bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of Combustion Noise of a Swirl-Stabilized Flame Using Laser Interferometric Vibrometry Validated by Acoustic Measurements
Authors: Greiffenhagen Felix , Peterleithner Johannes , Woisetschläger Jakob
Published: August 2017

Modern gas turbines rely more and more on premixed combustion systems. While they produce less emission, they are more prone to combustion instabilities. The combustion noise emitted by turbulent swirl-stabilized flames can be calculated directly if density fluctuations in the flame are known as a function of time and space. Recently it was shown that laser interferometry records density fluctuations in the flame quantitatively. In this work a swirl-stabilized, rotationally-symmetric unconfined methane flame at lean operation conditions and low air mass flow rate was scanned by laser interferometric vibrometry (LIV) in order to calculate the overall sound power emitted by the flame. To validate the outcome calculated from the LIV data, sound power was also measured in a half-hemisphere by microphones, using pressure-pressure-probes. These probes record the total sound power of the combustion noise emitted by the flame. To improve signal to noise ratio for this measurement, a siren was used to generate a reproducible excitation of the flame at 212Hz. Both measurement methods were in good agreement. With the LIV data detailed information about the local density fluctuations in the flame causing the sound emission was obtained. Also a preferred acoustic propagation direction between 40° and 80° to the burner axis in downstream direction was observed. This deviation from a uniform distribution is likely to be caused by temperature gradients in the flame. A discussion of systematic errors inherent to the LIV technique and data reduction concludes this publication.
The Design and Characteristics of a Novel Injector: A Lobed Swirl Injector
Authors: Gang Li , Yujun Zhao , Cunxi Liu , Xi Jiang , Qi Chen , Gang Xu , Yong Mu
Published: August 2017

The design procedure of a novel injector — a lobed swirl injector is presented. The lobed swirl injector can play an effective role in swirl generation and enhancing the mixing. Besides, by adjusting the axial position of the lobed swirler, non-premixed combustion can evolve into premixed combustion, and vice versa. It was tested in a low swirl burner configuration. Four perforated plates with different blockage ratios are used to bypass the inlet flow and adjust the turbulent intensity. Velocity distributions at the exit of the burner are captured with two-dimensional Particle Image Velocimetry. The fuel is methane and flames are visualized by camera. The experiments results indicate that the operation range is broadened by the lobed swirler. Compared with flame of vane swirler, flame of lobed swirler is more stable. With the lobed swirler, the blow off occurred gradually and smoothly rather than violently as with the vane swirler. With an increase of air flow, the flame volume of the lobed swirler shrinks significantly, and the leading flame front position moves downstream which means the lift-off height increases. The change in the blowoff behavior for flames can be attributed to the complicated vortices downstream of the lobed swirler as these act to increase turbulence intensity and turbulent flame speed, which in turn influences blowoff limits.
Exploring GasTurb 12 for Supplementary Use on an Introductory Propulsion Design Project
Authors: Byerley Aaron R. , Rouser Kurt P. , O’Dowd Devin O.
Published: August 2017

The purpose of this paper is to explore GasTurb 12, a commercial gas turbine engine performance simulation program, for supplementary use on an introductory propulsion design project in an undergraduate course. This paper will describe several possible opportunities for supplementing AEDsys (Aircraft Engine Design System Analysis) version 4.012, the engine design software tool currently in use. The project is assigned to juniors taking their first propulsion course in the aeronautical engineering major at the USAF Academy. This course, Aeronautical Engineering 361, which focuses on cycle analysis and selection, is required of all aero majors and is used to satisfy the ABET Program Criterion requiring knowledge of propulsion fundamentals. This paper describes the most recent design project that required the students to re-engine the USAF T-38 with the aim of competing for the Advanced Pilot Training Program (T-X) program. The goal of the T-X program is to replace the T-38 aircraft that entered service in 1961 with an aircraft capable of sustained high-G operations that is also more fuel efficient. The design project required the students to select an engine-cycle for a single, non-afterburning, mixed stream, low bypass turbofan engine to replace the two J85 turbojets currently in the T-38. It was anticipated that the high specific thrust requirements might possibly be met through the use of modern component measures of merit to include a much higher turbine inlet temperature. Additionally, it was anticipated that the required 10% reduction in thrust specific fuel consumption might possibly be achieved by using a turbofan engine cycle with a higher overall pressure ratio. This paper will describe the use of GasTurb 12 to perform the same design analysis that was described above using AEDsys as well as additional features such as numerical optimization, temperature-entropy diagrams, and the generation of scaled, two-dimensional engine geometry drawings. The paper will illustrate how GasTurb 12 offers important supplementary information that will deepen student understanding of engine cycle design and analysis.
Foreign Object Damage in 3-D Woven SiC/SiC Ceramic Matrix Composites of Varying Architectures at Ambient and High Temperatures
Authors: Presby Michael J. , Morscher Gregory N. , Iwano Craig , Sullivan Brian
Published: August 2017

