bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Analysis of Leading Edge Erosion Behavior of a High-Pressure Compressor in a Turbofan Engine
Authors: Türke Andreas , Schlüter Lukas , Voigt Matthias , Schmidt Robin , Vogel Andreas , Mailach Ronald
Published: August 2024

The demands for competitiveness, performance, and sustainability in civil aviation become more and more challenging and therefore an increase in the efficiency of aero engines is required. A potential starting point for optimization to reach these goals is the compressor. The influence of the compressor blade leading edges on the overall aerodynamic behavior and performance deterioration due to erosion are well-known topics. However, the effect of erosion on leading edge geometry still needs to be studied. Therefore, a Monte Carlo simulation based analysis of leading edge erosion, caused by ingestion of naturally occurring dust during operation, is presented. The influence of blade geometry, operating point, and particle configuration on erosive wear is investigated by the example of a 10.5-stage high-pressure compressor of a modern civil turbofan engine. By incorporating a one-way coupled Euler-Lagrangian approach, trajectories of solid particles through the compressor have been calculated. To replicate naturally occurring mineral dust and volcanic ash, different particle configurations have been studied, varying particle size, density, and drag behavior. Geometric effects have been taken into account by varying blade geometry based on a comprehensive database of optically measured ex-service blades. The blade geometry is characterized utilizing a parametric model capable of describing leading edge variability. By applying an erosion model the resulting geometry of artificially eroded compressor blades is derived. The results indicate that the change of geometry caused by erosive wear shows a characteristic behavior. This erosion characteristic is mostly independent of the operating point and blade geometry considered. Abrasive effects mainly influence the area close to the blade tip, increase asymmetry, and change the curvature of the leading edge. These results are consistent with the analysis of optically measured ex-service blades.
Multi-Disciplinary Surrogate-Based Optimization of a Compressor Rotor Blade Considering Ice Impact
Authors: Nyssen Florence , de Cazenove Jean , Nigro Rémy , Cracco Cédric , Baert Lieven , Ruess Jean-Sébastien , Valentin Vincent
Published: August 2024

Ice ingestion can lead to a range of detrimental effects, from diminished engine performance to potentially catastrophic failure, especially for the first compressor stages. As the ice is traveling through the engine, whether due to direct hail particle ingestion or due to shedding of ice accretions, the impact with engine components that rotate at high speed can result in severe mechanical damage. The leading edge of the blades in the low-pressure compressor are particularly prone to local damage. Therefore, it is important to consider ice impact simulations as soon as possible in the design process. In this context, the authors propose in this work a multi-disciplinary surrogate-based optimization strategy for a compressor rotor that includes ice impact simulations. For this purpose, a dedicated 3D blade parametrization is first introduced. Then, based on this set of design parameters, the proposed optimization chain is presented and each chain block is detailed. In particular, (1) aerodynamical simulations are considered at three different flight conditions, (2) maximum static stresses and frequency margins with respect to specific engine orders are evaluated, (3) the blade robustness to blade/casing contact events is assessed using the clearance consumption simplified criteria, and (4) ice impact simulations are carried out using transient response computations with an explicit time integration scheme and the ice fragment modeled with the Smooth Particle Hydrodynamics (SPH) method. A dedicated lower-fidelity model has been developed for the specific purpose of optimization loops to maintain reasonable computations times. The proposed strategy is applied to design a rotor blade of a low-pressure compressor. The aim is to satisfy all mechanical constraints to ensure the blade robustness in operation, without deteriorating its aerodynamic performance. The optimization process is detailed in the paper, and an in-depth analysis of the optimization results is presented.
Operation of a Fully Integrated Rotating Detonation Combustor in a T63 Gas Turbine Engine
Authors: Fievisohn Robert T. , Battelle Ryan , Karimi Miad , Klingshirn Christopher
Published: August 2024

The Air Force Research Laboratory (AFRL) has designed a rotating detonation combustor (RDC) as a replacement for the main burner in a T63 gas turbine engine. Unlike the stock combustor, this RDC operates on gaseous hydrogen. Previous AFRL efforts developed a similar RDC but in an open loop configuration. In that configuration, the air and cooling flows were fed from separate external sources and the compressor discharge was diverted and used to estimate compressor work. The focus of that project was to determine the impact of unsteadiness from an RDC on turbine efficiency. Results from the previous project showed that there was minimal impact to turbine efficiency when the detonation outflow was mixed with the cooling flows in a mixer/ejector configuration. The current work is a follow-on effort to design an RDC that operates in a closed loop configuration. Operation and cooling of the RDC is done with the compressor discharge with no external support. The main challenges associated with this effort are designing an RDC that has sufficient performance to close the engine cycle, the ability to work over the entire operating map, and thermal steady state operation. In this work, an RDC is developed that can operate continuously from startup to normal rated power. Results from a 6-minute test are presented where the combustor operates in a deflagrative mode at startup and transitions to detonative combustion as air and fuel flow rates are increased. The combustor was constructed of 304 stainless steel and suffered minor oxidative damage. Results from this work will be applied to a combustor made of Inconel 625 for a future test that is fully integrated in a T63 gas turbine engine.
Experimental Investigation of Rotor Passage Loss in S-CO2 Radial Turbine
Authors: Lee Seungkyu , Lee Jeong Ik , Kim Gihyeon , Baek Jeong Yeol
Published: August 2024

