Research On Underwater PIV Measurement Technology And Flow Mechanism Of Wake Field Of Model Ship

The interaction between ships and water shows the hydrodynamic performance of ships in water environment.The hydrodynamic performance of a ship depends largely on the viscous flow field around it.Wake field which is an important part of the flow field around ships is directly related to resistance performance(vortex resistance),propulsion performance(force,cavitation,and noise),and the vibration of stern area,excitation characteristics(fluid pulsation and flow separation)and the comfort of crews.In this paper,the flow mechanism and turbulence characteristics of wake field are studied based on Particle Image Velocimetry.The experiment is taken in the towing tank of Harbin Engineering University by using Two Dimension Three Component Stereoscopic PIV.The planar and spatial flow mechanism and turbulence distribution of 76000 DWT Panamanian bulk carrier are obtained.The main work of this paper is as follows:This paper makes an in-depth analysis of the importance of flow field testing technology and detailed flow field analysis and research on the hydrodynamic performance of ships in theoretical and methodological research from the aspects of regulations,specifications and industrial requirements.This paper describes the development process of the testing technology and measuring system of the ship flow field based on Laser,compares and analyzes the PIV velocity measurement system of towing tank and the Laser Doppler Velocimetry(LDV)velocity measurement system,and describes the testing of the PIV flow field of surface ships and underwater vehicles.The experimental equipment and methods are introduced,including basic test equipment and test model.This paper mainly introduces the 2D-3C SPIV measurement system and the testing method,including the calibration method and calibration support of PIV measurement system,the selection of particles and sowing method.The 2D-3c image processing,velocity field analysis,velocity gradient solution,velocity and turbulence characteristic parameters are introduced in detail.The measuring ability,precision,uncertainty and convergence of SPIV measurement system are analyzed.The PIV test of unstructured uniform flow with known towing speed and the PIV test of KCS international standard model were carried out respectively,and the verification of the unstructured uniform flow and the KRISO international standard flow field of KCS ship were carried out in detail after the test.After the verification of standard flow field,the potential error source in SPIV measurement process is analyzed and the uncertainty and convergence of SPIV velocity test in this paper is analyzed by using the uncertainty and convergence analysis method used by Italian pools for SPIV measurement test.SPIV flow field measurement and analysis of 76000 DWT Panamanian bulk carrier under design loading condition,ballast loading condition,different speed factors are carried out.The main velocity parameters measured are axial velocity u,spanwise velocity v,vertical velocity w,plane velocity S,total velocity L,velocity vector,streamline,average kinetic energy AKE,etc.Besides the analysis of time averaged velocity characteristic,the transient velocity characteristic of typical velocity samples 60,70,150 and 155 are analyzed in detail.The nominal wake field 76000 DWT Panamanian bulk carier under design loading condition,ballast loading condition,different speed factors are tested.The parameters such as turbulent velocity,turbulence,turbulent kinetic energy,Reynolds normal stress and Reynolds shear stress were analyzed,and the relationship between turbulence anisotropy,turbulence characteristics,fluid micro mass deformation rate,additional deformation rate and the stern shape in the wake field was analyzed and explained.The multi-2D sectional CT scan measurement of the wake field of 76000 DWT Panamanian bulk cargo ship and the spatial reconstruction of 3D-3C wake field were carried out.The spatial reconstruction process,different axial,spreading and vertical velocities were analyzed,and the spatial distribution of velocity and turbulence characteristics were also studied.The vortex distribution characteristics of the propeller disk area and the spatial distribution of vortex in wake field under the design and ballast condition of 76000 DWT Panamanian bulk carrier are studied,and the spatial evolution characteristics of bilge vortex,hub cap vortex generation,growth,development and transmission are analyzed.