Research On Dynamics And Stability Of Freely Falling Disks In Water

The dynamics and stability of free moving objects driven by gravity or buoyancy in flow field is one of the classical problems that need to be solved in fluid mechanics.This problem is related to many applications such as mechanical engineering,aerodynamics,meteorology and biomechanics.In this paper,the freely falling motion regimes ofeccentric disksin water,the freely falling motion regimes of windmill-like disksin water,and the change offalling motion regimesas well as the surrounding flow field after fixing rectangular bulges on the top,bottom or both sides on theedge ofdisks are systematically studied and analyzed by using experimental and numerical simulation methods.At last,taking the source analysis of V-shaped zinc dross in hot dip galvanizing bath as an example,the specific application of lifting kinetics and stability of object in liquid is demonstrated.The main research works as follows:?1?A method is proposed to process eccentric diskswithout influencing the surrounding flow field.By shooting the freely falling motion of eccentric disks with different parameters in a water tank with a high-speed camera,the influence of center of gravity offset on the falling regimes of the disks is analyzed,and six new motion regimes are found,including flutteringdominated motion,chaoticdominated motion,tumblingdominated motion,transition motion,gliding dominated motion andpure gliding motion.The newly discovered motion regimes are classified according to their motion patterns and trajectory characteristics.Four new types of eccentric disks falling regimes are proposed,including FCT dominated motion?includingflutteringdominated motion,chaoticdominated motion,tumblingdominated motion?,transition motion,gliding dominated motion,pure gliding motion,and their properties and characteristics are introduced and analyzed in details.Then based on the change of four different motion regimes with eccentricity e and dimensionless moment of inertia I*of the disks,a two-dimensional phase diagram is drawn.Based on this phase diagram,a thorough analysis is made and it is found that eccentricity e is a very important parameter in describing the falling motion regimes.?2?It is proved that the dimensionless moment of inertia I*of windmill-like disks with a specific shape are the same along any axis passing through the center of the disk?in the X-Y plane?,so we only need to calculate the I*value in any direction through the center of the windmill-like disk.The freely falling motions of windmill disks with different shapes and thicknesses are captured by high-speed camera in the water tank,and the influence of wavy edges on the falling regimes of the disks was analyzed.It is found that the stability of these disks in water increase with the decrease of the number of windmill blades.Through correlation analysis,this paper concludes that Reynolds number and dimensionless moment of inertia I*have little correlation with the stability of the disks,while the correlation between the isoperimetric coefficient Q and the stability of the disks is larger.The correlation between the minimum diameter and the maximum radius ratio R₂/R₁ and the stability of the disks is the largest.The improvement of the stability of windmill-like disks is due to the flow of fluid around the disks,which also leads to the largest correlation between the minimum radius and the maximum radius ratio of each disk and the stability of the motion regimes of disks.?3?Combining with the case of the control group,the numerical simulation method is used to investigate the falling directions,characteristics and motion regimes of three groups of different types of fallingdisks in water and the changes of the flow field around them after fixing rectangular bulges on the top,bottom or both sides on the edge of the disks.The correlation between the vorticity variation on both sides of the disks and the inclination of the disks is obtained by analyzing the streamline and pressure contour maps of certain range near the disk at some typical times during the falling process of three groups of disks.Based on the above analysis,the stability of four different types of disks in this chapter is ranked.It is found that the stability of the disks will be greatly increased when the rectangular bulges are added on the top side,bottom side or both sides of the edge of the disks.Adding rectangular bulges onboth sides of the edge is the best way to increase the stability of the disk;adding rectangular bulges below the edge is the second;and adding rectangular bulges above the edge is the third.?4?Taking the source analysis of V-shaped zinc dross in hot dip galvanizing bath as an example,the specific application of lifting kinetics and stability of objects in liquid is demonstrated.The numerical simulation method is used to analyze the flow field of zinc liquid in the hot dip galvanizing bath.In addition to the basic analysis of the flow field,the influence of heater on the flow field and the influence of liquid zinc reflux and air knife zinc blowing on the flow field arealso emphatically analyzed.On this basis,this paper uses numerical simulation method to analyze the source of zinc liquid entering V-shaped area,in order to understand the possible source of zinc dross adhering to strip steel,and provide reference for improving the quality of hotdip galvanized steel sheet.