Unsteady surface pressure obtained based on amplitude-calibration-based nonembedded measurement method PartI-calibration

Unsteady surface pressure (USP) is an important physical quantity to study blade loads and boundary layer flow. However, the characteristics of high-load compressor cascades with thin walls, narrow passages, and large geometric deflection angles make the measurement of USP considerably challenging. We developed an amplitude-calibration-based nonembedded measurement method (NEM) for USP measurement. The principle of this method is to perform indirect measurement by leading the airflow out of the measured surface through an air tube and correct the amplitudes by calibration. The data is used for amplitude calibration.Amplitude calibration was performed with six tube lengths of 80, 55, 49, 39, 37, and 33 mm. The calibration frequency is limited to 1–7 kHz due to the following two reasons. First, the amplitude of the signal obtained from the speaker decreases with the increase in the frequency in the calibration device. Second, the amplitude of the pressure wave cannot be enhanced by its reflection because the end cap is removed from the tube. Calibration presents information obtained by both the direct (reference) and NEM (measured) measurements of the frequency and amplitude. The calibration setup is shown in the figure attached. The pressure fluctuation signal is generated with the speaker. The blade with the hydrostatic pores is placed at the end of the dynamic calibration chamber with the end cap removed. A thin line pressure transducer (R, which represents reference signal, type: Kulite LQ-062-5D) is pasted close to the hydrostatic pore to measure the unsteady pressure directly, and a micro pressure transducer (M, which denotes measured signal, type: Kulite XCQ-080-5G) is connected to the hydrostatic pore with a soft connection.