bluuebunny/crossref_metadata_2025 huggingface dataset:
Tool Wear Prediction in Broaching Based on Tool Geometry
Authors: Zachert Christoph , Meurer Markus , Bergs Thomas
Published: August 2024

The aircraft engine is a safety-critical part of an aircraft. Constructive modifications resulting in ecological and economic improvements of the engine lead to necessary changes in manufacturing processes. The turbine discs in the low-pressure section are made of temperature resistant nickel-based superalloys. For the connection of the turbine blades with the disc, fir-tree slots are machined by broaching. The broaching process achieves high geometrical accuracy as well as process reliable rim zone properties. Alternative manufacturing processes such as milling or wire electrical discharge machining are still the subject of research in many applications and do not yet achieve the required process reliability.

Especially in finishing operations, tool geometry is complex. In previous research work, the local rake angle and, as a result, the acting cutting force were determined analytically and empirically. Based on these results, the relationship between tool geometry, cutting force, and tool wear will be investigated in this work to enable a cutting length dependent prediction of tool wear. The aim of this work is a model-based prediction of tool wear for a given cutting length and a previously unknown tool geometry. For this purpose, a method was developed to predict tool wear using empirical test data as well as internal machine data. With the results of this work, it is not only possible to identify critical points on newly developed broaching tools by maxima of the cutting force, but also to predict wear locally, depending on the cutting length. Thus, tools can be optimized, and efficiency of the broaching process is increased.
CFD Analysis of Inlet Flow Region in a Centrifugal Compressor
Authors: Sudheer Meera , Dhinne Giridhar Kumar , Hoch Greg
Published: August 2024

The inlet region of a typical multi-stage centrifugal compressor for oil and gas applications consists of an inlet flange/nozzle, splitter vanes, and inlet guide vanes (IGVs). Recent findings of an existing legacy multi-stage centrifugal compressor, which had been recently revamped, indicated a lower flow capacity than what is expected. Further testing of the compressor revealed a potential scope for improvement in flow capacity. After performing stage-by-stage analysis, it was determined that an improvement in the design of the inlet region could enhance the performance. The inlet region plays a crucial role in guiding the flow towards the impeller, ideally distributing the flow uniformly with minimal loss. Flow distortions may occur in any inlet, the extent of which may differ depending on its design and can further lead to poor performance characteristics of the compressor. This paper will describe the work completed to reduce the flow losses and distortions in the inlet region by performing Computational Fluid Dynamics (CFD) analysis with the help of a simulation software. A parametric study was carried out to optimize the flow characteristics in the inlet region, where it was observed that rotating the IGV angles by a certain amount, loss coefficient and pressure distortions are reduced. The results obtained and lessons learned can be used for enhancing the performance and improving existing correlations when designing future compressors.
Shear-Driven Hydrogen-Air Mixing in OP16 DLE Combustor: A Comparative Study Between URANS and LES
Authors: Donepudi Teja , Pecnik Rene , Peeters Jurriaan W. R. , Klein Sikke , Bouten Thijs , Axelsson Lars-Uno
Published: August 2024

This paper presents numerical predictions of the flow field in the swirl-stabilized OP16 DLE combustor using hydrogen as a fuel. Computational Fluid Dynamics (CFD) simulations employing unsteady Reynolds-Averaged Navier-Stokes (URANS) and Wall Modelled Large Eddy Simulations (WMLES) are performed without including reaction mechanisms. The objective is to gain insights into scalar mixing predictions of the two approaches when hydrogen and air undergo shear-driven turbulent mixing. Accurate scalar mixing predictions are crucial in the combustors’ design process to assess the uniformity of fuel-air mixing as localized regions of high fuel concentrations can lead to increased NOx emissions and to identify locations with a propensity for Boundary Layer Flashback (BLF). Results are compared and analyzed in terms of time-averaged equivalence ratio, unmixedness and Turbulent Kinetic Energy (TKE) profiles. TKE predictions are lower in URANS, leading to significantly lower fuel-air mixing levels than WMLES, indicating differences in their predictions of shear-layer interactions in the mixing region and the swirl section of the combustor.
Design and Analysis of a Liftfan for eVTOL Aircraft
Authors: Hine Rory D. , Cousins Dominic R. , Maden Leo , Walker Samuel J. , Atkins Nicholas R. , Grimshaw Samuel D. , Taylor James V.
Published: August 2024

Ducted liftfans can provide greater hovering efficiency to eVTOL aircraft than open propellers of an equal disk area. The goal of liftfan design is to minimise length in order to limit the weight added by propulsors and the drag incurred during forward flight. The increased complexity of liftfans over open propellers poses three challenges which are addressed in this paper.

First, instead of a single row propeller, the liftfan consists of a complete stage which must be designed as a whole. The preliminary and 3D design variables of the rotor row and splittered-diffuser stator row are optimised together using 3D CFD to maximise the hovering figure of merit, a non-dimensional measure of power consumption. The resulting prototype liftfan design is validated through experimental testing.

