Abstract Particle deposits that form in gas turbine engines can change flow dynamics and heat transfer, leading to performance degradation. A computational framework that models the coupled behavior of sand deposits with flow and heat transfer is developed. The coupling is done by using a multiphase framework in which a physics based collision model is used to predict the post-collision state-of-the sand particle. The collision model is sensitized to temperature dependent material properties of sand. Particle deposition is determined by the particle’s softening temperature and the calculated coefficient of restitution of the collision. The multiphase treatment facilitates conduction through the porous deposit and the coupling between the deposit and the fluid field. The coupled framework is used to model the behavior of sand particles in a laminar impinging jet flow field. The temperature of the jet and the impact surface are varied between 1000 to 1600 K, to observe particle behavior under different temperature conditions. The Reynolds number of the jet is varied between 20 to 100 to vary particle Stokes number between 0.5 to 3.2. The coupled framework was found to increase or decrease capture efficiency, when compared to an uncoupled simulation, by as much as 10% depending on the temperature field. Deposits that formed on the impact surface, using the coupled framework, altered the velocity field by as much as 130% but had a limited effect on the temperature field for the short duration of the simulations.

Abstract The present study focuses on evaluating fully-coupled conjugate heat transfer simulation in a ribbed cooling passage with a fully developed flow assumption using LES with the immersed boundary method (IBM-LES-CHT). The IBM-LES and the IBM-CHT frameworks are validated prior to the main simulations by simulating purely convective heat transfer in the ribbed duct, and a laminar boundary layer flow over a 2D flat plate with heat conduction, respectively. For the main conjugate simulations, a ribbed duct geometry with a blockage ratio of 0.3 is simulated at a bulk Reynolds number of 10,000 with a conjugate boundary condition applied to the rib surface. The nominal Biot number is kept at 1, which is similar to the comparative experiment. As a means to overcome a large time scale disparity between the fluid and the solid regions, the use of a high artificial solid thermal diffusivity is compared to the physical diffusivity. It is shown that while the diffusivity impacts the instantaneous fluctuations in temperature, heat transfer and Nusselt numbers, it has an insignificantly small effect on the mean Nusselt number. Comparison between IBM-LES-CHT and iso-flux heat transfer simulations shows that the iso-flux case predicts higher local Nusselt numbers at the back face of the rib. Furthermore, the local Nusselt number augmentation ratio (EF) predicted by IBM-LES-CHT is compared to experiment and another LES conjugate simulation. Even though there is a mismatch between IBM-LES-CHT predictions and other two studies at the front face of the rib, the area-averaged EF compares reasonably well in other regions between IBM-LES-CHT prediction and the comparative studies.

Abstract It is here proposed a numerical procedure aimed to perform transient aero-thermo-mechanical calculations of large power generation gas turbines. Due to the frequent startups and shutdowns that nowadays these engines encounter, procedures for multi-physics simulations have to take into account the complex coupled interactions related to inertial and thermal loads, and seal running clearances. In order to develop suitable secondary air system configurations, guarantee structural integrity and maintain actual clearances and temperature peaks in pre-established ranges, the overall complexity of the structure has to be reproduced with a whole engine modelling approach, simulating the entire machine in the real operating conditions. In the proposed methodology the aerodynamic solution providing mass flows and pressures, and the thermo-mechanical analysis returning temperatures and material expansion, are performed separately. The procedure faces the aero-thermo-mechanical problem with an iterative process with the aim of taking into account the complex aero-thermo-mechanical interactions actually characterizing a real engine, in a robust and modular tool, combining secondary air system, thermal and mechanical analysis. The heat conduction in the solid and the fluid-solid heat transfer are computed by a customized version of the open source FEM solver CalculiX ® . The secondary air system is modelled by a customized version of the embedded CalculiX ® one-dimensional fluid network solver. In order to assess the physical coherence of the presented methodology the procedure has been applied to a test case representative of a portion of a real engine geometry, tested in a thermal transient cycle for the assessment of the interaction between secondary air system properties and geometry deformations.

