bluuebunny/crossref_metadata_2025_split huggingface dataset:
A 3D Time-Accurate CFD Simulation of the Flow Field Inside a Vaneless Diffuser During Rotating Stall Conditions
Authors: Marconcini Michele , Bianchini Alessandro , Checcucci Matteo , Ferrara Giovanni , Arnone Andrea , Ferrari Lorenzo , Biliotti Davide , Rubino Dante Tommaso 
Published: September 2016

An accurate characterization of rotating stall in terms of inception modality, flow structures, and stabilizing force is one of the key goals for high-pressure centrifugal compressors. The unbalanced pressure field that is generated within the diffuser can be in fact connected to a non-negligible aerodynamic force and then to the onset of detrimental sub-synchronous vibrations which can prevent the machine from operating beyond this limit. An inner comprehension on how the induced flow pattern in these conditions affects the performance of the impeller and its mechanical stability can therefore lead to the development of a more effective regulation system able to mitigate the effects of the phenomenon and extend the left-side margin of the operating curve.
In the present study, a 3D-unsteady CFD approach was applied to the simulation of a radial stage model including the impeller, the vaneless diffuser and the return channel. Simulations were carried out with the TRAF code of the University of Florence. The tested rotor was an industrial impeller operating at high peripheral Mach number, for which unique experimental pressure measurements, including the spatial reconstruction of the pressure field at the diffuser inlet, were available. The comparison between experiments and simulations showed a good matching and corroborated the CFD capabilities in correctly describing also some of the complex unsteady phenomena taking place in proximity of the left margin of the operating curve.
Experimental Characterisation of a Humidified T100 Micro Gas Turbine
Authors: Montero Carrero Marina , De Paepe Ward , Magnusson Jan , Parente Alessandro , Bram Svend , Contino Francesco 
Published: September 2016

Despite the potential of micro Gas Turbines (mGTs) for Combined Heat and Power (CHP), this technology still poses limitations that curb its widespread adoption, especially for applications with a variable heat demand. In fact, whenever the user heat demand is low, mGTs are generally shut down. Otherwise, the high temperature exhaust gases have to be blown off and the resulting electrical efficiency is not high enough to sustain a profitable operation. If, instead of released, the heat in the exhaust gases is re-inserted in the cycle — by injecting hot water and transforming the mGT into a micro Humid Air Turbine (mHAT) — the electrical efficiency can be increased during periods of reduced heat demand, thus improving the economics of the technology.
Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at the Vrije Universiteit Brussel (VUB): based on the T100 mGT and equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addition, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed to better assess the effect of water injection.
Eperimental results demonstrate the patent benefits of water injection on mGT performance: at fixed rotational speed, the power output of the mHAT increases by more than 30%while the fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4.2% absolute points. Future work will involve further optimising the current facility to reduce pressure losses in the air and water circuits. In addition, we will carry out transient simulations and experiments in order to further characterise the facility.
Investigation of Different Solar Hybrid Gas Turbines and Exploitation of Rejected Sun Power
Authors: Kalathakis C. , Aretakis N. , Roumeliotis I. , Alexiou A. , Mathioudakis K. 
Published: September 2016

Solar hybrid gas turbine performance is studied through consideration of four engine configurations: a) single shaft, b) recuperated single-shaft, c) twin-shaft and d) two-spool three-shaft, intercooled, recuperated. For each configuration and for the same design point, the performance is obtained for two hybridization schemes: Fuel only engines Retrofitted for Solar operation (FRS) and engines designed with Solar only operation at the Design Point (SDP). In an attempt to further improve the benefits of hybridization, the concept of a Dual Fluid Receiver for exploiting the rejected solar power, during sunny hours with high irradiation, is demonstrated. Steam is produced by focusing the defocused mirrors of the heliostat field to a second receiver and injected into the combustion chamber.
For the cases examined, it can be concluded that FRS engines show better performance than SDP ones, since they exhibit higher thermal fuel efficiency and higher specific power. Concerning the configurations, an annual fuel saving of ∼35% and an annual output reduction, ranging from 4% for the recuperated single-shaft configuration to 9% for the twin shaft configuration compared to the corresponding fuel-only engines is demonstrated. The inclusion of a Dual Fluid Receiver in an FRS engine removes the power penalty while it maintains the fuel saving benefit.
Leveraging Correlation to Reduce Uncertainty in Efficiency Measurements for Low Pressure Ratio Fans
Authors: Ferrar Anthony M. , Schneck William C. , O’Brien Walter F. 
Published: September 2016

