bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Pressure-Based Coupled CFD Solver for Turbulent and Compressible Flows in Turbomachinery Applications
Authors: Mangani Luca , Darwish Marwan , Moukalled Fadl
Published: September 2014

In this paper we present a fully coupled algorithm for the resolution of compressible flows at all speed. The pressure-velocity coupling at the heart of the Navier Stokes equations is accomplished by deriving a pressure equation in similar fashion to what is done in the segregated SIMPLE algorithm except that the influence of the velocity fields is treated implicitly. In a similar way, the assembly of the momentum equations is modified to treat the pressure gradient implicitly. The resulting extended system of equations, now formed of matrix coefficients that couples the momentum and pressure equations, is solved using an algebraic multigrid solver.

The performance of the coupled approach and the improved efficiency of the novel developed code was validated comparing results with experimental and numerical data available from reference literature test cases as well as with segregated solver as exemplified by the SIMPLE algorithm. Moreover the reference geometries considered in the validation process cover the typical aerodynamics applications in gas turbine analysis and design, considering Euler to turbulent flow problems and clearly indicating the substantial improvements in terms of computational cost and robustness.
The Effect of Internal Cross-Flow on the Adiabatic Effectiveness of Compound Angle Film Cooling Holes
Authors: McClintic John W. , Klavetter Sean R. , Anderson Joshua B. , Winka James R. , Bogard David G. , Dees Jason E. , Laskowski Gregory M. , Briggs Robert
Published: September 2014

In gas turbine engines, film cooling holes are often fed by an internal cross-flow, with flow normal to the direction of the external flow around the airfoil. Many experimental studies have used a quiescent plenum to feed model film cooling holes and thus do not account for the effects of internal cross-flow. In this study, an experimental flat plate facility was constructed to study the effects of internal cross-flow on a row of cylindrical compound angle film cooling holes. Operating conditions were scaled, based on coolant hole Reynolds number and turbulence level, to match realistic turbine engine conditions. A cross-flow channel allowed for coolant to flow alternately in either direction perpendicular to the mainstream flow. Film cooling holes were operated at blowing ratios ranging from 0.5 to 2.0 at a density ratio of 1.5. There are relatively few studies available in literature that focus on the effects of cross-flow on film cooling performance, with no studies examining the effects of internal cross-flow on film cooling with round, compound angled holes. This study showed that significantly greater adiabatic effectiveness was achieved for cross-flow in the opposite direction of the span-wise direction of the coolant holes and provides possible explanations for this result.
Influence of Injection Ratio of Dual-Injection Type Air-Blast Fuel Nozzle on Emission Characteristics Applied to Rectangular Single-Sector Combustor Under Atmospheric Condition
Authors: Makida Mitsumasa , Kurosawa Yoji , Yamada Hideshi
Published: September 2014

In the TechCLEAN project of JAXA, experimental research had been conducted to develop a combustor for a small aircraft engine. The combustor was tuned to show the behavior of the Rich-Lean combustion through tests under atmospheric and practical conditions. Finally, through full annular combustion experiments under practical conditions, the combustor was tuned to reduce NOx emissions to almost 40% of the ICAO CAEP4 standard, also sustaining low CO and THC emissions. In the developing process of above combustors, to simplify the combustor system, air blast type fuel nozzles with single fuel injection and dual swirlers were applied. Successively, in this report, the fuel nozzle is modified to dual fuel injection type with triple swirlers, aiming to control combustion performance under varying load conditions. Fuel is injected from inner and outer injection circuits, and the injection ratio between them is treated as one of the parameters.

