bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed Design and Optimization of the First Stage of an Axial Supercritical CO2 Compressor
Authors: Ha Matthew , Holder Justin , Ghimire Saugat , Ringheisen Adam , Turner Mark G.
Published: October 2022

Advancement in energy storage technology is critical in the transition to increased renewable energy sources. The thermodynamic properties of S-CO2 allow for high thermal efficiency and power density potential in turbomachinery design. Relative to the Steam Rankine and Air Brayton cycles, S-CO2 cycles benefit in performance, size, and cost.

As S-CO2 gains acceptance in the industry, research must be conducted to understand the potentials and limitations of this new technology; this is key to the eventual commercial viability of S-CO2 applications. Currently, applications of S-CO2 in turbomachinery are limited to centrifugal design due to the complex fluid properties and flow interactions.

Advancements in compressor design now allow for the intelligent navigation of this complex design space. Optimization tools are utilized to evaluate parametrically defined blades in S-CO2 working fluid to explore advanced, high-performance geometries.

The first axial S-CO2 compressor is designed using this optimization based methodology. This design is the scaled 9 MW 3 stage version of a larger 100 MW 9 stage compressor that will be used for an energy storage application. The adiabatic efficiency of the first stage design is estimated at 91.6% with 3.14 MW of power at 19,800 rpm. The blade height at the rotor leading edge is 3.28 cm.

The first stage of the scaled 9 MW 3 stage compressor will be tested at the University of Notre Dame Turbomachinery Lab; testing of the complete 3 stage machine will follow the single stage testing.

Stage one design drawings have been finalized and submitted for manufacturing. The IGV and Stator 1 have been manufactured and received by the University of Notre Dame Turbomachinery Lab for assembly and testing in the Fall of 2022.
Fluid-Dynamics of Turbine Rim Seal Structures: A Physical Interpretation Using URANS
Authors: De Cosmo Giove , Scobie James A. , Lock Gary D. , Sangan Carl M. , Carnevale Mauro
Published: October 2022

Unsteady Reynolds-Averaged Navier-Stokes modelling (URANS) is a valuable and cost-effective tool for Computational Fluid Dynamics (CFD), including the investigation of mainstream-cavity interaction in turbines. Despite the gap in accuracy with higher order CFD methodologies, URANS is among the few simulation strategies of industrial interest suitable for predicting ingress/egress over a wide range of conditions.

This paper presents a numerical study of the flow-field in the upstream double-radial seal of a 1.5 stage turbine. Various configurations are tested, including non-purged and purged conditions. Rigour of the approach is ensured by a set of sensitivity analyses, allowing the delineation of a best practice on the use of URANS in rim seal simulations: this includes an assessment of the effects of sector size, cavity domain size and blade count.

Time-averaged and time-resolved flow predictions capture coherent structures in the rim gap. An association between the 3D morphology of these structures and different ingress/egress mechanisms is proposed. Regions of enhanced radial activity are identified to correspond with the blade leading edges. A frequency analysis of unsteady pressure signals probed in the rim gap leads to a calculation of the structure number and speed.

The structures are synchronous with the disc rotation for non-purged cases but rotate at slower speed when purge is introduced. The relative number of blades and vanes directly influences the structure count and velocity. The configuration with no blades is characterised by the slowest structures. The calculations have been conducted at three different flow coefficient for the annulus flow. There is a reduction in radial activity and structure speed at lower flow coefficient, fundamentally related to the reduced pressure asymmetry and gradient of swirl across the rim seal.
Development of Translucent Design Philosophy for the Cyclic Pattern Design of Fan Outlet Guide Vanes
Authors: Kulkarni Davendu Y. , di Mare Luca
Published: October 2022

The fan systems of typical high bypass civil engines encounter strong flow distortions originating in the intake and in the bypass ducts and its bifurcations. These flow distortions cause the fan stage operation point to vary from its design intent, thus reducing the fan stage performance and increasing low engine-order fan blade forcing. A cyclic pattern design for the fan Outlet Guide Vanes (OGV) can be effectively used to recover the fan stage performance and to control its system-level aeromechanical behaviour.

This paper presents the development of a OGV pattern design philosophy using numerical experimentation technique. Multiple fan-intake unsteady CFD computations are conducted by clocking the circumferential pressure profile at fan exit to understand its effect on fan rotor efficiency and 1EO fan forced response. The study revealed that a mild, low-harmonic fan back pressure field with a suitable clocking position is able to improve the fan efficiency and reduce the fan forcing simultaneously. Such a pattern can be generated by designing a cyclic OGV pattern that allows the bifurcation potential fields of controlled intensity and phase to pass through the OGV blade row. The notion of deliberately generating a clocked 1EO intra-stage static pressure field by means of cyclic OGV pattern design is termed as the translucent design philosophy.

