bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High Speed Turbine
Authors: Cernat Bogdan , Lavagnoli Sergio
Published: January 2021

While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. For the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. RANS simulations are employed to predict the aerodynamic and thermal field of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high frequency aerodynamic measurements to identify the rotor secondary flow structures.
Influence of Turboshaft Engine Architecture on Ash Particle Deposition: Reduced Order Model Application
Authors: Ellis Matthew , Bojdo Nicholas , Filippone Antonio
Published: January 2021

Particles ingested by aero gas turbines are capable of melting in the combustor and depositing on high pressure turbine vane surfaces, where they degrade aerodynamic and thermodynamic performance. The extent of the damage caused is a complex physical process dependent on the thermal and inertial properties of the particles, the operating state of the engine and importantly, engine architecture. The dominant architecture considerations are the position of the burner flames relative to the nozzle guide vane leading edges and the temperature difference across the burner flames. In this work, we investigate the influence of this on particle deposition by approximating the temperature variation of the hot streak as a sinusoidal profile. A parametric analysis is carried out using numerical simulations and an elastic-plastic particle deposition model, to evaluate the effect of mean temperature, temperature difference across the hot streak, and hot streak position on the deposition rate of a generic particle size distribution. Results show that the dominant effect driving particulate deposition is a combination of the gas temperature, hot streak position relative to the vane leading edge and the particulate type. The rate of deposition on a vane for sub-bituminous ash particles may be reduced by up to 56% if the combination of mean temperature, temperature difference across the hot streak, and hot streak position are chosen carefully.
Industrial Challenges in Large Thermally Enabled Structural Whole Engine Models
Authors: Tindall Michelle , Keskin Akin , Layton Andrew
Published: January 2021

Understanding gas turbine design at a system level presents a difficult challenge. Accurate predictions of gas turbine behaviour before whole engine tests are completed are invaluable in preventing costly design changes in the latter stages of the design life cycle. In this study a high fidelity whole engine model has been built — specifically, a thermally enabled structural model. This model can predict component displacements up to system level interactions across the whole engine. Knowledge from such a model can feed into multiple design areas contributing to performance, component design and structural understanding but can also be used to influence physical testing.

There are clear benefits in building such high fidelity models but also many challenges that need to be addressed, namely solver type, geometry interrogation, meshing, solver capability, computational power and finally, processing and validation of output data. Additionally, different applications have been used for thermal and structural modelling in order to utilise best capabilities in thermal and contact modelling but also enable scalability on high performance computing. However, utilising two different solvers involves meshes being tailored for each solver type but also introduces additional complexity of transferring information between the two models used.

The paper will discuss the challenges and analysis methodologies used to thermally solve the whole engine cycle, the mapping procedure to translate thermal data to a structural model, and the approach taken to solve the very large simulation model explicitly at a chosen condition to a pseudo-steady state. In order to validate the simulation results, a vast amount of time has been spent to compare the results to existing test data.

As model validation is a significant step in simulation to gain credibility of the results, a comparison of the predicted component displacements will be shown to X-ray data from a whole engine test. Results and limitations of this testing capability such as influence of engine vibration, shutter speed and noise in the data will be discussed and recommendations provided to improve accuracy of the results.
Cooling Improvement of Gas Turbine Rotary Blades
Authors: Rasimarzabadi Faezeh , Kamalimoghadam Ramin , Najafi Mahmoud , Mohammadi MohammadReza , Sahranavard Fard Nasrin
Published: January 2021

A new method is presented to improve cooling of the turbine blades by using active extraction from the compressor outlet to supply more cooling air with more energy. The cool air is extracted from the end of compressor through a set of peripheral holes to the air transferring channels on the disc edge or torque tube using the tangential velocity vector of the rotating shaft which results in increasing the amount and energy of the cooling air. In fact a forward angle of inlet holes for the channels is used to help the pressurized air overcome the air centrifugal force and to accelerate the flow going into the torque tube. To investigate the effect of new idea, both the original and proposed models are analyzed using 3D CFD simulation on a selected physical domain of a gas turbine. The compressible rotating Navier-Stokes equations are used for numerical simulation of two geometries. The governing equations, mesh treatment, boundary conditions and numerical setup are described. The calculation results are compared to those of the original turbine shaft to show the heat transfer improvement by enhancing the cooling flow rate and fluid energy.
Unsteady Effects due to Rotor Purge Flow Variations in a Dual-Spool Turbine Setup
Authors: Merli F. , Sterzinger P. Z. , Dellacasagrande M. , Wiesinger L. , Peters A. , Heitmeir F. , Göttlich E.
Published: January 2021

The paper discusses the impact of rotor purge flows on the unsteady flow field downstream of a two-stage, two-spool test turbine. The analyzed setup is representative of the second high-pressure turbine (HPT) and the first low-pressure turbine (LPT) stage in a modern turbofan aero-engine, with a turbine center frame (TCF) with non-turning struts in-between the two turbines. All measurements were carried out for an engine-representative test vehicle setup at the Transonic Test Turbine Facility at Graz University of Technology. The test rig features a secondary air system delivering five purge flows with independent temperature and mass flow control to the HPT and LPT cavities.