Abstract Aerodynamic cooling of hot components/surfaces such as those encountered in gas turbine engines is needed to avoid premature failure of parts due to thermo-mechanical stresses. An effective way of achieving this cooling is through the exchange of heat via effusion/film cooling holes on the hot surfaces. The gases absorb heat as they flow through the cooling holes and also by forming a protective layer of relatively cool gases near the hot surface. Modeling these processes allow for durable design of components and computational simulations offer a complementary way to design new parts or enable performance assessment of the existing parts at new operating conditions. However, in order to perform numerical simulations of heat transfer through effusion holes, the heat conduction through the solid liner and the convection from the gas phase must be coupled considering all the relevant length and time scales. The time scale separation between the solid and the gas phase makes this prohibitively expensive for large scale computations. In applications involving hundreds of effusion holes, resolving the geometry of each effusion hole along with the primary flow (with typically larger length scales) is very challenging. In the current work, we overcome the difficulties associated with the resolution of cooling holes by employing a local source method (Andreini et al, J. Eng. Gas Turb. Power, 2014) to model the heat transfer to the walls. This method is assessed in a canonical configuration based on experiments performed by Gustafsson (Gustaffson, Ph.D. Thesis, 2001). Large Eddy Simulations (LES) coupled with conjugate heat transfer (CHT) models are used in this study. Simulations that resolve the flow passages explicitly using mesh both in the fluid and the solid domains, were used to validate the fidelity of grid resolution, turbulence models and other simulation parameters in predicting velocity fields and wall temperature data. Although, resolving all the effusions passages provides the most accurate results, it is not practical in real applications. Hence, a local source model is employed to model the heat transfer that happens in the cooling-hole passages. In this method, the effusion passage is not resolved (using a mesh) and the mass transfer across the cooling hole passage is prescribed as an injection-extraction boundary condition. The heat transfer at the fluid-solid interface of the cooling-hole passage is also modeled based on Nusselt number correlations available in the literature. This modeling procedure enables simulations with flexible mesh topologies that can be generated at a relatively low cost in comparison to the fully resolved mesh configurations. The local source method is assessed and validated using the available experimental data. The results show that the meshes which resolve the penetration depth in the solid and which conform at the solid-gas interface provide better prediction of the wall temperatures.

Abstract A detailed analysis of film cooling performance on a double-walled effusion-cooled blade is essential for both the coolant consumption optimization and assessment of the film to offer the desired levels of the turbine blade protection. Yet there are hardly any film effectiveness studies on double-wall full-coverage film cooled turbine blades. This paper presents a detailed film cooling effectiveness study over the full surface of a double-walled effusion-cooled high-pressure turbine rotor blade using Pressure Sensitive Paint (PSP). PSP permitted a non-intrusive and conduction-errors-free means of obtaining clean and distinct local distribution of film effectiveness on the blade surface making it possible to extract valuable film cooling effectiveness performance data on the whole blade surface. Three large-scale circular pedestal double-wall blade designs with varying pedestal height, pedestal diameter and cooling hole diameter were tested in a high-speed stationary single-blade linear cascade running at engine-representative Mach and Reynolds numbers. All the blades were tested within a range of representative modern engine coolant mass flow, ṁ c to mainstream, ṁ g ratios; 1.6% < ṁ c /ṁ ∞ < 5.5%. High porosity blade exhibited a better flow distribution and was found to consistently perform the best.

Abstract Gas turbines operate at extreme temperatures and pressures, constraining the use of both optical measurement techniques as well as probes. A strategy to overcome this challenge consists of instrumenting the external part of the engine, with sensors located in a gentler environment, and use numerical inverse methodologies to retrieve the relevant quantities in the flowpath. An inverse heat transfer approach is a procedure used to retrieve the temperature, pressure or mass flow through the engine based on the external casing temperature data. This manuscript proposes an improved Digital Filter Inverse Heat Transfer Method, that consists of a linearization of the heat conduction equation using sensitivity coefficients. The sensitivity coefficient characterizes the change of temperature due to a change in the heat flux. The heat conduction equation contains a non-linearity due to the temperature-dependent thermal properties of the materials. In previous literature, this problem is solved via iterative procedures that however increase the computational effort. The novelty of the proposed strategy consists of the inclusion of a non-iterative procedure to solve the non-linearity features. This procedure consists of the computation of the sensitivity coefficients in function of temperature, together with an interpolation where the measured temperature is used to retrieve the sensitivity coefficients in each timestep. These temperature-dependent sensitivity coefficients, are then used to compute the heat flux by solving the linear system of equations of the Digital Filter Method. This methodology was validated in the Purdue Experimental Turbine Aerothermal Lab (PETAL) annular wind tunnel, a two minutes transient experiment with flow temperatures up to 450K. Infrared thermography is used to measure the temperature in the outer surface of the inlet casing of a high pressure turbine. Surface thermocouples measure the endwall metal temperature. The metal temperature maps from the IR thermography were used to retrieve the heat flux with the inverse method. The inverse heat transfer method results were validated against a direct computation of the heat flux obtained from temperature readings of surface thermocouples. The experimental validation was complemented with an uncertainty analysis of the inverse methodology: the Karhunen-Loeve Expansion. This technique allows the propagation of uncertainty through stochastic systems of differential equations. In this case, the uncertainty of the inner casing heat flux has been evaluated through the simulation of different samples of the uncertain temperature field of the outer casing.