This paper presents an experimental investigation of rotor passage loss in an S-CO2 radial turbine. It addresses the need to adapt existing design methodologies for S-CO2 turbomachinery due to its distinct physical behavior compared to ideal gas turbomachinery. This study involves selecting and calibrating existing rotor passage loss models, crucial for determining the pressure ratio and efficiency of a radial turbine. An S-CO2 Turbine-Alternator-Compressor (TAC) in KAIST is utilized for empirical measurements, leading to the calibration of existing Balje’s rotor passage loss model. The paper highlights the uniqueness of S-CO2 turbomachinery and contributes to the understanding and improvement of their design and operation.
Centrifugal Compressor Surge in Closed Loop Systems: Initial Modelling and Comparison With Experiments
Authors: Purushothaman Sreenath , Reggio Federico , Traverso Alberto , Niccolini Marmont Du Haut Champ Carlo Alberto , Silvestri Paolo , Halbe Chaitanya
Published: August 2024

Heat pumps are expected to play a primary role in electrification of thermal users in the residential and industrial sectors. Dynamic compressors are widely used in large size heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency and low acoustic emissions. The instability, which may occur in a compressor installed in closed loop cycle such as in a heat pump, is quite different from the classic open loop configuration involving dynamic compressors. This is mainly due to the complexity of the compressor instability mechanism coupled to a vapor compression system connected with two-phase heat exchangers, having different thermal and fluid dynamic capacitance properties, under a physical feedback loop.

The aim of this paper is to investigate the behavior of a dynamic compressor installed in an innovative heat pump prototype, of laboratory scale, under stable and unstable conditions. A preliminary simple dynamic model of the compression system consisting of a radial compressor, condenser and evaporator, is developed to represent the heat pump compression system, aiming at its time-dependent representation during compressor instable behavior. The evaporator and condenser are modelled using empirical correlations representing the heat exchange and phase change phenomena and including the thermal capacitances due to refrigerant mass and heat exchanger pipes. The preliminary validation of the dynamic model results is done through a dedicated experimental campaign, under different operating conditions. Results show the complexity of the interaction between the centrifugal compressor and the heat pump loop, discerning the different contributions to the time-dependent response of the system. Future steps will encompass a more detailed modelling of the heat pump loop and the use of updated field measurements, including liquid level meters in the heat exchangers.
Optimization of Smooth Straight-Through Labyrinth Seal Based on XGBoost and Improved GA
Authors: Hao Liu , Guoqing Li
Published: August 2024

Improving the sealing performance of labyrinth seal is beneficial in reducing the loss of downstream components as well as improving the aero-engines’ efficiency. Meanwhile, the optimization of labyrinth seal is more cost-effective than optimizing other components of aero-engines. Based on extreme gradient boosting (XGBoost) and improved genetic algorithm (GA), an automatic optimizer for smooth straight-through labyrinth seal is proposed. According to the ordering of feature importance, the 10 selected geometric parameters of smooth straight-through labyrinth seals with two gaps (0.1 mm, 0.25 mm) are optimized when the axial length of labyrinth seal is limited. The optimization results show that the leakage rate of the optimized labyrinth seal with two gaps is 19.67% and 23.80% lower than the reference labyrinth seal, respectively. It is found that the decrease of fin height, fin angle, fillet radius, and fin width, and the increase of fin pitch are beneficial to improve the sealing performance of smooth straight-through labyrinth seal. The analysis of flow field reveals the reasons for the improvement of sealing performance due to the change of geometric parameters. However, it must be noted that the optimization effect decreases as the pressure ratio increases, primarily as the result of the increase in carry-over coefficient. This work provides a new approach to optimize smooth straight-through labyrinth seal.
Influence of the Terminal Position of the Rotatable Ring of Controllable Speed Casing on the Flow Stability of a High-Load Compressor Stage
Authors: Zhong Jingjun , Hu Yi , Ao Zhao , Wu Wanyang
Published: August 2024