Further, a sensitivity study is performed to assess the effects of simultaneous distortions upstream and downstream of the fan in two flight conditions. The study showed that a correctly clocked intra-stage static pressure field can effectively counter the fan upstream flow distortions and at the same time improve the fan rotor performance and fan system aeromechanical behaviour. The implementation of the proposed translucent design philosophy in a new OGV pattern design tool is discussed.
A Novel Decomposition Approach Preventing Spurious Entropy Generation in Hybrid Thermoacoustic Stability Computations
Authors: Heilmann Gerrit , Liu Tong , Romero Vega Pedro , Sattelmayer Thomas
Published: October 2022

Prominent approaches for the computation of thermoacoustic stability are hybrid methods like the linearized Navier-Stokes equations (LNSE) or the linearized Euler equations (LEE). The transient fluctuations around a precomputed steady-state mean flow field solved with these sets of equations naturally include the energy transition between acoustic, vortical and entropic modes. It is common practice to account for flame-acoustic interactions by applying measured or computed flame transfer functions (FTF) as a volumetric source term proportional to the mean heat release rate in the energy equation. However, the underlying assumption of a static flame is the root-cause of spurious entropy production, which may ultimately falsify the thermoacoustic stability predictions. In the present paper, a methodology to include arbitrary flame movement in the governing set of equations is presented. The procedure makes use of an Arbitrary Lagrangian-Eulerian (ALE) description of conservation equations and is demonstrated for the Euler equations. The resulting set of linear perturbation equations is then applied to two test cases. First, the frequency response of a one-dimensional premixed air-methane flame is evaluated. Secondly, the frequency response of the first longitudinal eigenmode of an experimental premixed, swirl-stabilized combustor is computed. To demonstrate the reduction of spurious entropy waves, the results are compared to those of the classic LEE.
Improved Modeling and Experimental Evaluation of a Micro Gas Turbine for Solar-Hybrid Application
Authors: Fenner Chaz , van der Spuy Sybrand J.
Published: October 2022

This study contributes to the ongoing research to develop a turbocharger based dual-shaft Micro Gas Turbine (MGT) for a commercialized solar-hybrid system. The work in this study developed an improved model to predict the performance of the MGT which comprises of two turbochargers, with one turbocharger representing the gas generator turbine and the other, bigger turbocharger used as the power turbine unit. It did so by including the effects of heat transfer through a One-Dimensional Thermal Resistance Network (1-D TRN) to determine diabatic outlet temperatures and by accounting for the supposed incomplete combustion. Overall, the model’s temperature estimations were found to be within a maximum deviation of 5 % of the measured values and, 8 % for pressure. Combustor outlet temperature estimates were substantially improved to within 4 % of the measured value, which is a 15 % improvement on previous work. Despite the increased accuracy, the model was only validated for the smaller gas generator turbine. The larger power turbine was reasoned to have not reached thermal equilibrium as temperature estimates had substantially increased levels of deviation from the measured values. A subsequent energy audit of the facility demonstrated the utility of the 1-D TRN. The results of which were used to determine the scale of the heat transfer. It showed that the power turbine is in fact operating outside of its optimal range which resulted in the heat loss rate of the gas through the turbine being greater than the power it produced. The usefulness of the combustion model is also highlighted as a technique to estimate the combustor outlet temperature with acceptable levels of accuracy and with a rapid turn-around time due to its simplicity. The 1-D TRN was shown to estimate heat flows in the MGT accurately despite employing correlations for the heat transfer coefficients that were not developed for the machines. A combustor designed for solarized operation was benchmarked against a standard unit and the results indicated the significance of reducing parasitic pressure losses as a means to improve MGT performance.
Cost-Effective CFD Analysis of the Acoustic Response of a Perforated Plate
Authors: Dimola Nunzio , Stefanizzi Michele , Capurso Tommaso , Schuller Thierry , Torresi Marco , Camporeale Sergio Mario
Published: October 2022

Given the current practice to perform lean-premixed combustion to decrease NOx emissions, thermoacoustic instabilities have become one of the major drawbacks in gas turbine combustors. The necessity to control and limit such a deleterious phenomenon is mandatory to avoid structural damage of the burner. It has been demonstrated that perforated liners, if conveniently designed, can be very effective in reducing acoustic oscillations inside gas turbine combustors. Studying perforated plates traversed by bias flow can give a useful insight on sound absorption properties of liners, rather than investigate complex geometries. The present paper aims to carry out a numerically cost-effective, but reliable, CFD analysis to predict the acoustic impedance of perforated plates traversed by bias flow, and to grasp the details of the sound dissipation process. 2D axisymmetric simulations have been carried out and the governing equations solved by using the commercial code ANSYS Fluent®. Hypotheses, boundaries and operating conditions are described, focusing on the role of the Non-Reflecting-Boundary-Condition (NRBC) and the Transparent-Flow-Forcing condition (TFF) in treating acoustic waves. Numerical results are compared both with linear analytical models and experimental data from a case study, by proving a fast and reliable prediction of the acoustic response. Furthermore, effects of increasing bias flow temperature on the sound absorption property have been investigated, showing an increase in acoustic power losses as temperature rises. The proposed CFD model (2D-axisymmetric) proved to be a valid and versatile tool in evaluating the acoustic response of perforated plates under different operating conditions.
Investigation of Surge in a Transonic Centrifugal Compressor With Vaned Diffuser: Part 1 – Surge Signature
Authors: Lou Fangyuan , Harrison Herbert M. , Key Nicole L.
Published: October 2022

