bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigations on the Effect of Slot-Type Casing Treatments With the Aim of Improvement the Aerodynamic and Acoustic Characteristics of Advanced Fans
Authors: Mileshin Victor , Markov Sergey , Korzhnev Vladimir , Khaletskii Iurii 
Published: January 2021

Abstract
This paper presents experimental investigations of aerodynamic and acoustic characteristics for the C179-2 bypass fan model with different versions of a slot-type casing treatment (CT).
This work aims at optimization the CT configuration for a simultaneously improvement of aerodynamic parameters (efficiency and stall margin), as well as the use of this CT as a reactive type silencer to reduce fan noise.
All versions of the slot-type CTs under study are designed on the basis of a semi-empirical procedure developed by CIAM.
Three versions of a slot-type CT are designed and tested as applied to the C179-2 fan model. Based on the analysis of experimental data found by aerodynamic tests to study the effect of the number of CT rows, the geometry of CT slots, their relative positions and the height of its annular cavity on key aerodynamic characteristics of the C179-2 fan model, it is found that:
- all CTs under study considerably increase stall margins (by 8%–16%) of the fan in moderate and high modes determined by n-corrected rotational speed (n = 75–100 %). The stall margin at n = 54 % increases by approx. 30 %.
- relative position of slots in the three CTs with identical number of slots in both rows has a noticeable effect on the CT gas-dynamic efficiency. A half-step shift of axes of the slots relative to each other leads to a slight increase (by max. 1.6%) in stall margins in moderate and high modes and a considerable increase in efficiency (by avg. 2 %) in the same modes, except for n = 100 %.
The beneficial effect of the CT on an increase in stall margins ASM and efficiency (along the operating line) is found for the C179-2 single-row bypass fan model stage with total pressure ratio 1.56 in the bypass duct and corrected tip speed 404 m/s.
A series of experimental studies of acoustic characteristics of the C179-2 fan model stage with three versions of the slot-type casing treatment is completed in conditions of the C-3A acoustic test facility with an anechoic chamber. The acoustic tests of the fan model are carried out within n = 40–100 % corrected rotational speeds (as compared with the nominal speed). The specified speed range covers takeoff (n = 90.7 %), climb (n = 85.2 %), cruise (n = 100 %), and approach (n = 58.2 %) modes.
For all fan operating modes, narrow-band noise spectra and radiation patterns are compared for the C179-2 model configurations with a smooth flow passage and with the CT.
In addition to a substantial improvement in gas-dynamic characteristics, the use of the slot-type CT for the C179-2 bypass fan model stage results in a considerable improvement in its acoustic characteristics. In total, the sound power of the C179-2 single-row by-pass fan model decreases by 3 dB for three certification modes.
Multi-Fidelity Surrogate-Based Optimization of Transonic and Supersonic Axial Turbine Profiles
Authors: Razaaly Nassim , Persico Giacomo , Congedo Pietro Marco 
Published: January 2021

Abstract
Automated Fluid-dynamic Shape Optimization plays a key role in the design of turbomachinery and typically combines Computational Fluid Dynamics (CFD) solvers, parametrization techniques and numerical optimization methods, generally categorized as either direct or surrogate-based (SBO) ones. Here, a particular focus is given to SBO exploiting surrogate models constructed from low-fidelity models, often referred to as variable or multi-fidelity optimization. This study presents a multi-fidelity SBO approach for the optimization of a supersonic turbine cascade operating with an organic fluid and of the transonic LS89 high-pressure turbine vane. A cokriging method is used to simultaneously take into account quantities of interest (QoI) coming from models of different fidelities providing a global surrogate model. A classic Bayesian global optimization method permits to iteratively select promising designs. It relies on the maximization of the so-called Expected Improvement criterion. A geometrical parametrization technique based on B-splines is considered to describe the profile geometry. The total pressure loss coefficient is minimized while the mass flow rate is constrained. For both the application cases, the optimization study reveals a speed-up of 3 to 5 times in the convergence process with respect to classic optimization frameworks based on a single fidelity, while providing similar improvements in terms of fitness functions.
Detailed Description of the Fluidized Bed Mixing and Heat Transfer by Means of Eulerian Multi-Fluid Numerical Simulations
Authors: Ali Uzair Muhammad , Fornarelli Francesco , Camporeale Sergio Mario , Torresi Marco 
Published: January 2021