This paper presents the often-neglected correlation terms for uncertainty propagation and shows their importance for rigorous uncertainty analysis. It shows that these terms can be leveraged, often through simple experimental design changes to substantially reduce uncertainty. The efficiency equation is particularly suited to this approach, with order of magnitude uncertainty reductions possible. The paper will present this effect from both a theoretical study and from data measured behind a transonic fan during a distortion response program.
The efficiency equation is particularly suited to improving uncertainty by leveraging the correlation terms because the temperature uncertainty contributes most of the overall uncertainty. Systematic error sources usually dominate thermocouple measurement uncertainty because the slow time response leads to small random errors. The partial derivatives with respect to inlet and outlet total temperature have opposite signs. Correlations between these systematic errors are relatively easy to force through using a single data acquisition system and in-situ calibration standard. This paper presents performance comparisons of these effects for thermocouples. For a 1.35 pressure ratio, 85% efficiency fan, the uncertainty can be reduced by correlation from 85% ± 6.7% to 85% ± 0.48% for typical K-type thermocouples.
Particle Image Velocimetry Investigations of a Subsonic Compressor Tandem Cascade
Authors: Hertel Charlotte , Bode Christoph , Kožulović Dragan , Schneider Tim 
Published: September 2016

A highly loaded, optimized compressor tandem cascade for low speed application (Ma1 = 0.175) [1, 2] was investigated numerically and experimentally using the standard particle image velocimetry measurement technique. The investigated regions are divided in the inlet, the overlap and the outlet region and are investigated for three different inlet angles.
For all inlet angles investigated the results show a homogeneous velocity distribution. The analysis of the measured inlet angle shows a strong suction effect of the cascade starting far in front of the leading edge of the front blade. The acceleration in the overlap region and the change of the velocity distribution is measured for all inlet angles investigated and clarifies the conclusions resulting of former blade surface static pressure measurements [1]. Although the used PIV technique is only capable to resolve two velocity components, the results of the spanwise measured outlet flow fields allow a good analysis of the secondary flow and complete the standard measurement results [2]. The comparison of the experimental flow field results with the numerical results reveals the known numerical limits of secondary flow prediction regarding the extension and intensity [2].
Manufacturing Considerations in the Initial Design Process
Authors: Anderson Mark R. , Klein Peter L. 
Published: September 2016

