This simulation was inspired by The Slow Mo Guys’ video “90 ft. Vertical Spike Wave in Slow Mo” which shows the results of an experiment made by the FloWave Ocean Energy Research Facility. We use part of their video to compare results with our own simulation. https://www.youtube.com/watch?v=iWKFPTgkpXo&t=105s The Vertical Spike Wave The Vertical Spike Wave is the result of a concentric wave travelling towards its center. Depending on its velocity, the wave can collide in the middle and form a spike of water. This wave can be generated in a circular pool equipped of moving panels on the entire length of the perimeter that push in one coordinated motion the water towards the center. The pushers have to be activated simultaneously with the same motion in order to have the water travel in one single motion and collide at the same speed with the same energy. If the speed is high enough, the water will rise in the center of the pool in a high spike [Figure 1] and fall back splashing. Figure 1 - Vertical Spike Wave Model setup on FLOW-3D® FLOW-3D was used to setup the simulation of the Vertical Spike Wave, then the result was post-processed on FlowSight. In order to model the circular wave, the mesh was defined on cylindrical coordinates. That allowed to simulate only a part of the pool [Figure 2] then to duplicate it later on Flow Sight to make it look like the entire pool was modeled. Figure 2 - FLOW-3D setup Most of the measurements were given in The Slow Mo Guys’ video, so it was possible to give the simulation the real dimensions. The pool is about 50m wide and is equipped of 168 panels. We estimated that the pushers took 4s to motion back and forth once with an angle of 17.2°. To setup the simulation, a pool was created simply on FLOW-3D using the basic geometry provided by the software, then the panel was imported as an STL file. The pusher was setup as a moving object [Figure 3] to which a motion defined in advance was applied. The water is completely still at first, and a single push is sufficient to create the vertical spike wave. Figure 3 - Panels pushing the water Results The overall motion and energy correspond to the reality with a very good precision. Some differences can be seen only in the disrupted front of the spike: its effects are negligible for our comparison but could be taken into account with a complete 3D and 2-fluid simulation. Figure 4 - Experiment and Simulation side by side … [Read more...]
Increasing Discharge Capacity with the Piano Key Weir
Piano Key Weir Characteristics The Piano Key Weir is a particular model of the labyrinth discharge spillway. It is composed of an alternation of reclined surfaces, one is the direction of the flow, the other in the opposite direction. Each of these slopes is separated by a vertical wall that follows the geometry of the shape. Seen from above, it is a series of rectangles cut in equally sized sections widthwise. For each of these sections one of the side perpendicular to the stream is pushed down, creating a slope on which the water can either flow or accumulate, depending on which side the section is lowered. This structure tops a smaller wall. The Piano Key Weir is generally used at the outbound of a dam, the idea being to dispose of a construction that is solid enough to resist the pressure created by a high quantity of water contained in a dam or a river during flood season, that can evacuate the overflow of water, and that is simple enough not to be too expensive. Usage of the Piano Key Weir The Piano Key Weir is a free flow discharge spillway. Its geometry allows for a significantly higher evacuation capacity. The studies conducted on this type of spillway have two aims: build solid and cheap discharge spillways, as well as reinforce the older structures. This enables engineers to avoid accidents of dams that break or that don’t have the capacity to discharge water correctly and in a controlled manner when there is a flood. Usually the weir is placed after the dam and before the cities so as to allow a controlled discharge of water. This type of discharge spillway presents several crucial advantages. First it is easy to install on structures that are already there, as opposed to classic labyrinth discharge spillways. Moreover, its shape that alternates between ascending and descending slopes allows the formation of two different flows depending on whether the water arrives on one or the other slope. When the water flows over the descending slope it forms a jet that goes towards the bottom of the dam, and when it is first contained by an ascending slope it forms a kind of film which then flows towards the jet below. This division of flow slows the stream down consequently in a much more efficient way than classic dams do. Simulation results In order to observe the effects of the Piano Key Weir we used FLOW-3D® to make a simulation displaying the weir in a stream. The model setup is the most basic one, given that it has been proved that it enabled the results to be as close to reality as possible. The simulation shows the characteristic flow of the water over the “keys” of the piano as well as the decrease of the flow rate after the weir. We can see that the error percentage between experimental results and the simulation using FLOW-3D is only between 2% and 4% on average. The only determining factor is the mesh resolution when it comes to the accuracy of the simulation, but it only changes the error of 3% or 4% maximum, which means that overall the simulation doesn’t go above an error of 6%. … [Read more...]
