bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Vane/Blade Interaction for a Cooled Turbine Blade — Part II: Unsteady Pressure and Heat Transfer Distributions
Authors: Sperling Spencer , Christensen Louis , Mathison Randall , Aksoy Hakan , Liu Jong , Nickol Jeremy
Published: October 2022

Unsteady flow fields are generated in gas turbines due to interactions between rotating and stationary components. Increased understanding of unsteadiness and its effect on blade heat transfer is crucial to thermal durability predictions for turbine components. This study examines unsteady pressure, heat transfer, and film cooling on a rotating high-pressure turbine stage using experimental and unsteady computational tools. Comparisons between experimental and computational results identify several key elements necessary for successful computational models. Models benchmarked against experimental data provide valuable insight into the nature of flow field unsteadiness and its impact on blade heat transfer.

Comparisons presented in Part I of this paper identified a region near the leading edge of the suction surface of the airfoil where the computational and experimental results did not agree. Part II of the paper will examine the mechanisms driving unsteadiness in this region and how they can be better predicted. The source of this disagreement is that vane blade interaction causes large swings in incidence angle at the leading edge, which causes periodic separation on the suction surface. In addition, pressure fluctuations couple with unsteadiness in cooling flow at the leading edge to further amplify unsteadiness.

Examining the links between pressure and heat transfer fluctuations shows that the pressure surface and suction surface each had strong but unique correlations, and the leading edge is complicated by coupling between pressure and shower head cooling unsteadiness. This indicates a different turbulent Prandtl number may be required in different regions of the blade to accurately track heat transfer. Further complicating heat transfer predictions, small changes in the velocity field cause large levels of unsteadiness in film cooling. The relative movement of large-scale vortex structures over a vane pass increase time-averaged dissipation of cooling jets beyond steady prediction levels.

The results of this study shed light on the nature of unsteadiness, highlighting specific components of unsteadiness observed to augment heat transfer. Better characterizations of unsteadiness can help designers utilize computationally efficient design tools. With increased understanding of how unsteadiness impacts time-averaged performance, a more accurate representation of time-averaged performance can be leveraged from low-cost RANS computational tools.
Experimental Evaluation of a Wavy Trailing Edge Cooling Design as an Alternative to Pressure Side Cutback Cooling
Authors: Ullah Izhar , Burdett Timothy A. , Wright Lesley M. , Han Je-Chin , Lee Ching-Pang
Published: October 2022

This study measures the film cooling effectiveness along the trailing edge of a turbine blade in a linear cascade. The film cooling effectiveness is measured and analyzed using the pressure sensitive paint (PSP) technique. Two different trailing edge designs are investigated including the standard pressure side cutback and the new alternating discharge design (referred to as a wavy trailing edge design). The alternating discharge design is a new design with a wavy structure between the pressure and suction surfaces at the trailing edge. The new wavy structure allows the coolant to discharge from the trailing edge so that it alternates between the pressure and suction surfaces. Testing is carried out in a five-blade, linear, steady state cascade with inlet and exit Mach numbers of 0.20 and 0.30, respectively. The freestream turbulence intensity is measured to be 10.5% upstream of the blade leading edge. Coolant-to-mainstream mass flow ratios (MFR) vary from 0.30% to 1.25% and coolant to mainstream density ratios (DR) of 1.0, 1.5 and 2.0 are examined. The total pressure loss coefficients are also acquired to compare the aerodynamic loss between the two trailing edge designs. The pressure loss coefficient is acquired by traversing a group of pitot static probes across the blade span in a plane downstream of the trailing edge, resulting in a pressure map at the exit plane. A positive MFR and DR effect is witnessed with almost no change in aerodynamic loss. The results provide the potential of the alternating discharge as a promising trailing edge design and provide gas turbine designers with an improved trailing edge cooling scheme having acceptable aerodynamic loss.
The Validation of a Parametric Leading Edge Model for Probabilistic CFD Analyses of Post-Service Compressor Airfoils
Authors: Schlüter Lukas , Voigt Paul , Voigt Matthias , Mailach Ronald , Schmidt Robin , Rostamian Mirco , Becker Bernd
Published: October 2022

