Numerical Simulation Of Turbulent Flows In The Cylinders Of Internal Combustion Engines

Gas flows in reciprocating internal combustion engine cylinders are invariably complicated, three-dimensional and turbulent. Turbulent flows in engines are highly compressible, unsteady, rotational and anisotropical. For this reason, linear eddy-viscosity models(EVM) and linear algebraic stress models(ASM) are not suitable for the numerical simulation of in-cylinder turbulent flows in ICE. Because of its high cost, the application of the differential Reynolds stress models(DSM) to in-cylinder turbulent flows in ICE is limited at present. this thesis presents studies on modifying some new versions of EVM, i.e. RNG k- εmodel and nonlinear algebraic stress model which could be suitable, with moderate cost, for in-cylinder flows of ICE. The main works are as following:1. Under the assumption of rapid distortion the RNG k- ε turbulence model is modified to including the compressibility effects and applied to in-cylinder turbulent flows of internal combustion engines. The previous version of the model for the spherical compression are extended to the cases for the uniaxial and axisymmetrical compressions. Numerical results are given and compared with experimental results. It is shown that the RNG K- ε turbulence model is better than the traditional one.2. A nonlinear algebraic stress model is set up by applying the tensor invariance theory in which the pressure-strain correlation is based on the analytic solution from the rapid distortions theory by Lee. The effects of the mean flow distortion history are included in the model by introducing a parameter of the reference total strain. Numerical results for in-cylinder flows of several engines show that the new model may give better prediction than the K- ε model and the ASM based on LRR model do.. A new version of the k- ε?2 nonlinear three equation model is presented. This model adopts a cubic relation between the stress and strain/vorticity tensors and solves an additional (third) transport equation for the second invariant of the stress anisotropy tenser . Numerical results for in-cylinder flows in several engines show that the new model give better prediction than the k- E model .As all models in the category of EVM are not able predict anisotropy at TDC of compression stroke of the internal combustion engine with flat face pistons. This thesis introduces an a additional term to the nonlinear three equation model's constitution equation. Numerical results show that the modified nonlinear three equation model overcomes the default.4. comparisons among the above three models are made, indicating each one's advantages and deficiencies as well as its applicability. The best one from those, i.e.the presented k-ε-A2 model is employed to compute in-cylinder flows for engines with various combustion chamber configurations an different working parameters to investigate their effects on the in-cylinder turbulence characteristics and to explore possible means for intensifying the turbulence in the cylinder.