bluuebunny/crossref_metadata_2025 huggingface dataset:
Static Characteristics of Gas Foil Thrust Bearing Based on Gas Rarefaction Model
Authors: Yan Jiajia , Zhang Guanghui , Liu Zhansheng , Yang Fan
Published: August 2015

A modified Reynolds equation for bump type gas foil thrust bearing was established with consideration of the gas rarefaction coefficient. Under rarefied gas lubrication, the Knudsen number which was affected by the film thickness and pressure was introduced to the Reynolds equation. The coupled modified Reynolds and lubricating film thickness equations were solved using Newton-Raphson Iterative Method and Finite Difference Method. By calculating the load capacity for increasing rotor speeds, the lift-off speed under certain static load was obtained. Parametric studies for a series of structural parameters and assembled clearances were carried out for bearing optimization design. The results indicate that with gas rarefaction effect, the axial load capacity would be decreased, and the lift-off speed would be improved. The rarefied gas has a more remarkable impact under a lower rotating speed and a smaller foil compliance coefficient. When the assembled clearance of the thrust bearing rotor system lies in a small value, the lift-off speed increases dramatically as the assembled clearance decreases further. Therefore, the axial clearance should be controlled carefully in assembling the foil thrust bearing. It’s worth noting that the linear uniform bump foil stiffness model is not exact for large foil compliance ∼0.5, especially for lift-off speed analysis, due to ignoring the interaction between bumps and bending stiffness of the foil.
Aerodynamic Optimization of the Gas Outlet Casing of the Axial Turbine Stage in a Turbocharger With Experimental Validation
Authors: So K. K. , Sofia A. , Fischer M. , Phillipsen B. A.
Published: August 2015

This paper presents a design process for optimizing the aerodynamic performance of the gas outlet casing on single-stage turbines with high specific flow capacity.

A full-annulus flange-to-flange (inlet-to-outlet) steady-state CFD model of the turbine stage which takes into account the interaction between the rotor and the gas outlet casing and ensures an accurate inflow condition for the latter, is used to predict the turbine stage performance. A meta-model based optimization for the gas outlet casing is then performed and a simplified CFD model is used for sampling and optimization. The geometry of the gas outlet casing is fully parameterized to enable the simultaneous variation of diffuser and collector geometry and an ordinal regression optimization algorithm is adopted for the objectives of maximizing the static pressure recovery of the gas outlet casing and ensuring the design robustness.

Extensive test measurement of the turbine stage with its baseline and optimized gas outlet casing geometries on a full scale turbocharger test bench validates the CFD results and confirms the significant improvement of the exhaust casing pressure recovery, which leads to an improvement of turbine efficiency between 1.3 and 2.4 % points over the relevant considered operating range. Traverse measurement using five-hole probes and the flow field predicted by CFD are in good agreement. Evaluation of the CFD results highlights a significant loss in the collector despite a high pressure recovery at the end of the diffuser for the baseline gas outlet casing. For the optimized geometry, the more uniform flow at the diffuser outlet results in greatly reduced loss in the 90° turn in the casing, and thus higher pressure recovery and turbine efficiency.
Heat Transfer and Pressure Drop Measurements on Rotating Matrix Cooling Geometries for Airfoil Trailing Edges
Authors: Carcasci Carlo , Facchini Bruno , Pievaroli Marco , Tarchi Lorenzo , Ceccherini Alberto , Innocenti Luca
Published: August 2015

In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated.

Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different orientations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trailing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development.

Both the investigated geometries have a cross angle of 45deg between ribs and different values of sub-channels and rib thickness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg.

Matrix models have been axially divided in 5 aluminum elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal temperature was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test.

Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Res from 2000 to 10000 and the sub-channel Rotation number Ros from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions.

A post-processing procedure, which takes into account the temperature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.
Lumped Capacitance and 3D CFD Conjugate Heat Transfer Modelling of an Automotive Turbocharger
Authors: Burke R. , Copeland C. , Duda T. , Reyes-Belmonte M. A.
Published: August 2015

One dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process.

Initially a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre and post compression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency whereas at high speed αA had a similar influence to TIT. However, modelling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%.

