In a joint project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines, a two-stage low pressure turbine is tested at design and strong off-design conditions. The experimental data taken in the Altitude Test Facility (ATF) aims to study the effect of positive and negative incidence of the second stator vane. A detailed insight and understanding of the blade row interactions at these regimes is sought. Steady and time-resolved pressure measurements on the airfoil as well as inlet and outlet hot-film traverses at identical Reynolds number are performed for the midspan streamline. The results are compared with unsteady multistage computational fluid dynamics (CFD) predictions. Simulations agree well with the experimental data and allow detailed insights in the time-resolved flow-field. Airfoil pressure field responses are found to increase with positive incidence whereas at negative incidence the magnitude remains unchanged. Different pressure to suction side (SS) phasing is observed for the studied regimes. The assessment of unsteady blade forces reveals that changes in unsteady lift are minor compared to changes in axial force components. These increase with increasing positive incidence. The wake-interactions are predominating the blade responses in all regimes. For the positive incidence conditions, vane 1 passage vortex fluid is involved in the midspan passage interaction, leading to a more distorted three-dimensional (3D) flow field.
The measurement of unsteady total temperature is of great interest for the examination of loss mechanisms in turbomachinery with respect to the improvement of the efficiency. Since conventional thermocouples are limited in frequency response, several fast-response total temperature probes have been developed over the past years. To improve the spatial resolution compared to these existing probes and maintaining a high temporal resolution, a new fast-response total temperature probe has been developed at the Institute of Aircraft Propulsion Systems (ILA), Stuttgart, Germany in cooperation with Berns Engineers, Gilching, Germany. The design of the probe allows a sensitive measuring surface below 1 mm2. A detailed insight into the design of the probe, the measurement principle, the calibration process, and an estimation of the measurement uncertainty is given in the present paper. Furthermore, to prove the functionality of the probe, first experimental results of a simple test bed and of area traverses downstream of the first rotor of a two-stage low pressure turbine are presented. It is shown, that the new probe is capable of detecting rotor characteristic effects as well as rotor-stator-interactions. In addition, a hot-spot is investigated downstream of the first rotor of the turbine, and the findings are compared to the effects known from the literature.
A two-stage low pressure turbine is tested at the aerodynamic design point and a strong off-design point representing flight idle conditions. The tests are performed on an altitude test facility at engine representative conditions. Time-resolved measurements are performed with dual-film probes up- and downstream of the second NGV row. The aim is to study the flow field for secondary deviation and the generation of losses in the NGV row. The experimental results are compared with multistage URANS predictions. The simulations match the measured data and allow for detailed analysis of the time-resolved flow field. With off-design operation a strong increase in cross-flow is observed due to radial migration. Wake fluid from the first stage tends to migrate towards the hub section and changes the blockage unsteadily in the NGV row. At off-design operation a distinction between a two-dimensional primary flow to the secondary flow areas is no longer possible.
Computational fluid dynamics have become important in turbine design, because experimental tests can easily become very expensive and time consuming. The industrially used two-equation turbulence models have weaknesses in predicting the Reynolds stress anisotropy in complex flows. The free stream Reynolds stresses influence transition and separation on turbine airfoils and vice versa. Higher-order models are supposed to improve numerical prediction quality. For development and validation of these models, a good understanding of the Reynolds stress distribution is required. Therefore the full Reynolds stress tensor and its anisotropy are experimentally investigated in a two-stage low pressure axial turbine. The Reynolds stresses are resolved from 3D hot-film probe area traverses downstream of the first vane at three Reynolds numbers from 40,000 to 180,000, related to vane 1. Surface thin film gauge measurements on the suction side of the vane are used to determine transition and separation. The size of the separation bubble on the late suction side and the progress of transition vary with Reynolds number. This influences the Reynolds stress elements to different extents and thus the Reynolds stress anisotropy downstream of the vane.
In a joint project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines a two-stage low pressure turbine is tested at design and strong off-design conditions. The experimental data taken in the altitude test-facility aims to study the effect of positive and negative incidence of the second stator vane. A detailed insight and understanding of the blade row interactions at these regimes is sought. Steady and time-resolved pressure measurements on the airfoil as well as inlet and outlet hot-film traverses at identical Reynolds number are performed for the midspan streamline. The results are compared with unsteady multi-stage CFD predictions. Simulations agree well with the experimental data and allow detailed insights in the time-resolved flow-field. Airfoil pressure field responses are found to increase with positve incidence whereas at negative incidence the magnitude remains unchanged. Different pressure to suction side phasing is observed for the studied regimes. The assessment of unsteady blade forces reveals that changes in unsteady lift are minor compared to changes in axial force components. These increase with increasing positive incidence. The wake-interactions are predominating the blade responses in all regimes. For the positive incidence conditions vane 1 passage vortex fluid is involved in the midspan passage interaction leading to a more distorted three-dimensional flow field.
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