help reqd. :DATA SAMPLING FOR TIME STATISTIC

haris

dear friends, i am solving an unsteady problem (flow over a heated square cylinder) in fluent. the cylinder is confined with walls on both left and right side and flow takes place in vertically upward direction. Re.No: 100 Richardson Number: -0.1(negative 0.1) i.e opposed bouyancy. time step:0.02 No of time step:1211 No. of iterations per time step:30. after 1211 iterations i got good vortex shedding .i got frequency as 1.71 Hz therefore cycle time = 0.5847 sec now i want to get time average streamlines. i want to know how to set the SAMPLING INTERVAL such that DATA SAMPLING FOR TIME STATISTIC can be performed at the SPECIFIED FREQUENCY.

thanks for your help