bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards Reduced Order Models of Small-Scale Acoustically Significant Components in Gas Turbine Combustion Chambers
Authors: Kowshik Suhas A. , Shridhar Sumukha , Treleaven N. C. W.
Published: September 2021

Gas turbine combustion chambers contain numerous small-scale features that help to dampen acoustic waves and alter the acoustic mode shapes. This damping helps to alleviate problems such as thermoacoustic instabilities. During computational fluid dynamics simulations (CFD) of combustion chambers, these small-scale features are often neglected as the corresponding increase in the mesh cell count augments significantly the cost of simulation while the small physical size of these cells can present problems for the stability of the solver. In problems where acoustics are prevalent and critical to the validity of the simulation, the neglected small-scale features and the associated reduction in overall acoustic damping can cause problems with spurious, non-physical noise and prevents accurate simulation of transients and limit cycle oscillations. Low-order dynamical systems (LODS) and artificial neural networks (ANNs) are proposed and tested in their ability to represent a simple two-dimensional acoustically forced simulation of an orifice at multiple frequencies. These models were built using compressible CFD, using OpenFOAM, of an orifice placed between two ducts. The acoustic impedance of the orifice has been computed using the multi-microphone method and compared to a commonly used analytical model. Following this, the flow field downstream of the orifice has been modelled using both a LODS and ANN model. Both methods have shown the ability to closely represent the simulated dynamical flows at much lower computational cost than the original CFD simulation. This work opens the possibility of models that can dynamically predict the flow through, for instance, acoustic liners, dilution ports and fuel injectors in real engines during thermoacoustic instabilities without having to mesh and simulate these small-scale features directly. Such models may also assist in the accurate simulation of flame quenching due to cooling flows or the design of effusion cooled aerodynamic surfaces such as nozzle guide vanes (NGVs) and turbine blades.
Numerical Investigation of Loss Development in a Low-Pressure Turbine Cascade With Unsteady Inflow and Varying Inlet Endwall Boundary Layer
Authors: Schubert Tobias , Niehuis Reinhard
Published: September 2021

An investigation of endwall loss development is conducted using the T106A low-pressure turbine cascade. (U)RANS simulations are complemented by measurements under engine relevant flow conditions (M2th = 0.59, Re2th = 2·105). The effects of unsteady inflow conditions and varying inlet endwall boundary layer are compared in terms of secondary flow attenuation downstream of the blade passage, analyzing steady, time-averaged, and time-resolved flow fields. While both measures show similar effects in the turbine exit plane, the upstream loss development throughout the blade passage is quite different. A variation of the endwall boundary layer alters the slope of the axial loss generation beginning around the midpoint of the blade passage. Periodically incoming wakes, however, cause a spatial redistribution of the loss generation with a premature loss increase due to wake interaction in the front part of the passage followed by an attenuation of the profile- and secondary loss generation in the aft section of the blade passage. Ultimately, this leads to a convergence of the downstream loss values in the steady and unsteady inflow cases.
Experimental and Analytical Investigation of Cyclic Crack Initiation in Nickel Based Super Alloy With Stress Concentration Features
Authors: Torkaman Alex , Fiebiger Steve , O’Nora Nathan , O’Neal Devin , Gordon Ali
Published: September 2021

Accurate prediction of cycles to crack initiation in critical turbine components is a major issue in turbomachinery design, especially in components with highly concentrated stress such as turbine blades with cooling holes. Several viscoplastic and lifing methods have been used successfully to predict shakedown and cycles to failure, however complicating factors still exist that produce challenges for traditional methods. Therefore newer methods utilizing constitutive modeling with consideration for isotropic and polytropic hardening have been developed to better capture evolution of cyclic behavior of the material. Presence of mean stress and stress concentration factors are some of the complications that can be better accounted for using constitutive models. The present paper evaluates experimental and theoretical life of specimen made from nickel based super alloy with high stress concentration features under cyclic conditions with mean stress. The specimen geometry and loading were designed to mimic trailing edge holes in an F class IGT turbine blade. Experiments were conducted at an elevated temperature at two peak stress values to determine sensitivity to applied load at operating temperature similar to engine. Cycles to crack initiation are analytically evaluated using the well-known Manson-Coffin method with Morrow mean stress correction and two distinct methods for strain range evaluation. First method is the traditional Ramberg Osgood shakedown that has been extensively used in the industry. Second method is constitutive Chaboche based model run with linearized FEM results. Constants for Chaboche model are determined from Ramberg-Osgood constants with a method that takes into account yield surface evolution and hardening constants, in addition to rate dependent stress relaxation factor that can be used to model dwell time effects. Methods to decrease computational time with constitutive model are discussed. Analytical results are compared with the experimental data, and advantages and disadvantages of both methods including computational times are discussed.
The Development and Verification of a Fully Turbulent Discrete Adjoint Solver Using Algorithmic Differentiation
Authors: Wu Hangkong , Xu Shenren , Huang Xiuquan , Wang Dingxi
Published: September 2021

