## 6 Summary and Conclusions  
This work has been dedicated to study the flow characteristics as well as the modelling of turbulence in wakes produced by a porous disk. For this, disks of two porosities have been used as well as two instances of decaying and homogeneous turbulence inflows, identified by streamwise turbulence intensities (TI) of approximately 3% and 12% and corresponding longitudinal integral lengthscales (\(L_{1}\)) of 0.01 m and 0.03 m. To perform this study, a methodology has been developed and implemented in OpenFOAM that uses Large-Eddy Simulations (LES) to reproduce the main turbulence features of a turbulent flow generated in a wind tunnel. The Actuator Disk (AD) technique was used to model the porous disk and replicate the turbulence properties measured in the wake flow. The employed methodology is based on a procedure previously shown to provide good results in the simulation of wind turbine wakes in homogeneous turbulence and atmospheric flows. A comparison with prior work made with RANS was made wherever possible. To reproduce the grid-generated turbulence in the wind tunnel, a synthetic field of homogeneous isotropic turbulence was introduced at the inlet of an LES. An analysis of the decaying turbulence simulated by the LES demonstrated that the simulations reproduce the TI decay and the evolution of \(L_{1}\) predicted by the parametrizations predominant in the literature, in addition to replicating fairly well the experimental values at the measured locations. The wake field results obtained with the introduction of the AD showed a good agreement with the wind tunnel experiments for the velocity deficit, turbulence kinetic energy \(k\) and its dissipation \(\varepsilon\). It was also found that \(L_{1}\) evolves, for the most part, as in the decaying homogeneous turbulence. Remarkably, there was no apparent variation of \(L_{1}\) within the shear layer compared to the center of the wake or outside the wake envelope. A study of how the LES performs in the wake was also carried out, with the main interest of observing how the modelling ratio (the contribution of the resolved or SGS parts to the total value) is affected by the regions of high shear behind the AD in comparison with the outflow and the center of the wake. It was found that while the modelling ratio of \(k\) in the wake is largely maintained with respect to the outside flow, the subgrid part of \(\varepsilon\) increases within the shear layer, but only when the  
Figure 17: Contours of the vorticity field obtained with the Ti3 inflow and disk \(C_{T}=0.62\)**(top)** and the Ti12 inflow and disk \(C_{T}=0.71\)**(bottom)**. low TI inflow is used. From the results, it is seen that modelling in the freestream flow prevails in the wake just as the level of inflow turbulence increases. On the other hand, the wake results compare well with the velocity and \(k\) obtained with RANS. Likewise, LES and RANS results of \(\varepsilon\) match also in the low TI case, whereas the values yielded by RANS seem overestimated--in comparison with both measurements and LES--in the high TI case, particularly in regions of strong shear. Spectra computed at different axial positions in the wake reveal that shear causes a noticeable boost in the energy content of turbulence, but only in the low TI case. This causes that for the two furthermost positions (\(x=10D\) and \(14D\)), the energy levels are higher or at least as energetic as in the upstream region near the disks. Moreover, the turbulence at those positions shows a clear inertial range that was absent in the decaying turbulence at low TI. Conversely, for the high TI inflow, it is seen that, despite the fact that turbulence energy levels rise in the wake with respect to the decaying homogeneous flow, the relative decay is maintained from one position to the other. Considering the above, the central conclusions of this investigation are:  
* The evolution of \(L_{1}\) was not noticeably different in the wake in comparison to what was observed in the decaying homogeneous turbulence.