Foreign object damage (FOD) behavior in 3-D woven SiC/SiC composites of three different fiber architectures were characterized at ambient (21 °C) and high temperatures (1100 °C) using tungsten carbide projectiles impacted at approximately 350 m/s. Non-destructive evaluation (NDE) techniques such as electrical resistance (ER) and micro-computed tomography (micro-CT) were used to evaluate and compare the damage morphologies of the different architectures. Post-impact retained strength was also conducted using a four point flexural test while utilizing acoustic emission (AE) and ER to monitor the damage accumulation.
Experimental Investigation of Cycle Properties, Noise and Air Pollutant Emissions of an APS3200 Auxiliary Power Unit
Authors: Siebel Teresa , Zanger Jan , Huber Andreas , Aigner Manfred , Knobloch Karsten , Bake Friedrich
Published: August 2017

Auxiliary power unit (APU) operators face increasingly stricter airport requirements concerning exhaust gas and noise emission levels. To simultaneously reduce exhaust gas and noise emissions and to satisfy the increasing demand of electric power on board, optimization of the current technology is necessary. Prior to any possible demonstration of optimization potential, detailed data of thermodynamic properties and emissions have to be determined. Therefore, the investigations presented in this paper were conducted at a full-scale APU of an operational aircraft. A Pratt & Whitney APS3200, commonly installed in the Airbus A320 aircraft family, was used for measurements of the reference data. In order to describe the APS3200, the full spectrum of feasible power load and bleed air mass flow combinations were adjusted during the study. Their effect on different thermodynamic and performance properties, such as exhaust gas temperature, pressure as well as electric and overall efficiency is described. Furthermore, the mass flows of the inlet air, exhaust gas and fuel input were determined. Additionally, the work reports the exhaust gas emissions regarding the species CO2, CO and NOx as a function of load point. Moreover the acoustic noise emissions are presented and discussed. With the provided data the paper serves as a database for validating numerical simulations and provides a baseline for current APU technology.
Budgets of Disturbances Energy for Nozzle Flows at Subsonic and Choked Regimes
Authors: Huet Maxime
Published: August 2017

The noise generated by the passage of acoustic and entropy perturbations through subsonic and choked nozzle flows is investigated numerically using an energetic approach. Low-order models are used to reproduce the experimental results of the Hot Acoustic Test rig (HAT) of DLR and energy budgets are performed to characterize the reflection, transmission and dissipation of the fluctuations. Because acoustic and entropy perturbations are present in the flow in the general case, classical acoustic energy budgets cannot be used and the disturbances energy budgets proposed by Myers (J. Fluid Mech. 226 (1991) 383–400) are used instead. Numerical results are in very good agreement with the experiments in terms of acoustic transmission and reflection coefficients. The normal shock present in the diffuser for choked regimes is shown to attenuate the scattered acoustic fluctuations, either by pure dissipation effect or by converting a part of the acoustic energy into entropy fluctuations.
Introduction of an Integrated Turbo-Electrical Machine
Authors: Schuster Sebastian , Kreischer Christian , Brillert Dieter
Published: August 2017

Turbomachines are commonly designed for a high mass flow rate. However, because of new cycle concepts, turbomachines are also required to compress or expand at small mass flow rates. One example is the supercritical carbon dioxide Brayton cycle. The mass flow rate can be in the range of one kg/s at an almost high fluid density at the inlet to the compressor. This results in a small through flow area. In this paper, a turbomachine concept is presented that integrates the turbomachine parts into an electrical machine. Specifically, the turbomachine is located in the gap between the rotor and the stator of the electrical machine. In that way, a very compact design can be achieved. This paper aims to explain the basic concept. An aerodynamic design study is performed that demonstrates the important parameters for machine performance. Additionally, the design of the electrical machine is discussed based on a realistic application. Finally, conclusions for further development are drawn.
Free-Form Versus Ruled Inducer Design in a Transonic Centrifugal Impeller
Authors: Hazby Hamid , Robinson Chris , Casey Michael , Rusch Daniel , Hunziker Rene
Published: August 2017

The detailed design of the inducer of a high pressure ratio transonic radial compressor impeller with a design inlet tip relative Mach number of 1.4 is considered. Numerical analysis has been used to compare a datum impeller with ruled inducer design with a number of different free-form design concepts, generated following the same aerodynamic design philosophy. The datum stage and one with a free-form inducer, referred to as ‘barrelled forward swept’, with forward swept leading edge near the tip and increased chord at mid-span, have been manufactured and tested. The tests were performed with the same stationary components, including the casing, vaned diffuser and the volute. The design with a barrelled forward sweep of the inducer allows the designer more control of the strength and position of the passage shock at the inlet while meeting mechanical constraints. Interestingly, the performance is also enhanced at off-design points at lower tip-speeds. The measurements show that the stage tested with the swept impeller achieves higher efficiency of between 0.5% and 1.6% compared to the datum design, depending on the operating speed. The CFD simulations are used to further study the flow at part speeds, in order to explain the causes of the observed performance differences at off design conditions.
Numerical Investigation and Validation of the 1 090 MW Steam Turbine Exhaust Hood Flow Field
Authors: Živný A. , Macálka A. , Hoznedl M. , Sedlák K. , Hajšman M. , Kolovratník M.
Published: August 2017

The last-stage blade (LSB) rows and exhaust hood in low-pressure (LP) steam turbine sections are key elements of the entire LP turbine part. The cold end section affects significantly the whole LP turbine efficiency and overall turbine performance due to huge steam expansion. This expansion is strongly coupled with the diffuser and exhaust hood, which transforms kinetic energy at the stage exit into potential energy. Mentioned mechanism leads to expansion line prolongation between the stage inlet and diffuser outlet and higher turbine power output.

