FSI - MRF Coupling Approach For Faster Turbocharger 3D Simulation

Fluid-Structure Interaction (FSI) simulation approach can be used to simulate a turbocharger. However, this predictive 3D simulation encounters the challenge of a long computational time. The impeller speed can be above 100,000 rpm, and generally a CFD solver limits the maximum movement of the impeller surface per time step. The maximum movement must be a fraction (~0.3) of the cell length, thus the time step will be very small. A Multiple Reference Frame (MRF) approach can reduce computational time by eliminating the need to regenerate the mesh at each time-step to accommodate the moving geometry. A static local reference zone encompassing the impeller is created and the impact of the impeller movement is modeled via a momentum source. However, the MRF approach is not a predictive simulation because the impeller speed must be given by the User. A new simulation approach was introduced that coupled the FSI and MRF approach. Like in the FSI approach, the total moment of the impeller was calculated based on the resultant force acting over the impeller surface. This calculation was conducted for each time-step and the resulted moment was returned back to the solver to update the MRF zone moment. With this coupling approach, the computational time is similar to the MRF approach while maintaining similar accuracy to the FSI predictive approach. The coupling approach was applied to simulate a turbocharger of 15 L diesel engine. The work done by the turbine on the compressor was adjusted to match the impeller speed with the test data. The calculated pressure upstream from the turbine showed a good agreement with test data. The new approach was also used to guide the design of the exhaust manifold for better turbocharger performance.