A dam failure 3D-Shallow Water hybrid simulation on a real topography
The water and environmental simulation of the effect of a dam failure on a real extent topography was in the past a very hard goal because of the too many cells needed for the calculation. Since v11.0 of FLOW-3D® it is possible to use a hybrid approach, coupling a complete 3D simulation in the zone around the dam, where the splashing effects are more important, to a shallow water approach in the zone far away, having a solution to fast simulate such kind of situation. Moreover, since v11.1 of FLOW-3D®, it is possible to easily import raster file containing the topography with just one click, making the setup phase a matter of only some minutes. https://www.youtube.com/watch?v=Q7x55ohyDxA Video 1 : Overall view In the simulation a real topography of a lake with mountains has been used, the extension of the computational domain is around 5’000 km2, and a hypothetical large Dam has been created inside the topography. Using all the physical models described before, and the general moving object to simulate the dam failure in a 3D accurate way, it was possible to predict the effect of the failure, the affected zone and the submerged zone in the topography. The simulation lasts for more of 35 minutes of real time, simulating in a transient way the impact of the water on the topography up to the empty of the Dam. The resulting flow-rate across the broken dam is an interesting output of the simulation. All the post processing makes use of lot of Flow-Sight new features: moving camera, different realistic coloration for topography and water, fine tuning of light transparencies and reflections to make the visualization more realistic as possible, the use of textures to represent the surface of the dam, moving camera to follow the fluid path, different plots and viewports to show in one only visualization all the critical aspect of the simulation. https://www.youtube.com/watch?v=xsKx4L9QThI Video 2 : flow depth Video 1 represent an overall view of the water flow with realistic colors. The video 2 instead is a more “scientific analysis”: the water is colored with the fluid depth, using a 20-colors color scale in order to highlight the depth difference also in small portion of the scale; the terrain is colored with the elevation. Finally, a plot of the flow rate across a baffle positioned in correspondence of the dam wall is also reported. In the images a set of realistic rendering are saved, some of them with an evolution over time. … [Read more...]
Pelton turbine simulation – starting transient up to regime
Pelton turbines (or Pelton wheel) are the most worlwide used type turbines for electricity generation in hydraylics powerplant, due to their high efficiency. Its design belongs to 1870 but, with some modifications, they are still the first choiche in modern powerplants. In a Pelton turbine the energy is extracted from the kinetic energy of the water, in contrast with other types of turbines where the hydrostatic pressure is used: the water, coming from an upper basin, is accelerated and ejected against the Pelton paddles. Paddle geometry is designed properly to absorb as much as possible the kinetic energy of the fluid, starting rotating. The rotational speed of the turbine is then converted to electric power through a conductive coil. The simulation analyse the initial transient of the turbine, where water at over 100 m/s impact on the Pelton’s paddle providing torque and angular acceleration. https://www.youtube.com/watch?v=lb2xEbHmWKw All geometries and data used in the simulation are realistic and coherent with the real phenomena: wheel geometry has real shape and mass property, fluid is water with a reasonable speed, and the nozzle contains a doble valve, used in real turbines to adjust water flow rate. Interesting is the plot of the angular speed of the wheel. For Pelton turbines, it is known that the top efficiency is reached when the peripheral speed of the wheel is about half the speed of the water at the nozzle. For this purpose, a probe has been located at the centre of the nozzle in order to monitor the fluid speed, while another probe has been attached to a wheel paddle, in order to catch the peripheral speed. The two quantities can be directly showed as output from the simulation. The videos make a large use of Flowsight features: transparency based on the value of the variables, moving camera, fine tuning of light and reflections, multi-plots and multi-viewport visualization. https://youtu.be/TddbeL1lK9I … [Read more...]
