bluuebunny/crossref_metadata_2025 huggingface dataset:
Gasification of Oil-Palm Fiber Using Pure Oxygen, Pure Steam, and Oxygen-Steam Mixtures as Oxidizing Agent
Authors: Carranza Eliana M. , Gordillo Gerardo , Duran Juan José
Published: September 2014

The increasing concern for greenhouse emissions from fossil fuel combustion processes has encouraged the research on technologies that use alternative fuels. A feasible option is the use of biomass feedstock to produce gaseous and liquid fuels via thermal gasification. This is promising since biomass has net zero carbon footprint. Colombian oil-palm agroindustry produces a great amount of fiber wastes (mesocarp of the oil palm fruit), which, in many cases, can pollute natural sources (including global warming by way of potent greenhouse emissions such as CH4) due to the fact that waste handling systems, storage, and treatment structures are frequently not appropriate. Nevertheless, the concentration of this fiber in oil factories makes this resource a viable feedstock for local thermal gasification facilities. The current paper deals with oil-palm fiber (fruit mesocarp) thermal gasification (including pyrolysis) using oxygen, steam, and oxygen-steam mixtures for partial oxidation. The Chemical Equilibrium with Applications program (CEA), developed by NASA, was used to estimate the compositions of the gaseous fuels produced from pyrolysis, steam reforming and oxygen-steam adiabatic gasification. Based on gas composition, the energy densities of gaseous fuels produced along with the energy recoveries for all gasification process were also calculated. Operating parameters such equivalence ratio (Φ) and steam to fuel ratio (SF) were studied for adiabatic oxygen-steam gasification while temperature (T) and pressure were studied for non-adiabatic gasification (steam reforming (Φ = 0), and pyrolysis (Φ= 0 and SF = 0)). The effect of SF on pure steam gasification was also studied. In order to estimate the pyrolysis activation energy, thermogravimetric analyses (TGA) were carried out using N2 as carrier gas and under different heating rates (β: 10, 20, and 30 °C/min). Results from oxygen-steam gasification showed that at Φ < 3, increased Φ (less oxygen supplied) increases the production of H2 and CO but decreases the production of CO2. At Φ >3, increased Φ produces mixtures rich in H2 and CO2 but poor in CO. The productions of CO and H2 from pyrolysis and steam reforming are only possible at T between 700 K and 1100 K. At T > 1100 K, the effect of temperature on H2 and CO productions is negligible; however, under those operating conditions (T > 1100 K), increased SF results in mixtures composed basically of H2, CO, and low traces of CO2. The average value of the activation energy was 233 kJ/kmol.
A New Risk and Reliability Model for Compressor and Pump Installations
Authors: Garcia-Hernandez Augusto , Delgado-Garibay Hector , Rivera Reyes Rubén , Martínez Jose Luis , Martínez Gomez Lorenzo
Published: September 2014

Compression and pumping systems are constantly changing infrastructures, with many of the older compressor/pumping stations requiring updates, repairs and inspections to maintain safe and efficient operations. These stations operate over a wide range of pressures, flows, and working fluids under varying environmental conditions. Operating condition factors, as well as original design and materials, can significantly affect corrosion rates, structural integrity, and the flow capability of these compressor/pumping stations. Station equipment can be logically inter-related using failure trees and each critical sub-component be assigned a mean time between failure and failure probability using acceptable industry standards. These individual components are then allowed to interact to determine sub-system, system, and full station level failure probabilities. This type of analysis has historically not been utilized by the oil and gas industry but is common to other industries, such as the aerospace and nuclear power industries.

This paper presents a new, comprehensive, consistent, and effective process for predicting risk, integrity, and reliability of the compressor and pump stations as well as each major subsystem and component within these stations. The model considers predefined “threats” such as mechanical, materials, electrical, third party, environment and external forces, improper maintenance, and operation of all its components; thus, typical failures modes are included in these threats. A semi-quantitative methodology with factored risk indices is applied where weighting factors are used to adjust the model with operational data. These factors are generated from reliability data extracted from the station. Comparisons between the model predictions and the reliability data will allow tuning of the weighting factors. Weighting factors are defined for each of the identified threats. The probability of failure is computed at a component level; however, it can be obtained at any level in the system based upon the specified categorization. The probability of failure is represented as a function of three factors: exposure, resistance, and mitigation, while the consequence of failure is estimated using the same approach based on three factors: receptor, hazard, and reduction.

