Flow Diagnosis Technique And Time-Resolved PIV Analysis Of Water Entry Problem

The water entery problem has a wide range of engineering application background and important scientific research significance.It is very challenging for us to comprehend the problem,in that it contains the coupling between gas,liquid and solid,that consequently produces strong nonlinear and strong unsteady flow at the near free surface.Meanwhile,the PIV technology that appeared in the 1980s was a milestone in modern experimental fluid mechanics due to the characteristics of non-intrusive,instantaneous,and global flow field measurement.It broke through the limitations of traditional experimental techniques.It can provide a new cognitive perspective for traditional problems,and it can be a new exploration method of flow phenomena and research methods of fresh flow mechanism as well.This article mainly applies the high frequency time-resolved PIV system to the study water entry problem,and builds the corresponding water entry experimental facility and PIV system.For the traditional water entry problem of a rigid wedse,due to the boundary motion and free surface change in the process of water entry,an image boundary feature detection and dynamic image masking method based on Radon transform is proposed.TR-PIV technique is applied to study the detail of the slamming flow field,supplemented by corresponding numerical simulation and theoretical analysis.After obtaining the TR-PIV results,a block multipath pressure integration scheme based on the incompressible Navier-Stokes equation is proposed.It is used to achieve non-intrusive,instantaneous,global flow field evaluation of the slamming pressure.Through PIV technology,the slamming flow field is related to the motion response of the wedge,the instantaneous slamming pressure and the slamming load,which realizes the direct correlation between the macroscopic mechanical performance and the detailed flow field.For the water entry problem of arbitrary bow section,due to the complicated flow phenomena such as flow separation and gas entrainment,the TR-PIV/LIF coupling technology was further developed based on the previous TR-PIV.LIF technology is used to capture complex gas-liquid two-phase flow phenomena during slamming,and TR-PIV technology is used for detailed flow field measuring.We interpret the complex flow phenomena such as flow separation,formation and evolution of the air cavity,intersection of the flow and migration of the saddle point.The second impact phenomenon,which is the most severe and harmful in the process of hull slamming,was studied in depth.The pressure reconstruction method was introduced above to clarify the mechanism and effect of secondary impact.