Numerical study on effective parameters on block-ramps energy dissipation

One of the most efficient energy dissipatoion structures in open channels are block ramps; which has been considered and used most often recently because of the the simple performance. This kind of energy dissipatores can be assumed as a particular type of baffle block chutes, but with natural base materials and without cement structure. In laboratories, several physical models have been built and examined about their efficiencies. Regardless of the cost and time of tests and examinations, they have had the scale change problems. Today by using efficient computational fluid dynamics codes (CFD) fluid hydraulic behavior is more widely examined. This paper at first, reviews the classification of this structures from the point of fabrication and roughness from various point of views. Then deals with the formation of some types of flow regimes (volume flow rate) on them. In continue to the study, numerical simulation on one kind of this block ramps have performed and energy dissipation mechanism on various flow regimes on them have surveyed. For this reason, in this study Flow-3D software is utilized. In this research, incompressible fluid assumption, VOF method to calculate the free surface and LES turbulence model is used. The results showed the more energy dissipation with more turbulence and more turbulence with forming the recirculating flow and extending the distance of the reattachment point from the boulders. Consequently, energy dissipation is maximom for lower volume flow rate and higher slope of the ramp. Because in these two conditions, the flow involves with roughness of the ramp more and more; hence it gets easier for turbulent flow to happen. In other words, energy dissipation is also maximom for the non-submerged boulders. Flows in which boulders are submerged have different mechanism of energy dissipation. In these type of flows, energy dissipation is maximom for the wake-interface flow condition and isolated roughness flow condition respevtively. Therefore, in order to enhance the energy dissipation in flow over block ramps it is advised to reduce the effective cross section or reduce the submergence of scale roughness with holding the same effective cross section and the volume of fluid flowing over the structure. Because in these two conditions, the flow involves with roughness of the ramp more and more; hence it gets easier for turbulent flow to happen. In other words, energy dissipation is also maximom for the non-submerged boulders. Flows in which boulders are submerged have different mechanism of energy dissipation. In these type of flows, energy dissipation is maximom for the wake-interface flow condition and isolated roughness flow condition respevtively. Therefore, in order to enhance the energy dissipation in flow over block ramps it is advised to reduce the effective cross section or reduce the submergence of scale roughness with holding the same effective cross section and the volume of fluid flowing over the structure.