Abstract Modern turbomachine designs feature reduced nominal clearances between rotating bladed-disks and their surrounding casings in order to improve the engine efficiency. Unavoidably, clearance reduction increases the risk of contacts between static and rotating components which may yield hazardous interaction phenomena. In this context, the deposition of an abradable coating along the casing inner surface is a common way to enhance operational safety while mitigating interaction phenomena thus allowing for tighter clearances. Nonetheless, interactions leading to unexpected wear removal phenomena between a bladed-disk and a casing with abradable coating have been observed experimentally. Beside of blade damages such as cracks resulting from high amplitudes of vibration, experimental observations included very significant temperatures increase, particularly within the abradable coating, to a point that thermo-mechanical effects may not be neglected anymore. The aim of this work is to investigate the numerical modeling of thermal effects in the abradable coating and the casing due to contact interactions. In particular, the proposed model provides insight on the sensitivity of engines to contact events when the plane had reduced tarmac times between two consecutive flights. A strongly coupled thermo-mechanical model of the casing and its abradable coating is first described. A 3D cylindrical mesh is employed, it may be decomposed in two parts: (1) along the casing contact surface, a cylindrical thermal mesh is constructed to compute the temperature elevation and heat diffusion in the three directions of space within the abradable coating, and (2) the casing itself is represented by a simplified cylindrical thermo-mechanical mesh to compute both temperature elevation and the induced deformations following temperature changes. This 3D hybrid mesh is combined with a mechanical mesh of the abradable layer, dedicated to wear modeling and the computation of normal and tangential contact forces following blade/abradable coating impacts. The heat flux resulting from contact events is related to the friction forces and only heat transfer by conduction is considered in this work. In order to reduce computational times, the time integration procedure is twofold: the explicit time integration scheme featuring reduced time steps required for contact treatment is combined with a larger time step time integration scheme used for the casing thermo-mechanical model. An extensive validation procedure is carried out from a numerical standpoint, it underlines the convergence of the model with respect to time and space parameters.

Abstract Tilting Pad Thrust Bearings (TPTBs) control rotor axial placement in rotating machinery and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a 3D thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flow rate, shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad sub-surface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4°C and 11°C (< 10%) at laminar and turbulent flow conditions, receptively. Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2 mm thick babbitt layer (common usage), a steel pad with a 2 mm thick hard-polymer (polyether ether ketone, e.g PEEK ® ) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness, however, its demand for a too large supply flow rate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30°C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (> 3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.

Abstract Growing renewable energy generation share causes more irregular and more flexible operational regimes of conventional power plants than in the past. It leads to long periods without dispatch for several days or even weeks. As a consequence, the required pre-heating of the steam turbine leads to an extended power plant start-up time [1]. The current steam turbine Hot Standby Mode (HSM) contributes to a more flexible steam turbine operation and is a part of the Flex-Power Services™ portfolio [2]. HSM prevents the turbine components from cooling via heat supply using an electrical Trace Heating System (THS) after shutdowns [3]. The aim of the HSM is to enable faster start-up time after moderate standstills. HSM functionality can be extended to include the pre-heating option after longer standstills. This paper investigates pre-heating of the steam turbine with an electrical THS. At the beginning, it covers general aspects of flexible fossil power plant operation and point out the advantages of HSM. Afterwards the technology of the trace heating system and its application on steam turbines will be explained. In the next step the transient pre-heating process is analyzed and optimized using FEA, CFD and analytic calculations including validation considerations. Therefor a heat transfer correlation for flexible transient operation of the HSM was developed. A typical large steam turbine with an output of up to 300MW was investigated. Finally the results are summarized and an outlook is given. The results of heat transfer and conduction between and within turbine components are used to enable fast start-ups after long standstills or even outages with the benefit of minimal energy consumption. The solution is available for new apparatus as well as for the modernization of existing installations.

