bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combustion Characteristics of Isolated Free-Falling Droplets of Jet A Blended With Ethanol and Butanol
Authors: Muelas Álvaro , Remacha Pilar , Ballester Javier 
Published: August 2018

Recent studies on experimental gas turbines suggest that the addition of ethanol or butanol to Jet A are viable alternatives for reducing CO and NOx emissions while maintaining similar performance to that of pure Jet A. In light of this potential, experimental data regarding the burning characteristics of Jet A/ethanol and Jet A/butanol blends are required in order to better understand their combustion process.
Following a previous study on Jet A/butanol droplet combustion, the scope has been extended in order to also include ethanol and a Jet A/ethanol mixture as well as to perform a more detailed characterization. In this work the combustion characteristics of Jet A, butanol, ethanol and their mixtures (20% vol. alcohol in kerosene) are presented for different test conditions. The evaluated combustion characteristics include droplet, flame and soot shell size evolutions, burning rates and image-based soot estimations. The influence of oxygen availability is also ascertained.
The evolution of droplet diameter and burning rates for Jet A and its blends with both alcohols are very similar, whereas pure ethanol and butanol display more distinct behaviors. Soot indices are found to be quite different, with a clear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. These results support the feasibility of kerosene-alcohol mixtures as promising alternative fuels with similar combustion characteristics, but with much lower sooting propensity than pure kerosene.
Numerical and Experimental Investigation of Aerodynamic Characteristics of Model Ultra High Bypass Ratio Counter Rotating Fan
Authors: Druzhinin Iaroslav , Mileshin Victor , Korzhnev Vladimir 
Published: August 2018

One of the perspective schemes of air breathing engine is a scheme with Ultra High Bypass Ratio (BPR 16...25) Counter Rotating Fan. This solution potentially allows significant increase of fuel efficiency compared to modern conventional turbofans.
The model UHBR counter rotating fan named COBRA-1 was developed by CIAM within the framework of European Project COBRA (Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine). The fan was designed using up-to-date 1D, 2D and 3D methods. COBRA-1 is a 0.7 m diameter model of counter rotating fan driven by a planetary reduction gearbox. The bypass ratio of COBRA-1 is 20. The R2/R1 torque ratio was chosen to obtain 1.42-muliple prevalence in power for 2nd row. The blade numbers are 8/12 for R1/R2 correspondingly. Final geometry of airfoils was defined by 3D profiling process to achieve required aerodynamics and acoustic parameters. Application of control-diffusion airfoils allows reaching high integral performances: specific mass flow equals 211 kg/(s*m^2) and isentropic efficiency at design point is higher than 0.93.
The paper presents results of computational simulation of the flow in UHBR fan COBRA-1 based on 3D steady RANS method, 3D URANS and Non-Linear Harmonic method for different operation conditions in comparison with experimental data. Numerical simulation was carried out using Numeca FINE TURBO software package. Steady RANS approach was used during design process to make quick estimation of performances at different rpm. 3D URANS simulation was conducted to analyze unsteady wake-blade and shock-wave interaction and to make a decision about sufficient value of axial gap between rotors.
The COBRA-1 fan was tested in CIAM at C3-A test facility which allows conducting a wide range of measurements of local and integral parameters including acoustics of ducted counter rotating fan at different operating conditions.
Experimental results demonstrate a high level of integral performances and good agreement with computed values.
Significant part of numerical and experimental investigation is devoted to effect of gear-box requirements on aerodynamics. C3-A rig allows to set rotational speed of rotors independently and measure torques at each shaft to achieve required torque ratio and study the influence of small (3–5%) deviation in rpm on aerodynamic characteristics.
A Benchmarking Analysis of a Data-Driven Gas Turbine Diagnostic Approach
Authors: Loboda Igor , Pérez-Ruiz Juan Luis , Yepifanov Sergiy 
Published: August 2018

