Turbocharger Dynamic Analysis: Advanced design simulation in time domain using CFD predicted thermal bearing boundary conditions

Small changes of surface temperature, clearance and bearing profile can significantly change stiffness and damping characteristics of slider bearings. This may influence dynamics and in case of turbochargers the rotor radial deflection. NVH or durability issues like rotor colliding with housing may be generated as a consequence. This paper presents a new methodology for dynamic turbocharger investigation. It considers multi-body dynamics of a flexible rotor and housing coupled with full-flotaing ring bearing. The energy equation for the calculation of the oil film temperature is considered using thermal boundary condition obtained from 3D CFD simulation. Typical targets for CFD simulation within the turbocharger development process are flow investigation and to provide accurate thermal boundary condition for thermo-mechanical fatigue analysis. The CFD analysis uses fully coupled fluidstructure interaction where both domains are modelled within the same tool. However, the same CFD model can be used to provide the required boundary conditions for dynamic analysis. The bearing profile under thermal load is derived from FE analysis and based on the same thermal boundary conditions as well. The authors demonstrate the application of the methodology for a typical turbocharger design study applied for heavy-duty engines with full floating bushings that have radial bore connections between inner and outer oil films. The rotor operating speed reaches up to 110 krpm. Dynamic simulation results with nominal clearance and temperature are compared with the results obtained when CFD predicted boundary conditions are used. Based on results for the oil film pressure and flow through each oil film as well as flow between inner and outer oil film a valid conclusion about the rotor dynamic behaviour, bearing mechanical and thermal loads can be made. The presented methodology proves to be a next level approach in prediction of turbocharger simulation in the development process.