The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical c...The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble（air jet） move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.展开更多
The dynamics of the bubble collapse near a rigid boundary is a fundamental issue for the bubble collapse application and prevention. In this paper, the bubble collapse is modeled by adopting the lattice Boltzmann meth...The dynamics of the bubble collapse near a rigid boundary is a fundamental issue for the bubble collapse application and prevention. In this paper, the bubble collapse is modeled by adopting the lattice Boltzmann method （LBM） and is verified, and then the dynamic characteristics of the collapsing bubble with the second collapse is investigated. The widely used Shan-Chen model in the LBM multiphase community is modified by coupling with the Carnahan-Starling equation of state （C-S EOS） and the exact difference method （EDM） for the forcing term treatment. The simulation results of the bubble profile evolution by the LBM are in excellent agreements with the theoretical and experimental results. From the two-dimensional pressure field evolution, the dynamic characteristics of the different parts during the bubble collapse stage are studied. The role of the second collapse in the rigid boundary damage is discussed, and the impeding effect between two collapses is demonstrated.展开更多
When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attit...When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attitude and stability of the body. In the present work, characteristics of the natural cavitating flow around a 2-D symmetrical wedge in shallow water were investigated and the influences of two type boundaries on the flow pattern were analyzed. The Volume Of Fluid （VOF） multiphase flow method which is suitable for free surface problems was utilized, coupled with a natural cavitation model to deal with the mass-transfer process between liquid and vapor phases. Within the range of the cavitation number for computation （0.07-1.81）, the cavity configurations would be divided into three types, viz., stable type, transition type and wake-vortex type. In this article, the shapes of the free surface and the cavity surface, and the hydrodynamic performance of the wedge were discussed under the conditions of relatively small cavitation number （〈0.256）. The present numerical cavity lengths generally accord with experimental data. When the cavitation number was decreased, the cavity was found to become longer and thicker, and the scope of the deformation of the free surface also gradually extends. The free surface and the upper cavity surface correspond fairly to their shapes. However, the lower side of the cavity surface was rather leveled due to the influence of wall boundary. The lift and drag coefficients of this 2-D wedge basically keep linear relations with the natural cavitation number smaller than 0.157, whereas direct proportion for drag and inverse proportion for lift.展开更多
The underwater launch of high-speed vehicles involves complex bubble-structure interactions,which are not currently well understood.In this study,two small-scale experiments are carried out involving transient bubble-...The underwater launch of high-speed vehicles involves complex bubble-structure interactions,which are not currently well understood.In this study,two small-scale experiments are carried out involving transient bubble-cylinder interactions.We adopt the underwater electric discharge method to generate a high-pressure bubble that drives a cylinder to a maximum velocity of∼25 m/s within 1 ms.A tail bubble forms as the cylinder is ejected from the launch tube.Moreover,we observe a shoulder cavity around the head of the cylinder due to the pressure reduction in the flow.To better understand the complex interaction between bubbles and the high-speed cylinder,we use the boundary element method to establish a bubble—structure interaction model.Our numerical model reproduces the experimental observations quite well,including the cylinder motion and the transient evolution of the bubbles.Thereafter,a systematic study is carried out to reveal the dependence of the bubble-cylinder interactions on the initial pressure of the tail bubble p0.We obtain a scaling law for the maximum velocity of the cylinder v_(m) with respect to p_(0),namely,v_(m) ∝ p_(0)^(0.45).The findings from this study may provide a reference for subsequent research into underwater launches.展开更多
Although the prediction of propeller cavitation-induced pressure fluctuation strongly depends on the model-scalemeasure- ment in a cavitation tunnel, there is still a lack of correlation with full-scale data. This pap...Although the prediction of propeller cavitation-induced pressure fluctuation strongly depends on the model-scalemeasure- ment in a cavitation tunnel, there is still a lack of correlation with full-scale data. This paper deals with the enhancement of such a correlation deficiency by improving the conventional model-test technique, two majors of which are in the following. One is to take into account the boundary layer effect of wooden fairing plate at the ceiling of water cavitation tunnel. The other is to avoid the reso- nance frequency range of model-ship via adjusting the revolution speed of model propeller. Through a case study, for which both model and full-scale test data are available, the improved method in this study shows its validness, and furthermore a close correla- tion with full scale measurement.展开更多
