Rolls-Royce (United States)

Abstract Environmental barrier coatings (EBCs) offer protection to Silicon carbide (SiC)-based ceramic matrix composites (CMCs) against corrosion, oxidation, and water vapor for high temperature gas turbine applications. EBCs are often heat-treated to crystallize the amorphous phase, to change residual stresses, or heal cracks and pores. Properties such as elastic modulus and creep resistance at high temperatures are needed to assess EBC integrity and predict EBC response in a gas turbine environment. This paper highlights new experimental methods to measure EBC elastic moduli before, during and after heat treatment using compressive load-unload cycles. Strain from compression of cylindrical EBC material was measured by digital image correlation (DIC) through a window in a resistance heated SiC element furnace. Elastic modulus was initially measured at room temperature followed by at temperature measurements between 500°C and 1200°C at various temperature intervals for increasing as well as decreasing temperature excursions to assess the change in modulus with temperature and after crystallization. In addition, creep tests of individual layers of EBC were performed under four constant compressive stress at different temperatures from 1000°C up to 1200°C for at least 24 hours. This study found an increase in EBC elastic moduli from room temperature to final HT temperature, and no change once the EBC had been fully crystallized after HT.

Abstract A novel co-rotating, synchronous, reverse flow (RF) turbine mode operation in a centrifugal compressor (CC) is investigated, and methods to enable this mode, its working principles, flow field features, and key performance characteristics are described. This is done by using three-dimensional (3D) Reynolds–averaged Navier–Stokes (RANS) flow field simulations on a simplified variant of the NASA High Efficiency Centrifugal Compressor (HECC) geometry, which represents a typical state-of-the-art design practice. The novel co-rotating turbine mode is elucidated by first considering the baseline contra-rotating, reverse flow turbine mode as would be expected from the conventional four-quadrant CC operation map. This baseline contra-rotating turbine mode is also hitherto undescribed in the literature for CC. Therefore, the flow field and performance metrics in the baseline contra-rotating mode are utilized to provide insights into the possibility of engineering design elements that can enable the novel co-rotating turbine mode. The novel co-rotating, turbine mode is found to be enabled by the introduction of a suitable swirl generation mechanism that will direct the flow onto the impeller wheel suction side to give it a rotational impulse to spin from the suction to the pressure side as in nominal operation. The flow expansion through the reversed impeller wheel flow path with radius reduction enables power production. In the novel co-rotating, turbine mode, the flow leaves the impeller wheel in the same direction as it enters because of the direction of rotation and impeller inlet flow angle. However, this does not significantly impact power production because of the reduced radius weighting of the absolute swirl at the impeller inlet. An exemplary co-rotating turbine mode enabling configuration with 45 deg rotated diffuser vanes is found to handle up to 46% higher reverse flow and yield 6.25% higher peak power output even with a 16% lower absolute swirl velocity change as compared to the baseline contra-rotating mode. Additionally, the novel mode indicates better low speed power profile and wheel terminal speed as well. Alternative embodiments to enable the co-rotating mode like drilled feed ports and guide vane arrangements are discussed in the work. The hitherto undescribed co-rotating turbine mode operation is unique in its ability to produce and absorb power in the same shaft for bladed turbomachinery. Therefore, purposeful utilization of this mode could enable the design of better, robust, optimized systems for aerospace and energy applications.

Abstract Background Clinical guidelines recommend high-sensitivity cardiac troponin assays for the diagnosis of acute myocardial infarction. The next generation high-sensitivity cardiac troponin T Gen 6 assay has been developed to allow the rapid, quantitative determination of cardiac troponin T in serum and plasma. As such, the 99th percentile upper reference limit (URL) of this assay must be determined. Purpose The global REF-TSIX study was conducted to define the uniform and sex-specific 99th percentile URL of apparently healthy individuals, representing a diverse, global population, using the high-sensitivity cardiac troponin T Gen 6 assay. Methods Lithium-heparin (Li-Hep) plasma and serum samples were prospectively collected at a single time point from apparently healthy participants aged ≥20 years in a reference range study and measured using an automated high-throughput immunoassay analyser. Exclusion criteria (some a priori and some post hoc as per International Federation of Clinical Chemistry recommendations published mid-study) included history or symptoms suggestive of cardiovascular disease, recent chest trauma, hypertension, chronic kidney disease, diabetes mellitus, pregnancy, N-terminal pro-B-type natriuretic peptide ≥125 ng/L, therapy for hyperlipidaemia or hypertension, body mass index (BMI) <18 kg/m² or >35 kg/m², smoking, and chronic disease that could affect the heart.[1] Uniform and sex-specific 99th percentile URLs and corresponding non-parametric lower and upper confidence limits of apparently healthy individuals were determined in sample matrices individually and combined. Results Of 7,910 apparently healthy individuals recruited, 4,147 participants were included in the final analysis (2,176 [52.5%] female and 1,971 [47.5%] male) with a mean age of 46.5 (range: 20–88) years (Figure 1). Mean BMI was 25.1 kg/m² and mean systolic/diastolic blood pressure was 122/77 mmHg. Distribution of high-sensitivity cardiac troponin T Gen 6 values are shown in Figure 2A. For sample matrices combined (n=8,294), 89.7% of results were above the limit of detection. When stratified by sex, 81.0% and 99.2% of females and males, respectively, had a measurable value. The uniform 99th percentile URL of the high-sensitivity cardiac troponin T Gen 6 assay was 27 ng/L; sex-specific 99th percentile URLs were 18 ng/L and 32 ng/L for females and males, respectively (Figure 2B). Uniform and sex-specific 99th percentile URLs for Li-Hep and serum samples separately demonstrated very good comparability. Conclusion The REF-TSIX study determined uniform (27 ng/L) and sex-specific (18 ng/L, females; 32 ng/L, males) 99th percentile URLs for the high-sensitivity cardiac troponin T Gen 6 assay in a global, healthy reference population. The 99th percentile URLs showed excellent comparability irrespective of the matrix used.Figure 1 Figure 2

