bluuebunny/crossref_metadata_2025 huggingface dataset:
Volume of Fluid Based Model of Heavy Fuel Oil Droplet Evaporation and Combustion
Authors: Guida Paolo , Saxena Saumitra , Roberts William L.
Published: January 2021

Modern CFD simulations of combustion resolve simplified sub-models for droplet evaporation and combustion within a Lagrangian framework. Break-up effects like puffing and micro-explosions are usually neglected but, they eventually influence the evaporation and combustion behaviour of heavy fuel sprays. We are developing a Volume of Fluid (VoF)-based CFD solver that allows us to model single droplet differential evaporation with the break-up effects. Puffing/micro-explosion and droplet ejection proceed in three steps: nucleation of a bubble of a light component within the droplet, expansion/coalescence of the bubbles and finally eruption with sub-droplets formation. Our goal is to individually model each event and then combine them in a composite simulation. Henceforth we can get data in realistic conditions to be used in Lagrangian spray simulations. We identified three relevant features that are necessary to create a reliable representation: interface tracking, differential evaporation, and compressibility effect. The solver is based on the Volume of Fluid (VoF) technique and coded within the open-source OpenFOAM framework. VoF technique consists of transporting the volume fraction of one of the two phases (liquid or gas). The Navier-Stokes equations are solved for a single-phase but adapting the physical properties to the volume fraction value. A state-of-the-art method called iso-Advector was adopted to reconstruct the interface from the volume fraction field. The evaporation was implemented as a source term in the volume fraction equation, and the conservation equations were modified accordingly. In order to calculate the vapour and liquid physical properties, RKS equation of state (EOS) was implemented. The droplet was assumed to have 2 phases: light and heavy, having physical properties comparable to water and heavy fuel oil (HFO), respectively. The pressure closure equation was modified to handle large pressure differences during the internal evaporation of light components. The validation of the solver was performed through benchmark cases as multiphase shock-tube, droplet oscillation and boiling interface either with experimental works and analytical solutions. A single suspended droplet experiment was performed to measure the velocity of an ejected micro-droplet during puffing using a shadowgraphy technique. The code is able to predict ejection velocity within a 15% error, which seems to be promising. The present article documents part of the algorithm development and its validation. In particular, the step describing the ejection of the inner vapours is described.
Heat Transfer Characterization Inside a Rotating Rib Roughened Cooling Channel With Multiple Heated Walls
Authors: Lorenzon Andrea , Cucit Elica , Casarsa Luca
Published: January 2021

This work experimentally investigates the effects of walls heating conditions on the heat transfer coefficient distribution inside a rotating cooling channel. The model has a square cross-section with a hydraulic diameter of 50 mm and one ribbed side. The ribs are perpendicular to the main flow direction, the rib pitch-to-height ratio is 10, and the blockage ratio is 10%. Detailed heat transfer measurements were performed employing the liquid crystals thermography in steady-state approach under two thermal boundary conditions: only ribbed wall heated or equal heat fluxes set to ribbed wall and sidewalls. Inlet Reynolds number was 20000 and the tests were conducted in both static and rotating conditions up to a rotation number of 0.18, with the ribbed wall acting as trailing edge side. The results show that the wall heating conditions have a negligible effect on the heat transfer distribution for the stationary case, whereas, they lead to a modification of the heat transfer distribution under rotation with an overall enhancement when three walls are heated.
Experimental Study on Random Autoignition of N-Decane Spray in Crossflow at Evaluated Pressure
Authors: He Chunlong , Zhang Chi
Published: January 2021

Based on a flow reactor with optical access, the statistical characteristics of the autoignition of n-decane spray injected by transient transverse column jet into non-vitiated crossflow were studied at various conditions relevant to gas turbine combustor: the reactor pressure of 1.7MPa, the air temperature of 785–1000 K, the jet-to-crossflow momentum flux ratio of 55 and 72, the air Weber number of 290. The ignition delay time was defined as the time interval between the fuel injection into the flow reactor and the radical emission from ignition kernels. The results demonstrate that the ignition delay time of n-decane spray exhibits a random behavior in a given operating condition. In addition, the experimental probability densities of the ignition delay time were determined by statistical method. The results show that with the increase of temperature and momentum flux ratio, the statistical distributions of the ignition delay of the spray become more concentrated, and the sample data of ignition delays have smaller overall-central value in statistics. Furthermore, based on the images of fuel spray of n-decane taken by a high-speed camera, the results indicate that the random behavior of spray autoignition is associated with the random distribution of fuel concentration in spatial and temporal, which is mainly caused by the unsteady jet primary breakup and atomization process.
Experimental Investigation on the Loss Production Mechanisms in Transitional Boundary Layers
Authors: Dellacasagrande M. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P.
Published: January 2021

The present paper discusses the results of a large experimental data set describing transitional boundary layers. Time resolved Particle Image Velocimetry (PIV) measurements have been adopted to survey the boundary layer developing over a flat plate under prescribed adverse pressure gradients typical of turbomachinery components. The tests have been performed while varying the pressure gradient, the Reynolds number and the inlet free-stream turbulence intensity (FSTI). Two exemplary cases, referring to bypass and separated flow transition, are discussed by means of principal axis analysis and proper orthogonal decomposition (POD). The POD is used to provide statistical representation of the flow structures and to compute the turbulence production (i.e., the mean flow energy dissipation) due to the dynamical features observed for the different transition types.