Second, unlike an open propeller, a liftfan rotor is enclosed within a complete nacelle. To be viable, it must perform effectively during edge-on forward flight, as well as in pure hover. A low-order model is developed to investigate the maximum range for different fan designs with varying diffuser area ratios and forward flight tilt angles. Design selections are validated using full annulus 3D CFD and experimental wind tunnel tests.

Third, as the electric motor of a liftfan is mounted within the hub, fan-driven active cooling is necessary to prevent overheating. The stagnation pressure losses incurred by cooling airflow must be minimised without impeding heat transfer. Low-order models are developed to predict motor heat transfer and loss and to guide the design of a mixed-flow cooling fan. The addition of forward sweep and adoption of a high blade count are found to reduce cooling fan loss, confirmed through 3D CFD simulations and experimental testing.
Efficient Modelling of Blade Cooling Using a Hybrid 1D-3D Approach
Authors: Kainz Marc , Britz Vincent , Du Toit Bennie , Morales Juan Carlos
Published: August 2024

The first turbine stages downstream of the combustor are subjected to extreme high temperatures. Simulating the flow and heat transfer in and around the blades is therefore crucial for optimizing cooling and achieving the highest possible engine efficiencies.

The blade cooling optimization process requires iteration on many parameters. Due to the disparity in the geometrical length scale between the blade itself, the internal cooling channel structures, and the cooling holes, meshing and solving the cooling flow inside a turbine blade using a full 3D CFD model is very time-consuming and costly.

1D CFD codes allow for detailed and efficient modelling of the internal cooling flow in the conceptual design stage. The effort involved and the computational cost are orders of magnitude less than for a fully resolved 3D internal flow CFD simulation. In contrast, the main passage flow simulation is still well suited to a 3D CFD model.

The current work describes the coupling of a 1D flow and heat transfer network model to account for the internal cooling structures with a 3D CFD model for the main passage flow on a typical gas turbine vane geometry. The so-called injection region model was used to model the film cooling flow injection at the vane surface without having to resolve each hole patch by the surface mesh itself.

The paper presents a validation of the injection region model, and it compares the results of the different modelling approaches, including the hybrid 1D-3D model.

The 1D network model is able to predict accurate film cooling inflow conditions for the 3D CFD simulation. The results of the injection region model show good agreement with that of the fully resolved 3D simulation. Therefore, it has the potential to speed-up the film cooling simulations in the early design phase.
Numerical Investigation of Flow Structure and Pressure Drop Prediction for Radial Inflow Between Co-Rotating Discs With Negative Effective Inlet Swirl Ratio
Authors: Xu Yang , Ding Shuiting , Liu Peng , Zhao Yu , Qiu Tian
Published: August 2024

This paper presents a numerical simulation of the flow structure of radial inflow between co-rotating discs with a negative ceff (effective inlet swirl ratio), which may occur in a vortex reducer equipped with deswirl nozzles. When the value of ceff approaches zero, asymmetric flow structure is observed in the cavity, possibly as a result of the “Coanda effect”. Besides this, the flow structure inside the disc cavity at ceff < 0 can be divided into a source region, a sink region, an interior core region, and two Ekman layers, which is identical to the situation when 0 < ceff ≤ 1. However, there exist two distinct patterns: the stagnation point on the disc and on the peripheral. According to a theoretical analysis, ceff = −1/8 is used to distinguish between these two patterns.

Based on flow structure partitioning, a theoretical model for predicting the swirl ratio (V¯) radial distribution and pressure drop in a disc cavity with ceff < 0 was established. The model employs the turbulent boundary layer integral method, and von Karman’s assumption of velocity profile and wall shear stress for a free disc. The calculation results of the swirl ratio in the cavity are in good agreement with the CFD results except when the negative ceff approaches zero because of the deviation of the radial velocity profile from the “1/7” power law. Since the pressure drop in the cavity approaches zero at the same time when the negative ceff approaches zero, the absolute error of the theoretical model in predicting pressure drop is not significant and does not affect its practical application, which has been verified through comparison with public experimental results.
Attention-Based Model With Component Embedding for Aero-Engine Performance Estimation
Authors: Liang Yufeng , Xiao Hong , Song Shuo , You Rui
Published: August 2024

Prognostics and Health Management (PHM) technology plays a vital role in the condition-based maintenance of aeroengines. Real-time models that monitor and estimate aeroengine performance are essential in this domain. The precision, stability, and interpretability of models are paramount for aeroengine research. However, both conventional data-driven models and physics-based models grounded on the component characteristic exhibit areas that can be further refined and improved. Therefore, this study presents a novel approach to improve predictive precision by incorporating engine domain knowledge into performance estimation models. We introduce a component embedding technique that effectively captures the concealed interdependencies among parameters in the corresponding component. The features are mapped to a high-dimensional space, characterizing the different engine components separately. Furthermore, we present a pioneering model for aero-engine performance estimation based on the attention mechanism. The attention-based model implements an encoder-decoder architecture. The multiple stacked encoders are responsible for capturing crucial engine performance information at different scales. The decoder utilizes the feature map generated by the encoders to produce an accurate prediction. Experimental results on the historical operating data of turbofan engines demonstrate that our proposed model outperforms conventional models in exhaust gas temperature (EGT) estimation in both normal and degraded conditions. Naturally, the presented model can also be utilized for the estimation of other performance parameters, thus providing support for the optimization of maintenance schedules.
HFTsim: A Component Library for High-Frequency Gas Turbine Engine Performance Simulations
Authors: Güllü Emrah , Aran Gökhan
Published: August 2024