In an effort to better compare particular gas turbine diagnostic solutions and recommend the best solution, the software tool called Propulsion Diagnostic Method Evaluation Strategy (ProDiMES) has been developed. This benchmarking platform includes a simulator of the aircraft engine fleet with healthy and faulty engines. The platform presents a public approach, at which different investigators can verify and compare their algorithms for the diagnostic stages of feature extraction, fault detection, and fault identification.
Using ProDiMES, some different diagnostic solutions have been compared so far. This study presents a new attempt to enhance a gas turbine diagnostic process. A data-driven algorithm that embraces the mentioned three diagnostic stages is verified on the basis of ProDiMES. At the feature extraction stage, this algorithm uses a polynomial model of an engine baseline to compute deviations of actual gas path measurements from the corresponding values of a healthy engine. At the fault detection and fault identification stages, a common classification for fault detection and fault identification is firstly constructed using deviation vectors (patterns). One of the three chosen pattern recognition techniques then performs both fault detection and fault identification as a common process.
Numerous numerical experiments have been conducted to select the best configurations of the baseline model, a pertinent structure of the fault classification, and the best recognition technique. The experiments were accompanied by a computational precision analysis for each component of the proposed algorithm. The comparison of the final diagnostic ProDiMES metrics obtained under the selected optimal conditions with the metrics of other diagnostic solutions shows that the proposed algorithm is a promising tool for gas turbine monitoring systems.
Experimental Investigation of the Effect of Reynolds Number on the Efficiency of Single-Stage Axial Fans
Authors: Masi Massimo , Castegnaro Stefano , Lazzaretto Andrea 
Published: August 2018

Uncertainties surrounding the influence of Reynolds number on the performance of air handling turbomachines are as old as the study of turbomachinery fluid dynamics. In particular, all low-speed turbomachines and most axial-flow fans feature Reynolds numbers that are often lower than the critical value, above which the literature states a limited dependency of blades cascade aerodynamics on Reynolds number. Testing standards already account for this well-known issue, which arises mainly in the case of geometrically similar fans of different size and/or operating conditions.
On the other hand, one of the main practical issues in the design of low-speed machines is the disagreement among the most authoritative sources on the value of the critical Reynolds number for axial fans. The many definitions of Reynolds number, which are suited to either fan design purposes or fan performance assessment, introduce additional problems, as the corresponding values may differ by orders of magnitude depending on the chosen definition.
A less debated issue deals with the effect of Reynolds number on global performance and efficiency parameters for different axial-flow fan configurations.
This paper reports pressure and efficiency data measured at several rotational speeds of four axial fans that feature different configurations, hub-to-tip ratios, sizes and surface finishes. In particular, the tests consider two 315mm and one 630mm tube-axial fans, and one 800mm vane-axial fan with preswirler blading. Data on two vane-axial fans with straightener, and one preswirler-rotor-stator stage, available in the literature, widen the discussion on the Reynolds number effect on the entire category of single-stage axial fans.
Evaluation of Wire Electrochemical Machining With Rotating Electrode for the Manufacture of Fir Tree Slots
Authors: Klocke F. , Herrig T. , Klink A. 
Published: August 2018

