Modern low pressure turbine (LPT) architectures of aero engines are designed in order to optimize weight, decrease the fuel consumption and noise emissions. This can be achieved with the use of lighter materials or by reducing the size of the engine. In particular, decreasing the axial distances between the blade rows and shortening the turbine centre frame. As a consequence, it becomes more and more important to investigate the influence of inflow circumferential distortions of total pressure and temperature that can be originated by struts, flow injections and measurement instrumentation.
This work presents the results of an experimental investigation on the influence of total pressure inflow inhomogeneity on the aerodynamics and on the vibrations of a low pressure turbine stage. The measurements were carried out in a one and a half stage subsonic test turbine facility at nominal engine relevant operating conditions and during speed transient operation, including a resonance crossing. Steady and unsteady aerodynamic measurements were performed with a five-hole-probe (5HP) and a fast response aerodynamic pressure probe (FRAPP) respectively, while the LPT rotor vibration data were acquired using strain gauges applied on different blades, in combination with a telemetry system. Analysis in the frequency domain as well as a curve fitting method were applied to estimate the blades forced response and the critical damping. It will be shown that the distortion creates steady and unsteady aerodynamic alterations, causing direct effects on the rotor vibration characteristics.