Phase-locking in post-processing for pulsating flames

Abstract

A new approach to studying thermo-acoustically driven heat release fluctuations has been developed. By performing a phase correlation of the pulsation signal for each instant in time in post-processing, a number of advantages over the usual online processing technique are obtained: many frequencies can be analysed from the same data set allowing faster recording and introducing fewer errors than performing the phase correlation online. The method does not require complicated trigger and delay line setups and is most flexible. As an example of this technique, two different pulsation modes of a swirl combustor are resolved from only 300 chemiluminescence images. Further use of this method for a wide variety of applications is indicated.

An Experimental Investigation of the Nonlinear Response of an Atmospheric Swirl-Stabilized Premixed Flame

“…For each amplitude, 500 pictures were acquired with the ICCD camera. A trigger pulse from the camera system is recorded and is used in the post-processing to make a phase correlation for each image with the photomultiplier signal and perform a phase-locking average of the images [14], The phase-averaged images coiTespond to the projection of an approximately axisymmetric intensity distribution. An Abel deconvolution scheme [15] was applied to the phase-averaged images to recover the radial intensity distribution from the projection.…”

Liquid-Fuel Behavior in an Aeronautical Injector Submitted to Thermoacoustic Instabilities

“…To extract the temporal sequence of events leading to combustion instabilities, a statistical analysis of experimental data is then needed. The phase-averaged analysis is the most common method to study cyclic phenomena: in particular, in combustion experiments [5,[36][37][38][39][40][41]. Nonetheless, a periodical reference signal is needed to perform this analysis.…”

“…However, any analysis mistake cannot be corrected a posteriori, and variations in the instability frequency cannot be taken into account. These drawbacks are avoided by the second method [40], which is better suited for selfsustained thermoacoustic instabilities: for example, to obtain the phase of the OH chemiluminescence measurements by using the Hilbert transform [42]. In the present work, the pressure signal is sampled at 10 kHz simultaneously with a transistor-transistor logic (TTL) signal delivered by the cameras.…”

Chemiluminescence as diagnostic tool in the development of gas turbines

“…To visualise the pulsation behaviour and link this to the design of the burner as well as to validate the design tools, phase resolved detection is used allowing detection of flame positions and shapes also as function of the pulsation phase angle (for given frequency). There are in principle two ways to record this phase matched data: by online signal processing [39], fast processing and direct phase angle determination or by free running image recording parallel to the recording of the pressure signal and phase matching the data in a post-processing step [40]. The latter method allows for a much higher flexibility and robustness like the sorting for more than one frequency within one sample.…”