Measurement of temperature and velocity fluctuations in a turbulent diffusion flame by optical fiber thermometer and laser 2-focus velocimeter

Both fluctuations of local velocity and local temperature were measured in a steady turbulent diffusion flame of propane by using the semiconductor laser 2-focus velocimeter (L2F) and the optical fiber thermometer (OFT) respectively. The flame temperature and the soot particle density were calculated by applying the infrared two-color method to the measured radiant energy from the soot particles in the flame. In the analysis of the frequency power spectra of temperature and velocity fluctuations, the correlation-based slotting technique was adopted for those data with the nonuniform time interval. It is shown that the time mean value and the fluctuation of the flame temperature decrease gradually toward downstream in the luminous flame region, and those of the soot density increase due to decay of turbulence along the flame axis. On the other hand, both time mean and fluctuation of the flame temperature increase in the radial direction from the center to the periphery due to the effect of air entrainment marked in the peripheral region of the flame. Furthermore, the power spectrum of the velocity fluctuation is not always the same as that of the temperature fluctuation in the flame center.