This paper presents the development and verification of a discrete adjoint solver using algorithmic differentiation (AD). The computational cost of sensitivity evaluation using the adjoint method is largely independent of the number of design variables, making it attractive for optimization applications where the design variables are far more than objectives and constraints. To obtain the gradients of a single objective function or constraint with respect to many design variables, the nonlinear flow and the adjoint equations need to be solved once at every design cycle. This paper makes a detailed presentation of how AD is used to develop a discrete adjoint solver. The data flow diagrams of the nonlinear flow, linear and adjoint solvers are compared. Moreover, a comparison of convergence history of sensitivity, asymptotic rate of residual convergence and computational cost between the linear and adjoint solvers is also made. Two cases — the subsonic Durham turbine and transonic NASA Rotor 67 are studied in this paper. The results show that the adjoint solver has the same asymptotic rate of residual convergence and produces consistent convergence history of sensitivity as the linear solver, but the adjoint solver consumes more time and memory.
Aerodynamic Design Optimization of a Variable Geometry Nozzle Vane For Automotive Turbochargers
Authors: Galloway Lee , Kim Sung in , Park Jongyoon , Kwon Seong , Yoo Sejong
Published: September 2021

An aerodynamic design optimization study of the nozzle vane of a variable geometry turbine (VGT) turbocharger for a diesel engine application was conducted using the commercial software, ANSYS CFX and DesignXplorer. The nozzle design was optimized at three critical engine operating points. The nozzle shape was parameterized using key design parameters including theta angle, thickness value and opening angle. For a good balance of computational time and accuracy, the optimization approach adopted meta-models and response surfaces to represent the training data and reduce the number of simulations required to reach an optimal design.

Finally, more than 300 optimized designs were simulated to assess the performance and characteristics of each design. The final optimized nozzle design met all the design constraints and showed an improvement of up to 2% efficiency and reduced the maximum torque by 20% compared to the baseline nozzle.
Educational Effectiveness of Brayton Cycle Compare and Solve Interactive Gas Turbine Simulator
Authors: Christensen Louis , Mathison Randall
Published: September 2021

The air-breathing Brayton cycle is widespread throughout power generation and propulsion systems, making it a staple in every mechanical or aerospace engineering student’s repertoire. Students are typically introduced to cycle analysis in a thermodynamics course and may see more in-depth coverage of gas turbines in advanced technical elective courses. In the Air-Breathing Propulsion course at The Ohio State University, students perform thermodynamic analysis on Brayton cycle engines among other topics. Pedagogy research has shown active learning to be a potent tool for enhancing student learning, and it was decided to incorporate a new active learning module into the existing course. For the module to be successful, students must achieve the learning objectives, positively accept the experience, and the module must have a minimal impact on the course structure. One lecture and one homework assignment were devoted to the use of this tool to allow students to explore gas turbine cycle analysis. A new tool, Brayton Cycle Compare & Solve, has been developed for this module. The tool can accurately perform thermodynamic design point analysis of three types of Brayton cycle engines and allow users to graphically compare the results of their analyses.

This study is done to present the tool and active learning experience to educators, capture the effectiveness of the tool in an educational setting, and determine whether students enjoy the new tool. The program is evaluated through an Institutional Review Board approved study consisting of two parts. First, students participate in a survey based on the Student Response to Instruction Practices tool to determine how the students react to and accept the active learning experience. Second, a detailed analysis of their homework responses is conducted to determine the extent to which they satisfied the learning objectives. Students unanimously felt that the learning experience with Brayton Cycle Compare & Solve is a valuable addition to the course, and homework analysis shows that their understanding of Brayton cycle analysis improved.
Flow Check and Adiabatic Effectiveness Measurements on Traditionally Versus Additively Manufactured Film-Cooling Holes
Authors: Cubeda S. , Andrei L. , Innocenti L. , Paone F. , Cocchi L. , Picchi A. , Facchini B.
Published: September 2021

In the recent years Additive Manufacturing (AM) methods, such as the Direct Metal Laser Melting (DMLM) technology, are getting more and more attractive and feasible for the realization of components and subcomponents of gas turbines. In particular, they are receiving much attention since, on one hand, the manufacturing of complex 3D geometries is allowed and, on the other, manufacturing and delivery times can be cut down. At the current state of the art, although AM is entering and spreading within modern gas turbines at fast pace, to the authors’ knowledge only few applications have yet been commercialized relatively to cooling holes, due to the intrinsic difficulties associated with such a critical feature.

Lately, Baker Hughes is studying the possibility to manufacture film-cooling holes via the DMLM technology in order to exploit the flexibility of such innovative manufacturing method and hence eliminate additional processes and lead time. From the open literature it is known that additively manufactured holes can have a more irregular shape and higher roughness than traditional ones, which may lead not only to a reduction in coolant flow but more importantly to a decay of the film-cooling adiabatic effectiveness. For this reason, a test campaign has been conducted in collaboration with the University of Florence (Italy) with the objective of characterizing the performance (minimum passage diameter, flow check and adiabatic effectiveness) of AM vs traditional cylindrical holes on simple-geometry coupons built upon different construction angles.

