Velocity-temperature correlation in premixed flame

The velocity and the temperature were measured simultaneously with a laser Doppler anemometer and a compensated thermocouple, respectively, in the turbulent premixed flame, and their cross-correlation was calculated with a microcomputer. A seed deposition effect of the thermocouple on the cross-correlation coefficient was avoided by compensating for the temperature signal with a somewhat larger time constant than the theoretical value. The effect on the cross-correlation of separating of the measuring control volume of LDA and the thermocouple placed on the downstream side was also investigated. Though a small separation of the thermocouple downstream from the measuring control volume had little effect, the shift of radial direction had a severe effect. The axial velocity-temperature correlation gave large negative values in the whole region where the gradient of mean temperaturealong the axial direction δ/δ x was positive. This fact corresponds to the normal turbulent heat transfer and can be explained by a mechanism whereby temperature fluctuation is induced by velocity fluctuation. However, the radial velocity-temperature correlation showed positive values in the vicinity of the flame front where the radial temperature gradient η/δ r was still positive. This corresponds to an abnormal turbulent heat transport phenomenon. To clarify this phenomenon, the probability density functions and the macroscale of the velocity and the temperature fluctuations were also measured. The bimodal nature of the PDF appeared at the flame front in all fluctuating components, which suggests that the flame front structure of the flame studied was approximated by the wrinkled flame model. Abnormal turbulent heat transfer can be explained by the wrinkled flame front structure or the fluctuation of the heat generated at the measuring point, and cannot be neglected in the modeling of the combustion.