on the conservation laws for heat and momentum and a one-equation turbulence model, is used for the purpose. As the calculations include the viscous region, the turbulence model is extended to include low-Reynolds number effects. Verification studies are carried out by com paring predictions with data from laboratory experiments. The model is thereafter used to analyse the conversions of energy from its first appearance as a source term in the mean kinetic energy equation till it finally leaves as a boundary heat flux. The model provides a clear and consistent picture of all the details in the budgets and fluxes involved. RESUMEL'article présente une analyse détaillée des transformations d'énergie dans un écoulement turbulent pleinement développé en canal avec une pente constante. C'est l'abaissement du centre de gravité qui libère de l'énergie potentielle qui, bien évidemment, sortira finalement du domaine sous forme de flux thermique. Un modèle mathématique basé sur les lois de conservation de la chaleur et de Ia quantité de mouvement et un modèle de turbulence a une seule equation, sont utilises a cette fin. Comme les calculs incluent la zone d'écoulement visqueux, Ie modèle de turbulence est étendu pour prendre en compte les effets a bas nombre de Reynolds. Des études de verification sont réalisées par comparaison a des résultats d'essais en laboratoire. Le modèle est par la suite utilise pour analyser les transformations d'énergie de leur première forme prise comme terme source, en une equation d'énergie cinétique moyenne, jusqu'a finalement quitter le domaine sous forme de flux thermique en limite. Le modèle donne une image claire et precise de tous les détails concernés dans les bilans et flux d'énergie.