Reduced order model representations of the flow field are provided and their contribution to the total turbulence kinetic energy production is isolated. This analysis is closed by the inspection of the eigenvectors of the strain rate and Reynolds stress tensors. For the separated flow case, it is shown that the eigenvectors of strain rate and shear tensor are almost perfectly aligned downstream of the maximum displacement of the bubble. The reduced order model reconstruction of the Kelvin-Helmholtz shed vortices provides the largest part of the overall TKE production. For the high FSTI induced transition, the eigenvectors of the shear and stress tensors do not have the same direction. The loss generation is related to the local maximum Reynolds normal stress in the streamwise direction, induced by the boundary layer streaks and their breakdown.
Influence of Humidity and Fuel Hydrogen Content on Ultrafine Non-Volatile Particulate Matter Formation in RQL Gas Turbine Technology
Authors: Crayford Andrew , Bowen Philip , Durand Eliot , Pugh Daniel , Sevcenco Yura , Johnson Mark
Published: January 2021

To address the known Local Air Quality impacts of ultrafine combustion derived soot, the International Civil Aviation Organisation (ICAO) have recently adopted a non-volatile Particulate Matter (nvPM) regulation in addition to those of NOx, UHC’s and CO for civil aviation gas turbines. Increased water humidity is known to reduce the formation of NOx in flames through localised temperature reduction, however its impact on emitted nvPM is to date not clearly understood. To address this knowledge gap, nvPM formation mechanisms were assessed empirically at increasing water loadings both at atmospheric pressure — in a RQL representative optical combustor fuelled with Jet A and alternative fuel blends — and during a full-scale Rolls-Royce aero-derivative Gas Turbine test fuelled on Diesel.

In line with previous studies, in the RQL combustor rig it was observed that increased hydrogen content in the test fuel — associated with a 100% Gas-To-Liquid (GTL) derived aviation kerosene with low aromatic content (0.05%) — reduced nvPM number concentrations by an order of magnitude compared to a baseline Jet A-1 fuel with representative aromatic content (24.24%). For all fuels tested it was also observed that an elevated water loading in the primary combustion zone (≤ 0.05 kg /kg of dry air), representative of maximum global humidity levels, resulted in reductions of both nvPM number and mass concentrations of 40% and 60% respectively. During a full-scale Rolls-Royce gas turbine study similar trends were observed, with an 85% reduction in measured nvPM mass whilst water was injected into the combustor at flow rates 25% higher than the diesel fuel flow.

The nvPM reductions in both experiments are significantly larger than can be explained by water dilution effects alone, with less impact noted for fuels with higher hydrogen content. This suggests the reduction may be in part due to chemistry. Preliminary chemical kinetic investigations were undertaken using CHEMKIN-PRO and suggest that the soot reduction mechanism is potentially via a reduction in PAH formation within the flame zone. However, further analysis is required to validate if this mechanism is dominated by in-flame OH reduction mechanisms or influenced significantly by other factors associated with water dilution and reduced flame temperatures.
Numerical Investigation of Effects of Blockage, Inclination Angle and Hole-Size on Film Cooling Effectiveness at Concave Surface
Authors: Wang Fu-qiang , Pu Jian , Wang Jian-hua , Xia Wei-dong
Published: January 2021

Film-hole can be often blocked by the thermal-barrier coatings (TBC) spraying, resulting in the variations of film cooling performance and pressure loss. In this work, a numerical study of the effect of blockage ratio on the film cooling effectiveness of inclined cylindrical-holes was carried out on a concave surface to simulate the airfoil pressure side. Three typical blowing ratios (BRs) of 0.5, 1.0 and 1.5 were chosen at an engine-similar density ratio (DR) of 2.0. Two common inclination angles of 30° and 45° were designed. The blockage ratios were adjusted from 0 to 20%. The results indicated that the blockage near the trailing edge of hole-exit could enhance the penetration of film cooling flow to the mainstream. Thus, the averaged effectiveness and coolant coverage area were reduced. Moreover, the pressure loss inside of hole was increased. With the increase of BR, the decrement of film cooling effectiveness caused by blockage rapidly enhanced. At BR = 1.5, the decrement could be acquired up to 70% for a blockage ratio of 20%. The decrement of film cooling effectiveness caused by blockage was nearly non-sensitive to the injection angle; however, the larger injection angle could generate the higher increment of pressure loss caused by blockage. A new design method for the couple scheme of film-cooling and TBC was proposed, i.e. increasing the inlet diameter according to the blockage ratio before TBC spraying. In comparison with the original unblocked-hole, the enlarged blocked-hole not only can keep the nearly same area-averaged effectiveness, but also can reduce slightly the pressure loss inside of hole. The smaller injection angle could obtain the larger reduction of pressure loss. Unfortunately, application of enlarged blocked-hole at large BR could lead to a more obvious reduction of effectiveness near hole-exit, in comparison with the original common-hole.
Physical Mechanisms Investigation of Sharkskin-Inspired Compressor Cascade Based on Large Eddy Simulations
Authors: Li Zhihui , Du Juan , Zhang Hongwu
Published: January 2021

