Thermo-mechanical fatigue (TMF) is a critical degradation mechanism affecting gas turbine components. Testing under realistic loading conditions, such as TMF, is essential for these highly stressed, safety-relevant components. Most existing test setups utilize standard specimens that rarely represent the geometrical sizes of the actual engine components. Although there is interest in using smaller sized specimens to reduce material usage and allow for testing that closely resembles real-life conditions, only a few setups currently facilitate cyclic mechanical testing of small-scale specimens. This paper addresses the need for test rigs designed for TMF testing miniature specimens under realistic thermal gradients and mechanical loads. It focuses on developing a low-cycle fatigue miniature specimen test system validated with nickel-based superalloy Inconel 718. The study compares two specimen sizes to evaluate the impact of size, strain rates, and heating and cooling rates on fatigue life, applying cyclic temperature loading in both in-phase and out-of-phase loading conditions.

This paper deals with the design and description of a test rig for investigating 2-phase flows of alternative refrigerants such as methanol and ethanol in near-operational conditions in low-temperature polymer electrolyte membrane fuel cells (LT-PEMFC). The objective of the work is to investigate the two-phase cooling of different refrigerants in LT-PEMFCs and to establish heat transfer and pressure drop correlations under realistic boundary conditions. The parameter range for the investigation includes a mass flux 5 <= G <= 45 kg/m(2)s, a heat flux of 0 <= (q) over dot <= 1.5W/m(2) and a vapor mass fraction of 0 <= x <= 1. The object of investigation is a single-channel system with a channel length of about 390 mm. Various channel cross sections are considered including rectangular cross sections with hydraulic diameters dh of 0.3 - 1.0 mm as well as approximated fuel cell channel geometries with hexagonal cross-sections and hydraulic diameters dh of 0.64 mm. Due to the modular structure of the test section it is possible to investigate different channel cross sections. In perspective also parallel channels can be investigated. A unique feature of the test setup is the use of a special glass that allows both the observation of the flow pattern and the discrete thermographic temperature resolution of the fluid in all phases. By performing the investigation at different steady-state operating points and setting dynamic operating characteristics, the operation of an LT-PEMFC can be simulated for mobile applications and thus forms a fundamental scientific contribution to the thermodynamic behavior of a two-phase cooled LT-PEMFC as well as an extended understanding of thermal management especially with respect to FC systems with electric power outputs > 100 kW.

Aircraft manufacturers are currently developing concepts to bring a hydrogen-powered aircraft to market by 2035. One option to realize this goal is a fuel cell based system, which enables emission-free and efficient flying. In contrast to a conventional aircraft that employs a gas turbine as its primary power source, the heat generated in the fuel cell must be actively rejected into the surrounding environment in order to maintain functioning. In this paper, the potential of two-phase cooling for fuel cell systems in aircraft is compared to liquid cooling systems for a 100 kW-stack. For this purpose, Modelica-based simulations are performed to analyze the operation and function of the proposed cooling systems. Two-phase cooling can greatly improve performance by achieving higher heat transfer coefficients and enthalpies of vaporization. Results indicate that two-phase cooling systems can reduce the required pump power by more than 98 %, and a novel bypass architecture offers further benefits in this regard. Additionally, the two-phase cooling systems can decrease the air volume flow rate needed to dissipate heat to the environment by 36 %, leading to a reduction in drag on the aircraft. The temperature difference between the fluid and the membrane can be reduced to less than 1 K, resulting in a more homogeneous temperature distribution in the fuel cell. Further research is necessary to establish the conditions under which two-phase cooling systems can operate stably without exceeding the maximum membrane temperature.

The isothermal planar-biaxial fatigue behavior was studied for two different disk batches of nickel-base superalloy Inconel 718 using cruciform specimens at 400 degrees C and 630 degrees C under equi-biaxial and shear loading. Additionally, non-proportional tests were performed. The planar-biaxial test results were compared with uniaxial reference tests using the von Mises equivalent strain hypothesis, a shear strain parameter of the critical plane, and a modified crack-opening-displacement strain range approach. Additionally, the crack initiation mechanism was analyzed. Using a modified crack-opening-displacement strain range approach, the low-cycle fatigue lifetimes of the proportional planar-biaxial tests (i.e., lifetimes up to 40,000 cycles) were described within a scatter band of two. Thus, it was better than using the equivalent strain of von Mises or a shear strain parameter. The fatigue crack initiation took place at oxidized primary carbides at the surface. The crack paths were presented.

