| Ships burn heavy oil and most of the flue gas emitted is heavy gas,which may sink to the deck area due to factors such as the environment and release sources,and even entering the fresh air intake pipe causes secondary pollution of the crew’s living and working environment.This situation will be more prominent in berthing conditions that require ship power to work at low-load to maintain power supply.At present,the existing research on the smoke diffusion of ships is mainly based on the navigation conditions,and more attention is paid to the deck area and wake characteristics.However,there are few studies on the pollution of cabin air inlet by smoke diffusion in the specific quiet wind environment of berthing or port.In order to investigate the diffusion behavior of ship smoke and the distribution of pollutant concentration field under the condition of calm and stable weather,based on the validation of the heavy gas diffusion model,this paper studies the diffusion characteristics of single source heavy gas under the condition of calm and stable weather.By comparing the heavy gas diffusion behavior under different initial release temperature and release rate,it is found that the diffusion process is more affected by the former.Based on the ship’s multi stack emission design,the diffusion behavior of multi-source heavy gas is studied,and the multi-source aggregation with different release source spacing and the concentration superposition effect with different release source number is discussed.It is found that the smaller the release source distance,the stronger the multi-source convergence effect.When D/d>3,the multi-source heavy gas starts to separate from the convergence.In addition,according to the"white smoke"phenomenon caused by moisture condensation of flue gas,the small-scale model is numerically studied by using the steam condensation model.It was found that condensation mainly occurs in the jet boundary layer.And lowering the ambient temperature is beneficial to the condensation process of water vapor in the flow field.Under simulated conditions,the condensation rate of water vapor at 263K in winter is 1.7 times that of 303K in summer.Based on the actual ship size,a external flow field model was established to study the pollution of the ship deck and air intake system by the diffusion behavior of high-temperature smoke under calm and stable weather,and the effect of phase change of different content of water vapor on the diffusion behavior of flue gas is considered.Different from the pollution at the tail of the ship caused by the flue gas of navigation conditions,the pollution in the under calm and stable weather is mainly concentrated near the chimney area.The analysis shows that the higher the flue gas temperature,the less the pollution to the ship’s air intake system.And the temperature of flue gas conversion from heavy gas to neutral gas is about417K.In addition,considering the phase transition,the diffusion distance of the smoke on the deck area and the height of the gas cloud have a linear relationship with the change of the proportion of water vapor.When the proportion of water vapor is in the range of 0～20%,the increase of water vapor content and the decrease of CO2 component will promote the transformation of smoke cloud to lighter gas.In this paper,based on the research background of the smoke deposition of ships berthing in winter,through the establishment of the heavy gas diffusion model and the water vapor phase transition model,the smoke diffusion characteristics of the ship flow field and the pollution to the air inlet system under calm and stable weather are studied.The purpose is to provide scientific guidance for optimizing ship design and preventing the influence of flue gas pollutants on ship equipment and personnel. |
