Optimization of the injection process for drag-reducing additives

The primary objective of this experimental study was to determine the optimum combination of additive concentration, additive flowrate, injector angle and injector width for injecting a drag-reducing additive into a channel flow of water. The experiments were designed to keep an effective concentration of the additive in the buffer region where previous experiments have shown the additives directly affect the turbulent structures. Flow visualization of the wall-layer structures was conducted for the optimum combination of injection variables at the streamwise locations where the drag reduction peaked and where the additive became fully mixed with the channel flow of water.