Basic Research On Ship Drag Reduction Based On Collaboration Of Wall Heating And Ultrasonic Cavitation

Ship transportation has huge advantages in economy and safety,and occupy an unshakable position in the global cargo flow.However,the energy consumption and pollution problems caused by ships have also received widespread attention.The " Green Ecological Ship Code" was issued by China Classification Society which proposed new technologies for green ships,including the recovery of waste heat from ship engines and the micro-bubble drag reduction technology.Therefore,if the ship’s waste heat can be combined with the micro-bubble drag reduction technology to synergistically affect the ship’s resistance,this has far-reaching significance for the management of ship’s energy consumption and pollution problems.This paper proposes a new method of ship drag reduction based on the synergy of wall heating and ultrasonic cavitation,and related to basic research has been carred out and the following main work has been completed:(1)An experimental platform was built to study the influencing factors and rules of the synergistic effect of wall heating and ultrasonic cavitation.The effects of ultrasonic power and ultrasonic frequency on the heat transfer enhancement under different water temperature were mainly studied,and the results were used as a guide for subsequent experiments.(2)The influence of wall heating and synergism on ship resistance is analyzed theoretically,and a theoretical model was established to find out the key factors.In addition,using the results of the pre experiment,the ship model test device was designed.(3)The ship model test was used to test the individual heating drag reduction method and the synergistic drag reduction method.The two drag reduction methods were analyzed and compared to find the optimal test conditions.Through the above research work,the following conclusions are obtained:(1)When ultrasonic wave was added to wall heating,the heat transfer coefficient increases with the increase of ultrasonic power at different water temperature,and the highest heat transfer coefficient is obtained at 400W;The heat transfer coefficient first increases and then decreases with the increase of ultrasonic frequency,and the highest heat transfer coefficient is obtained at 66KHz frequency under all experimental conditions.(2)When the ship model adopts the drag reduction method of single wall heating,the drag reduction rate will increase with the increase of heating power on the premise that the ship model’s speed does not change,and the maximum drag reduction rate can reach 11.651%;on the premise that the heating power does not change,the minimum drag reduction rate will be 1.818%with the increase of speed.(3)When the ship model adopts the cooperative drag reduction method,the change trend of the drag reduction rate is basically the same as that when single wall heating,the maximum drag reduction rate can reach 14.584%,and the minimum drag reduction rate of the ship model is 2.203%.The results show that under the same speed and heating power,the drag reduction rate under the synergistic effect is higher than that under the single wall heating.Therefore,in the experimental range of this paper,wall heating and ultrasonic cavitation synergistic drag reduction method is more excellent.