Study On Flow And Erosion Characteristics Of Seawater-ice Two-phase Flow In Pipeline Under Vibration Condition

The ship seawater pipeline system refers to the pipes which pump seawater from the outside to cool the marine engine,auxiliary machinery and other power devices,or supply the ballast tank.Which just like the blood vessel of human,maintaining the ‘vitality’ of ships.However,when ships sail in the polar region,the pipeline will inevitably vibrate due to factors such as power device operation,ice-breaking shock and fluid pulsation.The vibration with low frequency has huge energy and far spreading,which will lead to changes in flow field inside the tube.In addition,many tiny sea ice particles are sucked into the seawater system during polar navigation,forming seawater-ice two-phase flow,which is prone to cause erosion.The vibrating wall forms fluid-solid coupling with the inside fluid area,and will change the flow characteristics of the two-phase flow,then the wall erosion becomes more complicated and difficult to predict.It can be said that the two-phase flow erosion problem under vibration condition seriously affects the life time of seawater system and threatens the safe navigation of ships.It has become one of the key issues that need to be solved in the design and construction of polar ships.In view of the complexity of flow and erosion in pipe under vibration condition,this paper models the widely existing 90° elbows on ships,simplifies the vibration model as a sinusoidal function,and adopts Fluent Euler-Lagrangian discrete model,turbulence model and erosion model.UDF dynamic grid technology is used to define different vibration conditions,focusing on studying the changes of seawater-ice two-phase flow and erosion characteristics under different vibration condition.The main conclusions are as follows:1)Analyzing the results show that vibration has great impacts on two phases flow characteristics,and clearing that vibration plays a major role in the increase of the flow velocity,the velocity gradient change,the pressure sudden change and the increase of the flow resistance,and the variation of the turbulent energy perfectly match the velocity and pressure distribution.2)In the case of other conditions remain unchanged,with the enhancement of vibration conditions,the severe erosion area transmit from the top of the the inside of the elbow and the sides of the straight pipe,then the flow separation area of the straight pipe is worse eroded.The erosion rate of the pipe increases with the increase of frequency and amplitude,the growth rate is slower and then has index increase;H-H pipe is more serious eroded at the direction of lateral vibration than the longitudinal vibration;the service life of the pipeline is predicted to decrease drastically with the intensity of vibration,and at the condition of 80 Hz and 1 mm,the life time is reduced by 7 times than static condition.3)In addition,the multi-attribute changes were simulated coupling with vibration.The results show that the pressure drop and erosion rate of the pipe are larger than those of the static pipe under the same condition;as the grey correlation analysis method shows that the IPF and the velocity play major roles in the maximum erosion rate along the pipeline,followed by the particle rotation and diameter,and they have some impact on it,and then the fluid flow direction has the least impact on the maximum erosion rate.The seawater pipeline of the polar ship should be arranged in the H-V direction,the flow rate is controlled at 2-3m/s,the IPF is reduced as much as possible,and the particle diameter is 0.3mm,to ensure the seawater pipeline transportation performance and service life be optimal.4)Designing experiment to measure the variation of flow resistance under different conditions,and the experimental data is basically consistent with the simulation results,which verifies the rationality of the selected model,then that provides reference for the design and protection of seawater pipeline on polar carrier.