Research On Impingement Flow And Heat Transfer Mechanism Of Shaker Cooling Of Diesel Engine Piston

Highly efficient cooling of heavy duty marine diesel engine piston is one of the key parts of modern advanced engine piston design.Due to high efficience of shaker cooling system,it is extensively used.While it is influenced by many factors,lots of research work has been done on this problem.Most researches are focused on calculation method of heat transfer coefficients or effects of different piston structures on temperature distribution.Rare work has been done on coolant flow in piston under coupling of reciprocating,buoyance and inertial force until now.With the development of numerical methods and computer technology,computational fluid dynamics(CFD)numerical simulations gradually become a powerful tool to accurately investigate the transient flow and heat transfer mechanism inside the piston gallery.Detailed cooling oil flow and heat transfer behavior inside the gallery can be simulated,and oil fill rate and wall heat transfer coefficient distributions under different crank angles are obtained.The predicted value of heat transfer coefficient from the CFD model is helpful to provide precise thermal boundary conditions and improve prediction of piston temperature in finite element analysis,so as to achieve the optimized design of pistons.Based on the impinging jet in oil gallery cooling system,using CFD method,the flow and heat transfer characteristics of impinging jet have been numerically investigated in this paper to explore various factors on heat transfer with 13 widely used turbulence models,and unveil the mechanism of heat transfer under piston reciprocation motion.First,13 widely used turbulence models for the prediction of flow and heat transfer under turbulent impinging jet are analyzed by comparison with available experimental and numerical data.The Spalart-Allmaras model that is rarely used in impinging jet system is also included.From the analysis,it is found that SST k-w model with Low-Re Corrections shows best agreement with the experimental data.Effect of various flow conditions are also carried out,such as jet inlet velocity profile and turbulence intensity.Second,various factors on heat transfer of slot and round impinging jet are studied,including Reynolds number,nozzle-to-plate spacing,angle of impingement,inlet pulsation,plate surface structure,Prandtl number,and Biot number,and empirical correlations are proposed based on the available data,which is agreed well with related literature.Finally,this paper studies numerically the transient heat transfer of the oil gallery cooling system in diesel engines,the reciprocal motion of the engine piston is accomplished through a more computationally efficient non-inertial reference frame model instead of dynamic mesh method,and the two phase interface motion is modeled by the VOF(volume of Fluid)multiphase model.Detailed oil flow and heat transfer processes have been numerically investigated at different engine operation speeds.The results show that the oil can remove a lot of heat from the gallery,which reduces piston temperature effectively.