## 2 Experimental Setup and Data Processing
### Data Acquisition and Processing  
Detailed acoustic tests are presented in Figures 1b and 5, where nine free-field microphones of type G.R.A.S 46 AE (GRAS Sound and Vibration, Holte, Denmark) were used to collect acoustic data, while only the measured signals perpendicular to the airflow (see Figure 5) are shown in this paper for easier processing. This microphone was positioned out of the airflow, and its head was 1.0 m apart from the rear end of the airfoil at \(\alpha=0^{\circ}\) in the midspan plane. The acquired data were recorded at a 51.2 kHz sampling rate over 30 s of sampling time. The sound pressure level (SPL) was subsequently calculated using an 8192-point Hanning window function and 50% data overlap. Then, the overall sound pressure level (OASPL) could be computed by integrating the SPL between 100 Hz and 25.6 kHz, where the lower frequency is limited by the cutoff frequency of the anechoic chamber and the upper frequency corresponds to the Nyquist frequency of the measured signal. A free-field correction of different angles of incidence is not performed in this work  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Configuration** & \(d_{h}\) **(mm)** & \(c_{h}\) **(mm)** & \(s_{h}\) **(mm)** & **Subregions** \\ \hline L04M04N04 & 0.4 & 2.0 & 10.0 & L/M/N \\ L06M06N06 & 0.6 & 2.0 & 10.0 & L/M/N \\ L08M08N08 & 0.8 & 2.0 & 10.0 & L/M/N \\ L00M06N06 & 0.6 & 2.0 & 10.0 & M/N \\ L00M00N06 & 0.6 & 2.0 & 10.0 & N \\ L00M06N00 & 0.6 & 2.0 & 10.0 & M \\ L06M00N00 & 0.6 & 2.0 & 10.0 & L \\ L04M05N06 & 0.4, 0.5, 0.6 & 2.0 & 10.0 & L, M, N \\ L06M05N04 & 0.6, 0.5, 0.4 & 2.0 & 10.0 & L, M, N \\ L04M06N08 & 0.4, 0.6, 0.8 & 2.0 & 10.0 & L, M, N \\ L08M06N04 & 0.8, 0.6, 0.4 & 2.0 & 10.0 & L, M, N \\ L04M08N12 & 0.4, 0.8, 1.2 & 2.0 & 10.0 & L, M, N \\ L12M08N04 & 1.2, 0.8, 0.4 & 2.0 & 10.0 & L, M, N \\ L06M06N06-\(c_{h}\)4 & 0.6 & 4.0 & 10.0 & L/M/N \\ L06M06N06-\(c_{h}\)1 & 0.6 & 1.0 & 10.0 & L/M/N \\ L06M06N06-\(c_{h}\)2 & 0.6 & 2.0 & 20.0 & L/M/N \\ L06M06N06-\(c_{h}\)5 & 0.6 & 2.0 & 5.0 & L/M/N \\ \hline \hline \end{tabular}
\end{table}
Table 1: Structured porous trailing edges with different pore parameters.  
Figure 4: Pattern of the pore design.  
because the effect is the same for both baseline trailing edges and porous trailing edges, and our analysis is based on the measured noise level differences.  
The difference in sound pressure level (\(\Delta\)SPL) between a structured porous edge and the baseline nonporous edge is defined in Equation (1):  
\[\Delta\text{SPL}=\text{SPL}_{\text{p}}-\text{SPL}_{\text{b}}, \tag{1}\]  
where \(\text{SPL}_{\text{p}}\) and \(\text{SPL}_{\text{b}}\) are the SPL measured for the porous and baseline edge, respectively.  
Similarly, the difference in overall sound pressure level (\(\Delta\)OASPL) between a structured porous edge and the baseline solid edge is defined in Equation (2):  
\[\Delta\text{OASPL}=\text{OASPL}_{\text{p}}-\text{OASPL}_{\text{b}}. \tag{2}\]  
Both \(\Delta\)SPL and \(\Delta\)OASPL can be used to evaluate the acoustic performance of the different structured porous edges, where a negative value represents noise reduction while a positive value indicates noise increase.