An experimental investigation of the flow field in the exhaust hood is very economically and procedurally expensive and not commonly feasible. Nowadays, capable numerical simulations can provide relatively fast and accurate results on any studied model. On the other hand, the flow behavior inside the LSB and the exhaust hood is very complex and it is still challenging to investigate the whole system using CFD codes.

The purpose of this paper is to validate complex three-dimensional CFD methodology of the flow field in the operating 1 090 MW steam turbine exhaust hood with radial diffuser and condenser neck. The exceptional contribution of this paper is the fact that unique data obtained by measurement on operating Nuclear Power Plant (NPP) steam turbine are available. The comparison is focused mainly on the pressure, velocity and steam wetness distribution along the LSB height at the stage exit/diffuser inlet. Wall static pressures and the pressure recovery coefficient of the exhaust hood were also determined and compared with experimental data. The complete CFD study helps to understand the flow behavior inside the whole exhaust throat and locate critical parts that negatively affect aerodynamic design.
Selecting Rational Parameters for Ultra-Low Power Two-Stage Axial Turbine With Pressure Stages
Authors: Kalabukhov D. S. , Grigoriev V. A. , Rad’ko V. M.
Published: August 2017

Ultra-low power turbine drives are used as energy sources in auxiliary power systems, energy units, terrestrial, marine, air and space transport within the confines of shaft power Ntd = 0.01...10 kW. They represent a set of input, output devices and an ultra-low power turbine (ULPT).

The main objective of this article is to describe and to validate a new modified method for selecting rational parameters of two-stage axial ULPT with pressure stages that is based on the multi-objective optimization in conditions of initial data uncertainty. Using this method allows to design a high-performance turbine already at the preliminary design.

This paper proposes an approach to the development of surrogate models for evaluating the integrated efficiency of two-stage ultra-low power turbine with pressure stages that is based on the use of existing mathematical models of turbine stage efficiency and mass.

The paper describes the basic features of subroutine algorithm for parameters optimization and for efficiency criteria evaluating of a two-stage turbine. This method is intended for use at the preliminary design of a turbine drive. Results of optimization through this method can be applied at the stages of 3D gas-dynamic flow simulation, design and manufacturing of a turbine physical model.

The method was tested at preliminary design of an air starter turbine for starting a diesel engine in cold climatic conditions. Validation of the method was carried out by comparing the results of optimization calculations and numerical gas-dynamic simulation in the Ansys CFX package. The results indicate a sufficient accuracy of the developed method for selection of two-stage turbine parameters.
On LES Based Conjugate Heat Transfer Procedure for Transient Natural Convection
Authors: Fadl M. , He L.
Published: August 2017

Natural convection prediction closely relevant to flexible operations (e.g. fast and frequent startups and showdowns) of gas turbines and steam turbines presents considerable challenges. The strong inter-dependence between fluid and solid parts points to the need for conjugate heat-transfer (CHT) methods. However, the long time scales of the practical operation processes of interest, and the fundamental fluid-solid time scale disparity raise general issues regarding the computational costs of the CHT methods. In particular, if a high-fidelity flow model (e.g. LES) needing to resolve smaller time scales of turbulence is adopted, we also face an additional question regarding the consistency and accuracy of the fluid-solid interface treatment.

In this paper, we address the issues by the means of a loosely coupled CHT procedure based on the multi-scale methodology recently proposed for transient conjugate heat transfer predictions. The multi-scale framework provides an efficient way for accurately solving problems with a huge scale disparity. A particular emphasis of the present work is on efficient and accurate transient CHT solutions in conjunction with the turbulence eddy resolved modelling (LES) for natural convection. A multi-scale flow decomposition associated with the corresponding time step split is adopted. The resultant triple timing formation of the flow equations can be solved efficiently for the fluid-solid coupled system with very disparate time scales. The methodology will be presented with case studies supported by a new interface analysis to underpin the problem statement and motivation of the present work, and to demonstrate the validity and effectiveness of the methodology and implemented procedure.
Bending Fatigue of Thermal Barrier Coatings
Authors: Eriksson Robert , Chen Zhe , Jonnalagadda Krishna Praveen
Published: August 2017