This work extends the results shown in two recent publications analyzing the time-resolved flow through the same two-stage setup at fixed purge flow rates. The paper aims to provide additional input about the driving sources of unsteadiness in gas turbines for aeronautic applications, by isolating the HPT and LPT purge air contributions.

The time-resolved flow field at the LPT exit was acquired with a Fast Response Aerodynamic Pressure Probe (FRAPP) for three different purge conditions (reference case, no HPT purge case, no LPT purge case), to separate and quantify the impact of HPT and LPT purge contributions on the main flow field. The so-called Rotor Synchronic Averaging (RSA) technique was used as phase-averaging approach, to account for the unsteadiness due to both rotors. Proper Orthogonal Decomposition (POD) was then applied to isolate the most important structures and identify their origins. The comparison of the three data-sets shows a significant influence of the HPT purge on the entire flow field at the LPT exit, even though the HPT is located far upstream, while the LPT purge impact appears to mostly affect the end-wall region.
A Self-Tuning Model Framework Using K-Nearest Neighbors Algorithm
Authors: Yang Shu-Bo , Alafate Julaiti , Wang Xi , Tian Zhen
Published: January 2021

Benchmark models are indispensable for gas turbine engine monitoring and diagnostics. In most cases, benchmark models are used to predict engine data. When the measured data from a real engine does not match up the predicted data, it means that something undesirable is going on and the engine may need servicing.

Generally, the benchmark models are also thermodynamic models. They are either offered by engine manufactures or obtained using the technique called “performance adaptation”. In both cases, those models have a major limitation: they cannot reflect the development of engine deterioration over time, i.e., deterioration parameters of these models are fixed unless manually adjusted. In practice, however, most engines deteriorate continuously and gradually over time. Due to the increasing mismatch of deterioration, the accuracy of the benchmark model will get worse gradually.

To address the mismatch, this paper presents a self-tuning model framework that intends to improve the existing benchmark models. In the framework, a set of deterioration models are introduced and attached to the original benchmark model. The deterioration models represent the deterioration conditions of all major components. They are machine learning models and can be updated automatically according to the engine measurements. With the aid of the k-nearest neighbours algorithm and gas path analysis techniques, the deterioration models can track the real deterioration conditions through self-tuning and are robust under noise. The proposed model framework is applied to a model turbofan engine. Simulation results show that the accuracy of the benchmark model improves significantly after using the self-tuning framework.
Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays
Authors: Otto Marcel , Gupta Gaurav , Tran Patrick , Ghosh Shinjan , Kapat Jayanta
Published: January 2021

Arrays of staggered pin fins are a typical geometry found in the trailing edge region of modern airfoils. If coolant is supplied by bleeding from the mid-section of the airfoil instead of provided through the root, the channel length is not long enough to reach a fully developed flow which is commonly found from the fifth row downstream. This present study focuses on the developing section (four rows) of a staggered array with a height to diameter ratio of 2 and a spanwise and streamwise spacing of 2.5 respectively. Measurements are conducted at two Reynolds numbers of 10,000 and 30,000 based on the maximum velocity and pin diameter. Stereoscopic PIV is used to describe the flow field and turbulence characteristics in the wake of the first and third row pin. It is found that the dominating vortical structures depend highly on the Reynolds number. A transient thermochromic liquid crystal technique is used to obtain local heat transfer coefficients on the endwall which are then discussed in the context with the vortical structures. The structure of the horseshoe vortex and the transient wake shedding behave differently in the first and second row. The interaction of both vortex systems affects directly the endwall heat transfer. The results are supplemented by a thorough discussion of TLC and PIV uncertainty.
Numerical and Experimental Aerodynamic Investigation of an S-Shaped Intermediate Compressor Duct With Bleed
Authors: Siggeirsson Elias M. V. , Andersson Niklas , Burak Olander Markus
Published: January 2021

