CFD for air induction systems with OpenFOAM

Abstract

CFD is a very important tool in today's design of automotive air induction systems. The simulations enable the flow in a proposed design to be evaluated without manufacturing the system. Most commercial software's used for this are expensive, and in the ever increasing competition lowering costs is a key issue for a carmaker such as Volvo Car Corporation. This thesis evaluates the use of the open source CFD code OpenFOAM for simulating the flows in air induction systems. Two test cases are used and compared to the commercial code Fluent sold by ANSYS, Inc. The results from both codes are also compared to results from physical tests. Results from the test cases are that although a lot of time has been spent on finding viable numerical schemes and solver settings, there is still a lot of work to be done before the OpenFOAM simulations show the same numerical stability as the Fluent simulations. Because of this and that the same boundary conditions could not be used OF shows results further from the experimental results than Fluent. During the project a problem in OpenFOAM concerning oscillating velocities in the interface to porous media was discovered. Put together there is still work to be done before OpenFOAM can be used for complete air induction system simulations. When there is no air filter involved, OpenFOAM is very suitable to use in topology optimisation. Since it is command line based it is easy to couple with optimisation software such as modeFrontier. Also investigated in this thesis is the adjoint solver in OpenFOAM. It is a simple adjoint optimiser but to be truly usable it needs extension. Adjoint optimisation in general is very useful as a guide to designers, but the results are not suitable to use directly since it doesn't take variables such as manufacturability into account.