The combination of swirl direction of the three swirlers is selected at first through ignition and blowout tests. Secondly, spray patterns of the selected fuel nozzle are observed with different fuel injection ratios. Thirdly, the nozzle is applied to a rectangular single-sector combustor, and tested under atmospheric pressure with inlet temperature of 500K. NOx, CO, CO2, THC and O2 compositions in the exhaust gas are measured, and correlation among measured emissions data and fuel injection ratio is estimated to examine the influence of the injection ratio on combustion characteristics of the Rich-Lean type aero engine combustor.
Adiabatic Effectiveness Measurements for a Baseline Shaped Film Cooling Hole
Authors: Schroeder Robert P. , Thole Karen A.
Published: September 2014

Film cooling on airfoils is a crucial cooling method as the gas turbine industry seeks higher turbine inlet temperatures. Shaped film cooling holes are widely used in many designs given the improved performance over that of cylindrical holes. Although there have been numerous studies of shaped holes, there is no established baseline shaped hole to which new cooling hole designs can be compared. The goal of this study is to offer the community a shaped hole design, representative of proprietary and open literature holes that serves as a baseline for comparison purposes. The baseline shaped cooling hole design includes the following features: hole inclination angle of 30° with a 7° expansion in the forward and lateral directions; hole length of 6 diameters; hole exit-to-inlet area ratio of 2.5; and lateral hole spacing of 6 diameters. Adiabatic effectiveness was measured with this new shaped hole and was found to peak near a blowing ratio of 1.5 at density ratios of 1.2 and 1.5 as well as at both low and moderate freestream turbulence of 5%. Reductions in area-averaged effectiveness due to freestream turbulence at low blowing ratios were as high as 10%.
Experimental Study on NOx and CO Emissions of Aviation Kerosene and Coal-to-Liquid Synthetic Aviation Fuel in a Jet Stirred Combustion Reactor
Authors: Xue Xin , Lin Yuzhen , Zhang Chi , Tian Ye , Sung Chih-Jen
Published: September 2014

The ever increasing consumption of non-renewable fossil fuels for global economic development leads to serious energy crisis and environmental pollution. Consequently, new alternative fuels and high-efficiency combustion are required to aid the sustainable development of human society. The present paper took the RP-3 aviation kerosene and coal-to-liquid synthetic aviation fuel (manufactured through the Fischer Tropsch process., FT) for object, and experimentally investigated the influences of pressure, inlet temperature and equivalence ratio on the productions of NOx and CO in a jet stirred combustion reactor. The tests were performed under the pressures of 2bar and 3bar, and inlet air temperatures of 550K and 650K, respectively. The equivalence ratio ranged from 0.5 to 1.2. The mean residence time was approximately 8ms. Probe sampling followed by on-line emissions analyzer permitted to measure the concentration of the products. The experimental results show that these two fuels obey the same law with the variations of pressures, inlet temperatures and equivalence ratios. The NOx production increases with the pressure and inlet temperature increasing. The CO decreases with the pressure increasing, while slightly increases with the inlet temperature increasing. Numerical simulations were also performed to investigate the combustion products of these two fuels in the jet stirred combustion reactor. Two PSRs were introduced to simulate the jet flame region and post flame in the recirculation region, respectively. The combustion products of second PSR (PSR2) agreed well with the experimental results by regulating the volume ratio of first PSR (PSR1). Based on the reaction pathway analysis of NO production in present state, it is considered that for these two fuels the NOx production is led by the thermal NO above the equivalence ratio of 0.65, while by the N2O at lower equivalence ratios. With the application of the present alternative fuel and its reaction mechanism, the experimental results of aviation kerosene and Coal-to-Liquid synthetic aviation fuel can be predicted well within a certain state, which requires a further verification in a wider range. Furthermore, the numerical results show that the NO release is insensitive to the reaction components within present experimental states.
Dynamic Stress Analysis of a Blade in a Partially Blocked Engine Inlet
Authors: Drewczynski Marcin , Rzadkowski Romuald , Ostrowska Zofia
Published: September 2014

One of the greatest dangers to properly working aircraft engines, apart from human error, is the ingestion foreign objects into the compressor. These objects may be birds, dust, hail, volcanic ash, ice on wings but also aircraft parts or simply garbage. Modern jet engines can suffer major damage from even small objects being sucked into the engine. We want to show how foreign object debris affects the dynamic stress level of a rotor blade. A comparison between an undisturbed engine inlet and one with an ingested foreign object is carried out. The analysis will focus on the first stage compressor blade of an aircraft engine with a partially blocked radial inlet.

