The Simulation Research On Heat-Fluid-Solid Multi-Field Coupling Of Diesel Engine Cylinder Head

The cylinder head under high intensity mechanical load and heat load in the process of operation, and also exists many physical field such as the intake and exhaust flow field and cooling fluid flow field,the temperature produced by high-temp gas,the stress field produced by bolt pre-tightening force and the gas pressure, and it is one of the major parts to guarantee the normal work of diesel. In the traditional numerical computation of the temperature field and stress field of cylinder head, there are two kinds of method of the temperature field boundary conditions applied of the cylinder head: One kind is to use empirical formulas, this method error estimate is bigger; Another method is to analysis fluid domain separately, the result as a solid domain analysis required boundary conditions, this method is multifarious. In view of the above questions, this article implementing flowing and heat emission direct coupling on cylinder head and cooling system, obtain the temperature field of the cylinder head;Then coupling this temperature field and the stress field produced by bolt pre-tightening force and the gas pressure, realized the cooling liquid (flow) and head (solid), cooling fluid and cylinder head of heat transfer between (hot) coupling, simplified the boundary conditions, the definition of complex process enhances the calculation precision.This paper takes a v-shaped 12-cylinder engine as an example, takes a whole tank and two half cylinders as the solid domain of hot-flow coupling system, takes the cooling fluid of cylinder and engine body as the fluid field of hot-flow coupling system, implementing flowing and heat emission direct coupling on cylinder head and cooling system using the theory of disperse integrally and solve integrally, obtain the boundary conditions needed for cylinder analysis; And on the basis of the result, this research achieved direct coupling analysis for heat, flow and solid through the method of unit conversion, making the analysis of flow field, temperature field and stress field can be realized in a single calculation model. In addition, the impact of boundary conditions for the cylinder cooling was analyzed using above method, providing engineering significant for the selection of parameters of cooling system.The mainly working content of the paper is as follows:1)Taking the large fluid dynamics CFX software as tools,by analyzing the physical process of complex flow and heat transfer in the diesel engine cylinder head , the paper is to determine the physical model of complex flow and heat transfer of the cylinder head when the diesel in stable operation condition according to its characteristics of heat transfer regularity and cooling fluid flow. The physical model is three-dimension, steady-state, none internal heat source viscous incompressible fluid turbulent flow and heat transfer. The mathematical model is enclosed equations which are energy conservation equation, momentum conservation equation (3), mass conservation equation, k equation andεequation. Different areas exerting different heat exchange boundary conditions, based on proper division on the combustion chamber and other external surface. Take the gas equivalent temperature of combustion chamber surface as environmental temperature; the boundary conditions of cylinder head outside surface and intake-exhaust way regional refer to similar type and experience formula obtained. Take the most robust combination flow boundary conditions of import and export boundary condition, which is speed/quality flow as entrance boundary conditions, the pressure as outlet boundary conditions. Adopting k ?εstandard two equations turbulence model, solved the momentum conservation equation, energy conservation equation and turbulent equation using the control volume method, and got the flow field and temperature field of coupling system finally. The numerical simulation results are compared with experiment results, verified the feasibility of this method.2)Transfer the heat-flow analysis unit into the other unit which can be used for calculating thermal stress and mechanical stress on the basis of heat-flow analysis by using the finite element software ANSYS. Then carry out thermal-machine coupling numerical simulation for transformation model of cylinder head in different conditions which are preloaded force, preloaded force-breakout pressure, preloaded force-thermal stress-breakout pressure working conditions, obtain the distribution of the stress and strain of cylinder head, meet the required strength, provide theoretical basis on design and improvement for cylinder head.3)Calculating the fluid-structure coupling for cylinder head through setting different coolant mass flow, cooling fluid entrance inlet temperature and cooling water surface roughness, analyzes the impact of different parameters on the cooling flow and heat transfer, Obtain the impact curves on the temperature of cylinder head and the cooling liquid wall under different coolant mass flow,inlet temperature and wall roughness, providing the reference on choosing influence of flow and heat transfer for cooling system boundary conditions.