The identification of stall inception mechanisms and stability-limiting components in a centrifugal compressor is required for development of effective surge suppression approaches. Part 1 of this two-part paper investigates the surge signature of a centrifugal compressor at subsonic, transonic, and supersonic inlet tip conditions, and Part 2 considers the relationship of the surge signature with the compressor static pressure characteristics as well as the impeller leading edge relative tip Mach number. Experiments were performed in the Single Stage Centrifugal Compressor (SSCC) facility at Purdue University with both steady performance and dynamic pressure data recorded. Results show the presence of both mild and deep surge on the compressor map. Deep surge occurs at subsonic and supersonic impeller tip relative Mach numbers while mild surge is observed as the tip relative Mach number nears unity. Long length-scale modal oscillations can be detected only at the transonic operating condition while spike disturbances are identified as the precursor to instability at subsonic and supersonic tip relative Mach numbers. Finally, the impeller is determined to be the origin of instability throughout most of the compressor map. The observation of impeller-induced instability refreshes the conventional understanding that the diffuser is typically the stability-limiting component for centrifugal compressors with vaned diffusers and suggests various surge suppression approaches may be necessary to achieve range extension throughout a compressor map.
Investigation of Surge in a Transonic Centrifugal Compressor With Vaned Diffuser: Part 2 – Correlation With Subcomponent Characteristics
Authors: Lou Fangyuan , Harrison Herbert M. , Brown William J. , Key Nicole L.
Published: October 2022

In the first part of the paper, surge signatures and the underlying mechanisms thereof for a high-speed centrifugal compressor were investigated using signals from fast-response transducers installed along the flow path. The compressor surge signature is observed to vary as the impeller inlet tip flow transitions from subsonic to supersonic conditions. Spike-type deep surge is observed at subsonic and supersonic impeller inlet tip conditions while modal-type mild surge occurs at 90% speed with transonic inlet tip conditions. In Part 2 of the paper, a detailed analysis of the static pressure rise characteristics at the stage, component, and subcomponent levels is conducted. Additionally, the influence of the impeller inlet conditions on the instability are also considered. A connection between the surge mechanism and component static pressure rise characteristics is shown which exhibits the potential for prediction of the stall inception mechanism including identification of the destabilizing component. Furthermore, the transition from subsonic to transonic impeller inlet conditions is shown to be the cause of the unique mild surge instability at 90% speed. Lastly, both experimental and computational results are utilized to investigate the development of a shock wave at the impeller leading edge. The shock is considered to be critical to stage stability at speeds where the compressor experiences transonic inlet conditions.
Performance Assessment of Tesla Expander Using 3D Numerical Simulation
Authors: Renuke Avinash , Traverso Alberto
Published: October 2022

Bladeless or Tesla turbines consist of several flat parallel disks mounted on a shaft with a narrow gap between them. The analytical solution of Navier-Stokes equations for the flow between disks has been extensively studied in the past. However, there is a significant impact of the stator exit-flow conditions on the performance and flow behavior inside the rotor of the Tesla turbine. There has been limited research on flow characterization and performance evaluation of stator-rotor interaction of the Tesla expander using 3D numerical simulation. The challenge arises due to a very high aspect ratio of the Tesla rotor (diameter to gap ratio > 1000). In order to accurately evaluate the torque on the disks due to shear forces, a very fine resolution mesh is necessary. 3D numerical modeling with a hexahedral mesh of the nozzle/stator with the commercial software is presented. A steady-state solution is obtained using a density-based solver for solution stability. The simulation is performed for a wide range of inlet pressures and rotational speeds. The numerical solution does not consider the effects of ventilation losses, end-disk leakages, exit kinetic energy and bearing losses. This work focuses on the stator performance, the stator-rotor interaction, the rotor entry losses due to disk tip, the rotor tip velocity ratio and the degree of reaction on the performance of the Tesla expander. Challenges in modelling and key fluid dynamic features are extensively discussed. The peak efficiency of 58% is predicted for 3 bar inlet pressure and a rotational speed of 30000 rpm for a 3 kW machine with air as a working fluid. The 3D numerical analysis provides insights on flow characterization, mainly stator-rotor interaction and flow between disks at different mass flows, with the aim to contribute to the fundamental knowledge towards further improvement of the Tesla turbine performance. Numerical results are also compared with experimented test results performed on a 100-W and a 3-kW air expander.
Performance Optimization of Semi-Closed Oxy-Combustion Combined Cycle (SCOC-CC) for Current and Future Blade Materials
Authors: Risimini Gabriele Pio , Martinelli Matteo , Chiesa Paolo , Martelli Emanuele
Published: October 2022

