FSI – MRF Coupling Approach For Faster Turbocharger 3D Simulation 2019-01-0007
Fluid-Structure Interaction (FSI) simulation approach can be used to simulate a turbocharger. However this predictive 3D simulation encounters a challenge in term of long computational time. The blade speed can be above 100,000 rpm and generally a CFD solver limits the maximum movement of the blade surface per time step. The maximum movement must be a fraction (~0.3) of the cell length and thus the time step will be very small. A Moving Reference Frame (MRF) approach can reduce the 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 blade is created and the impact of the blade movement is modeled via a momentum source. However MRF approach is not a predictive simulation because the blade speed must be given the User.
A new simulation approach was introduced that coupled FSI and MRF approach. Like in the FSI approach, the total moment of the blade was calculated based on the resultant force acting over the blade surface. This calculation was conducted each time step via a User-Defined-Function (UDF). The resulted moment was then 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 with FSI predictive approach.
The coupling approach was applied to simulate a turbocharger of 13 L diesel engine. The work done by the turbine on the compressor was adjusted to match the blade speed with the test data. The simulation result with the coupling approach showed a good agreement with the FSI result. The new approach was also used to guide the design of the exhaust manifold for better turbocharger performance.
Zainal Abidin, Andrew Morris, Jason Miwa, Jasim Sadique, Yunliang Wang
Southwest Research Institute, Convergent Science Inc.
International Powertrains, Fuels & Lubricants Meeting