Many factors come into play in a successful turbomachinery design, but peak aerodynamic performance, maximum operating range, stress levels, and manufacturability are generally the dominant concerns. Depending on the application, other considerations such as acoustics, size, weight, and environmental issues can also come into the picture. The most effective designers take a holistic approach, which tries to incorporate all of these concerns at the beginning of the design process. One of the challenges facing aerodynamicists is a basic understanding of how these downstream issues can be accommodated in the initial design process. Typically, an aerodynamic engineer has minimal knowledge of manufacturing methods such as 5-axis machining. This paper will provide a basic understanding of the subsequent manufacturing impact of various decisions typically made during the preliminary and detailed aerodynamic design process. The paper will focus on radial turbomachinery, but much of the information provided is common for axial turbomachinery produced by 5-axis Computer Numerical Controlled (CNC) machining.
In the initial phase of the design, basic layout decisions generally dictate the overarching manufacturing process. For components produced with 5-axis machining, these would typically be: flank milled or point milled, open or covered impeller, and for covered impellers, integral or welded shroud. The relative costs of these processes are considered in this work along with first-order estimates of their typical impact on aerodynamic performance and stress levels. Once a general layout (and accompanying manufacturing process) is determined, other geometric parameters of the components drive secondary costs in the manufacturing process. The secondary parameters include main blade count, the presence of splitter blades, the blade length, thickness, curvatures, leading and trailing edge shapes, and fillet radii. The use of Computational Fluid Dynamics (CFD) and numerical optimization has driven even more choices into blade shapes, such as splitter blades with different shapes and offsets from the main blade, bowed blades, irregular blade patterns, and non-axisymmetric hub shapes. In many cases, the aerodynamicists and CFD analysts have pushed geometry further than manufacturing capabilities are ready to accept. These secondary costs, and the aerodynamic compromises needed to reduce them, are also considered here. This paper attempts to lay out the basic principles of cost-effective manufacturing, and how these can be considered as early in the design process as possible. Specific examples are considered, and quantitative information is provided which can help guide the designer from the beginning and avoid expensive reworks resulting from downstream revisions. This paper will provide a framework for collaboration between aerodynamic engineers and the manufacturing teams assigned to produce the parts they have designed.
Development of Efficient Small Scale Axial Turbine for Solar Driven Organic Rankine Cycle
Authors: Al Jubori Ayad , Al-Dadah Raya K. , Mahmoud Saad , Khalil Khalil M. , Bahr Ennil A. S. 
Published: September 2016

Recently, the increase in fossil fuel consumption and associated adverse impact on the environment led to significant interest in renewable energy sources like solar. This paper presents a new methodology that integrates the ORC cycle analysis with modeling of an efficient small scale subsonic axial turbine at low temperature heat sources using wide range of organic working fluids like R123, R134a, R141b, R152a, R245fa, R290 and isobutene. The work involves detailed turbine analysis including 1D mean line approach, extensive 3D CFD simulations and ORC cycle analysis at inlet total pressure ranging from 2–5 bar corresponding to temperature range from 275K–365K to achieve the best turbine and cycle performance. This work provides a more reliable data base for small scale organic working fluids instead of using the map of large scale gas turbine.
The numerical simulation was performed using 3D RANS with SST turbulence model in ANSYS-CFX. Using iterative CFD simulations with various working fluids with subsonic inlet conditions, Mach number ranging from 0.6–0.65, results showed that using working fluid R123 for a turbine with mean diameter of 70mm, the maximum isentropic efficiency was 82% and power output 5.66 kW leading to cycle efficiency of 9.5%.
Defect Detection in an Annular Swirl-Burner-Array by Optical Measuring Exhaust Gases
Authors: von der Haar Henrik , Hartmann Ulrich , Hennecke Christoph , Dinkelacker Friedrich , Seume Joerg R. 
Published: September 2016

Defects in combustion chambers of aircraft engines might have an impact on the reliability of the downstream turbine and the machine’s performance. Detecting failures in the combustion chamber of an aircraft engine during operation may improve the resource management and the availability of the system. Aim of the ongoing research project is to find an approach to evaluate the state of the jet engine by analyzing the temperature and emissions field in the exhaust jet.
This investigation is part of the collaborative research center SFB 871. The SFB 871 deals with the improvement of the regeneration process of complex capital goods such as aircraft engines. Maintenance, repair, and overhaul processes would be more efficient if the internal status of the engine would be known while still on the wing before it is disassembled.
The feasibility of this approach is investigated for a pilot scaled model combustor, which provides optical access and allows the selection of “defined errors” in the combustor. It consists of an atmospheric tubular combustor with an array of eight premixed swirl burners with a maximum output of 160 kW. The operating conditions of one of the eight burners concerning power and air-fuel ratio, can be controlled. A power distribution between the burners is typical fault in an aircraft combustor and will be investigated in this study. It is observed that it is possible to determine small deviations by measuring density profiles applying a tomographic background-oriented schlieren (BOS) technique behind the combustor. Additionally, particle image velocimetry is used to measure differences in the velocity field of the exhaust gases. This study shows that a minimum power deviation of one burner in an array of a total of eight burners is detectable in the exhaust plane with the above mentioned measurement techniques.
Experimental and Numerical Investigation of Direct and Indirect Combustion Noise Contributions in a Lean Premixed Laboratory Swirled Combustor
Authors: Kings Nancy , Tao Wenjie , Scouflaire Philippe , Richecoeur Franck , Ducruix Sébastien 
Published: September 2016