Among the technologies for carbon capture and storage (CCS) from natural gas, oxy-turbine plants are a very promising solution thanks to the high efficiency, absence of stack and nearly 100% capture rate. This paper investigates the efficiency which can be achieved by the Semi-Closed Oxy-Combustion Combined Cycle (SCOC-CC) with state-of-the-art and future blade materials. In particular, the analysis considers class-H turbine super-alloys with a maximum blade wall temperature of 900 °C and Ceramic Matrix Composites with blade wall temperatures of 1300 °C. Sensitivity analyses are performed to determine the optimal pressure ratio and turbine inlet temperature. The results indicate that state-of-the-art superalloys allow the SCOC-CC to achieve 54% net electric efficiency with 96% carbon capture rate, while CMC blades boost the efficiency up to 60%. For both cases, critical factors are the high temperature gradients across the blade coatings (TBC for superalloy, EBC for CMC) and the blade thickness caused by the large heat flux exchanged between hot gases and cooling flows.
Turbine Vane Passage Experiments Documenting Evolution of Secondary Flows With Changes in Combustor Coolant Injection Flowrates
Authors: Nawathe Kedar P. , Kim Yong W. , Simon Terrence W.
Published: October 2022

A secondary flow system with a dominant passage vortex pattern has been observed in many gas turbine vane passage studies in which there is no upstream coolant injection or only near-passage endwall coolant injection (no combustor cooling). However, it was shown in recent studies that combustor coolant introduced upstream of the vane passage changes secondary flow patterns in the passage. This results in a different secondary flow vortex system, called the ‘impingement vortex’ system. It was discussed in recent literature having combustor coolant injection. Until now, there has been no study on how increases in combustor coolant momentum effect transition from the passage vortex system to the impingement vortex system. Such a study is presented in the present paper. Velocity component measurements are taken using a five-hole probe at three axial locations in the vane passage to document secondary flow development throughout the passage. Four combustor coolant flowrate cases are considered along with a comparison case having no coolant injection. It is shown that as the combustor coolant flowrate increases, the passage vortex system weakens and, at a sufficiently high combustor coolant flowrate, the impingement vortex system appears. Knowing the detailed flow physics of this transition between the two secondary flow systems is helpful for turbine thermal designers who wish to understand how secondary flows transport coolant within the turbine vane passage.
Improving Gas Turbine Maintenance Quality
Authors: Angello Leonard , Scheibel John , Noble David , Smith Nick
Published: October 2022

Planned maintenance outages account for over 70% of gas turbine unit unavailability. A complete overhaul of a large frame-sized gas turbine can require up to 10–12 weeks. Improper reassembly procedures and wrongly applied maintenance practices can ultimately result in catastrophic failure and loss of human life. To address owner/operator growing concerns regarding the quality of gas turbine planned maintenance outages, EPRI in conjunction with its member companies has developed and demonstrated key tools, methods, and guidance for improving the disassembly, inspection, reassembly, and re-commissioning gas turbine units during planned outages, including:

• Key maintenance activity check lists that include disassembly and reassembly hold points, verification points, and witness points with acceptance criteria

• Inspection techniques and quality control Inspection Assessment Data Sheet (IADS) forms for the rotating, stationary, combustion, and structural turbine parts. Each IADS includes a sketch or photo of the part, expected dimensions, typical findings, and field repair methods with GO- or NO-GO acceptance criteria.

• Companion field guidance (FG) for each IADS, with recommendations for typical damage findings

• Reassembly hold points, verification points, and witness points with acceptance criteria (both typical and not-to-exceed criteria)

• Application of PCRT testing for part quality control verification

This paper discusses outages in detail and giving insight on best practices and how advances in diagnostics and knowledge transfer are improving these activities for utilities.
Insights Into the Unsteady Shock Boundary Layer Interaction
Authors: Hergt A. , Klinner J. , Willert C. , Grund S. , Steinert W.
Published: October 2022

The flow through a transonic compressor cascade is characterized by high unsteadiness due to the shock boundary layer interaction. Investigations in recent years have shown that a detailed understanding of the causes of unsteady shock oscillation is necessary to develop successful approaches to influence it. Therefore, an experimental investigation of the unsteadiness of the shock boundary layer interaction in a transonic compressor cascade has been conducted within the transonic cascade wind tunnel at DLR in Cologne. At an inflow Mach number of 1.05, detailed measurements were carried out with a time-resolved PIV system in combination with a high-speed shadowgraphy setup. In this way it was possible to simultaneously measure both the shock movement and the flow field of the boundary layer under the shock. The analysis of the measured data showed a correlation between the oscillation behaviour of the passage shock and the unsteady flow behaviour within the boundary layer in front of the shock. In the shock oscillation spectra a dominat frequency at 1683 Hz and their first harmonic was found. This frequencies are also be found in the boundary layer flow below and in front of the shock with different amplitutes at three analysing points in the measured PIV Region. A detailed analysis of the measured data shows that the information of the unsteady shock oscillation propagates under the shock foot over the boundary layer upstream. It becomes clear that the propagation of the oscillating pressure information has an influence on the velocity component normal to the blade surface. This leads to a oscillating flow angle close to the blade. Through this effect, the inflow in itself interacts with the shock front and influences the shock position and structure. Based on this, a new thesis of self-exciting shock oscillation is developed. In addition, the used time-resolved PIV measurement enables an acquisition of the blade vibration behaviour. Within the results of the blade vibration four Eigenmodes are observable. In this context it has been shown that the Eigenmodes of the blades are not stimulated by the flow. On the other hand there is also no exciting interaction of the blades with the flow detectable. The measured data of transonic flow within a compressor cascade presented here are unique and provide new insight into shock movement and interaction with the boundary layer.
Using Blade Surface Heat Transfer for Partial Intercooling and Thrust Augmentation
Authors: Gannon Anthony J. , Morgan Thomas , Smith Walter C. , Hobson Garth V.
Published: October 2022