The steady partially cavitating flow around two-dimensional hydrofoils war simulated numerically by the low-order potential-based boundary integration method. The cavity shape and length are determined for given cavit...The steady partially cavitating flow around two-dimensional hydrofoils war simulated numerically by the low-order potential-based boundary integration method. The cavity shape and length are determined for given cavitating numbers in the course of iteration by satisfying the kinematic and dynamic boundary conditions. The re-entrant jet model and the pressure-recovery close model are adopted to replace the high turbulent and two-phase wake forming behind the cavity. The results are compared with the other published numerical ones.展开更多
Viscous scale effects on propeller TVC were investigated by testing a series of three geosim propeller models in the large cavitation Tunnel of CSSRC without and with two different turbulence stimulators. Tests includ...Viscous scale effects on propeller TVC were investigated by testing a series of three geosim propeller models in the large cavitation Tunnel of CSSRC without and with two different turbulence stimulators. Tests included flow visualization by oil film method and cavitation observation for five different stages of development of propeller TVC: desinent, unattached, attached, developed and fully developed TVC. The main findings are: 1)there existed a size effect of the boundary-layer transition on propeller models which could be analyzed by using the critical roughness Reynolds number and a newly defined quasi-critical Reynolds number, 2)the preliminary results of the blackboardpaint used as a tripping device was encouraging, 3)the Reynolds number exponent n of TVC scaling rules was found to be dependent upon the blade surface condition, the stage of development of TVC and the thrust loading of propeller models.展开更多
When the shock wave of underwater explosion propagates to the surfaces of different boundaries, it gets reflected. Then, a negative pressure area is formed by the superposition of the incident wave and reflected wave....When the shock wave of underwater explosion propagates to the surfaces of different boundaries, it gets reflected. Then, a negative pressure area is formed by the superposition of the incident wave and reflected wave. Cavitation occurs when the value of the negative pressure falls below the vapor pressure of water. An improved numerical model based on the spectral element method is applied to investigate the cavitation effect of underwater shock near different boundaries, mainly including the feature of cavitation effect near different boundaries and the influence of different parameters on cavitation effect. In the implementation of the improved numerical model, the bilinear equation of state is used to deal with the fluid field subjected to cavitation, and the field separation technique is employed to avoid the distortion of incident wave propagating through the mesh and the second-order doubly asymptotic approximation is applied to simulate the non-reflecting boundary. The main results are as follows. As the peak pressure and decay constant of shock wave increases, the range of cavitation domain increases, and the duration of cavitation increases. As the depth of water increases, the influence of cavitation on the dynamic response of spherical shell decreases.展开更多
In this paper, the catastrophe of a spherical cavity and the cavitation of a spherical cavity for Hooke's material with 1/2 Poisson's ratio are studied. A nonlinear problem, which is a moving boundary problem ...In this paper, the catastrophe of a spherical cavity and the cavitation of a spherical cavity for Hooke's material with 1/2 Poisson's ratio are studied. A nonlinear problem, which is a moving boundary problem for the geometrically nonlinear elasticity in radial symmetric, is solved analytically. The governing equations are written on the deformed region or on the present configuration. And the conditions are described on moving boundary. A closed form solution is found. Furthermore, a bifurcation solution in closed form is given from the trivial homogeneous solution of a solid sphere. The results indicate that there is a tangent bifurcation on the displacement_load curve for a sphere with a cavity. On the tangent bifurcation point, the cavity grows up suddenly, which is a kind of catastrophe. And there is a pitchfork bifurcation on the displacement_load curve for a solid sphere. On the pitchfork bifurcation point, there is a cavitation in the solid sphere.展开更多
基金supported by the Ministry of Science and Technology of China (Grant Nos. 2007CB714105 and 2008BAB29B04)
