The aerothermal performance of highly loaded high-pressure turbines is abated by the unsteady impact of the vane shocks on the rotor. This paper presents a detailed physical analysis of the stator-rotor interaction in a state-ofthe-art transonic turbine stage at three pressure ratios. The experimental characterization of the steady and unsteady flowfield was performed in a compression tube test rig. The calculations were performed using ONERA's code elsA. This original comparison leads to an improved understanding of the complex unsteady flow physics of a high-pressure turbine stage. The vane shock impingement on the rotor originates a separation bubble on the rotor crown that is responsible for the generation of high losses. A model based on rothalpy conservation has been used to assess the pressure loss. The analysis of the unsteady forcing relates the shock patterns with the force fluctuations. NomenclatureH = turbine span height, m M is = isentropic Mach number Nu = Nusselt number P = pressure, Pa S = curvilinear abscissa along wall surface, m T = temperature, K T r = rotor passing period, s T rotation = wheel rotation period, s T s = stator passing period, s t = time, s x = turbine axial direction, m y = turbine radial direction, m y = normalized distance of first wall cell Subscripts w = wall s = static 0 = freestream, total conditions 1 = stator inlet 2 = stator-rotor interface 3 = rotor outlet

Efficiency is a crucial design parameter in any turbine development. This research presents a detailed investigation on the efficiency of a modern transonic high-pressure turbine. The work focuses on the study of the efficiency loss at different stage loading factors (ranging from H /U 2 = 1.3 to 2.7) and various flow factors (V ax /U = 0.41 to 0.90). In particular, the present research is of utmost importance to understand the effect of the vane trailing edge shocks in the turbine stage efficiency.The experimental work was carried out in a compression tube facility that allows testing of the turbine at temperature ratios, Re and Mach numbers, encountered in real engines. The efficiency is measured by the mechanical method. Experiments were performed with two different vanes (cooled and uncooled) at two stagger angles, four rotational speeds (4570-6500 r/min) and three pressure ratios (p 01 /p s3 ranging from 2.42 to 5.12). The effect of the change of reaction and rotor incidence is correlated with the performance. Three-dimensional Navier-Stokes calculations aid the interpretation of the results.

The understanding of shock interactions and mixing phenomena is crucial to design and analysis of advanced turbines. A nozzle guide vane (NGV) is experimentally investigated at subsonic and transonic off-design conditions (M2is of 0.6 and 0.95) in an annular sector at the Royal Institute of Technology (KTH). The effect of cooling ejection (3% of main stream mass flow rate) on the downstream flow field is also studied. The airfoil loading is monitored with pneumatic taps. The downstream pressure field is characterized at four different axial locations using a 5-hole probe and a total pressure probe that contains a single piezo-resistive transducer. The probe with a piezo resistive transducer is also used as a virtual 3-hole probe to measure the flow angle. The time-averaged yaw angle measured with the virtual 3-hole probe is in agreement with the 5-hole probe data. At subsonic conditions the wake causes a pressure loss of 7% of the upstream total pressure and covers 25% of the pitch whereas the pressure deficit is doubled in transonic operation. The coolant ejection results in an additional loss of 2% of the upstream total pressure. The flow speed does not have a significant effect on the wake width at 7% Cax. However, the low pressure region has different width at far downstream depending on the flow velocity. The fillet at the hub region has a significant effect on the secondary flow development. The frequency spectrums at the different conditions clearly reveal the shear layers. The results aim to help the characterization of mixing phenomena downstream of the NGV.

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In this paper the aerodynamics of an innovative multisplitter low pressure (LP) stator downstream of a high pressure turbine stage is presented. The stator row, located inside a swan necked diffuser, is composed of 16 large structural vanes and 48 small airfoils. The experimental characterization of the steady and unsteady flow fields was carried out in a compression tube rig under engine representative conditions. The one-and-a-half turbine stage was tested at three operating regimes by varying the pressure ratio and the rotational speed. Time-averaged and time-accurate surface pressure measurements are used to investigate the aerodynamic performance of the stator and the complex interaction mechanisms with the high pressure (HP) turbine stage. Results show that the strut blade has a strong impact on the steady and unsteady flow fields of the small vanes depending on the vane circumferential position. The time-mean pressure distributions around the airfoils show that the strut influence is significant only in the leading edge region. At off-design condition (higher rotor speed) a wide separated region is present on the strut pressure side and it affects the flow field of the adjacent vanes. A complex behavior of the unsteady surface pressures was observed. Up to four pressure peaks are identified in the time-periodic signals. The frequency analysis also shows a complex structure. The spectrum distribution depends on the vane position. The contribution of the harmonics is often larger than the fundamental frequency. The forces acting on the LP stator vanes are calculated. The results show that higher forces act on the small vanes but largest fluctuations are experienced by the strut. The load on the whole stator decreases 30% as the turbine pressure ratio is reduced by approximately 35%.