The main subject of this paper concerns transferring a CFD analysis pressure field as a surface load to the structural model of a blade.

First a CFD calculation of a nominal and disturbance regime was conducted. In both cases an unsteady pressure was calculated.

Calculations were carried out on a first stage compressor blade. Ansys 12.1 was used to calculate the entire structure. Unsteady CFD calculations used Fluent for a 1.5 stage axial compressor model. A non-viscous flow was used for the numerical calculations. The unsteady forces were calculated on 10 control cross-sections of a rotor blade. The transient results obtained from the CFD calculations were transferred onto a structural rotor blade model using APDL language script.
Investigation of a Novel Discrete Slot Film Cooling Scheme
Authors: Shalash Karim M. , El-Gabry Lamyaa A. , Abo El-Azm Mohamed M.
Published: September 2014

The future of the gas turbine industry is strongly relying on the development of new efficient cooling schemes. Film cooling is one popular and reliable cooling technique, one way to increase the film cooling effectiveness is through the use of shaped holes. In this paper two proposed shaped holes are being studied and compared thoroughly against the conventional round hole film cooling. The two proposed holes are based on the theoretically perfect continuous slot film cooling, however, these slots are not continuous, and preserves the solid surface to the total blade surface ratio. The first design to be studied is the Rectangular Divergent Slot, and the second is the Aeroslot, which is a discrete aerodynamically shaped slot; both designs showed an increase in the centerline film cooling effectiveness when compared to the conventional round holes. The Aeroslot showed a large increase in film cooling effectiveness for the same blowing ratio, and mass flow rate of coolant, when compared to the other shapes. A sensitivity study of the blowing ratio to the centerline film cooling effectiveness is carried out for several blowing ratios, covering different jet in cross flow behaviors, fully attached jet, and detached-reattached jet.
Comparison of Transient Blade Row Methods for the CFD Analysis of a High-Pressure Turbine
Authors: Witteck Dirk , Micallef Derek , Mailach Ronald
Published: September 2014

Usually, in a turbine an uneven number of blades are selected for vane and blade rows to reduce the level of interaction forces. To consider all unsteady flow phenomena within a turbine the computation of the full annulus is required causing considerable computational cost. Transient blade row methods using few passages reduce the numerical effort significantly. Nevertheless, those approaches provide accurate results. This contribution presents three different unsteady approaches to compare the accuracy and the computational effort, using a full annulus unsteady CFD simulation as a reference. The first approach modifies the blade-to-blade ratio whereas the second method scales the circumferential flow pattern to reach spatial and temporal periodicity. Third approach is based on time-inclining method to overcome unequal blade pitches with less numerical effort. All unsteady CFD simulations are carried out for the transonic test turbine VKI BRITE EURAM using the commercial CFD solver ANSYS CFX 14.5. The resulting unsteady pressure disturbances and blade forces of the different transient blade row methods are compared to each other as well as to experimental data. Finally, the accuracy and the computational costs are discussed in more detail.
Development of a Liquid Fuel System for GE MS5002E Gas Turbine: Rig Test Validation of the Combustor Performance
Authors: Zucca Alessandro , Khayrulin Sergey , Vyazemskaya Natalya , Shershnyov Borys , Myers Geoff
Published: September 2014

Analysis of the Oil & Gas market segment showed that potential MS5002E customers could benefit from firing the gas turbine with distillate oil as a back-up fuel, mainly to provide power when the fuel gas is not available (e.g. when the plant itself is being commissioned). To address this customer need, the design of a dual fuel system for such mission should target simplicity, reliability and minimize the additional cost with respect to the single gas version. To achieve these targets, the development of the dual fuel system for the MS5002E leveraged the efforts made by GE for the design of a liquid fuel system for Frame 9F-1 series with no need of atomization air. Moreover, the emission capability during liquid fuel operation was enhanced allowing the mixing of water and fuel before injection in the combustion chamber and using of improved injection technology, thus improving the efficiency of water injection with a significant reduction in the required water flow rates; the importance of this achievement is related to both the increasingly stringent regulation on this subject and the often poor availability of water in the Oil & Gas market segment. The system is capable of continuous operation without water injection for applications where emissions are not critical; in these cases a small amount of demineralized water is employed occasionally for fuel line cooling and flushing, thus helping to guarantee constant performances of the injectors, and to maintain liquid fuel start-up capability over time.

