Influence of surfactant on drag reduction characteristic of an underwater vehicle

To reduce the drag of underwater vehicle, experiment is carried out to study the turbulent drag-reducing of underwater vehicle injected with surfactant in a water tunnel. For the experimental work presented here, surfactant is injected from the head of the vehicle. The drag reduction (DR) of surfactant as a function of fluid velocity and surfactant concentration are investigated. The influences of the surfactant on the lift-force and drag-force with different attack angle are analyzed. Surfactant solutions at different concentrations, namely 200, 400, 600, 800 and 1000 mg/L, are used to examine the influence of surfactant on drag coefficient. The flow velocities are set between 4 and 10 m/s. The present results show the DR effect is weak when the surfactant concentration is 200 mg/L. With the increase of the surfactant concentration to 1 000 mg/L, the drag coefficient is reduced by about 40.8%. The DR ratio ranges between 12.5% and 40.8% at all flow velocities up to 10 m/s from 4 m/s when the surfactant concentration is 1 000 mg/L. With the increase of surfactant concentration, the drag coefficient of the vehicle with angle of attack is also reduced and there is slight effect on the lift-force coefficient.