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.

In this paper, a numerical investigation of the effect of a miniaturized five-hole probe downstream of a transonic low-pressure turbine vane row is presented. Firstly, a numerical calibration of the probe was performed. The effect of the probe on the flow-field throughout the vane segments was then evaluated by performing a comparison between a setup with vanes-only (no probe) and with vanes and probe. To assess the accuracy of the quantities ‘measured’ by the probe, the probe-determined flow-field was compared to the flow-field of the vanes-only setup. A non-negligible modification of the probe-determined local distributions of Mach number, yaw and pitch angle is revealed with respect to the undisturbed flow. A correction is used to account for the effects of the non-uniformity of the flow and its impact is evaluated on 2D and 3D flow regions. A significative effect of the correction was found on the probe-determined yaw angle, in which the difference from the vanes-only data was reduced to below 1 degree, except near the endwalls where larger discrepancies remain due to probe-endwall interactions. A shortfall of the correction was instead observed on the probe-determined Mach numbers. Finally, the pitch-wise averaged quantities were evaluated. It was observed that the highest differences between probe-determined and undisturbed data occur where radial gradients of total pressure are stronger and that the correction had almost negligible impact on the pitch-wise averaged quantities.

Modern low pressure turbines (LPT) are designed in order to fulfil a various number of requirements such as high endurance, low noise, high efficiency, low weight, and low fuel consumption. Regarding the reduction of the emitted noise, different designs of LPT exit guide vanes (aerodynamically and/or acoustically optimized) of the turbine exit casing (TEC) were tested, and their noise reduction capabilities and aerodynamic performance were evaluated. In particular, measurements of TEC-losses were performed, and differences in the losses were reported. Measurements were carried out in a one and a half stage subsonic turbine test facility at the engine relevant operating point approach. This work focuses on the study of the unsteady flow field downstream of an unshrouded LPT rotor. The influence on the upstream flow field of a TEC design including acoustically optimized vanes (inverse cut-off TEC) is investigated and compared with a second TEC configuration without vanes (Vaneless TEC), by means of fast response aerodynamic pressure probe (FRAPP) measurements. The second configuration served as a reference concerning the influence of turbine exit guide vanes (TEGVs) onto the upstream located LPT rotor. The interactions between the stator and rotor wakes, secondary flows, and the TEGVs potential effect are identified via modal decomposition according to the theory of Tyler and Sofrin. The main structures constituting the unsteady flow field are detected, and the role of the major interaction effects in the loss generation mechanism and in the acoustic emission is analyzed. This study based on the modal analysis of the unsteady flow field offers new insight into the main interaction mechanisms and their importance in the assessment of the aerodynamic and aeroelastic performance of modern LPT exit casings.

One of the main goals for modern aircrafts is to lower the fuel consumption and noise emissions without worsening the aerodynamic performance. One possibility to lower the fuel consumption is to reduce the skin-friction losses of vanes and blades inside the engine. Therefore, this paper is about the aeroacoustical as well as the aerodynamical effects of a riblet foil applied on the suction side surface of turbine exit guide vanes (TEGVs) of a 1½ stage low pressure turbine (LPT). There have been numerous studies concerning riblets but none using them in a LPT. In general, if riblets are applied on the suction side of vanes or blades, they lower the drag and increase the lift. Test runs were performed under two different operating points in a subsonic test turbine facility for aerodynamic, aeroacoustic, and aeroelastic investigations (STTF-AAAI) located at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. One operating point was the design point of the riblets and the second one an off-design point. During the test campaign, two different set-ups have been investigated. One configuration with riblets applied on the suction side of the TEGVs, and one configuration with a smooth foil on the vanes to achieve the same thickness as the first set-up. This smooth configuration serves as a reference case. The tested riblet structure was of trapezoid type with 45 μm tip distance and a height to tip distance ratio of 0.45. The acoustical data has been obtained by using flush mounted condenser microphones, rotated over 360 deg around the flow channel. The aerodynamical data was obtained by using an aerodynamic five-hole-probe as well as a trailing edge probe. Measuring in planes up- and downstream of each TEGV allowed the comparison of a rough pressure loss estimation between the two studied set-ups. The present work gives a closer insight into the change of the acoustical and aerodynamical behaviour by applying riblets to LPT vanes.

The present work gives a closer insight into the aerodynamic parameters obtained for turbine exit guide vanes (TEGV) of a low pressure turbine (LPT) with riblets applied on their suction side. Experimental data was obtained by using an aerodynamic five-hole-probe including a thermocouple as well as a trailing edge probe. Additionally, a comparison between the flow fields of the experimental data and the numerical results, obtained by performing a steady state Reynolds-Averaged Navier-Stokes (RANS) simulation, was done. The investigated flow fields are located up-and downstream of the TEGV's and show a good overall agreement. Additionally, aeroelastic investigations show an influence of the changed surface structure onto the vibrations of the upstream located rotor blades. For a visual examination of the flow field, oil flow visualizations are performed and compared with results obtained by CFD simulations.