A series of CFD simulations are performed to analyse the effects a rotor off-take bleed has on the performance of an Intermediate Compressor Duct (ICD). To validate the CFD results, a comparison is made to measurements obtained from an experimental facility located at GKN Aerospace Engine Systems in Sweden. To achieve a deeper understanding of the flow physics, hybrid RANS/LES simulations are performed for a single operating condition. The CFD simulations are capable of predicting the behavior when extracting large amount of air through the bleed pipe, where an improved prediction is obtained with the hybrid simulation. The performance of the ICD is severely compromised with increased amount of bleed as the flow delivered to the downstream component is highly disturbed. The disturbed flow is caused by the extraction of axial flow through the bleed pipe, increasing the incidence into the low-pressure compressor’s outlet guide vanes resulting in unfavorable velocity profiles into the ICD. This behavior causes the flow to separate at the OGV blades, where the separation increases with increase bleed. Furthermore, when including the full bleed system, significant circumferential distortions are observed, showing the necessity of the integrated design.
Interaction Between Coriolis Forces and Mistuning on a Cyclic Symmetric Structure With Geometrical Nonlinearity
Authors: Tacher Anthony , Thouverez Fabrice , Armand Jason
Published: January 2021

An investigation of the interaction between Coriolis forces and mistuning on a cyclic symmetric structure is presented in this paper. The sensitivity of the eigenvalues and eigenvectors to mistuning is first studied with the perturbation method. A lumped parameter model is used to perform a modal analysis using a numerical approach after which geometrical nonlinearity is added to compare behavior with the linear case. Two different modes are thoroughly investigated for different rotational speeds, the first with an eigenvalue isolated from the others and the second presenting a frequency veering zone. The evolution from a standing wave domination at low speeds to a travelling wave domination at high speeds is observed for the isolated mode, whereas a standing wave domination remains around the veering zone for the second mode studied. It is also shown that the geometrical nonlinearity reinforces the mistuning effect versus the Coriolis forces.
Unsteady Numerical Investigation on Film Cooling Characteristics of the Trailing Edge Cutback With Upstream Cylinder Hole
Authors: Xiao Xiangtao , Wang Pei , Xu Qingzong , Du Qiang , Liu Jun , Chang Sheng
Published: January 2021

The trailing edge cutback is often applied when designing the film cooling structure of a high-pressure turbine. Previous studies have demonstrated strong unsteady film mixing process which is indeed influenced by the vortex shedding from the pressure side lip. Thus, adiabatic film cooling effectiveness on cutback rapidly declines at streamwise direction. To obtain high film cooling performance, this paper arranges a cylinder hole on pressure side upstream of the trailing edge cutback flat-plate model. The film cooling characteristics of combined configuration are investigated with unsteady numerical method. DES turbulence model has been proved to capture the vortex shedding well. The mainstream Reynold number is Rem = 360000 based on the length from inlet to lip. The total coolant-to-mainstream blowing ratio is M = 0.5 and cylinder hole is arranged at three different positions (X/H = −4, −6, −8). Firstly, film cooling performance of two configurations (cutback, cutback with a cylinder hole at X/H = −6) are compared. The results indicate that the mainstream temperature and velocity greatly reduce due to hole coolant ejection. The vortex shedding downstream of lip is weakened contributing to less film mixing on the trailing edge cutback. The lateral-averaged adiabatic film cooling effectiveness increases especially downstream of cutback. Then three combined configurations of hole at different positions show that all configurations can improve film cooling performance of the trailing edge cutback. When cylinder hole is arranged closer to lip, adiabatic film cooling effectiveness increases more.
Numerical Study of a Small-Scale Micro Gas Turbine-ORC Power Plant Integrated With a Biomass Gasifier
Authors: Reale Fabrizio , Sannino Raniero , Calabria Raffaela , Massoli Patrizio
Published: January 2021

The paper is focused on coupling a small-scale power plant, based on a micro gas turbine (mGT) and a bottoming Organic Rankine Cycle (ORC), with a biomass gasifier. The aim of this study is to define the optimal strategies to maximize the benefits related to distributed generation and to promote the organic solid waste gasification, in terms of energy efficiency and renewable sources exploitation. In particular, they were investigated the energetic performances of the system when the micro gas turbine was fed with several fuel blends, made by specific volume concentration of syngas and biogas. The low heating value of both considered fuels implies the necessity of operating the mGT in peculiar conditions as determined by the performance maps of compressor and turbine. Then, the thermodynamic analyses of the whole energy system have been carried out to evaluate the performance for each fuel. The high hydrogen content of syngas and the different thermodynamic properties of the studied fuel blends required a deeper investigation of the combustion process. In order to analyze the combustion stability and the fluid dynamic aspects, an accurate investigation of combustion chamber has been performed through a CFD solver. Finally, a comparison of the plant performances for each fuel blend have been reported, along with opportunities and critical aspects related to power plant integration.
Using Blade Tip Timing and Pressure Data to Characterise Compressor Stall and Surge
Authors: Przysowa Radoslaw , Russhard Peter , Wachlaczenko Michal
Published: January 2021