The impact of geometric variation of compressor airfoils due to manufacturing scatter and operational effects on the aerodynamic performance is a well-addressed topic in the research field of turbomachinery. Thereby, the airfoils’ leading edge (LE) shapes are highly relevant to their aerodynamic behavior, potentially causing increased losses and separation. In previous probabilistic computational fluid dynamics (CFD) analyses, the LEs were usually modeled as semi-circles or semi-ellipses, whereas their noticeable deviation from these simplified shapes is given comparatively little attention. The study at hand aims to fill this gap by introducing a parametric model for the quantification and parametric recreation of the variability of high pressure compressor (HPC) LE shapes. A set of digitized mid stage HPC rotor blades originating from several jet engines with differing fields of operation are used for the demonstration of the introduced approach. The individual LE 2D-contours are extracted on multiple sections over the blade’s height and compared to a symmetric reference shape. This yields characteristic difference curves enabling the detailed quantification of the variability with a minimum amount of parameters. The derived parametric model allows the statistical reproduction of the measured variability, which is geometrically and aerodynamically validated in the following. The approach’s capabilities in regard to probabilistic CFD analyses are demonstrated by conducting and evaluating two- and three-dimensional flow simulations. Furthermore, the observed geometric variability is linked to the rotor row’s aerodynamic behavior highlighting its importance for the performance variance of HPC rotors.
Interface Reduction in an Equivalent Linearization Algorithm for Nonlinearly Coupled Systems Under Random Excitation
Authors: Förster Alwin , Panning-von Scheidt Lars
Published: October 2022

Stochastic excitation is a rarely discussed topic regarding the vibrational behavior of turbine blades. While the calculation of stochastic quantities describing the stochastic steady-state vibration response is comparatively straightforward in the linear case, it becomes much more challenging in the case of nonlinear couplings. A method suitable for calculating approximations of the stochastic steady-state vibration response is the equivalent linearization method. However, the efficiency of this method decreases with an increasing number of degrees of freedom. This is especially challenging if the number of nonlinearly coupled degrees of freedom is large, as in the case of an extended contact interface, such as a shroud contact. While the uncoupled part of the system can be reduced using a component mode synthesis, the remaining nonlinear interface degrees of freedom have to remain unreduced to evaluate the nonlinear forces. To address this problem, this paper presents an approach to reduce the interface degrees of freedom within the framework of the equivalent linearization method. The presented method is based on a representation of the dynamics of the contact interface by means of a reduced set of Legendre polynomials. However, the evaluation of the nonlinear force still takes place in physical coordinates. The presented procedure is demonstrated using a beam model with different contact pairings as well as a more realistic model of a bladed disk assembly.
Bayesian Calibration of Kinetic Parameters in the CH Chemistry Towards Accurate Prompt-NO Modelling
Authors: Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M.
Published: October 2022

Significant efforts made by the gas turbine industry have helped reduce nitrogen oxides (NOx) emissions considerably. To meet and surpass the increasingly stringent regulations, accurate and robust thermochemical mechanisms are needed to help design future sub-10 ppm combustion systems. Uncertainty in kinetic modelling, however, can result in large prediction uncertainty and significant discrepancy between models that hinder the identification of promising combustors with confidence. Direct reaction rate measurements are seldom available for some reactions, especially when involving short-lived radicals like methylidyne, CH. As the main precursor to the prompt-NO formation pathway, its large parametric uncertainty directly propagates through the nitrogen chemistry preventing accurate and precise emissions predictions. Recent independent CH concentration measurements obtained at various operating conditions are used as indirect rate measurements to perform statistical, or Bayesian, calibration. A subset of important reactions in the CH chemistry affecting peak-CH concentration is identified through uncertainty-weighted sensitivity analysis to first constrain the parametric space of this prompt-NO precursor. Spectral expansion provides the surrogate model used in the Markov-Chain Monte Carlo method to evaluate the posterior kinetic distribution. The resulting constrained CH-chemistry better captures experimental measurements while providing smaller prediction uncertainty of a similar order as the uncertainty of the measurements, which can increase the confidence in simulation results to identify promising future low-emissions configurations. For the quasi-steady state species CH, fuel decomposition reactions leading to CH production are constrained while little impact is observed for intermediate reactions within the CH-chemistry. The reduction in prediction uncertainty results mainly from the constrained correlations between parameters which greatly limit the set of feasible reaction rate combinations. Additional independent direct and indirect measurements would be necessary to further constrain rate parameters in the CH chemistry, but this calibration demonstrates that predictions of radical species can be improved by assimilating enough data.
Development of an Open-Source Autonomous CFD Meta-Modeling Environment for Small-Scale Combustor Optimization – Part I
Authors: Briones Alejandro M. , Rankin Brent A.
Published: October 2022

This work presents an open-source autonomous CFD meta-modeling environment (OpenACME) for small-scale combustor design optimization in a deterministic and continuous design space. OpenACME couples several object-oriented programming open-source codes for conjugate-heat transfer, steady-state, multiphase incompressible RANS CFD-assisted engineering design meta-modeling. There are fifteen design variables. Non-parametric rank regression (NPRR), global sensitivity analyses (GSA), and single-objective (SOO) optimization strategies are evaluated. The Euclidean distance (single-objective criterion) between a design point and the utopic point is based on the multi-objective criteria: combustion efficiency (η) maximization and pattern factor (PF), critical liner area factor (Acriticol), and total pressure loss (TPL) minimization. The SOO approach conducts Latin Hypercube Sampling for reacting flow CFD for subsequent local constraint optimization by linear interpolation. The local optimization successfully improves the initial design condition. The SOO approach is useful for guiding the design and development of future gas turbine combustors. NPRR and GSA indicate that there are no leading-order design variables controlling η, PF, Acritical, and TPL. Therefore, interactions between design variables control these output metrics because the output design space is inherently non-smooth and nonlinear. In summary, OpenACME is developed and demonstrated to be a viable tool for combustor design meta-modeling and optimization studies.
Effect of Strong Azimuthal Swirl on Ignition and Light-Around in an Annular Combustor
Authors: Kwah Yi Hao , Agostinelli Pasquale Walter , Richard Stéphane , Exilard Gorka , Pascaud Stéphane , Gicquel Laurent , Dawson James R.
Published: October 2022

