Research And Application Of The Finite Volume Method For The Thermal Barrier Coated Piston

The piston of the internal combustion engine works in severe environment subjected to large mechanical and thermal forces of high frequency.The piston with thermal barrier coating(TBC)possesses advantages of multiphase materials,which provides technical support for the improvement of the reliability and the increasement of the lifetime of the new-style internal combustion engine.In order to make the TBC piston satisfy the technical requirement,it is necessary to evaluate its performance accurately before the production.So it is of important significance to develop a numerical method as the predictive tool for the thermoelastic analysis of TBC pistons.The TBC piston has complicated geometry and varying material properties in space,which requires the capability of the numerical method for unstructured meshes and heterogeneous materials.On the other hand,numerical efficiency and computational cost also need to be considered.Since the finite volume method(FVM)is capable of unstructured meshes and reliable in solid problems,it is preferred as the basic method for the development of numerical tool for TBC pistons.Cell-centered FVM(CC-FVM)and cell-vertex FVM(CV-FVM)have been established for the thermoelastic analysis of the TBC structures.The material variation has to be taken into account explicitly in the course of discretization.In the present CC-FVM,the central differencing formula is applied to calculate the related material properties on cell faces,which introduces material variation into the discretized equations.In the present CV-FVM,the staggered grid technique is adopted to include material variation in the control volume by defining unknown variables and material properties at different places.Numerical tests have been accomplished for the validation and assessment of CC-FVM and CV-FVM.According to the results,CC-FVM has lower calculation accuracy,computational efficiency and numerical order than CV-FVM,while it costs less computer memory than CV-FVM.It is found that CC-FVM requires much computational time to obtain convergent results for the problem with unstructured meshes and for some case the calculation may even divergent.In allusion to this problem,the discretized equations have been rearranged which helps to improve the convergence speed but can not avoid the divergence for some case.For the functionally graded materials(FGM),both CC-FVM and CV-FVM are able to avoid numerical discontinuities caused by material variation.For the laminated materials,CC-FVM obtains the results with numerical oscillation near the interface of different materials,while CV-FVM predicts accurate results.Compared to the existed composite numerical methods,CV-FVM owns better solution economy than the finite volume theory(FVT)and better application than the graded finite element method(FEM),since CV-FVM is still usable when the load is parallel to the material gradient direction while the graded FEM fails.CV-FVM is further developed to consider the nonlinear problem caused by the temperature gradient and the problem with microstructures.CV-FVM is applied to simulate thermoelastic fields of several TBCs to analyze the effects of nonlinear heat conduction,the shape of the interface between different materials,the material variation in the FGM layer and the distribution of microstructures on the thermoelastic performance of the TBCs.The comparison between the present results and other numerical results validates the capability of CV-FVM for complicated TBCs.CV-FVM is adopted to predict the thermoelastic performance of different pistons.The difference between the TBC piston and the ordinary piston has been analyzed.The results show that the adoption of TBC is able to decrease the deformation,increase the temperature on the top of the piston,decrease the load near the ring grooves and cause the stress concentration in the TBC.The influences of the material distribution and the coating method on the TBC pistons under thermal load or thermomechanical load have been discussed.It is found that the maximum stress exists at the interface between the bond coat layer and the ceramic layer or the FGM layer,which is mainly caused by the thermal load and the mismatch of the material properties.And the mechanical load has little influence on the piston deformation.The successful application shows that CV-FVM can be used to predict the thermoelastic performance of TBC pistons.