Results were then analyzed in order to fully compare the performance of AM vs traditional film-cooling holes at different operating regimes. In addition, selected holes were inspected through tomography in order to reveal the microscopic characteristics of lateral and outlet surfaces and get a further appreciation of the two different technologies. Ultimately the dependency of AM holes performance on print angles is sought with the purpose of characterizing the impact of such manufacturing technology on film-cooling holes design.
Computational Model of Mechano-Electrochemical Effect of Aluminum Alloys Corrosion
Authors: Ali Hessein , Stein Zachary , Fouliard Quentin , Ebrahimi Hossein , Warren Peter , Raghavan Seetha , Ghosh Ranajay
Published: September 2021

Stress corrosion is a critical issue that leads to high costs in lost equipment and maintenance, affecting the operation and safety of aircraft platforms. Most aerospace structural components use the aluminum alloys 7xxx series, which contain Al, Cu, Zn, and Mg, due to the combined advantage of its high-strength and lightweight. However, such alloys, specifically AA7075-T4 and AA7075-T651, are susceptible to stress corrosion cracking (SCC) when exposed to both mechanical stresses and corrosive environments. SCC gives rise to a major technological challenge affecting aerospace systems as it leads to the degradation of mechanical properties. In addition, such corrosion presents an important yet complex modeling challenge due to the synergistic action of sustained tensile stresses and an aggressive environment. In light of this, we develop a finite element (FE) multiphysics model to investigate the interplay of mechanical loading and electrochemistry on the stress corrosion of aluminum alloys. The model includes a multiphysics coupling technique through which the kinetics of corrosion can be predicted in the presence of elastic and plastic deformation modes. The presented model provides useful information towards the kinetics of corrosion via tracking localized corrosion and stress distribution. Although the model is general, it has been made considering the characteristics of AA7xxx series, more specifically, taking AA7075.
Decarbonizing Materials and Machining for the Gas Turbines Sector Through Life Cycle Assessment
Authors: Musacchio Alessandro , Serra Angela , Cencioni Luca , Colantoni Simone , Bartocci Pietro , Fantozzi Francesco
Published: September 2021

Nowadays the Energy Industry and Industrial Power Plants are committed to support sustainable development balancing environmental, social and economic benefits. Turbomachinery products, in particular gas turbines design, have to overcome the barriers imposed by: performance, lifetime and costs requirements. A new approach based on Life Cycle Assessment (LCA) is needed to define the correlation between carbon footprint and costs for different materials, manufacturing processes and production regions. To develop a decision-making tool to design sustainable products in the gas turbine sector high quality data are needed to model what is the impact of: materials and operations. Manufacturing operations (like forging and casting) and machining operations (like drilling, milling, turning, together with coating operations) are taken into account in this study. These processes have been customized to model the processes of the real supply chains used in Baker Hughes to build up a database, which is more focused on gas turbines, respect to the ones which can be found in the commercial LCA databases.
Design and Performance Analysis of a Supercritical CO2 Centrifugal Compressor With Variable Geometry
Authors: Fan Gang , Chen Kang , Zheng Shaoxiong , Du Yang , Dai Yiping , Wang Jiangfeng , Zhao Pan
Published: September 2021

The supercritical carbon dioxide (SCO2) Brayton cycle is one of the most promising power cycles due to its high efficiency, compactness and environmentally friendliness. The centrifugal compressor is a key component of small and medium SCO2 Brayton cycles, and its efficiency has a significant impact on the cycle efficiency. Since the required electric load of power cycles always fluctuates over the year, the SCO2 compressor will operate away from its design point and the narrow stable operating range of a compressor is always a restriction. In this paper, the variable-geometry method, which refers to the combination of a variable inlet-guide-vanes and variable diffuser vanes is proposed for the operating range extension of SCO2 compressors. A set of one-dimensional (1D) loss correlations has been found to accurately predict various losses of the SCO2 compressor components. Based on the 1D thermodynamic model, two programs with internal MATLAB codes coupled with the NIST REFPROP database have been developed for preliminary optimization design and off-design performance predictions of the variable geometry SCO2 compressor. The contributions from the variable-inlet prewhirl and variable diffuser vanes to the shifts of the surge line and choke line are discussed in this paper. The results show the variable-geometry SCO2 compressor has a superior performance at off-design conditions and a wider operating range.
Developing an Implicit Creep Model From Open Literature Data
Authors: Day William David
Published: September 2021