This paper presents the expected performance, in terms of ignition capability, emissions, operability and expected hardware durability on LF/water-fuel emulsion operation, based on a single can rig test campaign. The new liquid fuel cartridges were tested from ignition to base load at ISO and extreme simulated ambient conditions, both with and without water injection, showing promising performance in terms of combustor operability and emissions. All the combustor components were instrumented with thermocouples to assess variations in the hardware thermal levels with respect to the single gas conditions, and identify possible issues related to the transient and steady-state liquid fuel operation. Further development and testing will be carried out in the next phases of the development, and the performance will be confirmed by a dedicated engine test at the first commercial opportunity.
Vibration Characteristics of Segmented Stator Assemblies in Axial Compressors
Authors: Meyer Michael , Gentry-Grace Cassandra
Published: September 2014

A common component in axial compressors used in turbo machinery applications is the segmented stator assembly with fixed airfoils attached to inner and outer bands forming a partial ring. Understanding the potential for vibratory responses of these components during engine operation is vital to avoid harmful vibrations. However, an accurate prediction of segmented stator assembly vibratory characteristics is difficult due to the partial nature of their cyclic symmetry and high part to part manufacturing variation. Numerous analyses related to laboratory tests, engine tests and theoretical studies have been performed to advance the understanding and better quantify the segmented stator assembly dynamic behavior. A summary of the component dynamic behavior is provided through a series of lessons learned from the various analyses completed.

The segmented stator assemblies can be thought of as cyclically symmetric parts with properties of extreme mistuning. These properties are realized when one attempts to evaluate the components using experimental and theoretical approaches traditionally reserved for cyclically symmetric components. Specifically, harmonic indices are often employed to identify modes of interest in a cyclically symmetric system with reference to known engine order excitations. However, with segmented stator assemblies, there is a high density of modal frequency distribution across the engine operating range and mode shapes can suffer from significant contamination of the diametral patterns. These observations complicate linking specific modes to known engine order excitations. This study implements traditional FEA approaches and reduced order models in an attempt to predict the key vibratory modes of concern and to show which component features most significantly affect the vibratory characteristics of segmented stator assemblies. Observations made during bench tests are compared to theoretical analyses and confirm the challenges of assessing the dynamic properties of segmented stator assemblies. This work supports emerging segmented stator design evaluation techniques, an area that is critical to successful integration of these components into turbo machinery applications.
Research Activities on Supercritical Carbon Dioxide Power Conversion Technology in China
Authors: Wang Junfeng , Huang Yanping , Zang Jinguang , Liu Guangxu
Published: September 2014

Supercritical carbon dioxide (S-CO2) Brayton cycle has attracted substantial attention in recent years due to its higher efficiency, simpler cycle layout and lower cost. S-CO2 Brayton cycle is not only suitable for next generation nuclear reactors, but also considered in other conventional and renewable energy applications including fossil-fueled power plant, ship propulsion, and solar energy system and so on. In 2010, Nuclear Power Institute of China (NPIC) initially started to investigate the concept and some fundamental issues related to S-CO2 power conversion technology in China. This paper presents recent research and development progress obtained in China including thermodynamic analysis and evaluation, thermohydraulic investigation, code development, and integral test loop design. The research plan in the near future for S-CO2 power conversion technology in China is also presented.
Impact of the Secondary Air System Design Parameters on the Calculation of Turbine Discs Windage
Authors: Rey Villazón Jose Maria , Wildow Toni , Benton Robert , Göhler Moritz , Kühhorn Arnold
Published: September 2014