Components with best surface integrities — without any white layer or mechanically damaged rim zones — and regardless of mechanical properties of the material can be produced with electrochemical machining (ECM). Wire ECM combines the outstanding advantages of the ECM working principle with the kinematic of wire electrical discharge machining (wire EDM). A task-specific tool design — such as for classical sinking ECM — is not required for cutting 2.5-dimensional geometries like fir tree slots in turbine discs. Established manufacturing technologies for fir trees are broaching and recently wire EDM. However, high requirements on surface integrity of these turbine parts afford cost intensive finishing processes. Thus, wire ECM could be an attractive cost efficient alternative manufacturing process.
Due to an insufficient flushing concept, a process development of wire ECM for fir tree slots with relevant disc heights failed in the past. A combination of an axial flushing with rotating structured electrode provides a promising approach to meet these challenges.
Therefore, this paper presents investigations of cutting Inconel 718 direct-aged using the new flushing principle. Workpieces with heights up to 40 mm are machined, which is comparable to a low pressure turbine disc height. Reachable feed rates respectively cutting rates are presented. Due to the process specific edge rounding, the formation of the leading edges is examined. Finally, the evolving surface integrities with the help of surface roughness, cross sections and residual stresses are investigated and discussed.
Continuous-Scan Phased Array Measurement Methods for Turbofan Engine Acoustic Testing
Authors: Shah Parthiv N. , White Andrew , Hensley Dan , Papamoschou Dimitri , Vold Håvard 
Published: August 2018

Imaging of aeroacoustic noise sources is routinely accomplished with geometrically fixed phased arrays of microphones. Several decades of research have gone into improvement and optimization of sensor layouts, selection of basis models, and deconvolution algorithms to produce sharper and more localized images of sound-producing regions in space. This paper explores an extension to conventional phased array measurements that uses slowly, continuously moving microphone arrays with and without coupling to rigid fixed arrays to improve image quality and better describe noise mechanisms on turbofan engine sources such as jet exhausts and turbomachinery components.
Three approaches are compared in the paper: fixed receiver beamforming (FRBF), continuous-scan beamforming (CSBF), and multireference CSBF (MRCSBF). The third takes advantage of transfer function matrices formed between fixed and moving sensors to achieve effective virtual arrays with spatial density one to two orders of magnitude higher, with practical sensor budgets and scan speeds.
The MRCSBF technique produces array sidelobe rejection that approaches the theoretical array pattern of a continuous 2-D aperture. The implications of this finding are that better source localization may be achieved with conventional delay and sum (DAS) beamforming (BF) with practical sensor budgets, and that an improved starting image of the sound source can be provided to deconvolution algorithms. These findings are demonstrated on analytical and experimental examples from a low-cost rotating phased array using point sound sources, as well as linear scanning array experiments of an impinging jets point source and a near-sonic jet nozzle exhaust.
Testing of a New Turbocompressor for Supercritical Carbon Dioxide Closed Brayton Cycles
Authors: Pasch Jim , Stapp David 
Published: August 2018

Sandia National Laboratories (SNL) has recently purchased a supercritical carbon dioxide (sCO2) turbocompressor that operates at 118,000 rpm, 750 °C turbine inlet temperature, and 42.9 MPa compressor discharge pressure, and is sized to pressurize the flow for a 1 MWe closed Brayton cycle. The turbocompressor is a line replaceable unit designed by Peregrine Turbine Technologies (PTT) located in Wiscasset, Maine, as part of their closed Brayton electric power genset rated at 1 MWe. Both this machine and a 6MW variant are intended for commercial applications burning a variety of aircombustible fuels including biomass materials.
Sandia purchased this turbocompressor as the first phase of a program to construct a 1 MWe commercially viable sCO2 recompression closed Brayton-cycle system. During this phase, the development platform resident at the SNL Brayton Lab was reconfigured to support testing of the PTT turbocompressor to moderate, or idle, conditions. The testing infrastructure at the Brayton Lab limited maximum pressure to 13.8 MPa. This pressure limitation consequently limited turbocompressor operations to a speed of 52,000 rpm and a turbine inlet temperature of 150 °C. While these conditions are far removed from the machine design point, they are sufficient to demonstrate a range of important features. Numerous testing objectives were identified and researched, most notably: the development of a reliable cycle bootstrapping process for a motorless turbocompressor; the demonstration of consistent start, steady state, and shutdown performance and operations; performance demonstration of the numerous internal seals and bearings designs that are new to this environment; demonstration of controllability via turbine back pressuring and turbine inlet temperature; and turbomachinery performance map validation.
This paper presents the design and development of the testing platform, the PTT turbocompressor and progress achieved on each of the objectives.
Effects of Reacting Conditions on Flow Fields in a Swirl Stabilized Lean Premixed Can Combustor
Authors: Park Suhyeon , Gadiraju Siddhartha , Pandit Jaideep , Ekkad Srinath , Liberatore Federico , Ho Yin-Hsiang , Srinivasan Ram 
Published: August 2018

