bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Conceptual Design Study of an Open Rotor Powered Regional Aircraft
Authors: Larsson Linda , Lundbladh Anders , Grönstedt Tomas 
Published: September 2014

Today many of the routes between small to medium sized airports and large hubs are operated by regional aircraft, powered by turboprop or turbofan engines. In the future the open rotor engine might provide an alternative option. The open rotor would combine the possibility of high cruise speed with high propulsive efficiency. Also, since the open rotor essentially is a turboprop with the possibility to fly fast, there is a benefit of high specific range at low cruising speeds, thus giving it a wide range cruise operation.
In this paper a regional aircraft for 70 passengers and 3000 km range is studied. The aircraft is evaluated with both a counter rotating open rotor and a turbofan engine. Aircraft design parameters such as wing area and sweep are varied together with engine parameters such as engine power and propeller disc loading.
Results show that the open rotor aircraft has a 17.0 % higher specific range at the optimal cruise Mach number compared to the turbofan aircraft. For higher speeds, at Mach 0.78, the difference is reduced to 15.0 %. The long range cruise Mach number is around Mach 0.7 for the open rotor aircraft while for the turbofan aircraft it is slightly higher, around Mach 0.72.
Second Law Analysis of Integrated Solar Combined Cycle Power Plants
Authors: Gülen S. Can 
Published: September 2014

Integrated Solar Combined Cycle (ISCC) is an operationally simple, clean electric power generation system that is economically more attractive vis-à-vis stand-alone Concentrating Solar Power (CSP) technology. The ISCC can be designed to achieve two primary goals: (1) replace natural gas combustion with solar thermal power at the same output rating to reduce fuel consumption and stack emissions and/or (2) replace supplementary (duct) firing in the Heat Recovery Steam Generator (HRSG) with “solar firing” to boost power generation on hot days.
Optimal ISCC design requires a seamless integration of the solar-thermal and fossil-thermal technologies to maximize the solar contribution to the overall system performance at the lowest possible size and cost. The current paper uses the exergy concept of the second law of thermodynamics to distill the quite complex optimization problem to its bare essentials. The goal is to provide the practitioners with physics-based, user-friendly guidelines to understand the key drivers and the interaction among them. Ultimately, such understanding is expected to help direct studies involving heavy use of time consuming system models in a focused manner and evaluate the results critically to arrive at feasible ISCC designs.
The Application of Flamelet-Generated Manifold in the Modeling of Stratified Premixed Cooled Flames
Authors: Donini Andrea , Bastiaans Robert J. M. , van Oijen Jeroen A. , de Goey L. Philip H. 
Published: September 2014

CFD predictions of flame position, stability and emissions are essential in order to obtain optimized combustor designs in a cost efficient way. However, the numerical modeling of practical combustion systems is a very challenging task. As a matter of fact, the use of detailed reaction mechanisms is necessary for such reliable predictions. Unfortunately, the modeling of the full detail of practical combustion equipment is currently prohibited by the limitations in computing power, given the large number of species and reactions involved. The Flamelet-Generated Manifold (FGM) method reduces these computational costs by several orders of magnitude without loosing too much accuracy. Hereby FGM enables the application of reliable chemistry mechanisms in CFD simulations of combustion processes. In the present paper a computational analysis of partially premixed non-adiabatic flames is presented. In this scope, chemistry is reduced by the use of the FGM method. In the FGM technique the progress of the flame is generally described by a few control variables. For each control variable a transport equation is solved during run-time. The flamelet system is computed in a pre-processing stage, and a manifold with all the information about combustion is stored in a tabulated form.
This research applies the FGM chemistry reduction method to describe partially premixed flames in combination with heat loss, which is a relevant condition for stationary gas turbine combustors. In order to take this into account, in the present implementation the reaction evolution is described by the reaction progress variable, the heat loss is described by the enthalpy and the local equivalence ratio effect on the reaction is represented by the mixture fraction. A series of test simulations is performed for a two dimensional geometry, characterized by a distinctive stratified methane/air inlet, and compared with detailed chemistry simulations. The results indicate that detailed simulations are reproduced in an excellent way with FGM.
The Effects of Rotation and Mass Flow on Local Heat Transfer in Rotating Cavities With Axial Throughflow
Authors: Günther André , Uffrecht Wieland , Odenbach Stefan 
Published: September 2014