In this paper we investigate the effect of strong azimuthal swirl on ignition dynamics in a laboratory-scale annular combustor. Bulk azimuthal swirl was produced by a novel angled injector configuration, producing swirling jet flames oriented downwards towards the combustor backplane and in the azimuthal direction, replicating a simplified version of the SAFRAN spinning combustor concept. To provide more realistic flow conditions, the design included Rich-Quench-Lean (RQL) staging via a circumferential distribution of dilution ports and an effusion cooled combustor backplane. High-speed imaging and an azimuthal array of photomultipliers to measure OH* chemiluminescence were used to characterise the ignition dynamics for different injector velocities and global equivalence ratios. The mass flows through the injectors, dilution ports, and effusion cooled backplane were independently metered so that the injector equivalence ratio and global equivalence ratio could be separately controlled. The light-around times were found to have no clear correlation with the injector velocity since the rich injector equivalence ratio meant the flame burned in a non-premixed mode even though the global equivalence ratio was lean due to the RQL staging. However, it was found that lower injector velocities extended the lean ignition limit based on the global equivalence ratio. The ignition sequence during light-around (order in which the injectors are ignited) was found to be highly repeatable, igniting each consecutive injector in the anticlockwise direction (the direction of bulk swirl). In rare cases, the ignition sequence was observed to branch in both directions. Finally, in an effort to extend the lean ignition limit, the effect of azimuthal staging was investigated. Two configurations were tested. In the first configuration, the injectors on one half of the annulus were operated at a fixed equivalence ratio whereas the other half of the annulus was operated at a different equivalence ratio. In the second configuration, every second injector had the same equivalence ratio. Both configurations extended the lean extinction limit but the first configuration was the most effective.
Low Mach Preconditioning for Turbomachinery Flow Simulations With Cavities and Variable Gas Compositions
Authors: Sivel Pierre , Frey Christian , Kügeler Edmund , Keil Markus
Published: October 2022

The optimization of turbomachines increasingly relies on highly accurate numerical performance predictions. Loss predictions require the cavities of the machine to be included in numerical simulations. Commonly, in cavities, the velocity of the simulated fluid is small. For density-based solvers, this results in slow convergence and inaccurate computations. Further, the fluid in cavities is often composed of several gases. This paper presents the low Mach preconditioning method for multi-component thermally perfect gas of DLR’s inhouse solver TRACE.

Two low Mach academic test cases, a lid driven cavity and an air and exhaust gas mixing layer, are computed to validate the preconditioner. Both test cases show an accelarated convergence and an improved accuracy, when preconditioning is used.

A 1.5 stage low-pressure turbine rig with a labyrinth seal is computed with thermally perfect air. The result shows a good agreement with the experimental reference. The fluid is then changed to exhaust gas, and two air inflows are added in the labyrinth seal, to analyze the effect of low Mach preconditioning on the mixing of the two gases. The preconditioned computation shows an improved convergence in the cavity. Moreover, the wall temperature and the gas distribution in the cavity differ, when preconditioning is applied.
A Nonlinear Rotordynamics Model for Automotive Turbochargers Coupled to a Physical Model for a (Semi) Floating Ring Bearing System
Authors: Jung Wonbae , San Andrés Luis , Kim Jungbae
Published: October 2022

Automotive turbochargers (TCs) use an engine oil lubricated bearing system to produce acceptable performance (as per the engine volumetric efficiency) and proven reliability. However, the bearings also cause TC rotordynamic responses that are rich in subsynchronous whirl motions through reaching stable limit cycles. The paper describes the lubrication model for a finite length semi-floating ring bearing (SFRB) system and its coupling to the rotor and ring structure models for prediction of both linear and nonlinear system responses and their characterization in terms of motion amplitudes and whirl frequency content. The SFRB model includes a thermal energy transport network for the inner and outer films in both radial bearings and the thrust bearings located on the end sides of the ring. The large temperature difference between the hot shaft and a cold housing induces a three-dimensional thermal gradient in the fluid films and the floating ring, further exacerbated by the heat generated from drag power losses in the inner films adjacent to the rotor. The temperature gradients affect the lubricant viscosity and the bearing system operating clearances. The integration of the rotor and bearing system (RBS) equations of motion accounts for the SFRB nonlinear forces and starts from a static equilibrium position, if existing. Analysis of the start-up speed response of a commercial TC, from 500 Hz (30 krpm) to 4,000 Hz (240 krpm), and for particular mass imbalance conditions, shows dominant subsynchronous vibrations (SSV) with frequencies ranging from approximately ¼ to ∼ ½ of shaft speed and a transition from conical to cylindrical-bending rotor mode shapes. The model predictions of nonlinear behavior are accurate when benchmarked to a set of measurements procured in a gas stand test rig. The analysis also investigates the influence of the bearing inner clearance and rotor mass imbalance distribution on the onset, persistence and severity of SSV.
Economizer Location Optimization for a Centrifugal Compressor With Refrigerant as Working Fluid
Authors: Urcia Jose , Yan Jin , Fagundes Tadeu
Published: October 2022

