Analysis On Aeration Characteristics Near Buildings Under Wave Action

Waves travel from the open sea to the coast.Under the influence of topography and buildings,waves will interact with buildings.At the same time,the interaction between waves and buildings causes the strong turbulence and tumbling of water flow,and a large number of air bubbles are formed along with the involvement of a large number of air.The dissipation of a large amount of energy caused by waves and buildings may aggravate the damage to buildings after aeration,which has certain influence on engineering practice and environmental problems.Therefore,it is of great practical significance to study the aeration characteristics in the vicinity of buildings under the action of waves in order to solve the engineering practice and environmental problems in coastal areas.In this study,a large number of flume experiments were carried out to investigate the characteristics of air entrainment in the vicinity of offshore buildings under the action of waves.The smooth slope fixed bed model was used to generalize the nearshore topography and buildings.Regular waves and isolated waves were used as incident waves to study the generation,evolution and transport process of air bubbles in the vicinity of buildings.The distribution of air bubbles in size,quantity and void fraction was analyzed,and the distribution,transport and dynamic characteristics of air bubbles were explored.At the same time,open foam is used to carry out numerical simulation research.On the basis of model validation,the evolution of bubbles in the vicinity of buildings under wave action is discussed by using numerical model.The characteristics of velocity,vorticity and turbulence kinetic energy distribution in the vicinity of buildings and their relationship with the evolution of bubbles are analyzed.The results show that:Under regular wave action,the particle size of the bubbles near the building obeys the distribution of p?d?,and there is a power exponential relationship between the chord length d and the probability density p of the bubbles.The probability density of bubbles decays exponentially with the increase of the particle size of bubbles.Taking Hinze characteristic scale as the boundary,the particle size distribution of bubbles follows different distribution rules.When the bubble size is larger than Hinze characteristic scale,bubbles are liable to burst under the influence of turbulence and shear flow.Bubbles smaller than this scale remain relatively stable due to surface tension.in this experiment,Hinze characteristic scale is about 2 mm.The number of bubbles in different sections decreases with the increase of depth.The number of bubbles in water is the largest near the water surface,and decreases with the increase of depth.There is a complex interaction between vortex structure and bubble evolution.The evolution of gas cavity in shear flow has experienced the process of gas cavity breaking,merging and overflowing water surface.The time-averaged voidage and the time-averaged turbulence kinetic energy have a linear relationship,while the turbulence kinetic energy has a linear relationship with the number of bubbles.For the evolution of bubbles in the vicinity of a building under solitary waves,the bubble cloud above the building usually goes through three stages:bubble cloud birth,development and dissipation.The vortex above the building is divided into three stages from generation to dissipation.The vortex generation stage coincides with the bubble cloud primary stage in space and time.The vortex generation results in the appearance of the bubble cloud.The vortex development stage coincides with the bubble cloud development stage basically,which shows that vortex check the bubble cloud convergence and separation vortex plays a vital role in the bubble cloud split.The diameter of the bubble cloud at the top of the building is linearly related to its nearby pressure and turbulence kinetic energy respectively.The larger the turbulent energy,the larger the bubble cloud diameter,and the larger the negative pressure,the larger the bubble cloud diameter.