TOBIAS BERG ANNA WIKSTRÖM Fan Modelling for Front End Cooling with CFD

In this thesis, performed at Volvo Cars, some concepts of modelling cooling fans with Computational Fluid Dynamics are evaluated by comparison with experimental data. Focus is set on the method Multiple Reference Frame (MRF) but the Body Force and Mixing Plane Models are also investigated. All measurements were carried out in Volvo Cars component test rig where pressure jump and air flow rate through a cooling fan and shroud mounted on a heat exchanger were measured. In order to make relevant comparisons, a detailed numerical model of the test rig with fan, shroud and heat exchanger were created. A mesh with high node density, in total 14 million tetrahedral elements, was used and the simulations were carried out with the standard k-ε turbulence model. The comparisons were performed for different air flow rates, rotational speeds, cooling packages, and for setups with open and closed speed flaps. The Multiple Reference Frame approach reproduces fan performance with good accuracy for most cases. For these cases measured and computed data differ with less than 3.5% air flow rate. Moreover, the MRF approach generates good results for open and closed speed flaps as well as for idle conditions. It also introduces swirl leading to a realistic prediction of the velocity distribution downstream the fan. The MRF method is well suited when doing flow simulations within the engine room and is therefore recommended to use. Furthermore, improvements concerning the procedure to numerically represent heat exchangers and the use of the Body Force Model are described.