In order to survive in a complex environment, nature has produced efficient and versatile resource-rich structures. One of the novel drag reduction designs comes from the efficient movement of sharks through microscope riblets aligned along the flow direction. In this paper, the effectiveness of sharkskin-inspired riblets in reducing the aerodynamic loss of compressor cascade flow was investigated by using high-fidelity numerical simulation method. Two key normalized parameters were selected to parameterize various riblet designs, and the corresponding relative change in cascade performance was first investigated based on the uRANS simulations with/without transition model. Then, the large eddy simulations in conjunction with the wall-adapted local eddy viscosity model were conducted to investigate the cascade flow with the selected riblet design cases. By comparing the flow resistance, transition positions, vortex formations and turbulence fluctuations of the boundary flow, the flow control mechanisms of the riblets were finally studied. Simulation results show that compared with the prototype case, the total pressure loss can be reduced by up to 20.5% in the fully turbulent environment. This is because the spanwise fluctuation of the turbulent vortices is impeded, and the turbulent vortices are lifted above the riblet tip. Low-speed streaks inside the riblet valleys generate relatively low shear stresses, while the high-shear stresses occur only at the riblet tips. However, when considering transition from laminar to turbulent boundary flow, the aerodynamic performance of compressor cascade strongly depends on the riblet position relative to the transition on cascade SS. The total pressure loss can only be reduced by up to 8.1%, and even most riblet designs will degrade the cascade performance. The major reason is that the riblets are located upstream of the transition zone, especially at the small incidence angles. Due to the installation of riblets, the contact area between the laminar flow and the wall surface is increased, and the downstream laminar-to-turbulent transition is promoted.
Experimental Drag and Mixing From Lobed Nozzles Under High Swirl Conditions From a Ducted Fan
Authors: Zawislak Maverick , Birk Michael
Published: January 2021

The availability of aerodynamic performance and vorticity production data from mixers under swirl was a challenge for future full-scale design and CFD validation. This paper presents an experimental comparison of drag and mixing performance of a circular trialing edge, lobed nozzle and scalloped nozzle under high swirl conditions as produced by a ducted fan in a subsonic wind tunnel. The design methodology is shared in detail allowing for geometry reproduction. Swirl angles produced by the fan naturally varied between 12° up to 45° according to a free-vortex profile. Performance is compared in terms of net thrust, uniformity factor and vorticity production as measured by 6-component loadcells and a seven-hole pressure probe traverse. The goal of this work was threefold: to study the axial and normal vorticity production from mixers produced by the design methodology, a preliminary investigation into lobed mixers potential in engine plume cooling and to provide a data set for RANS-CFD validation.

A better understanding of lobed mixer mixing mechanisms relative to performance is offered. It is shown that the change in minimum throttle to achieve forward thrust varied between devices as did the twist load due to angular forces. A 4% reduction in required fan power to achieve forward thrust was achieved with the lobed mixer. Furthermore, maximum net thrust increased up to 20% with the mixing nozzles compared to the standard round nozzle suggesting flow straightening can lead to thrust gain in high swirling jet flows to a level that counters increases in drag. Axial and normal vorticity were clearly identified. Co-rotating vortex pairs were produced by the mixers of physical size proportional to the lobe height and wavelength. Axial vorticity levels integrated up to 110% of the round nozzle and occupied 5 times the area. Similarly, integrated normal vorticity increased up to 80% over an area 120% larger. Uniformity factor was best for the scalloped mixer due to enhanced mass flow entrainment through the notch and not the vortex production itself.
LM9000 Free Power Turbine: Advanced Test Bench
Authors: Mazzola Manfredi , Bulleri Andrea , Pennacchi Paolo , Chatterton Steven
Published: January 2021

In Oil and Gas framework, the need of innovative turbomachineries in terms of efficiency, weight, and flexibility is quickly growing.

For these reasons, the new LM9000 is entirely designed with aviation design criteria. It is composed by a gas generator derived from the GE90-115B twin shaft turbofan, coupled to a free power turbine (FPT). Both the gas generator and the FPT use rolling element bearings that contribute to reduce the weight and the complexity of the engine and its auxiliary systems architecture. The free power turbine represents the new element.

