Reducing Blade Force Response in a Radial Turbine by Means of Jet Injection

Abstract

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.

Forced response freeform optimization of a radial turbine using the adjoint method

“…There are a number of possibilities to influence the fluid-structure-interaction of the blade and the wakes downstream of the guide vanes: Intentional mistuning is a promising path to alter the wheel's vibration patterns and aerodynamic damping to reduce its response, see Nakos et al [2021]. Netzhammer et al [2019] proposed a jet injection at the shroud contour of a radial turbine to reduce the blades' response and showed its benefits both numerically and experimentally. Another possibility is given by the choice of the number of guide vanes n gv : Not only does this choice affect the aerodynamic load at resonance conditions but also the applicable aerodynamic damping, see Beirow et al [2016].…”