HFTsim is a gas turbine engine component library for high-frequency pre and post-stall transient performance simulations. Standard component models are extended using gas dynamic equations for duct and volume elements. This extension allows us to model the temporary accumulation of mass, momentum, and energy within the components, which is important for high-frequency transients. Gas dynamic equations, together with dynamic equations for spool inertia, delays, and heat soakage, are integrated using the implicit Euler method. HFTsim has a flexible structure to allow the formation of any gas turbine engine configuration. The accuracy and stability of the gas dynamic equations set are first checked by a simple 1-D plenum-duct system, using data from CFD computations. This data includes cases with sinusoidal boundary condition transients of different frequencies. Then, the Rolls-Royce Viper engine, a single-spool turbojet engine, is modeled using HFTsim, and its pre and post-stall behavior is validated using the literature data. Shaft-breakage simulations of the Viper engine are conducted to showcase the application of the developed methodology. Surge provides passive protection during an HP-spool breakage by reducing turbine airflow and causing an eventual combustor blowout. Terminal speeds can also be reduced by detecting the breakage and cutting the fuel. These two strategies are compared and it is concluded that the selection of the strategy depends on compressor recovery, combustor stability, and heat-soakage characteristics.
Development of a Toroidal Jet-Stirred Reactor for Lean Blowoff and Emissions Studies of Ammonia-Hydrogen Mixtures
Authors: Zamora David , Ahmed Marzuqa , Barrios Cadenas Guillermo , Maia Amanda , Garai Priyankar , Bobi Shahzad , Rahman Ramees K. , Urso Justin , Vasu Subith S.
Published: August 2024

The present paper describes the design of a toroidal jet-stirred reactor (TJSR) for lean blowoff and emissions studies of ammonia-hydrogen mixtures at atmospheric pressure, with provisions for high-pressure testing in the future. The TJSR is a kind of well-stirred reactor experiment that has been used by other researchers for understanding the combustion characteristics of fuels. It consists of a ceramic torus, jet ring, casing, and exhaust pipe. Chemkin-Pro was used to approximate the flow rate through and the temperature inside the ceramic torus. The jet ring was made from Inconel 625; its design is a tradeoff between having sufficient wall thickness for storing pressure while minimizing the length of the nozzles. Thermomechanical simulations were conducted in Ansys Mechanical to determine the stresses and expansion of the reactor at operating conditions. ASME codes were used to design the exhaust pipe and flanges. Laser absorption spectroscopy will be used to measure the chemical species in the exhaust, so optical ports were designed to fit in the exhaust pipe’s flanges. Passages were designed in the optical ports for cooling the windows. Future work will consist of testing the reactor at atmospheric pressures and then modifying it to fit in a pressure vessel for high pressure.
Evaluating Thin-Film Thermocouple Performance on Additively Manufactured Turbine Airfoils
Authors: Berdanier Reid A. , Nunn Margaret R. , Brumberg Justin T. , Barringer Michael D. , Fishbone Scott , Thole Karen A.
Published: August 2024

As gas turbine engine designs continue to target higher turbine entry temperatures for increased thermal efficiency, gas turbine manufacturers and operators require additional feedback from life-limited engine components. Moreover, additively manufactured (AM) hardware is becoming more prevalent in the engine development cycle to reduce component lead times and associated costs. Although additive manufacturing unlocks unique capabilities for sensor integration, the inherent roughness from additive surfaces poses unique challenges to the direct-write sensor installation processes. The current study addresses these realities by demonstrating sensor operation on additively manufactured vane hardware in a turbine research facility operating at scaled conditions. Thin-film thermocouples were deposited on fully-cooled AM turbine vanes and tested over a range of operating conditions in a one stage research turbine at Penn State University. The low-profile surface-mounted sensors were compared with traditional small-diameter embedded thermocouples in terms of calibration accuracy and durability. A comparison between traditional masked thermal spray and direct-write installation was also evaluated as part of the sensor integration strategy for the AM vanes. Ultimately, this study shows thin-film thermocouples on additively manufactured airfoils can operate reliably over an extended test campaign in rig-scaled conditions. Furthermore, the measurement accuracy of thin-film thermocouples demonstrated through this study is equivalent to traditional mineral-insulated thermocouple sensors showing the utility of these technologies for future turbine research and development applications.
Numerical Analysis of a Nozzle Guided Vane Filled With Lattice Structures
Authors: Senegaglia Ivan , Grossi Tommaso , Macoretta Giuseppe , Monelli Bernardo Disma , Fardelli Andrea , Tripoli Girolamo , del Turco Paolo , Colantoni Simone
Published: August 2024