This predictive risk and failure model has been defined based on international specifications and is consistent with actual operating conditions, capacity planning, and remaining life expectations, while assuring that the stations meet the day-to-day operational demands of the system. The model also is able to predict each individual equipment failure probability within the station systems and provides for easy output of the data in graphical form for proper operating, maintenance, repair, and testing decisions.
Experimental Observations of Flow Over an Airfoil in a Confined Duct
Authors: Crawford James , Birk A. M.
Published: September 2014

The flow around a NACA 0020 airfoil strut placed in the centre of a rectangular duct has been studied. The performance of the strut was characterized in terms of its effect on the mean flow, as well as in terms of overall losses. It was shown that the main influences of increasing the confined mixing length downstream of the airfoil wake were to reduce the total system dump loss (kinetic energy loss) through the use of a Carnot diffuser, and to slightly increase the wake spreading rate. In addition to creating a reference dataset for CFD comparison and validation, some phenomenon were particularly identified for future CFD investigation. It was shown that there may be some benefit to adjusting the turbulent Prandtl number for Turbulent Kinetic Energy during CFD simulations of this same problem. It was also shown that studying the particular effects of the Carnot diffuser on the development and migration of the wall-airfoil interface vortices would give useful insight into the physical mechanisms driving this change in performance.
An Experimental Study of Mist Film Cooling With Fan-Shaped Holes on an Extended Flat Plate: Part 1 — Heat Transfer
Authors: Ragab Reda , Wang Ting
Published: September 2014

Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments using fan-shaped holes over an extended downstream length in this study. Both an existing wind tunnel and test facility, used in previous work, have been retrofitted. The first modification was extending the length of the flat plate test section to cover longer distances downstream of the injection holes, up to X/D = 100, in order to investigate whether mist cooling can be harnessed farther downstream where single-phase film cooling is not effective. The second modification was to incorporate a fan-shaped diffusion hole geometry in order to investigate whether mist can further enhance the film cooling performance of the already highly effective fan-shaped holes. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part 1 is focused on the heat transfer result on the wall, and Part 2 is focused on the two-phase droplet multiphase flow behavior. Three blowing ratios are investigated.

The results show that, at low blowing ratios when the film is attached to the surface, the enhancement of the mist film cooling effectiveness, compared to the air-only case, on the centerline of the hole ranges from 40% in the near hole region to over 170% at X/D = 100. Due to the diffusive nature of the fan-shaped hole, the laterally-averaged enhancement is on par with that on the centerline. The significant enhancement over the extended downstream distance from X/D = 40–100 is attributed to the evaporation time needed to evaporate all of the droplets. Each droplet acts as a cooling sink and flies over a distance before it completely vaporizes. This “distributed cooling” characteristic allows controlled cooling by manipulating the size distribution of the water droplets to extend the cooling effects of the droplets farther downstream from the injection location. At higher blowing ratios, when the cooling film is lifted off from the surface, the cooling enhancement drops below 40%. Although the enhancement in the near hole region X/D < 40 is about 20% lower than that achieved by using the cylindrical holes, the magnitudes of the mist adiabatic film cooling effectiveness using fan-shaped holes are still much higher than those of the cylindrical holes.
Experimental Studies of Supersonic Steam Flow in the Flat Nozzle Blade Cascade at Different Initial Steam Conditions
Authors: Gribin Vladimir , Tishchenko Aleksandr , Gavrilov Ilya , Tishchenko Victor , Khomyakov Sergey , Popov Vitaliy
Published: September 2014

The results of experimental studies of supersonic steam flow downstream the flat turbine nozzle blade cascade has been considered. The investigations were carried out in a broad range of steam initial conditions (superheated, dry saturated) and isentropic Mach (M1t) number downstream the object of study. The schlieren method was used to obtain the visual information about shock waves structure. The flow parameters oscillations were measured by pressure transducers situated at different locations downstream the object of study.

It is shown that the occurrence of condensing shock at conditions of superheated steam upstream the nozzle blade cascade leads to the sufficient unsteadiness of shock waves system. This is due to the complex relationship between the boundary layer and a shock wave system. With changing of initial steam conditions the rearrangement of static pressure frequency spectra is observed.
Proper Orthogonal Decomposition Analysis of Non-Swirling Turbulent Stratified and Premixed Methane/Air Flames
Authors: Kamal M. Mustafa , Duwig Christophe , Balusamy Saravanan , Zhou Ruigang , Hochgreb Simone
Published: September 2014