In a typical HVAC chiller, centrifugal compressors are used to compress the refrigerant. These compressors are of single or multi-stage cycles that can be configured for a reinjection between cycles. This reinjection introduces cascade cycle options while improving the Coefficient of Performance (COP). One cascade cycle option that has become industry standard is an economizer cycle. During this process, the goal becomes to reinject flow back into the compressor between stages while the remaining flow continues through the cycle. The exact location of the economizer where its benefit would be at a maximum has yet to be determined. This paper develops a high-fidelity full compressor model where an economizer may be simply added into any location. A thermodynamic cycle analysis is used to highlight the locations where an economizer may be most beneficial thus limiting the number of locations to investigate. Initially, three different full compressor models are developed with increased model complexity for model validation. The most complex agreed with experimental results with high-accuracy and was used for further economizer testing. The most complex compressor model is investigated under 100% the design speed without the added economizer where a baseline is achieved. The thermodynamic cycle analysis is then implemented to identify the optimal economizer location based on the interstage pressure. Four locations are determined to fit the criteria. Two economizer locations were found to exhibit improved performance when compared to the remaining locations, increasing the aerodynamic efficiency of the base model by 10%.
Jet Entrance Configurations and Swirl Motion Effects on Heat Transfer Characteristics Inside Blade Leading Edge of the Gas Turbine
Authors: Elwekeel Fifi , Abdala Antar , Zheng Qun
Published: October 2022

In the present work a simulation is conducted by CFD to predict the cooling performance in a chamber with a swirl motion using nine shapes of injection entrances. The injection entrances are with different cross sections; rectangular (case A), circular (case B), half circular (case C), square (case D), elliptical (case E), equilateral triangular (case F) and three configurations of convergent shapes (case G, H, I). The simulation is performed at constant hydraulic diameter for all shapes and at varied Reynolds number. The investigation parameters are temperature distribution in swirl chamber, circumferential and total velocities, circumferential and axially averaged Nusselt numbers, friction factor and thermal performance parameter. The results show that the temperature increases in all cases compared to the rectangular entrance shape. The convergent shapes give high performance in the heat transfer as well as high friction. Circular entrance shape has a higher circumferential and total velocity compared to all cases.
Study on the Vibration Characteristics of Bladed Disks With Damping Mistuning
Authors: Kaneko Yasutomo , Watanabe Toshio , Furukawa Tatsuya
Published: October 2022

Bladed disks with slight blade variations are referred to as a mistuned system. Many researchers have suggested that while mistuning induces an undesirable effect on the forced response, it provides a beneficial (stabilizing) effect on the blade flutter (self-excited vibration). However, almost all studies have focused on the deviation in the blade frequency, and few studies have investigated damping mistuning. In a blisk (integrally manufactured bladed disk), damping mistuning appears to be negligible because material damping is dominant and its deviation is small. However, in a bladed disk where the blade root is inserted into the disk groove, damping mistuning caused by partial contact between the root and groove during rotation cannot be neglected in predicting the resonant response of a bladed disk. Some works suggest that the structural damping of a root-type bladed disk measured using the half-power method during rotation tests largely fluctuates in each individual blade. Damping mistuning may also affect the stability of the blade flutter. Therefore, in predicting the stability of a blade flutter, the effect of damping and frequency mistuning should be considered. From these backgrounds, in the current study, by incorporating the damping mistuning into a reduced-order model, namely, fundamental mistuning model, frequency response and stability analyses of bladed disks are systematically performed. From the calculated results, the effect of damping mistuning on the forced and self-excited vibrations of bladed disks is clarified. In addition, although the authors proposed a simultaneous optimization method for mistuned bladed disks for forced vibration and amount of unbalance in a previous work, damping mistuning was not considered. In the present study, the robustness of an optimal mistuned system for damping mistuning is also evaluated.
Effect of Counter- and Co-Swirl on Low-Frequency Combustion Instabilities of Jet A-1 Spray Flames
Authors: Ahn Byeonguk , Kim Kyu Tae
Published: October 2022

