Abstract

MARTINEZ-REYES, Javier  and  GARCIA-VILLANUEVA, Nahún Hamed. Effects of the blockage ratio due to hydrokinetic turbines for producing energy in irrigation channels. Tecnol. cienc. agua [online]. 2020, vol.11, n.3, pp.190-235.  Epub June 10, 2024. ISSN 2007-2422.  https://doi.org/10.24850/j-tyca-2020-03-06.

In this paper, the effect of the blockage ratio generated by the hydrokinetic turbines upon the obtainable hydraulic power in an open channel is analyzed in order to validate part of the theory related to the calculation of the maximum obtainable power by the hydrokinetic turbines, by using porous discs in an experimental open channel. This analysis is supplemented with the study and characterization of the way in which is developed the wake, that is produced downstream, and the experimental results are compared with those of a one-dimensional numerical model.

During the development of the experimental study, three different blockage ratios were analyzed, for which the hydraulic variables were kept fixed in the experimental open channel. Under these conditions, in order to characterize the behavior of the flow and obtain the components of the instantaneous velocity an acoustic Doppler velocimeter was utilized; and to measure the hydrodynamic thrust on the discs a load cell was employed.

Among the main results it was found that the velocity in the zone of the far wake has a 90% recovery at approximately 12 diameters downstream from the disc. It is noteworthy that, at this distance, the turbulent intensity was 8%, while the mean turbulence intensity in the section of the open channel where the porous discs are located, before its placement, it was 5.7%.

The power coefficients obtained for the different blockage ratios show a 59% increase between the lowest blockage ratio B 1 = 0.090 and the highest B 3 = 0.197. The differences between the power coefficients of the experimental tests and the maximums obtained with the one-dimensional theory are 19.45% for the case of B 1 = 0.090; 4.13% for B 2 = 0.156; and 0.84% for B 3 = 0.197. In general, according to the one-dimensional theory, using a blockage ratio of around 0.20 the values of the power coefficient are similar to the maximums expected, and using lower values than 0.10, this coefficient falls by around 20% compared with the maximum theoretical coefficient.

Keywords : open channel flow; thrust coefficient; power coefficient; porous disc; energy; blockage ratio; hydrokinetic turbines.