As pressure ratios and firing temperatures continue to rise, creep becomes of greater concern everywhere within a gas turbine engine. As a rule of thumb, just a 14°C increase in metal temperature can halve the expected rupture life of a part. In the past, companies might be satisfied with conservative creep estimates based on Larson-Miller-Parameter curves and 1D calculations. Now companies need functional implicit-creep models with finite element analysis for an ever-increasing number of materials. Obtaining adequate test data to create a good creep prediction model is an expensive and time-consuming proposition. Test costs depend on temperature, material, and location, but a single, 10,000hr, rupture test may reasonably be expected to cost > $20,000. Other than large OEMs, small companies and individuals lack the resources to create creep models from their own data. This paper will lead the reader through the creation of a modified theta projection creep model of Haynes 282, a high-temperature, combustion alloy, using only literature data. First, literature data is collected and reviewed. Data consists of very few complete curves, estimated stresses for rupture and 1% strain, and discrete times to individual strains for individual tests. When adequate data exists, individual tests are fit to theta projection model curves. These “local” theta fits of different test conditions are used as input for the global model. Global fits of theta parameters, as a function of stress and temperature, are made from the full data set. As the global creep model is improved, correction factors introduced to account for true stress and strain effects. A statistical analysis is made of actual rupture time versus predicted onset of failure time, theta5=1. A time-based scatter factor is determined to evaluate temperature margin required to ensure reliability. After the creep model was completed, Haynes International, the material inventor, provided specific test conditions (stress and temperature) of 5 tests that had already been run. Creep predictions were generated for these test conditions, before viewing the actual results. The creep model predicted strain curves matched actual tests very well, both in shape and time to rupture. Continued refinement is possible as more data is acquired.
Associated Gas Utilization Using a Reheat Gas Turbine – Part 1: The Impact of Engine Degradation on the Optimized Power, Energy, and Revenue From Sold Electricity
Authors: Obhuo Mafel , Aziaka Duabari S. , Igbong Dodeye I. , Obhuo Ibirabo M.
Published: September 2021

This study presents a methodology for optimizing the power from a fleet of engines that use associated gas as fuel. The effects of engine degradation on optimized power, energy, and electricity revenue have been evaluated.

The Cranfield University TURBOMATCH has been used to simulate a 296MW reheat gas turbine. Four scenarios were considered — clean, optimistic, medium, and pessimistic. Genetic algorithm was used in optimizing the power generated from the fleets.

In the sequence of clean, optimistic, medium, and pessimistic fleets, the optimization results show that the total optimized power values are 7324.6, 7245.1, 7164.0, and 7074.4MW respectively. In the same sequence, the total energy generated is 64.2, 63.5, 62.8, and 61.9 billion kWh. In a similar sequence still, the electricity revenue is 8.487, 8.390, 8.298, and 8.192 billion US dollars respectively. In comparison with the clean, engine degradation resulted in a 1.09%, 2.19%, and 3.42% decrease in energy for the optimistic, medium, and pessimistic degraded fleets respectively. In the same sequence as the decrease in energy, degradation resulted in a 1.15%, 2.23%, and 3.48% decrease in electricity revenue.

The methodology and results presented in this paper would serve as a guide for associated gas investors in the economic utilization of this fuel resource. This is innovative; it has not been done with the Alstom GT-26 engine.
CFD Evaluation of Internal Flow Effects on Turbine Blade Leading-Edge Film Cooling With Shaped Hole Geometries
Authors: Easterby Christopher C. , Moore Jacob D. , Bogard David G.
Published: September 2021

In gas turbine engines, the highest heat loads occur at the leading-edge areas of turbine blades and vanes. To protect the blades and vanes, a “showerhead” configuration of film cooling holes is often used for this location, in which several rows of holes are configured closely together to maximize film coverage. Typically, these film cooling holes are fed by impingement cooling jets, helping to cool the leading edge internally, but also changing the internal flow field. The effects of these internal flow fields on film cooling are not well known, and experimental research is very limited in its ability to analyze them. Because of this, computational fluid dynamic (CFD) simulations using RANS were used as a way to analyze these internal flow fields. To isolate the effects of the impingement jet, results were compared to a pseudo-plenum internal feed, and rotation in the hole was found to be a key factor in performance. Computational results from both coolant feed configurations were compared to experimental results for the same configurations. The CFD RANS results were found to follow the same trends as the experimental results for both the impingement-fed and plenum-fed cases, suggesting that RANS is able to accurately model some of the important physics associated with leading-edge film cooling.
Thermoacoustic Behaviour of a Hydrogen Micromix Aviation Gas Turbine Combustor Under Typical Flight Conditions
Authors: Abbot David , Giannotta Alessandro , Sun Xiaoxiao , Gauthier Pierre , Sethi Vishal
Published: September 2021

Hydrogen micromix is a candidate combustion technology for hydrogen aviation gas turbines. The introduction and development of new combustion technologies always carries the risk of suffering from damaging high amplitude thermoacoustic pressure oscillations. This was a particular problem with the introduction of lean premixed combustion systems to land based power generation gas turbines.

There is limited published information on the thermoacoustic behaviour of such hydrogen micromix combustors. Diffusion flames are less prone to flashback and autoignition problems than premixed flames and conventional diffusion flames are less prone to combustion dynamics issues. However, with the high laminar flame speed of hydrogen, lean fuel air ratio (FAR) and very compact flames, the risk of combustion dynamics for micromix flames should not be neglected and a comparison of the likely thermoacoustic behaviour of micromix combustors and kerosene fueled aviation combustors would inform the early stage design of engine realistic micromix combustors.