Controllable Speed Casing (CSC) is an innovative casing treatment technology designed to enhance the flow stability of compressors. This technology improves the compressor stage’s flow stability by exerting an additional circumferential force through a rotating ring on the rotor tip region flow. This paper investigates the effect of varying the terminal position of the rotating ring on the stability expansion capability of the CSC, with its initial position fixed at the rotor tip leading edge. The findings indicate that when the rotatable ring’s terminal position is set before the position where the tip leakage vortex begins to break down, the CSC primarily boosts compressor flow stability by suppressing the development of the tip leakage vortex and controlling the tip leakage flow. However, if the rotatable ring’s terminal position is set after the position where the tip leakage vortex begins to break down, the circumferential additional force range exerted by the CSC expands, further diminishing the original driving force of the tip leakage flow. This also causes the leakage vortex to undergo circumferential deflection, distancing it from the adjacent blade pressure surface, thereby enhancing the flow capacity of the compressor stage. As the terminal position of the rotatable ring moves continuously towards the rotor tip trailing edge, the stability expansion capability of the CSC is progressively improved. When the terminal position of the rotatable ring reaches the rotor trailing edge position, the CSC can increase the stable operating margin of the compressor stage by a maximum of 45.11%.
Enhancing Gas Turbine Component Life Predictions Using Fleet Data and Probabilistic Methods
Authors: Kapitzke Kristopher , Maxted Joshua , Meyer Christopher , Moffat Andrew
Published: August 2024

Flexible operation of Industrial Gas Turbines is becoming more commonplace as a solution to reduce life cycle cost and increase sustainability. OEMs are developing digital twin technology to understand the effect of this variable operation on component life. This technology can also be used to accurately forecast turbine operation to a potential future maintenance period or end of service interval. The consideration of available fleet machine data is required to manage the risk and enable these future predictions of damage in life-limiting components.

Probabilistic methods, utilizing Monte-Carlo approaches, can be leveraged to model physically realistic operation, material variation, and uncertainties in important parameters such as metal stress and temperature. A key technology in leveraging Probabilistic methods is the ability to translate engine operation parameters into component stress and temperature variables using Reduced Order Models (ROMs). This in conjunction with damage models, representing mechanisms such as creep, fatigue, oxidation, and corrosion, provides the mathematical structure necessary to produce many hundreds of thousands of potential damage results within a reasonable computation time.

This paper aims to outline techniques to characterize a subset of fleet data to provide fleet models of operation. The integration of these fleet models into Probabilistic frameworks and how they are used to manage data driven upper bound damage predictions where operational data is not available will also be discussed.
Impact-Enhanced Resonant Vibration Absorber for Turbomachinery Blisks
Authors: Cimpuieru Mihai , Kripfgans Alexander D. , Kelly Sean T. , Epureanu Bogdan I.
Published: August 2024

The study of blisks is essential to the development of safe and efficient turbomachines. Blisks are geometrically complex structures exposed to high temperatures and pressures that operate at high rotational speeds, and thus are susceptible to fatigue. Therefore, reducing vibration amplitudes in blisks is paramount to avoid failure of these systems. This paper extends previous studies of blisk dampers based on tuned vibration absorbers by analyzing the effects of including energy dissipation through impacts. In this work, the absorber has a ring architecture that also allows impacts. A finite element model of an as-manufactured blisk with 22 blades is used throughout the analysis, and the damper is tuned for experimental operating conditions. Impacts are modeled microscopically, using a novel impact-contact characterization. Results show that impacts significantly enhance the blade response reduction through energy dissipation. Furthermore, impacts slightly increase shift resonant frequencies and are effective for specific combinations of contact surface geometry and material properties.
Experimental Study of Natural Gas and Hydrogen Co-Firing Characteristics Using Different Types of Single Nozzles of F-Class Practical Gas Turbine Combustors
Authors: Lee Sanghyup , Park Jungkeuk , Park Seik , Choi Nakjeong , Shin Jugon
Published: August 2024

Recently, research through the co-firing of natural gas and hydrogen, a carbon-free clean fuel, is attracting attention because to reduce greenhouse gas emissions from aging gas turbine power generation is one of the key energy issues. This can enhance the capability of old gas turbines and contribute stably to an increase in the proportion of combined cycle power plant utilization following the gradual shutdown of coal-fired power plants in Korea. The purpose of this study is to find the optimal operating conditions of mixed fuels without hardware modification of the F-class gas turbine combustor. The experiment was performed according to the load and the co-firing rate using four different types of fuel nozzles (F-Class DLN combustors), and the flame characteristics according to the change in conditions could be analyzed. Under this study, co-firing test was performed with natural gas and hydrogen. The test conditions were selected based on actual machine operating conditions from 30% to 100% thermal load and the hydrogen co-fired with natural gas up to 70% at each load. OH high-speed imaging and an OH-PLIF technique were used to analyze the flame structure, and flame characteristics of co-fired flame in detail. In addition, dynamic pressure was measured to check the combustion instability and exhaust gas emissions were measured to evaluate combustion characteristics of co-fired flame. Major findings are critical co-firing rates of each nozzle based on NOx emission level and combustion dynamics. As the hydrogen co-firing rate increased, the flame length decreased compared to natural gas combustion, and it was confirmed that NOx increased rapidly with the co-firing rate over about 30%vol. In addition, the measured dynamic pressure oscillation results for each nozzle did not show significant variations compared to natural gas combustion. Through this study, it was possible to derive the characteristic operation map of a single nozzle according to the hydrogen co-firing rate.
Feasibility Study of Decentralized Lubrication System Design Through Branch and Bound and Genetic Algorithm for Turbomachinery Trains
Authors: Chen Yuzheng , Maier Bill , Buckenberger Andy , Zhao Yaoyao Fiona
Published: August 2024