The present article experimentally investigates the influence of pilot swirling directions on low-frequency combustion instabilities of pilot diffusion flames in a laboratory-scale combustor with Jet A-1 fuel and air at atmospheric pressure. Airblast atomization nozzles with either counter-rotating (CTR) or co-rotating (COR) pilot swirl flows were examined using nonlinear time-series analyses and high-speed flame imaging measurements under idle and sub-idle operating conditions. We show that while the amplitude and frequency of limit cycle oscillations are observed to be similar for both cases, detailed examinations of measured experimental data reveal marked differences in stabilization mechanisms and pressure-heat release coupling processes. The spray flame dynamics subjected to counter-rotating swirl flows are governed by large-amplitude pressure oscillations, even under the influence of destructive pressure-heat release rate interference. The mechanism of destructive interference is closely related to the interactions between a spiral diffusion flame and a periodically-detached reaction zone. Non-premixed liquid-fueled flames involving co-rotating swirl, on the other hand, feature a more compact and intense reaction zone.
Particle Rebound/Deposition Modelling in Engine Hot Sections
Authors: Jiang Lei-Yong , Trembath Patrick , Patnaik Prakash , Capurro Michele
Published: October 2022

The current state of the art in experimental and analytical research on environmental particle ingestion related to engine hot sections was reviewed, with greater emphasis focussed on sand particles. From these efforts, the available experimental data for model calibration were identified, and a particle rebound/deposition model has been developed. A semi-empirical approach is selected to model sand particles bouncing off metal surfaces, where the coefficients of restitution measured in a temperature range of 297–1323 K from Delimont et al are used to calculate particle bounce-back velocity components. The developed deposition model is based on non-dimensional parameters and the analysis over more than seventy experimental datasets related to particle deposition in engine hot sections carried out by Suman et al. Moreover, the metal surface temperature, one of two critical parameters in particle deposition, is also included in the model. The developed rebound/deposition model was successfully implemented into the ANSYS CFD Premium solver and checked step by step. The model is calibrated by two cases: sand [or Arizona road dust (ARD)] particle impingement on a circular plate and Mt. St. Helens volcanic ash (comparable with ARD particles in terms of chemical composition) impinging on a first-stage air-cooled nozzle guide vane (NGV). For the former case, the calibrated model predicts fairly well the variation of particle capture efficiencies with flow/particle temperatures. The latter case indicates that the particle capture efficiency at engine operating conditions can be assessed by the developed model. Due to the lack of experimental data that would permit a full calibration/validation, for the time being it could be only used under limited conditions. Certainly, the model will be continuously improved as the relevant experimental data appears.
Effects of Bleed Slot Size on the Shock-Wave/Boundary-Layer Interactions in a Transonic Compressor Stator
Authors: Li Bai , Zhou Xun , Luo Lei , Du Wei
Published: October 2022

A numerical investigation of shock-wave/boundary-layer interaction in a transonic compressor stator with different slot widths is presented in the current work. The fluid in boundary layer is bled through the suction slot into a plenum to control the separation. Three different slot widths at inlet Mach number of 1.0 are studied. Numerical results show that all sizes of slot are capable of reducing the total pressure loss coefficient. The maximum amplitude of decline in pressure loss is 75.7% compared to the cascade without bleed. The optimum bleed pressure and corresponding optimum bleed mass in terms of minimizing pressure loss appear in three different slots. The wider slot leads to a lower pressure loss at the optimum bleed pressure. The shock wave on the suction surface is reorganized by the slot bleed. At the same bleed pressure, the wider slot causes the modified shock wave closer to the downstream. The expansion in front of modified shock wave could change the flow direction over slot. The tangential momentum of boundary layer at slot downstream edge is increased by the slot bleed. This enhances the ability of the boundary layer to withstand the adverse pressure gradient.
Investigation of Adaptive Mesh Refinement on an Industrial Gas Turbine Combustor
Authors: McManus Liam , Karalus Megan , Munktell Erik , Rogerson Jim
Published: October 2022

An adaptive mesh refinement (AMR) method is demonstrated for Large Eddy Simulations (LES) of an industrial gas turbine combustor, the SGT-100 provided by Siemens Energy Industrial Turbomachinery Ltd.

In this paper, the Simcenter STAR-CCM+® solver is used to dynamically refine a series of Large Eddy Simulations with a Flamelet Generated Manifold (FGM) combustion model as applied to the SGT-100. Mesh refinement criteria are defined using second gradients of mixture fraction and reaction progress.

