Estudio experimental y numérico de los sistemas de captación de fondo

Abstract

Bottom intake systems can become effective infrastructure to derive flows in ephemeral streams, where sediment transport reaches important values. The optimization of these systems is a cause for research in semiarid areas. Briefly, these systems can be divided into the following parts: i) bottom rack; ii) transport channel; iii) sand trap. This thesis has focused on the bottom rack. Influence of longitudinal rack slope, as well as the approach flow conditions, is stablished for the: i) amount of derived flows; ii) profile adopted by the water surface and iii) discharge coefficient, taken as the variable defined experimentally by relating the derived flow rate and energy height. Several authors recognize this influence from experimental work (Orth, 1954; Frank, 1959. White et al 1972). Others do not consider this influence due to lack of sufficiently large slopes measurements (Noseda, 1956), or because them reached values higher than 35% (19°), where such influence is no longer observed when analyzing the water surface profile (Brunella et al. 2003). The work has been carried out in the laboratory of hydraulics of the UPCT for T shaped bars and for rates ranging from 0.16 to 0.28 bar space and slope from 0 to 33%. Velocity field and flow pressures measurements along the racks, using PIV (Particle Image Velocimetry) and pitot tubes, has allowed to establish the relationship between the discharge coefficient and pressure on the slit (Krochin, 1978), as well as differences between existing theoretical developments of pressure field along the flow over the racks (Castro-Orgaz and Hager, 2011). From information of several experimental works carried out to date, a multiparameter adjustment is proposed, based on variables obtained from a dimensional analysis. From this is defined an abacus to obtain the equivalent discharge coefficient value for different conditions as: Froude number at the beginning of the rack, Fr0, bar type and void ratio, m. Finally, the study of sedimentation of materials carried by the flow in the space between bars has established the most efficient longitudinal slope at 30%. Similarly, it has proposed increasing rack length that includes this phenomenon. Experimental test with flow that include gravels are taken in the hydraulic device allowing study of occlusion phenomena.