What is unsteady drive

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Various types of pressure transducers are used at the IST to measure unsteady pressures, which differ greatly depending on the application and operating conditions. If only the fluctuating signal components are of interest, piezoelectric pressure sensors are often used, which can be used in a variety of ways due to their robust design. The charge shifts generated due to the pressure forces are converted into voltage signals with the aid of charge amplifiers. If, in addition to the fluctuating signal components, the stationary components are still of interest, piezoresistive pressure sensors are often used, which are used in particular in applications that are characterized by high pressure fluctuations. Due to their compact design, they offer an extremely high spatial resolution. Modern transient recorders from different manufacturers can be used for data acquisition, which enable the synchronous recording of several channels in real time. The relationship between the measured voltage signal and the applied pressure is determined on the basis of calibration tests and can be highly non-linear depending on various factors. The pressure, the temperature, the frequency of the pressure signal and the installation situation play a role here. The sensors are calibrated both statically and dynamically and, depending on the application, is carried out directly at the IST or by long-term partners. In this way, the step response of the signal generator can be determined in the shock tube that is frequently used, whereby conclusions can be drawn about the frequency and phase response.

Application and field of application

In various research projects at the IST, aeroacoustic phenomena are examined in both axial and radial machines. Due to the high pressures and temperatures that frequently occur in turbo machines, the use of microphones is often unthinkable, which is why piezoelectric and piezoresistive sensors are used for these investigations. The pressure fluctuations can be assigned to acoustic modes on the basis of the information about the amplitude and phase of the signals obtained at various measuring points. Due to the high circumferential mode orders that occur, a very large number of measuring points is necessary in order to be able to determine the modes. To reduce the number of measuring points, modern signal processing methods from the area of ‚Äč‚Äčcompressed sensing are used at the IST, which enable the solution of the system of equations, provided that the number of mode orders that occur is limited. Furthermore, transient pressure sensors are also used to measure total pressures transiently. For example, probe rakes and probes are used to analyze the backflow phase during the pumping cycle of a compressor.