Three dimensional CFD analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA=0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the pre-compression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.
The Benefits of an Inverted Brayton Bottoming Cycle as an Alternative to Turbo-Compounding
Authors: Copeland Colin D. , Chen Zhihang
Published: August 2015

The exhaust gas from an internal combustion engine contains approximately 30% of the thermal energy of combustion. Waste heat recovery systems aim to reclaim a proportion of this energy in a bottoming thermodynamic cycle to raise the overall system thermal efficiency. The inverted Brayton cycle considered as a potential exhaust-gas heat-recovery system is a little-studied approach, especially when applied to small automotive power-plants. Hence, a model of an air-standard, irreversible Otto-cycle and the inverted Brayton cycle using finite-time thermodynamics (FTT) is presented to study heat recovery applied to an automotive internal combustion engine. The other two alternatives power cycles, the pressurized Brayton cycle and the turbo-compounding system, are compared with the inverted Brayton cycle (IBC) to specify the strengths and weaknesses of three alternative cycles. In the current paper, an irreversible Otto-cycle model with an array of losses is used as a base for the bottoming cycle. The deviation of the turbomachinery from the idealized behavior is described by the isentropic component efficiencies. The performance of the system as defined as the specific power output and thermal efficiency is considered using parametric studies. The results show that the performance of the inverted Brayton cycle can be positively affected by five critical parameters — the number of compression stages, the cycle inlet temperature and pressure, the isentropic efficiency of the turbomachinery and the effectiveness of the heat exchanger. There exists an optimum pressure ratio across the IBC turbine that delivers the maximum specific power. In the view of the specific power, installing a single-stage of the inverted Brayton cycle appears to be the best balance between performance and complexity. Three alternative cycles are compared in terms of the thermal efficiency. The results indicate that the pressurized and inverted Brayton cycles can improve the performance of the turbocharged engine only when the turbomachinery efficiencies are higher than a value which changes with the operating condition. High performance of the IBC turbomachinery is required to ensure that the turbocharged engine with the inverted Brayton cycle is superior to that with turbo-compounding system.
The Influence of Tip Clearance on Supercritical CO2 Centrifugal Compressor Performance
Authors: Zhao Hang , Deng Qinghua , Zhang Hanzhen , Feng Zhenping
Published: August 2015

The supercritical CO2 (SCO2) compressor is the key component of the SCO2 Brayton cycle. It is considered as one of the most promising power conversion systems, because the compressor could consume small compression work as operating condition near the critical point. In this paper, a researched SCO2 compressor was designed to operate with slightly above the vapor-liquid critical point of CO2. The flow characteristics were investigated by NUMECA FINE/Turbo, coupled with the thermophysical properties of CO2 in REFPROP database. Particular attention was paid on the blade tip clearance flow characteristics. The formation and development mechanism of the blade tip low pressure regions and the parameters distributional difference were studied. Then, the effects of different blade tip clearance types on the low pressure regions of the blade leading edge tip and the aerodynamic performance of SCO2 compressor stage were compared and discussed.

The combined effects of the injecting action, the blade leading edge tip shedding vortex, and the flow acceleration can lead the fluid thermodynamic state to enter the low pressure and low temperature regions at the leading edge of both the main blade and splitter blade tip. Especially, the condensation maybe exist at sharp corner of the blade tip leading edge. However, the tip clearance leakage vortex can significantly inhibit and weaken the low pressure regions. With the increase of tip clearance, the distribution and development tendency of the static pressure and temperature on the main blade leading edge tip are similar, but there is a significant influence for the splitter blades tip. Furthermore, because the tip clearance increases, the SCO2 compressor stage pressure ratio and isentropic efficiency have degraded in whole operating range, but the stable operation range is expanded. Therefore, the above comprehensive factors should be considered during the design process in order to select the suitable tip clearance shape.
A Quasi-First Order Optimization Method and its Demonstration on the Optimization of a U-Bend
Authors: Akin M. Bugra , Sanz Wolfgang
Published: August 2015

Optimal shape design is widely used today to improve a variety of designs. It is a challenging task and several methods have been developed. These methods are generally classified by the order of derivatives used. They are zero, first and second order methods, which, as their names imply, use only the function values, first and second order derivatives, respectively. There are two common approaches to first order methods. These are the finite difference method and the adjoint method. The finite difference method requires an additional CFD calculation for each parameter, which quickly becomes computationally very expensive as the number of parameters rise. The adjoint method provides a computationally efficient alternative in such cases. But the computational cost of the adjoint method also becomes expensive if additional constraints are introduced or when multi-objective optimizations are considered.