This paper reports proper orthogonal decomposition (POD) analyses for the velocity fields measured in a test burner. The Cambridge/Sandia Stratified Swirl Burner has been used in various studies as a benchmark for high resolution scalar and velocity measurements, for comparison with numerical model prediction. Flow field data was collected for a series of bluff-body stabilized premixed and stratified methane/air flames at turbulent, globally lean conditions (ϕ = 0.75) using high speed stereoscopic particle image velocimetry (HS-SPIV). In this paper, a modal analysis was performed to identify the large scale flow structures and their impact on the flame dynamics. The high speed PIV system was operated at 3 kHz to acquire a series of 4096 sequential flow field images both for reactive and non-reactive cases, sufficient to follow the large-scale spatial and temporal evolution of flame and flow dynamics. The POD analysis allows identification of vortical structures, created by the bluff body, and in the shear layers surrounding the stabilization point. In addition, the analysis reveals that dominant structures are a strong function of the mixture stratification in the flow field. The dominant energetic modes of reactive and non-reactive flows are very different, as the expansion of gases and the high temperatures alter the unstable modes and their survival in the flow.
Convective Heat Transfer From a Free Rotating Disk Subjected to a Forced Crossflow
Authors: Helcig Christian , aus der Wiesche Stefan
Published: September 2014

The understanding of the heat transfer and flow field behavior of rotating systems is essential from a fundamental point of view and for turbo machinery design. The majority of the publications considers enclosed rotating disk systems and only little is known about the convective heat transfer of free rotating disk systems in a forced flow. In this paper, a free rotating disk system, with particular look on the angle of incidence was investigated. The convective heat transfer from a rotating disk depends at least on three characteristic variables, namely the crossflow, rotational Reynolds numbers and the angle of incidence which are determining the mean Nusselt number. A clear study of the symmetry behavior of the flow field was conducted based on the measurement of the convective heat transfer coefficients. The angle of incidence was scanned with high angular resolution over the entire range between the both extreme cases of a perpendicular disk and a disk in a parallel forced flow. A large number of crossflow and rotational Reynolds numbers were covered by the experiments, too. Based on the experimental and theoretical results, a discussion of the different phenomena and heat transfer regimes is given in this paper.
A Comparative Study of Combined Heat and Power Systems for a Typical Food Industry Application
Authors: Saidi Karim , Orth Ulrich , Boje Sven , Frekers Christian
Published: September 2014

In the food industry, there is typically a requirement for electric power, process steam as well as cooling capability. Based on actual requirements of a specific site, a study was performed to define two different Combined Heat and Power (CHP) options and to compare them over a one year period regarding the extent to which they satisfy the operator’s needs.

CHP is defined as the sequential generation of two different forms of usable energy from a single fuel source. It is mechanical energy and thermal energy. The mechanical energy may be used either to drive a generator to produce electricity, or to drive rotating equipment such as a compressor. Thermal energy can be used either directly for process applications or indirectly to produce steam, hot water (district heating), or chilled water for cooling purposes. Combined Heat and Power technologies are proven, reliable and cost-effective. MAN can offer different CHP concepts adapted to specific customer requirements.

This paper presents the results of a comparative study based on the typical requirements of the food industry. The CHP system has to cover the demand for power, saturated steam at two pressure levels, and cooling. Two different CHP options were studied and compared regarding technical and economic considerations.

The first system proposed is based on a MAN’s gas turbine (model: THM1304-10N) in the 10 MW class, a Waste Heat Recovery Unit for steam production and one Absorption Chiller (ammonia/water) for cooling process. A share of the steam produced is used for driving the chiller.

The second system includes a combined cycle with MAN’s new MGT6100 gas turbine in the 6 MW class. A Waste Heat Recovery Unit and a back pressure steam turbine with two extractions at two intermediate pressure levels are used. A part of the saturated steam at the outlet of the steam turbine drives the absorption chiller and the remainder is used for the third steam process.

For both options, a supplementary firing is also considered. A technical and economical comparison between the two solutions is provided in order to show the advantages and the disadvantages of each system with regard to the requirements of the specified application.
Evolution of Swirl Boundary Layer and Wall Stall at Part Load: A Generic Experiment
Authors: Stapp Dennis , Pelz Peter F.
Published: September 2014

The influence of Reynolds number, roughness and turbulence on the onset of wall stall is up to now not sufficiently understood. To shed some light onto the interdependency of near wall flow with growing swirl component, the simplest “machine” is tested. The apparatus we examine is a circular pipe at rest followed by a rotating co-axial pipe segment. In the sense of a generic experiment this machine represents a very basic model of the inlet of an axial machine. Due to the wall shear stress a swirl boundary layer is formed in the rotating pipe segment, interacting with the axial boundary layer. The evolution of the swirl velocity profile with increasing axial distance from the rotating pipe inlet is measured for various Reynolds numbers, flow numbers and degrees of turbulence by means of Laser Doppler Anemometry. We observe a self-similarity in the swirl velocity profile, for subcritical flow number and develop a scaling law for the velocity distribution in the transition section of a rotating pipe. At critical flow number the boundary layer is separating, resulting in a ring vortex at the inlet of the rotating pipe. Our work fills the gap of previous experimental works, with respect to high Reynolds numbers and low flow numbers. The parameter field we examine is most relevant for turbomachinery application and wall stall. In addition our boundary layer resolution is sufficient to resolve the swirl boundary layer thickness. Only this high resolution enables us to generalize the experimental findings by means of a similarity distribution of the velocity profile within the swirl boundary layer.
Measurement of Heat Transfer Coefficients in Gaseous Flow: First Test of a Recent Sensor Concept for Stationary and Oscillating Flow
Authors: Eschmann Gunter , Kuntze Alexander , Uffrecht Wieland , Odenbach Stefan
Published: September 2014