The rotating components in gas turbines are very highly stressed as a result of the centrifugal and thermal loads. One of the main functions of the secondary air system (SAS) is to ensure that the rotating components are surrounded by air that optimizes disc lifing and integrity. The SAS is also responsible for the blade cooling flow supply, preventing hot gas ingestion from the main annulus into the rotor-stator cavities, and for balancing the net axial load in the thrust bearings. Thus, the SAS design requires a multidisciplinary compromise to provide the above functions, while minimizing the penalty of the secondary flows on engine performance.

The phenomenon known as rotor-stator drag or windage is defined as the power of the rotor moment acting on its environment. The power loss due to windage has a direct impact on the performance of the turbine and the overall efficiency of the engine. This paper describes a novel preliminary design approach to calculate the windage of the rotor-stator cavities in the front of a typical aero engine HP turbine. The new method is applied to investigate the impact of the SAS design parameters on the windage losses and on the properties of the cooling flows leading to the main annulus.

Initially, a theoretical approach is followed to calculate the power losses of each part of the HPT front air feed system. Then, a 1D-network integral model of the cavities and flow passages of the HPT front is built and enhanced with detailed flow field correlations. The new 1D-flow network model offers higher fidelity regarding local effects. A result comparison between the theoretical calculation and the prediction of the enhanced flow network model puts forward the relevance of the local flow field effects in the design concept of the SAS.

Using the enhanced 1D-flow network models, the SAS design parameters are varied to assess their influence on the windage and pumping power calculation. As a conclusion, the paper shows how the SAS design can have a significant influence on the HPT overall power and the air that is fed back into the turbine blade rows. Controlling these features is essential to bid a competitive technology in the aero engine industry.
Improvement of Flat-Plate Film Cooling Performance by Double Flow Control Devices: Part II — Optimization of Device Shape and Arrangement by Experiment- and CFD-Based Taguchi Method
Authors: Kawabata Hirokazu , Funazaki Ken-ichi , Nakata Ryota , Tagawa Hisato , Horiuchi Yasuhiro
Published: September 2014

This paper, as a second part of the study on the double flow control device (DFCD) which has been proven in Part I [1] to improve the flat plate film cooling considerably, describes an approach to optimize the device shape and arrangement using Taguchi method. The target cooling holes are conventional cylindrical ones of 3.0d pitch with 35 deg angle to the flat plate surface. The shape of the double flow control device to be optimized is based on the hemi-spheroid used in Part I.

The optimization process in this study is categorized as “static problem”, in which S/N ratios of “larger-the-better” characteristics are calculated for control parameters against their noise factor. The “larger-the-better” characteristics adopted in this study is the area averaged film effectiveness over the downstream region of the cooling hole. L18 orthogonal array is used to accommodate the experiment. Blowing ratios of the cooling air to the main flow used in this study are 0.5, 0.75 and 1.0, which are regarded as noise factor. Seven control parameters such as fillet radius, installation angle of the device are chosen and their effects on the film effectiveness are evaluated by the measurement as well as by RANS simulation. In this research, the optimization which used Taguchi method was at the same time carried out by an experiment and numerical simulation. From a comparison between the optimal parameter combinations attained from the measurement-based and CFD-based approaches, one can have an idea about the dependency of the optimal parameter combination on the characteristic evaluation approach. Additional investigation is also made on the effects of turbulence model upon the optimal parameter combination.