This paper presents a novel optimization strategy which can be classified as a quasi-gradient based optimization method. As with the finite differences method an additional CFD calculation is performed for each parameter. But in order to save computational time the simulations are not performed to full convergence so that the derivatives are not calculated accurately. The only information that can be obtained in this way is whether the chosen contour manipulation leads to an improvement. A line search method is introduced that can find an optimum using this incomplete gradient information. The optimization method is demonstrated by the quasi-3d optimization of a U-bend.
Automated Calibration of Compressor Loss and Deviation Correlations
Authors: Schnoes Markus , Nicke Eberhard
Published: August 2015

Throughout preliminary design of multistage axial compressors performance prediction is based on fast 2D throughflow codes incorporating models for loss, deviation and secondary flow effects. To achieve high solution quality these models have to be calibrated on experimental or simulation data. Particularly 2D cascade loss and deviation correlations are of major importance. Correlations available in literature are mostly based on data from early cascade wind tunnel tests of NACA-65 and DCA profile families. In general, calibrations for state-of-the-art airfoil shapes are not published.

This paper describes a methodology to re-calibrate parameters of well-known empirical loss and deviation correlations to CFD simulations of compressor cascades. Correlations describing choke incidence, on- and off-design loss and deviation are presented, resolving dependencies on inlet flow angle, Mach number, Reynolds number and MVDR. Based on a set of loss and deviation polars, nonlinear least-squares problems are solved to determine the empirical parameters. By including shock losses and choking incidence, the model is suited for subsonic as well as supersonic inlet conditions.

Results of the calibration process are shown for two state-of-the-art compressor cascades. The overall model is evaluated on a sub- and a transonic compressor as well as on a transonic fan comparing throughflow results with 3D CFD and experimental data. A high level of automation makes the methodology applicable to arbitrary profile families or in combination with programs for parametric airfoil design.
Progress in the Development of Low Drift Nickel Based Thermocouples for High Temperature Applications
Authors: Scervini Michele
Published: August 2015

Recent progresses on the new Nickel based thermocouples for high temperature applications developed at the Department of Materials Science and Metallurgy of the University of Cambridge are described in this paper. Isothermal drift at temperatures above 1000°C as a function of the thermocouple diameter has been studied for both conventional Nickel based thermocouples and the new Nickel based thermocouple. The new Nickel based thermocouple experiences a much reduced drift compared to conventional sensors. Tests in thermal cyclic conditions have been undertaken on conventional and new Nickel based thermocouples, showing a clear improvement for the new sensors at temperatures both higher and lower than 1000°C. The improvements achievable with the new Nickel based thermocouple in both isothermal and thermal cycling conditions suggest that the new sensor can be used at high temperatures, where current conventional sensors are not reliable, as well as at temperatures lower than 1000°C with improved performance compared to conventional sensors.
A Simplified Hybrid Approach to Dynamic Model a Real HRSG
Authors: Rossi Iacopo , Sorce Alessandro , Traverso Alberto , Pascucci Fabio
Published: August 2015

This paper proposes a dynamic simplified approach to model a Heat Recovery Steam Generator of a Gas Turbine Combined Cycle (GTCC) and its validation against field data. The adopted framework begins with some physical considerations on global HRSG structure, and then focuses on a specific application for a real plant, i.e. a 390 MW multi-shaft combined cycle based on the AEN94.3 A4 frame. Moreover the model embodies some parameters, which are easily derived from historical data to enhance the forecasting capabilities of the software, resulting in a hybrid model which covers a high range of working conditions. The whole model is designed to run in Excel/Visual Basic environment to allow for extended use by people who have limited experience in advanced modelling software. The model so created has been handled through a training process based on 10 days of experimental data, in order to create the basis for true system flexibility. Therefore, the feasibility of this approach has been verified using a Gas Turbine (GT) load profile accomplished in everyday working operations and validating the results against field data.
Advanced Turbine Preliminary Design Environment for the Automatic Generation of Secondary Air System Models
Authors: Villazon Jose Maria Rey , Wildow Toni , Benton Robert , Eydam Tobias , Kühhorn Arnold
Published: August 2015

The design and development process of an aero engine is a complex and time-consuming task that involves many disciplines and company departments with different objectives and requirements. Along the preliminary design phase, multiple concepts are assessed in order to select a competitive technology. The engine design process, which was traditionally subdivided into modular component tasks, is nowadays considered as a multi-disciplinary workflow. Having recognized the need for developing advanced turbine preliminary design tools, this work focuses on enhancing the integration of turbine design disciplines, improving the accuracy of models and speeding the time to generate models.

