The effect of polymeric additives PAM on the time-correlation structure of turbulence in the cenerline region of a rectangular pipe was investigated experimentally with a 2-dimensional laser Doppler velocimeter.It was found under the condition of drag reduction that the time-correlation charactenristics of turbulent fluctuating velocities showed obvious changes.At the same Rynolds number

all the time scales of longitudinal autocorrelation

transversal autocorrelation and cross-correlation increased with the additive concentration. This trend of change is consistent with that of drag reduction ratio.A new phenomenon

the time-effect of cross-correlation coefficient at the centreline

is reported for the first time．These results provide further theoretical investigation with new experimental facts

and support the role of viscoelasticity in the mechanism of drag reduction.