Abstract Hydrodynamic thrust bearings are vital components of rotating machinery and often undergo high axial loads and temperatures. High loads and the consequent shear heating result in high temperature development and viscosity drop of the lubricant. This phenomenon is captured in the solution of a three dimensional energy equation problem. The inlet flow temperature via a groove mixing model and its interaction with outflow from the previous pad is also included in the analysis. Traditionally, capturing the heat conduction at the lubricant solid interfaces in the energy solution for the fixed pad, lubricant, and rotating disk (runner) have faced significant convergence problems. In this study, an integrated method is proposed to remedy this issue. The effects of various model features on the computed results are investigated.

A double-wall cooling scheme combined with effusion cooling offers a practical approximation to transpiration cooling which in turn presents the potential for very high cooling effectiveness. The use of the conventional conjugate CFD for the double-wall blade can be computationally expensive and this approach is therefore less than ideal in cases where only the preliminary results are required. This paper presents a computationally efficient numerical approach for analysing a double-wall effusion cooled gas turbine blade. An existing correlation from the literature was modified and used to represent the two-dimensional distribution of film cooling effectiveness. The internal heat transfer coefficient was calculated from a validated conjugate analysis of a wall element representing an element of the aerofoil wall and the conduction through the blade solved using a finite element code in ANSYS*. The numerical procedure developed has permitted a rapid evaluation of the critical parameters including; film cooling effectiveness, blade temperature distribution (and hence metal effectiveness) as well as coolant mass flow consumption. Good agreement was found between the results from this study and that from literature. This paper shows that a straightforward numerical approach that combines an existing correlation for film cooling from the literature with a conjugate analysis of a small wall element can be used to quickly predict the blade temperature distribution and other crucial blade performance parameters.

Gas turbine design has been characterized over the years by a continuous increase of the maximum cycle temperature, justified by a corresponding increase of cycle efficiency and power output. In such way turbine components heat load management has become a compulsory activity and then, a reliable procedure to evaluate the blades and vanes metal temperatures, is, nowadays, a crucial aspect for a safe components design. In the framework of the design and validation process of HPT (High Pressure Turbine) cooled components of the BHGE NovaLT™ 16 gas turbine, a decoupled methodology for conjugate heat transfer prediction has been applied and validated against measurement data. The procedure consists of a conjugate heat transfer analysis in which the internal cooling system (for both airfoils and platforms) is modeled by an in-house one-dimensional thermo-fluid network solver, the external heat loads and pressure distribution are evaluated through 3D CFD analysis and the heat conduction in the solid is carried out through a 3D FEM solution. Film cooling effect has been treated by means of a dedicated CFD analysis, implementing a source term approach. Predicted metal temperatures are finally compared with measurements from an extensive test campaign of the engine, in order to validate the presented procedure.

This study presents a cooling structure with a sloping sheet to improve the internal cooling of gas turbine blades, inspired by the concept of aircraft wing tip vortex. In this paper, the numerical simulation for the sloping sheet cooling structure has been carried out, which takes into account the heat conduction of the metallic material and the heat transfer of the external high temperature flow field. The results indicate that the structure utilizes the pressure difference between two sides of the sloping sheet to produce a strong vortex pair. The vortexes are led to the inner wall surface of the turbine blade by the downwash. Thanks to such a strong pair vortex, the high temperature air close to the inner wall is quickly blown out and the low temperature coolant is induced to impact on the internal surface, thus achieving an efficient cooling effect. Due to the strong vortex strength and the same vortex vector along the coolant flows, the pair vortex will travel a long distance in the cooling channel, and cool larger areas of the inner wall surface. According to the calculation results, such structure can make the overall temperature of the solid region decreased by 40K as compared to the smooth channel. The sloping sheet cooling structure can reduce the total pressure loss by 63% as compared to the array of pin fins which achieve the same cooling effect. Furthermore, the influence of the sloping sheet’s inclination angle, length and width on the cooling characteristics has also been studied. Through the strength analysis by FEM method, the maximum von Mises stress is 21.9 MPa and it verifies that the sloping sheet can work securely and firmly.