Combustors are contributing to the core noise emission of aero-engines in terms of direct and indirect combustion noise. The first is caused by the unsteady heat release rate, the second by the acceleration of inflow inhomogeneities, such as entropy fluctuations, at the combustor outlet or in the turbine.
This work aims to investigate combustion noise generation mechanisms of a choked laboratory scale combustor by a combined experimental and numerical study. Therefore, the temperature fluctuations at the combustor outlet were determined experimentally as well as numerically and cross-checked together with pressure and OH* emission data in the frequency domain. A similar spectral content was found.
Furthermore, the acoustic and entropy fluctuations at the combustion chamber outlet were evaluated for different operation conditions to estimate the direct and indirect combustion noise contributions of a laboratory combustor.
Investigation of Bypass Transition in the Presence of a Separation Bubble With Tomographic PIV
Authors: Lyko Christoph , Michaelis Dirk , Peitsch Dieter , Dittmar Mirko 
Published: September 2016

Low pressure turbines of small and medium sized engines may operate at very low Reynolds numbers. In consequence transition is delayed to an extend where laminar separation, detached transition and reattachment occur. The wakes from upstream blade rows lead to overall high turbulence levels which play a key role in the transition process. Freestream eddies buffeting the laminar boundary layer induce streamwise vortices known as Klebanoff Modes. To investigate this type of flow a flat plate was exposed to a pressure distribution. It is based on the PAK-B suction side and was created by a contoured wall facing the plate. The PAK-B is a Pratt & Whitney design and a Mach number scaled version of a highly aft loaded low pressure turbine airfoil. Due to the latter it suffers from a large separation bubble at low Reynolds numbers.
The flow has been intensively investigated by hot-wire anemometry with a very high spatial resolution. This allows obtaining very precise information about the location of characteristic flow areas; for instance the separation and reattachment positions. Based on this information, Tomographic PIV was employed to expose detailed features in specific areas of the flow field. This technique provides the velocity vector information inside a flow volume. It complements hot-wire results, which give a time resolved information but only planar velocity magnitudes. Combining these techniques and comparing their results is therefore an excellent way to raise the physical understanding of the flow behaviour. This has been done using velocity profiles, skin friction coefficients and integral boundary layer parameters. As the 3D-PIV information allows calculation of derived quantities, like the vector field rotation, a picture of the coherent structures can be drawn.
Retracted: “Multi-Objective Aerodynamic Optimisation of a Real Gas Radial-Inflow Turbine” [ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, Volume 2C: Turbomachinery, Seoul, South Korea, June 13–17, 2016, Conference Sponsors: International Gas Turbine Institute, ISBN: 978-0-7918-4971-2, Copyright © 2016 by ASME. Paper No. GT2016-58132, pp. V02CT45A032; 9 pages; doi:10.1115/GT2016-58132]
Authors: ASME  
Published: September 2016

The above referenced paper has been removed from publication. June 29, 2017.
Copyright © 2017 by ASME
Technical Note: Multicenter study of TrueBeam FFF beams with a new stereotactic diode: Can a common small field signal ratio curve be defined?
Authors: Cagni Elisabetta , Russo Serenella , Reggiori Giacomo , Bresciani Sara , Fedele David , Iori Mauro , Marino Carmelo , Nardiello Barbara , Ruggieri Ruggero , Strigari Lidia , Mancosu Pietro 
Published: September 2016

