Simulation driven design with Computational Fluid Dynamics has been used to evaluate the flow downstream 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. The simulations are however considered to capture the important features of the flow in a way that makes them viable for attraction water 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 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.
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.
The flow field inside and downstream of an open channel placed near the surface of a free flow (such as the tail water of a turbine) is characterized in detail. The channel cross-section is U-shaped and in the downstream end is placed a ramp on the bottom which accelerates the flow passing through the channel. This flow is intended to catch the attention of fish and improve their entrance to fishways, which has also been successfully demonstrated in field tests.
One way to upgrade iron ore is to process it into pellets. Such a process includes several stages involving complex fluid dynamics. In this work the focus is on the grate-kiln pelletizing process and especially on the rotary kiln, with the objective to get a deeper understanding of itsthe aerodynamics. A down-scaled, simplified model of a full-scale kiln is created and both a numerical and an experimental analysis of the flow field are performed. Conclusions are that steady state simulations can be used to get an overview over the main features of the flow field. Precautions should though be taken when analysing the recirculation zone since the steady state simulations do not capture the transient, oscillating behaviour of the flow seen in the validation experiments, which affects the size of the recirculation zone.
One way to upgrade iron ore is to process it into pellets. Such a process includes several stages involving complex fluid dynamics. In this work, focus is on the grate-kiln pelletizing process and especially on the rotary kiln, with the objective to get a deeper understanding of the aerodynamics in order to improve the combustion. A down-scaled, simplified model of the real kiln is created and both numerical and experimental analyses of the flow field are performed. Conclusions are that steady state simulations can be used to get an overview over the main features of the flow field. Precautions should though be taken when analyzing the recirculation zone since steady state simulations do not capture the transient, oscillating behavior of the flow seen in the physical experiment. These oscillations will under certain conditions considerably affect the size of the recirculation zone.
Turbulent secondary flows are motions in the transverse plane, perpendicular to a main, axial flow. They are encountered in non-circular ducts and can, although the velocity is only of the order of 1–3% of the streamwise bulk velocity, affect the characteristics of the mean flow and the turbulent structure. In this work, the focus is on secondary flow in semi-circular ducts which has previously not been reported. Both numerical and experimental analyses are carried out with high accuracy. It is found that the secondary flow in semi-circular ducts consists of two pairs of counter rotating corner vortices, with a velocity in the range reported previously for related configurations. Agreement between simulation and experimental results are excellent when using a second moment closure turbulence model, and when taking the experimental and numerical uncertainty into account. New and unique results of the secondary flow in semi-circular ducts have been derived from verified simulations and validating laser-based experiments.
The utilization of rivers for hydropower production leads to problems for migrating fish, such as Atlantic salmon (Salmo salar) and sea trout (Salmo trutta). Both salmon and trout reproduce in fresh water, but spend their adult years at sea. To overcome man-made obstructions to and from the spawning grounds the fish needs help. Fishways for upstream migrating fish is an old technique; however the efficiency is often low due to inefficient attraction water. The upstream migrating fish are attracted to high water velocities and often approach the dominating flow from the turbine outlet instead of entering the fishway. For the downstream migrating smolt (young fish) the only way to pass a power plant is often via the turbines, with a high mortality as a result. The smolt follow the main flow in the river on the way downstream avoiding high accelerations or retardations. This thesis covers investigations on both an attraction channel to increase the water velocity at the inlet of a fishway for upstream migraters and a smolt guidance device to guide the smolt away from the turbine inlet to a safer passage route. To investigate the properties of the attraction channel both model and field experiments have been carried out, as well as numerical studies. The velocity in the channel has been examined with Laser-Doppler-Velocimetry and the flow field in the channel was studied using Particle-Imaging- Velovimetry. The results show that the water can be accelerated 38 % compared with the surrounding velocity. How far the increase in velocity is present depends on the depth of the attraction channel. The field tests carried out at Sikfors hydropower plant in Piteå River (Sweden) show that the fish do swim through the channel, providing that the channel is black. The flow around a smolt guidance device has been studied using numerical simulations. The aim of the device is to redirect the surface flow from the turbines to the spillway. By doing this, the shallow swimming smolt will also be guided towards the spillway and a much safer route. The results show that the guidance device successfully redirects the surface flow without creating any strong acceleration that may scare the fish.
When Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) migrates upstream rivers they encounter obstructions such as hydropower plants. To increase the water velocity at the fish inlet of a fishway an attraction channel is used. The channel increases the velocity without using extra attraction water from the reservoir. Field experiments show that fish use the channel, and lab experiments show that the water velocity out of the channel is 38 % higher than the surrounding velocity and the increased velocity lasts for about 18 water depths down stream.
A flow device that accelerates turbine tail water (or any free stream) to act as an attraction for migrating fish is field tested. The device consists of an open (U-shaped) channel which accelerates the incoming flow by a local constriction of the cross-sectional area. The velocity increase has previously been investigated in a lab-scale model and an increase of 38% has been established. In the summers of 2004 and 2005, a full-scale prototype of the attraction channel was tested at the Sikfors hydropower plant in the Pite River in Sweden. The channel was equipped with underwater cameras to monitor and record the fish swimming through it. The tests show that the fish do swim through the attraction channel. During the same time period in 2004 and 2005, 57 and 471 fishes swam through the channel, respectively. The major change of the channel between the two years was that it was painted black for 2005.
Downstream migrating smolt must be guided around hydropower plants to avoid fish mortality due to the turbines. In Piteå River, which is already regulated, open spillways serve this purpose but few fish find this route. Hence, action must be taken to enhance downstream fish migration. One way to attract the fish to the spillways is to direct the surface flow towards them by means of a guiding device. The hydrodynamic design of one such device is outlined using numerical calculations of the flow upstream the spillways and by the assumption that the fish moves near the surface of the water. A number of geometries are evaluated by starting from a straight impermeable barrier that extends 2 m down from the water surface and stretches over a part of the river. A major result is that it is possible to redirect the surface water towards the spillways at very low spilling rates which means high energy efficiency. Another finding was that the device should stretch over a large part of the river. For optimal functionality, the spilling should match the guiding device geometry. High spilling implies that the guiding has a low impact while for low spilling the geometry is crucial for successful downstream migration.
When forming fiberboards, a large amount of air is evacuated from the dry fiber mat and the fibers are subjected to forces generated by the flow. If the forces become too strong, the fiber mat bursts and the process stops with financial loss as a result. A simplified model for the pressure field during the pressing has been derived, by starting from first principles. This model indicates that the velocity of the belt can be increased as long as the length of the press is increased, or the viscosity of the penetrating fluid is decreased in a prescribed manner. The model furthermore suggests that the pressure distribution will be unaffected by variations in the basis weight of the fiber mat as long as the basis weight is matched with an equal change in the density of the fibers. Furthermore, by numerically deriving the pressure field as a function of boundary conditions, it is shown that minor variations in the pressure at the nip may result in huge differences in the pressure at the entrance of the press. In a validating procedure, it is shown that model parameters can be adjusted in a physically reasonable way to obtain acceptable agreement with experimental data, but also that the model must be considerably improved in order to obtain quantitative conformity.
The utilization of rivers for hydropower production leads to problems for fish migration. Migratory fish that swim upstream for reproduction need to overcome obstructions to reach their spawning grounds. On their way upstream they follow high water velocities. Since most of the water in regulated rivers flow through the power plants the fish is often attracted to the turbine outlets. To guide the fish past the power plants, fishways are often used. However the efficiency is often low due to inefficient attraction water. An attraction channel that uses a small fraction of the tailwater, or any free stream, is studied. The channel is open and U-shaped. A local acceleration of the water is created by changing the cross sectional area in the downstream end of the channel. The flow in the channel is measured with LDV in a lab setup to examine the acceleration of the water, and in full-scale to investigate the fish tendency to use the channel. The results show that the velocity out of the channel can be as much as 38 % higher than the approaching flow. The acceleration is detectable downstream the channel up to 18 times the exit water depth of the channel. The results from the field work shows that fish do use the channel and it is important that it is painted dark.