Assessment of Actuator Line and Rotor Disk as Alternative Approaches for the Numerical Simulation of Rotating Wheels

Wheel and wheelhouses contribute up to 20-30% of the aerodynamic drag of passenger cars. Simulating the flow field around wheels is challenging due to the complexity of the flow structures generated by tires and rims, wheel rotation, tire deformation and contact with the ground. High accuracy is usually obtained with transient simulations that treat rim rotation with the Sliding Mesh (SM) approach, which is also computationally expensive. Previous studies have confirmed that the application of a tangential velocity component to the rim surface is unphysical for open rims, while a Moving Reference Frame (MRF) is lacking accuracy and the averaged results depend on the initial spokes position. These methods do not consider the dynamic nature of the problem. This work proposes the use of the Actuator Line (AL) and Rotor Disk (RD) approaches as alternatives for simulating open rims with much lower computational cost. They are based on the introduction of volume forces to resemble the presence of the spokes and require a preliminary aerodynamic characterization of the body. The new methods are compared to SM, Rotating Wall Boundary Condition (RWBC) and MRF applied to an isolated rotating wheel case. A good agreement is observed for the most relevant flow features, with consistent reductions in computational cost. Specifically, AL keeps the transient features of the problem, while RD provides a much less expensive steady-state solution. As a result, both AL and RD are promising alternatives for the simulation of rotating wheels.