The planar-biaxial thermo-mechanical fatigue behavior of nickel-base superalloy Inconel 718 was studied for selected proportional loading conditions, in particular biaxial strain ratios of 1.0, 0.6, and − 1.0. The cyclic temperature loading with minimum and maximum temperatures of 400 °C and 630 °C and a duration of 250 seconds was either In-Phase or Out-of-Phase to the mechanical axes. Besides the multiaxial tests, uniaxial thermo-mechanical fatigue tests were conducted In-Phase and Out-of-Phase with the same temperature cycle and cycle duration. The performed thermo-mechanical fatigue tests were analyzed regarding the deformation and lifetime behavior and compared with high-temperature isothermal low-cycle fatigue tests from a previous work of the authors. On the side of the lifetime description, a strain- and a stress-based approach were presented. For the planar-biaxial tests, the crack initiation mechanism and crack paths were shown.

Gas turbines and aircraft engines are dominated by cyclic operating modes with fatigue-related loads. This may result in the acceleration of damage development on the components. Critical components of turbine blades and discs are exposed to cyclic thermal and mechanical multi-axial fatigue. In the current work, planar-biaxial Low-Cycle-Fatigue (LCF) tests are conducted using cruciform specimens at different test temperatures. The influence on the deformation and lifetime behaviour of the nickel-base disk alloy Inconel 718 is investigated at selected cyclic proportional loading cases, namely shear and equi-biaxial. The calculation of the stress and strain distribution of the cruciform specimens from the experimental data is difficult to obtain due to complex geometry and temperature gradients. Therefore, there is a need for Finite Element (FE) Simulations. A viscoplastic material model is considered to simulate the material behaviour subjected to uniaxial and the selected planar-biaxial loading conditions. At first, uniaxial simulation results are compared with the uniaxial experiment results for both batches of IN718. Then, the same material parameters are used for simulating the biaxial loading cases. The prediction of FE simulation results is in good agreement with the experimental LCF test for both shear and equi-biaxial loadings. The equivalent stress amplitude results of the biaxial simulation are compared with the uniaxial results. Furthermore, the lifetime is calculated based on the stabilized cycle from the simulation and by using Crossland and Sines multi-axial stress-based approaches. The Crossland model predicts fatigue life significantly better than the Sines model. Finally, the simulated lifetime results are compared with the experimental lifetime.

Flexible gas turbine operation requires adapted hot gas parts design and lifetime assessment methods. The High Temperature Cyclic Test Rig (HTCTR) is developed to cyclically test internally cooled components from combustor and turbine sections of gas turbines in close-to-engine conditions for a wide range of operating conditions in order to improve component lifetime management. These advanced tests should serve as basis for new model development and validation for conditions that are more representative of those in an engine than the standard material specimen tests.

Material characterization is usually based on standard specimen testing. In contrast, small-scale specimens require less testing material and offer additional advantages like investigation of size effects with impact on material properties (specimen diameter equivalent to wall thickness of buckets and liners) and testing of samples of virgin or service-exposed turbomachinery components. The paper highlights the small-scale specimen test setup and its application for LCF- and HCF-testing. Innovative small-scale specimen testing with close-to-component structural features enables direction dependent and spatially resolved determination of material characteristics. Cast and forged gas turbine nickel-based alloys and a typical steam turbine steel are the materials of interest in this study. Substrate temperature levels ranges from room temperature up to 1000 °C. Test system, radiation heating, instrumentation and two types of small-scale specimen geometries according to German standard DIN 50100 will be presented. Benefits and limitations of application of small-scale specimens will be discussed. Finally the authors report about application of small-scale specimen testing for remaining life time determination of service exposed gas turbine buckets. Small-scale specimens have been directly extracted from a gas turbine. Bucket root material (conventionally cast nickel-base alloy IN738) and literature data serve as reference base for initial state of the material. Tensile and LCF tests have been carried out at a representative material temperature for service conditions of 850 °C. Published material data of IN738 are available at this temperature. On that basis, fatigue life consumption has been estimated. The presented procedure for remaining life time prediction can also be applied to other turbomachinery components.