Gas turbines play a critical role in industries such as power generation and aviation. Additive manufacturing has emerged as a game-changing technology for gas turbine components, offering superior design flexibility and performance enhancements. The present work provides an overview of a multistep approach for integrating lattice structures into a specific gas turbine component, the Nozzle Guide Vane (NGV), using additive manufacturing technology. The first step involves a comprehensive assessment of lattice structures’ influence on the mechanical and thermal properties of the exposed part of NGV. Through computational simulations and experiments, an ideal lattice geometry is determined, optimizing structural integrity and heat transfer properties while minimizing volume usage. The second step sets the baseline performances of the current NGV system components, which were investigated and selected for additive manufacturing analysis. The third step focuses on the overall effect of additive manufacturing capabilities in the NGV system. The fourth and final step optimizes the additive manufacturing process for fabricating gas turbine components with lattice structures. Laser Powder Bed Fusion (L-PBF) technology, united with advanced Topological Optimization analyses, and high-temperature alloys were selected to withstand the demanding gas turbine operating conditions. This multistep approach represents a significant step forward in gas turbine technology, capitalizing the advanced mechanical applications as lattice designs and additive manufacturing, aiming in enhanced performance, reduced weight, and improved efficiency. These developments hold the potential to achieve more sustainable and cost-effective energy generation and transportation systems.
Digital Value Tool for Gas Turbine Digitized Cross Section
Authors: Moscardini Marigrazia , Filice Valentina , Cini Gianni , Tapinassi Libero , Berti Matteo , Brogelli Riccardo , Del Turco Paolo , Ragni Giacomo
Published: August 2024

Digital Value Tool (DVT), an innovation tool, has been developed to digitalize the conceptual Cross Section of Gas Turbines (GTs). The tool aims at reducing the lead time of the conceptual design process, speeding up the development of the conceptual cross section, pursuing a standardized approach in order to improve quality. DVT is programmed in C++ and C#, and it is built by .dll files developed in the NXOpen environment. The digitalization of the cross section is based on: GT input data, component pre-sizing based on design rules and verification loops, dynamic environment and interface automatization obtained by a dedicated parametrization. One of the main goals is shifting from the manual generation of conceptual design of cross section to a digitalized one, which is characterized by the components and their sketches being stored inside the .prt file of the 2D model. In order to achieve this goal, virtual blocks containing geometrical and non-geometrical information are automatically generated and associated to the designed components. This guarantees the storage of the engine’s DNA inside a unique file. A dedicated feature allows exporting the information inside an .xml file, which organizes data according to a tree structure resembling the engine modules. Both the .xml and .prt file cover the whole communication protocol with external tools carrying out conceptual analysis such as: component conceptual costs, rotodynamic analysis, secondary flows and thermal evaluation, clearances assessment.

The tool is constantly updated and populated for a continuous improvement being at the cutting edge of new technologies. Moreover, DVT is implemented in most of referenced industrial GT configurations.
Adjoint-Based Optimization for the Venturi Mixer of a Burner
Authors: Xu Min , Radwan Akram , Xia Yu
Published: August 2024

The optimization of Venturi mixers in burners is critical for enhancing combustion efficiency and minimizing emissions. In this study, we utilize the adjoint method to analyze and refine the design of a Venturi mixer. Our numerical simulations integrate the species transport equation with the Eddy Dissipation Model (EDM) for reacting flow and the generalized k-ω (GEKO) model to simulate turbulence. By solving adjoint equations, we effectively compute the shape sensitivity for various observables, including pressure drop, outlet fuel variance/uniformity deviation index, air and fuel mass flow rates, and outlet CO mass fraction. The shape sensitivity analysis uncovers the interplay between the observables and the appropriate weights for multiple objective optimizations. Subsequently, we perform gradient-based optimizations to enhance the mixer’s performance, employing both shape sensitivity and mesh morphing techniques. We conduct a series of case studies focusing on both cold and reacting flows. The optimization of cold flow provides an in-depth exploration of various optimization strategies, encompassing single-objective and multi-objective optimization with diverse weight combinations. Following this, the optimization under reacting flow conditions improves the fuel/air mixing, leading to the increase of combustion efficiency and hence the reduction of CO emissions. Our findings showcase the potential of an adjoint-based optimization framework in designing Venturi mixers that are efficient and emit lower levels of pollutants.
Aerodynamic Performance Improvement and Noise Control for the Multi-Blade Centrifugal Fan in Air Conditioner by Using Concave Volute Tongue
Authors: Lei Jian , Qin Guoliang , Cui Qin
Published: August 2024