Gas turbine engines are widely used prime movers in aircraft. A thermodynamic tool to analyze the improvement to aircraft high bypass ratio engines using existing aerodynamic stator and outlet guide vane surfaces for heat exchange to achieve decreased specific fuel consumption is presented. The potential benefits are twofold, heat removed from the high pressure compressor stator blade rows reduce the compressor work while rejecting this heat to expand the bypass flow increases the thrust. Concepts for recuperated and intercooled gas turbine engines for aviation have been investigated but these usually make use of additional heat exchange devices through the cycle. While these approaches are successful on land based systems, weight and integration issues limit their benefit in aviation. While previous work has shown that the equivalent heat exchanger effectiveness, ε, is only expected to be 0.2 but this is offset by the limited weight gain and potentially simpler integration into a flight worthy system. A system to transfer the heat between blade rows is required and a heat pipe or heat pipe loop is proposed. The method is applied to a representative engine where the decreased compressor and increased bypass flow thrust is shown to improve the specific fuel consumption by 2.99% for the static thrust case and 9.34% at cruise conditions.
Sensitivity of Adiabatic Cooling Effectiveness to Mainstream and Coolant Temperatures in Transonic Flow Over an Idealized Blade Tip Model
Authors: Ma Haiteng , Zeng Wei , Dai Siming , Jiang Hongmei
Published: October 2022

Film cooling, as a key technology to ensure turbine survival in new generation gas turbines, has been studied profusely in subsonic flows. But in transonic flow, the determination of adiabatic cooling effectiveness faces a dilemma in the state of the art. Specifically, derivation of reference temperature, or local recovery temperature, in adiabatic effectiveness is disputable. Some researchers designate it to be the adiabatic wall temperature for the uncooled model (linear regression method, LRM), but others calculate it from an iterative procedure based on a pair of cooling tests (dual linear regression method, DLRM). As the first of the kind effort to explore this dilemma, this paper carried out transient thermal measurements by infrared thermography, for transonic flow over an idealized blade tip model. Heat transfer experiments were conducted for the uncooled and cooled cases, at two mainstream temperatures of 340K and 325K, and two coolant temperatures of 276K and 287K. Data from these six experimental groups were processed by LRM and DLRM respectively, to obtain heat transfer coefficient and adiabatic effectiveness, whose sensitivity to mainstream and coolant temperatures is tested and compared. It is found that heat transfer coefficient is basically insensitive to temperature boundary conditions and data reduction methods, as expected. However, for adiabatic effectiveness, LRM results are sensitive to the 11K decrease of coolant temperature in areas confined to the upstream of cooling injection, and much less so to the 15K rise in mainstream temperature. DLRM result, derived from the test pair with two coolant temperatures, reduces globally and conspicuously with 15K increase in mainstream temperature. Furthermore, adiabatic effectiveness obtained by LRM is qualitatively different to that by DLRM, which is mainly attributed to the large discrepancy of reference temperature between the two methods.
Wall Curvature Effect on Overall Thermal Performances of Film Cooling Covered by Thermal Barrier Coatings With Various Geometries
Authors: Zhou Wen-li , Pu Jian , Zhang Tiao , Wang Jian-hua , Wu Wei-long , Su Hang
Published: October 2022

Film cooling coupling with surface thermal barrier coating (TBC) has been widely adopted, bringing to an intensive need of comprehensive overall thermal characteristics. In present work, combined effects of hole-geometry, wall curvature, and cooling air flowrate on the metal overall effectiveness and wall heat flux were discussed. Typical local regions of turbine vanes were simplified as convex, concave, and flat walls. Spraying TBC generated four hole-configurations, including Standard Cylindrical-hole (SC), transverse Trenched-hole (TT-hole), and two modified trenched-holes with Semicircle-shaped Trench (ST) and Sine Wave-shaped Trench (SWT). The ST reduces the exposed area and the SWT improves the fluid-diversion effect of TT. Based on the engine-matched hot-side Biot-numbers, overall cooling effectiveness measurements were carried out under typical blowing ratios (BRs) from 0.5 to 2.0, through capturing wall temperatures by an infrared thermal sensor and thermocouples. Conjugate heat transfer simulations were also conducted, showing good agreement with the experimental data and hence providing additional insights into the heat transfer features and film cooling jet behaviors. The results indicated that the wall curvature effects on overall thermal parameters are relatively weaker, in comparison with the hole-geometry and BR. The trenches can further weaken the wall curvature effect. Comparisons of trench-designs reveals that achievement of strong fluid-diversion in trench is an important principle of trench-modification, which can acquire not only superior overall cooling characteristics, but also a relatively large ability to prevent the hot gas ingestion and the hole-blockages by harmful contaminant-depositions.
Investigations on Cooling Hole Patterns Over a Turbine Endwall for Improving Cooling Effectiveness
Authors: Yang Xing , Zhao Qiang , Wu Hang , Feng Zhenping
Published: October 2022