Abstract INCEFA-SCALE is a five-year project within the European Commission HORIZON 2020 programme starting in October 2020. Nuclear plant operators have generally observed that the number of failure events attributable to Environmentally Assisted Fatigue (EAF) are fewer than predicted by current assessment methodologies. It is recognised that a contributor to this discrepancy is the transferability of data from laboratory-scale tests to real nuclear components. This is the main knowledge gap addressed by INCEFA-SCALE. This is being achieved through the combination of testing, analysis, and materials characterisation to provide laboratory testing data, and the required meta data to understand the resulting behaviour, generated under conditions that are more representative of those experienced by plant components. The EAF assessment methodology described in NUREG/CR-6909 Rev 1 designed for use with the ASME BPVC Section III fatigue design curves (using factors of 12 on life and 2 on stress/strain) provides an international benchmark and technical justification. This benchmark has been the subject of over a decade of research defining the levels of conservatism provided and proposing alternative approaches to clearly define appropriate margins in EAF assessment methods. One such approach, initiated by the Japanese ‘Subcommittee on Design Fatigue Curve’ and further developed by Rolls-Royce, offers modifications to the design curve approach through the use of ultimate tensile strength dependent mean curves, justification of a new approach to transference factors, the use of the Smith-Watson-Topper mean stress correction approach and explicitly accounting for variable amplitude loading in the high cycle regime of fatigue. Substantial research has been conducted and improvements proposed for the low-cycle regime of the design curves (where the factor on life applies for the ASME approach). However, research data in relevant high temperature water environments relating to the transference factors influencing the factor of 2 on stress/strain is limited. Part of this value is defined by loading history and understanding how to account for this phenomenon in a fatigue assessment requires the production of research data that enables the behaviour of materials subjected to variable loading to be understood. Variable loading is known to affect hardening and mean stress behaviour. Additionally, failure modes where a crack can initiate under larger loading amplitudes and grown to failure by sub-endurance limit loading may be important. This means laboratory testing under relevant environments and variable strain amplitudes is required to advance this area and define new benchmark methods that can adequately account for such behaviours while providing an appropriate level of conservatism. This paper focuses on the presentation and analysis of test data produced by the INCEFA-SCALE project. The data investigates the effects of loading history, environment, and surface finish, through the application of single and variable amplitude waveforms to 316L stainless steel uniaxial fatigue specimens in both air and simulated Pressurised Water Reactor primary coolant environments. By altering the above variables, the aim of this paper is to provide an understanding of how the method outlined in NUREG/CR-6909 and the alternative method proposed by the Subcommittee on Design Fatigue Curve accounts for these effects. It is shown that at time of writing the data would provide support for reducing the NUREG transference factor on stress to 1.4, however a recommendation on reducing the factor on cycles requires more analysis. The reduction in the stress factor is consistent with the approach of the Japanese ‘Subcommittee on Design Fatigue Curve’. There is however inconsistency between the use of elastic pseudo stress amplitudes used in fully reversed design life predictions, and the yield stress value used to govern the boundaries of stress-based mean stress corrections which should be considered in any new design curve approaches.

