## 7 Design of a Splittered Axial-Flow Rotor and Model Validation  
### Design Specifications  
An axial-flow rotor with SVs based on the flowpath of the Low-Speed Large-Scale Axial Compressor test platform at Beihang University [(20; 21)] was designed to validate the model. The test platform has been rebuilt for an improved hub-to-casing ratio of 0.75 to simulate the environment of high-pressure core compressors more accurately. The flowpath is in a parallel annulus, which has a constant radius for both the hub and casing. The design parameters for the rotor are shown in Table 7.  
Figure 18: Calculation steps of the correlation model.  
In order to exclude the interaction of upstream and downstream blade rows for the model, a single rotor was designed. The meridional stream surface was solved by using a simple radial equilibrium equation with radially uniform work input, resulting in a free vortex design. Accordingly, the relative inflow and outflow angles could be calculated at different spanwise locations from hub to casing, which were the inputs of the blading design process shown in Figure 18. A design line of the relative inflow and outflow angle is given in Figure 19.  
Along the design line, the camber angles and stagger angles spanned from hub to casing could be obtained to match the velocity triangles. It should be noted that, if the blade was designed with a constant equivalent solidity of 1.60 from hub to casing, the inflow and outflow angles could be determined based on the results shown in Figure 19. However, in actuality, the equivalent solidity at different spanwise location should be set based on the demand of work input, the limitation of diffusion factor, and the limitation of structural strength. Therefore, the design line shown in Figure 19 only provides initial guesses of the stagger and camber angles, and the final result should be calculated based on the iteration process given in Figure 18. The final blades were stacked along a radial straight line that passed through the gravity center of principal blades at different spanwise locations.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline design flow coefficient, \(\varphi=V_{x}/U_{\text{mid}}\) & 0.65 \\ design work coefficient, \(\psi=\Delta h/U_{\text{mid}}^{2}\) & 0.51 \\ mass flow rate (kg/s) & 28.2 \\ rotation speed (rev/min) & 1100 \\ hub/casing diameter (mm) & 750/1000 \\ tip clearance (mm) & 1.25 \\ Chord (mm) & 114 \\ PB/SV number & 24/24 \\ hub/mid/tip ES & 1.86/1.59/1.39 \\ aspect ratio & 1.1 \\ chord ratio, CR & 0.60 \\ percent pitch, PP & 0.50 \\ diffusion factor, DF\({}_{\text{mid}}\) & 0.45 \\ relative inlet Mach number, M\({}_{\text{mid}}\) & 0.175 \\ Reynolds number, Re\({}_{\text{mid}}\) & \(1.0\times 10^{6}\) \\ \hline \hline \end{tabular}
\end{table}
Table 7: Design parameters for a splittered axial-flow rotor.  
Figure 19: Reference minimum-loss inflow and outflow angles with camber angles and stagger angles as functions according to the 2D correlations.  
This setting could readily satisfy the restriction of structural strength and stress. Figure 20 presents the 3D blades of a splittered axial-flow rotor designed using the developed model.  
The rotor designed by the 2D model (R2D as a simplification) is utilized to validate the 2D correlation, and to provide a spanwise distribution of AVDR, which is used to redesign the rotor by using the 3D model. The redesigned rotor is named as R3D for simplification. The redesigned result showed that the flow deflection angles should be increased about two degrees at all spanwise locations to compensate the work deficit due to blade tip clearance leakages and thickened endwall boundary layer.