Due to the FPT dimensions, weight and characteristics, it was necessary to realize a dedicated test bench that is in a class by itself in the Oil and Gas industry. To give an idea of the dimensions, the ball bearing installed has a bore diameter of 320mm with a ball diameter close to 60mm.

The test bench was crucial to validate the sump configuration for on-shore and off-shore applications and to define the inputs range in which the FPT will operate properly.

The first part of the paper aim at describing the solutions adopted to realize the test bench. The main results are reported in the second part of the paper.

Moreover, the test bench provides flexibility to perform complex tests for different configurations thanks to its 20 tons allowable payload, considerable volume for the test article installation and its modular design.
High Fidelity Transient Forced Response Analysis of Mistuned Bladed Disks Under Complex Excitation and Variable Rotation Speeds
Authors: Tong Jing , Zang Chaoping , Petrov Evgeny
Published: January 2021

An effective method is developed for the efficient calculation of the transient vibration response for mistuned bladed disks under complex excitation and varying rotation speeds. The method uses the large-scale finite element modelling of the bladed disks allowing the accurate description of the dynamic properties of the mistuned bladed disks. The realistic distributions of the excitation forces are considered, which resulted in the multiharmonic excitation loads. The transient response calculation is based on the analytically derived expressions for the transient forced response and the effective method used for the model reduction.

The effects of the varying rotation speed on the natural frequencies and mode shapes of the mistuned bladed disk and its effects on the amplitude and the spectral composition of the loading are allowed for. The different functions of the rotation speed variation can be analyzed.

Numerical studies of the transient forced response and the amplitude amplification in mistuned bladed disks are performed when the resonance regimes are passed during gas-turbine engine acceleration or deceleration. The effects of different types of excitation force and mistuning on transient amplitude amplification are illustrated by a large number of the computational results and comparative analysis. These results and analysis of transient forced response are shown on an example of a realistic mistuned bladed disk.
Effects of Axial Casing Grooves on the Structure of Turbulence in the Tip Region of an Axial Turbomachine Rotor
Authors: Chen Huang , Li Yuanchao , Shankha Koley Subhra , Katz Joseph
Published: January 2021

Challenges in predicting the turbulence in the tip region of turbomachines include anisotropy, inhomogeneity, and non-equilibrium conditions, resulting in poor correlations between the Reynold stresses and the corresponding mean strain rate components. The geometric complexity introduced by casing grooves exacerbates this problem. Taking advantage of a large database collected in the refractive index-matched liquid facility at JHU, this paper examines the evolution of turbulence in the tip region of an axial turbomachine with and without axial casing grooves, and for two flow rates. The semi-circular axial grooves are skewed by 45° in the positive circumferential direction, similar to that described in Müller et al. [1]. Comparison to results obtained for an untreated endwall includes differences in the distributions of turbulent kinetic energy (TKE), Reynolds stresses, anisotropy tensor, and dominant terms in the TKE production rate. The evolution of TKE at high flow rates for blade sections located downstream of the grooves is also investigated. Common features include: with or without casing grooves, the TKE is high near the tip leakage vortex (TLV) center, and in the shear layer connecting it to the blade suction side tip corner. The turbulence is highly anisotropic and inhomogeneous, with the anisotropy tensor demonstrating shifts from one dimensional (1D) to 2D and to 3D structures over small distances. Furthermore, the correlation between the mean strain rate and Reynolds stress tensor components is poor. With the grooves, the flow structure, hence the distribution of Reynolds stresses, becomes much more complex. Turbulence is also high in the corner vortex that develops at the entrance to the grooves and in the flow jetting out of the grooves into the passage. Consistent with trends of production rates of normal Reynolds stress components, the grooves increase the axial and reduce the radial velocity fluctuations compared to the untreated endwall. These findings introduce new insight that might assist the future development of Reynolds stress models suitable for tip flows.
A Design Tool for Supercritical CO2 Radial Compressors Based on the Two-Zone Model
Authors: El Hussein Ihab Abd , Hacks Alexander Johannes , Schuster Sebastian , Brillert Dieter
Published: January 2021

