## 2 Materials and Methods
### 1D Model  
Analogies were used to ensure similarity between RT and ST when validating ST using the 0.5 mm gap height because of the 3:1 proportion scale on these models. Two different similarities were used; on the one hand, Mach, and on the other hand, Reynolds similarity were set. When searching for a lookalike Mach distribution in the stator, a similar blade loading was expected to appear. When chasing the same Reynolds number, the same patterns of flow near walls are expected to be found. This is detachment and separation in the boundary layer. Thus, Reynolds similarity would be more appropriate to study the tip leakage flow through the gap since it is a region highly affected by wall effects. Since the operating points in the real turbine have to fulfill the requirements to meet the aforementioned similarities, the scaled model defines the reference operating point. A point with the highest pressure and mass flow that the experimental test bench can supply was chosen since that would be the one tested by the 3D model scaled turbine when the experimental campaign would take place. The decision to apply the maximum of these parameters (pressure and mass flow) is based on the fact that the viscous effects and flow separation are more notorious at this point. Figure 2: Polyhedral unstructured mesh with refinements near walls. (**a**) Mesh upper view. (**b**) Prism layer meshing surrounding vanes. Due to the Mach similarity, both static and absolute values can be compared indistinctly. The increase of density derived from the highest pressure resulted in reducing mass flow. Regarding the temperature imposed for the simulations, quasi-adiabatic measurements are widely used in research, having relatively low temperatures at the inlet. In addition, some authors, such as [PERSON] et al. (2018) and [PERSON] et al. (2019), demonstrated that the reduced mass flow map of the turbine offered the same efficiency for hot and cold temperatures through adiabatic measurements. The materials of the printed model and the instrumentation that would be employed when the experimental campaign is performed are not designed to endure such high temperatures. For that reason, the inlet temperature of the turbine is set in the model at 343.15 K. This boundary condition is ubiquitous independently of the VGT opening or the similarity studied. This temperature was similar to the obtained values in the experiments performed over the real turbine by [PERSON] et al. (2019) in the quasi-adiabatic experiments and simulations. Two studies were performed for the ST, one with the maximum MFR that the experimental test bench can provide to study Mach similarity, and another with the maximum scaled MFR that the RT can manage that permits to simulate [PERSON] similarity. Boundary conditions for the VGT60 case can be seen in Table 2, where \(ST_{Max}\) study was linked to the \(RT_{Ma}\) one, showing that RT had about one-ninth of the MFR that ST presented. The imposed inlet temperature for each studied case was the same, assuming an adiabatic behavior on the turbine. Figure 3 shows that for both RT simulated cases, a good agreement with the experimental results was found, being within their confidence interval.