The lubrication system functions are crucial in a mechanical system, where friction needs to be controlled and managed. These functions include preventing excessive wear and tear, minimizing heat generation, and prolonging the machinery components’ lifespan. Improper lubrication can incur substantial costs in repairing damaged or replacing worn-out parts and unscheduled downtime. Although turbomachinery trains centralized circulating lubrication systems developed over half a century ago are reliable, they now require an updated design philosophy. These systems are challenged by issues such as low efficiency, complex piping networks, additional footprint space, and high costs.

To address these issues, this study explores improvement methods employed in similar centralized industrial systems, like those in the energy and wastewater sectors. A common design trait of these systems is decentralization, transforming a large-scale centralized infrastructure into decentralized, smaller, localized units. These units can leverage local resources and distribute them according to specific requirements. Decentralization has demonstrated improvements in resilience, reliability, efficiency, cost-effectiveness, and environmental impact. Given the comparable challenges faced by centralized circulating lubrication systems, the feasibility of applying decentralization to lubrication systems was investigated.

This paper introduces the concept of the decentralized lubrication system comprising multiple compact lubrication units that collectively satisfy the turbomachinery train lubrication demand. To identify the optimal decentralized combination of lubrication units, two optimization models using Branch-and-Bound and Genetic Algorithm techniques were developed. The objective of these models was to minimize three key parameters, namely footprint space, tank volume, and investment cost, while adequately meeting the overall lubrication demand (in terms of flow rate). The comparison between the optimized decentralized lubrication system and the existing centralized lubrication system revealed that the former offers significant improvements in the three key parameters. Furthermore, these optimization models demonstrated their adaptability by effectively identifying the optimal combinations of lubrication units for various lubrication demands.
A Collaborative Framework for Design and Validation of Next-Generation Transonic Low-Pressure Turbines
Authors: Cernat Bogdan , Halby Alexandre , Lavagnoli Sergio , Rubechini Filippo , Guidolotti Stefano , Hanifi Ardeshir , Mihaescu Mihai , Lengani Davide , Bertini Francesco
Published: August 2024

This paper presents the design of a transonic low-pressure turbine (LPT) for the next-generation fighter air-breathing engines. The study focuses on the design of a cascade profile representative of an LPT Nozzle Guide Vane (NGV), that follows conventional literature guidelines for transonic turbine airfoils. The paper reports on the numerical and experimental methods that will be employed for a detailed understanding of the flow physics for this baseline solution.

The experimental setup includes a high-speed linear cascade that can be operated at a wide range of inlet turbulence levels (Tu = 5%–8%) and outlet Mach numbers (M = 0.8–1.2). The test section inlet is equipped for hot-wire anemometry measurements, while a purposely designed multi-hole probe is traversed to measure the aerodynamic flow quantities at the cascade outlet. The central passage airfoils feature arrays of pneumatic pressure taps to evaluate the blade loading and hot films to study the status of the boundary layer. Optical sidewalls enable full-field Schlieren and Background-Oriented Schlieren imagery to study cascade shock patterns and unsteady shock-boundary layer interactions. The test section is designed with provision for time-resolved stereo-PIV measurements to cross-validate the cascade velocity field and quantify the turbulence statistics and transport mechanisms through the transonic LPT passage.

A detailed planning for high-fidelity flow simulations (LES and DNS) is presented in the second part of the paper. State-of-the-art computational methodologies will be employed along with advanced post-processing techniques including mode decomposition to enhance the understanding of the flow physics, assess the limitations of traditional numerical methods and complement the experimental findings.
Integration of Cooling Holes Into a Turbine Vane Made Using Additive Manufacturing
Authors: Gailey Nicholas L. , Barringer Michael D. , Berdanier Reid A. , Thole Karen A.
Published: August 2024