Heat transfer coefficients are very important for the design of the various flow paths found in turbomachinery. An accurate measurement of heat transfer is difficult considering gaseous flow in combination with good thermal conductivity of the boundaries along the flow path. The majority of the measurement methods applied frequently have at least one of the following problems. The measurement setup as for instance a heat flux sensor is a thermal barrier or introduces, for measurement reasons, a lot of heat into the object of interest. In both cases the main error results from the modification of the system, which is critical for the investigation of any sensitive flow condition. Furthermore, insufficient fluid reference temperature and/or heat flux with changing sign corrupts any attempt to calculate reasonably heat transfer coefficients.

Recent research and development activities are often focused on non-stationary effects as for instance caused by blade passing and combustor noise or any other source of transient or non-stationary flow in turbomachinery. This is not limited to the main gas path. A lot of attention is also paid to these effects for the internal air system for example the intensification of heat transfer by usage of non-stationary effects is very interesting for efficient cooling along the hot gas path. Therefore, the measurement of heat transfer coefficients becomes even more important for transient/non-stationary flow conditions.

This contribution presents a new test rig and an experimental investigation of local heat transfer coefficients in oscillating and superposed stationary and oscillating gaseous flow with metallic boundaries. The measurements presented are based on a novel measurement/sensor concept tested first time in non-stationary flow. The measurement setup features miniaturized sensor dimensions, low energy consumption, low backlash of the measurement on the flow and improved resolution compared to other concepts for the conditions addressed.

Furthermore, measurements of the radial distribution of the heat transfer coefficient on a flat plate in front of an oscillating and superposed stationary and oscillating free jet are presented. For the continuous jet, the air flows through a cavity and a nozzle for stationary conditions. The oscillating or so called synthetic jet is a zero mass flow jet through a nozzle generated by a pulsating diaphragm. Additionally, the superposition of continuous and synthetic jet results in the pulsed jet. All jets described are examined in an orthogonal impingement setup for Reynolds between 1000 and 9000. The nozzle-to-plate distances are varied between 0.5 and 7 nozzle diameters covering a flow region from stagnation point up to five nozzle diameters off the jet axis. Additionally a comparison with correlations found in literature as well as a discussion of the results is included.
High Temperature Thermal Barrier Coating Made by the Solution Precursor Plasma Spray Process
Authors: Jordan Eric H. , Gell Maurice , Jiang Chen , Wang Jiwen , Nair Balakrishnan
Published: September 2014

Yttrium aluminum garnet (YAG) is well-known to have desirable physical and mechanical properties, including high temperature phase stability, relatively low thermal conductivity, high hardness, and low density. This combination of properties makes it desirable to pursue YAG as an advanced TBC. Unfortunately, thermal cycle durability is poor because it has higher thermal expansion mismatch stresses compared to conventional 7YSZ. Recently, 250 micron thick YAG TBCs have been produced by the solution precursor plasma spray (SPPS) process. These SPPS YAG TBCs exhibit good thermal cycling properties compared to APS 7YSZ because of the presence of stress-relieving, through-thickness cracks. The SPPS YAG TBCs also exhibit low thermal conductivity, low density and high hardness.
Modeling the GTE Under Its Dynamic Heating Conditions
Authors: Yepifanov Sergiy V. , Zelenskyi Roman L. , Loboda Igor
Published: September 2014

A modern gas turbine engine (GTE) is a complex non-linear dynamic system with the mutual effect of gas-dynamic and thermal processes in its components. The engine development requires the precise real-time simulation of all main operating modes.

One of the most complex operating modes for modeling is “cold stabilization”, which is the rotors acceleration without completely heated up the turbine elements. The dynamic heating problem is a topical practical issue. Solving the problem requires coordinating a gas-path model with heat and stress models, which is also a significant scientific problem.

The phenomenon of interest is the radial clearances change during engines operation and its influence on engines static and dynamic performances. To consider the clearance change, it is necessary to synthesize the quick proceeding stress-state models (QPSSM) of a rotor and a casing for the initial temperature and dynamic heating.

The unique feature of the QPSSM of GTEs is separate equation sets, which allow the heat exchange between structure elements and the gas (air) and the displacements of the turbine rotor and the casing. This ability appears as a result of determining the effect of each factor on different structural elements of the engine. The presented method significantly simplifies the model identification, which can be performed based on a precise calculation of the unsteady temperature fields of the structural elements and the variation of the radial clearance.