In supercritical Carbon Dioxide (sCO2) cycles, the compressor inlet conditions are selected near the critical point where compressibility factor reaches values as low as 0.2. Consequently, conventional compressor design approaches formulated for fluids obeying the ideal gas law are not verified. Therefore, this paper proposes a design approach for sCO2 radial compressors that consists of a performance prediction model in addition to a set of geometry parameters suitable for radial compressors. The compressor model is based on the two-zone modeling approach, in which the Span and Wagner equation of state for CO2 is integrated. At first, the compressor model is presented in addition to the required correlations. Afterwards, a sensitivity analysis is performed on the model main parameters. Thereafter, a plausibility check is performed against experimentally obtained data. Finally, an overall design approach is proposed and its capability to deliver new geometries is assessed by comparing the tool predictions against the results from a verified CFD code for several test cases. The Comparison shows a maximum deviation of less than 2 percent for the pressure ratio and less than 3.5 percentage points for the efficiency. The results indicate the ability of the proposed approach to predict the performance of sCO2 compressor from correlations that originate from experience with conventional fluids. Additionally, the adopted geometric relations proved its applicability to sCO2 compressors.
Variance in Compressor Turndown When Implementing Surge Control Fallback Strategies
Authors: Garceau Sean W.
Published: January 2021

A centrifugal compressor surge prevention system is used to protect a compressor from surging while in operation. When using an invariant coordinate system for the compressor performance map within the surge protection system, reduced head versus reduced flow, surge control fallback strategies can be implemented within the control system to maintain operation of the compressor when instrumentation fails without placing the unit into a surge event, increasing unit availability. This paper reviews the different fallback strategies that can be implemented based on the function of the instrumentation that faulted and determine the variance between the calculated and actual turndown when different fallback strategies are active. Depending on the fallback strategy implemented, additional turndown margin may be required to ensure compressor surge is prevented by the surge prevention control system. This paper also reviews how the specific gravity, compressor pressure ratio, and compressor flow impact the variance between actual and calculated turndown when a given fallback strategy is active.

Knowing the variance in the turndown allows the operator of the compressor to correctly select the desired fallback strategies and determine the needed control margin to safety operate the compressor without process disruptions. Several recommendations are outlined in the paper.
Time-Resolved Measurements of the Unsteady Boundary Layer in an Annular Low-Pressure Turbine Configuration With Perturbed Inlet
Authors: Sinkwitz Martin , Winhart Benjamin , Engelmann David , di Mare Francesca
Published: January 2021

In this study the unsteady behavior of the boundary layers developing on a LPT stator profile and their effect on secondary flow patterns in a 1.5-stage turbine configuration are investigated under the influence of periodic inflow perturbations. The experimental setup previously employed to analyze the unsteady secondary flow in the stator wake has been enhanced by hotfilm sensor arrays placed on the stator profiles at different blade height positions to provide time-resolved data from within the passage. The turbine inflow is perturbed by periodically passing circular bars and a modified T106-profile has been considered for the blading. The modified profile, labeled as T106RUB, was developed for matching the transition and separation characteristics of the original T106 profile at low flow speeds, thus facilitating measurements to be taken in a large-scale test rig with its improved accessibility. The transition phenomena occurring in the profile boundary layers are investigated under both unperturbed and periodically perturbed inflow by means of spectral analysis, the semi-quantitative characterization of the wall-stress system and an evaluation of the statistic quantities. In particular, the periodic changes of the suction side boundary layer flow region towards the trailing edge are studied in detail. Furthermore, time-resolved hot-film measurements at different blade height positions facilitate a detailed comparison of the quasi two-dimensional mid-span profile flow and the near end wall profile flow which is subject to influence of secondary flow structures. These information are employed to assess to which extent the additional turbulence originating from the wakes affects the blade boundary layers and thus the secondary flow structures. Furthermore, the role of the perturbation frequency on the coupled system of boundary layers and secondary flow structures is evaluated.
Pressure Gain Combustion by Using Shock Flame Interaction Pressure Rise
Authors: Gundogdu Birol , Rose Martin G.
Published: January 2021

Pressure loss across a combustor in a gas turbine reduces thermal efficiency and increases specific fuel consumption. Theoretically, any pressure gain across the combustor results in higher thermal efficiency and lower specific fuel consumption. This work aims to obtain ‘time-averaged pressure rise across the combustor by using shock-flame interaction’. Multiple shock flame interaction increases the chemical heat release rate by two orders of magnitude. In this study, an impulsive heat addition for 30 microseconds with different heat release rates (10,30 and 100) is applied to a spherical zone within the primary zone of the combustor after a quasi-steady URANS combustion and the results are evaluated. A further study, the experimental part, will be based on shock flame interaction with different strengths of shocks. Inlet and outlet total pressures will be measured via high-pressure and high-temperature pressure transducers. Any pressure gain combustion can save billions of USD as gas turbines consume 13.9% of the total energy consumption.
Modal Analysis of Turbine Blades by Means of Distributed Optical Fiber Sensors
Authors: Pennacchi Paolo , Cazzulani Gabriele , Silva Alejandro
Published: January 2021

This paper investigates the possibility of identifying and monitoring the modal shapes of a turbine blade by means of continuous optical fiber sensors based on Optical Backscatter Reflectometry (OBR). The advantage of this approach would be the possibility of embedding the sensors in future carbon fiber blades, in order to make this modal analysis approach available also for the blade operating conditions, since no modifications in the blade fluid-structure interaction occur. The paper describes the proposed method and provides some experimental results obtained on a 3D printed model of an existing steam turbine blade.
Aero Engine Concepts Beyond 2030: Part 2 — The Free-Piston Composite Cycle Engine
Authors: Kaiser Sascha , Schmitz Oliver , Klingels Hermann
Published: January 2021

Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. Part one focuses on the steam injecting and recovering aero engine concept. This second part presents the free-piston composite cycle engine concept. A third publication, building upon those two concepts, presents the project which aims for demonstrating the proof of concept with numerical simulation and test-bench experiments up to a technology readiness level of three.