Additive manufacturing (AM) has emerged as a method to prototype novel designs for turbine airfoil cooling with complex internal and film cooling geometries. Creating engine scale features with AM comes with challenges that impact flow and heat transfer, which consequently affect the overall performance of the component. While AM has proven to be faster and more cost effective than traditional casting methods, the scalability of AM requires further investigation. The purpose of this study was to integrate various film-cooling hole geometries identified through large-scale models and true-scale simple coupons into a true-scale turbine vane to assess overall cooling effectiveness. The National Experimental Turbine (NExT) vane was additively manufactured with a singular cooling passage feeding two rows of film-cooling holes: a row of baseline 7-7-7 holes; and a row of holes containing both parametrically optimized 15-15-1 holes and modified adjoint optimized cross flow (X-AOpt) holes. The internal passage was designed to have a section with ribs and a section without ribs to assess how internal features impact the cooling holes’ performance. The vane was tested in the Steady Thermal Aero Research Turbine (START) rig over a range of film cooling blowing ratios. A combination of computed tomography (CT) scanning and non-contact infrared (IR) thermal imaging measurements were used to evaluate how as-built geometries impacted the overall cooling effectiveness on the NExT vane for each hole group. The 15-15-1 film cooling holes with no internal ribs was shown to be the most effective in lowering surface temperatures relative to the other cooling hole configurations. Also, the 15-15-1 holes with no internal ribs to affect the cooling flow entrance to the hole was the least affected by blowing ratio changes. The 7-7-7 hole was found to have a negative impact on the vane because the downstream surface was warmed by a separating internal channel wall.
Aeroelastic Influence of Blade-Shaft Coupling in a 1 1/2-Stage Axial Compressor
Authors: Maroldt Niklas , Seume Joerg R.
Published: August 2024

During the design process of turbomachinery, it is often not possible to use aerodynamically optimal designs due to aeroelastic constraints. The design choices are limited by possible structural failure, which can be caused by high vibration amplitudes, for example due to self-excited vibrations (flutter) or forced response. In particular, the modal damping has an important impact on these phenomena. In the absence of frictional contacts, damping is mainly created by aerodynamics. In this paper, the influence of additional damping created by the rotor bearing on the total damping and on forced vibrations will be investigated. This influence becomes relevant when blade vibrations with nodal diameters 1 and −1 couple with the shaft vibrations. The coupling is caused by a structural dynamic interaction of these two components. To investigate the blade-shaft coupling, a simulation process is set up to best represent the physical effects during operation. This simulation process is essentially based on a full structural dynamic model of the blisk-shaft assembly and a harmonic balance CFD model to account for the aeroelastic effects. In addition, mistuning identification is performed based on an experimental modal analysis at standstill. All results are incorporated into a structural reduced order model that calculates the vibrational behavior of the blading. These results are compared to damping determined during operation using an acoustic excitation system and measured forced frequency responses. The numerical results agree well with the experimental results, i.e. within the measurement uncertainty, both with respect to the damping and the mistuned frequency responses. Furthermore, the blade-shaft coupling results in significant changes of the eigen-frequencies and damping. As a consequence, damping increases by up to twelve times when taking the coupling into account. This reduces amplitudes by a factor of nine for the mistuned blade responses. Consequently, higher structural safety factors can be achieved by taking the blade-shaft coupling into account so that the remaining potentials in the aerodynamic design could be better exploited.
Mitigation of Laminar Separation Bubble Through Leading-Edge Modification of an Aerofoil With Herringbone Riblets
Authors: Kumar Ravi , Singh Pradeep , Sarkar Subrata
Published: August 2024

The present study describes the potential of a passive technique involving the leading-edge modification using herringbone riblets with a triangular cross-section in mitigating the leading-edge separation at various angles of attack (α). Pressure and instantaneous flow measurements by hotwire were performed over a semicircular leading-edge aerofoil for α — 0°, 3° and 5° with and without leading-edge modification. The Reynolds number (Re), based on the chord length and the inlet freestream velocity, was 1.6 × 105, where freestream turbulence (fst) being 1.2%. A laminar separation bubble is witnessed on the hydrodynamically smooth leading-edge aerofoil at all α where the transition is governed by inviscid instability. Leading-edge modification with herringbone riblets induced higher turbulence in proximity to the wall, resulting in an earlier transition of the shear layer and a reduction in bubble length by 36–20% for α = 0–5° along with a change in the transition mechanism. In brief, herringbone riblets show promising results in reducing the leading-edge separation.
Economic Modeling of Renewable Integration and the Application of Energy Storage to the ERCOT Energy Grid
Authors: Karg Bulnes Fernando , Hofer Douglas , Smith Natalie R. , Schmitt Joshua , Pryor Owen , Khawly George , McClung Aaron
Published: August 2024

As the energy sector transitions to lower carbon emission solutions, there is a need to better understand the limitations and impacts of increased renewable energy generation sources on the grid. This study investigates the potential for energy storage technology across Texas using historical data of renewable energy sources. The Texas electric grid currently relies mostly on wind and natural gas to meet its load, with both seasonal and daily variations due to the availability of renewables. The Texas electric grid data for 2022, published by ERCOT, showed a yearly consumption of over 428,000 GWh, out of which 36% is covered with natural gas, 25% with wind, 6% with solar, 17% with coal, and the rest using other electric sources. This study focuses on a techno-economic evaluation of behind-the-meter commercial microgrids to evaluate the impacts of energy cost and renewable penetration on the Texas energy landscape by increasing the levels of solar photovoltaic and wind generation along with energy storage and decreasing the state’s reliability on fossil fuels (coal and gas). The results are assessed from the perspective of a large commercial user with a dedicated behind-the-meter microgrid used to minimize or replace purchased grid power across eight different regions. To complete the analysis, an in-house tool will be used to assess the techno-economics for different levels of renewable energy generation and decarbonized generation with various energy storage sizes with a specific energy cost and load in the distinct load zones across the Texas grid. Conclusions are drawn for optimal renewable penetration at this scale with the addition of the proper amount of storage.
Dry Gas Seal Condition Monitoring With Embedded Acoustic Emissions Sensors
Authors: Palmer Christopher , Fritz Colleen , Kotar Chris
Published: August 2024