Rotating stall and surge are common phenomena in compressors, and related research has been carried out since the invention of the gas-turbine engine. Signals of fast response pressure sensors analysed with spectral methods based on Fourier transform are primarily used to characterise compressor stall. This article focuses on the application of blade tip timing (BTT) for this purpose and aims to demonstrate current analysis capabilities, issues and challenges related to practical applications. By using real engine test results, we show that BTT provides more information at the cost of more complex analysis. The signals of four tip timing and three pressure probes installed in the first compressor stage are processed. We observed flow disturbances and blade responses caused by objects located in the inlet at a constant speed and also surge events during snap acceleration. All-blade spectrum and modal tracking are used to identify the presence of non-integral vibration and to determine the nominal frequency and nodal diameter. This data seeds the Least Squares Fitting, which delivers amplitude and phase. A method for sensor fusion is presented. For the selected non-integral responses, tip timing and pressure results are evaluated to show how they can complement each other. The proposed methodology can be used both for compressor development and Blade Health Monitoring.
Application of Immersed Boundary Method on Instrumented Turbine Blade With LES
Authors: Ubald Bryn N. , Watson Rob , Cui Jiahuan , Tucker Paul , Shahpar Shahrokh
Published: January 2021

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a coupled blade and probe requires the generation of a high quality mesh which can take a significant amount of an engineers time. The application of Immersed Boundary Method (IBM) and Large Eddy Simulation is shown in this paper to enable the use of an extremely simple mesh to observe the primary flow features generated due to the blade and probe interaction effects, as well as quantify downstream pressure loss to within a high level of accuracy. IBM is utilised to approximately model the probe, while fully resolving the blade itself through a series of LES simulations. This method has shown to be able to capture downstream loss profiles as well as integral quantities compared to both experiment and fully wall-resolved LES without the need to spend a significant amount of time generating the ideal mesh. Additionally, it is also able to capture the turbulence anisotropy surrounding the probe and blade regions.
Integrally Bladed Rotor Mistuning Identification and Model Updating Using Geometric Mistuning Models
Authors: Beck Joseph A. , Brown Jeffrey M. , Gillaugh Daniel L. , Carper Emily B. , Kaszynski Alex A.
Published: January 2021

Non-uniform manufacturing variations and uneven usage wear and damage, referred to as mistuning, can drastically alter the dynamic response of Integrally Blade Rotors (IBR)s. Optical scanners, combined with Finite Element Model (FEM) mesh metamorphosis algorithms, have provided capabilities to create analytical models that reduce the effect of geometrical uncertainties in numerical predictions. However, deviations in material properties cannot be obtained via optical scanning, so additional approaches are needed. A geometric mistuning Reduced-Order Model (ROM) is developed and modified to solve for unknown IBR sector eigenvalues that are linearly proportional to Elastic modulus. The developed approach accounts for both proportional and non-proportional mistuning and allows updating of the Elastic modulus for each sector in the ROM. Different tuned and mistuned modal reduction procedures are employed to understand the implications of each for identifying mistuning. Simulated test data with known inputs indicate the efficiency and accuracy of the method and improvements over using a traditional, tuned mode approach. The developed methods are then extended to bench-level traveling wave excitation data to discern how sector frequencies vary due to geometry and modulus mistuning.
Numerical Investigation on Unsteady Characteristics in Different Rim Seal Geometries: Part B
Authors: Lian Zengyan , Du Qiang , Liu Guang , Wang Ruonan , Xie Lei
Published: January 2021

Hot gas ingestion into the wheel space can reduce the lifetime of vulnerable components in gas turbine like the turbine disk. Rim seal structure at the periphery of the wheel-space is designed to protect the turbine disk from hot gas. This paper describes the steady and unsteady Reynolds-averaged Navier-Stokes (RANS and URANS) computation method with Shear Stress Transport (SST) turbulent model using commercial CFD code and the validation of grids. The RANS and URANS computation have been carried out in a one stage turbine model with different rim seal configurations: fish-mouth rim seal and double rim seal. A 10.91° sector computation model comprises one pitch in a row of stator vanes, and rotor blades is set up and simulated with different sealant flow rate. Results show that the fish-mouth rim seal can achieve higher sealing effectiveness with low sealant flow rate by installing the inner shell at high radius on the stator disk. The comparison between the steady and unsteady results indicates that the RANS computation underpredicts the level of the hot gas ingestion, especially in the double rim seal configuration. It can be found in the URANS computation results at different time steps that, when the rotating effect is considered, the interaction between the vane wake and the wave of the blade leading edge can lead to more serious pressure asymmetry, which worsens the hot gas ingestion. The counter-rotating vortex induced at outer wheel space and the Kelvin-Helmholtz-like vortices caused by velocity difference of mainstream and sealing flow can further aggravate the ingress.
Optimisation of CO Turndown for an Axially Staged Gas Turbine Combustor
Authors: Rivera Jacob E. , Gordon Robert L. , Talei Mohsen , Bourque Gilles
Published: January 2021

This paper reports on an optimisation study of the CO turndown behaviour of an axially staged combustor, in the context of industrial gas turbines (GT). The aim of this work is to assess the optimally achievable CO turndown behaviour limit given system and operating characteristics, without considering flow-induced behaviours such as mixing quality and flame spatial characteristics. To that end, chemical reactor network modelling is used to investigate the impact of various system and operating conditions on the exhaust CO emissions of each combustion stage, as well as at the combustor exit. Different combustor residence time combinations are explored to determine their contribution to the exhaust CO emissions.

