## 1 Introduction
Thereby, the computational power and time of the RSM model are justified under the presence of a high number of eddies or secondary flows. These authors also indicate that the large eddy simulation (LES) model, which belongs to the filtered-type models, calculates eddies directly in an unsteady simulation. Neither of them makes assumptions on the eddies with a size lower than the mesh element size; these are simply neglected, thus decreasing the computing time. The LES models are not suitable for very complex geometries. Nevertheless, in the case of eddy flows, the LES models approach experimental values in a better way than the RANS-type models. The direct numerical simulation (DNS) calculation method simulates the whole turbulence range from the Kolmogorov smallest microscale to the integral scale, avoiding the application of eddy models. The main limitation of this method is that it requires some previous meshing calculations that depend on the Reynolds number. In the case of water, the number of meshing processes is of the order of \(10^{11}\), which is impossible to address with the actual processing technology. Therefore, different models must be used for the calculations of eddies. For the Reynolds stress calculation, the Reynolds stress tensor or the Boussinesq eddy viscosity hypothesis can be used, given that these relate to the Reynolds stress with the velocity gradients. If the latter is applied, then different calculation methods can be considered to obtain the eddy viscosity, such as the Spalart-Allmaras method, the k-\(\varepsilon\) and the k-\(\upomega\) methods or any of their variations. In the case of the Spalart-Allmaras method, a single additional equation is used, whereas the k-\(\varepsilon\) and k-\(\upomega\) methods include two additional equations. On the contrary, the very large eddy simulation (VLES) models filter a large amount of the eddies, as they apply the k-\(\varepsilon\) or k-\(\upomega\) methods to subsequently apply a filter. The scale adaptive simulation (SAS) model is the improved version of the unsteady RANS models, as it is based on the Rotta scalar length equation reformulation, representing a combination of the Rotta and the k-kl (k-kl- \(\omega\) transient) models. This model's performance is similar to detached eddy simulation (DES) models, overcoming the RANS and LES models for poor meshes. Lastly, the DES model was formulated in order to solve the caveats of the LES methods, particularly for bounded flows at high Reynolds numbers, where the LES simulation takes a very high computing power. The DES model is a LES-RANS hybrid, as it is based on a LES model. However, the boundary layer and surroundings were simulated with RANS models, such as the Spalart-Allmaras, the realizable k-\(\epsilon\) and the SST k-\(\omega\), that were modified for unsteady systems. The diagram shown in Figure 1 depicts a classification of the main CFD calculation methods currently used and previously commented. AM, as well as 3D printing (3 DP) [20], allow the manufacture of any type of complex geometry whose processes imply the addition of layers upon layers of material until obtaining the part or the prototype pre-designed in 3D using a CAD software tool [21]. Some authors have called these techniques computer-aided tissue engineering (CATE) [22] and other designed applications, based on the same concept [23; 24]. According to [25; 26], among these additive technologies, FDM is one of the most widely used methods due to its simplicity, versatility, low cost and the large number of materials that it is able to carry [27]. Within FDM, the properties of the materials are highly influenced by the processing parameters (3D printers) [28]. For these reasons, it is necessary to test this manufacturing technology with some biocompatible materials capable of reproducing geometric architectures required by 3D scaffolds. In this work, a comparative analysis is carried out to find the most adequate turbulence method for the design of a 3D scaffold by FDM 3D printing techniques [12; 29].