Dry gas seals (DGS) are commonly used in turbomachinery applications when handling gases. These applications include centrifugal compressors, expanders, and turbines. Historically, DGS have been monitored via leakage and pressure measurements taken outside of the compressor. In recent years, researchers and DGS manufacturers have developed monitoring systems with sensors embedded in the seal. These systems allow seal designers, equipment manufacturers, and machinery operators to monitor the condition of the seal during operation via direct seal measurements as opposed to the traditional downstream or upstream measurements.

Acoustic Emission (AE) sensors measure high frequency elastic waves. Embedding these sensors into a DGS offers an exciting possibility to measure elastic waves propagating through the DGS metalwork.

This paper will show how measuring acoustic vibrations on a test rig and on field installations provides the opportunity to monitor the health of a DGS.
Investigation on Flow Field Characteristic in a Double-Wall Configuration Using MRV and CFD
Authors: Duan Jingtian , Zhang Ke , Wang Zirui , Chen Ruoyu , Yang Yibo , Lei Jiang , Wu Junmei
Published: August 2024

The three dimensional full flow field distribution of a double-wall cooling structure including impingement jets, pin fins and film effusion holes is measured by magnetic resonance velocimetry (MRV). The flow field in the same geometry is simulated numerically using commercial code as well. Flow field results from MRV are used to validate the reliability of different turbulent models. MRV resolves the complex three dimensional flow field inside and outside the double-walled sandwich. The affecting regions of impingement jets on the target wall, as well as the interaction between the film jet and mainstream boundary layer is discussed. Flow establishment, shear layer and jet deflection regions of impingement jet inside double-wall structure are identified using measured flow field. Possible cooling mechanism in the double-wall structure is discussed based on the resolved full-field three dimensional flow.
Effect of Frequency Characteristics and Swirl Brakes on Fluid Destabilization Force Acting on Compressor Closed Impeller Leakage Path
Authors: Iwasaki Makoto , Nishida Shingo , Yamashita Shuichi , Oda Takashi
Published: August 2024

In turbomachinery, the trend toward higher performance, smaller size, and higher speed has led to a decrease in the rigidity of the rotor system and an increase in the pressure and flow velocity, which in turn has increased the fluid destabilization force and increased the risk of vibration problems. The fluid destabilization forces generated at the front shroud and labyrinth seal components have been studied for many years. However, there are few measured data on the frequency characteristics of the fluid destabilization force in a system-level test combining a front shroud and a labyrinth seal. In this paper, dynamic characteristic tests were conducted using air as the working fluid in a closed impeller single-stage test rig.

In the closed impeller single-stage dynamic characteristic test, the rotor was excited with a hydraulic shaker while the 381mm diameter impeller was rotating at a maximum of 11,000 rpm. From the measurement results, it was confirmed that pressure fluctuations of the same order of magnitude as those of a labyrinth seal were generated in the front shroud. Since the front shroud has a larger pressure receiving area than the labyrinth seal, it was confirmed that the front shroud has a very large effect on the fluid destabilization force in the closed impeller leakage path.

As a device to reduce the fluid destabilization force in the closed impeller leakage path, this paper proposes the installation of the swirl brakes on the front shroud instead of at the labyrinth seal inlet. To validate the effectiveness of the swirl brakes, dynamic tests were conducted without and with the swirl brakes. Comparative test results showed that the swirl brakes can significantly reduce the fluid destabilization force.

Transient CFD analysis was conducted as a method for predicting the fluid destabilization force, and the prediction accuracy of the CFD analysis method was confirmed by comparing the CFD analysis results with the measured fluid destabilization force. Furthermore, by visualizing a portion of the leakage path with glass, the surface distribution of pressure fluctuations acting on the closed impeller leakage path was measured using Pressure-Sensitive Paint (PSP). The visualization test results also confirmed that significant pressure fluctuations were generated not only at the labyrinth seal but also at the front shroud, thus confirming the validity of the CFD analysis method.
Reduction of the Excitation of Volute on Turbine Rotor by a Groove Treatment
Authors: Wang Yv , Chen Hua
Published: August 2024

Nozzleless volutes are often used to provide required flow conditions to downstream radial and mixed flow turbine rotors. These flow conditions are generally not circumferentially uniform, with a sharp change around volute tongues. Due to this non uniformness, rotors blades will experience an aerodynamic force excitation in rotor rotating frequency. This excitation could cause high cycle fatigue (HCF) of rotor blades if the natural frequencies of rotor blades coincide with those of its harmonics. To avoid this HCF, turbine rotors are designed typically with their natural frequencies several times above the highest rotating frequency of rotors, but this increases rotor weight and reduces rotor efficiency.

