Thermodynamic Analysis Of Engine Piston Based On Fluid-solid Coupling

The piston is an important component of the underwater vehicle engine,During operation,the top surface of the piston undergoes repeated flushing of high-temperature and high-pressure gas.The high-temperature thermal causes the piston to generate thermal expansion and deformation,the pressure causes the piston to mechanically deform,which will inevitably affect operating performance,safety and stability of the engine.Therefore,the calculation and analysis of the strength of the overall piston is particularly important.Cracks can be avoided to ensure the steady operation of the engine.At present,most of the research on the engine piston strength is based on the cyclic average load to calculate the deformation and stress,while ignoring the non-uniformity of the pressure field and temperature field on the top surface of the piston,it will inevitably affect the calculation results.In this paper,the cam engine of a certain underwater vehicle is used as the research object,the fluid calculation software FLUENT is used to calculate the flow field in the cylinder,the Workbench is used to caculate the deformation and stress of the piston based on the fluid-structure coupling.In this paper,the mathematical model of intake,exhaust and cylinder work is established based on the structural parameters of an underwater vehicle piston cam engine,the appropriate wall heat transfer model is selected,the performance index of the engine and the relationship between pressure,temperature in the cylinder and the crank degree are obtained through MATLAB numerical simulation.Based on the physical model of the valve seat and the cylinder,a fluid domain calculation model was established.Using the k-? turbulence model,the SIMPLEC coupling algorithm and the second-order upwind style was used to calculate the flow state and law of the fluid change in the cylinder by the finite volume method,to obtain the convection heat transfer coefficient and pressure field on the top surface of the piston.While calculating the temperature field and strength of the piston,cyclic average method and fluid-structure coupling method were used to analyze the variation of the temperature field and heat flux of the piston,and then total deformation distribution,axial and radial deformation distribution,and equivalent stress distribution were caused by the temperature load,mechanical load and the coupling effect between the two load were analyzed and studied.It is found that the heat transfer model suitable for the piston engine of the underwater vehicle is Woschini's formula,and the zero-dimensional simulation and flow field numerical simulation can both accurately calculate the performance parameters of the engine;The flow field is complex,in the intake stage,the pressure and temperature in the cylinder,the pressure and the heat transfer coefficient on the top surface of the piston,are all relatively hige,and there is a hige gradient,as the crank angle changes,it gradually decreases and tends to uniform.The temperature of the top surface of the piston is hige,and gradually decreases along the axial direction when based on the cyclic average method,the deformation caused by the thermal load is the largest at the top surface,the maximum deformation under the mechanical load occurs at the edge of the top surface near the side of the guide groove,the maximum equivalent stress is on the upper face of the shaft hole of the roller;when the effect of fluid-structure interaction is considered,the non-uniform convection heat transfer coefficient produces a non-uniform temperature field,and the thermal deformation of the piston increases radially toward the center of the distribution circle of the cylinder.At the same time,fluid-structure interaction has no significant effect on the coupling deformation and stress distribution of the piston.