Abstract New civil engines must demonstrate, either by testing or analysis, that a shaft failure event will not result in hazardous engine effects. Without an accurate method of predicting levels of turbine overspeed, disk design tends to be pessimistic which leads to a weight penalty. This paper presents an alternative approach based on a highly integrated, multi-disciplinary, dynamic whole-engine simulation tool capable of predicting a gas turbine engine’s behaviour following the failure of a shaft. It describes the methodology and validation of a 1D through-flow compressor model capable of post-stall simulation, coupled with a transient combustor model and a quasi-steady turbine solver for overspeed modelling. The individual components are integrated aerodynamically and mechanically to produce a transient whole-engine model which is resolved at timesteps ranging from 1 to 100 μs. Control and aerodynamic effects impacting turbine overspeed predictions include changes in handling bleeds, fuel supply, turbine capacity reduction due to overspeed, frictional torque and variable geometry malschedule. The modelling of a gas turbine engine’s response following a surge event is required for overspeed modelling which is achieved using compressor characteristics defined from normal operation to reverse flow. The whole engine simulation tool is validated against a 3-spool experimental gas turbine engine which experienced a shaft failure event on a test stand. The simulation model correctly predicted the turbine’s terminal speed within a 4% error margin and blowdown rate following a surge event until recovery.

Abstract Combustor turbulence in a gas turbine engine greatly influences the efficiency of the downstream high-pressure turbine stage. Here we use a multifidelity computational optimization methodology to modify the geometry of a nonreacting combustor simulator such that turbulence properties are optimized at the combustor-turbine interface. We modify the size, orientation, and positioning of the primary and dilution jets to minimize turbulence intensity at the combustor exit while demonstrating negligible or favorable changes to the pressure loss and mixing characteristics of the combustor. The optimization is performed using a machine learning surrogate-assisted genetic algorithm coupled with large eddy simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) simulations. The optimization is performed in three phases: (i) we develop a continuously learning artificial neural network surrogate model, (ii) we perform a stochastic optimization with RANS simulations to narrow the parameter space, and (iii) we perform a stochastic optimization with a coarse-grid LES to identify the optimal solution. Using this approach, we are able to achieve a 5.35% reduction in turbulence intensity and a 0.42% reduction in pressure loss while maintaining good mixing uniformity at the combustor exit. These changes are enabled primarily by changing the aspect ratio, diameter, and spacing of the primary zone and dilution jets, as well as the chute height of the primary zone jets. This successful demonstration of multifidelity optimization in the combustor simulator can be extended in the future to the design of improved gas turbine combustors.

Abstract This paper develops a numerical procedure to accelerate the convergence of the Favre-averaged non-linear harmonic (FNLH) method. The scheme provides a unified mathematical framework for solving the sparse linear systems formed by the mean flow and the time-linearized harmonic flows of FNLH in an explicit or implicit fashion. The approach explores the similarity of the sparse linear systems of FNLH and leads to a memory-efficient procedure, so that its memory consumption does not depend on the number of harmonics to compute. The proposed method has been implemented in the industrial computational fluid dynamics solver Hydra. Three test cases are used to conduct a comparative study of explicit and implicit schemes in terms of convergence, computational efficiency, and memory consumption. Comparisons show that the implicit scheme yields better convergence than the explicit scheme and is also roughly 7–10 times more computationally efficient than the explicit scheme with four levels of multigrid. Furthermore, the implicit scheme consumes only approximately 50% of the memory required by the explicit scheme with four levels of multigrid. Compared with the full-annulus unsteady Reynolds-averaged Navier–Stokes simulations, the implicit scheme produces comparable results to URANS with computational time and memory consumption that are two orders of magnitude smaller.

Abstract Short-duration facilities, with testing time on the order of milliseconds to seconds, offer cost-effective solutions to achieve engine-relevant pressure and temperature ratios. Short-duration facilities have high levels of heat loss that require careful accounting for efficiency calculation[1]. The Purdue Small Turbine Aerothermal Rotating Rig (STARR) was developed to test engine-representative hardware for small core turbine applications. The STARR facility is a two-stage rotating test turbine running at engine-representative Reynolds and Mach numbers capable of fast transients and steady operation for up to 6 hours with the enhanced pressure vessels in development. The facility is purpose-built to test advancements in critical technologies for clean aviation, pushing towards higher OPR engines, hybrid propulsion, and multi-stream engines. The facility is designed to be modular, allowing faster turnaround times for new test articles. This paper presents the design, control, and operation of the facility. Efficiency measurements in engine-representative test rigs are a challenging prospect due to the narrow uncertainty band required, ideally less than 0.5% uncertainty, to detect the incremental improvements achieved by turbine designers. For a small core turbine, accurately quantifying the tip clearance is also critical to assess relative changes in performance. To that end, the instrumentation used for efficiency measurement and resolving unsteady flow phenomenon is presented. The inlet characterization and commissioning of the test section are presented. Uncertainty is quantified on efficiency measurement through a comprehensive framework [2] that includes both precision and absolute level of uncertainty. The uncertainty is propagated from the individual sensor to the final efficiency calculation. The total uncertainty for mechanical efficiency presented is of the order of 0.55%. The challenges faced in the operation of such a facility are highlighted, along with the steps proposed to mitigate them.