The structural formation of the multi-blade centrifugal fan’s volute tongue results in a complex flow pattern. This study focuses on the design of a concave volute tongue structure to address the issues of volute tongue backflow and blade path backflow. A Bezier curve with five control points was utilized to accurately shape the profile of the concave volute tongue. Five different solutions for the concave volute tongue were developed. Comparative analysis results show that the depth of the volute tongue depression has minimal impact on the fan’s efficiency performance. However, the amplitude of noise reduction initially increases and then decreases as the depth of the volute tongue depression increases. Experimental tests and numerical simulations indicate that the implementation of the concave volute tongue structure effectively suppresses volute tongue backflow and blade channel backflow at the impeller outlet, resulting in a maximum reduction in aerodynamic noise of 0.8 dB. The sound pressure level of the multi-blade centrifugal fan with the concave volute tongue structure is lower in most frequency band under low static pressure conditions compared to its original design. The V3 multi-blade centrifugal fan demonstrates better static pressure performance across all working conditions, particularly at high flow rates. The V3 multi-blade centrifugal fan exhibits a 10.1 Pa increase in the maximum static pressure level compared to its original design. These improvements in static pressure and flow capacity of the multi-blade centrifugal fan contribute to energy savings and a reduction in pollutant emissions.
Film Cooling Performance Comparison of Blade Tips With a Trailing Edge, Pressure Side Cutback or a Suction Side Squealer in a Transonic Linear Cascade
Authors: Yeh Ming-Feng , Burdett Timothy A. , Wright Lesley M. , Han Je-Chin
Published: August 2024

Film cooling effectiveness and leakage flow play crucial roles in turbine blade heat transfer. In contrast to the conventional trailing edge cutback squealer blade tip (CB-tip), this study aims to compare the film cooling effectiveness of a suction side squealer tip (SS-tip) under different blowing ratios (M = 1.0, 1.5, 2.0) and density ratios (DR = 1.0, 1.5, 2.0).

This experiment is conducted in a 3-blade cascade wind tunnel under transonic conditions, with inlet and outlet Mach numbers equal to 0.29 and 0.75, respectively. While applying the Pressure Sensitive Paint (PSP) technique for film cooling effectiveness measurements, both top-view and side-view perspectives were employed to illustrate the distribution of local cooling effectiveness across various regions of the blade. Furthermore, two coolant injection scenarios were investigated: (i) combined tip and pressure side cooling and (ii) pressure side-only cooling. In addition to measuring the surface effectiveness, PSP can also be used to estimate the leakage flow across the blade tip by analyzing the local static pressure distribution.

For the CB-tip, the film cooling effectiveness within the cavity increases as both the blowing ratio and density ratio increase. The PSP technique clearly captures the accumulation of coolant within the cavity and the coolant discharge near the trailing edge in the vicinity of the squealer cutback. When the blade tip is outfitted with only a suction side squealer, the film cooling effectiveness on the blade tip is comparable to that of the full squealer with the trailing edge cutback. This similarity is achieved as the CB-tip design requires 14–20% more coolant to achieve the same blowing ratios as the SS-tip. The advantage of the suction side squealer is further demonstrated as leakage flow across the tip is reduced compared to the conventional, full squealer with a trailing edge cutback.
Design of Broadband Liner Based on Cremer Concept
Authors: Zhang Ji , Qiu Xianghai , Du Lin , Sun Xiaofeng
Published: August 2024

In recent years, various novel acoustic liners have been proposed to meet the broadband noise reduction requirements of turbomachinery, such as multi-degree-of-freedom liners. However, the increasing number of adjustable geometric parameters brings about the complexity of liner design. The Cremer concept has commonly been employed to the rapid preliminary design of acoustic impedance. This paper presents a broadband liner design method, which achieves rapid design of liner geometric parameters by incorporating the impedance prediction model into the Cremer concept. Moreover, this method maximizes the match between the optimal impedance spectrum and the liner impedance spectrum, thereby achieving the desired objective of broadband sound absorption for the liner. Taking the uniform single- and double-degree-of-freedom liner as examples, three optimization strategies are evaluated in this paper: 1) the least squares method; 2) minimization of cavity depth; 3) multi-frequency optimization. Extensive optimization results show that the noise reduction bandwidth of a single-degree-of-freedom liner is related to the cavity depth, and the widest bandwidth liner can be designed by targeting two specific Helmholtz numbers. Similarly, the noise reduction bandwidth of a double-degree-of-freedom liner is related to the cavity depth near the fluid, and the widest bandwidth liner can be designed by targeting four specific Helmholtz numbers. For more complex liners, as long as an appropriate impedance model is available, this method is expected to expedite the design process and alleviate design complexity.
Unsteady Flow, Turbulence and Acoustic Measurements on the Counter-Rotating DLR Turbo Fan Stage CRISPmulti, With and Without Inlet Distortions
Authors: Meyer Robert , Tapken Ulf , Klähn Lukas , Behn Maximilian , Lengyel-Kampmann Timea
Published: August 2024

Extensive aerodynamic and acoustic measurements were carried out on a counter-rotating turbofan (CRISP) stage under the influence of inlet distortions that are representative of the boundary layer ingestion of an engine embedded in the aircraft fuselage. The unsteady flow field was measured and analyzed using hot-wire anemometry upstream, between and downstream of the rotors, both with and without inlet distortions. Acoustic measurements were carried out using extensive microphone arrays on the intake and exhaust sides of the fan. This article presents exemplary measurement results, which show the significant effect of inlet distortions on turbulence and fan sound excitation.
Experimentally Verified Optimization of a Two-Stage Real Gas Centrifugal Compressor Using an Industrial-Ready Adjoint Method
Authors: Hanimann Lucian , Fleischli Benno , Mangani Luca , Casartelli Ernesto , Weickgenannt Ansgar , Lehr Andreas
Published: August 2024

