Ceramic matrix composites (CMC) for application in gas turbine hot sections have been a topic of research for the last three decades. Until now, CMCs have found only limited use due to their mechanical limitations, economic factors and availability of the base material Silicon Carbide. Currently, a new manufacturing process combining 3D braiding technology with slurry die casting based on aluminum oxide is being developed within a collaborative research project. It aims to create CMCs that can withstand the thermal and mechanical stresses while having a longer life cycle than conventional nickel-based super alloys used in industrial gas turbines. One task within the collaborative research project is to derive the impact of the application of the new type CMC on the gas turbine thermal cycle behavior. Thus, the objective of this paper is to show the potential of the 1st stage vane made of the new 3D braided Al2O3-CMC in terms of thermodynamic efficiency enhancement by cooling air reduction. The first stage vane of a generic 30 MW industrial gas turbine is analyzed as reference case by means of aero- (CFD), heat transfer (CHT) and mechanical (FEA) simulations at different cooling air mass flows in case of conventional vane material and the new type CMC in comparison. A thermodynamic model of the gas turbine is then used to show the implications on the cycle and its efficiency in case the material of the first stage vanes is changed to the new type CMC. The results show that the positive potential in thermal efficiency depends significantly on the further usage of the cooling passing through the hollow CMC vane.

One common approach for anti-erosion measures in low pressure steam turbines is to equip a hollow stator vane with slots on the airfoil surface in order to remove the water film by suction and consequently reduce the amount of secondary droplets. The purpose of this paper is to build an understanding of the predominant effects in fluid-film interaction and to examine the suitability of modern numerical methods for the design process of such slots. The performance of a suction slot in terms of collection rate and air leakage is investigated numerically in a flatplate setup with upstream injection of water. In order to model the relevant phenomena (film transport, edge stripping of droplets, transport of droplets in the surrounding fluid, wall impingement of droplets) an unsteady Eulerian-Lagrangian simulation setup is applied. The accuracy of the numerical approach is assessed by comparison with experimental measurements. The comparison of four cases with the measured data demonstrates that the chosen simulation approach is able to predict the main features of film flow and interaction with the surrounding fluid. The collection rate as well as fluid film properties show the same qualitative dependency from water mass flow rate and air velocity.

As a result of an ever-increasing share of volatile renewable energies on the worldwide power generation, conventional thermal power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction and determination of the metal temperature distribution inside these components is crucial. Therefore, boundary conditions in terms of local fluid temperatures as well as heat transfer coefficients (HTCs) with sufficient accuracy are required. As modern numerical modeling approaches, like 3D-conjugate-heat-transfer (CHT), provide these thermal conditions with a huge calculation expense for multistage turbines, simplified methods are inevitable. Analytical heat transfer correlations are thus the state-of-the-art approach to capture the heat transport phenomena and to optimize and design high efficient startup curves for flexible power market. The objective of this paper is to understand the predominant basic heat transfer mechanisms such as conduction, convection, and radiation during a startup of an intermediate pressure (IP) steam turbine stage. Convective heat transport is described by means of heat transfer coefficients as a function of the most relevant dimensionless, aero-thermal operating parameters, considering predominant flow structures. Based on steady-state and transient CHT simulations, the heat transfer coefficients are derived during startup procedure and compared to analytical correlations from the literature, which allow the calculation of the heat exchange for a whole multistage in an economic and timesaving way. The simulations point out that the local convective heat transfer coefficient generally increases with increasing axial and circumferential Reynolds' number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The heat transfer coefficients at vane, blade, hub, and labyrinth-sealing surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds' number. The comparison illustrates that the analytical correlations underestimate the convective heat transfer by approximately 40% on average. Results show that special correlation-based approaches from the literature are a particularly suitable and efficient procedure to predict the heat transfer within steam turbines in the thermal design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.

