# Investigation on Characterization of Typical Characteristic in Compressor Based on Flat Plate Model
## 3 Noise Experiments and Results
### Analysis of Noise Characteristics under Abnormal Vibration of Rotor Blades  
The compressor with the deflection angle of IGV of it works at a specific speed (about 9960 r/min) for a period of time, the abnormal vibration with a relatively large amplitude is observed at the first stage of the rotor blade of the high-pressure compressor. Figure 4 shows the variation rhythm of the noise signal before and after the abnormal vibration of Rotor1 occurs with a relatively large amplitude at discrete rotor speed ranges, respectively. The red data in the figure indicates the operational condition when the rotor blade occurs a relatively large amplitude vibration. Figure 3: Diagram of rotor blade vibration measurement positions. Figure 2: Diagram of noise measurement positions. It can be seen from Figure 4 that the internal noise spectrum of the compressor presents typical broadband noise characteristics, and there are several characteristic frequencies with discrete pure sound components. It is obvious that the pure sound component appears at 1402 Hz when the abnormal vibration of high-amplitude value occurs in the first stage of the rotor blade of the high-pressure compressor. In order to reveal the horizontal distribution of noise sound pressure level along the axial direction of the compressor before and after Rotor1 of the high-pressure compressor vibrates with a relatively large amplitude, the sound pressure level distributions of the noise signals at four different measuring points in the compressor flow channel are analyzed. The sound pressure level distributions of the noise signal at 1402 Hz measured at different measuring points are present in Table 1 and Figure 5. \begin{table}
\begin{tabular}{c c c c c} \hline
**Rotor Speed** & **IGV** & **IGV/Rotor1** & **Rotor** & **Stator1** \\ (r/min) & **(dB)** & **(dB)** & **(dB)** & **(dB)** \\ \hline
9600 & 120.4 & 129.2 & 144.2 & 138.3 \\
9660 & 122.0 & 128.5 & 144.0 & 138.2 \\
9720 & 122.5 & 129.2 & 144.8 & 139.7 \\
9780 & 122.6 & 130.6 & 146.3 & 139.7 \\
9840 & 124.1 & 134.0 & 149.7 & 142.9 \\
9900 & 125.4 & 137.2 & 152.1 & 144.9 \\
9960 & 124.4 & 136.3 & 151.4 & 144.1 \\
10,020 & 123.3 & 134.4 & 149.1 & 141.7 \\
9960 & 124.6 & 137.3 & 153.4 & 144.8 \\
9960 & 126.0 & 138.8 & 153.4 & 146.3 \\
9960 & 125.6 & 138.6 & 153.3 & 146.1 \\
9960 & 125.3 & 138.7 & 153.5 & 146.2 \\
9960 & 124.8 & 138.5 & 153.4 & 146.1 \\ \hline \end{tabular}
\end{table} 
Table 1: Distribution of sound pressure level at 1402 Hz of noise signals at different measurement positions. Figure 4: The change of noise signal spectrum before and after rotor blade abnormal vibration. Through the above analysis, it is found that the sound pressure levels of the noise signals were measured at four different measuring points along the axial direction of the compressor at the characteristic frequency of 1402 Hz, before and after the abnormal vibration of the first stage of the rotor blade of the high-pressure of the compressor occurs, are all the maximum value at the position directly above the measuring point. When the vibration amplitude of the rotor blade sustains a relatively large value, the sound pressure level of the noise signal measured at all measuring points also reaches the maximum at this characteristic frequency. In addition, the sound pressure level directly above the rotor blade is the highest, which is up to 154 dB. Through the analysis in Figure 4, it is found that, when the high-pressure first-stage rotor blades vibrate with a large amplitude, the characteristic frequency structure and a high-amplitude discrete pure tone component of 1402 Hz appear in the noise spectrum of the compressor internal flow channel.