Information about heat release can be used to discuss the flame dynamics and stability behavior of turbulent combustion systems. The most common experimental approach to determine heat release fluctuations is the recording of OH*-chemiluminescence. Since there is a strong dependence of chemiluminescence on strain rate and mixture gradients, spatial information must be judged with care. As already shown in previous work, Laser Interferometric Vibrometry (LIV) directly detects the line-of-sight values of density fluctuations along the laser beam axis. Neglecting friction, losses of thermal radiation and conduction and assuming only small fluctuations of pressure in the reaction zone, heat release fluctuations can be calculated directly from density fluctuations. With available LIV techniques only pointwise scanning was feasible, resulting in time-consuming traversing of the flame to cover the whole flame field. A new camera-based full-field-LIV-system, developed at Technische Universität Dresden, is capable to simultaneously determine spatial information of heat release within the whole field with only one measurement, lasting a few minutes. This leads to a dramatical reduction of measurement time and furthermore reduces experimental efforts. Since the system is able to measure the complete flame at once, it is also possible to get information about the transient behavior of the combustion process. In this work the full-field-LIV system was applied for the first time on a swirl stabilized, lean and premixed methane flame. The results of this newly developed technique were checked against those of a commercially available single-beam LIV-system. Finally, the flame transfer function (FTF) was recorded with full-field-LIV and OH*-chemiluminescence and compared against each other.

In modern turbomachine designs, the nominal clearances between rotating bladed-disks and their surrounding casing are reduced to improve aerodynamic performances of the engine. This clearance reduction increases the risk of contacts between components and may lead to hazardous interaction phenomena. A common technical solution to mitigate such interactions consists in the deposition of an abradable coating along the casing inner surface. This enhances the engine efficiency while ensuring operational safety. However, contact interactions between blade-tips and an abradable layer may yield unexpected wear removal phenomena. The aim of this work is to investigate the numerical modeling of thermal effects within the abradable layer during contact interactions and compare it with experimental data. A dedicated thermal finite element mesh is employed. At each time step, a weak thermo-mechanical coupling is assumed: thermal effects affect the mechanics of the system, but the mechanical deformation of the elements has no effect on temperatures. Weak coupling is well appropriated in the case of rapid dynamics using small time step and explicit resolution schemes. Moreover, only heat transfer by conduction is considered in this work. To reduce computational times, a coarser spatial discretization is used for the thermal mesh comparing to the mechanical one. The time step used to compute the temperature evolution is larger than the one used for the mechanical iterations since the time constant of thermal effect is larger than contact events. The proposed numerical modeling strategy is applied on an industrial blade to analyze the impact of thermal effects on the blade’s dynamics.

The continuous drive for ever higher turbine entry temperatures is leading to considerable interest in high performance cooling systems which offer high cooling effectiveness with low coolant utilisation. The double-wall system discussed here, is an optimised amalgamation of more conventional cooling methods including impingement cooling, pedestals, and film cooling holes in a more closely packed array characteristic of effusion cooling. The system entails two walls, one with the impingement holes, and the other with the film holes. These are mechanically connected via the bank of pedestal thereby allowing conduction between the walls and increasing coolant wetted area and turbulent flow. However, in the open literature, data — and particularly experimental data — on such systems is sparse. This study presents a newly commissioned experimental heat transfer facility designed to investigate double-wall cooling geometries. The paper discusses some of the key features of the steady-state facility, including the use of infrared thermography to obtain overall cooling effectiveness measurements. The facility is designed to achieve both Reynolds and Biot (to within 10%) number similarity to those seen at engine conditions. The facility is used to obtain overall cooling effectiveness measurements for a circular pedestal, double-wall test piece at three coolant mass-flow conditions with the results presented and discussed. A fully conjugate CFD model of the facility was also developed providing greater insight into the internal flow field. Additionally, a computationally efficient, decoupled conjugate method developed by the authors for analysing such double-wall systems is run at conditions to match the experiments. The results of the simulations are encouraging, particularly given how computationally efficient the method is, with area-weighted, averaged overall effectiveness within a small margin of those obtained from the experimental facility.

Many laboratory-scale combustors are equipped with viewing windows to allow for characterization of the reactive flow. Additionally, pressure housing is used in this configuration to study confined pressurized flames. Since the flame characteristics are influenced by heat losses, the prediction of wall temperature fields becomes increasingly necessary to account for conjugate heat transfer in simulations of reactive flows. For configurations similar to this one, the pressure housing makes the use of such computations difficult in the whole system. It is therefore more appropriate to model the external heat transfer beyond the first set of quartz windows. The present study deals with the derivation of such a model which accounts for convective heat transfer from quartz windows external face cooling system, free convection on the quartz windows 2, quartz windows radiative properties, radiative transfer inside the pressure housing and heat conduction through the quartz window. The presence of semi-transparent viewing windows demands additional care in describing its effects in combustor heat transfers. Because this presence is not an issue in industrial-scale combustors with opaque enclosures, it remains hitherto unaddressed in laboratory-scale combustors. After validating the model for the selected setup, the sensitivity of several modeling choices is computed. This enables a simpler expression of the external heat transfer model that can be easily implemented in coupled simulations.