The proposed process facilitates an automated turbine Secondary Air System (SAS) and turbine discs concept definition. Furthermore, the process of CAD models and flow network models generation is accelerated via automation of the engineering workflow. This is accomplished through a novel Java based data model, where the design of turbine discs and SAS features is captured in a programmable framework.

In the application section, the preliminary design definition of a reference HP turbine subsystem is replicated using the newly developed common design environment. The automated workflow is then used to generate the corresponding CAD models, recognize the subsystem flow network, and generate the 1D flow network model. The results are then compared to the experimentally validated model of a reference engine. As conclusion, the automated workflow offers a quick and parametric model generation process, while providing a good level of fidelity for the preliminary design phase.
Wind Turbine Design Optimization Under Environmental Uncertainty
Authors: Caboni Marco , Campobasso M. Sergio , Minisci Edmondo
Published: August 2015

Wind turbine design optimization is typically performed considering a given wind distribution. However, turbines so designed often end up being used at sites characterized by different wind distributions, and this results in significant performance penalties. This paper presents a probabilistic integrated multidisciplinary approach to the design optimization of multi-megawatt wind turbines accounting for the stochastic variability of the mean wind speed. The presented technology is applied to the design of a 5 MW rotor to be used at sites of wind power class from 3 to 7, where the mean wind speed at 50 m above the ground ranges from 6.4 to 11.9 m/s. Assuming the mean wind speed to vary stochastically in such range, the rotor design is optimized by minimizing mean and standard deviation of the levelized cost of energy. Airfoil shapes, spanwise distributions of blade chord and twist, internal structural layup and rotor speed are optimized concurrently, subject to structural and aeroelastic constraints. The probabilistically designed turbine achieves a more favorable probabilistic performance than the initial baseline turbine. The presented probabilistic design framework is portable and modular in that any of its analysis modules can be replaced with counterparts of user-selected fidelity.
Thermodynamic Analysis and Process System Comparison of the Exhaust Gas Recirculated, Steam Injected and Humidified Micro Gas Turbine
Authors: Ali Usman , Palma Carolina Font , Hughes Kevin J. , Ingham Derek B. , Ma Lin , Pourkashanian Mohamed
Published: August 2015

Stringent environmental emission regulations and continuing efforts to reduce carbon dioxide (CO2) from the energy sector, in the context of global warming, have promoted interest to improve the efficiency of power generation systems whilst reducing emissions. Further, this has led to the development of innovative gas turbine systems which either result in higher electrical efficiency or the reduction of CO2 emissions. Micro gas turbines are one of the secure, economical and environmentally viable options for power and heat generation. Here, a Turbec T100 micro gas turbine (MGT) is simulated using Aspen HYSYS® V8.4 and validated through experimental data. Due to the consistency and robustness of the steady state model developed, it is further extended to three different innovative cycles: (i) an exhaust gas recirculated (EGR) cycle, in which part of the exhaust gas is dried and re-circulated to the MGT inlet; (ii) a steam injected (STIG) cycle, and (iii) a humid air turbine (HAT) cycle. The steam and hot water are generated through the exhaust of the recuperator for the STIG and HAT cycle, respectively. Further, the steam is directly injected into the recuperator for power augmentation, while for the HAT cycle; the compressed air is saturated with water in the humid tower before entering the recuperator. This study evaluates the impact of the EGR ratio, steam to air ratio, and water to air ratio on the performance and efficiency of the system. The comparative potential for each innovative cycle is assessed by thermodynamic properties estimation of process parameters through the models developed to better understand the behavior of each cycle. The thermodynamic assessment indicates that CO2 enrichment occurs for the three innovative cycles. Further, the results indicate that the electrical efficiency increases for the STIG and HAT cycle while it decreases for the EGR cycle. In conclusion, the innovative cycles indicates the possibilities to improve the system performance and efficiency.
Transient Flow Characteristics of Contra- and Co-Rotating Swirler Arrangements of an Industrial Combustor
Authors: Wu X. , Norster E. R. , Xie Gang
Published: August 2015