Redistributions of film hole patterns over the endwall region of a turbine vane are investigated in this work, for providing effective coverage for the entire endwall surface. Air enters the linear cascade with a turbulence intensity of 10.8% that is measured in front of the cascade inlet and exits the cascade passage with an averaged Reynolds number of 5.52 × 105. Three film injection patterns are employed: a baseline scheme in which coolant is injected from twelve pressure-side (PS) and four suction-side (SS) discrete holes as well as an upstream slot, a curtain cooling scheme in which two rows of discrete holes (totally thirteen holes) are included in the PS region at the passage inlet, and a hole-redistributed scheme in which the number of the PS holes is reduced and the PS and SS holes are redistributed. Film cooling effectiveness over the endwalls cooled by the three injection patterns is measured using the pressure-sensitive paint (PSP) technique for a density ratio of 1.5 and typical coolant flow rates found in a real engine. Additionally, aerodynamic data is measured by a five-hole probe at the cascade exit to demonstrate the effects of the injection from different hole patterns on flow fields throughout the cascade passage. Comparisons among the three hole patterns reveal that by increasing coolant rates, cooling effectiveness from the slot injection is significantly increased while that from the curtain injection upstream the passage inlet and hole injection within the passage is slightly varied. Although the slot injection is an effective cooling source, it leaves the PS region of the endwall passage uncovered, which can be well alleviated by using the curtain cooing instead of the PS hole injection. Overall, the curtain cooling provides better cooling effectiveness at an equal or even lower coolant flow rate, compared with the baseline configuration, and the hole-redistributed scheme generates better local cooling performance.
Investigation on Exhaust Energy Recovery System Using Radial Turbine in High-Power Proton Exchange Membrane Fuel Cells
Authors: Jiuxuan Wei , Mingxu Qi , Hong Zhang , Xue Li
Published: October 2022

With the increased power density and capacity of the proton exchange membrane fuel cell (PEMFC) stack, the intake air pressure level is getting higher and can reach up to 3.5bar in some cases, leading to a higher exergy level of the exhaust gas at the fuel cell cathode. To improve the system efficiency of the PEMFC, the energy of the fuel cell exhaust gas at the cathode side can be recovered with a turbine and partially drive the compressor to save part of the power needed by the electric motor. To evaluate the potential capability of the PEMFC exhaust gas recovery, detailed insights regarding the energy recovering capability of the turbine from exhaust gas energy as a result of gas supply pressure, air stoichiometric ratio, current density and operating temperature are presented in the current study. A systematic model of the fuel cell system is established and validated. The model includes the air supply system, electric motor driven turbocharger, fuel cell stack components and necessary pressure drop as well as the gas dynamic model inside the stack. The model can be used to simulate the recovery process of the exhaust gas energy at arbitrary fuel cell operation loadings. It can be used to predict the system energy recovery efficiency once the loading condition of the fuel cell is known. Results indicate that the energy recovery system performance is determined by the fuel cell operating conditions. Results also show that the gas inlet state, current density, electrochemical reaction process and pressure loss play a key role in the recovery efficiency of the turbine and the ratio of recovery power to fuel cell output power. The recovery efficiency is higher at a larger pressure ratio and current. To verify the accuracy of the system model, a high-power fuel cell is used for validation, the rated power of the proton exchange membrane fuel cell stack is calibrated through the electrochemical model from the energy recovery system and good agreement is achieved between the simulation and experiment.
Adjoint Optimization of Centrifugal Compressor Rotor Accounting for Manufacturing Uncertainties
Authors: Aissa Mohamed H. , Racca Alberto , Mueller Lasse , Verstraete Tom , Williams Carnell E.
Published: October 2022

The paper addresses the problem of the design optimization of turbomachinery components while considering the impact of manufacturing uncertainties.

Standard optimization procedures evaluate only the component nominal shape, which is altered till the achievement of the project targets. The verification of the influence of the geometrical tolerances on the robustness of the machine is performed during the late validation phase, thus exposing the design activity to the risk of incurring in unfeasible solutions, when considering the full envelope of real shapes determined by the manufacturing process.

The present work tackles the issue of robust optimizations by developing a strategy based on the Uncertainty Quantification (UQ) method within an adjoint-based multidisciplinary optimization framework. The novel methodology exploits the capability of gradient-based methods in converging to the optimal solution in few design iterations, while the addition of a UQ technique based on an extension of the Probabilistic Collocation method allows the propagation of the uncertainties on the design parameters to the mechanical constraints and the gradients of the constraints.

