Jet engine spare parts are expensive. Hence, for economic reasons, as many components as possible should be repaired. For planning the repair or regeneration process, defects must be identified early. The present paper explores whether the detection and examination of inhomogeneities in the temperature distribution in an exhaust gas stream of a jet engine can be used for the identification and localization of defects before engine disassembly. In order to be able to assign the defects to the resulting temperature non-uniformity in the exhaust gas, the mixing characteristics of the temperature inhomogeneities in the turbine caused by the defects are examined. A three-dimensional unsteady CFD-simulation of a whole turbine with a complex temperature distribution at the inlet is carried out. The simulations show, that the temperature inhomogeneities are barely mixed out with the surrounding flow. To describe the mixing effects a coefficient (turbine mixing factor) is derived. The factor enables an integral assessment of the mixing behaviour of inhomogeneities within and outside of turbine stages.

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It is a well known fact that turbocharger works with pulsating exhaust flow in its entire operating life, hence the need to predict unsteady performance. This paper presents the unsteady performance prediction resultof a single entry nozzleless mixed flow turbine under steady flow and 60 Hz pulsating flow at 43.0 rps/ √ K operating speed. The modeling method coupled one-dimensional gas dynamic modelwith a mean-line model to predict the turbine efficiency by appropriate losses consideration. The coupled method assumes that the turbine volute has a large volume and length, so that unsteadiness effect of the pulsating flow is significant while the rotor is assumed to behave quasisteadily. A pressure drop boundary is used to simulate pressure drop across the turbine volute. The coupled method was validated with the experimentally measured steady state results of the same turbine. Experimentally measured total conditions of the flow were used as inlet conditions for the model during unsteady analysis. The predicted isentropic power averaged results show convincing match with the experimental data. This will set forward a systematic approach for engine designers to evaluate turbine performance beyond what will be normally provided by turbocharger manufacturers, which is the steady state map.

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Mixing losses due to cavity related flows in axial steam turbines contribute considerably to overall aerodynamic losses. The coherent study presented in this paper examines the influence of rotor inlet cavity geometry on stage efficiency. The experimental work is supported by computational analysis. Inlet cavity geometry has been varied by reducing the axial and radial cavity lengths along with the volume. Six different configurations have been examined, focusing mainly on the flow interactions occurring at the zone between the cavity and main flow and their impact on stage efficiency. An upper stator-casing platform prolonged by 17% and 34%, and a radial wall length shortened by 13% and 25% offered a cavity volume reduction of 14% and 28%, respectively, compared to the initial cavity volume. The axial cavity wall length reduction impacts drastically on the vortex formation inside the cavity. A 17% length reduction leads initially to the bifurcation and re-connection of the vortex during inflow, whereas the 34% length reduction completely eliminates the presence of any vortex. On the other hand, the radial cavity wall length reduction affects the vortex positioning. Generally, the cases with radial wall length reduction show higher efficiency relative to the axial cavity length reduction. For the 14% cavity volume reduction cases this difference rises to 1%, and for the 28% cavity volume reduction the difference is even higher, attaining a 1.7% efficiency increase.

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