As a result of the expansion process within low pressure steam turbines, the last stages typically operate in the two-phase flow regime. Consequently, water droplets are carried with the steam flow leading to the potential risk of water droplet erosion on rotating blades. This operation situation overtime leads to performance degradation, reduction of service lifetime and thus increased product costs. In order to improve reliability and safety of steam turbine modules, special design features can be applied to reduce the erosion risk. One common approach utilizes suction slots on the stationary airfoils of guide vanes, intending to drain the deposited water from the vane surface and consequently diminish the amount of coarse water droplets. This paper presents the development and validation of a model using numerical and experimental methods to determine and assess the performance accuracy as a design and optimization approach for hollow vane suction slots. The analysis focuses on previous investigations for a flat-plate arrangement and is extended to a vane nozzle setup intending to consider surface curvature effects on water rivulets paths. Based on steady-state and transient multiphase Eulerian-Lagrangian framework simulations for different operating conditions, the suction slot performance for both applications is derived by means of collection rate and air leakage considering predominant multiphase flow phenomena (film building, transport, stripping of droplets and wall impingement of droplets). The resulting numerical dataset is used in comparison to available measurement data (air flow and film conditions) and for validation as well as calibration of the prediction accuracy of the simulation model. Results for flat-plate and nozzle setup show that the numerical approach is able to predict the main phenomena of film flow and breakup into droplets. Comparison with test data illustrates that an error of less than 15% is achieved for the slot efficiency based on the water film collection rate and water film properties. Overall, the ability of the modelling approach to predict the performance of suction slots is confirmed. Results thus lead to the conclusion that the numerical model is sufficiently accurate to represent geometric changes relevant during design procedure of hollow guide vane suction slots.

Within the last three years, Kawasaki Heavy Industries Ltd. and B&B-AGEMA have worked on a technology to support experimental tests for development of the Micromix combustor of pure hydrogen, allowing a very close online visual (Visible and Infrared light) access to the burner. The invented borescope has been designed by means of Conjugate Heat Transfer (CHT) and Finite Element (FE) simulations. Different design variations have been tested numerically. Within this course, the internal cooling pathways have been improved and the structure enhanced to ensure an acceptable life time of the highly loaded borescope head located directly downstream of the flame. Here, the local temperature reaches values around 1600 K. After digital development and manufacturing, the first borescope prototype could have been successfully operated in two low pressure and two high pressure tests (two times with a visible light (VIS) and two times with an Infrared (IR) camera). In the paper, the development process as well as the operational experience and the experimental test results are presented. The information on the Micromix combustor behavior revealed by the borescope technology help to better understand the behavior of the combustor, improve the design and plan the operation strategy within the real gas turbine.

Civil aviation is growing 4.7% per annum. Alternative propulsion systems are necessary to reduce emissions causing global warming. The electrification of aircraft propulsion systems has the potential to use renewable energy and reduce the environmental footprint of aviation. At present, full electric flight appears to be feasible for small aircraft only, due to the power density of batteries which is approximately 45-times lower than that of kerosene. Hybrid electric concepts may present a bridging technology towards more electrified aviation for short/mid-range aircraft. The hybrid concept combines the benefits of electrical power with conventional turboshaft engine technology. Within the framework of the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), a hybrid electric concept for a short/mid-range 19 PAX aircraft is studied. In this paper the results of a preliminary design exercise of the gas turbine used in this concept is presented. Conventional aircraft gas turbines deliver maximum power only at take-off for a short period of time. At this power setting temperature and stress levels are at the extreme and dominate overall engine life consumption. In the HyFly concept, the gas turbine inlet temperature is kept constant during the entire flight. The engine is not driven into the extreme take-off power setting, resulting in a significant increase of engine life. The constant power setting also offers the opportunity to optimize efficiency especially around the base load point. For take-off and an emergency power rating, extra power is provided by batteries. In this paper, a survey of existing engine technology is presented considering suitability for the concept. The impact of improvement of component efficiencies, increase in cycle pressure ratio and turbine inlet temperature, relative to the state-of-the-art, is analyzed using a B&B-AGEMA in-house gas turbine simulation tool. In addition, a weight model is presented for preliminary estimation of engine mass. Finally, requirements for the individual gas turbine sub-component design and performance are defined. This will build the basis for further component design.