The free-piston composite cycle engine concept is composed of a gas turbine topped with a free-piston system. The latter is a self-powered gas generator in which the internal combustion process drives an integrated air compressor. Here, several free-piston engines replace the high-pressure core of the gas turbine. Through the ability to work at much higher temperatures and pressures, the overall system efficiency can be increased significantly, and fuel burn as well as CO2 emissions reduce.

The proposed free-piston composite cycle engine design is described in detail, and the sources of thermodynamic benefits are stated. Concrete engineering solutions consider the implementation into an aircraft. The free-piston design enables lower weight and size compared to a crankshaft-bound piston engine, as no mechanical transmission and lubrication system is required. The absence of a crankshaft and connecting rods eliminates reactive forces, reduces mechanical losses, and allows higher mean piston velocities. Facilitated through air lubrication, higher cylinder temperatures are viable. The reduction of heat losses enables cooling of the piston-cylinder with core fluid. The use of a sequential combustion chamber can enhance operability and tailor the production of NOx in low-altitude operation. A discussion of emissions affecting the environment shows the potential to reduce the climate impact of aviation.
Blade Tip Clearance Measurement Systems for High Speed Turbomachinery Applications and the Potential for Blade Tip Timing Applications
Authors: Stubbs Jack David , Shahid Muhammad Arslan
Published: January 2021

As turbomachinery OEMs focus efforts to further increase reliability, power and efficiencies, the running clearance between blade tips and stator continue to be of the utmost importance.

This paper investigates the capability of capacitive tip clearance systems to perform individual blade tip clearance measurements on high speed rotors of up to 90,000rpm. A rotor was designed using finite element analysis; unique blade responses have been predicted.

The objective of this investigation was to consider two different approaches to the application of blade tip clearance measurements and the system requirements to accurately measure low levels of radial displacement of a target rotating between 1,000rpm and 90,000rpm. The first uses the standard approach with passive probes and the second, a new technique using active probes that have demonstrated bandwidths of 1.2MHz and increased measuring range with a lower level of measurement uncertainty. Both systems’ approaches are compared, and their capabilities are evaluated for high-speed applications.

The higher bandwidth capabilities of the latter system, combined with smaller sensor diameters, produces comparable signal rise times to the optical systems used in blade tip timing measurements. The difference in approach offers the potential of contamination resistant sensors for long term blade tip timing applications and measurement probes that do not require cooling systems to withstand higher temperature applications.

The use of different probe configurations, in a number of applications, has demonstrated a two-fold improvement in the measurement range whilst producing lower levels of noise and uncertainty when applied to blade targets made from composites, aluminium and nickel-alloy materials. The measurement data presented includes individual blade’s radial displacement, identified shaft axial displacement, effects of resonance in the test system and the identification of the main drivers of measurement uncertainty along with an achievable value. The capacitive measurement systems’ performance for blade tip clearance is analysed and reported.

The capability to perform other measurement techniques such as blade tip timing with a dual use measurement probe is also analysed and reported. This is done by correlating measurement results between the capacitive systems with that of a repeat measurement of the same target using an optical BTT system.
Soot Emission Simulations of a Single Sector Model Combustor Using Incompletely Stirred Reactor Network Modeling
Authors: Gkantonas Savvas , Foale Jenna M. , Giusti Andrea , Mastorakos Epaminondas
Published: January 2021

The simulation of soot evolution is a problem of relevance for the development of low-emission aero-engine combustors. Apart from detailed CFD approaches, it is important to also develop models with modest computational cost so a large number of geometries can be explored, especially in view of the need to predict engine-out soot particle size distributions (PSDs) to meet future regulations. This paper presents an approach based on Incompletely Stirred Reactor Network (ISRN) modeling that simplifies calculations, allowing for the use of very complex chemistry and soot models. The method relies on a network of Incompletely Stirred Reactors (ISRs), which are inhomogeneous in terms of mixture fraction but characterized by homogeneous conditional averages, with the conditioning performed on the mixture fraction. The ISRN approach is demonstrated here for a single sector lean-burn model combustor operating on Jet-A1 fuel in pilot-only mode, for which detailed CFD and experimental data are available. Results show that reasonable accuracy is obtained at a significantly reduced computational cost. Real fuel chemistry and a detailed physicochemical sectional soot model are consequently employed to investigate the sensitivity of ISRN predictions to the chemical mechanism chosen and to provide an estimate of the soot particle size distribution at the combustor exit.
The Effect of Hub Configuration on the Performance of an Air-Cooled Steam Condenser Fan
Authors: Meiring Z. , van der Spuy S. J. , Meyer C. J.
Published: January 2021

Axial flow fans used in air-cooled condensers are typically analysed with smooth rounded hubs as they offer superior performance when compared to other hub configurations. However, such a hub configuration is impractical and may increase the manufacturing and installation costs of air-cooled condensers. As such, it is desirable to use a simpler, yet effective, hub configuration in order to reduce the installation cost.