Ozone depletion and global warming are major drivers for the development of cooling systems. Accordingly, new governmental regulations for the equipment are continuously introduced. The redesign of corresponding centrifugal compressors for new refrigerants is therefore necessary and remains a very challenging task. The vicinity to the two-phase region requires accurate real gas models and the complexity of the flow patterns a robust numerical integration of the underlying governing equations. This is particularly true for the considered low flow coefficient two stage centrifugal compressor. Classical design and optimization methods are limited in their flexibility because of the geometry parametrization, thus affecting the development of the next generation of turbo compressors.

This article describes the development and application of a fully-coupled, pressure based CFD framework, incorporating a highly flexible discrete adjoint method used for redesign and optimization purposes. The maturity of the underlying CFD and of the optimization algorithm makes it possible to account for real gas and turbulence effects, as well as multiple mixing-plane stage interfaces. Accordingly, it is possible to fully exploit the major advantage of this gradient based optimization strategy, the independency between computational effort and the number of degrees of freedom in the geometrical description.

Using a two-stage centrifugal compressor, the return channel is optimized to achieve an overall reduction in entropy generation. Although being a single point optimization, the resulting performance characteristic shows a consistent improvement over the whole operating range with maximum values of up to two percent. The resulting geometry is manufactured and experimentally tested on the test rig. The computationally obtained efficiency increase can be confirmed by the experimental data.
Effects of the Geometric Uncertainties of Bladed Disks Through the Analytical Derivatives of the Finite Element Matrices
Authors: Bouras Abdelhakim , Carassale Luigi
Published: August 2024

Manufacturing processes and wear are known to create imperfections in mechanical components that may result in a significant deviation of the modal properties from their predicted values. This is especially true for symmetric structures such as bladed disks, where even small variations in the blade geometry can cause mistuning. The effect of parameter variations on the model is commonly assessed through sensitivity analysis within the framework of uncertainty propagation or structural optimization. Different formulations are available when dealing with the variation of a single scalar parameter. The problem becomes more complicated when the source of the variation is the whole component geometry. To deal with this case, it is necessary to define a representation able to describe the shift from the nominal geometry through a finite set of parameters and compute the derivatives of the system matrices with respect to those parameters. This paper proposes to compute analytically the derivatives of the system matrices with respect to the geometric variations. The derivatives are calculated at the finite element (FE) level, and then are assembled into global derivative matrices. Using directional derivatives, the sensitivities of the system matrices are computed with standard FE numerical schemes based on the nominal geometry.
Performance Simulation and Off-Design Performance Control of Reheat Gas Turbine Engines
Authors: Li Yi-Guang , Liu Yang
Published: August 2024

A reheat gas turbine engine with a sequential combustion system has the potential to offer high cycle efficiency at moderate turbine entry temperatures. Consequently, it has one more degree of power setting control, which offers more flexible but also more complex control of engine off-design operations. An example of such a design with reheat is GT24/GT26 industrial gas turbine engines. In this paper, a novel simulation method for off-design thermodynamic performance of reheat gas turbines has been introduced and a novel performance control schedule for part-load operations at various ambient conditions have been proposed aiming to keep the relative workloads between the two turbine sections constant. The proposed control schedule is simple and can be adapted easily. By applying the off-design performance control schedule to a model reheat industrial gas turbine engine similar to GT24/GT26 gas turbine engines, the performance of the model engine is simulated at different part-load and at different ambient pressures and temperatures. The results show that by applying the proposed off-design performance control schedule, the model reheat gas turbine engine could operate effectively at different part-load operating conditions and at different ambient conditions with both turbine sections keeping nearly constant workload distributions.
Smart Industrial Gas Turbine Low-Cost IoT Architecture
Authors: Panov Vili , Cruz-Manzo Samuel , Goloshchapov Egor
Published: August 2024

The smart energy systems, based on the numerous digital technologies, became an integral part of the current efforts to revolutionize energy production. One of the main cornerstones of smart energy concept is connectivity, which is typically enabled through Industrial Internet-of-Things (IIoT) technology.

In this contribution we present a development of Low-Cost Internet-of-Thing (IoT) architecture with the intention to provide a secure and reliable connection of Industrial Gas Turbine (IGT) systems with Cloud environment. We utilized simulation environment, to explore integration of the Executable Digital Twin with IoT Gateway, with subsequent deployment onto dedicated Low-Cost Edge platform.

The developed IoT gateway architecture encompasses key features related to connectivity, computing power, and communication capability. The proposed Low-Cost IoT architecture supports Live Data Streaming (LDS) which allows remote monitoring and Real-Time (RT) analytics of IGT system. The IoT gateway platform satisfies the requirements attributed to secure and fast onboarding process, and moreover cost efficiency and scalability.