To prevent ingestions of the combustion gas into the cavity between the stationary components and rotating disks, coolant flow from the compressor is used to seal and purge the area against the hot gas.Specific geometries are used to improve the performance of those rim seals in order to save coolant while maintaining a save operation condition for the rotating components.Therefore accurate performance predictions in the early design steps are important to save time and costs.But numerical performance predictions for rim seal applications are still challenging especially for small and mediate enterprises (SME's).Therefore the authors of this paper are looking for methods to reduce time and costs of numerical performance predictions for rim seal geometries, whereas this paper initiates this proposition by investigating the current limits of the available methods for SME's.This paper compares steady and unsteady RANS (URANS) simulations.The investigations are based on measurement and geometry data taken from a test rig design of a single stage test turbine at RWTH Aachen University.The RANS simulations did not show a significant ingestion of hot gas whereas the URANS approach has shown increased hot air ingestion.In order to achieve a converged flow field in the URANS simulations, a large number of full rotation cycles have to be calculated.The results show, that pressure oscillations driven by the blade pressure field, as well as acoustics frequencies have been captured by the URANS approach.Nevertheless the investigated URANS simulation approach still shows significant deviation in the prediction of the hot gas ingestion compared to the experimental test data.This is due to the fact that the fundamental equations and the applied closure by isentropic turbulence models are not capable of resolving sufficiently characteristic flow phenomena inside the wheels space and the sealing gap.Wheel space clearance Seal gap clearance Static Temperature at surface 1 Total Temperature Circumferential length of the sector model at R Axial machine coordinate Root of the Bessel function Mass fraction of cavity air (CA) Specific heat ratio Dynamic viscosity at surface 1 Dynamic viscosity at SAS inlet Density at surface 1 Density at SAS inlet Tangential machine coordinate FVV

In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti Counter -Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration. The present study involves simulations of a baseline fan shaped hole configuration ("777 hole" investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for dry-low-NOx (DLN) hydrogen combustion. Thus, the development of DLN combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines. The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flash-back and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames. The micromix combustion technology has been already proven experimentally and numerically for pure hydrogen fuel operation at different energy density levels. The aim of the present study is to analyze the influence of different geometry parameter variations on the flame structure and the NOx emission and to identify the most relevant design parameters, aiming to provide a physical understanding of the micromix flame sensitivity to the burner design and identify further optimization potential of this innovative combustion technology while increasing its energy density and making it mature enough for real gas turbine application. The study reveals great optimization potential of the micromix combustion technology with respect to the DLN characteristics and gives insight into the impact of geometry modifications on flame structure and NOx emission. This allows to further increase the energy density of the micromix burners and to integrate this technology in industrial gas turbines.

Combined with the storage and use of renewable energy sources and the application of the integrated gasification combined cycle (IGCC) technology, high hydrogen content fuels represent a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for dry-low-NOx (DLN) hydrogen and syngas combustion. Thus, the development of DLN combustion technologies is an essential task for the future of hydrogen and syngas fueled gas turbines. The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flash-back and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames. The present study aims to investigate the applicability of the micromix principle to the combustion of syngas with a composition of 90%-Vol. hydrogen and 10%-Vol. carbon-monoxide and compare different combustion models for the numerical characterization of the micromix flames. The micromix principle has been applied to design a DLN syngas burner for the application in gas turbine combustors. The designed burner has been successfully tested at atmospheric conditions and has shown a stable and typical micromix flame and low NOx emission. Different combustion models have been applied to simulate the micromix syngas combustion numerically. The numerical study revealed the ability of the applied numerical approach to simulate the micromix combustion and to capture the typical micromix flame anchoring and structure and supported the identification of adequate reaction mechanisms that allow an acceptable prediction of NOx emissions.

April 10-15, 2016 Abstract Great efforts are still put into the design process of advanced film-cooling configurations. In particular, the vanes and blades of turbine front stages have to be cooled extensively for a safe operation. The conjugate heat transfer (CHT) calculation technique is used for the three-dimensional thermal load prediction of an extensively cooled 1 st nozzle test vane installed in a highest-efficient industrial gas turbine. With the CHT approach it is possible to take the interaction of internal flows, external flow, and heat transfer into account without estimation of heat transfer coefficients. The utilized numerical model contains all geometrical features (e.g. pin-fins, ribs, impingement sheets etc.) of the real test vane without simplifications. The comparison with thermal index paint measurements inside the test engine shows that a qualitatively and quantitatively good agreement between the CHT and the measurements results can be found. A consideration of advanced-shaped film cooling holes at the vane platforms also offers high potential to further reduce the material temperatures and decrease thermal stresses by lowering of platform temperatures and homogenization of the temperature distribution