This study develops a micromix combustor concept suitable for a modern three spool, high bypass ratio engine and derives the acoustic Flame Transfer Function (FTF) at typical engine operating conditions for top of climb, take-off, cruise, and end of runway. The FTF is derived using CFD and FTF models based on a characteristic flame delay. The relative thermoacoustic behaviour for the four conditions is assessed using a low order acoustic network code. The comparisons suggest that the risk of thermoacoustic instabilities associated with longitudinal waves at low frequencies (below 1kHz) is small, but that higher frequency longitudinal modes could be excited. The sensitivity of the combustor thermoacoustic behaviour to key combustor dimensions and characteristic time delay is also investigated and suggests that higher frequency longitudinal modes can be significantly influenced by combustion system design.

The characteristic time delay and thus FTF for a Lean Premixed Prevapourised (LPP) kerosene combustor is derived from information in the literature and the thermoacoustic behaviour of the micromix combustor relative to that of this kerosene combustor is determined using the same low order modelling approach. The comparison suggests that the micromix combustor is much less likely to produce thermoacoustic instabilities at low frequencies (below 1kHz), than the LPP combustor even though the risk in the LPP combustor is small.

It is encouraging that this simple approach used in a preliminary design suggests that the micromix combustor has lower risk at low frequency than a kerosene combustor and that the risk of higher frequency longitudinal modes can be reduced by appropriate combustion system design. However, more detailed design, more rigorous thermoacoustic analysis and experimental validation are needed to confirm this.
Simulation of Air/Mist Cooling Among Shock Waves and Passing Wakes Interactions in a Transonic Gas Turbine Stage
Authors: Wang Ting , Abdelmaksoud Ramy
Published: September 2021

This paper presents a 2-D numerical investigation of the effect of interactions of moving wakes and shock waves on mist cooling performance over airfoils in the first stator-rotor stage of a transonic gas turbine. The discrete phase model (DPM) is used to simulate and track the evaporation and movement of the tiny water droplets. Breakup and coalescence sub-models are used to simulate the interaction between the droplets themselves. A linear sliding mesh technique is used to study the transient stator-rotor interaction. The results show that the passing unsteady wakes caused by the blade rotation press the mist on the blade suction side flowing near the blade surface, providing more enhanced film cooling effectiveness. The weak oblique shock waves do not exert a significant effect on the air/mist cooling effectiveness. Injecting a 10% mist ratio noticeably improved the cooling enhancement by reducing the wall temperature values up to 200 K in some locations. Injecting the tiny water droplets does not cause a noticeable pressure loss compared to the air-only cooling case. Injecting mist doesn’t alter the effect of shocks.
Flow Field Analysis and Optimized Design of a Centrifugal Compressor Volute
Authors: Ale Martos Pablo , Barrera-Medrano Maria Esperanza , Martinez-Botas Ricardo , Tomita Isao , Kanzaka Tadashi , Ibaraki Seiichi
Published: September 2021

Turbocharging has become a fundamental technology to realize engine downsizing, which is an attractive strategy for low carbon vehicles in the near term. The stable operation of turbocharger compressors at low and high flow rates is crucial to provide peak torque demand and rated power for turbocharged automotive engines.

The scroll or volute is a key component in centrifugal compressors as its design not only impacts the compressor efficiency but also affects the operating range. This component causes a distorted pressure field upstream which can contribute to stall on the impeller, inducing surge. As the flow inside the volute is fully three dimensional and turbulent, a better understanding of flow mechanisms is key to enable a volute design methodology.

In this study, a centrifugal compressor stage has been modelled numerically and validated by experimental results, to identify the geometric parameters of the volute which contribute to the main flow losses. By solving Reynolds average Navier-Stokes (RANS) equations using a commercial code, the threedimensional flow field of the compressor was modelled. Based on detailed analysis of this flow field, and the impact of various geometric parameters, an optimized volute was developed. The results showed that the total-to-total isentropic efficiency and surge margin could be improved by 1.5% and 4.5%, respectively at design speed.
Effect of Microcylinder and D-Cylinder at the Leading Edge of a Wells Turbine Harvesting Wave Energy
Authors: Sadees P. , Kumar P. Madhan , Samad Abdus
Published: September 2021