The flow fields in the downstream region of the optimal DFCD are observed using 3D Laser Doppler Velocimeter in order to understand how the device works on the ejected cooling air. In addition, Large-Eddy-Simulation (LES) is also executed in order to grasp unsteady flow structures created by the device and their interaction with the cooling air. It is found from the measurement as well as the LES analysis that the optimal DFCD generates comparatively large-scale longitudinal vortices, causing the drastic increase in film effectiveness.
Computational Analysis of Unsteady Flow in a Partial Admission Supersonic Turbine Stage
Authors: Tokuyama Yuki , Funazaki Ken-ichi , Kato Hiromasa , Shimiya Noriyuki , Shimagaki Mitsuru , Uchiumi Masaharu
Published: September 2014

Turbines used in upper stage engine for a rocket are sometimes designed as a supersonic turbine with partial admission. This study deals with numerical investigation of supersonic partial admission turbine in order to understand influences on the unsteady flow pattern, turbine losses and aerodynamic forces on rotor blades due to partial admission configuration. Two-dimensional CFD analysis is conducted using “Numerical Turbine” code. Its governing equation is URANS (Unsteady Reynolds Averaged Navier-Stokes Simulation) and fourth-order MUSCL TVD scheme is used for advection scheme.

The unsteady simulation indicates that strongly non-uniform circumferential flow field is created due to the partial admission configuration and it especially becomes complex at 1st stage because of shock waves. Some very high or low flow velocity regions are created around the blockage sector. Nozzle exit flow is rapidly accelerated at the inlet of blockage sector and strong rotor LE shock waves are created. In contrast, at rotor blade passages and Stator2 blade passages existing behind the blockage sector, working gas almost stagnates. Large flow separations and flow mixings occur because of the partial admission configuration. As a result, additional strong dissipations are caused and the magnitude of entropy at the turbine exit is approximately 1.5 times higher than that of the full admission.

Rotor1 blades experience strong unsteady aerodynamic force variations. The aerodynamic forces greatly vary when the Rotor1 blade passes through the blockage inlet region. The unsteady force in frequency domain indicates that many unsteady force components exist in wide frequency region and the blockage passing frequency component becomes pronounced in the circumferential direction force. Unsteady forces on Rotor2 blades are characterized by a low frequency fluctuation due to the blockage passing.
Effect of the Compressor Discharge Casing Geometry on Combustor Exit Temperature Profiles in a Multi-Can Gas-Turbine Combustor
Authors: Agarwal Krishna Kant , Gori Stefano
Published: September 2014

Temperature profile variations in gas turbine combustors are important from the considerations of thermal stresses and material fatigue. The specific profile being addressed in this study is the combustor exit gas temperature profile in radial direction at first stage nozzle entry (also called the combustor transition-piece (TP) exit profile). Normally, in multi-can combustor configurations, this profile is assumed to be constant along the circumferential direction or from one can to another. However, field test on one of the GE-MS5002D class machine revealed that the shape of the combustor TP exit temperature profile is varying across the different cans. It is important to assess the reason of this behavior in order to define thermal input for stage 1 nozzle thermal design and define an average temperature profile for turbine bucket verification.

For investigating the reasons of varying TP exit profiles across different cans, a reacting flow CFD study is performed for a combined multiple combustor-cans geometry. This is a challenging attempt considering that mesh for a single can liner is itself typically quite large (∼30 million) for capturing all flow features. The present multi-can study was made feasible with judicious simplification of combustor geometry, retaining only important flow features and using adequate mesh to capture system physics. Results indicate that the varying flame shape across different cans is indeed captured in the CFD. Hence, this effect could be something associated with the combustor design. Subsequent detailed post-processing of CFD results revealed the root cause to be associated with the presence of unsymmetrical arrangement of struts in the compressor discharge casing region. This effect is a slight flow-recirculation created much upstream due to the struts, which eventually results in asymmetric distribution of the flow across the combustor dilution holes. This leads to the flame shifting in different orientation for different cans with a systematic reference to the struts position. In conclusion, this paper describes the approach used for multi-can CFD analysis of the combustor, flow behavior in presence of unsymmetrical strut and its impact on the combustor exit temperature profile much downstream.
Innovative Measurement Techniques for a Cooled Turbine Casing Operating at Engine Representative Thermal Conditions
Authors: Dann Andrew G. , Thorpe Steve J. , Lewis Leo V. , Ireland Peter
Published: September 2014