Thermal barrier coatings (TBCs) are ceramic coatings used in gas turbines to lower the base metal temperature. During operation, the TBC may fail through, for example, fatigue. In the present study, a TBC system deposited on a Ni-base alloy was tested in tensile bending fatigue. The TBC system was tested as-sprayed and oxidized and two load levels were used. After interrupting the tests, at 10000–50000 cycles, the TBC tested at the lower load had extensive delamination damage whereas the TBC tested at the higher load was relatively undamaged. At the higher load, the TBC formed vertical cracks which relieved the stresses in the TBC and retarded delamination damage. A finite element analysis was used to establish a likely vertical crack configuration (spacing and depth) and it could be confirmed that the corresponding stress drop in the TBC should prohibit delamination damage at the higher load.
Flow Topology Optimization of a Cooling Passage for a High Pressure Turbine Blade
Authors: Iseler J. , Martin T. J.
Published: August 2017

This paper deals with a topology optimization of internal cooling passages within high pressure turbine blades in order to deliver fully three dimensional designs that optimize the local flow physics. By applying the implemented optimality criteria, a new individual passage design with minimized amount of recirculation is achieved, leading to a reduced total pressure loss. In contrary to traditional parametric approaches, where a CFD run is needed after each design modification, the applied topology optimization acts as a co-simulation and is finished after a single run where the initial geometry represents the available design space. The CFD runs for optimization and the subsequent verification of the flow passages assume steady state take-off conditions. The verification includes a flow simulation to check the pressure loss of the optimized passage design. In a second step, a loosely coupled conjugate heat transfer procedure including external turbine flow, coolant flow and heat conduction of the solid (blade, platform and attachment) is applied to predict the impact on the heat transfer. By running a FEM simulation afterwards, the stresses are computed and compared with those from the reference design.
Nonlinear Harmonic Method Applied to Turbine Conjugate Heat Transfer Analysis for Efficient Simulation of Hot Streak Clocking and Unsteady Heat Transfer
Authors: Mehdizadeh Omid Z. , Vilmin Stéphane , Tartinville Benoît , Hirsch Charles
Published: August 2017

High pressure turbine (HPT) optimum thermal design is critical in further improving gas turbine efficiency. However, this is a challenging task as it requires accurate simulation of unsteady flows in conjunction with heat transfer simulation of the airfoil solid structure, which in turn requires large computational resources.

In this work, the nonlinear harmonic (NLH) method is applied to conjugate heat transfer (CHT) simulation to provide an effective tool for turbine thermal design and analysis. The NLH method can be seen as a computationally affordable alternative to the traditional time-marching unsteady simulation particularly in turbomachinery applications, where the unsteadiness is mostly periodic. When applied to CHT simulations, it also addresses the difficulty of dealing with large time-scale mismatch between fluid and solid domains by casting the periodic perturbations into the frequency domain. Furthermore, it naturally allows for the study of hot streaks clocking effects by means of space harmonics.

These capabilities are demonstrated on the HPT of the NASA/GE Energy Efficient Engine (E3), where hot streaks clocking effect on the metal temperature of the nozzle guide vane (NGV) is simulated. Also, the time variation of the rotor blade metal temperature as it crosses the hot streaks is simulated. The results confirm that, with only a single NLH solution, different aspects of the thermal design of a multi-stage turbine can be explored with little additional computational effort with respect to the standard steady approach.
Flow Computations of Rib-Roughened Cooling Channels With RANS and Scale Resolving Simulation Models
Authors: Görgülü İlhan , Hepkaya Ender
Published: August 2017

In this research, experimental studies conducted by Casarsa [1] were used as test case to validate flow simulation methods. In the numerical simulations, four RANS turbulence models (k-ε, k-ω, V2-f and Reynolds Stress Model) and a URANS model which are widely used in industrial applications were employed for preliminary analyses. In addition, Scale-Adaptive Simulation (SAS), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) models are conducted to examine the capabilities of Scale Resolving Simulation (SRS) models. All numerical simulations were performed on two different grid resolutions. Relevance of the grid resolutions to the applied SRS methodologies have been assessed both with crude estimations obtained from the RANS simulations and examination of LES solutions. Findings were presented at various parallel and perpendicular planes with respect to the side walls and different over and inter-rib space locations in the form of mean and root mean square (rms) velocity profiles. In all comparisons, SRS results revealed an inarguable superiority over RANS models as expected. Among the SRS models, SAS model has been considered as the most promising industrial purpose model because of providing similar quality results by allowing higher time steps and coarser grid resolutions.
CFD Study of a Micro-Combustor Under Variable Operating Conditions
Authors: Cameretti Maria Cristina , De Robbio Roberta , Tuccillo Raffaele
Published: August 2017

New concepts for power generation are discussed as a response to CO2 emissions from the combustion of fossil fuels. These concepts include low-carbon fuels as well as new fuel supplies will be used, with (biogenic) low-caloric gases such as syngas with an amount of hydrogen, with a share of 50% and even higher. However, hydrogen mixtures have a higher reactivity than natural gas (NG) mixtures, burned mostly in today’s gas turbine combustors.

The authors discuss in this paper the potential of a micro gas turbine (MGT) combustor when operated under unconventional conditions, both in terms of variation in the fuel supplied and concerning the part-load or off-design operation.