The methodology is applied to the robust optimization of a turbocharger centrifugal compressor rotor. The proposed approach provides a more reliable design against manufacturing tolerances with a computational overhead exceeding less than 30% the cost of a corresponding deterministic optimization.
Magnetic Resonance Velocimetry of a Turbine Blade With Engine-Representative Internal and Film Cooling Structures
Authors: Ma Haiteng , Liu Yisu , Lai Youkui , Ouyang Hua , Ning Jia , Jiang Xianwang , Xu Qin
Published: October 2022

As a key technology to ensure the survival of turbine blade, gas turbine cooling encompasses a whole range of cooling strategies with ever-increasing geometric complexities. Flow measurement for turbine blade with such intricate internal and external cooling structures is very challenging, and calls for non-intrusive, three-dimensional measuring techniques. As a response, this work measures the three-dimensional velocity field in a gas turbine blade cooling design by Magnetic Resonance Velocimetry (MRV). A scaled GE-E3 turbine blade with engine-representative internal and film cooling structures was employed. The internal cooling structure includes leading edge impingement cooling, U-shaped serpentine passage with/without turbulence ribs at blade mid-chord and trailing edge pin fins. The external cooling structure includes film holes near the leading edge stagnation point, at the blade tip and in the trailing edge. The experiment was performed using water as the working fluid and the Reynolds number local to the leading edge, mid-chord and trailing edge cooling channels is 1.3 × 103, 5.1 × 103 and 2.3 × 103, respectively, which falls within the range typically found in literature. This is the first time that MRV is used to measure the flow field of a gas turbine blade with all the typical internal and external cooling geometries combined. The results show that MRV has great capacity in measuring the complex fluid flow of a gas turbine blade cooling design. Vortical flow features in leading edge impingement cooling, and at the U-bends of three-pass serpentine channel are captured. Interestingly, internal flow around pin fins at the blade trailing edge redistributes the velocity of external flow injected from trailing edge slots and film holes, indicating strong coupling between the internal and film cooling flow of the turbine blade.
Design Considerations and Validation of a Near Wall Cooled Stator Heat Shield With Sequential Impingement Cooling
Authors: Peschke P. , Naik S. , Henze M.
Published: October 2022

The reduction of cooling air for first stage turbine components plays a vital role in improving the performance of heavy-duty gas turbines. To achieve this goal detailed knowledge of the external heat loads is required as well as introducing novel technologies to reduce the cooling air consumption.

This paper gives an overview of the design considerations and validation for a technology upgrade of an Ansaldo Energia heavy-duty gas turbine first stage stator heat shield.

The heat transfer of the heat shield surface flow is influenced by the complex flow pattern that is created by the interaction of the rotating blade tip with the surface boundary layer, in the presence of leakage air and the wake of the upstream vane trailing edge. The present paper discusses results from CFD computations and laboratory experiments that investigate this interaction, as well as results from full scale engine tests. It is shown that both the wake of the upstream vane and the blade passing have a crucial influence on the heat transfer that needs to be considered during the design phase of the stator heat shield.

Furthermore, the implementation of a novel cooling concept with sequential impingement cooling from laboratory tests to engine ready technology is shown. A comparison of airflow measurements of the new heat shield with a conventional impingement design demonstrates a significant reduction in cooling air flow. Metal temperature measurements in full scale engine test with thermal paint, thermocouples and thermal crystals show similar metal temperatures compared to the conventional design.
Dynamic Response of Stratified Flames to Acoustic Excitation in a Multi-Swirler Model Combustor
Authors: Liu Weijie , Jin Ming , Ge Bing , Xue Ranran , Su He , Zang Shusheng
Published: October 2022

Flame response is a key element in predicting thermoacoustic instabilities in gas turbine combustors. Flame dynamic response of single swirling flames to acoustic excitation was well studied in the past decades, while the unsteady dynamic of multi-swirling flames, such as stratified flames, is not fully reported. This paper presents dynamic response of stratified flames in a multi-swirler combustor which includes a main stage and a pilot stage. The stratified flame contains an outer main flame and an inner pilot flame. The overall Flame Transfer Function (FTF) of the stratified flame is extracted during the experiment. High-speed camera and high-frequency Particle Image Velocimetry (PIV) are used to capture the evolution of the flame and flow structure.

Experimental results show the overall flame transfer function of the stratified flame features several discrete peaks and valleys in a narrow frequency range which is slightly different with a typical simple swirling flame. The main flame is stabilized at the inner shear layer region of the main flow while the pilot flame settles at a position where turbulent flame speed equals to the local pilot flow speed. The effect of the acoustic driving on the topology structure of the stratified flame is not apparent. Proper orthogonal decomposition of the stratified flame shows a wave of alternating positive and negative values across the flame indicating flame fluctuations are in axial modes. Proper orthogonal decomposition of the multi-swirling flow reveals coherent structures are formed in the shear layer of the main flow which dominates the stratified flame response.
Development of a Fuel Flexible H2-Natural Gas Gas Turbine Combustion Technology Platform
Authors: Witzel Benjamin , Moëll Daniel , Parsania Nishant , Yilmaz Ertan , Koenig Michael
Published: October 2022

Siemens Energy is developing the required technologies to operate its gas turbines on up to 100% H2 by 2030 to support the target of limiting global warming to 1.5 degrees Celsius. A focused effort has been undertaken to develop a technology platform for the Siemens Energy GT portfolio which will enable GT operation across the entire range H2/natural gas blends within emissions compliance. A first engine demonstration of these technologies in an industrial application will be conducted in an SGT-400 engine in 2023 as part of HYFLEXPOWER, an EU Horizon 2020 funded consortium project.