Two meshes are assessed with and without AMR. The results are then compared to a refined static mesh and experimental data. The accuracy and computational cost of the static and adaptively refined meshes are discussed. It is shown that AMR can provide close to 2x speed up compared to a refined static mesh with similar predictions of mean and RMS quantities of the flow field, flame temperature and major species.
Numerical Study on the Performance of Hybrid Darrieus-Savonius Vertical Axis Wind Turbines Having Twisted Blades
Authors: Saad Ahmed S. , Ahmed Mahmoud
Published: October 2022

Darrieus and Savonius rotors are the main types of vertical axis wind turbines. Darrieus rotors exhibit high power coefficient but suffer from lower self-starting capabilities. On the other hand, Savonius rotors demonstrate relatively high self-starting capabilities but with an inferior power coefficient. Therefore, the current study proposes three hybrid Darrieus-Savonius designs with different angles of twisting aiming at having a compact turbine with high coefficient of power and easy to self-start. The Savonius turbine is placed inside the Darrieus turbine in the three proposed hybrid designs. Accordingly, the trends of coefficient of power against ratio of rotor tip speed in addition to coefficient of torque over a whole cycle (360 degrees) are computed. The coefficient of static torque during a whole cycle is also calculated. Therefore, three dimensional, incompressible, and unsteady Reynolds-Average Navier-Stokes equations in conjunction with the turbulence model of k-ω shear-stress transport is developed and numerically simulated utilizing ANSYS Fluent. The devolved numerical model is validated using the available measurements from literature. The predicted characteristics of flow field over the three suggested hybrid designs are analyzed and presented.

Accordingly, results illustrated that a significant enhancement of the coefficient of power is attained by suggested hybrid designs with twisting blades in comparison with the straight-bladed design. The model with twisted-bladed Darrieus and Savonius turbines with angles of twisting of 90° and 45°, respectively attains the largest peak of coefficient of power of 0.353. This hybrid configuration exhibits lower static torque fluctuations with positive values during the whole cycle. Consequently, using the suggested hybrid turbine with twisting blades improves both coefficient of power and the self-starting capability of the turbine.
Nanostructured CVD W/WC Coating Protects Steam and Gas Turbine Blades Against Water Droplet Erosion
Authors: Zhuk Yuri
Published: October 2022

Gas turbine compressor blades operating with air inlet fogging can suffer from Water Droplet Erosion (WDE). WDE can also affect the last rows of steam turbines where expanding steam produces water condensation, especially under start-up and low load conditions. WDE damages the blades’ leading and sometimes trailing edges, increasing turbine rotation drag, reducing efficiency and leading to costly maintenance. This paper reports the testing of Hardide® nano-structured W/WC metal matrix composite coating as a protection against WDE.

The Chemical Vapor Deposition (CVD) technology crystallizes the coating atom-by-atom from the gas phase and produces a uniform pore-free coating on complex shaped parts like turbine blades, vanes and pump impellers, including non-line-of-sight areas. Two variants of CVD W/WC coatings were tested: “A” type is 50–100 microns thick and has a hardness range of 800–1200 Hv and “T” type is 35–65 microns thick with a higher hardness of 1100–1600 Hv. Both coating types are made of Tungsten Carbide nanoparticles dispersed in metal Tungsten matrix. This composition and structure produce a combination of enhanced fracture toughness with high hardness and enables the deposition of exceptionally thick hard CVD coatings to provide durable protection against WDE and solid particle erosion. The coatings are pore-free thus also provide an effective barrier against corrosion.

The coatings were tested for WDE resistance by the UK National Physics Laboratory (NPL) using 350 μm water droplets at 300 m/sec velocity. Uncoated 410 SS control samples suffered from a major loss of material after just 7-hours of exposure to WDE, forming a 200 μm deep scar across the whole tested area. After a much longer exposure of 90 hours, the coating samples showed negligible WDE damage, only measurable on the samples’ edges. The coating also outperformed Stellite, which is widely used as WDE protection in the form of welded overlay or plates brazed to the blade’s leading edge. The thicker and less hard type “A” CVD coating showed better performance when compared to the thinner, harder type “T”.

The effects of the coatings’ thickness, hardness, and residual stresses on the WDE resistance are discussed.

The rig testing showed that the CVD WC/W coating can protect steam and gas turbine blades against WDE thus increasing the service life of equipment and maintaining its optimal performance for longer, reducing CO2 emissions and cutting the life-cycle costs.

Hardide coatings are used by major oil service companies, pump and valve producers to improve durability in abrasive and corrosive environments. Airbus has approved Hardide-A coating as a REACH-compliant replacement for Hard Chrome plating on aircraft components. Other customers include BAE Systems, EDF Energy, Leonardo Helicopters and Lockheed Martin. The Hardide coating service is provided from state-of-the-art coating facilities near Oxford (UK) and in Virginia (US). Production and quality control are accredited to ISO9001, AS9100 and NADCAP standards.
A Fluid-Structure Interaction Tool Using a Van der Pol Based Reduced-Order Model for Buffet and Non-Synchronous Vibrations
Authors: Hollenbach Richard , Kielb Robert , Hall Kenneth
Published: October 2022

