Resumen de Experimental characterization of turbulance in steep rough streams
Torrential flows have so far been studied less than have river flows, due to the difficulty of faithfully reproducing them in the laboratory, and the few field measurements available. For this reason, this present research tries to shed some light on the turbulent description of this type of flows, evaluating the effects posed by the energy slope and the roughness of the bed. With this study we have made a significant contribution to the knowledge of how turbulent properties develop along the profile of the depth of the flow and thus improve all the engineering aspects that affect the high mountain flows, from the valuation of the energy losses produced in the rough layer until the beginning of movement of the particles.
For this purpose, different flows have been characterized by the description of classic turbulent parameters (turbulent intensity, turbulent kinetic energy, Reynolds shear stress, dissipation, length scales, etc.). In addition, a detailed analysis of quadrants has been carried out due to the implications of bursting turbulence at the beginning of particle movement. Some of the results obtained from the analysis of quadrants have shown that the turbulence does not happen randomly, showing certain temporal and spatial patterns that can be of great help in the development of generation models of synthetic velocity series. The analysis of quadrants has been complemented with an analysis of the pulses, promoted for the temporary coherence observed in the quadrant sequences. One pulse is defined as the uninterrupted time that an event u'w' remains in the same quadrant. This analysis yields very interesting results since they show a certain proportionality in both quantity and duration of turbulent pulses, as if it were a condition to be fulfilled by all flows.
Many authors have shown that the impulse applied (force x time application) is responsible for the initial movement of the particles rather than only the magnitude of the applied force. This idea has been the point of departure for the realization of a conceptual model to assess the rate of transport of sediment of a flow. This model is based on the consideration that Reynolds shear stress has the most important role in the beginning of the bed material’s movement. Therefore, the time in which the bed shear stress applies in the same direction defines the intensity of the impulses applied to a surface. This last hypothesis together with the concept of pulses and pulse sequence are the bases for a methodology for assessing the transport rate of a flow and a specific sediment. The conceptual model has been evaluated by comparison with the transport rates measured in the laboratory.