This paper assesses the impact that a simpler hub configuration may have on the performance of an axial flow fan. This is done through a comparison of three hub configurations: a cylindrical hub with a flat nose, a cylindrical hub with a hemispherical nose, and a disk hub, installed on the B2a-fan. Computational fluid dynamics modelling, utilising OpenFOAM, is used to simulate each hub configuration.

It is found that the impact on performance due to hub configuration is dependent on the volumetric flow rate through the fan. A thin disk hub exhibits superior performance at low flow rates, resulting in a 8.4% improvement in total-to-static pressure rise and a 5.7% point improvement in total-to-static efficiency. As volumetric flow rate increases, the effectiveness of the disk hub configuration reduces while the hemispherical and flat nosed cylindrical hub configurations result in similar performance metrics at the design point flow rate. At above design point flow rate, the flat nosed cylindrical hub configuration shows an improvement in performance over the hemispherical nose cylindrical hub configuration, with a 9.5% increase in total-to-static pressure rise and a 5.1% point improvement in total-to-static efficiency.
Structural Dynamic Design Process of NovaLT™ Annular Combustors
Authors: Lal Bihari , Dabiru Venkata Rambabu , Provenzale Michele , Funghi Federico , Pucci Egidio , Allegorico Maddalena , Del Puglia Eugenio
Published: January 2021

NovaLT™ family gas turbines are new addition to Baker Hughes product portfolio covering 0–35MW power segment, setting a new standard in their class. These Gas Turbines are designed for high efficiency, maximized availability, longer maintenance intervals with modular replacement approach and equipped with low emission annular combustors.

Combustors are typically subjected to several failure mode mechanisms such as Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF), creep, buckling, oxidation, wear out and their interactions. The design of combustor for High Cycle Fatigue (HCF) is key challenge due to many unknown/uncertain parameters in operation such as constraints of hardware, damping capability, nature and magnitude of dynamic loads.

This paper is focused on structural dynamic design process of NovaLT™ annular combustors. While operating in inherent vibratory environment, caused by either combustion process or stationary/rotating structure, can result in HCF cracking of hardware due to resonance conditions coupled with unavailability of adequate damping in system.

Thus, a robust yet proportionately conservative structural dynamic design, successfully operating in various engine conditions, allowing flexible combustion operability limits, is needed.

Main purpose of this paper is to discuss about product design cycle, challenges and key observations through Annular Combustor design case studies, including experimental measurement of vibratory loads and dynamic response in real operating conditions, as well as a data matched structural dynamic prediction.
High-Fidelity Calculation of Floating Offshore Wind Turbines Under Pitching Motion
Authors: Ortolani Andrea , Persico Giacomo , Drofelnik Jernej , Jackson Adrian , Campobasso M. Sergio
Published: January 2021

The unsteady aerodynamics of floating offshore wind turbine (FOWT) rotors is more complex than that of fixed–bottom turbine rotors, and the uncertainty of low-fidelity aerodynamic predictions, such as those of the blade element momentum theory (BEMT) codes, is higher for the former rotors. Navier-Stokes CFD can improve the understanding of FOWT rotor and wake aerodynamics, and help improve lower-fidelity models. To highlight this potential, blade–resolved analyses of the in-house compressible CFD COSA code and the commercial incompressible CFD code FLUENT were used to investigate the unsteady flow of the NREL 5 MW rotor subjected to prescribed harmonic pitching past the tower base. CFD results were compared to the predictions of the FAST wind turbine code, using BEMT for rotor aerodynamics. Improved tuning of the COSA numerical set-up enabled close matching of the FAST rotor power and loads in fixed–tower mode, and high resolution of the near field wake dynamics; similar agreement levels were obtained with the FLUENT simulations. A novel user-defined function approach, enforcing an additional rigid body motion of the rotor grid conformal to the tower motion, enabled the FLUENT FOWT rotor simulations of this study, and provided new general-purpose FLUENT functionalities for FOWT analyses. All predicted periodic patterns of rotor power and thrust were found to be qualitatively similar, but the power peaks of both CFD predictions were significantly higher than those of FAST. Inspection of the CFD profiles of blade static pressure highlighted and quantified significant compressible flow effects on FOWT rotor power and loads. The blade–resolved analyses of the rotor downstream flow field revealed wake features unique to pitching turbine rotors, primarily the space- and time–dependence of the wake generation, highlighted by the intermittency of the tip vortex shedding.
Effects of Jet Impingement on Convective Heat Transfer in Effusion Holes
Authors: Huelsmann Nathan C. , Thole Karen A.
Published: January 2021