This paper discusses experimental results from a two cavity test rig representative of the internal air system of a high pressure compressor. Thermal steady state measurements of the time-averaged, local heat fluxes based on surface temperatures on both sides of the mid disc are presented for the case of axial throughflow of cooling air. Additionally, measurements of the air temperature and the static pressure inside the cavities are given. Tests were carried out for a wide range of rotational Reynolds numbers up to 107 and axial Reynolds numbers up to 2×105 with a uniformly heated shroud. The method of heat flux determination and the approach to calculating the uncertainties are described and discussed. The local heat flux results from different rotational frequencies, and mass flows are compared and interpreted in terms of assumed flow structures. Using the results of air temperature and static pressure measurements, simple theoretical models of the density gradient and the mixing mass flow which radially enters the cavity, deliver deeper insight into the flow structure and its influence on the heat transfer.
The results show that the heat flux increases with increasing mass flow. The influence of rotation on the heat flux is weaker and more complex than the effect of mass flow. The flow can be separated into four parts, the existence and strength of which depend on the test conditions: rotating cavity flow, impinged flow and resultant secondary flow, instabilities due to a negative radial density gradient respective to the buoyancy-induced flow, and instabilities of the incoming jet. For the geometry with a small inlet gap tested here, the flow and heat transfer are dominated by the throughflow or rather by the secondary flow for Rossby numbers Roz > 1.5. The buoyancy-induced flow is negligible. For Rossby numbers Roz < 1.5, the rotation dominates the flow structure. Buoyancy-induced flow can increase radial mixing between the throughflow and the cavity flow as well as the heat transfer to and from the disc. However, at high rotational frequencies, the density gradient becomes positive due to the increase in pressure induced by the centrifugal force which reduces mixing and heat transfer to/from the disc. Therefore, the highest heat transfer at the disc is measured at medium rotational frequencies.
Time-Resolved Pressure Measurements at a Dual-Cavity Test Rig for Research on the Internal Air System of an Industrial Gas Turbine
Authors: Günther André , Uffrecht Wieland , Caspary Volker 
Published: September 2014

This paper reports about time-resolved examination of the pressure in a dual-cavity test rig for research on the cooling air supply of industrial gas turbines. The test rig has stationary and telemetric instrumentation. Both systems are capable of time-resolved pressure measurement. The design of the test rig is based on a simplified geometry of the internal cavities of the high pressure turbine with receiver holes and simulates the restriction imposed by internal blade cooling flow circuits. The test rig consists of a rotor-stator cavity and a rotor-rotor cavity. The Stage One and Stage Two supplies are separated inside the rotor-stator cavity. The air enters axially without pre-swirl at the outer radius of the stator and leaves the rotor-stator cavity through three rotating, axially directed connecting holes at a radius that varies among the investigated cases. Therefore, different flow paths in the cavities are studied. The research is focused on the branched cooling air supply system, but the flow path can also be analyzed separately. The rim seal flow is not examined in the research work presented here.
Pressure fluctuations in the main gas path caused, for instance, by blade passing and combustor noise, are a well-known phenomenon and therefore the subject of current research, whereas experimental examinations of the pressure fluctuations in the internal air system of gas turbines are very rare. A detailed examination of the pressure in the internal air system is significant in light of the pressure difference between the main gas path and internal air system, which is the driving force for hot gas ingestion. In that sense, the difference between the average pressure on the main gas side to the average pressure in the internal air system is not enough to avoid hot gas ingestion.
Therefore, this paper focuses on pressure fluctuations in the internal cavities. The measurements of the pressure fluctuations in the rotor-stator cavity are presented for different operating conditions. The influence of the rotational speed, the mass flow rate, the flow path and the sensor position in the cavity on the time-resolved pressure is examined. Furthermore, time-resolved pressure measurements from the rotor-rotor cavity are presented. Variations of the axial gap size and the radial location of the connecting holes respective to the outlets of the rotor-stator cavity are described.
Simulation of Soot Volume Fraction and Size in High-Pressure Lifted Flames Using Detailed Reaction Mechanisms
Authors: Naik Chitralkumar V. , Puduppakkam Karthik V. , Meeks Ellen 
Published: September 2014