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NO x and soot in particular). Its implementation, however, involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. A reduced coolant mass flow rate in conjunction with higher compressor discharge temperature negatively affect the cooling potential thus requiring the exploitation of efficient schemes such as effusion cooling. This work describes the experimental and numerical final validation of an aeronautical effusion-cooled lean-burn combustor. Full annular tests were carried out to measure temperature profiles and metal temperature distributions at different operating conditions of the ICAO cycle. Such an outcome was obtained also with an in-house developed CHT methodology (THERM3D). RANS simulations with the Flamelet Generated Manifold combustion model were performed to estimate aerothermal field and heat loads, while the coupling with a thermal conduction solver returns the most updated wall temperature. The heat sink within the perforation is treated with a 0D correlative model that calculates the heat pickup and the temperature rise of coolant. The results highlight an overall good capability of the proposed approach to estimate the metal temperature distribution at different operating conditions. It is also shown how more advanced scale-resolving simulations could significantly improve the prediction of turbulent mixing and heat loads.

Hydrogen represents a possible alternative gas turbine fuel for future low emission power generation once it can be combined with the use of renewable energy sources for its production. Due to its different physical properties compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for Dry Low NO x (DLN) Hydrogen combustion. This makes the development of new combustion technologies an essential and challenging task for the future of hydrogen fueled gas turbines. The newly developed and successfully tested “DLN Micromix” combustion technology offers great potential to burn hydrogen in gas turbines at very low NO x emissions. The mixing of hydrogen and air is based on the jet in cross-flow (JICF) principle, where the gaseous fuel is injected perpendicular into the crossing air stream. The reaction takes place in multiple miniaturized diffusion flames with an inherent safety against flashback and the potential of low NO x emissions due to a short residence time of the reactants in the flame region. Aiming to further develop an existing burner design in terms of an increased energy density, a redesign is required in order to stabilize the flames at higher mass flows while maintaining low emission levels. For this reason, a systematic numerical analysis using CFD is carried out, to identify the interactions of combustion, radiation and heat conduction in the adjacent burner wall by conjugate heat transfer (CHT) methods. Different combustion models are applied, starting from a hybrid eddy break-up model to more advanced turbulence-chemistry interaction approaches considering detailed chemical mechanisms. Those allow an improved prediction of the different NO-pathways of production and consumption. The results of the simulations are in good agreement with atmospheric test rig data of optical flame structure, measured combustor surface temperatures and NO x emissions. The numerical methods help reducing the effort of manufacturing and testing to few designs for single validation campaigns, in order to confirm the flame stability and NO x emissions in a wider operating condition field. Further on, the more detailed CFD-simulations support the understanding of decisive mechanisms to reduce the numerical work to the most important models for further industrial applications in future.

Most of the optimization researches on film cooling have dealt with adiabatic film cooling effectiveness on the surface. However, the information on the overall cooling effectiveness is required to estimate exact performance of the optimization configuration since hot components such as nozzle guide vane have not only film cooling but also internal cooling features such as rib turbulators, jet impingement and pin-fins on the inner surface. Our previous studies [1,2] conducted the hole arrangement optimization to improve adiabatic film cooling effectiveness values and uniformity on the pressure side surface of the nozzle guide vane. In this study, the overall cooling effectiveness values were obtained at various cooling mass flow rates experimentally for the baseline and the optimized hole arrangements proposed by the previous study [1] and compared with the adiabatic film cooling effectiveness results. The tests were conducted at mainstream exit Reynolds number based on the chord of 2.2 × 10 6 and the coolant mass flow rate from 5 to 10% of the mainstream. For the experimental measurements, a set of tests were conducted using an annular sector transonic turbine cascade test facility in Korea Aerospace Research Institute. To obtain the overall cooling effectiveness values on the pressure side surface, the additive manufactured nozzle guide vane made of polymer material and Inconel 718 were installed and the surface temperature was measured using a FLIR infrared camera system. Since the optimization was based on the adiabatic film cooling effectiveness, the regions with rib turbulators and film cooling holes show locally higher overall cooling effectiveness due to internal convection and conduction, which can cause non-uniform temperature distributions. Therefore, the optimization of film cooling configuration should consider the effect of the internal cooling to avoid undesirable non-uniform cooling.