This paper builds upon a two-degree-of-freedom Van der Pol oscillator based Reduced-Order Model for studying the mechanisms around Non-Synchronous Vibrations (NSV) in turbomachinery. One degree tracks the fluid motion utilizing a combination of a traditional Van der Pol Oscillator and a Duffing Oscillator; the other degree of freedom is a mass on a spring and a damper, in this case a cylinder. Thus, this model can be considered one of fluid-structure interaction. The cubic stiffening from the Duffing Oscillator proved to improve the match to experimental data. Using this model to study the time-history of the fluid and the structure oscillation, additional parameters are extracted to understand the underlying mechanisms of frequency lock-in and limit cycle oscillation. First, the phase shift between the vortex shedding and the structural motion is calculated when it locks-in then unlocks. Second, the work done per cycle is analyzed from the contributions of the mass, spring, and damping forces to determine the dominant contributor when locking-in versus unlocking. Third, the phase portrait is plotted on a Poincare Map to further study the locked-in versus unlocked responses.

This model is then validated against not only experimental data, but also computational simulation results and previous reduced-order models. The finalized model can now serve as a preliminary design tool for turbomachinery applications. For more realistic and accurate modeling, a third degree-of-freedom in the form of an airfoil pitching motion will be added in a separate paper as well.
PDA Laser Measurements of Droplet-Laden Flows in a Four Stage Axial Compressor
Authors: Doerr Tobias , Schuster Sebastian , Brillert Dieter
Published: October 2022

Droplet-laden flows play a significant role in the development of turbomachinery. For example, fine water droplets are injected into the flow path of axial compressors to increase the power output of gas turbines by making use of evaporation cooling, often referred to as Wet Compression. Another example is the ingestion of rain droplets in aircraft engines. Therefore, thermodynamic and aerodynamic measurements of air and liquid are indispensable in order to better predict the following behaviour of the droplets in the gas flow.

This paper presents a new PDA measurement setup for a droplet-laden four-stage axial compressor in order to analyse the droplet behaviour in swirled flows. To reduce optical disturbances of the laser beam path, liquid films at the casing are suppressed by a boundary layer air injection. Supplementary investigations with this treatment show a negligible influence on the compressor behaviour. In order to minimize refraction effects of the laser beams at the casing window, the laser device with the optical probes can be translated and rotated, thus having 4 degrees of freedom. Furthermore, the collected droplet data is compared with a mathematical description of velocity slip in superimposed air flows.

For the first time, it can be shown experimentally that droplets smaller than 10 μm attain the velocity of air one stage after injection. For larger droplets, however, deviations from the air Mach number of up to 0.05 remain. In addition, detached liquid films behind the trailing edge of the stator blades with low velocities can be clearly detected.
Sound Generation in Multicomponent Nozzle Flows With Dissipation
Authors: Jain Animesh , Magri Luca
Published: October 2022

Low emission aircraft engines burn in a lean regime, which makes the combustor susceptible to unsteady combustion. Along with improper mixing and air cooling, the unsteady combustion process gives rise to flow inhomogeneities. The acceleration of these inhomogeneities in the nozzle downstream of the combustor generates indirect combustion noise. If the acoustic waves that are reflected off the nozzle are sufficiently in phase with the heat released by the flame, thermoacoustic instabilities can occur. The generation and transmission of sound through the nozzle guide vane are typically modelled with a compact and isentropic nozzle model. Because the flow is non-isentropic due to losses from wall friction and recirculation zones, in the literature, a mismatch is observed between experimental and theoretical predictions in subsonic-choked regimes. In this work, we propose a low-order physical model to predict indirect noise in a multi-component nozzle flow with dissipation using conservation laws whilst modelling non-isentropicity using a friction factor. The model is generalized for finite-length (non-compact) arbitrary geometry nozzles. We show that the friction factor can account for wall friction and two (or three) dimensional effects, such as flow recirculation in a cross-averaged sense. We analyse the model numerically for both subsonic and supersonic nozzles, emphasizing the importance of non-isentropic and non-compact assumptions with compositional inhomogeneities. Further, we show the effect of the nozzle geometry. The results are validated with existing experimental data from the literature.
Plume Model for Buoyancy-Induced Flow and Heat Transfer in Closed Rotating Cavities
Authors: Tang Hui , Owen J. Michael
Published: October 2022

