Experimental study of the characteristics on turbulence in drag reducing flow using surfactant additives

The phenomenon of drag reduction of turbulence water flow added with surfactant (CTAC+NaSal)was investigated experimentally in the work. The conditions of temperature, concentration of surfactant and Reynolds number that drag reduction may occur were studied. By using LDV, the turbulence properties of the flow in a two-dimensional channel were measured. It is concluded that the low drag of surfactant solution flow can be maintained at Reynolds numbers pertinent to turbulent flow of the case for water alone if the Reynolds number does not exceed a critical Reynolds number. The critical Reynolds number however increases with the surfactant concentration and decreases with increasing the temperature of the solution. Under drag reducing flow, the main velocity profile shifts its shape to that of a laminar flow however, still remains certain level of turbulent intensities although quite weak than that of water flow under the same Reynolds number. While there are turbulent intensities, the turbulent Reynolds stress is almost zero or even has depletion, which reflects the change of correlation of turbulence intensities in different directions in the flow.