Thus, the present paper addresses a new method to model the engine dynamics considering its heating up. The method is based on the integration of three models: the gas-path dynamics model, the clearance dynamics model and the model of the clearance effect on the efficiency. The paper also comprises the program implementation of the models. The method was tested by applying to a particular turbofan engine.
Forward and Backward Mode Excitation of Flexible Rotor Supported by Tilting Pad Bearings: Numerical and Experimental Investigation
Authors: Wang Weimin , Li Qihang , Gao Jinji , Dimond Timothy , Allaire Paul
Published: September 2014

Understanding rotor modal excitations is crucial for high performance centrifugal compressors and other rotating machines. Assuring low vibration levels of such machines at operating conditions before delivery is important both for original equipment manufacturers (OEMs) and end users. In this paper, transient simulations of a full scale test rig rotor subject to sine sweep excitations are performed to investigate the forward and backward rotor whirling response. The applied sine sweep excitations are circular forward, circular backward, and elliptical forward, respectively. The effects of excitation force amplitude are also investigated to determine the minimum force required to accurately identify the rotor system modal parameters.

The transient simulation results are then used to investigate a forward and backward mode system identification method for rotating machinery stability based on sine-sweep excitations. Both simulations and experimental testing on a full size rotor with an electromagnetic actuator were performed to verify and validate the method. The traditional Multiple Input Multiple Output (MIMO) Frequency Response Function (FRF) is transformed into a directional Frequency Response Function (dFRF) form. This transformation recasts the real number field into complex number field via a transformation matrix. This transformation separates the MIMO FRFs into forward and backward components, which improves the accuracy of the identified results. This method is used to identify the first forward bending modal parameters to estimate rotor stability. The rational polynomial method is used to fit and identify both the dFRFs. Excellent correlation was obtained between simulation results and the identification experiments. The results of this paper provide new insights for avoidance of rotor instability in centrifugal compressors.
Strain and Phase Mapping of Ceramic Matrix Composites and Protective Coatings
Authors: Thornton John , Dale Darren , Zonneveldt Matthew , Wood Chris , Almer Jon
Published: September 2014

Coatings are frequently required to provide oxidation protection for high temperature materials. Silicon carbide (SiC) coatings have been used to protect carbon-carbon composites on leading edges and zirconia coatings are used as thermal barriers on gas turbine aerofoils. The effectiveness and durability of these coatings is dependent on the residual strains created in these coatings during their formation or deposition and also during service. Tensile strains in the plane of the coating can lead to through thickness cracks that expose the substrate, while compressive strains can cause the coating to delaminate. This paper presents strain measurements of these high temperature material systems obtained with high energy X-ray diffraction. The diffraction also provided useful information on phase, crystallite size and texture as a function of depth. Tensile strains were found in the SiC coatings, and compressive strains were found in the zirconia coatings. Both these strains were parallel to their coatings’ surfaces. The differences in thermal expansion coefficients between the coatings and their substrates can account for both the compressive strain in the zirconia and the tensile strain in the SiC.
Stall Margin Improvement in Three-Stage Low Pressure Compressor by Use of Slot Type Casing Treatments
Authors: Gelmedov F. Sh. , Mileshin V. I. , Kozhemyako P. G. , Orekhov I. K.
Published: September 2014

The Central Institute of Aviation Motors (CIAM) has been engaged in the development of methods and technologies extending the range of stable operation for GTE axial compressors on the basis of systematic experimental and theoretical investigations of processes before and after flow disturbances for many years. The general sources of experimental data were stage models of various types. They are first supersonic stages with 0.3–0.45 hub ratio and subsonic stages with 0.75 hub ratio, as well as high-loaded stages with low aspect ratio.

As a result of these investigations, a structural configuration of the casing treatment (CT) was designed to prevent local flow separation on flow passage surfaces of a compressor stage.

The CT structure includes the following components:

- Slotted spacer installed above the inlet rotor section;

- Attached ring covering the slotted spacer.

An approximate procedure for selecting the optimal CT geometric parameters and their interrelations was developed for CT designing. Using this procedure, special investigations were completed and detected the CT effects on operation of the axial compressor.

These effects are:

- Effect of air back and forward leakage through slots between the blade tips and the inlet rotor section;

- Effect of stall deceleration in the stage flow passage;

- Pulsation damping at the stage tip when flowing around the CT slotted spacer.

Based on this methodology, CT prototypes were developed and tested in various single-stage and multi-stage compressors. As an example of CT advantages, we can show test results for a three-stage low-pressure compressor (LPC) designed by CIAM.

