Laser Doppler Velocimetry : Effect of Refractive Index Change at Flame Front

Abstract

In application of laser doppler velocimetry (LDV) to the flow field including flames, there are interactions of the laser beams with flames. Those interactions are schlieren effect and phase effect. In this study, such interactions were investigated experimentally and theoretically. The main results of the investigation are as follows : (1) The effect of interaction between laser beams and flame front on LDV was measured actually. (2) The effect is serious only for near-tangential incidence of laser beams to flame front, when large pseudo-velocities are produced in very short time interval. (3) The value of pseudo-velocity is proportional to the flame speed, and it increases with the flame size. (4) The pseudo-velocity maybe become serious when the relative incidence angle of laser beam to flame front fluctuates by such a high frequency as in strong turbulent flames.