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Obtención de relaciones de diseño de canales con rugosidad artificial (Rugosidad Tipo A) mediante modelo numérico

Abstract:

The importance in the design process of a structure that transports water it’s essential to maintain a threshold that avoids deterioration, weathering, material dragging and structural damage; that is, optimum conditions must be guaranteed within its useful life. In the particular case of water slopes where velocity is the main factor that must be controlled, due to high values that occur, it’s necessary to implement complementary works to maintain a desirable flow regime. Nowadays there´s two methods to control de flow velocity on steep canals: steps and artificial roughness. The steps method can be too expensive so it’s unusual to use, however artificial roughness is the best cost efficiency alternative on construction, and can give security and stretch its lifespan. Artificial roughness, which consists in incorporating protruding elements in the canal’s perimeter, generating an additional resistance that helps to reduce the kinetic energy. Although this phenomenon has not been widely studied, there are abacuses and design equations presented mainly by authors such as Pikalov F. (1935) and Aivazian (1977); however, these theories were developed under different slope conditions, roughness block height, considering the phenomenon of aeration, and other factors; so, their validation will allow us to have greater certainty when using them for design, however, these theories have not enough information/data on the flow conditions and factors applied, there´s also a lack of linked studies to validate/confirm such theories, by which is not possible to generalize a theory that allows a basis for valid artificial roughness channel design therefore is necessary/required/essential to authenticate current design. This phenomenon is analyzed with Computational Fluid Dynamics (CFD) using OpenFOAM, a free software widely used to model three-dimensional flows that iteratively solves the Navier-Stokes governing equations through a numerical procedure based on the Finite Volume method. The application of the CFD methodology for flow analysis requires the construction of the threedimensional model (Salome-Meca), the specification of the initial conditions, the turbulence modeling, the solving of the governing equations (OpenFoam) and, finally, the data post-processing (Paraview). This study is based on the channel geometry of the Hydraulics and Fluid Dynamics Laboratory of the University of Cuenca, and the previous calibration of the parameters for the simulation (absolute roughness) in terms of replicating flow variables of the laboratory measurements, which were taken from previous investigations performed under the same approach. Subsequently, simulations are realized in the channel with and without artificial roughness Type A in the channel bottom, varying the flow rate and the spacing between roughness blocks as recommended in the manuals, in order to compare the effectiveness when using artificial roughness according to the proposed theoretical models (Aivazian and Pikalov), in addition to proposing a potential adjustment to their expressions and design parameters.