The LPC in take-off conditions provides the following design parameters:

- Pressure ratio: 3.4;

- Corrected tip speed: 418 m/s;

- Stall margin: 20% … 21% within 0.5–1.0 corrected RPM.

According to experimental investigations, the use of CT results in a considerable increase in LPC stall margin without losses in other design parameters. Additionally, the results of 3D viscous flow calculation are shown for compressor performance analysis.
Operational Modal Analysis of Torsional Modes in Rotating Machinery
Authors: Carden Eoin Peter , Lindblad Mattias
Published: September 2014

Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses in order to identify the mode shape, natural frequency and damping factor of each mode. Applying a controlled and measured excitation to a rotor train when in operation is logistically difficult and especially challenging in the field. Operational modal analysis (OMA) identifies the modal parameters of a system from measurement of response due to some (unknown) excitation. OMA has proven successful over the past several decades on non-rotating structures but has relatively rarely been applied to rotating machinery. Case studies are presented demonstrating the use of OMA in identifying torsional modes on an electric motor driven reciprocating compressor, on a diesel engine driven fire water pump and on a marine propulsion system. In contrast to lateral modes, torsional modes of rotor trains are typically not speed dependent. However phenomena exist whereby the torsional modes may be different at stand still, off-load and at different loads. The case studies provide examples of such phenomena and also of significant differences between predicted and measured behaviour which suggests that improvements in industrial practice would be beneficial. Such improvements should be based on reconciliation of measured and predicted behaviour and OMA offers a valuable tool to facilitate this. OMA provides a significant benefit in investigating and understanding torsional behaviour in operation.
Numerical Investigation of Turbulence Modelling on Condensing Steam Flows in Turbine Cascade
Authors: Patel Yogini , Turunen-Saaresti Teemu , Patel Giteshkumar , Grönman Aki
Published: September 2014

Understanding the condensation process at the low-pressure (LP) turbine is important because condensation introduces extra losses, and erosion caused by the droplets wear turbine blades. The paper presents an investigation of the turbulence modelling on the non-equilibrium homogeneous condensing steam flow in a stationary turbine cascade employing 2D compressible Navier-Stokes (NS) equations. The classical nucleation theory is utilized to model the condensation phenomena. The performance of various turbulence models (i.e., the Spalart-Allmaras, the k-ω, the k-ε, the RNG k-ε, the Realizable k-ε, and the SST k-ω) in condensing steam flows is discussed. The SST k-ω model is modified and implemented into a commercial computational fluid dynamics (CFD) code. Substantial improvements in the prediction accuracy are observed when compared with the original SST k-ω model. Overall, the modified model is in excellent agreement with the measurements in all studied test cases of the turbine cascade. The qualitative and quantitative analysis illustrates the importance of turbulence modeling in wet-steam flows.
Simulation of Thermal Fluid-Structure Interaction in Blade-Disc Configuration of an Aircraft Turbine Model
Authors: Lück Hannes , Schäfer Michael , Schiffer Heinz-Peter
Published: September 2014

This paper describes the impact of structural deformations on interstage cavity flow dynamics by adopting thermal fluid-structure interaction methods. These coupled numerical approaches solve the fluid-solid heat transfer in conjunction with the geometrical deformation due to mismatched centrifugal and thermal expansion of rotating and stationary turbine discs. Especially the changing clearances at the interstage labyrinth seal, at the rotor blade tips and at the rotor stator rim seals can be captured to calculate the correct flow physics at these locations. A manual explicit coupling approach in ANSYS is utilized that couples the CFX CHT solver with the FE solver Mechanical. The validation of a 3D sector model with experimental data shows improvements in predicting the metal temperature of the rotating walls but also disclose problems with the overheated stationary parts, mainly due to the utilization of steady state mixing planes. Additionally, a surrogate 2D model of the 3D model is introduced to compare the explicit coupling approach with an implicit approach exploiting the ANSYS MFX interface between the fluid and the solid domain. Thereby, the manual coupling approach reveals to be much more efficient for the examined thermal fluid-structure interaction.
Axial Inclination of the Bristle Pack, a New Design Parameter of Brush Seals for Improved Operational Behavior in Steam Turbines
Authors: Schwarz H. , Friedrichs J. , Flegler J.
Published: September 2014