The radial clearance between the rotating blades and stationary casing of a gas turbine compressor depends on the radial growth of the rotating discs to which the blades are attached, and this growth depends on the buoyancy-induced flow and heat transfer in the air-filled cavities between adjacent discs. In some engines, the cavities are sealed, which creates a closed rotating cavity. A theoretical model has been developed to calculate the radial distribution of the temperature of the disc in a closed rotating cavity. The principal assumptions are that the convective heat transfer from the hot shroud to the cold hub of the cavity is via plumes of fluid in which the cold fluid moves radially outward, and the hot fluid inward, inside an inviscid quasi-axisymmetric core of rotating fluid. The fluid core is surrounded by boundary layers on all rotating surfaces, with free-convection layers on the surfaces of the shroud and hub and laminar Ekman layers on the surface of the discs. In addition to the convection, heat is transferred by one-dimensional radial conduction in the rotating discs. Using the model, equations have been derived to calculate the radial distribution of temperature in the discs and fluid core. These equations reveal that the non-dimensional temperatures for the disc and core, θd and θc, are controlled by three independent non-dimensional parameters: Reϕ, βΔT and χ, the rotational Reynolds number, the buoyancy parameter, and the compressibility parameter, respectively. The compressibility parameter is defined as χ=defMa2/βΔT where Ma is a Mach number, and χ is shown to strongly affect the radial distribution of the core temperatures. There will be a critical value of χ at which the core temperature equals that of the heated shroud. For a closed cavity with adiabatic discs and xα = 0.5, the critical value is 6.7. Above this critical value, stratification is expected to occur and heat transfer from the shroud to the core will be by conduction rather than by convection. The theoretical model predicts radial distributions of temperatures in the discs and fluid core that are in good agreement with the experimentally derived values in a companion paper.
Estimation of Dynamical Thermoacoustic Modes Using an Output Only Observer Kalman Filter-Based Identification (O3KID) Algorithm
Authors: Balasubramanian Nikhil , Rouwenhorst Driek , Hermann Jakob
Published: October 2022

Thermoacoustic instabilities have plagued the operation of gas turbine engines for years and significant research is being conducted in detecting and understanding them. In this paper, an output only identification technique is employed for a noise induced dynamical system representing combustion dynamics. Background turbulent flow in a combustor has a significant influence on combustion dynamics. In general, this flow noise is referred to as background noise, whose characteristics are unknown apriori. Identification of combustion dynamics with output only identification becomes challenging since the system dynamics and background noise dynamics are indistinguishable. To simplify the problem and identify both deterministic and stochastic components, a two-step identification using state space modelling is implemented. The data is transformed to accommodate an observer, which predicts the current state of a system from its previous states. The observer takes the form of a Kalman filter and in solving for the Kalman filter gain would solve the original problem yielding all the system matrices of the state space model. This approach is called the Output only Observer Kalman filter identification (O3KID) and its first step solves for least squares from a set of algebraic equations constructed from just the measured output. The least squares solution gives the Markov parameters (impulse response) and the output residuals. The subsequent step takes the Markov parameters or the residuals to solve for the system matrices using any deterministic sub-space identification method. In this paper, classical methods such as the Eigenvalue Realization Algorithm (ERA) using the Markov parameters is employed to solve for the system matrices. In using this direct non-iterative two-step algorithm, it is possible to estimate the eigenmodes and damping coefficients from output measured data. To validate the algorithm, a system of independent harmonic oscillators, excited by random noise is used to generate surrogate data representing pressure oscillations in a combustor prior to an instability. The O3KID algorithm could identify the eigenmodes with exactly the degrees of freedom required to define it i.e., a system with three harmonic oscillators could be defined with a 6-order model, which implies 6 coefficients. The same method was applied to pressure fluctuations data from a laboratory burner. The estimation of the most energetic modes was accurate with as few as 10 modes. This fast direct approach could be used to provide an early warning indicator in industrial gas turbines by tracking the rate of damping of dominant eigenmodes. Additionally, saving the state space parameters periodically can serve as a data-lean option to track changes of the dynamics and across a gas turbine fleet.
An Optimization Methodology for Turbines Driven by Pulsed Detonation Combustors
Authors: Asli Majid , Stathopoulos Panagiotis
Published: October 2022

A step-change in efficiency of gas turbine technology and, subsequently, an emissions reduction from this technology requires conceptual changes. Substituting conventional combustion chambers with pressure gain combustion in the form of pulsed detonation combustion (PDC) is one of the promising methods that can reduce gas turbine emissions significantly. Nevertheless, the component matching for the respective systems and specifically that of turbine expanders working with the exhaust flow of PDC tubes is still not solved. The unsteady nature of PDC exhaust flow makes 3D-CFD simulations too expensive to be applied in optimization loops in early design stages. To address this question, the present paper introduces a new cost-effective but reliable methodology for turbine analysis and optimization, based on the unsteady exhaust flow of pulsed detonation combustors. The methodology unitizes a robust unsteady one-dimensional solver, a meanline performance analysis, and an adaptive surrogate optimization algorithm. A two-stage axial turbine is optimized considering all unsteady flow features of a hydrogen-air PDC configuration with five PDC tubes. A threedimensional URANS simulation is performed for the optimized geometry and the baseline to evaluate the methodology. The results showed that the optimized turbine produces 16% lower entropy than the original one. Additionally, the turbine output power is increased by 14% by the optimized design. Based on the results, it is concluded that the approach is fast and reliable enough to be applied in optimizing any turbine working with unsteady flows, more specifically in PDC applications.