文摘The motion of a spark-induced cavitation bubble and an air bubble near a rigid boundary is experimentally studied by using high-speed photography.Several dimensionless parameters are used to describe the geometrical configuration of the bubble-bubble-boundary interaction.The bubble-bubble interaction can be considered in two different conditions.The cavitation bubble will collapse towards the air bubble if the air bubble is relatively small,and away from the air bubble if the air bubble is relatively large.The two zones are identified in the bubble-boundary interaction,and they are the danger zone and the safety zone.The relative position,the bubble-boundary distance and the bubble-bubble distance play important roles in the bubble-bubble-boundary interaction,which can be considered in several conditions according to the responses of the bubbles.Air jets are found to penetrate into the cavitation bubbles.The cavitation bubble and the air bubble（air jet） move in their own way without mixing.The motion of a cavitation bubble may be influenced by an air bubble and/or a rigid boundary.The influence of the air bubble and the influence of the boundary may be combined,like some thing of a vector.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.11274092,11274091 and 1140040119)the Natural Science Foundation of Jiangsu Province(Grant No.SBK2014043338)
文摘The dynamics of the bubble collapse near a rigid boundary is a fundamental issue for the bubble collapse application and prevention. In this paper, the bubble collapse is modeled by adopting the lattice Boltzmann method （LBM） and is verified, and then the dynamic characteristics of the collapsing bubble with the second collapse is investigated. The widely used Shan-Chen model in the LBM multiphase community is modified by coupling with the Carnahan-Starling equation of state （C-S EOS） and the exact difference method （EDM） for the forcing term treatment. The simulation results of the bubble profile evolution by the LBM are in excellent agreements with the theoretical and experimental results. From the two-dimensional pressure field evolution, the dynamic characteristics of the different parts during the bubble collapse stage are studied. The role of the second collapse in the rigid boundary damage is discussed, and the impeding effect between two collapses is demonstrated.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11002089, 10832007)the Shanghai Leading Academic Discipline Project (Grant No.B206)
文摘When a body navigates with cavity in shallow water, both flexible free surface and rigid bottom wall will produce great influences on the cavity shape and hydrodynamic performances, and further affect the motion attitude and stability of the body. In the present work, characteristics of the natural cavitating flow around a 2-D symmetrical wedge in shallow water were investigated and the influences of two type boundaries on the flow pattern were analyzed. The Volume Of Fluid （VOF） multiphase flow method which is suitable for free surface problems was utilized, coupled with a natural cavitation model to deal with the mass-transfer process between liquid and vapor phases. Within the range of the cavitation number for computation （0.07-1.81）, the cavity configurations would be divided into three types, viz., stable type, transition type and wake-vortex type. In this article, the shapes of the free surface and the cavity surface, and the hydrodynamic performance of the wedge were discussed under the conditions of relatively small cavitation number （〈0.256）. The present numerical cavity lengths generally accord with experimental data. When the cavitation number was decreased, the cavity was found to become longer and thicker, and the scope of the deformation of the free surface also gradually extends. The free surface and the upper cavity surface correspond fairly to their shapes. However, the lower side of the cavity surface was rather leveled due to the influence of wall boundary. The lift and drag coefficients of this 2-D wedge basically keep linear relations with the natural cavitation number smaller than 0.157, whereas direct proportion for drag and inverse proportion for lift.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFC2803500)the National Natural Science Foundation of China(Grant No.52088102)This work was supported by the Natural Science Foundation of Heilongjiang Province,China(Grant No.YQ2022E017).
文摘The underwater launch of high-speed vehicles involves complex bubble-structure interactions,which are not currently well understood.In this study,two small-scale experiments are carried out involving transient bubble-cylinder interactions.We adopt the underwater electric discharge method to generate a high-pressure bubble that drives a cylinder to a maximum velocity of∼25 m/s within 1 ms.A tail bubble forms as the cylinder is ejected from the launch tube.Moreover,we observe a shoulder cavity around the head of the cylinder due to the pressure reduction in the flow.To better understand the complex interaction between bubbles and the high-speed cylinder,we use the boundary element method to establish a bubble—structure interaction model.Our numerical model reproduces the experimental observations quite well,including the cylinder motion and the transient evolution of the bubbles.Thereafter,a systematic study is carried out to reveal the dependence of the bubble-cylinder interactions on the initial pressure of the tail bubble p0.We obtain a scaling law for the maximum velocity of the cylinder v_(m) with respect to p_(0),namely,v_(m) ∝ p_(0)^(0.45).The findings from this study may provide a reference for subsequent research into underwater launches.