Within this paper, the axial inclination of the bristle pack as a new design parameter for brush seals for use in a steam turbine and other rotating equipment is discussed. It is widely known that the behavior of brush seals can be influenced by important main design parameters of the bristle pack such as, but not limited to, the bristle thickness, the lay angle or the bristle length. Furthermore, the variation of the front and back plate results in different seal characteristics [1]. Each one of these parameters also has an influence on bristle damping, the blow down capability and thus the leakage flow. In addition, under changing and transient operating conditions, the radial adaptivity, which is essential for accommodating shaft deflection, is also a very important property. For a comprehensive seal design, the wear characteristic and deterioration effects have to be considered beside the above mentioned properties. At the Technical University of Braunschweig, brush seals are experimentally investigated with above focus on different test rigs. These rigs allow a detailed sealing performance investigation including live bristle pack observations and blow down measurement using cold air as well as brush seal investigations using live steam conditions up to 50bars and 450°C and a rotating shaft with representative rotational velocity. The paper shows and discusses experimental results of different axial inclinations of the bristle pack, while testing with constant front and back plate designs. The influences on the blow down, the axial behavior of the bristle pack, the leakage flow and the bristle pack stiffness are shown. The new effect of a rotating blow down type of bristle oscillation is also shown and discussed and finally a classification of the seal behavior depending of the different axial inclination is given.
Reactor Network Analysis to Assess Fuel Composition Effects on NOx Emissions From a Recuperated Gas Turbine
Authors: Colorado Andrés , McDonell Vincent
Published: September 2014

This paper addresses the numerical prediction of NOx emissions from a micro turbine generator (MTG) using a chemical reactor network (CRN). In particular, the effect of fuel composition on NOx formation is analyzed. The numerical predictions are compared with available experimental results. The results obtained with the reactor network analysis (RNA) for the mixtures with heavier alkanes are in good agreement with the experimental results; however the methodology indicates that the prediction is sensitive to the selection of the reaction mechanism. Also, it was possible to predict measured trends for the effect of the dilution with CO2, but the slope of the trend differs from the experiments. The analysis of the results indicates that most of the NOx measured at the turbine exit for the conditions of this study is formed through the N2O route. This is the dominant pathway for this system, regardless of the fuel composition or the reaction mechanism used.
A Smooth Curvature-Defined Meanline Section Option for a General Turbomachinery Geometry Generator
Authors: Nemnem Ahmed F. , Turner Mark G. , Siddappaji Kiran , Galbraith Marshall
Published: September 2014

The blade geometry design process is integral to the development and advancement of compressors and turbines in gas turbines or aeroengines. An airfoil section design feature has been added to a previously developed open source parametric 3D blade design tool. The second derivative of the mean-line (related to the curvature) is controlled using B-splines to create the airfoils. This is analytically integrated twice to obtain the mean-line. A smooth thickness distribution is then added to the airfoil with two options either the Wennerstrom distribution or a quartic B-spline thickness distribution. B-splines have also been implemented to achieve customized airfoil leading and trailing edges. Geometry for a turbine, compressor, and transonic fan are presented along with a demonstration of the importance of airfoil smoothness.
Towards a Highly Efficient Small Scale Turboshaft Engine: Part I — Engine Concept and Compressor Design
Authors: Kröger G. , Siller U. , Moser T. , Hediger S.
Published: September 2014

Today’s UAV helicopter industry faces a lack of highly reliable, SFC optimized turboshaft engines in the 40kW to 100kW class, resulting in a significant drawback for the overall flight envelope and the system availability of these aircraft. This paper describes the design process for a turboshaft engine with a shaft power output of about 80kW. A thermodynamic cycle model is derived from the flight envelope of the Swiss UAV NEO S-350 helicopter drone. Different compressor configurations are analysed and discussed with regard to the power output and SFC of the engine as well as to manufactural constraints. Combining a high flow density with a high isentropic efficiency and pressure ratio, a three stage compressor configuration was selected. The design is based on two axial front stages with a total pressure ratio of 1.55 and 1.45, respectively, and a diagonal last stage with a total pressure ratio of 2.8. Finally, the aero-mechanical design and optimization process of the compressor is depicted and the manufactural process is described. The engine prototype is expected to be tested the first time in 2014.
Balancing Configuration and Refinement in the Design of Two-Spool Multistage Compression Systems
Authors: Jarrett Jerome P. , Ghisu Tiziano
Published: September 2014

Despite many advances in both optimization methods and computational fluid dynamics, the timely automatic selection and refinement, via physics-based and empirical methods, of “optimal” configurations of compression systems remains challenging. This is due, in part, to the large number of design parameters (with associated high computational cost) operating over wide ranges that can be non-smooth, if not discontinuous (to which many optimization algorithms, developed for smooth problems, are ill-suited). It is further complicated by the phasic nature of turbomachinery design and the associated need to balance the amount of time and computational resource devoted to selecting the most promising configurations with that expended in their refinement. This paper compares a number of combinations of a multi-fidelity approach for configuration selection with a high-fidelity method for design refinement. The system is tested on the aerodynamic design of a complete two-spool core compression system for a generic high bypass ratio turbofan. The resulting designs are obliged to meet familiar constraints for overall design point pressure rise and surge margin together with a number of mechanical constraints including maximum shaft speeds. Through the configuration phase, the number of stages and the duty split between the spools are permitted to change. It is shown that the performance of the design refinement phase is only a weak function of the preceding configuration phase provided that the latter is well into diminishing returns with respect to approaching a converged solution. It is hence shown possible to obtain equally good designs in around half the computational run-time by exploiting this weak dependence by effectively decoupling the configuration and refinement phases and starting the latter before the former has apparently finished. It is also shown that if either configuration or refinement is allowed to dominate the design process, inferior designs result. The best designs are associated with between half and three-quarters of the design effort being devoted to configuration selection.
An Intercooled Recuperative Aero Engine for Regional Jets
Authors: Kormann Maximilian , Schaber Reinhold
Published: September 2014