The two-stage combustor modelled in this study consists of a primary (Py) and a secondary (Sy) combustion stage, followed by a discharge nozzle (DN), which distributes the exhaust to the turbines. The Py is modelled using a freely propagating flame (FPF), with the exhaust gas extracted downstream of the flame front at a specific location corresponding to a specified residence time (tr). These exhaust gases are then mixed and combusted with fresh gases in the Sy, modelled by a perfectly stirred reactor (PSR) operating within a set tr. These combined gases then flow into the DN, which is modelled by a plug flow reactor (PFR) that cools the gas to varying combustor exit temperatures within a constrained tr. Together, these form a simplified CRN model of a two-stage, dry-low emissions (DLE) combustion system. Using this CRN model, the impact of the tr distribution between the Py, Sy and DN is explored. A parametric study is conducted to determine how inlet pressure (Pin), inlet temperature (Tin), equivalence ratio (ϕ) and Py-Sy fuel split (FS), individually impact indicative CO turndown behaviour. Their coupling throughout engine load is then investigated using a model combustor, and its effect on CO turndown is explored. Thus, this aims to deduce the fundamental, chemically-driven parameters considered to be most important for identifying the optimal CO turndown of GT combustors.

In this work, a parametric study and a model combustor study are presented. The parametric study consists of changing a single parameter at a time, to observe the independent effect of this change and determine its contribution to CO turndown behaviour. The model combustor study uses the same CRN, and varies the parameters simultaneously to mimic their change as an engine moves through its steady-state power curve. The latter study thus elucidates the difference in CO turndown behaviour when all operating conditions are coupled, as they are in practical engines. The results of this study aim to demonstrate the parameters that are key for optimising and improving CO turndown.
Quantitative Evaluation and Optimization of Feeding-Back Previous Cycles Information for CFD Periodic Convergence
Authors: Contreras Jesus , Crespo Javier
Published: January 2021

Unsteady simulations represent an expensive sub-set of CFD simulations in terms of computational resources. Among the unsteady simulations the time periodic cases are of special interest in many applications such as turbomachinery. The special characteristics of these cases allow specific methodologies to improve its periodic convergence behavior, neglecting the physical transient to achieve it. The scope of this paper is focused on these unsteady periodic simulations.

In this context, departing from a plain Dual Time Step methodology, where the standard generic procedure is to converge every physical time step from the solution of the previous one, the effect of feeding-back the previous period information to re-start the convergence of the equivalent time steps in the new period is assessed in this paper. With that aim, options to alleviate the possible penalties of the procedure are presented, and the parameter set election and boundary conditions optimized to define a complete methodology.

Finally, a benchmarking of the defined methodology is performed against the standard plain Dual Time Step technique and the much more efficient Harmonic Balance methodology. For that comparison, harmonic torsion vibration in a basic 2D case and in a more realistic 3D compressor, as well as two rotorstator configurations are computed and presented here.

The results show that a comparable efficiency to the Harmonic Balance technique is achieved with lower memory requirements, meaning that the performance of the plain Dual Time Step methodology are greatly improved just changing small parts of its formulation.
Numerical and Experimental Investigation of a Low Order Radial Turbine Model for Engine-Level Optimisation of Turbocharger Design
Authors: Hohenberg Karl , Martinez-Botas Ricardo , Łuczyński Piotr , Freytag Carola , Wirsum Manfred
Published: January 2021

This paper presents the development and validation of a meanline model by means of numerical and experimental methods, to determine it’s feasibility as an optimisation tool for turbocharger matching. Using a parametric turbine model, numerical experiments were conducted accounting for variations of several key turbine design parameters and a wide operating range. The resulting dataset was used to test the accuracy of the meanline model when calibrated to a baseline design and thus evaluate it’s ability of extrapolating to different designs. The loss models were examined in more detail, and a set of loss models which provided the most accurate results is presented. The meanline model was further validated experimentally using dynamometer test results of 6 turbine designs from the same parametric turbine model. The result showed that for design point and high power operation, an error of less than 3.1% and 2.0% was achieved for efficiency and mass flow parameter respectively. This led to the conclusion that the model would be sufficiently accurate to represent design changes relevant to turbocharger matching.
Low-Cycle Fatigue Life of Continuously Cyclic-Hardening Material
Authors: Zhang Zhong , Wu Xijia
Published: January 2021