The devised Edge system, via reliable connection to the IGT control system, is able to collect, enrich and transfer data, for the purpose of the local and remote analytics and visualization. The Gas Turbine (GT) trackable data (sensor measurements and control signals) are enriched with the virtual engine data (soft sensors and internal health parameters) generated by the Executable Digital Twin (xDT) and streamed to the Cloud platform, where the Real-Time analytics and optimization of assets are carried out.

Feasibility and viability of proposed design are disused in this study, and we present Live Data Streaming into Amazon Web Services (AWS) Cloud environment, configured for the Real-Time monitoring of the Industrial Gas Turbine engine.
A Comprehensive Thermodynamic Analysis of Gas Turbine Combined Cycles With Pressure Gain Combustion Based on Humphrey Cycle
Authors: Dubey Abhishek , Sorce Alessandro , Stathopoulos Panagiotis
Published: August 2024

The paper describes a comprehensive thermodynamic analysis of the gas turbine combined cycle (CC) equipped with pressure gain combustion (PGC) based on the Humphrey cycle. PGC is represented by a steady-state zero-dimensional constant volume combustion (CVC) model with practical loss models for a realistic interpretation. Simulations were performed in WTEMP (Web-based Thermo-Economic Modular Program) software, a modular cycle analysis tool developed at the University of Genova. PGC gas turbine combined cycle is studied using methane as fuel with three different configurations of heat recovery steam generator, namely, one pressure-level without reheat, two pressure-level with reheat and three pressure-level with reheat, in order to study a wide range of CC application. An on-design performance map of the PGC gas turbine is presented and a sensitivity analysis is performed to understand the impact of cycle loss parameters and turbine cooling technology. Results were analyzed at the optimistic and realistic PGC loss scenarios. For the PGC open cycle, with optimistic combustor losses, efficiency was higher than Joule at all operating conditions. However, with realistic combustor losses, a higher TIT was found to alleviate some of the losses in the combustor and at a pressure ratio of 25, a 1700°C TIT cycle showed a benefit of 1.7 p.p., while 1300°C TIT showed no advantage. Moreover, with the reduction in first turbine stage efficiency from pulsating outflow, only the high TIT cycle showed benefit at pressure ratios less than 15. Looking into combined cycles with realistic combustor losses, PGC was found to be advantageous in terms of specific work but not efficiency at actual operating conditions. However, with a further reduction of combustor-related losses, the PGC CC could outperform the Joule equivalent in terms of efficiency. The sensitivity analysis with losses showed that the mitigation of constant pressure combustion loss is more important than the inlet pressure loss for PGC in CC application. Finally, it was shown that the improvements in turbine cooling technology could increase the efficiency of a high TIT PGC combined cycle by 0.25 p.p. and specific work output by 4.1 p.p.
Combined Effects of Fluid Inertia and Gas Rarefaction on The Performance of Textured Gas Bearings
Authors: Xu Kefan , Zhang Guanghui , Lu Yiken , Han Jiazhen , Huang Zhongwen , Gong Wenjie
Published: August 2024

Considering the significant discretization effort required to describe texture shapes and possible strong fluid recirculation phenomenon in the deep textured area, this paper attempts to solve the above two hurdles by introducing the multigrid method and inertial correction operation. Furthermore, the first-order slip model and perturbation method were adopted to incorporate gas rarefaction and inertia terms in the compressible Reynolds equation. Moreover, the finite difference method and multigrid algorithm were employed to discretize the pressure governing equations and quickly reduce the iterative residuals of linear systems of equations, respectively. The effects of rotational speed, eccentricity, nominal clearance, state of the lubricated surface, and texture parameters on the static performance of gas bearings were studied. On this basis, the CPU time statistics results show that the computing efficiency of multigrid can be increased by more than 46% compared with the traditional direct solution under the same operating parameters. In addition, it is observed that slip flow and fluid inertia usually reduce the predicted load capacity of gas bearings, and the effect of fluid inertia is stronger than that of the slip flow when the rotational speed is high, the clearance is large, and the dimple texture is deep. The above study supports textured foil journal bearings’ rapid and accurate design in the following engineering practices.
Risk Assessment and Probabilistic Projection of IN706 Gas Turbine Rotor
Authors: Scheibel John , Shi Huawei , Dewey Robert
Published: August 2024

As the limits of starts or hours are approached, a GT owner is presented with several options: replace with a new rotor, swap for a rebuilt rotor, or ship to a shop for disassembly and full inspection. This paper outlines a general two-step procedure which has been used to assess the potential risks of extending the OEM’s interval limits. The approach starts with a failure mode and effects analysis (FMEA). It focuses on and ranks the most relevant durability issues based on a review of the rotor design features, operating history, and maintenance – inspection records. For the F-class, particular attention is focused on the high nickel IN706 turbine discs and spacers, which have been susceptible to both creep and stress-assisted grain boundary oxidation (SAGBO) degradation. The importance of this issue has led to an extensive test program of IN706 specimens, in order to better document and define the material properties, which in turn are used to characterize its resistance to SAGBO and creep. Once the durability issues have been ranked, a probabilistic assessment is performed. The assessment focuses on one or more of the most predominant issues, which pose the highest risk of failure. The probability or chances to achieve a projected interval of hours or starts is calculated, based on historical of GT operating data.
Experimental Evaluation of High Lift, High Work LPT Blades in a Transonic Cascade
Authors: Sauder Ryan R. , Wolff Mitch , Savela Gloria E. , Norris Geoffrey B. , Lethander Andrew T. , Posada Natalia A. , Clark John P.
Published: August 2024