Abstract
The hydrodynamics and heat transfer of a binary mixture of sand and biomass in a fluidized bed have been numerically investigated. The Eulerian multi-fluid model MFM incorporating kinetic theory of granular flow was used to numerically investigate fluidized bed. A commercial code has been used together with user-defined functions to correctly predict the hydrodynamics and the heat transfer. Numerical results were validated against the experiment in terms of pressure drop across the bed and concentration of biomass at different heights of the bed. Influence of additional parameters, such as superficial gas velocity and sand sizes on hydrodynamics were investigated. Additionally, heat transfer in the fluidized bed was also studied highlighting the influence of the temperature dependent properties of air on the results. The present results reveal that better mixing is achieved for smallest sand size, also promoting more uniform temperature of biomass.
Investigation of Turbulence Modeling and Harmonic Balance Methods Towards Accurately Predicting Compressor Flow Fields
Authors: McManus Liam , Hodges Justin , Beary Ilyas 
Published: January 2021

Abstract
Numerical investigations of the NASA stage 37 compressor case are presented. Simcenter STAR-CCM+ is used for RANS based aerodynamic quantifications of the transonic compressor, with specific attention to the near stall and the peak efficiency operating points. In these axial turbomachines, the unsteady effects are non-trivial, and need to be accounted for in the design methods. Typically, transient simulation of fully realistic engine hardware is unrealistic in terms of the computational expense. However, using a harmonic balance approach in computational fluid dynamic (CFD) simulation has been shown to have a proficiency in capturing the dominant unsteady behaviors at a relatively lower computational cost. As such, the performance of the NASA stage 37 compressor is characterized with both steady and harmonic balance approaches. Furthermore, a thorough exploration and sensitivity study on the turbulence modeling is conducted. The lag elliptic blending k-ε turbulence model is considered, due to its capability for improved predictions in highly separated turbomachinery flows, as compared to the k-O SST and k-O BSL model results.
Experimental Evaluation of 200mm Hybrid Air Foil Bearing Aimed for MW Scale Turbomachinery
Authors: Kim Daejong , LaTray Nguyen , Honavara-Prasad Srikanth 
Published: January 2021

Abstract
The nonlinear characteristics of foil bearings often add complexities to analysis and design of foil bearings over wide size ranges. Previously, scaling laws for bearing clearance and areal stiffness of supporting foil structure for differently sized foil bearings were proposed to address these challenges. The scaling laws enable to design large foil bearing by scaling up existing small foil bearing. To verify the proposed scaling law and demonstrate the feasibility of a large foil bearing, a 200mm (in diameter) hybrid air foil bearing with potential use for 2MW generator was designed and manufactured by scaling up an existing 50mm foil bearing following the scaling laws. The 200mm hybrid foil bearing was tested for its static performance. The bearing features a three-pad offset preload with total six hydrostatic injection ports to improve the load carrying capacity at low speed. A great effort was put into designing a test rig to demonstrate the bearing static performance. The test rig is configured with a series of ball bearings-supported test rotor and the hybrid foil bearing is floating on the rotor. A pneumatic actuator is used to apply external load to the foil bearing and a torque rod measures the friction torque of the foil bearing. The test rig was designed with maximum allowable speed of 18,000rpm and the rotordynamics of the test rig was analyzed to ensure its integrity under the testing conditions. Two hybrid modes, i.e., with all injection ports open and only bottom injection ports open, were compared. The hybrid foil bearing can withstand up to 2000N at zero speed under 5 bar absolute supply pressure for both hybrid modes. Twenty start/stop cycles test at 1000rpm over extended period under 2000N in hybrid modes show the bearing temperature changes very little, demonstrating very robust bearing function. The hybrid foil bearing was also tested in hydrodynamic mode at 4400rpm under 2000N, verifying the full functionality of the bearing in hydrodynamic mode. A preview of a 2MW permanent magnet generator featuring the 200mm hybrid foil bearing is also presented as one of the potential applications.
Volume of Fluid Based Model of Heavy Fuel Oil Droplet Evaporation and Combustion
Authors: Guida Paolo , Saxena Saumitra , Roberts William L. 
Published: January 2021

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.