Dynamic pressure probe response tests for robust measurements in periodic flows close to probe resonating frequency

Abstract

A single-hole probe was designed to measure steady and periodic flows with high fluctuation amplitudes and with minimal flow intrusion. Because of its high aspect ratio, estimations showed that the probe resonates at a frequency two orders of magnitude lower than the fast response sensor cut-off frequencies. The high fluctuation amplitudes cause a non-linear behavior of the probe and available models are neither adequate for a quantitative estimation of the resonating frequencies nor for predicting the system damping. Instead, a non-linear data correction procedure based on individual transfer functions defined for each harmonic contribution is introduced for pneumatic probes that allows to extend their operating range beyond the resonating frequencies and linear dynamics. This data correction procedure was assessed on a miniature single-hole probe of 0.35 mm inner diameter which was designed to measure flow speed and direction. For the reliable use of such a probe in periodic flows, its frequency response was reproduced with a siren disk, which allows exciting the probe up to 10 kHz with peak-to-peak amplitudes ranging between 20%–170% of the absolute mean pressure. The effect of the probe interior design on the phase lag and amplitude distortion in periodic flow measurements was investigated on probes with similar inner diameters and different lengths or similar aspect ratios (L/D) and different total interior volumes. The results suggest that while the tube length consistently sets the resonance frequency, the internal total volume affects the non-linear dynamic response in terms of varying gain functions. A detailed analysis of the introduced calibration methodology shows that the goodness of the reconstructed data compared to the reference data is above 75% for fundamental frequencies up to twice the probe resonance frequency. The results clearly suggest that the introduced procedure is adequate to capture non-linear pneumatic probe dynamics and to reproduce time-resolved data far above probe resonant frequency.

Flow structure of pressure transmission tube and its influence on unsteady pressure measuring results in compressible flow

“…The transmission mechanism of amplitude can be explained based on the model in section 3.3. The amplitude of p 2 (t) is determined by the mass flow rate and the stagnation enthalpy change according to equation (19). Hence a conceptual ideal measurement system can be introduced to characterize the amplitude ratio of a given tube.…”

“…The equivalent stagnation temperature ratios under different conditions in Fig. 22 are calculated based on CFD results according to equation (19). η is sensitive to the Mach number, but not sensitive to the frequency.…”

“…Fotia et al [18] experimentally studied the response of tubes to non-linear pressure fluctuations with a rotating detonation engine. Sahin and Schiffmann [19] used a siren disk to reproduce periodic flows for dynamic calibration and introduced a modified correction method based on Fourier series. These calibration experiments were mostly conducted in static air or subsonic airflow, but the calibration results in incompressible flow may be invalid for compressible flow because of the strong interaction between the pressure tap and the cross flow.…”

Technology Development of Fast-Response Aerodynamic Pressure Probes

“…The dynamic calibration of fast-response pressure instrumentation poses, at first, technical issues related to the generation of input signals featuring unsteady perturbations at sufficiently high frequency. Siren disks [30] are used to generate periodic stimulus signals while shock tubes [6,24], are used to generate a transient non-periodic signal, as the travelling shock wave produces a step signal in very good approximation.…”

“…Siren disks [30] are used to generate periodic stimulus signals while shock tubes [6,24], are used to generate a transient non-periodic signal, as the travelling shock wave produces a step signal in very good approximation.…”