In particular, the authors’ methodology relies on an advanced CFD approach that makes use of extended kinetic mechanisms coupled with the turbulent interaction of the reacting species. A preliminary set-up of the combustion model is based on data provided by experimental tests of the micro-turbine.

In the paper, several computational examples are discussed, namely:

- The comparison of combustion stability and efficiency and pollutant production with several fuels.

- The analysis of the combustor response with reduced load.

- The use of the pilot and main injectors for supplying different fuels.
Dynamic and Thermal Analysis of Rotor Drop on Sleeve Type Catcher Bearings in Magnetic Bearing Systems
Authors: Kang Xiao , Palazzolo Alan
Published: August 2017

The catcher bearing is a crucial part of the magnetic bearing system. It can support the rotor when the magnetic bearing is shut down or malfunctioning and limit the rotor’s position when large vibration occurs. The sleeve bearing has the advantages of a relatively large contact surface area, simple structure and an easily replaced surface. There are already many applications of the sleeve type catcher bearings in the industrial machinery supported by the magnetic bearings. Few papers though provide thorough investigations into the dynamic and thermal responses of the sleeve bearing in the role of a catcher bearing. This paper develops a coupled elastic deformation — heat transfer finite element (FEM) model of the sleeve bearing acting as a catcher bearing. The FEM model investigates the dynamic and thermal behavior when a flexible rotor drops onto the sleeve catcher bearing. The thermal load caused by the thermal expansion is also considered. The flexible rotor is composed of Timoshenko beam elements. A coulomb friction model is used to model the friction force between the rotor and the sleeve bearing surface. The contact force and 2-D temperature distribution of the sleeve bearing are obtained by numerical integration. To validate the FEM code developed by the author, firstly, both the mechanical and thermal static analysis results of the sleeve bearing model are compared with the results calculated by the commercial software, “SolidWorks Simulation”. Secondly, the transient analysis numerical results are compared with the rotor drop test results in reference 13. Additionally, this paper explores the influences of different surface lubrication conditions, different materials, such as stainless steel, bronze, and aluminum, on rotor-sleeve bearing’s dynamic and thermal behavior. This paper lays the foundation of the fatigue life calculation of the sleeve bearing and provides the guideline for the sleeve type catcher bearing design.
Stress Corrosion Cracking in Steam Turbine: Two Case Studies
Authors: Gowreesan Vamadevan , Grebinnyk Kirill
Published: August 2017

Stress corrosion cracking in steam turbines had been an old problem though some modern steam turbines have almost eliminated this problem by several methods. The methods include design modification to reduce the stress levels below the threshold stress level for stress corrosion cracking, inducing compressive stress by different means and using pure steam [1, 2]. Some of the older steam turbine discs are prone to stress corrosion cracking. Two cases where such machines experienced stress corrosion cracking in their discs are discussed here.

The row 6 disc of an integral steam turbine rotor developed cracks in the root sections. Some of the cracks were mechanically opened for the evaluation. Evaluation of the fracture surfaces with a scanning electron microscope showed evidence of intergranular mode of cracking. Optical microscopy of a cracked root confirmed intergranular mode of cracking. In addition, it showed branching of cracks. Based on these findings, it was concluded that stress corrosion cracking was the reason for the cracks. In addition, finite element analysis was used to calculate the stress distribution in the blade root of the disc. The location of the maximum equivalent stress coincided perfectly with that of the actual crack location in the disc root section. Unfortunately, redesign of the root geometry to minimize the local stress concentration is very difficult due to the size limitation of the blade roots. Small amount of chlorine was identified on the fracture surface and the chlorine could have come from the steam used. The customer was advised to analyze their steam quality and to improve the quality of the steam if needed. The cracked portion was removed from the disc and weld-build up to machine new root sections with the same type of roots.

Root section of the row 6 disc of another steam turbine developed failure. This disc had radial entry type blades. Portion of the disc root and some blades were liberated from the disc due to the cracking. The fracture surface had heavy oxide layer on it. Evaluation of the fracture surface with a scanning electron microscope revealed intergranular mode of failure. Energy dispersive spectroscopy analysis of the fracture surface found oxides on the fracture surface. Optical microscopy showed secondary cracking and branched cracking. All these evidences confirmed that the failure occurred due to stress corrosion cracking. In addition, it was suspected that forging was not heat treated properly due to measured lower toughness and different microstructure. The lower toughness was believed to be a result of improper heat treatment rather than that of embrittlement. Methods to mitigate the risk of stress corrosion cracking were proposed.
Ignition Delay Times of High Pressure Oxy-Methane Combustion With High Levels of CO2 Dilution
Authors: Pryor Owen , Koroglu Batikan , Barak Samuel , Lopez Joseph , Ninnemann Erik , Nash Leigh , Vasu Subith
Published: August 2017