To optimize the efficiency of modern aero-gas turbine engines the turbine tip clearances must be tightly controlled so as to minimize leakage losses. In addition, the clearance control system must be able to respond with sufficient rapidity to engine thermal transients. One method of achieving turbine tip-clearance control is to manipulate the turbine casing temperature, and thereby radial growth, by convective cooling. The consequent clearance control system represents a particularly complex thermo-mechanical design problem. The current experimental study aims to simulate the heat loads to which the internal surfaces of the casing are typically exposed and to characterize the radial and axial displacement of the free-body casing under varying external cooling conditions. Importantly, the newly commissioned test facility allows a realistic assessment of the casing cooling impact on dimensional control, and also the rapid characterization and comparison of different concepts. The test facility comprises a model of a high-pressure/intermediate-pressure turbine casing with generic impingement cooling manifolds. A radiant heater is mounted within the casing model such that a near-uniform heat flux condition can be established on the casing wall inner surface. Extensive surface mounted thermocouples are welded to the casing wall to monitor variations in metal temperature. Radial and axial displacement of the casing is monitored using laser triangulation and linear variable differential transformer sensors. Experiments have been conducted over a range of heat load conditions and with engine representative levels of casing cooling applied. Importantly, the new test facility allows for the characterization of the casing cooling system as a whole.
A Numerical and Experimental Assessment of the Use of a Turbine Utilizing Splitter Blades for an Automotive Variable Geometry Turbocharger
Authors: Walkingshaw Jason , Spence Stephen , Filsinger Dietmar , Thornhill David
Published: September 2014

Automotive manufacturers require improved part load engine performance to further improve fuel economy. For a swing vane VGS (Variable Geometry Stator) turbine this means a more closed stator vane, to deal with the low MFRs (Mass Flow Rates), high PRs (Pressure Ratios) and low rotor rotational speeds. During these conditions the turbine is operating at low velocity ratios. As more energy is available at high pressure ratios and during lower turbocharger rotational speeds, a turbine which is efficient at these conditions is desirable. Another key aspect for automotive manufacturers is engine responsiveness. High inertia designs result in “turbo lag” which means an increased time before the target boost pressure is reached. Therefore, designs with improved performance at low velocity ratios, reduced inertia or an increased swallowing capacity are the current targets for turbocharger manufacturers.

To try to meet these design targets a CFD (Computational Fluid Dynamics) study was performed on a turbine wheel using splitter blades. A number of parameters were investigated. These included splitter blade merdional length, blade number and blade angle distribution.

The numerical study was performed on a scaled automotive VGS. Three different stator vane positions have been analysed. A single passage CFD model was developed and used to provide information on the flow features affecting performance in both the stator vanes and turbine.

Following the CFD investigation the design with the best compromise in terms of performance, inertia and increased MFP (Mass Flow Parameter) was selected for manufacture and testing. Tests were performed on a scaled, low temperature turbine test rig. The aerodynamic flow path of the gas stand was the same as that investigated during the CFD. The test results revealed a design which had similar performance at the closed stator vane positions when compared to the baseline wheel. At the maximum MFR stator vane condition a drop of −0.6% pts in efficiency was seen. However, 5.5% increase in MFP was obtained with the additional benefit of a drop in rotor inertia of 3.7%, compared to the baseline wheel.
Experimental Investigation of Separated Shear Layer Over a Flat Plate for Various Angles of Attack and Tail Flap Deflections
Authors: Anand K. , Sarkar S.
Published: September 2014

