Organized by the Western States Section of the Combustion Institute and hosted by the University of Utah May 19-22, 2013 High speed imaging and analysis of turbulent flames

摘要: The study of time-dependent phenomena in turbulent flames requires detailed knowledge of both the chemistry and flowfield interactions that are present in regions of localized extinction or ignition. Recent developments in burst-mode laser technology, coupled with high-speed CMOS detectors, allow imaging at rates sufficient to resolve small-scale variations in highly turbulent flows. The pulse-burst laser systems employed in the current work are capable of achieving pulse burst lengths in excess of 30 ms (with all-diode pumping), and in excess of 10 ms (with flashlamp pumping). Pulse-burst laser systems consist of a pulse sliced continuous-wave or pulsed oscillator which is subsequently amplified through an Nd: YAG amplifier chain. This design allows great flexibility in the pulse repetition rate, burst duration (or total number of pulses), and the energy per pulse. The long pulse duration and high repetition rate ensures that a large range of important temporal frequencies ranging from 100 Hz to 50 kHz can be captured in a single burst. The system design targets> 200 mJ/pulse at 20 kHz, with> 35 mJ/pulse at 355 nm. The efficient frequency conversion of these laser systems allows investigation of UV-accessible transitions of OH, CH2O, CH, NO, and acetone for planar laser-induced fluorescence (PLIF), as well as scattering experiments in the visible range. This paper discusses the current capabilities for planar imaging of combustion species and mixture fraction. The data are also evaluated to determine the requirements for sufficiently resolving spatio-temporal dynamics in turbulent flows. In particular, the application of wavelet analysis to …