PurposeSmall radiation fields (<30 mm) are typically involved in stereotactic body radiation therapy procedures. Output factor measurements are subjected to large uncertainties. The signal ratio (SR) readings, defined as the ratio of central axis reading, respectively, in the actual field size and in the reference field size, were evaluated in several centers and a common mathematical description of the SR curve was investigated.MethodsA couple of new unshielded stereotactic diodes (Razor, IBA) was tested under eight different TrueBeams using 10 MV flattering filter free beams with high dose rate (2400 MU/min). Small fields, ranging from 6 to 50 mm, were analyzed in terms of profiles and central axis point measurements. SRs were normalized to 30 mm field and were calculated as a function of nominal field size (NFS) and effective field size (EFS). From SRs acquired using Razor1 (four centers), a theoretical equation was extrapolated. Three centers with Razor2 were used to test the mathematical relationship. Finally, the two diodes were directly compared in the last center.ResultsThe EFS was systematically smaller than NFS (p < 0.01) for all field size ranges, with mean difference of 0.9 ± 0.5 mm. The SR fits using the NFS and EFS had, respectively, R2 = 0.989 and R2 ≫ 0.999. The Razor2 centers’ mean deviation from the predicted SRs, using the NFS and EFS fits, was, respectively, 3.4% and 0.5%. The maximum deviations were 5.0% (6 mm field size) for NFS and 1.9% for EFS. Maximum deviation of 0.5% between the two Razors was observed.ConclusionsEFS measurements were confirmed to be mandatory when comparing SRs over different centers. An equation establishing a functional relation between SRs and the EFS was obtained and tested for the new Razor diode.
Polyvinyl chloride as a multimodal tissue‐mimicking material with tuned mechanical and medical imaging properties
Authors: Li Weisi , Belmont Barry , Greve Joan M. , Manders Adam B. , Downey Brian C. , Zhang Xi , Xu Zhen , Guo Dongming , Shih Albert 
Published: September 2016

PurposeThe mechanical and imaging properties of polyvinyl chloride (PVC) can be adjusted to meet the needs of researchers as a tissue‐mimicking material. For instance, the hardness can be adjusted by changing the ratio of softener to PVC polymer, mineral oil can be added for lubrication in needle insertion, and glass beads can be added to scatter acoustic energy similar to biological tissue. Through this research, the authors sought to develop a regression model to design formulations of PVC with targeted mechanical and multimodal medical imaging properties.MethodsThe design of experiment was conducted by varying three factors—(1) the ratio of softener to PVC polymer, (2) the mass fraction of mineral oil, and (3) the mass fraction of glass beads—and measuring the mechanical properties (elastic modulus, hardness, viscoelastic relaxation time constant, and needle insertion friction force) and the medical imaging properties [speed of sound, acoustic attenuation coefficient, magnetic resonance imaging time constants T1 and T2, and the transmittance of the visible light at wavelengths of 695 nm (Tλ695) and 532 nm (Tλ532)] on twelve soft PVC samples. A regression model was built to describe the relationship between the mechanical and medical imaging properties and the values of the three composition factors of PVC. The model was validated by testing the properties of a PVC sample with a formulation distinct from the twelve samples.ResultsThe tested soft PVC had elastic moduli from 6 to 45 kPa, hardnesses from 5 to 50 Shore OOO‐S, viscoelastic stress relaxation time constants from 114.1 to 191.9 s, friction forces of 18 gauge needle insertion from 0.005 to 0.086 N/mm, speeds of sound from 1393 to 1407 m/s, acoustic attenuation coefficients from 0.38 to 0.61 (dB/cm)/MHz, T1 relaxation times from 426.3 to 450.2 ms, T2 relaxation times from 21.5 to 28.4 ms, Tλ695 from 46.8% to 92.6%, and Tλ532 from 41.1% to 86.3%. Statistically significant factors of each property were identified. The regression model relating the mechanical and medical imaging properties and their corresponding significant factors had a good fit. The validation tests showed a small discrepancy between the model predicted values and experimental data (all less than 5% except the needle insertion friction force).ConclusionsThe regression model developed in this paper can be used to design soft PVC with targeted mechanical and medical imaging properties.