PIV measurements to understand the flow differences between reacting and non-reacting conditions were conducted in an optically accessible single can combustor. An industrial fuel nozzle was installed at the inlet of the test section to generate the swirl flow for flame stabilization and simulate realistic conditions of a gas turbine combustor. Five different equivalence ratios between 0.50 and 0.75 were tested with propane as fuel. Main air flow was also varied from Reynolds number from 50000 to 110000 with respect to the fuel nozzle diameter. Effect of preheating was tested by changing inlet air temperature from 23 to 200°C. The pressure at the test section was close to atmospheric condition throughout the tests.
The measurements were performed with a 2-D PIV system. Time-averaged flow velocity, vorticity and turbulent kinetic energy (TKE) were obtained from PIV data and flow structures under different conditions were compared. Swirl jet impingement location on the liner wall was determined as well to understand the impact on the liner wall. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows.
An Approach to Approximate the Full Strain Field of Turbofan Blades During Operation
Authors: Fu Gen , Untaroiu Alexandrina , O’Brien Walter 
Published: August 2018

The measurement of the aeromechanical response of the fan blades is important to quantifying their integrity. The accurate knowledge of the response at critical locations of the structure is crucial when assessing the structural condition. A reliable and low cost measuring technique is necessary. Currently, sensors can only provide the measured data at several discrete points. A significant number of sensors may be required to fully characterize the aeromechanical response of the blades. However, the amount of instrumentation that can be placed on the structure is limited due to data acquisition system limitations, instrumentation accessibility, and the effect of the instrumentation on the measured response. From a practical stand point, it is not possible to place sensors at all the critical locations for different excitations. Therefore, development of an approach that derives the full strain field response based on a limited set of measured data is required.
In this study, the traditional model reduction method is used to expand the full strain field response of the structure by using a set of discrete measured data. Two computational models are developed and used to verify the expansion approach. The solution of the numerical model is chosen as the reference solution. In addition, the numerical model also provides the mode shapes of the structure. In the expansion approach, this information is used to develop the algorithm. First, a cantilever beam model is created. The influences of the sensor location, number of sensors and the number of modes included are analyzed using this cantilever beam model. The expanded full field response data is compared with the reference solution to evaluate the expansion procedure. The rotor 67 blade model is then used to test the expansion method. The results show that the expanded full field data is in good agreement with the calculated data. The expansion algorithm can be used for the full field strain by using the limited sets of strain data.
Efficient Adjoint-Based Mesh Adaptation Applied to Turbo-Machinery Flows
Authors: Vivarelli Guglielmo , Qin Ning , Shahpar Shahrokh , Radford David 
Published: August 2018

Within an industrial setting, mesh adaptation has so far found very limited use. This is, in part, due to the complexity of the geometries and flow features that are to be dealt with. However, the successful utilisation of grid modification techniques, could help engineers achieve more accurate estimates of quantities of interest quickly and efficiently. For this reason, in this paper, adjoint error mesh adaptation technology is developed and applied to steady-3D turbo-machinery solutions.
The grid modification strategy proposed comprises of a combined mesh movement and mesh refinement procedure, entirely based on errors related to the functional of interest. The node addition scheme makes use of the output to the flow adjoint solver and an interpolation to an embedded grid. The determined error is used in an edge-refinement approach developed in the in-house MeshPost software. The mesh relocation technique, instead, employs the sensitivity of the functional of interest with respect to the nodes’ coordinates to compute a Riemmannian metric. This parameter is then equi-distributed over the mesh by applying a spring-stiffness approach.
Damping of Combustion Instabilities Through Pseudo-Active Control
Authors: Oliva Jesús , Luciano Ennio , Ballester Javier 
Published: August 2018