Many lean-burn combustors are prone to high levels of pressure oscillations resulting in early structural failure. These oscillations have their origins with the natural acoustic characteristics of the combustor flow/geometry and amplification and excitations factors associated with well-mixed flames. The coincidence of the frequency of these excitations with the mechanical vibration modes of the combustor may result in resonance and high cycle fatigue failure. Often with high levels of pressure oscillations the fuel system itself can become coupled driving the dynamics to higher levels. Thus detailed acoustic and mechanical vibration analysis of the combustor becomes important. This paper describes the numerically predicted transient flow characteristics of two configurations of DLN combustor double swirler in contra- and co-rotating arrangements with the sole difference being in the orientation of rotation of the inner nozzle airflow. Although much useful information has been obtained from the previous steady-state analysis, there remain many unresolved issues such as discrepancies of vortex breakdown and acoustic instabilities, which is also important for a final design selection. The transient analysis was performed for each configuration to compare flow instability and acoustic characteristics where the model includes the inlet air annulus, double swirler, main reaction zone and dilution duct. The studies indicate that there is a significant discrepancy in flow structures when the vortex breaks down between the two configurations. And there exists a strong interaction for the remaining swirl with the dilution jets, resulting in the hot core penetrating far downstream inside the transient duct in the co-rotating case. An FFT analysis indicates a significant discrepancy on main low acoustic frequencies and the magnitudes of oscillatory pressure.
On Turbulence Measurements and Analyses in a Two-Stage Two-Spool Turbine Rig
Authors: Bauinger Sabine , Behre Stephan , Lengani Davide , Guendogdu Yavuz , Heitmeir Franz , Goettlich Emil
Published: August 2015

Since the experiment in turbulence research is of very high importance for evaluating turbulence hypothesis, turbulence measurements were carried out in a two-stage two-spool transonic turbine test rig at the Institute for Thermal Turbomachinery and Machine Dynamics in Graz in which the two rotors are counter-rotating with two different rotational speeds. For the current measurement campaign, triple hot-wire probes, which represent a very new measurement technique in this test rig, were used and their results validated with a fast response aerodynamic pressure probe. Based on the data measured with this device, turbulence intensities may be determined using a method developed by Persico et al. [1]. If the classical ensemble averaging procedure with only one trigger is applied, the periodic fluctuations of the other rotor will artificially increase the stochastic fluctuations. Therefore, the two trigger signals of the two rotors require a special analysis method, which was established at Graz University of Technology by Lengani et al. The results from this method will be compared to the classical triple decomposition, which uses only one trigger signal. With this analysis tool, it is not only possible to evaluate unsteady signals triggered by one of the two rotors but also the unsteady interactions of the rotors can be determined and investigated.
Modelling of Crack Growth With Dwell Time for Aero Engine Spectra Loadings in a Ni-Based Superalloy
Authors: Storgärds Erik , Simonsson Kjell , Sjöström Sören , Gustafsson David , Månsson Tomas
Published: August 2015

Testing and simulation of aero engine spectra with dwell times are reported in this paper. The modelling concept used is built on LEFM and provides a history dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra, 1) cyclic loads, 2) combined sustained load and cyclic loads and 3) slow load ramps and cyclic loads, all for surface cracks at 550°C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.
Frequency Domain Predictions of Acoustic Wave Propagation and Losses in a Swirl Burner With Linearized Navier-Stokes Equations
Authors: Zahn Max , Schulze Moritz , Hirsch Christoph , Betz Michael , Sattelmayer Thomas
Published: August 2015

A low-cost, high-quality hybrid CFD/CAA-methodology is used to predict the acoustic properties of a swirl burner including its complex swirl flow conditions. The numerically determined burner transfer matrix is validated against experimental data. The results demonstrate the capability of this low-cost hybrid approach to predict the acoustic characteristics of combustor components with high geometrical complexity. Most importantly it captures the effect of mean flow quantities on the fluctuating field. This causes the loss of acoustic energy and thus constitutes sources of acoustic damping. In this regard, reliable data can be obtained to characterize complex acoustic components at relatively low computational cost. Therefore, experimental efforts can be reduced which are generally required to provide data e.g. to set up low-order network models.

The insight into the field of fluctuating quantities allows the analysis of linear acoustic damping phenomena. Essentially, in the context of isentropic conditions acoustic energy is lost due to the formation of vorticity disturbances. Source regions for vorticity disturbances are identified at flow separation edges and within the multiple shear layers of the complex swirl flow.
Experimental Results of the First Two Stages of an Advanced Transonic Core Compressor Under Isolated and Multi-Stage Conditions
Authors: Prahst Patricia S. , Kulkarni Sameer , Sohn Ki H.
Published: August 2015

NASA’s Environmentally Responsible Aviation (ERA) Program calls for investigation of the technology barriers associated with improved fuel efficiency for large gas turbine engines. Under ERA, the highly loaded core compressor technology program attempts to realize the fuel burn reduction goal by increasing overall pressure ratio of the compressor to increase thermal efficiency of the engine. Study engines with overall pressure ratio of 60 to 70 are now being investigated. This means that the high pressure compressor would have to almost double in pressure ratio while keeping a high level of efficiency.

