We experimentally investigate the drag reduction characteristics of heated spheres falling into water by using a highspeed camera. In 25-℃ water, with the increase of the sphere temperature the average velocity incre...We experimentally investigate the drag reduction characteristics of heated spheres falling into water by using a highspeed camera. In 25-℃ water, with the increase of the sphere temperature the average velocity increases to a maximum value at a temperature of 400℃ and then decreases until the temperature reaches 700℃, the average velocity will increase while the sphere temperature continually rises until the temperature reaches 900℃. The average and the maximum velocity of the heated sphere are larger than those of the room-temperature sphere. The flow separates at the rear of the heated sphere,leading to low pressure drag. The drag reduction effect of the stable film boiling is lower than that of the nucleate boiling.In the nucleate boiling regime, the average velocity decreases with the increase of water temperature, the drag of the sphere with gentle boiling intensity is smaller. The vapor layer formed in the stable film boiling regime can improve the stability of the fall trajectory. The intense turbulence caused by the nucleate boiling can make the sphere largely deviate from rectilinear motion.展开更多
This paper presents a numerical study of the hydroelastic coupling during the free-surface water entry of deformable spheres of different material densities.The focus is on the hydrodynamic forces,the stress loads,the...This paper presents a numerical study of the hydroelastic coupling during the free-surface water entry of deformable spheres of different material densities.The focus is on the hydrodynamic forces,the stress loads,the sphere deformations,the wetted areas of the sphere and the cavity dynamics,including the impacting of the elastic spheres and the hydroelastic coupled behaviors in the free surface flows.It is shown that the elastic wave propagation in the sphere scales with the sphere density.For elastic spheres immersed in the water,the variation of the sphere deformations and its energy transformation mechanism are discussed.From the contact point positions of the cavity,it can be seen that the wetted area of the sphere is closely related with the sphere deformation.The first deformation cycle is a turning point in the relation between the wetted area and the sphere density.Based on the map of m*−ηsummarized in this work,the influence of the sphere deformation on the shape of the cavity can be roughly predicted from the material properties and the impact conditions.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.11672094)
文摘We experimentally investigate the drag reduction characteristics of heated spheres falling into water by using a highspeed camera. In 25-℃ water, with the increase of the sphere temperature the average velocity increases to a maximum value at a temperature of 400℃ and then decreases until the temperature reaches 700℃, the average velocity will increase while the sphere temperature continually rises until the temperature reaches 900℃. The average and the maximum velocity of the heated sphere are larger than those of the room-temperature sphere. The flow separates at the rear of the heated sphere,leading to low pressure drag. The drag reduction effect of the stable film boiling is lower than that of the nucleate boiling.In the nucleate boiling regime, the average velocity decreases with the increase of water temperature, the drag of the sphere with gentle boiling intensity is smaller. The vapor layer formed in the stable film boiling regime can improve the stability of the fall trajectory. The intense turbulence caused by the nucleate boiling can make the sphere largely deviate from rectilinear motion.
基金Projects supported by the National Natural Science Foundation of China(Grant Nos.11972138,11672094).
文摘This paper presents a numerical study of the hydroelastic coupling during the free-surface water entry of deformable spheres of different material densities.The focus is on the hydrodynamic forces,the stress loads,the sphere deformations,the wetted areas of the sphere and the cavity dynamics,including the impacting of the elastic spheres and the hydroelastic coupled behaviors in the free surface flows.It is shown that the elastic wave propagation in the sphere scales with the sphere density.For elastic spheres immersed in the water,the variation of the sphere deformations and its energy transformation mechanism are discussed.From the contact point positions of the cavity,it can be seen that the wetted area of the sphere is closely related with the sphere deformation.The first deformation cycle is a turning point in the relation between the wetted area and the sphere density.Based on the map of m*−ηsummarized in this work,the influence of the sphere deformation on the shape of the cavity can be roughly predicted from the material properties and the impact conditions.