Zusammenfassung In diesem Beitrag wird ein Sensorkonzept zur simultanen Messung der Temperatur und der Dampffeuchte eines Dampf-Flüssigkeits-Gemisches, insbesondere Wasser, auf der Basis der Infrarot-Spektroskopie vorgestellt. Schwingungsspektren von Reinstoffen hängen neben der Temperatur auch von dem Aggregatzustand und damit dem Phasengehalt einer Probe ab. Es wird beschrieben, wie diese, aus der Literatur bekannten, physikalischen Phänomene in ein technisches Messverfahren übertragen werden können. Dazu werden unterschiedliche Algorithmen zur simultanen Temperatur- und Dampffeuchteauswertung vorgeschlagen.

Heat exchange applications at high temperatures of greater than 800 °C under corrosive or abrasive conditions require heat exchangers based on ceramic materials instead of conventionally used metals. Heat exchangers based on heat pipes are exceptionally suitable since temperature gradients and correspondent thermal stresses are inherently low for this design. At high temperatures greater than 800 °C, the structural material SSiC and working fluids sodium or zinc appear to be the most promising options. Encapsulating the working fluid in ceramic heat pipes with a sealing joint ensuring long term stability and high temperature resistance is particularly challenging. A nickel‐based alloy has been identified as solder material for SSiC heat pipes using sodium as working fluid and a glass solder was used in case of zinc filled heat pipes. Manufactured heat pipes were tested in a hot‐gas test rig at temperatures up to 1000 °C.

Rotor blades are the highest thermal-mechanical loaded components of gas turbines. Their service life is limited by interaction of creep, low cycle fatigue (LCF), high cycle fatigue (HCF) and surface attack. Because assurance of adequate HCF strength of the rotor blade is an important issue of the blade design the European project PREMECCY has been started by the European aircraft engine manufacturers and research institutes to enhance the predictive methods for combined cycle fatigue (CCF), as a superposition of HCF and LCF. Although today’s predictive methods ensure safe blade design, there are certain shortcomings of assessing fatigue life with Haigh or “modified Goodman diagrams”, such as isolated HCF assessment as well as uni-axial and off-resonant testing. HCF and LCF are considered without taking into account their interaction. PREMECCY is aimed to deliver new and improved CCF prediction methods for exploitation in the industrial design process. Beside development of predictive methods the authors are involved in the design and testing of advanced specimens representing rotor blade features. In this connection the paper presents a novel test specimen type and a unique hot gas rig for CCF feature test at mechanical and ambient representative conditions.

The policy document of the Federal Government for an integrated energy and climate program represents the basis for the Regulation Concerning Assurance of Air Quality Standards (37. BlmSchV) which comprises the revision of emission limits with consequences for gas turbines. After commencement of this regulation gas turbine plants of firing heat capacity > 100 MW with gases from public gas supply will be faced with tightened limits for nitrogen oxide emissions. Because gas turbine technology has a relevant share in ecologically compatible and reliable energy supply, the authors show the necessary link of gas turbine efficiency to nitrogen oxide emission limits on the basis of thermodynamical considerations. Thus, a conflict of objective between climate protection and air pollution prevention and a discrimination of high efficient gas turbines can be avoided. The "eta algorithm" is a proper approach which doesn't privilege these plants at all. By its linear increase of the NO x emission limit with the ratio of net efficiency to reference efficiency this definition comprises the requirement of combustion technology advancement. It meets the thermodynamical principles much better than a limit definition which is only based on the exhaust gas flow rate for ISO reference conditions. That the "eta algorithm", which is already implemented in the existing document "13. BlmSchV", will also be adopted in the "37. BlmSchV" can be considered as an achievement although this approach should be applied for combined-cycle plants as well.

Depending on design and operation of the gas turbine combustion chamber, more or less non-uniform hot gas temperatures result along the circumference of the combustion chamber outlet. In areas with highest thermal stresses this may result in damage even before reaching the planned end of lifetime, i.e. before replacement of the component. It is shown for two typical combustion chamber designs how to determine the non-uniform hot gas temperature at the turbine inlet and what are the likely uncertainties.