The efforts to improve the process efficiency of modern gas turbines usually lead to competing objectives for the design of the cooling system as turbine inlet temperatures are continuously increased. Typically, the designer of modern cooling systems is confronted with the requirement to achieve a wall temperature below the maximum allowable wall temperature which is fixed by the material and life span requirements. Simultaneously, a homogenous temperature distribution is desired in order to reduce thermal stresses due to temperature gradients. To maximize cycle efficiency, all this should be achieved by minimizing the necessary cooling air consumption. The Double Swirl Chamber (DSC) cooling technology is a promising configuration to satisfy these design requirements combined. The DSC cooling technology is an advanced kind of internal cooling passage which is created by the merging of two standard single swirl chambers. In the DSC cooling configuration, two anti-rotating large scale swirls are generated which enhance the mixing of the cooling air. This leads subsequently to an increased internal heat exchange. Additionally, the recurring reattachment of the swirl flows at the center of the chamber leads to a linear impingement effect due to local velocity elevations which makes the DSC configuration very suitable for an effective and uniform cooling of thermally high loaded blade leading edges as turbine inlet temperatures are further increased. Thus, the DSC cooling technology has great potential to lengthen the life span of gas turbine blading. In the present work, two DSC configurations are compared numerically to the state-of-the-art leading edge impingement cooling technology with a conjugate heat transfer approach of a simplified blade leading edge geometry. The two investigated DSC are similar, but with the second one being slightly modified in its geometry in order to ease the manufacturing process. With the same numerical setup in terms of applied boundary conditions and under consideration of Reynolds similarity, the DSC configurations show a local temperature reduction of 1.0-1.3% of the turbine inlet temperature in comparison to the impingement cooling case. The total pressure drop in the DSC configurations is in the same range as in the impingement cooling configuration and even slightly decreased by 0.15-0.20%. The heat transfer is 12-16.2% higher in the DSC configurations, which shows the potential for improving the internal cooling performance of a system by the application of the DSC cooling technology in real engine conditions.

In modern gas turbines, the film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). As a result, the cooling air remains close to the wall and spreads in lateral direction along the surface. The ACRV result from the specialized shape of the expanding hole exits (NEKOMIMI-shape). Thus, the design parameters have a crucial impact to the film cooling effectiveness behind the hole. In the present study the design parameters are varied and in order to explore the design space for a defined test case with respect to the maximum achievable averaged adiabatic film cooling effectiveness. This illustrates the capabilities of the technology. Additionally, the design space of a laidback fan-shaped film cooling configuration is explored and compared to the result obtained with the NEKOMIMI-shaped geometry. In order to show the robustness of the configurations with respect to compound angles of the cross flow, two advanced configurations — one NEKOMIMI and one shaped hole — are analysed with compound angles up to 16°.

It is known that the leading edge has the most critical heat transfer area of a gas turbine blade. The highest heat transfer rates on the airfoil can always be found on the stagnation region of the leading edge. In order to further improve the gas turbine thermal efficiency the development of more advanced internal cooling configurations at leading edge is very necessary. As the state of the art leading edge cooling configuration a concave channel with multi inline jets has been widely used in most of the blades. However, this kind of configuration also generates strong spent flow, which shifts the impingement off the stagnation point and weakens the impingement heat transfer. In order to solve this problem a new internal cooling configuration using double swirl chambers in gas turbine leading edge has been developed and introduced in this paper. The double swirl chambers cooling (DSC) technology is introduced by the authors and contributes a significant enhancement of heat transfer due to the generation of two anti-rotated swirls. In DSC-cooling, the reattachment of the swirl flows always occurs in the middle of the chamber, which results in a linear impingement effect. Compared with the reference standard impingement cooling configuration this new cooling system provides a much more uniform heat transfer distribution in the chamber axial direction and also provides a much higher heat transfer rate. In this study, the influences of different geometrical parameters e.g. merging ratio of two cylinder channels, the jet inlet hole configurations and radius of blunt protuberances in DSC have been investigated numerically. The results show that in the DSC cooling system the jet inlet hole configurations have large influences on the thermal performance. The rectangular inlet holes, especially those with higher aspect ratios, show much better heat transfer enhancement than the round inlet holes. However, as the price for it the total pressure drop is increased. Using blunt protuberances instead of sharp edges in the DSC cooling can improve the heat transfer enhancement and reduce the total pressure drop.

