Influence of varying tip gaps and cooling air parameters on the aeroelasticity of a two-stage axial turbine

In turbomachinery, the aerodynamics and aeroelasticity of vanes and blades is affected by geometry variances. A further impact is created by cooling air. In this work, the influence of different tip gaps on the excitation of a downstream vane row is investigated using unsteady flow simulations. Furthermore, the impact of cooling air parameters on blade vibrations is studied. With increasing tip gaps, an increase of the tip leakage vortex is observed, as expected. This induces differences in the static and unsteady pressure distributions on the downstream vane which indicate a change in excitation forces. Regarding the effect of cooling air, an influence on the vibration excitation of the downstream blades was found by systematically varying the cooling air mass flow rate and temperature. Low cooling air mass flow rates reduce the total pressure deficit in the cooled vanes' wake, thus, reducing the vibration amplitude of the following blade. Larger cooling air mass flow rates cause a disturbance in the vanes' wake, leading to an increase in vibration amplitudes. Even though for the cooling air temperatures investigated, no changes in the vibration amplitudes of the downstream blades were observed. This paper shows that the effects of tip gap and cooling air variations need to be considered during the aerodynamic and aeroelastic design stage of an axial turbine.