Wells turbine is a self-rectifying axial flow reaction turbine used to harvest energy from the ocean waves. It suffers from a premature stall at higher flow rates. The present study discusses a comparative performance analysis with a turbine-blade leading-edge (LE) microcylinder (LEM) and D-cylinder (LED). The space between the LE and the cylinder was fixed as 1.5% of chord length (c). The sizes of the cylinder were varied from 0.5% to 0.75% of the chord. The unstructured tetrahedral mesh elements were used to discretize the computational flow domain that consists of a single blade passage with periodic boundary conditions. The Reynolds-Averaged Navier-Stokes equations with the k-ω shear stress transport (SST) turbulence equations were solved in a commercial CFD code Ansys CFX 18.1. The flow was considered incompressible. The present numerical study was compared with available open literature. The modified rotor blades showed a significant performance enhancement compared to the reference turbine. The peak efficiency was improved by 11.29% at a particular flow coefficient in 0.5%c radius LED-turbine. The presence of the cylinders delayed the flow separation and enhanced the operating range up to 11.11%.
Numerical Investigation on Propagation Characteristics of Inlet Total-Pressure Distortion in a Centrifugal Compressor
Authors: Wang Mingyi , Wang Zhiheng , Xi Guang , Li Yurun
Published: September 2021

The propagation characteristics of inlet total-pressure distortion in a centrifugal compressor are investigated by full-annulus unsteady three-dimensional numerical simulation. The inlet distortions considered in the paper are the total-pressure distortions covering a 60-deg sector (60deg distortion) and three 20-deg sectors (3*20deg distortion), respectively. One is the classical distortion form, and the other is to simulate the downstream flow of the axial section of a centrifugal-axial combined compressor. By analyzing the distributions of flow parameters, the propagation of the total-pressure distortion in the centrifugal compressor is interpreted. The results show that, with the distortion propagating to the downstream, the low-pressure region produces a phase deviation along the streamwise direction relative to the opposite direction of impeller rotation direction, and the range of distortion region is reduced. Additionally, the propagation of the inlet distortion makes the three-dimensional characteristics of airflow more complex. The flow angle increases with different amplitudes along the direction of blade height corresponding to the distorted sector. The distortion region affects the location of blades which are in a low-pressure area, and the intensity of the distortion affects the increase of the flow angle. The distortion region causes more local relative flow losses, especially near the leading edge of blade suction surface.
Investigation on Flowfield and Fuel/Air Premixing Uniformities of Low Swirl Injector for Lean Premixed Gas Turbines
Authors: Sun Fujun , Suo Jianqin , Liu Zhenxia
Published: September 2021

Based on the development trend of incorporating fuel holes into swirler-vanes and the advantages of wide operating conditions as well as low NOx emissions of LSI, this paper proposes an original lean premixed LSI with a convergent outlet. The influence of key structures on flowfields and fuel/air premixing uniformities of LSI is investigated by the combination of laser diagnostic experiments and numerical simulations. The flowfields of LSI shows that the main recirculation zone is detached from the convergent outlet and its axial dimensions are smaller than that of HSI, which can decrease the residence time of high-temperature gas to reduce NOx emissions. The fuel/air premixing characteristics show that the positions and diameters of fuel holes affect fuel/air premixing by changing the penetration depth of fuel. And when the penetration depth is moderate, it can give full play to the role of swirling air in enhancing premixing of fuel and air. In addition, the increase of the length of the premixing section can improve the uniformity of fuel/ar premixing, but it can also weaken the swirl intensity and increase the residence time of the combustible mixture within the LSI, which can affect flame stability and increase the risk of auto-ignition. Therefore, the design and selection of LSI structural parameters should comprehensively consider the requirements of fuel/air mixing uniformity, flame stability and avoiding the risk of auto-ignition. The results can provide the technical basis for LSI design and application in aero-derivative and land-based gas turbine combustors.
Test and Theory for a Refined Structural Model of a Hirth Coupling
Authors: Kim Baik Jin , Oh Joseph , Palazzolo Alan
Published: September 2021

Hirth coupling transmits high torques in the rotating assemblies of compressors and turbines. Their mating surface contacts cause local changes in lateral shaft stiffness. This is affected by the teeth geometry, contact surface area, coupling preload, and surface finish at the contact faces. Industry practice ignores localized lateral flexibility from the Hirth coupling, or is guided by limited experience-based rules of thumb. The authors provide a novel modeling approach utilizing 3D solid finite elements which accounts for contact deformations, intricate interface teeth geometries, stress concentration, and surface finish. This provides an increased accuracy localized stiffness model for the Hirth coupling, to improve rotordynamic response predictions. Free-free natural frequencies of a test rotor including a Hirth coupling are experimentally measured. The rotor is instrumented with strain gauges for preload force measurements, and the Hirth coupling contacting surface profiles are measured with a stylus type surface profiler. A GW contact model is obtained from the measured surface profiles. An iterative computation algorithm is utilized to calculate Hirth coupling contact stiffness and contact pressure at the complex-shaped contact surfaces. Predicted and measured natural frequencies are compared vs. preload.
Influence of Roughness on the Transition Modeling in Compressor Flows
Authors: Tolksdorf Vera , Gokhale Anubhav , Kessler Daniel , Benjamin Leroy , Bode Christoph , Friedrichs Jens
Published: September 2021

