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Identification and measurement of combustion noise from a turbofan engine using correlation and coherence techniques. ph.d. thesis
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Karchmer, A. M. |
| Copyright Year | 1977 |
| Description | Fluctuating pressure measurements within the combustor and tailpipe of a turbofan engine are made simultaneously with far field acoustic measurements. The pressure measurements within the engine are accomplished with cooled semi-infinite waveguide probes utilizing conventional condenser microphones as the transducers. The measurements are taken over a broad range of engine operating conditions and for 16 far field microphone positions between 10 deg and 160 deg relative to the engine inlet axis. Correlation and coherence techniques are used to determine the relative phase and amplitude relationships between the internal pressures and far field acoustic pressures. The results indicate that the combustor is a low frequency source region for acoustic propagation through the tailpipe and out to the far field. Specifically, it is found that the relation between source pressure and the resulting sound pressure involves a 180 deg phase shift. The latter result is obtained by Fourier transforming the cross correlation function between the source pressure and acoustic pressure after removing the propagation delay time. Further, it is found that the transfer function between the source pressure and acoustic pressure has a magnitude approximately proportional to frequency squared. These results are shown to be consistent with a model using a modified source term in Lighthill's turbulence stress tensor, wherein the fluctuating Reynolds stresses are replaced with the pressure fluctuations due to fluctuating entropy. |
| File Size | 9637942 |
| Page Count | 156 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_19770026218 |
| Archival Resource Key | ark:/13960/t3hx64n1h |
| Language | English |
| Publisher Date | 1977-09-01 |
| Access Restriction | Open |
| Subject Keyword | Aircraft Propulsion And Power Tail Assemblies Reynolds Stress Fourier Transformation Acoustic Measurement Coherence Coefficient Cross Correlation Turbofan Engines Pressure Measurement Combustion Chambers Noise Measurement Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Thesis |