文摘Although the prediction of propeller cavitation-induced pressure fluctuation strongly depends on the model-scalemeasure- ment in a cavitation tunnel, there is still a lack of correlation with full-scale data. This paper deals with the enhancement of such a correlation deficiency by improving the conventional model-test technique, two majors of which are in the following. One is to take into account the boundary layer effect of wooden fairing plate at the ceiling of water cavitation tunnel. The other is to avoid the reso- nance frequency range of model-ship via adjusting the revolution speed of model propeller. Through a case study, for which both model and full-scale test data are available, the improved method in this study shows its validness, and furthermore a close correla- tion with full scale measurement.
文摘The steady partially cavitating flow around two-dimensional hydrofoils war simulated numerically by the low-order potential-based boundary integration method. The cavity shape and length are determined for given cavitating numbers in the course of iteration by satisfying the kinematic and dynamic boundary conditions. The re-entrant jet model and the pressure-recovery close model are adopted to replace the high turbulent and two-phase wake forming behind the cavity. The results are compared with the other published numerical ones.
文摘Viscous scale effects on propeller TVC were investigated by testing a series of three geosim propeller models in the large cavitation Tunnel of CSSRC without and with two different turbulence stimulators. Tests included flow visualization by oil film method and cavitation observation for five different stages of development of propeller TVC: desinent, unattached, attached, developed and fully developed TVC. The main findings are: 1)there existed a size effect of the boundary-layer transition on propeller models which could be analyzed by using the critical roughness Reynolds number and a newly defined quasi-critical Reynolds number, 2)the preliminary results of the blackboardpaint used as a tripping device was encouraging, 3)the Reynolds number exponent n of TVC scaling rules was found to be dependent upon the blade surface condition, the stage of development of TVC and the thrust loading of propeller models.
基金financially supported by the National Natural Science Foundation of China(Grant No.51509228)Postdoctoral Applied Research Project of Qingdao Citythe Fundamental Research Funds for the Central Universities(Grant No.201513041)
文摘When the shock wave of underwater explosion propagates to the surfaces of different boundaries, it gets reflected. Then, a negative pressure area is formed by the superposition of the incident wave and reflected wave. Cavitation occurs when the value of the negative pressure falls below the vapor pressure of water. An improved numerical model based on the spectral element method is applied to investigate the cavitation effect of underwater shock near different boundaries, mainly including the feature of cavitation effect near different boundaries and the influence of different parameters on cavitation effect. In the implementation of the improved numerical model, the bilinear equation of state is used to deal with the fluid field subjected to cavitation, and the field separation technique is employed to avoid the distortion of incident wave propagating through the mesh and the second-order doubly asymptotic approximation is applied to simulate the non-reflecting boundary. The main results are as follows. As the peak pressure and decay constant of shock wave increases, the range of cavitation domain increases, and the duration of cavitation increases. As the depth of water increases, the influence of cavitation on the dynamic response of spherical shell decreases.
文摘In this paper, the catastrophe of a spherical cavity and the cavitation of a spherical cavity for Hooke's material with 1/2 Poisson's ratio are studied. A nonlinear problem, which is a moving boundary problem for the geometrically nonlinear elasticity in radial symmetric, is solved analytically. The governing equations are written on the deformed region or on the present configuration. And the conditions are described on moving boundary. A closed form solution is found. Furthermore, a bifurcation solution in closed form is given from the trivial homogeneous solution of a solid sphere. The results indicate that there is a tangent bifurcation on the displacement_load curve for a sphere with a cavity. On the tangent bifurcation point, the cavity grows up suddenly, which is a kind of catastrophe. And there is a pitchfork bifurcation on the displacement_load curve for a solid sphere. On the pitchfork bifurcation point, there is a cavitation in the solid sphere.
