“…This slope is commonly observed with eduction techniques. 4,9 Figure 10.Results obtained for both samples with all three methods. No-flow condition and 130 dB at the facesheet probe.…”
Section: Resultsmentioning
confidence: 99%
“…This slope is commonly observed with eduction techniques. 4,9 The increase in SPL is expected to induce an increase in the liner resistance due to higher nonlinear effects on the perforated facesheet. Also, this non-linear component is expected to reduce as the percentage of open area gets higher.…”
Section: No-flow Resultsmentioning
confidence: 99%
“…However, the results obtained with the in situ technique do not follow the same pattern in comparison to those obtained via impedance eduction, that is the in situ resistance is nearly constant with frequency, whereas the educed resistance shows a strong frequency-dependence. Serrano et al 9 also compared the in situ technique with three impedance eduction methods. Good agreement was also observed for the results obtained with the different eduction methods, but it is less evident for the in situ results.…”
Several techniques are available to characterize acoustic liners when subject to grazing flow and high sound pressure level (SPL). Although the in situ technique started as the primary experimental procedure, impedance eduction techniques have gained popularity over the past years. However, there is a lack of comparison between these group of methods, especially at conditions typically found in turbofan engines. In this work, in situ and impedance eduction techniques are compared at high flow velocities and SPL using typical acoustic liner test samples and considering uniform flow. Both upstream and downstream acoustic wave propagation will also be considered in view of the discrepancies recently observed by eduction methods. A new method to compensate the instrumentation effect in the in situ technique is proposed and validated. Results are obtained for bulk Mach numbers up to 0.5 and SPLs up to 145 dB for both in situ and two eduction techniques. The three methods presents good agreement in the absence of flow. Unexpected results are observed with higher flow Mach numbers using the eduction technique.
“…This slope is commonly observed with eduction techniques. 4,9 Figure 10.Results obtained for both samples with all three methods. No-flow condition and 130 dB at the facesheet probe.…”
Section: Resultsmentioning
confidence: 99%
“…This slope is commonly observed with eduction techniques. 4,9 The increase in SPL is expected to induce an increase in the liner resistance due to higher nonlinear effects on the perforated facesheet. Also, this non-linear component is expected to reduce as the percentage of open area gets higher.…”
Section: No-flow Resultsmentioning
confidence: 99%
“…However, the results obtained with the in situ technique do not follow the same pattern in comparison to those obtained via impedance eduction, that is the in situ resistance is nearly constant with frequency, whereas the educed resistance shows a strong frequency-dependence. Serrano et al 9 also compared the in situ technique with three impedance eduction methods. Good agreement was also observed for the results obtained with the different eduction methods, but it is less evident for the in situ results.…”
Several techniques are available to characterize acoustic liners when subject to grazing flow and high sound pressure level (SPL). Although the in situ technique started as the primary experimental procedure, impedance eduction techniques have gained popularity over the past years. However, there is a lack of comparison between these group of methods, especially at conditions typically found in turbofan engines. In this work, in situ and impedance eduction techniques are compared at high flow velocities and SPL using typical acoustic liner test samples and considering uniform flow. Both upstream and downstream acoustic wave propagation will also be considered in view of the discrepancies recently observed by eduction methods. A new method to compensate the instrumentation effect in the in situ technique is proposed and validated. Results are obtained for bulk Mach numbers up to 0.5 and SPLs up to 145 dB for both in situ and two eduction techniques. The three methods presents good agreement in the absence of flow. Unexpected results are observed with higher flow Mach numbers using the eduction technique.
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