A general fatigue life equation is derived by modifying the Tanaka-Mura-Wu dislocation pile-up model for variable strain-amplitude fatigue processes, where the fatigue crack nucleation life is expressed in terms of the root mean square of plastic strain range. Low-cycle fatigue tests were conducted on an austenitic stainless steel. at 400°C and 600°C, the material exhibits continuously cyclic-hardening behaviour. The root mean square of plastic strain ranges is evaluated from the experimental data for each test condition at strain rates ranging from 0.0002/s to 0.02/s. The variable-amplitude Tanaka-Mura-Wu model is found to be in good agreement with the LCF data, which effectively proves Miner’s rule on the stored plastic strain energy basis.
Assessment of Current Capabilities and Near-Term Availability of Hydrogen-Fired Gas Turbines Considering a Low-Carbon Future
Authors: Emerson Benjamin , Wu David , Lieuwen Tim , Sheppard Scott , Noble David , Angello Leonard
Published: January 2021

A confluence of technology development, policy support, and industry investment trends are accelerating the pace of Hydrogen (H2) technology demonstrations, increasing the likelihood of power sector impacts. In preparation for a large-scale power sector shift toward decarbonization for a low-carbon future, several major power equipment manufacturers are developing gas turbines that can operate on a high H2-volume fuel. Many have H2 capable systems now that range from 5 to 100% H2. Units with 100% H2 capabilities are either using a diffusion burner or some version of a wet low emissions (WLE) burner. Most dry low emission/dry low NOx (DLE/DLN) technologies are currently limited to ∼60% H2 or less. Therefore, research is currently underway to develop low NOx gas turbine combustion systems with improved Hydrogen capability. This paper provides an overview of the technical challenges of Hydrogen combustion and the probable technologies with which the manufacturers will respond.
Detailed Experimental Study of the Flow in a Turbine Rear Structure at Engine Realistic Flow Conditions
Authors: Vikhorev Valentin , Chernoray Valery , Thulin Oskar , Deshpande Srikanth , Larsson Jonas
Published: January 2021

A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency and reducing emissions from aero-engines. This paper presents a detailed experimental evaluation of an engine realistic TRS which was studied in an engine-realistic rig at Chalmers University of Technology, Sweden. The TRS test section was equipped with three types of outlet guide vanes (OGVs) which are typical of modern state-of-the-art TRS: regular vanes, thickened vanes and vanes with an engine mount recess (a shroud bump). Each of the three vane geometries were studied under on-design and off-design conditions at a fixed flow Reynolds number of 235,000. The study shows that the off-design performance of the TRS strongly depends on the presence of the local flow separation on the OGV suction side near the hub, which is greatly affected by the vane pressure distribution and inlet conditions. Similarly, the OGVs with increased thickness and with a vane shroud bump are shown to affect the performance of the TRS by influencing the losses on the OGV suction side near the hub. Furthermore, the presence of the bump is shown to have noticeable upstream influence on the outlet flow from the low-pressure turbine and noticeable downstream influence on the outlet flow from the TRS.
Magnetic Bearings for High-Temperature sCO2 Pumped Heat Energy Storage
Authors: Rimpel Aaron , Smith Natalie , Allison Tim , Masala Andrea
Published: January 2021

Supercritical carbon dioxide (sCO2)-based cycles have been investigated for pumped heat energy storage (PHES) with the potential for high round-trip efficiencies. For example, PHES-sCO2 cycles with hot-side temperatures of 550°C or higher could achieve round-trip efficiencies greater than 70%. The energy storage cycle and equipment also synergize well with other systems incorporating thermal storage and/or sCO2 power blocks, e.g., concentrating solar power. These sCO2 cycles are closed Brayton cycles whose efficiency and system cost and complexity are sensitive to leakage and makeup/recompression requirements for long-term application. Therefore, incorporating hermetically-sealed machinery is an attractive option for minimizing system leakage and improving system cost and performance. Bearings that enable hermetic machines include sCO2 process-lubricated bearings and magnetic bearings. Ongoing developments in sCO2-lubricated bearings are addressing the well-known limitations that have challenged their use in megawatt-scale machinery (load capacity, damping), yet magnetic bearings have decades of performance in commercial applications at that scale and are worthy of consideration. This paper discusses a proposed sCO2-based PHES system application, and a cycle model establishes nominal conditions that define CO2 environment pressures and temperatures that magnetic bearings would have to operate in. A sensitivity study of the cycle’s round-trip efficiency is presented to see the impact of improved compressor and turbine efficiencies, which would result from expected windage loss and seal leakage reduction from a hermetic machinery configuration compared to one using conventional oil-film bearings. The result is approximately two points of round-trip efficiency for each point of isentropic efficiency from all machines. In the nominal cycle, the highest process temperatures exist for the charge mode compressor and discharge mode turbine, which would require magnetic bearings capable of operating up to 410°C. This exceeds the capabilities of typical commercial magnetic bearings (200°C), though it is within temperature ranges demonstrated for high-temperature magnetic bearings operating in low-pressure air (550°C). However, high-pressure sCO2 presents unique challenges that require further development. The paper discusses how these technical issues can be addressed to advance magnetic bearings for sCO2 applications.
Methane Emissions Reduction Solutions: Product Development and Standardization
Authors: Garceau Sean , Jawalkar Amar , McKennon Ryan , Moffatt Christopher , Pocengal Anthony , Thomas Michella
Published: January 2021

