Role of dynamic unbalance in dynamics of turbocharger rotors

Rotating unbalance is one of the key reasons for high vibration levels in turbochargers. The current studies consider the rotating unbalance as a series of static (force) unbalances and acknowledge the importance of their allocation and orientation. However, the displaced mass or material nonhomogeneity, which is the source of the unbalance in real-world rotors, results also in so-called dynamic unbalance. Such an unbalance creates nonzero products of inertia relative to the axis of rotation, meaning that the central principal axis does not coincide with the axis of rotation. The rotor is subjected to additional inertial forces, described in this research using a multi-body dynamics formalism. The results indicate that the dynamic unbalance amplifies the synchronous vibration and induces several types of asynchronous motions. The phenomena described in the article were proven experimentally in previous works but have been difficult or impossible to simulate without using unrealistically high values of the static unbalance. Furthermore, the work provides fundamental results regarding the interaction between the static and dynamic unbalance and proposes analytic relations describing how the balancing procedure affects the products of inertia.