Effects of screens and perforated plates (grids) on free-stream turbulence are studied in several test flow conditions. The level, structure and decay of the turbulence generated by such ‘manipulators’ depend in part on their shear-layer instabilities, and can therefore be modified by inserting additional devices immediately downstream. The performance of screens and some perforated plates is found to depend on the characteristics of the incoming flow such as velocity, turbulence level and spectra. Combinations of perforated plates and screens are found to be very effective flow manipulators. By optimizing the intermanipulator separation and carefully matching the scales between the manipulator pair, the turbulence decay rate downstream of a grid can be quadrupled.