Flying requires a high power density in the propulsion system. Currently only turbofan engines can provide the required power at a low system mass. To counter a potential negative impact of aircraft emissions on global climate, the agreement Flightpath 50, created by European research establishments and industries, has set the target to reduce overall CO2 emissions from the year 2000 to 2050 by 75 %. In contrast, the air traffic volume has been growing constantly since the 1980s and will be growing further. Hence the fuel burn of aero engines has to be reduced to reach the Flightpath 50 target. High-end component technology has nearly exhausted full potential in the improvement of conventional turbofan engines. Further significant progress can only be achieved by new engine concepts. The geared turbofan has proven the feasibility of this approach. The introduction of a gear allows the IPC and LPT to run at more suitable speeds with the consequence of a lower stage count compared to conventional turbofans. According to Pratt&Whitney this will reduce the fuel burn by ”15–16% versus today’s best engines” [1]. As a next step towards Flightpath 50 MTU Aero Engines AG envisioned the Intercooled Recuperative Aero Engine (IRA) for long-haul application. This concept increases the thermodynamic efficiency of the core engine by utilizing two heat exchangers: an intercooler reduces the work which is necessary for the compression. A recuperator transfers heat of the exhaust gas to the compressed gas entering the burner. In long-haul aircraft the increased engine mass due to the heat exchangers has a lower influence on the fuel burn. To broaden the research, this paper investigates the application of the IRA for regional jets. An extensive predesign parameter study was performed to find the optimal IRA configuration for regional jets. Not only has fuel consumption been taken into consideration, additionally the influence of the increased weight of the IRA has been included. In optimum, the fuel burn on a regional mission according to this study could be reduced in the order of 1–2%. However, the overall pressure ratio is much lower compared to modern turbofan engines, which leads to relatively low NOx emissions. It allows the introduction of Lean Premixed Prevaporized (LPP) burner technology, promising an additional significant reduction in NOx emissions compared to modern turbofan engines. Compared to a longhaul application the heat exchangers are not a scaled version but the result of a cycle optimization considering the available space. The paper also gives an outlook for an innovative three dimensional heat exchanger. The novel heat exchanger arrangement promises a better integration into the annulus at turbine exit and less aerodynamical pressure losses due to 3D-effects.
Structural Analysis of a Small H-Darrieus Wind Turbine Using Beam Models: Development and Assessment
Authors: Bianchini Alessandro , Cangioli Francesco , Papini Susanna , Rindi Andrea , Carnevale Ennio Antonio , Ferrari Lorenzo
Published: September 2014

In the present wind energy research, Darrieus-type vertical-axis wind turbines are increasingly appreciated, especially in small installations. In particular, H-shaped turbines can provide attractive spaces for novel design solutions, aimed at reducing the visual impact of the rotors and then at improving their degree of integration with several installation contexts (e.g. a built environment); moreover, novel small rotors are thought to be able in the near future to make large use also of new and cheaper materials (e.g. plastic or light alloys) which could notably reduce the final cost of the produced energy. As a consequence, the structural analysis of the rotors becomes more and more important: a continuous check between the design solutions needed to maximize the aerodynamic performance of the blades and the structural constraints must be provided. In addition, the requirements of international standards for certification encourage the development of proper numerical tools, possibly with low computational costs for the manufacturers.

In this study, the structural analysis of a novel three-helix-bladed Darrieus turbine is presented; the turbine is a real industrial machine almost entirely produced with plastic with a new complex aesthetic design. In detail, a structural modeling based on beam elements has been developed and assessed in comparison to more complex models, as it was thought to provide a notable reduction of the computational cost of the simulations with an acceptable decrease of the accuracy.

Moreover, the 1D structural model was exploited to verify the capabilities of a novel software, able to verify the dynamic response of the wind turbine in real functioning, i.e. with mechanical loads and interactions with the wind flow.

Benefits and drawbacks of the proposed modeling approach are finally discussed by analyzing both the calculation time and the accuracy of the simulations.