A common design for cooling the combustor liner of gas turbines is a double-wall composed of impingement jets that feed effusion cooling holes. An important cooling mechanism associated with the effusion hole is the convective cooling provided to the liner wall, which is in contact with the hot main gas flowing through the combustor. While the combination of impingement jets and effusion holes have been studied before, mostly in terms of cooling effectiveness, investigators have not fully evaluated the effect the impingement jet has on the local internal convection within the effusion hole. This study evaluates the detailed effects of the impingement geometry on the local convective heat transfer coefficients within the effusion hole, which provides insights as to the design decisions for cooling combustor liners. Using a scaled-up, 3D-printed effusion hole with a constant heat flux boundary condition, local convective heat transfer coefficients were measured for a range of impingement geometries and positions relative to the effusion holes. Results showed a strong influence on the convective heat transfer resulting from the placement of the impingement hole relative to the effusion hole. In particular, the results showed a strong sensitivity to circumferential and radial placement of the impingement jet with little sensitivity to the jet-to-effusion distance.
Nozzle Passage Endwall Effectiveness Values With Various Combustor Coolant Flow Rates: Part 2 — Endwall and Vicinity Surface Effectiveness Measurements
Authors: Nawathe Kedar P. , Zhu Rui , Lin Enci , Kim Yong W. , Simon Terrence W.
Published: January 2021

Effective coolant schemes are required for providing cooling to the first stage stator vanes of gas turbines. To correctly predict coolant performance on the endwall and vane surfaces, these coolant schemes should also consider the effects of coolant streams introduced upstream in the combustor section of a gas turbine engine. This two-part paper presents measurements taken on a first-stage nozzle guide vane cascade that includes combustor coolant injection. The first part of this paper explains how coolant transport and coolant-mainstream interaction in the vane passage is affected by changing the combustor coolant and endwall film coolant flow rates. This paper explains how those flows affect the coolant effectiveness on the endwall. Part one showed that a significant amount of coolant injected upstream of the endwall is present along the pressure surface of the vanes as well as over the endwall. Part two shows effectiveness measurement results taken in this study on the endwall and pressure and suction surfaces of the vanes. Sustained endwall coolant effectiveness is observed along the whole passage for all cases. It is uniform in the pitch-wise direction. Combustor coolant flow significantly affects cooling performance even near the trailing edge. The modified flow field results in the pressure surface being cooled more effectively than the suction surface. While the effectiveness distribution on the pressure surface varies with combustor and film coolant flow rates, the suction surface remains largely unchanged.
Analysis of the Heat Transfer Within Combustor Liners Using a Combined Monte Carlo and Two-Flux Method
Authors: Johnson Andressa L. , Zhao Xinyu
Published: January 2021

One of the consequences of increasing the efficiency of gas turbine combustors is the higher combustion temperatures within the chamber. Advances on managing larger heat loads have been made to protect the combustor wall and turbines. Among those are thermal barrier coatings (TBCs) deposited on metal walls and forced air cooling such as through effusion holes. Historically, both the flame and TBCs have received a simplified gray treatment using effective absorptivities and emissivities. However, studies have shown that the gray analysis can considerably under-predict the cold metal side temperature resulting in misguided combustor life estimates. In this study, non-gray radiation is compared to gray and black radiation by combining three-dimensional Monte Carlo Ray Tracing (MCRT) solution of non-gray flames in a model gas turbine combustor to one-dimensional energy balance within combustor liners. A recent large eddy simulation (LES) of a gas turbine combustor is analyzed, where both gray and non-gray models are exercised. A two-band spectral model is employed for the TBC, where a translucent band and an opaque band are identified. A line-by-line treatment for gas-phase radiation is adopted, and the incident radiative energy on the combustor wall is collected using the MCRT solver, where the fraction of radiative energy within the translucent band is collected and compared with those obtained from the blackbody assumption. The temperature distributions along the multi-layered combustor wall are computed and parametric comparison is conducted. The effects of the nongray flame radiation are more prominent at elevated pressures than at atmospheric pressure, leading to a difference of approximately 150 K in the prediction of peak temperature on the hot side of the TBC. The gray model is found to over-predict the TBC temperature at downstream locations, but under-predict the TBC temperature near the flame locations. The present study proposes a methodology to estimate the wall temperatures when radiation within the TBC is considered. Future work includes application of the methodology to more realistic combustors where both radiative fluxes and convective fluxes can be accurately captured.