NASA and GE teamed to address this challenge by testing the first two stages of an advanced GE compressor designed to meet the requirements of a very high pressure ratio core compressor. Previous test experience of a compressor which included these front two stages indicated a performance deficit relative to design intent. Therefore, the current rig was designed to run in 1-stage and 2-stage configurations in two separate tests to assess whether the bow shock of the second rotor interacting with the upstream stage contributed to the unpredicted performance deficit, or if the culprit was due to interaction of rotor 1 and stator 1. Thus, the goal was to fully understand the stage 1 performance under isolated and multi-stage conditions, and additionally to provide a detailed aerodynamic data set for CFD validation. Full use was made of steady and unsteady measurement methods to understand fluid dynamics loss source mechanisms due to rotor shock interaction and endwall losses.

This paper will present the description of the compressor test article and its measured performance and operability, for both the single stage and two stage configurations. We focus the paper on measurements at 97% corrected speed with design intent vane setting angles.
Design Improvement Survey for NOx Emissions Reduction of a Heavy-Duty Gas Turbine Partially Premixed Fuel Nozzle Operating With Natural Gas: Numerical Assessment
Authors: Innocenti Alessandro , Andreini Antonio , Facchini Bruno , Cerutti Matteo , Ceccherini Gianni , Riccio Giovanni
Published: August 2015

A numerical investigation of a low NOx partially premixed fuel nozzle for heavy-duty gas turbine applications is presented in this paper. Availability of results from a recent test campaign on the same fuel nozzle architecture allowed the exhaustive comparison study presented in this work.

At first, an assessment of the turbulent combustion model was carried out, with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. In particular, the Fluent partially premixed combustion model and a flamelet approach are used to simulate the flame. The laminar flamelet database is generated using the Flamelet Generated Manifold (FGM) chemistry reduction technique. Species and temperature are parameterized by mixture-fraction and progress variable. Comparisons with calculations with partially premixed model and the steady diffusion flamelet (SDF) database are made for the baseline configuration in order to discuss possible gains associated with the introduced dimension in the FGM database (reaction progress) which makes it possible to account for non-equilibrium effects. Numerical characterization of the baseline nozzle has been carried out in terms of NOx. Computed values for both the baseline and some alternative premixer designs have been then compared with experimental measurements on the reactive test rig at different operating conditions and different split ratios between main and pilot fuel. Numerical results allowed pointing out the fundamental NOx formation processes, both in terms of spatial distribution within the flame and in terms of different formation mechanisms. The obtained knowledge would allow further improvement of fuel nozzle design.
Estimation of the Rotordynamic Coefficients of a Compressor Mounted on Gas Bearings Using the Phase Diagram and the Unbalance Response
Authors: González Claudia Aide , Jáuregui Juan Carlos , De Santiago Oscar , Solórzano Víctor
Published: August 2015

This paper presents a novel method for identifying the dynamic parameters of a gas bearing, whose force coefficients are strong functions of frequency. The method is based on the analysis of the phase diagram with the model assuming a mass-damper-spring system with time-dependent force coefficients. Usually, it is necessary a controlled mechanism to find the transfer function, this condition limits the application of the method. On the other hand, estimation of the damping and stiffness parameters under real loading is very cumbersome and requires a special care on identifying the excitation forces. One of the main difficulties is the isolation of noise and those vibration signals with an unidentified source. In this work, the excitation force was taken from the unbalance loading of a rotor test. Therefore, there is no need for a special test rig. The dynamic parameters can be estimated analyzing data from the actual rotor mounted on the gas bearings. Identifying the parameters that cause gas bearing instabilities is a big challenge. The gas properties are very sensitive to temperature and pressure changes, and, as a consequence the bearing rotor-dynamic coefficients change drastically and the rotor behaves chaotically, which means that the dynamic parameters are nonlinear. In this research a methodology based on the phase diagram construction to identify nonlinear instabilities of gas bearings is presented. The results show the method capability to estimate the dynamic coefficients by the analysis of the energy variation.

