Measurements of the Reynolds stress in the turbulent premixed flame

Abstract

It has been shown in our previous study that the bi-modal distribution is seen in the radial component of the gas velocity obtained in the turbulent flame brush, implying that the shear component of the Reynolds stress conditioned on the unburnt mixture and burnt gas can be measured if the coincident measurement of the three components of the gas velocity is conducted. Therefore, in this study, an attempt has been made to measure the shear component of the Reynolds stress within the turbulent flame brush of a turbulent premixed propane-air flame. Since the radial component of the gas velocity is bi-modal feature, the conditioned measurement of the gas velocity is indispensable. The unconditioned measurement overestimates the radial component of the average velocity and the RMS of the velocity fluctuation to unrealistic values, leading to fatal errors. It has been shown that the shear component of the Reynolds stress of non-reacting flow is much larger than those of the conditioned unburnt mixture and burnt gas. Due to the thermal expansion of gas across the flamelet, the gradient of the axial component of the gas velocity with respect to the radial direction decreases, the shear component of the Reynolds stress of the conditioned on the unburnt mixture and burnt gas decreases. Moreover, the correlation between the fluctuation of the radial and axial components of the gas velocity of the unburnt mixture and burnt gas decreases.

Keywords

• flame
• premixed combustion
• turbulence
• laser doppler velocimeter
• reynolds stress