Active instability control techniques have demonstrated very good capabilities to correct combustion oscillations but, due to high costs and other practical reasons, have not achieved the success expected in gas turbines engines. A different approach, named here as ‘pseudo-active instability control’, has been explored and the first results are presented in this work. In this case, the flow of non-premixed pilot fuel is modulated by passive methods: the pressure oscillation in the combustion chamber induces a velocity fluctuation at the secondary fuel injector. In principle, damping of the instability may be achieved if the heat release oscillations due to the secondary fuel are out of phase with those of the main flame.
This work reports a first exploration of this strategy, aimed mainly at performing a proof of the concept. An experimental study has been carried out in a laboratory premixed combustor with pilot fuel injection. The relationship between the fluctuations of pressure in the combustion chamber and those of velocity at the injector was studied both experimentally (hot wire anemometry) and theoretically (1-D acoustic model of the injection line). Combustion tests in limit cycle conditions demonstrated that modifications in the geometry of the secondary injection affected the pressure fluctuations inside the combustion chamber. Depending on the geometry (and, hence, acoustic impedance), the instability was enhanced or damped. This demonstrates that the proposed ‘pseudo-active control’ can produce similar effects (at least, qualitatively) to those of active control, but only using passive means, as initially postulated.
Development and Validation of Test Rig for Measurements of Leakage and Rotordynamic Performance of Interlocking Labyrinth Seals
Authors: Ramirez Mauricio , Childs Dara , Gary Keith 
Published: August 2018

Understanding the rotordynamic and leakage characteristics of gas annular seals is important for the design of efficient and reliable turbomachinery. This work sets the foundation to advance the understanding of gas interlocking labyrinth seals. Data for such seals are vague and scarce. A test rig for interlocking seals is developed and validated via tests for a see-through tooth-on-stator labyrinth seal. Test procedures by Millsaps in 1994 and Wagner et al. in 2009 are adapted. Dynamic forces are integrated from the perturbed pressure fields created inside the seal cavities while precessing the rotor using magnetic bearings. Measurements are made by adapting a test rig at the Turbomachinery Lab at Texas A&M University. The see-through seal has eight stator teeth and a smooth rotor. The seal has a 75 mm radius, 3.5 mm tooth height, and 0.2 mm radial clearance. Tests at a rotor speed of 10 kRPM are performed for a range of inlet pressures, pressure ratios, and precession frequencies between 15 and 50 Hz. Forward and backward precessions are imposed. Measured leakage values and rotordynamic coefficients validate the performance of the test rig, making way for interlocking seal tests in the future.
Experience showed that differential pressure transducers, a well-machined stator, and precise alignment are required for accurate measurements. Two sensors 180° apart from each other in a representative cavity demonstrate the development of a correct pressure wave inside the seal. All results are repeatable. Static pressure measurements in the seal cavities show pressure drops linearly across the seal’s cavities. Results show frequency-independent rotordynamic coefficients.
As remarked above, only one of the seal’s cavities was provided with dynamic pressure measurements, and the following rotordynamic coefficients apply for that cavity, not the entire seal. Negative values of direct stiffness K and cross-coupled damping c confirm the lagging dynamic pressure wave is behind the rotor, pushing it radially into the stator. Positive values of cross-coupled stiffness k (where Kxy = −Kyx = k) and direct damping C counteract each other in the circumferential direction, the former being destabilizing. Effective damping Ceff combines the stabilizing impact of direct damping C and cross-coupled stiffness k. Measured cavity Ceff values are negative, and thus destabilizing in the circumferential direction. Future work involves testing interlocking labyrinth seals and using the test results to benchmark CFD codes.