Among nonparametric methods, the phase diagram or phase space is in use to identify nonlinearities in dynamic systems. The identification is conducted through the analysis of the energy variations. The energy variations can be represented as a three dimensional function E(x,v,t). In this way the phase diagram can be related to the frequency and the dynamic parameters of the system. According to Taken’s theorem, a dynamic system can be obtained by reconstructing the phase diagram. Then, using this method, the damping and stiffness coefficients are estimated.
Adjoint Sensitivity Analysis of Hydrodynamic Stability in a Gas Turbine Fuel Injector
Authors: Tammisola Outi , Juniper Matthew P.
Published: August 2015

Hydrodynamic oscillations in gas turbine fuel injectors help to mix the fuel and air but can also contribute to thermoacoustic instability. Small changes to some parts of a fuel injector greatly affect the frequency and amplitude of these oscillations. These regions can be identified efficiently with adjoint-based sensitivity analysis. This is a linear technique that identifies the region of the flow that causes the oscillation, the regions of the flow that are most sensitive to external forcing, and the regions of the flow that, when altered, have most influence on the oscillation. In this paper, we extend this to the flow from a gas turbine’s single stream radial swirler, which has been extensively studied experimentally (GT2008-50278) [8].

The swirling annular flow enters the combustion chamber and expands to the chamber walls, forming a conical recirculation zone along the centreline and an annular recirculation zone in the upstream corner. In this study, the steady base flow and the stability analysis are calculated at Re 200–3800 based on the mean flow velocity and inlet diameter. The velocity field is similar to that found from experiments and LES, and the local stability results are close to those at higher Re (GT2012-68253) [11].

All the analyses (experiments, LES, uRANS, local stability, and the global stability in this paper) show that a helical motion develops around the central recirculation zone. This develops into a precessing vortex core. The adjoint-based sensitivity analysis reveals that the frequency and growth rate of the oscillation is dictated by conditions just upstream of the central recirculation zone (the wavemaker region). It also reveals that this oscillation is very receptive to forcing at the sharp edges of the injector. In practical situations, this forcing could arise from an impinging acoustic wave, showing that these edges could be influential in the feedback mechanism that causes thermoacoustic instability.

The analysis also shows how the growth rate and frequency of the oscillation change with either small shape changes of the nozzle, or additional suction or blowing at the walls of the injector. It reveals that the oscillations originate in a very localized region at the entry to the combustion chamber, which lies near the separation point at the outer inlet, and extends to the outlet of the inner pipe. Any scheme designed to control the frequency and amplitude of the oscillation only needs to change the flow in this localized region.
Interferometric Investigation of the Thermoacoustics in a Swirl Stabilized Methane Flame
Authors: Peterleithner Johannes , Marn Andreas , Woisetschläger Jakob
Published: August 2015

In this work, an atmospheric model combustion chamber was characterized employing Laser Vibrometry, chemiluminescence and Particle Image Velocimetry. The test object was a variable geometry burner enclosed with a liner, with the flame optically accessible through four fused silica windows. In this burner with adjustable flame conditions the cavity of the atmospheric model combustion chamber was excited at a frequency around 200Hz. Resonant and non-resonant flame conditions were investigated and compared by laser vibrometer interferometry, schlieren visualization and OH*/CH* chemiluminescence. Additionally, the velocity field was recorded with Particle Image Velocimetry, while the aerodynamics of the burner plenum was analyzed with Computational Fluid Dynamics.
Quantitative MRI Measurements of Hot Streak Development in a Turbine Vane Cascade
Authors: Yapa Sayuri D. , Elkins Christopher J. , Eaton John K.
Published: August 2015

Hot streaks from the combustor and cool streaks from nozzle vane film cooling impose strong inlet temperature variations on high pressure turbine blades, which can lead to local hot or cold spots, high thermal stresses, and fatigue failures. Furthermore, the complex three dimensional flows around the vane may act to concentrate cool or hot fluid exiting the vane row. In order to optimize the cooling design of the turbine blades, the designer must be able to predict the temperature distribution entering the turbine rotor. Therefore, it is important to understand and predict how combustor hot streaks are dispersed as they pass through the vane row. The goal of the present work is to provide detailed three dimensional velocity and temperature data for simulated combustor hot streaks developing through a film cooled vane cascade using the Magnetic Resonance Velocity/Concentration experimental technique. The measurements show that the hot streaks are thinned by acceleration through the vane cascade and diffused by turbulence. The turbulent diffusivity is suppressed by acceleration and leaves significant temperature nonuniformity in the vane wake.
New Profile Loss Model for Improved Prediction of Transonic Axial Flow Compressor Performance in Choking Region
Authors: Kim Sangjo , Kim Donghyun , Kim Kuisoon , Son Changmin , Kim Myungho , Min Seongki
Published: August 2015