Engine operating cost contributes a major share to an aircraft’s direct operating cost. Thus, the knowledge of the current and future state of their engines is a major concern to any airline operator. To be able to schedule shop visits, state-of-the-art diagnostic and prognostic tools including CFD methods are employed. These RANS-based turbulence and transition models are used to predict the overall efficiency and operational behavior of the engine components. Aerofoil surfaces undergo dynamic change during operation and surface roughness increases in complex non-homogeneous ways due to corrosion, erosion, and fouling processes; depending on the engine component and the environmental condition encountered. The influence of real fouling based roughness on the boundary layer transition is investigated experimentally and numerically within this study. For this purpose, the rotor midspan from the second HPC rotor of the CFM56 is used as the basis for experimental and numerical investigations. Realistic fouling based roughness is applied and investigated both in a cascade tunnel and a low speed compressor rig. The results shown here indicate that laminar boundary layers and their transition to turbulence must be included in the RANS model combination used. Furthermore, it is necessary to consider roughness effects in the respective turbulence and transition model. While the consideration of roughness for the turbulence models has already found wide acceptance, the results in this work motivate the additional extension of the transition model to include roughness effects.
Thermoacoustic Instabilities of Hydrogen-Enriched Partially Premixed Flames in a Swirl Combustor
Authors: Gong Y. , Fredrich D. , Marquis A. J. , Jones W. P. , Boxx I.
Published: September 2021

Large eddy simulations (LES) of premixed hydrogen-enriched swirling flames were performed to investigate the flame topology and combustion instabilities with different hydrogen concentrations. A compressible LES approach is utilised to account for the self-excited combustion dynamics. A transported probability density function (pd f) approach is adopted to account for sub-grid scale (sgs) turbulence-chemistry interaction, and the solution to the joint sgs – pd f evolution equation of the scalars is obtained by the stochastic field method. The chemistry is represented using a reduced chemical reaction mechanism containing 15 reaction steps and 19 species. The results revealed that as the concentration of hydrogen increases, the flame is shortened in the injecting direction and more confined in the cross-sectional direction, which is consistent with experimental observations. The self-excited limit-cycle oscillations for all considered cases were successfully reproduced, with the predicted peak frequencies of the chamber pressure spectra in excellent agreement with the measured values. The feedback loop of the oscillations is successfully captured and analysed with the temporal evolution of axial velocity and heat release presented.
Adjustment and Validation of Monitoring System Algorithms on the Simulated Historical Data of an Aircraft Engine Fleet
Authors: Loboda Igor , Pineda Molina Victor Manuel , Pérez-Ruiz Juan Luis
Published: September 2021

In the field of gas turbine diagnostics, a significant gap is observed between the variety of proposed and investigated diagnostic solutions and a narrow group of algorithms employed in real monitoring systems. One of the explanations is that diagnostic algorithms of a monitoring system (system components) are usually developed and verified separately from each other. An additional explanation is related to simplified simulated data used to verify the algorithms.

The present paper aims to adjust and validate the joint operation of the algorithms of a gas turbine monitoring system during the whole lifetime. The software tool called the Propulsion Diagnostic Method Evaluation Strategy (ProDiMES) provides the input data. This tool realistically simulates the steady-state parameters of an aircraft engine fleet. The simulation embraces a total engine life and includes different variations of deterioration and various engine, actuator, and sensor faults.

Using ProDiMES, some diagnostic solutions have been verified so far. However, they do not include all necessary monitoring system components, use a short fixed-time interval of input data, and do not analyze long-term deterioration. In contrast, this paper presents an attempt to enhance a whole diagnostic process. It considers the operation of various data-driven algorithms of a monitoring system during engine life. The paper focuses on the tuning of the algorithms themselves and adjustment of their interactions.
Numerical Investigation of the Interaction Between Gas-Turbine Engine Components With Dynamic Mode Tracking
Authors: Pérez Arroyo Carlos , Dombard Jérôme , Duchaine Florent , Gicquel Laurent , Odier Nicolas
Published: September 2021

Optimizing the design of aviation propulsion systems using computational fluid dynamics is essential to increase their efficiency and reduce pollutant as well as noise emissions. Nowadays, this design process is increasingly aided by computational fluid dynamic methods for which and with the adequate modeling approach it is possible to perform meaningful unsteady computations of the various components of a gas-turbine engine. However, these simulations are often carried out independently of each other and only share averaged quantities at the component interfaces minimizing the impact and interactions between components. The present work investigates the interactions between fan, compressor and annular combustion chamber at takeoff conditions by simulating a 360 azimuthal degrees large-eddy simulation of over 2100 million cells of the DGEN-380 demonstrator. In that case, the domain includes: 14 fan blades; 42 outlet-guide vanes (OGV); the impeller with 11 main blades and 11 splitter blades; a radial and an axial diffuser with 22 and 55 vanes, respectively; and the annular combustion chamber with a contouring casing and 13 swirlers on the back of the chamber. At take-off conditions it is found that the compressor operates in transonic conditions in the rotating frame of reference of the impeller and a shock is formed at the leading edge of the main blades which propagates upstream towards the fan and it is perceived at half the impeller blade-passing frequency (BPF). Preliminary results also show that pressure fluctuations at the impeller BPF generated by the interaction of the impeller blades with the diffuser vanes are propagated through the axial diffuser and enter the combustion chamber through the dilution holes and the swirler. The objective of this paper is to provide a deeper analysis of the interactions between components through the use of the novel operator-based analysis called dynamic mode tracking method (DMT). Indeed, this method facilitates the analysis of three-dimensional results despite the billion-size mesh and the complexity of the simulation, since it extracts modes at specific frequencies on-the-fly within the code. The frequencies corresponding to the fan, impeller and half the impeller BPF are analyzed in the domain and compared against traditional and more computationally demanding methods like the well-known Dynamic Mode Decomposition or the Direct Fourier transform.
Effects of Increased Tooth Clearance on the Performance of a Labyrinth Seal With Oil-Rich Bubbly Laminar Flow
Authors: Zhang Min , Childs Dara W.
Published: September 2021

