# Experimental and Numerical Research on End-Wall Flow Mechanism of High-Loading Tandem Stators
## 2 Research Object and Method
### Research Methodology
#### 2.2.1 Experimental Methods  
The experiment was conducted at the Low-Speed Large-Scale Axial Compressor (LSLSAC) test facility, Beihang University. The test section of the test facility consists of five rows of blades (as shown in Figure 2), including the inlet guide vane (IGV), inlet stage stator (S0), first stage rotor (R1), first stage stator (S1), and outlet guide vane (OGV). R1 and S1 are tested stages. S0 and IGV simulate the repeated stage environment of a multi-stage compressor together, and OGV transferred airflow into the axial direction. In the test section, the casing diameter is 1000 mm, and the hub-to-tip ratio is 0.75. The design rotating speed is 1100 r/min. All blades incorporated in this study are fabricated using resin-based 3D printing technology, ensuring precision and consistency. The stator assembly is securely mounted onto the hub by an annular dovetail base, and the tip clearance is completely sealed to prevent leakage. A detailed introduction of the compressor test facility could be seen in Reference [26]. In order to measure the performance of the tandem stator, measurement planes were set before and after the stator. The velocity and pressure fields were measured by L-shaped five-hole probes. The arrangement of measuring points was shown in Figure 3. Specifically, 33 measuring points were uniformly distributed along the forward spanwise direction, spanning from 2.4% to 97.6% of the blade height at the stator's entry section. Furthermore, to ensure comprehensive coverage across a single stator pitch, 14 equidistant circumferential measuring points were implemented. To address potential interference emanating from the \begin{table}
\begin{tabular}{c c c c} \hline
**Parameters** & **FB** & **RB** & **Total** \\ \hline Middle span chord (mm) & 69.8 & 58.1 & 128.2 \\ Aspect & 1.8 & 2.1 & 0.98 \\ Solidity (mid) & 1.28 & 1.06 & 2.35 \\ Inlet metal angle (mid,\({}^{\circ}\)) & \(-49.1\) & \(-35.1\) & \(-49.1\) \\ Outlet metal angle (mid,\({}^{\circ}\)) & \(-27.1\) & 6.9 & 6.9 \\ AO & / & / & \(-0.01\) \\ PP (mid/hub) & / & / & \(0.85/0.65\) \\ DF at DE & / & / & \(0.50\) \\ DF at NS & / & / & \(0.62\) \\ \hline \end{tabular}
\end{table} 
Table 1: Geometry and flow parameters of the tandem stator. Figure 2: Low-speed, large-scale axial compressor test facility [25]. stator leading edge, a local enhancement of the measurement density was carried out in the circumferential direction, thereby increasing the resolution in this critical region. At the stator's exit, a similar strategy was employed with 33 measuring points aligned in the forward spanwise direction. In addition, the circumferential arrangement was augmented to include 19 measuring points, thereby furnishing a more precise representation of the flow field. Considering the large flow angle range when the corner separation occurs, the zone method developed by [PERSON] et al. [27] was used to process the measured data of the five-hole probe. Rosemount 3051S series pressure transducers were used in the pressure measurement. The measuring range and accuracy were \(\pm\)6.22 kPa and 0.025% full scale, respectively. The pressure transducers were calibrated before the experiment each time to guarantee the measurement accuracy. The measurement error of five-hole probes mainly came from calibration error and data processing error, and the final relative error was about \(-0.09\) for deflection angle, \(-0.15\) for pitch angle, \(-0.36\)% for static pressure coefficient, and \(-0.17\)% for total pressure coefficient. In order to describe the flow structure in the end region of tandem stators, this study employed the oil flow visualization technique to derive the topological configuration of the limit streamline on both the suction surface and the end-wall of the stator blades. Conventionally, the process of delineating limit streamline by uniformly brushing oil across the entire blade surface is time-consuming. A novel approach was adopted to expedite the oil flow visualization process in the present research.