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...]

## Interaction Between Waves and Breakwaters

This article is an adapted version of an article published in the journal of the Engineering Association for Offshore and Marine in Italy by Fabio Dentale, E. Pugliese Carratelli, S.D. Russo, and Stefano Mascetti. The first three authors are users at the University of Salerno; Mr. Mascetti is an engineer at XC Engineering, Flow Science’s associate for Italy and France. The design of breakwaters must be based on the full understanding of the interaction of a complex natural system (the sea and shores) with artificial structures (breakwaters). Typically, design work entails extensive physical modelling, which can be quite expensive and time-consuming. Until recently, the complex aspects of breakwater behavior were considered too challenging for detailed numerical simulations. This is especially the case for breakwaters consisting of rubble mounds composed of blocks of concrete or rocks in which water flows through complex paths with unsteady motion. The gap between numerical and physical, investigations, has narrowed, thanks to the advancement of computing technology. It is now possible to accurately represent a solid structure consisting of individual blocks which interacts with the flow, so as to create a numerical flow domain within the empty spaces between the blocks. This enables the evaluation of the effect of the full hydrodynamic behavior, including convective terms, and the effects of turbulence, which cannot be taken into account with the classical Darcy scheme in which the breakwaters are approximated as homogeneous porous media. Modeling Rubble Mound Breakwaters The following examples describe cases where rubble mound breakwaters are modelled on the basis of their real geometry, taking into account the hydrodynamic interactions with the wave motion. Figure 1: Artificial blocksFigure 2a: Submerged BreakwatersFigures 2b and 2c: Emerged Breakwater – Accropode regular & Accropode irregular The work takes into consideration a schematic representation of a natural stone mound, reproduced as a set of spheres, and was further developed to consider commonly-used artificial blocks such as the cube, the modified cube, the antifer, the tetrapod, the accropode, the accropode II, the coreloc, the xbloc,and the xbloc base (Fig. 1). Breakwaters, both submerged and emerged, were sized by making use of standard empirical formulas as available in the literature and numerically constructed by overlapping individual blocks following real geometric patterns, modelling the structure as in the full size construction and in the physical modelling (Fig. 2). In order to validate the quality of the proposed procedure, three different geometries were considered for the submerged breakwater: solid, porous, solid-porous (Fig. 2a), while for the emerged breakwater, two different geometries were used, according to the shape of the elements: regular and random (Fig. 2b – 2c). Read more... … [Read more...]