A simulation study of high-pressure lifted flames in a constant-volume chamber has been conducted using detailed reaction mechanisms in CFD to investigate ignition times, flame lift-off lengths, soot production, and fuel effects. The fuels considered include n-heptane, a two-component surrogate fuel (SR), conventional U.S. No. 2 diesel (D2), and world-averaged jet fuel (Jet-A). Conditions for the flames are those of the experiments performed at Sandia National Laboratories; the n-heptane flame is labeled Spray H [Idicheria and Pickett, SAE 2005-01-3834], and the conditions for all other fuels studied are labeled Spray A [Kook and Pickett, SAE 2012-01-0678]. 3D CFD simulations have been performed using the FORTÉ CFD package. Complex fuels D2 and Jet-A have been modeled using multi-component surrogates. Detailed reaction mechanisms for fuel combustion and emissions formation have been used in the simulations. The size of the fuel mechanisms varied from 326 species to 1000 species for the different fuels. For soot predictions, two different models were used in the simulations: a detailed soot-surface mechanism and a seven-step phenomenological soot model. Both soot models were coupled with the fuel mechanism precursor predictions that included aromatics from benzene to pyrene. While using the detailed soot-surface mechanism, particulate (PM) size and number density were determined using the Method of Moments, which is implemented in the CFD software to calculate particle size distribution characteristics.
Results show excellent prediction of flame location and ignition for all fuels. Location and magnitude of soot fractions in the various flames show good agreement with the published data. Both the phenomenological soot model and the detailed soot-surface mechanism estimated comparable soot fractions in all flames. In addition, PM size information was predicted using the detailed soot-surface mechanism. Impacts of fuel, temperature, pressure, and oxygen concentrations on combustion and soot fractions have been captured by the simulations.
Operational Modal Analysis of Lateral Rotordynamic Modes of Rotating Machinery
Authors: Carden Eoin Peter , Morosi Stefano 
Published: September 2014

The lateral rotordynamic response of turbomachinery is typically speed dependent due to hydrodynamic lubricated bearings, seals, gyroscopic and centrifugal effects, etc. Rotordynamic tools are used to predict the behavior of the machine during operation, however validating these results is challenging. Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses. However, during operation this is unpractical, as the actual excitation force is rarely known.
Operational modal analysis (OMA) can identify the modal parameters of a system over its entire operational range from measurement of response due to some (unknown) excitation. OMA has proven successful on non-rotating structures, but has seldom been applied to rotating machinery.
Three case studies are presented demonstrating the use of OMA in identifying lateral rotors modes based on measurements from existing radial proximity probes during normal production undertaken as part of commissioning campaigns.
Challenges encountered in using and interpreting OMA results are discussed. The results show that proximity probe data acquired during normal operation may be used as input to OMA for the assessment of stability margins of rotating machinery, to produce experimentally derived Campbell diagrams and to identify backwards as well as forwards whirling modes.
Control Strategy for a Direct-Fired Fuel Cell Turbine Hybrid Power System
Authors: Pezzini Paolo , Tucker David , Traverso Alberto 
Published: September 2014

A hardware-in-the-loop-simulation (HiLS) procedure for a direct-fired fuel cell turbine hybrid power system was evaluated for an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behaviour. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and quantify risk mitigation strategies.
The previous implementation of emergency shut-down control strategies resulted in turbomachinery hardware failure. The primary linking event in these cases was compressor stall and surge resulting from the sudden loss of fuel during implementation of the standard double block and bleed strategy used during emergency failure. A new mitigation strategy involving automated ramps is proposed and described in detail to control the system from start-up to forced emergency shut-down. The control architecture shows how the virtual fuel cell model can be coupled to the real gas turbine safely, in all of stage of operations. The paper includes improvements to the emergency shutdown procedure, failure analyses, and the comparison of experimental data with previous results.
Three-Dimensional Structural Evaluation of a Gas Turbine Engine Rotor
Authors: Das Partha S. 
Published: September 2014

Engine rotors are one of the most critical components of a heavy duty industrial gas turbine engine, as it transfers mechanical energy from rotor blades to a generator for the production of electrical energy. In general, these are larger bolted rotors with complex geometries, which make analytical modeling of the rotor to determine its static, transient or dynamic behaviors difficult. For this purpose, powerful numerical analysis approaches, such as, the finite element method, in conjunction with high performance computers are being used to analyze the current rotor systems.
The complexity in modeling bolted rotor behavior under various loadings, such as, airfoil, centrifugal and gravity loadings, including engine induced vibration is one of the main challenges of simulating the structural performance of an engine rotor. In addition, the internal structural temperature gradients that can be encountered in the transient state as a result of start-up and shutdown procedures are generally higher than those that occur in the steady-state and hence thermal shock is important factor to be considered relative to ordinary thermal stress. To address these issues, the current paper presents the steady-state & quasi-static analyses (to approximate transient responses) of two full 3-D industrial gas turbine engine rotors, SW501F & GE-7FA rotor, comprising of both compressor & turbine sections together. Full 3-D rotor analysis was carried out, since the 2-D axisymmetric model is inadequate to capture the complex geometries & out of plane behavior of the rotor. Both non-linear steady-state & transient analyses of a full gas turbine engine rotor was performed using the general purpose finite element analysis program ABAQUS.
The paper presents in detail the FEA modeling technique, overall behavior of the full rotor under various loadings, as well as, the critical locations in the rotor with respect to its strength and life. The identification of these critical locations is needed to help with the repair of the existing rotors and to improve and extend the operational/service life of these rotors.
Investigation of Flame Stabilization in a High-Pressure Multi-Jet Combustor by Laser Measurement Techniques
Authors: Lammel Oliver , Rödiger Tim , Stöhr Michael , Ax Holger , Kutne Peter , Severin Michael , Griebel Peter , Aigner Manfred 
Published: September 2014