The Oil & Gas industry and environmental agencies around the world are working to find solutions to reduce greenhouse gas (GHG) emissions. A comprehensive study by the US EPA found that emissions from compressor stations, blow down and purge, accounted for 97.7 Bscf or just over 31% of the total methane emissions attributed to the Natural Gas industry. [1] With methane (CH4) having 25 times the impact on global warming compared to carbon dioxide (CO2), and global legislation like the Regulations Respecting Reduction in the Release of Methane and Certain Volatile Organic Compounds Upstream Oil and Gas Sector (or also called Canadian Methane Rule) and regional methane reduction regulations, developing solutions to further mitigate methane emissions from process gas vents and centrifugal gas compressor seals becomes necessary as the industry moves towards near-zero targets.

This paper addresses the design requirements and selection of a process gas vent recapture system and primary dry seal vent recapture system. In addition, this paper will review the design consideration during the design phase to the data collected during site operation.
Free-Stream Turbulence Induced Boundary-Layer Transition in Low-Pressure Turbines
Authors: Ðurović Kristina , De Vincentiis Luca , Simoni Daniele , Lengani Davide , Pralits Jan , Henningson Dan S. , Hanifi Ardeshir
Published: January 2021

The aerodynamic efficiency of turbomachinery blades is profoundly affected by the occurrence of laminar-turbulent transition in the boundary layer since skin friction and losses rise for the turbulent state. Depending on the free-stream turbulence level, we can identify different paths towards a turbulent state. The present study uses direct numerical simulation as the primary tool to investigate the flow behaviour of the low-pressure turbine blade. The computational set-up was designed to follow the experiments by Lengani & Simoni [1]. In the simulations, the flow past only one blade is computed, with periodic boundary conditions in the cross-flow directions to account for the cascade. Isotropic homogeneous free-stream turbulence is prescribed at the inlet. The free-stream turbulence is prescribed as a superposition of Fourier modes with a random phase shift. Two levels of the free-stream turbulence intensity were simulated (Tu = 0.19% and 5.2%), with the integral length scale being 0.167c, at the leading edge. We observed that in case of low free-stream turbulence on the suction side, the Kelvin–Helmholz instability dominated the transition process and full-span vortices were shed from the separation bubble. Transition on the suction side proceeded more rapidly in the high-turbulence case, where streaks broke down into turbulent spots and caused bypass transition. On the pressure side, we have identified the appearance of longitudinal vortical structures, where increasing the turbulence level gives rise to more longitudinal structures. We note that these vortical structures are not produced by Görtler instability.
Implicit GPU Accelerated Numerical Simulations via the Use of Ghost Cell Immersed Boundary Method
Authors: Zacharzewski Piotr , Jefferson-Loveday Richard
Published: January 2021

Flow as well as geometry inside turbomachinery components such as turbine blades is complex and difficult to handle accurately. Computationally affordable Reynolds Averaged Navier Stokes (RANS) simulations are often not suitable and partly resolving simulations such as Large Eddy Simulation (LES) or hybrid RANS-LES are needed for sufficient accuracy in the area. Within industrial turbine design, these are not deployed routinely, if at all, due to their presently unaffordable computational cost and time-consuming grid generation for complex geometries.

General Purpose Graphic Processing Units (GPGPUs) and other modern heterogeneous hardware offer much cheaper computational power, however, so far remain mostly unharnessed in the field of CFD due to difficulty of creating structured datasets required to utilise the GPUs effectively. While unstructured or hybrid grids can be used on massively parallel platforms, the typically irregular memory access patterns they demand usually prohibits effective scaling and GPU remains mostly idle, negating the benefits. Within CFD, structured datasets with ordered memory access patterns are most easily obtained with structured multiblock grids and such grids are an excellent candidate for GPU platforms. This is not without challenges as creating high quality structured grids over complex geometries is known to be a highly time consuming and difficult process.

Another limitation of GPUs is difficulty of solving tridiagonal systems of equations efficiently on those platforms. Solution of such systems of equations is typically required for implicit time advancement or convergence acceleration techniques such as AMG and it is well established that implicit numerical schemes provide significant computational savings due to their efficiency. In the present work a novel Alternating Direction Implicit (ADI) library is integrated into the CFD system to enable scalable solution of tridiagonal systems on GPUs.

