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.

The purpose of the paper is to characterize the aerodynamic behavior of a rotor-downstream hub cavity rim seal in a high-pressure turbine (HPT) stage. The experimental data are acquired in the Transonic Test Turbine Facility at the Graz University of Technology: the test setup includes two engine-representative turbine stages (the last HPT stage and first LPT stage), with the intermediate turbine duct in between. All stator-rotor cavities are supplied with purge flows by a secondary air system, which simulates the bleeding air from the compressor stages of the real engine. The HPT downstream hub cavity is provided with wall taps and pitot tubes at different radial and circumferential locations, which allows the performance of steady pressure and seed gas concentration measurements for different purge mass flows and HPT vanes clocking positions. Moreover, miniaturized pressure transducers are adopted to evaluate the unsteady pressure distribution, and an oil flow visualization is performed to retrieve additional information on the wheel space structures. The annulus pressure asymmetry depends on the HPT vane clocking, but this is shown to have negligible impact on the minimum purge mass flow required to seal the cavity. However, the hub pressure profile drives the distribution of the cavity egress in the turbine channel. The unsteady pressure field is dominated by blade-synchronous oscillations. No non-synchronous components with comparable intensity are detected.

The efficiency assessment of a high-pressure turbine (HPT) stage is complicated by the presence of upstream and downstream purge flows. In fact, the efficiency calculation is often based on mass flow-averaged values of total temperature at the stage inlet and outlet planes. Moreover, the purge flow distribution in the annulus is usually unknown and therefore assumed to be uniform. This paper presents and applies an alternative method to calculate the efficiency of a fully purged HPT stage. Such a definition relies on seed gas concentration measurements at the HPT stage outlet plane to determine the outlet purge flow distribution. After comparing the alternative method to the standard definition (based on the assumption of uniform purge) for the nominal purge case, the efficiency variation between the case with nominal purge and the case without purge is investigated.

The urgent need to reduce the emission of greenhouse gases, in combination with high fuel expenses, motivates manufacturers to design more efficient civil aircraft engines. In the case of directly driven jet engines, this is possible through the increased by-pass ratios for high propulsive efficiencies. This tendency implies a change in the operating condition of the low-pressure turbine (LPT) towards lower rotational speeds at larger diameters. Turbine vane frames (TVFs) constitute a new generation of inter-turbine ducts that guide the airflow from the high-pressure turbine (HPT) to the LPT in radial and circumferential direction. The TVF setup integrates turning vanes, and thus removes the need for a separate vane blade-row in the first LPT stage. Consequently, the TVF yields a benefit for overall engine weight and length, resulting in overall efficiency gains. This paper offers new insight into airflow through a TVF duct. Experimental measurements have been conducted at the two-spool test rig at the Graz University of Technology, consisting of a single-stage HPT, the TVF, and the first LPT rotor. Engine-relevant flow conditions are achieved at the TVF inlet, including HPT tip clearance and purge air effects. Particle Image Velocimetry (PIV) was used to capture the flow field in between two struts of the TVF. Inside each strutted segment, splitter vanes are located along the second half of the TVF axial length. This paper presents new results for a TVF based on measurements from a PIV test section located upstream of the splitter vanes in the first half of the TVF duct. Flow data in the area of strong transient interactions between the HPT and the TVF is recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded at six serial stator-rotor positions. In addition, two data sets of varying HPT purge flows were obtained and discussed in order to characterize the effect of purge air inside the measurement domain.