Various efforts have been made to reduce the excitation force created by nozzleless volutes. Here we propose a simple method by adding in turbine housing a small groove located near rotor leading edge (LE) shroud. The idea is that when a rotor blade rotates passing through the groove, blade loading around LE will reduce suddenly, creating an excitation to the blade, and by circumferentially positioning the groove correctly, the excitations from volute and the groove will partially cancel each other. A hypothesis to allow easy prediction of the best positions of the groove is also put forward.

The idea was applied to an industrial turbocharger turbine for heavy truck application to reduce the 3rd order excitation generated by its turbine volute. The nozzleless volute was well designed so that the 4th order excitation is no longer an issue. The Campbell diagram was first used to obtain the rotor speed of resonance, and unsteady computational fluid dynamics (CFD) then applied to obtain the excitation force on rotor blades both with and without the groove. The resultant alternative vibratory stress of blades was obtained by a harmonic response method and results were compared. They show more than 55% reduction of the maximum vibratory stress, while turbine mass flow is reduced by 0.89% and efficiency by 0.45% points.
Influence of the Tip Winglet Structure Modeling on Leakage Flow at a High-Load Compressor Stage
Authors: Zhong Jingjun , Zhao Ao , Hu Yi , Wu Wanyang
Published: August 2024

Tip winglet technology is an effective method for increasing the stable operating range of compressors. This paper examines six types of pressure-side tip winglets with varying circumferential widths and chord lengths, to assess their influence on the stability expansion ability and flow structure of the compressor stage. The effectiveness of stability expansion via tip winglets is enhanced with increased tip winglet width. Specifically, when the tip winglet width reaches twice that of the rotor blade tip width, the stable operating margin improvement can attain 11.43%. Moreover, when the tip winglet width is 1.5 times the rotor blade tip width, the full-chord tip winglet yields the most significant stability expansion effect, surpassing that of partial-chord length tip winglets.

Tip winglets mitigate the leakage mass flow rate by balancing the mismatch in flow velocity components, exacerbating leakage flow deterioration. Concurrently, the degree of leakage vortex fragmentation is weakened, controlling the accumulation of low-energy fluid within the passage. Furthermore, tip winglets prevent the concentration of low-energy fluid in the radial region, effectively enhancing the flow structure and stability of the compressor. When designing the tip winglet structure, it is crucial to maximize the stable operating margin of the compressor stage without compromising efficiency. To this end, extending the blade into the passage from the 90% chord to the rotor trailing edge should be avoided.
Spatial Temperature Measurements in a Swirl-Stabilized Hydrogen-Air Diffusion Flame at Elevated Pressure Using Laser-Induced Grating Spectroscopy
Authors: Chaib Oussama , Weller Lee , Giles Anthony , Morris Steve , Williams Benjamin A. O. , Hochgreb Simone
Published: August 2024

Laser-induced grating spectroscopy (LIGS) is applied, for the first time, to a swirling non-premixed hydrogen-air flame in a high-pressure combustion facility. A portable LIGS unit is used to probe 35 different axial and radial locations in the flame and a new conditioned processing approach based on laminar flame simulation is introduced to infer temperatures from instantaneous LIGS spectra. Thermal and electrostrictive frequencies are used to produce a spatial map of temperatures in the combustor. Temperatures up to 2,500 K are measured in this work, which constitute the highest temperatures ever measured using LIGS. Challenges associated with the deployment of the technique in turbulent stratified hydrogen flames are discussed, as are potential measures to overcome them, including the use of data-driven clustering techniques.
Roughness Effects on Dense-Gas Turbine Flow: Comparison of Experiments and Simulations
Authors: Gloerfelt Xavier , Hake Leander , Bienner Aurélien , Matar Camille , Cinnella Paola , aus der Wiesche Stefan
Published: August 2024

This paper presents a combined numerical and experimental study of the high-subsonic organic vapor flow in a linear turbine cascade. The profile geometry is the well-documented LS59 highly-loaded rotor blade and the working fluid is Novec649, a dense gas used in organic Rankine cycles. Large-eddy simulations are carried out with and without the roughness introduced by the additive manufacturing process. The results for the rough blade are in fair agreement with experiments, while the smooth surface induces a change in the vortex shedding regime. A detached shedding, characterized by a long recirculation downstream of the trailing edge and a base-pressure plateau, is obtained in the experiments and by discretizing the roughness in the simulation. By contrast, a transonic vortex shedding is established when the surface is smooth: intense vortices roll up immediately after the trailing edge, yielding a short bubble and a lattice of shock waves. A strong pressure drop is observed at the trailing edge, resulting in high profile losses. In both cases, the boundary layer is turbulent ahead of the separation but its thickness is significantly greater in the rough configuration, which may be the reason for the change of regime.
Numerical Surface Roughness Influence on the Aerodamping of an Axial Transonic Compressor at Nominal Speed and Part-Speed
Authors: Tavera Guerrero Carlos , Gutierrez Salas Mauricio , Glodic Nenad , Deshpande Srikanth
Published: August 2024