Ignition delay times and methane species time-histories were measured for methane/O2 mixtures in a high CO2 diluted environment using shock tube and laser absorption spectroscopy. The experiments were performed between 1300 K and 2000 K at pressures between 1 and 31 atm. The experimental mixtures were conducted at an equivalence ratio of 1 with CH4 mole fractions ranging from 3.5%–5% and up to 85% CO2 with a bath of argon gas as necessary. The ignition delay times and methane time histories were measured using pressure, emission, and laser diagnostics. Predictive ability of two literature kinetic mechanisms (GRI 3.0 and ARAMCO Mech 1.3) was tested against current data. In general, both mechanisms performed reasonably well against ignition delay time data. The methane time-histories showed good agreement with the mechanisms for most of the conditions measured. A correlation for ignition delay time was created taking into the different parameters showing that the ignition activation energy for the fuel to be 49.64 kcal/mol. Through a sensitivity analysis, CO2 is shown to slow the overall reaction rate and increase the ignition delay time. To the best of our knowledge, we present the first shock tube data during ignition of methane under these conditions. Current data provides crucial validation data needed for development of future methane/CO2 kinetic mechanisms.
Effects of Fuel Molecular Weight on Emissions in a Jet Flame and a Model Gas Turbine Combustor
Authors: Makwana Anandkumar , Iyer Suresh , Linevsky Milton , Santoro Robert , Litzinger Thomas , O’Connor Jacqueline
Published: August 2017

The objective of this study is to understand the effects of fuel volatility on soot emissions. The effect of fuel volatility on soot is investigated in two experimental configurations: a jet flame and a model gas turbine combustor. The jet flame experiment provides information about the effects of fuel on the spatial development of aromatics and soot in an axisymmetric, co-flow, laminar flame at atmospheric pressure. The data from the model gas turbine combustor illustrate the effect of fuel volatility on net soot production under conditions similar to an actual engine at cruise, operated at 5 atm, an inlet temperature of 560 K, and an inlet global equivalence ratio of 0.9 to 1.8. Two fuels with different boiling points are investigated: n-heptane/n-dodecane mixture and n-hexadecane/n-dodecane mixture. The n-hexadecane has a boiling point of 287° C as compared to 216° C for n-dodecane and 98° C for n-heptane. The jet flames investigated are non-premixed and premixed flames (jet equivalence ratios of 24 and 6) in order to have fuel rich conditions similar to those in the primary zone of an aircraft engine combustor. The results from the jet flames indicate that the peak soot volume fraction produced in the n-hexadecane fuel is slightly higher as compared to the n-heptane fuel for both non-premixed and premixed flames. The comparison of aromatics and soot volume fraction in non-premixed and premixed flames shows significant differences in the spatial development of aromatics and soot along the downstream direction. The results from the model combustor indicate that, within experiment uncertainty, the net soot production is similar in both n-heptane and n-hexadecane fuel mixtures. In comparing the results from these two burner configurations, we draw conclusions about important processes for soot formation in gas turbine combustors and what can be learned from laboratory-scale flames.
The Effect of Area Ratio Change via Increased Hole Length for Shaped Film Cooling Holes With Constant Expansion Angles
Authors: Haydt Shane , Lynch Stephen , Lewis Scott
Published: August 2017

Shaped film cooling holes are used as a cooling technology in gas turbines to reduce metal temperatures and improve durability, and they generally consist of a small metering section connected to a diffuser that expands in one or more directions. The area ratio of these holes is defined as the area at the exit of the diffuser, divided by the area at the metering section. A larger area ratio increases the diffusion of the coolant momentum, leading to lower average momentum of the coolant jet at the exit of the hole and generally better cooling performance. Cooling holes with larger area ratios are also more tolerant of high blowing ratio conditions, and the increased coolant diffusion typically better prevents jet liftoff from occurring. Higher area ratios have traditionally been accomplished by increasing the expansion angle of the diffuser while keeping the overall length of the hole constant. The present study maintains the diffuser expansion angles and instead increases the length of the diffuser, which results in longer holes. Various area ratios have been examined for two shaped holes: one with forward and lateral expansion angles of 7° (7-7-7 hole) and one with forward and lateral expansion angles of 12° (12-12-12 hole). Each hole shape was tested at numerous blowing ratios to capture trends across various flow rates. Adiabatic effectiveness measurements indicate that for the baseline 7-7-7 hole, a larger area ratio provides higher effectiveness, especially at higher blowing ratios. Measurements also indicate that for the 12-12-12 hole, a larger area ratio performs better at high blowing ratios but the hole experiences ingestion at low blowing ratios. Steady RANS simulations did not accurately predict the levels of adiabatic effectiveness, but did predict the trend of improving effectiveness with increasing area ratio for both hole shapes. Flowfield measurements with PIV were also performed at one downstream plane for a low and high area ratio case, and the results indicate an expected decrease in jet velocity due to a larger diffuser.
Large Eddy Simulation of Conventional and Bias Flow Acoustic Liners
Authors: Ramdani Soufiane , Yamasaki Nobuhiko , Inokuchi Yuzo , Ishii Tatsuya
Published: August 2017

This study deals with the acoustic behavior of acoustic liners and the flow field around the perforated plate by solving numerically the compressible Navier-Stokes equations. The difficulty of visualizing the flow around the small holes of the plate makes the numerical simulations very attractive in order to well understand the acoustic behavior of the liner.

