Turbocharger turbine blades are subjected to resonant excitation that can lead to High Cycle Fatigue (HCF). In vaneless turbines the excitation primarily stems from asymmetries in the turbine housing such as the volute and the tongue. Given the nature of such asymmetries, the excitation is of a Low Engine Order (LEO) type. The present study deals with the effect of radial turbine housing design on LEO resonant excitation of turbine blades. The study focuses on two geometrical key design parameters of a twin-scroll turbine housing for a radial turbine which is the rotor-tongue distance and the circumferential angle between both tongues. The generalized force approach is used to identify the critical blade surface regions in order to understand the excitation mechanism of each specific design and to assess the differences of design variants with respect to the baseline design. The presented approach is highly practicable, because it is less expensive than full FSI-simulations. This approach is validated on tip timing test data from full-scale experiments. Correlation to test data shows that the presented approach is capable of capturing the relative trends reliably and hence can efficiently be employed in an industrial design process such as to minimize blade vibration amplitudes. It is shown that a reduction of blade vibration amplitudes by a factor of 10 could be achieved.

Radial turbines consisting of a spiral volute inlet casing, such as those found in turbochargers, are subject to excitations caused by the inlet flow. In the absence of inlet guide vanes, the asymmetries from the volute are accentuated and lead to Low Engine Order (LEO) excitations. These excitations can be particularly troublesome as they are likely to resonate with the first bending mode (M1) at high rotational speeds, causing large vibration displacement amplitudes which will result in High Cycle Fatigue (HCF). It is therefore imperative to ensure these vibration amplitudes are low enough to make certain blade failure will not occur. This paper deals with the possibility of actively influencing the excitation pressure pattern on the blades such that the amplitude and phase of the forcing is affected. This active influence is through the use of an air jet injection at the tip of the turbine blade and has the potential to substantially reduce the blade vibrations caused by the LEO excitations. This theory of using air jets to alter the blade vibration amplitude is investigated in this paper both experimentally, using standard turbine housing equipped with a rotatable device with a single jet nozzle, and numerically, using Computation Fluid Dynamics (CFD) software ANSYS CFX. The tests yielded positive results indicating that a single air injection was able to significantly decrease, as well as increase, the blade vibration amplitude. At certain jet injection locations, decreases in blade vibration amplitude of 70% were measured which was backed up by numerical results. To numerically calculate these differences in the vibration amplitude, the generalized force approach was used successfully. The positive results obtained from this study show real potential for this method to become a useful tool in keeping blade vibration to a safe level and avoiding failures in turbomachines.