This paper will present the results of numerical and experimental investigations of several candidate dry low NOx technologies. The candidate technologies are all lean, premixed designs and include: a swirled flame primary stage, a jet-based flame primary stage and an axial stage. The experimental results are conducted at elevated pressure and temperature conditions representative of the Siemens Energy gas turbine fleet. Additionally, a comparison of different kinetics mechanisms which offer the potential to accurately model flames burning H2, natural gases, and combinations of these fuels will be presented. The mechanisms include GRI 3.0 as well as three mechanisms which have been previously developed to improve the accuracy with high H2 content fuels.
Experimental and Numerical Investigation of a Novel Method for Gradient Temperature Measurement
Authors: Schönheit Markus , Thiele Marcus , Ginzbursky Edward , Thomas Anastasia
Published: October 2022

Hot gas temperature and mass flow rates are continuously increasing to meet future gas turbine power, efficiency and emission targets. Moreover, expectations for flexible operating capability can add conditions for frequent cold starts and load changes. To realize such gas turbine developments, improved cooling concepts are required to guarantee the lifetime of thermally highly loaded components such as turbine blades, vanes, blisks and combustor rings. In addition to design and metallurgical adjustments to the components, this also requires validated calculation and design methods. As described by Thiele et. al. [1], a visco-plastic material model has been developed which shows the significant influence of superimposed thermal gradients on the low-cycle failure life. Reliable temperature gradient measurements are required to validate the material models, FEM and CFD simulations and the fatigue life. Accurate in-situ measurement capability in real engine conditions is particularly challenging which existing measurement methods only cover to a limited extent.

A novel application using Uniform Crystal Temperature Sensors (UCTS) with two different minimally invasive application methods is proposed and evaluated here. The sensor installation package is micro size, with a diameter that can be less than 1mm and a length that can be adjusted to the available wall thickness of the part and the expected gradient through the wall. Experimental work to validate the measurement accuracy of the UCTS was carried out using a highly efficient, patented radiation furnace reported in GTP-18-1482, which can apply a heat flux of q ≥ 1.5 MW/m2 and a thermal wall gradient of up to 65 K/mm.

In order to validate the novel measurement system both experimentally and numerically, measurements with calibrated thermocouples and thermo-mechanical simulations were performed. For the temperature gradient data generation, the UCTS were integrated in a MAR-M247 hollow cylinder specimen in various configurations. The conventional cast nickel based alloy MAR-M247 is a typical turbine blade material. Its thermo-physical properties are well studied and it has been part of thermally loaded and temperature gradient investigations for several years. The paper focuses on the validation and application of the UCTS measurement system and shows its potential for investigating actual operating conditions of highly thermally loaded real engine components. Information from this study will be applicable to gas turbine design and development engineers needing in situ gradient measurements for rig or real engine testing programs.
Life-Cycle-Assessment for Rough Machining of Inconel 718 Comparing Ceramic to Cemented Carbide End Mills
Authors: Fricke Kilian , Zimmermann Richard , Ganser Philipp , Gierlings Sascha , Bergs Thomas
Published: October 2022

Nickel-based alloys such as Inconel 718 belong to the group of heat-resistant super alloys. Combined with good mechanical properties over a wide range of temperatures nickel alloys are used extensively in the aero engine sections exposed to elevated temperatures. Besides turbine blades and discs, integrally designed compressor rotors (Blisks) in the high-pressure compressor (HPC) are increasingly made of Ni-alloys. This is the result of an efficiency-driven increase in temperature levels in the rear compressor stages. The machining of these hard-to-machine materials is characterized by low productivity and high tool wear. Compared to the machining with conventional cemented carbide end mills, innovative SiAlON ceramics offer a significant potential to increase the performance of these machining processes while saving cooling-lubricants. Besides an increase in productivity, the evaluation of the overall environmental impact of specific manufacturing processes is gaining importance in the context of more sustainable product life-cycles. This paper focuses on the comparison of different milling strategies in the production of high-pressure compressor rotors made from Inconel 718 in a cradle-to-gate assessment based on DIN EN ISO 14040/44. Thus, the ecological impact of both the state-of-the-art and the novel SiAlON roughing strategy are evaluated considering the consumption of energy, water and compressed air as well as the tool wear. The Life-Cycle-Impact-Analysis (LCIA) will be performed as a midpoint analysis taking multiple indicators into account such as the Global Warming Potential (GWP).