The chosen liner was previously studied by Tam et al. [1] experimentally and using the Direct Numerical Simulation for the case of a conventional acoustic liner under normal sound wave incidence. The results obtained by Tam et al. [1] serve for the validation of the results obtained in the present research. Moreover, in this study, the focus is on the numerical simulation of the influence of bias flow on the absorption performance of a slit liner using the large eddy simulation.

Two different methods are used to calculate the absorption coefficient in the computational aeroacoustics (CAA) simulation of the resonator. The first method is the transfer function method, and it simulates the impedance acoustic tube used in the experiment. The second method is the viscous dissipation method, and it calculates the power at which the acoustic energy is converted in viscous dissipation.

The viscous dissipation method gives good agreement for the calculated absorption coefficients at the sound source pressure level of 150 dB. Shed vortices are developed in this case, and are considered to be the main cause of sound dissipation.

The transfer function and the viscous dissipation methods used to calculate the absorption coefficients give good results for frequencies higher and equal to 2 kHz when the sound source pressure level is set to 130 dB. Only at the frequencies of 1 kHz, the obtained values are different from the values obtained by Tam et al. [1]. Shed vortices are not observed when the resonator is under only normal sound wave incidence of 130 dB.

The introduction of a bias flow passing through the aperture of the resonator is investigated. The acoustic performance of the liner in this case and a comparison of the flow behavior at the aperture with a conventional liner is highlighted. When the sound pressure level is equal to 130 dB, an increase in the absorption is obtained for frequencies above the resonance frequency when the bias flow passing through the aperture is introduced. On the other hand, the absorption is reduced for the resonance frequency. However, when the SPL is equal to 150 dB, the absorption coefficient is higher near the resonance frequency, while for higher frequencies the absorption coefficient is lower.
Influence of Turbine Blade Leading Edge Profile on Film Cooling With Shaped Holes
Authors: Zhang Mingjie , Wang Nian , Chen Andrew F. , Han Je-Chin
Published: August 2017

This paper presents the turbine blade leading edge model film cooling effectiveness with shaped holes, using the pressure sensitive paint (PSP) mass transfer analogy method. The effects of leading edge profile, coolant to mainstream density ratio and blowing ratio are studied. Computational simulations are performed using the realizable k-ε turbulence model. Effectiveness obtained by CFD simulations are compared with experiments. Three leading edge profiles, including one semi-cylinder and two semi-elliptical cylinders with an after body, are investigated. The ratios of major to minor axis of two semi-elliptical cylinders are 1.5 and 2.0, respectively. The leading edge has three rows of shaped holes. For the semi-cylinder model, shaped holes are located at 0 degrees (stagnation line) and ± 30 degrees. Row spacing between cooling holes and the distance between impingement plate and stagnation line are the same for three leading edge models. The coolant to mainstream density ratio varies from 1.0 to 1.5 and 2.0, and the blowing ratio varies from 0.5 to 1.0 and 1.5. Mainstream Reynolds number is about 100,900 based on the diameter of the leading edge cylinder, and the mainstream turbulence intensity is about 7%. The results provide an understanding of the effects of leading edge profile and on turbine blade leading edge region film cooling with shaped-hole designs.
Cycle Modeling and Optimization of an Integrally Geared sCO2 Compander
Authors: Bennett Jeffrey , Wilkes Jason , Allison Timothy , Pelton Robert , Wygant Karl
Published: August 2017

This paper presents the selection of a system configuration and off-design control method for an integrally geared compander based on cycle modeling and optimization. The goal of the cycle modeling was to determine a cycle configuration that would reach an efficiency of 50% at design conditions and to optimize off-design control to maintain high efficiencies. The compander is being developed for use in a concentrated solar power supercritical carbon dioxide power plant with expected turbine inlet temperatures of 705°C and utilizing dry cooling leading to compressor inlet temperature varying between 35°C and 55°C. The compander is unique as it consists of eight turbomachinery stages on four pinions all being driven by a single bull gear. The separate stages offer the opportunity to consider a variety of flow splits and cycle configurations including intercooling and multiple stages of reheat.

Cycle modeling was conducted in two stages: on-design and off-design. On-design modeling was simulated with all components operating at their design point. This was used to compare the performance of different cycle configurations and design temperatures. Off-design modeling was then performed to investigate the temperature dependence of the cycle efficiency and power output and to develop a control strategy. Strategies considered and discussed include: turbine bypass, compressor recycle, inlet guide vanes, and inventory control. To determine the best operating conditions for each configuration and control strategy, a genetic algorithm was implemented to optimize the cycle performance across the range of operating temperatures being considered. The final selection of cycle configuration, design temperature and control strategy is also presented.
Numerical Study on the Flow and Heat Transfer Characteristics in Rectangular Channels With Grooves and Different Protrusions
Authors: Zhang Feng , Wang Xinjun , Li Jun , Zheng Daren , Zhou Junfei
Published: August 2017