A family of low-pressure turbine stages was recently developed to investigate the limits of achievable work and lift for future engines applicable to unmanned air systems. Subsequently, mid-span sections of a pair of turbine blades from those stages were manufactured for testing in a transonic cascade facility to verify predicted performance at both on- and off-design conditions. Both turbine blades were designed at the meanline level to a work coefficient of 2.80, and the velocity triangles and pitch-to-chord ratios were consistent with incompressible Zweifel coefficients of 1.60 and 1.78. At design conditions, the airfoils provided 123° of flow turning at an exit isentropic Mach number of 0.78. Both inlet- and exit-total pressure traverses were conducted, and the inlet turbulence intensity and length scale were measured at a pair of locations upstream of the instrumented airfoils in the mid-passage. The experimental datasets presented herein include loading variations as well as loss variations versus Reynolds number. It was found that neither airfoil experienced separation at the lowest Reynolds number achievable at design exit Mach number. Accordingly, it was necessary to operate the cascade at reduced total-to-static pressure ratios to observe significant effects of separation on the loading and loss results. The experimental results presented here are compared against design-level predictions using Reynolds Averaged Navier-Stokes (RANS) codes with transition modeling as well as Large Eddy Simulation (LES). The results are encouraging and bode well for the development of future engines that have reduced part-count, weight, and cost while providing acceptable performance lapse at altitude.
Application of an Improved Workflow for the Identification of Flame Dynamics to Swirl Stabilized Wet Combustion
Authors: Désor Marcel , Haeringer Matthias , Hiestermann Marian , Niebler Korbinian , Silva Camilo F. , Polifke Wolfgang
Published: August 2024

The estimation of a flame transfer function (FTF)from time series data generated by large eddy simulation (LES) via system identification (SI) is an established and important element of thermoacoustic analysis. To achieve results with low uncertainties, continuous (non-truncated) time series of adequate length are required. This can be a challenge in the case of turbulent flames, where signal-to-noise ratio may be low. Because LES codes do not scale to an arbitrarily high degree of parallelism, the wall-clock-time required for confident FTF estimation may be excessive. The present paper tackles this challenge by exploiting characteristic features of linear time-invariant systems. Specifically, we explore how the superposition of multiple simulations with the same excitation signal, but varying initial conditions, increases signal-to-noise ratio and leads to more robust identification, i.e. estimates with narrow confidence intervals. In addition, the established SI approach, which relies on broadband excitation, is compared to excitation with approximate Dirac and Heaviside signals, with the advantage of simpler pre- and post-processing.

Results demonstrate that the proposed workflow, which is inherently parallel because it is based on superposition, reduces significantly the wall-clock-time required for robust FTF identification in the case of broadband excitation. This reduction in wall-clock-time requires more simultaneous simulation runs, i.e. more parallel computational resources, but it does not significantly increase the overall computational cost. Furthermore, the new workflow facilitates FTF estimation when exciting with a Heaviside signal.

The proposed method is assessed for the case of a partially premixed, steam enriched (“WET”) swirl burner with significant turbulent noise levels. Steam enrichment is a combustion concept that reduces harmful emissions such as NOx and CO2 while increasing engine efficiency. However, the effect of steam on the flame response, i.e. the FTF, needs to be better understood. To this end, a combustion model that includes an optimized global chemical mechanism for partially premixed wet methane combustion, has been formulated and validated against experimental data.
Evaluation of Subfilter Model Performance for LES of Supercritical Fluids
Authors: Purushotham Dhruv , Oefelein Joseph C.
Published: August 2024

The accuracy of three large-eddy simulations (LES) is assessed using a reference dataset obtained via direct numerical simulation (DNS). All of the LES simulations employ the dynamic Smagorinsky model to close the momentum equation and a dynamic gradient model to close the total energy equation. The LES data are obtained on three grids with resolutions spanning from the wall-resolved LES limit to two successive levels coarser in the spatial and temporal domains. The configuration employed for the study is a three-dimensional spatially evolving turbulent shear layer. The working fluid is pure carbon dioxide. The system is maintained at a supercritical state near the critical point such that the field is dominated by strongly nonlinear thermophysics. This allows the analysis to occur under conditions where the subfilter closures are significantly strained by the thermodynamics. Results explore characteristics of the turbulence from both a modeling and fundamental perspective. First, mixing layer growth rates are quantified. Discrepancies are found between the reference DNS data and the LES data. Energy spectra, turbulent transport coefficients, and Reynolds stress anisotropy results are presented to explore the origins of this mismatch.