In recent years, multiphase pumps have become more and more popular because of the capability to simplify the process, reduce the footprint, and lower the cost. To compensate for the axial thrust force, an annular seal is normally used as a balance piston seal, and the labyrinth seal is one of the choices. A typical labyrinth seal consists of a surface with teeth and a smooth surface. The teeth are either on the rotor or the stator. To protect the machine, one side (either the teeth or the smooth surface) is made of a material that can be safely sacrificed during a rub. After the rub, the teeth clearance is increased. This paper studies the impact of the increased teeth clearance on the performance of the labyrinth seal under oil-rich bubbly flow conditions. The test fluid is a mixture of silicone oil (PSF 5cSt) and air with inlet Gas Volume Fraction GVF up to 9%. Tests are conducted with pressure drop PD = 34.5 bars, rotor speed ω = 5 krpm, and radial tooth clearance Cr = 0.102 mm and 0.178 mm. Test results show that, for all test conditions (before and after injecting air bubbles into the oil flow), increasing Cr from 0.102 mm to 0.178 mm increases the mass flow rate by about 40% but barely changes the test seal’s rotordynamic coefficients; i.e., the increased tooth clearance would not change the pump vibration performance.
Dynamic Characteristics Analysis of Flexible Rotor System With Pedestal Looseness
Authors: Hong Jie , Dai Qiyao , Wu Fayong , Ma Yanhong
Published: September 2021

Due to the limitation of assembly conditions and working load environment, the design of pedestal looseness is often used in the structural design of aeroengine multi support flexible rotor, which affects the vibration response and stability of the rotor system. In this paper, a dynamic model of a flexible rotor system with pedestal looseness is established for a practical aeroengine flexible rotor system. Next, a nonlinear modal analysis process for the multi degree of freedom nonlinear rotor system is proposed. Based on this, the nonlinear modal characteristics of the flexible rotor system with pedestal looseness are analyzed. An interval prediction method of modal damping interval for stability analysis of rotor system is presented, and the influence of key characteristic parameters on modal damping and vibration stability of rotor system is explored. Finally, the vibration characteristics of the rotor system are obtained by numerical integration method. The results show that the modal characteristics of the rotor vary with the amplitude of the rotor, and have the feature of interval distribution; vibration stability mainly depends on tangential friction and additional lateral constraint; when the amplitude of the rotor is large, the backward whirling motion may occur and the vibration may be unstable. This paper will provide a theoretical method for dynamic optimization of multi support flexible rotor system, which is helpful to ensure the reliability and safety design of aeroengine.
Thermohydrodynamic Modeling of a Tapered-Land Thrust Bearing With Validation Against Experimental Data
Authors: Gokaltun Seckin
Published: September 2021

In this work, a computational fluid-film bearing analysis model has been utilized in order to investigate the conjugate heat transfer problem for a tapered-land bearing using computational fluid dynamics (CFD) analysis. The academic model is based on the 2D Reynolds equation for the pressure distribution in the film the 3D energy equation is solved for the the bearing pad and the fluid film; therefore, the lubricant properties such as viscosity and density could be made temperature-dependent. The runner is modeled using a 2D axisymmetric mesh. The current analysis excludes the mechanical or thermal deformations of the bearing and the runner since it was observed that the results for output quantities such as film temperature, film pressure, torque and load capacity were within reasonable agreement with the benchmark data obtained from the experiments for the majority of the speed and load cases studied. Comparisons of modeling results against the benchmark data was obtained for cases ranging from 2000 rpm to 10,000 rpm at loads varying from 1000 N to 8000 N. The importance of proper boundary conditions used in the heat transfer model is emphasized as well as the coupling of heat transfer between the film and the solid surfaces of collar and the bearing is described. The results obtained here yielded that a thermohydrodynamic (THD) model that includes the energy transfer into the structures surrounding the fluid film is sufficient enough to predict the performance of a tapered-land bearing at a wide speed and load range in the case where the runner is thick enough that the effect of deformations on the results can be ignored.