Abstract
The modelling of rotating parts, such as axial fans, is one of the main challenges of current CFD simulations of industrial applications. Different methods are available, but the most commonly used is the multiple reference frame (MRF) method. This paper investigates how different flow properties, such as temperature, pressure and velocity, develop when passing through the MRF domain. The results are compared to the more physical rigid body motion (RBM) approach. It is found that the MRF method transports the upstream properties with the streamlines of the relative velocity from the upstream to the downstream interface. This leads to a non-physical rotation by an angle that is dependent on the length of the domain and the ratio between axial and tangential velocity in the MRF region. The temperature field is more affected than the flow field, since wake structures from upstream obstacles are destroyed due to the wake of the blades. Downstream structures affect the flow in the upstream region by an increase in static pressure, which causes the streamlines in the MRF zone to slow down. Depending on the size of the obstacle, this can cause substantial distortions in the upstream and downstream flow field.
Highlights
One of the aims in current automotive development is to reduce the energy consumption of the vehicles, amongst others by reducing the aerodynamic drag
It can be observed that the temperature field in the multiple reference frame” (MRF) case has experienced a rotation of ≈90 deg, while the temperature field in the rigid body motion (RBM) simulation, as expected, did not rotate
Special focus was given to the transport of a non-uniform temperature field over the MRF region, and the effect different objects being placed up- and downstream of the MRF domain have on the flow field
Summary
One of the aims in current automotive development is to reduce the energy consumption of the vehicles, amongst others by reducing the aerodynamic drag. A substantial contribution to the aerodynamics drag comes from the air that passes through the cooling system for the driveline components. The MRF approach is relatively simple to implement and suitable for steady state simulations, which makes it a computationally inexpensive method. This approach is often used in industrial applications, such as cooling of electrical components [1,2], ventilation [3,4], tidal current turbines [5,6]
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