New off-design profile loss models have been developed by performing thorough investigations on compressor performance prediction using one-dimensional stage-stacking approach and three-dimensional computational flow dynamics (CFD) results. Generally, a loss model incorporating various compressor geometry and operating conditions is required to predict the performance of various types of compressors. In this study, three sets of selected loss models were applied to predict axial flow compressor performance using stage-stacking approach. The results were compared with experimental data as well as CFD results. The comparison shows an interesting observation in choking region where the existing loss models cannot capture the rapid decrease in pressure and efficiency while CFD predicted the characteristics. Therefore, an improved off-design profile loss model is proposed for better compressor performance prediction in choking region. The improved model was derived from the correlation between the normalized total loss and the incidence angle. The choking incidence angle, which is a major factor in determining the off-design profile loss, was derived from correlations between the inlet Mach number, throat width-to-inlet spacing ratio, and minimum loss incidence angle.

The revised stage-stacking program employing new profile loss model together with a set of loss models was applied to predict a single and multistage compressors for comparison. The results confirmed that the new profile loss model can be widely used for predicting the performance of single and multistage compressor.
Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions: Part II — Detailed LCT Measurements
Authors: Mayo Ignacio , Lahalle Aude , Gori Gian Luca , Arts Tony
Published: August 2015

The present two-part work deals with a detailed characterization of the flow field and heat transfer distribution in a model of a rotating ribbed channel performed in a novel setup which allows test conditions at high Rotation numbers (Ro). The tested model is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with 8 ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitch to height ratio is 10.

In this second part of the study, the heat transfer distribution over the wall region between the 6th and 7th ribs is obtained by means of Liquid Crystal Thermography (LCT). Tests were firstly carried out at a Reynolds number of 15000 and a maximum Ro of 1.00 to evaluate the evolution of the heat transfer with increasing rotation. On the trailing side, the overall Nusselt number increases with rotation until a limit value a 50% higher than in the static case, which is achieved after a value of the Rotation number of about 0.3. On the leading side, the overall Nusselt number decreases with increasing rotation speed to reach a minimum which is approximately 50% of the one found in static conditions. The velocity measurements at Re=15000 and Ro=0.77 provided in Part I of this paper are finally merged to provide a consistent explanation of the heat transfer distribution in this model. Moreover, heat transfer measurements were performed at Reynolds numbers of 30000 and 55000, showing approximately the same trend.
Turbine Wheel Shape Optimization: Design Criteria, Multidiscipline Design Tools and Simulation Processes
Authors: Di Sisto Paolo , Grosso Massimiliano
Published: August 2015

Gas turbine rotors must be reliable, stable and durable because they operate in a demanding centrifugal and thermal environment without being maintained and replaced for many years. The design of a rotor is one of the most challenging tasks that gas turbine design team should face because its basic architecture has to be decided in the early design stage together with the gas turbine flow path and combustion architecture. A wrong initial decision may require a substantial modification of the gas turbine cross section and consequently have a dramatic impact on the project schedule.

This paper introduces readers to the main aspects of the gas turbine rotor design, including the multidiscipline design tools that allow a quick rotor components shaping nowadays. Thanks to the use of some of the most popular gas turbines in the O&G application, this paper will explain how the rotor design has developed over the last decades. An example of how today a new rotor is designed will be provided, by describing some of the main topics analyzed during the conceptual design phase of a General Electric (GE) engine that will be on the market since the 2016. The paper also describes some of the biggest challenges that rotor design teams will have to face in the next future.
Numerical Evaluation of Pin Fin Inclination by Conjugate Heat Transfer Simulation With URANS
Authors: Yamane Takashi
Published: August 2015

Short pin fins are often used as one of the blade cooling technologies inside the trailing edge of turbine blades. In our previous study we focused on the effects of pin inclination for overall cooling performance especially including heat conduction between the pins and endwall by both experiments and the conjugate heat transfer simulations, then the forwardly inclined pin-fins are found to effectively enhance the cooling, but we also found that the steady conjugate heat transfer simulation underestimates the cooling performance of the straight pin-fins due to highly unsteady flow structure. In this study the URANS is coupled with the steady thermal conduction by using the time smoothing method in the flow region, thus the underestimate of the heat transfer for the straight pin-fins was significantly improved.