CROSS SPECTRA BETWEEN TEMPERATURE AND PRESSURE IN A CONSTANT AREA DUCT DOWNSTREAM OF A COMBUSTOR.

Theory indicates that pressure-temperature cross-spectra are necessary in predicting noise in regions of velocity gradients. In the present study, the feasibility of measuring pressure-temperature cross-sprectra and coherence and temperature-temperature cross-spectra and coherence at spatially separated points along with pressure and temperature auto-spectra in a combustion rig was investigated. The measurements were made near the inlet and exit of a 6. 44 m long duct attached to a J-47 combustor. For this study the fuel used was Jet A. The cross-spectra and coherence measurements show the pressure and temperature fluctuations correlate best at low frequencies. At the inlet the phenomena controlling the phase relationship between pressure and temperature could not be identified. However, at the duct exit the phase angle of the pressure is related to the phase angle of the temperature by the convected flow time delay.