In this contribution, comprehensive optical and laser based measurements in a generic multi-jet combustor at gas turbine relevant conditions are presented. The flame position and shape, flow field, temperatures and species concentrations of turbulent premixed natural gas and hydrogen flames were investigated in a high-pressure test rig with optical access.
The needs of modern highly efficient gas turbine combustion systems, i.e., fuel flexibility, load flexibility with increased part load capability, and high turbine inlet temperatures, have to be addressed by novel or improved burner concepts. One promising design is the enhanced FLOX® burner, which can achieve low pollutant emissions in a very wide range of operating conditions. In principle, this kind of gas turbine combustor consists of several nozzles without swirl, which discharge axial high momentum jets through orifices arranged on a circle. The geometry provides a pronounced inner recirculation zone in the combustion chamber. Flame stabilization takes place in a shear layer around the jet flow, where fresh gas is mixed with hot exhaust gas. Flashback resistance is obtained through the absence of low velocity zones, which favors this concept for multi-fuel applications, e.g. fuels with medium to high hydrogen content.
The understanding of flame stabilization mechanisms of jet flames for different fuels is the key to identify and control the main parameters in the design process of combustors based on an enhanced FLOX® burner concept. Both experimental analysis and numerical simulations can contribute and complement each other in this task. They need a detailed and relevant data base, with well-known boundary conditions. For this purpose, a high-pressure burner assembly was designed with a generic 3-nozzle combustor in a rectangular combustion chamber with optical access. The nozzles are linearly arranged in z direction to allow for jet-jet interaction of the middle jet. This line is off-centered in y direction to develop a distinct recirculation zone. This arrangement approximates a sector of a full FLOX® gas turbine burner. The experiments were conducted at a pressure of 8 bar with preheated and premixed natural gas/air and hydrogen/air flows and jet velocities of 120 m/s.
For the visualization of the flame, OH* chemiluminescence imaging was performed. 1D laser Raman scattering was applied and evaluated on an average and single shot basis in order to simultaneously and quantitatively determine the major species concentrations, the mixture fraction and the temperature. Flow velocities were measured using particle image velocimetry at different section planes through the combustion chamber.
CFD Simulation of an Aeroengine Bearing Chamber Using an Enhanced Volume of Fluid (VOF) Method: An Evaluation Using Adaptive Meshing
Authors: Crouchez-Pillot Alexandre , Morvan Hervé P. 
Published: September 2014

In aero engines, the rotating shafts are supported by a set of bearings, which are enclosed in bearing chambers. Cooling and lubrication oil escapes from the bearings and these chambers are designed to capture and recycle it. A good understanding of the oil behaviour inside bearing chambers is therefore desirable in order to limit the oil volume involved and minimize transmission losses whilst managing the engine core heat in the best possible manner.
This study is focused on the simulation of the oil behaviour inside such a chamber and special attention is given to the so-called KIT bearing chamber. The oil phase in the chamber can take different forms e.g. sprays, droplets, thin films or a combination of those. Assuming the oil we want to track remains dominantly as a film and large droplets/filaments, the Volume of Fluid (VOF) method is used in order to track the oil and the oil/air interface in the chamber, hereby investigating the feasibility and merits of such an approach and extending the earlier work carried out by the authors and colleagues. An Enhanced VOF approach coupled with level-set is used here unless stated otherwise. The simulated pump outlet condition, proposed by the University of Nottingham, is also employed in this study, to replicate an engine displacement pump.
Since the use of VOF requires a refined mesh in the oil region, an adaptive mesh approach based on the volume of fluid gradient is developed and validated to control the total cell count for some of the cases reported here and limit simulation costs. The Adaptive Mesh Approach (AMA) can allow a better resolution of critical interfaces, better compute the oil break-up (within the limitation of the physical models used) and then track the droplets and filaments. Therefore, not only the CPU time cost might be reduced compared to a fixed mesh approach but significant physical aspects of the problem should be better accounted for. In order to inform the set up and parameters used with this method, and appraise its value for the proposed application, the experimental study of Fabre is used before the approach is applied to the KIT chamber.
Good insight is obtained in terms of run time acceleration for such problem when combining the proposed VOF setup with adaptive meshing. Key set up parameters are quantified. The simulations carried out with the proposed set up are proving to be fairly robust and stable. Qualitative (physical) evidence is also encouraging and confirms the value of such an approach to the study of aeroengine bearing chambers.