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for dry-low-NOx (DLN) hydrogen combustion. Thus, the development of DLN combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines. The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NOx emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flash-back and the low NOx emissions due to a very short residence time of reactants in the flame region of the micro-flames. The micromix combustion technology has been already proven experimentally and numerically for pure hydrogen fuel operation at different energy density levels. The aim of the present study is to apply and compare different combustion models for the characterization of the micromix flame structure, its interaction with the flow field and its NOx emissions. The study reveals great potential for the successful application of numerical flow simulation to predict flame structure and NOx emission level of micromix hydrogen combustion, help understanding the flow phenomena related with the micromixing, reaction zone and NOx formation and support further optimization of the burner performance.

The gas turbine blade leading edge area has locally extremely high thermal loads, which restrict the further increase of turbine inlet temperature or the decrease of the amount of coolant mass flow to improve the thermal efficiency. Jet impingement heat transfer is the state of the art cooling configuration, which has long been used in this area. In the present study, a modified double swirl chambers cooling configuration has been developed for the gas turbine blade leading edge. The double swirl chambers cooling (DSC) technology is introduced by the authors and comprises a significant enhancement of heat transfer due to the generation of two anti-rotating swirls. In DSC cooling the reattachment of the swirl flows with the maximum velocity at the middle of the chamber leads to a linear impingement effect, which is most suitable for the leading edge cooling for a gas turbine blade. In addition, because of the two swirls both suction side and pressure side of the blade near the leading edge can be very well cooled. In this work, a comparison among three different internal cooling configurations for the leading edge (impingement cooling, swirl chamber and double swirl chambers) has been investigated numerically. With the same inlet slots and the same Reynolds number based on hydraulic diameter of channel the DSC cooling shows overall higher Nusselt number ratio than that in the other two cooling configurations. Downstream of the impingement point, due to the linear impingement effect, the DSC cooling has twice the heat flux in the leading edge area than the standard impingement cooling channel.

Increasing the efficiency of steam cycle power plants is extremely important for the reduction of their CO2 emissions. Today’s best steam cycle power plants have a net plant efficiency of 46 %. Since the worldwide average efficiency is still in the range of 30 %, there exists a great potential in reduction of CO2 emissions by replacing old power stations with new ones. A further great potential lies in achieving even higher efficiencies by increasing live steam temperatures to more than 700 °C, so that the efficiency of steam power plants is pushed over the 50 % mark. Within a research project funded by the German government the challenges associated with material’s behaviour under elevated temperatures are investigated. In this project, a bypass-valve was installed in an experimental set-up in a real power station and is supplied with over 700 °C steam and investigated under long-term cyclic operation. Thermocouple measurements on reference points on the valve body and thermo graphic camera measurements deliver information about the real transient thermal behaviour of the valve. Numerical investigations aim to accurately model the transient thermal behaviour of the valve during cyclic operation and calculate corresponding three-dimensional temperature distributions, which are essential for conducting reliable mechanical integrity analysis for the applied Nickel-base material. Applying standard FEM thermal analyses that are based on heat transfer boundary conditions is often related with uncertainties regarding the convective heat transfer and corresponding coefficients. The application of a hybrid stepwise frozen conjugate heat transfer calculation approach aims to make use of the advantage of the conjugate heat transfer approach with respect to high accuracy in heat transfer calculation and reduce the calculation effort by freezing the fluid domain at different steps along the loading cycle and coupling it to the transient thermal load calculation in the solid domain. Both the standard FEM thermal analysis method and the hybrid stepwise frozen conjugate heat transfer calculation approach have been applied to calculate the transient thermal load in the valve. A validation of the numerical results has been performed for the reference points on the valve body and shows that the hybrid approach has better accuracy than the standard approach and shows very good agreement with the experimental results.

The dry-low-NOx (DLN) micromix combustion principle is developed for the low emission combustion of hydrogen in an industrial gas turbine APU GTCP 36-300. The further decrease of NOx emissions along a wider operation range with pure hydrogen supports the introduction of the micromix technology to industrial applications. Experimental and numerical studies show the successful advance of the DLN micromix combustion to extended DLN operation range. The impact of the hydrogen fuel properties on the combustion principle and aerodynamic flame stabilization design laws, flow field, flame structure and emission characteristics is investigated by numerical analysis using an eddy dissipation concept combustion model and validated against experimental results.