bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.