In a turbomachine, with time, wear and depositions modify the surface from smooth to rougher characteristics. These effects are also prevalent in emerging manufacturing technologies such as additive manufacturing (AM). Surface roughness characterization is based on a correlation between a physical length scale or surface statistic moments, and a non-physical equivalent sand-grain roughness (ks). Depending on the flow characteristics and ks, three wall regimes can be considered: hydraulically smooth, transitional or fully rough. In compressors, an increase in surface roughness translates into a reduction in efficiency and pressure ratio. While steady-state roughness effects over airfoils and stage performance are well documented, its consequences over the aerodynamic damping are not. This paper aims to investigate numerically the effect of surface roughness on the aero-damping for the three wall regimes. The test geometry is the first stage of an open-source transonic axial compressor. Operating points considered are peak efficiency and near-stall conditions at nominal speed (N100) and part-speed (N70). The presented numerical simulations are obtained using the commercial software Ansys CFX with SST as the turbulence model with a reattachment modification. At near-stall part-speed, there are non-physical separation regions that are mesh independent but assumed to come from the numerical roughness implementation. Amplitude fluctuations in the aerodynamic damping per unit area, ζ*, are driven by the tip gap presence as well as normal shocks at N100 whereas the presence of separated flow regions appear to have a negligible effect at N70. The phase between the pressure and blade motion appears to remain almost constant regardless of the wall regimes, implying that only the amplitude distribution drives the aerodynamic damping stability. This numerical observation is aimed to be experimentally tested at the transonic linear cascade at KTH Royal Institute of Technology.
Novel Applications of Data Analytics in Gas Turbine Operation for Distributed Power Generation
Authors: Thirumurthy Deepak , Scudamore Mark
Published: August 2024

Recent advancements in data analytics and digitalization has increased the value which power generating assets, such as gas turbines, bring to power plant customers. Distributed power generation customers are increasingly partnering with gas turbine original equipment manufacturers and third-party digital service providers for cooperation in technology, innovation, and asset management using real-time data. In the past, it has been discussed that data analytics can be a key enabler in addressing challenges such as operational flexibility and efficient asset management.

This paper presents some of the novel applications of data analytics developed by Siemens Energy for gas turbine operation, condition monitoring, and real-time decision making. Specifically, the paper presents the idea, application, and test case of remote diagnostic system, enhanced vibration analytics, and myFleetRisk™.

Remote diagnostic system increases uptime, reduces operating cost by resource optimization, and improves plant output. This paper discusses both the reactive and proactive approach to gas turbine maintenance and how remote diagnostic system can be used with data analytics landscape for deviation monitoring.

In addition to an overview of the underlying concept and its novelty, real-world applications are presented to show the benefits to distributed power generation customers. MyfleetRisk offers optimized and tailored maintenance solutions resulting in significant life cycle cost reduction. Enhanced vibration analytics module enables reliability centered maintenance and thereby addresses key challenges to customers.
An Efficient and Robust Rotor-Stator Interfacing Method Capable of Handling Reverse Flows and Variable Specific Heat Within Multistage Turbomachines
Authors: Wu Hangkong , Tian Xiaopei , Qin Hao , Huang Xiuquan , Wang Dingxi
Published: August 2024

This paper presents the study of an efficient, robust, conservative, and nonreflective rotor-stator interfacing method for aerodynamic analysis of multirow turbomachines. This rotor-stator interfacing method computes flow variable differences by flux differences based on a control volume concept. It is found that this method is robust and can handle flow reversals. So far, the application of this method is restricted to analyzing flow fields with constant specific heat and its application to variable specific heat has not been reported in the open literature. This work will extend this rotor-stator interfacing method from constant to variable specific heat. To showcase its advantage over Holmes’ and flow-based methods, two multirow test cases, i.e. the NASA Stage 35 and the E3 high-pressure turbine, are adopted. The turbine case necessitates the use of variable specific heat due to the big temperature variation in the flow field. The results show that this novel method is more stable than Holmes’ method, especially for reverse-flow cases. Compared with the flow-based method, the novel method, as one type of flux-based mixing plane method, can well guarantee flux conservation. Furthermore, this novel method presents a unified approach for both constant and variable specific heats. It is more efficient and easier to implement in a flow solver than Holmes’ method since there is no need to use the Newton-Raphson method to compute mixed-out flow variables from circumferential area-averaged flux for variable specific heat.