The inspection of aero engines is a complex and time-consuming process, often requiring the disassembling of the engine or boroscopic examinations. The development of a method to locate and characterize defects and damage at an early stage, without disassembling the engine would accelerate the inspection process. For that purpose, the spatial density distribution pattern of the exhaust jet of aircraft engines may be measured with the Background Oriented Schlieren method (BOS). The hypothesis is that defects in the hot gas path have a noticeable impact on the density pattern of the exhaust jet. To establish the connection between defects and measurable patterns, in the present paper numerical simulations of an aero engine are performed including three potential defects. Non-uniformities resulting from a burner malfunction, the increase of the radial gap between blade tip and casing as well as burned trailing edges are propagated with only small degree of dispersion through the turbine and reach the engine exit. The paper shows that each considered defect results in a different exhaust density pattern.

Reducing the uncertainties in the prediction of turbine inlet conditions is a crucial aspect to improve aero engine designs and further increase engine efficiencies. To meet constantly stricter emission regulations, lean burn combustion could play a key role for future engine designs. However, these combustion systems are characterized by significant swirl for flame stabilization and reduced cooling air mass flows. As a result, substantial spatial and transient variations of the turbine inlet conditions are encountered. To investigate the effect of the combustor on the high pressure turbine, a rotating cooled transonic high-pressure configuration has been designed and investigated experimentally at the DLR turbine test facility ‘NG-Turb’ in Göttingen, Germany. It is a rotating full annular 1.5 stage turbine configuration which is coupled to a combustor simulator. The combustor simulator is designed to create turbine inlet conditions which are hydrodynamically representative for a lean-burn aero engine. A detailed description of the test rig and its instrumentation as well as a discussion of the measurement results is presented in part I of this paper. Part II focuses on numerical modeling of the test rig to further extend the understanding of the measurement results. Integrated simulations of the configuration including combustor simulator and nozzle guide vanes are performed for leading edge and passage clocking position and the effect on the hot streak migration is discussed. The simulation and experimental results at the combustor-turbine interface are compared showing a good overall agreement. The relevant flow features are correctly predicted in the simulations, proving the suitability of the numerical model for application to integrated combustor-turbine interaction analysis.

Within the scope of European Commission FP7 project FACTOR, dedicated to combustor-turbine-interaction research, a clean-sheet design of a rotating turbine test rig featuring a non-reacting combustor simulator was created and built among the partners. German Aerospace Center DLR provided the operational facility NG-Turb to which the rig was adapted and was responsible for global rig integration and operation, also including aerodynamic probe measurements of the flow field. The rig and experimental set-up is described and post-processed results from probe traverses in several measurement planes are presented and discussed. Special attention is paid to the comparison and influence of two combustor-NGV clocking positions on the periodic turbine flow field, made possible by rig adaptation during the campaign. The strongly distorted and nonuniform turbine inlet flow created by the combustor simulator proved challenging for the probe measurements, but at the same time set a realistic boundary condition enabling the analysis of ‘CTI’ by flow structures migrating through the blade rows.

Modern aero-engine blades are optimized for high performance and long service life, but manufacturing requirements are not considered adequately during the design process. Thus, time-consuming, iterative re-designs become necessary until a producible component evolves. The multidisciplinary design optimization method presented in this paper addresses not only the aerodynamic efficiency and structural reliability of a new turbine blade, but also ensures the castability of the design and thereby accelerates the entire design process and reduces the time-to-production. Because real casting process simulations are very time-intensive, they were substituted by checks of experimentally and numerically validated geometrical constraints. Different engineering tools were assembled in a joint process chain using an integration framework, which manages and distributes the calculations and hence the workload in a shared network. Based on a preliminary design of a new turbine section, the selected initial low pressure turbine blade was neither castable nor reliable. The multidisciplinary optimization achieved a blade design that satisfies the requirements for a successful casting process, has a low failure probability and, although not as high as from a pure aerodynamic optimization, exhibits an efficiency improvement.

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