In the current paper a GPU-accelerated Immersed Boundary Method (IBM) code is presented and validated for turbo-machinery applications. It is shown that the combination of IBM, a high-level Oxford Parallel library for Structured applications (OPS) and an ADI solver provide the geometric as well as computational flexibility unmatched by traditional unstructured solvers. A single source code exists for major hardware platforms and the parallel implementation is decoupled from the scientific codebase, making the code scalable and easily adaptable to any emerging, future architectures.
Experimental Study of Cyclic Synchronous Vibration of an Integrally Geared Centrifugal Compressor for Air Separation Application
Authors: Luo Zhusan , Schwarz Carl L. , Martins Fabio , Rosati Anthony
Published: January 2021

This paper presents an experimental study of high cyclic synchronous vibration observed on the top pinion of an integrally geared centrifugal compressor. This cyclic synchronous vibration was different from the previously reported Morton effect. In a typical cycle, the vibration began with a long quiet period, then took off and followed by settle-down. Sometimes, vibration peaked above a shutdown limit, which subsequently tripped the compressor and then the air separation plant. Frequency spectra showed this new cyclic vibration was dominated by synchronous vibration. To obtain reliable and meaningful phase information for the diagnosis, a new signal processing technique was developed to analyze the historic vibration data captured without a key phasor. An experimental study of this new rotordynamic phenomenon was conducted on the machine in operation. Test data showed the high cyclic synchronous vibration was closely related to Morton effect though it does not have a significant phase shift. An effective remedy measure was therefore taken, and the cyclic synchronous vibration was eliminated. Since then, this compressor has been running smoothly for 17 months. A possible mechanism of the cyclic vibration is discussed in this paper.
An Experimental and Numerical Investigation of the Three-Dimensional Flow Field and Heat Transfer of a Row of Impinging Jets
Authors: Saglam Simla , Krewinkel Robert , Domnick Clemens , Takeishi Ken-Ichiro
Published: January 2021

Impingement cooling is a well-established technique to reduce the thermal load of hot gas components in gas turbines. Although the technique is widely used, correlations are nonetheless the standard design method, as the flow field and heat transfer are notoriously difficult to predict with state-of-the-art commercially viable CFD calculations. The primary challenges to CFD are phenomena such as shear layers and crossflow interactions. Therefore, a demand for spatially highly resolved measurements exists.

An experimental investigation of a confined row of round jets impinging on a flat surface representative of gas turbine geometries with and without an initial crossflow has been conducted. The effect of the distance between the impingement plate and the target surface as well as the effect of the crossflow flow rate on the interaction of the jets with each other and with the crossflow are assessed. The three-dimensional impingement flow field and the heat transfer characteristics on the target surface are measured. The former has been visualised by Magnetic Resonance Velocimetry (MRV). This measurement technique is relatively novel for engineering applications, but very well suited for low-Mach number flows in complex geometries. It yields millions of measurement points and is thus ideal for a comparison with CFD. The local Nusselt number distribution is obtained using steady-state Thermochromic Liquid Crystals (TLC) on the same test set-up. Secondary losses and errors associated with this method are evaluated by means of an energy balance.

The experiments are accompanied by a CFD simulation using an approach typically used for designing impingement configurations in industry as well as a more advanced method.
Influence of Large Relative Tip Clearances for a Micro Radial Fan and Design Guidelines for Increased Efficiency
Authors: Wagner Patrick H. , Van herle Jan , Gu Lili , Schiffmann Jürg
Published: January 2021

The blade tip clearance loss was studied experimentally and numerically for a micro radial fan with a tip diameter of 19.2mm. Its relative blade tip clearance, i.e., the clearance divided by the blade height of 1.82 mm, was adjusted with different shims. The fan characteristics were experimentally determined for an operation at the nominal rotational speed of 168 krpm with hot air (200 °C). The total-to-total pressure rise and efficiency increased from 49 mbar to 68 mbar and from 53% to 64%, respectively, by reducing the relative tip clearance from 7.7% to the design value of 2.2%. Single and full passage computational fluid dynamics simulations correlate well with these experimental findings. The widely-used Pfleiderer loss correlation with an empirical coefficient of 2.8 fits the numerical simulation and the experiments within +2 efficiency points. The high sensitivity to the tip clearance loss is a result of the design specific speed of 0.80, the highly-backward curved blades (17°), and possibly the low Reynolds number (1 × 105). The authors suggest three main measures to mitigate the blade tip clearance losses for small-scale fans: (1) utilization of high-precision surfaced-grooved gas-bearings to lower the blade tip clearance, (2) a mid-loaded blade design, and (3) an unloaded fan leading edge to reduce the blade tip clearance vortex in the fan passage.