On the Extension of a Laser-Doppler Velocimeter to the Analysis of Oscillating Flames

Optical and probe techniques are used to analyse the coupling mechanism between pressure, velocity and temperature fluctuations typical of pulsed flames, through the combination of laser velocimetry, digitally-compensated thermocouples and a probe microphone. The system is based on a digital signal microprocessor and is shown to run up to 12.5 kHz of data ready velocity signals, allowing the time-resolved representation of vectors of turbulent heat flux along a typical cycle of oscillation. The detailed results obtained along the oscillating reacting shear layer show time sequences of zones characterised by gradient and non-gradient turbulent heat flux, which are structurally similar to previous results reported in the literature for steady recirculating flames.