The present work represents a numerical study on the flow and heat transfer characteristics in rectangular channels with protrusion-grooved turbulators. The Reynolds averaged Navier-Stokes equations, coupled with SST turbulence model, are adopted and solved. In this paper, six geometric protrusion shapes (circular, rectangular, triangular, trapezoidal, circular with leading round concave and circular with trailing round concave) are selected to perform the study. The flow structure, heat transfer enhancement, friction factor as well as thermal performance factor of the rectangular channel fitted with combined groove and different protrusions have been obtained at the Reynolds number ranging from 5000 to 20000. The results indicate that the protrusion shapes affect the velocity distribution near the groove surface. The case of circular protrusion with leading round concave provides the highest overall heat transfer enhancement, while it also causes the highest pressure loss penalty. The case of rectangular protrusion has the lowest overall heat transfer enhancement with high pressure loss penalty. The case of circular protrusion has similar overall heat transfer enhancement with cases of trapezoidal protrusion as well as circular protrusion with trailing round concave, but the pressure loss penalty of the case of circular protrusion is the lowest. In addition, the best overall thermal performance can be observed for circular protrusion-grooved channel.
A Hybrid Approach for 3D Full-Field Measurement on a Closed Slinger Combustor by Hydraulic Simulations
Authors: Jia Lichao , Yang Lili , Yuan Huijing , Jia Yongxia , Wang Yiyang , Feng Yang
Published: August 2017

This hybrid approach proposed in the present study is a mixture algorithm of the 3D PTV and Tomo-PIV based on a two-camera system, which is able to measure the flow field in a closed system with high refractive without in situ calibration. Knowing the calibration data in the air and refractive indices of different optical media, a simplified multimedia photogrammetry model is established based on the least square method. A new particle matching algorithm using the concept of match probability between the twin image frames has been developed to reconstruct the physical position of the particles. In order to overcome the disadvantage of low particle density, time-resolved PIV is utilized at a sampling rate being 2000 Hz to acquire the instantaneous particle images. Then, the spectrum superposition of the cross-correlation distribution is applied to increase the signal-to-noise ratio in the velocity prediction.

The technique proposed here can be used to overcome the difficulty in conventional calibration method for closed measurement objects. Both the computer simulation and some experiments imaging a calibration target reference field are conducted to show the accuracies of the calibration and reconstruction process. The capability of the technique in real experimental conditions is assessed with the measurement of the flow structure in a closed slinger combustor by hydraulic simulations.
Influence of Combustor Flow With Swirl on Integrated Combustor Vane Concept Full-Stage Performance
Authors: Jacobi Simon , Rosic Budimir
Published: August 2017

The integrated combustor vane concept for power generation gas turbines with can combustors has been shown to have significant benefits compared to conventional nozzle guide vanes. Aerodynamic loss, heat transfer levels and cooling requirements are reduced while stage efficiency is improved by approximately 1.5% (for a no-swirl scenario). Engine realistic combustor flow with swirl however leads to increased turning non-uniformity downstream of the integrated vanes. This paper thus illustrates the altered integrated vane stage performance caused by inlet swirl. The study shows a distinct performance penalty for the integrated vane rotor as a result of increased rotor incidence and the rotor’s interaction with the residual swirl core. The stage efficiency advantage of the integrated combustor vane concept compared to the conventional design is thus reduced to 0.7%. It is furthermore illustrated how integrated vane profiling is suitable to reduce the turning variation across the span downstream of the vane, further improve stage efficiency (in this case by 0.23%) and thus mitigate the distinct impact of inlet swirl on integrated vane stage performance.
Preliminary Investigation on the Effect of the Modification of the Sweep Angle at the Blade Tip of Forward Swept Axial Fans
Authors: Masi Massimo , Lazzaretto Andrea
Published: August 2017

The flow path close to the suction side of fan rotor blades mostly affects the overall drag of the blading. The blade lift is affected as well because of the separation of the low energy boundary layer that drives the blade into stall at low fan flow rates.

Forward sweep allows to position the airfoil sections of blades featuring a positive circulation gradient along the span so that they “accompany” the near-wall flow trajectories at the blade suction side. So, rotor efficiency and stall margin of the fan can be improved. On the other hand, blade end effects play a relevant role in high hub-to-tip and low aspect ratio rotors and may compromise the effectiveness of forward sweep. Nevertheless, some authors in the literature stated the beneficial contribution of changing the sweep angle at the ends of the blade both at design and off-design conditions.

The paper studies the end effects on constant-swirl design rotors by means of CFD simulations focusing on the distribution of blade sweep in the near-tip region. In particular, the performance and efficiency calculated for a forward swept tube-axial fan featuring a hub-to-tip ratio equal to 0.4 are compared with those estimated for the corresponding unswept fan at equal duty point. Several modifications of the sweep distribution in the blade tip region are considered in the swept fan to quantify their effect on performance, efficiency and stall margin.

Results show that the addition of up to 6 degrees of local forward sweep at the blade tip to the unswept blading does not affect fan pressure at design operation.

On the other hand, this local increase of the sweep angle allows for a very notable increase of the peak pressure and efficiency at flow rates close to stall inception.