# Calibration of the energy extraction

Several comparisons of LES and RANS modelling techniques have been reported due to their increased importance in modelling turbulent flows. It is generally agreed that RANS is the simpler technique but it lacks accuracy especially in applications where there are more complex flows such as vortex shedding, large GSK 1349572 zones, and high streamline curvature [14], [15], [16] and [17]. In particular, RANS relies on an implicit assumption that there is a scale separation between all turbulent components of the flow, which will be replaced by a statistical model, and any deterministic transient motions such as vortex shedding, pulsatile pumping or (as here) flow components associated with the blade motions. In cases such as esophagus one where there is a significant overlap between the deterministic and large turbulent scales, LES is known to be the preferred approach. Despite this, an initial set of simulations was conducted for the new MRL device in order to compare the two modelling techniques for this turbine. The analysis indicated that the LES modelling technique showed better results for the MRL device. The detailed discussions and comparisons of the two models are reported in Ref. [13]. Thus the LES modelling technique has been implemented for this research work.