Shear layer development over a thick flat plate with a semi-circular leading edge is investigated for a range of angles of attack under different imposed pressure gradients for a Reynolds number of 2.44×105 (based on chord and free-stream velocity). The features of the separated shear layer are very well documented through a combination of surface pressure measurement and flow visualization by particle image velocimetry (PIV). The instability of the separated layer occurs because of enhanced receptivity of perturbations leading to the development of significant unsteadiness and three-dimensional motions in the second-half of the bubble. The onset of separation, transition and the point of reattachment are identified for varying angles of attack and imposed pressure gradients. The reattachment point shifts from 12.5% to 53% of chord resulting in enhancement of bubble length from 5% to 47%, while onset of transition shifts upstream from 14% to 7.5% as α increases. The Reynolds number based on the length of laminar shear layer is found to be in the range of 0.7×104 to 2.0×104. The separated shear layer fails to reattach attributing to bubble bursting at α = 12° for β = −45°, while, it bursts at α = 5° for β = +45°. The bubble falls in the category of short bubble for α < 3°, whereas, it becomes long for α ≥ 3°. The data concerning laminar portion and reattachment points agree well with the literature.
Aerodynamic Investigation on the Excitation of a Laminar Separation Bubble by Secondary Jets
Authors: AnnapuReddy Samson , Sarkar S.
Published: September 2014

Aerodynamic interactions of a separated shear layer from the semi-circular leading edge of a constant thickness aerofoil model with jets ejecting in the vicinity of reattachment from a row of discrete holes at an angle of 30° in the streamwise direction are elucidated. Experiments are carried out for two Reynolds numbers (ReD) 25000 and 55000 (based on the leading-edge diameter) and two velocity ratios (V.R) 0.5 and 1. The time-averaged velocity and turbulence quantities are measured using Laser-Doppler Anemometry (LDA) at different streamwise locations along the centre line of the jet, while the instantaneous flow filed is obtained using Particle Image Velocimetry (PIV). Measurements reveal that the flow undergoes separation at the blending point of semi-circle and flat plate owing to sudden change in geometry. It is observed that in the absence of the jet, the separated shear layer undergoes transition with formation Kelvin-Helmholtz (K-H) rolls and a significant growth of Reynolds stress in the second-half of the bubble is evident. With injection, the separation bubble length in the upstream of jet has decreased with increased growth rate of velocity fluctuations. However, the characteristics of the flow in the separated region remains almost unchanged and the transition criteria even follows the universal intermittency characteristics of Dhawan and Narasimha [35]. The instantaneous results elucidate that K-H rolls from the separated shear layer interact with the injected jet resulting in its oscillation. In the downstream of injection, the presence of the jet is felt with enhanced turbulence activities in the outer layer, particularly for high V.R. Further, the onset and end of transition of the separated flow are compared with correlations available in the literature.
LES of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques
Authors: Amirante Dario , Hills Nicholas J.
Published: September 2014

Large-Eddy Simulations of wall bounded, low Mach number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES procedure.

Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds number Reb = 44 × 103 based on the pipe diameter, and a confined rotor-stator flow at the rotational Reynolds number ReΩ = 4 × 105 based on the outer radius. In both cases the mean flow and the turbulent statistics agree well with existing DNS or experimental data.
Liquid Jet in Cross Flow Modeling
Authors: Sekar Jayanth , Rao Arvind , Pillutla Sreedhar , Danis Allen , Hsieh Shih-Yang
Published: September 2014

All key combustor performance & operability characteristics like emissions, exit profile, durability, LBO etc. have a dependence on spray quality. Hence it is important to accurately predict spray characteristics for accurate combustor modeling. In this paper, a CFD based liquid jet in cross flow spray modeling approach adopted at GE Aviation is presented. Liquid jet in cross flow is a complex phenomenon that broadly involves jet trajectory evolution, surface breakup, column fracture and dispersion of secondary droplet particles. A two-phase steady state Volume of Fluid (VOF) approach is used to predict the liquid jet trajectory. A combination of output from VOF and empirical correlations (Sallam et. al; Oda et. al) is used to predict droplet distribution that includes diameter, velocity components and mass flow rate. Surface breakup is modeled by injecting droplets along the leeward surface of the liquid jet with spanwise perturbation to capture the transverse spread. Jet column breakup is modeled by injecting droplets including effects of unsteady fluctuations empirically to mimic the column fracture behavior. Discrete particles are then transported in a lagrangian frame coupled with secondary breakup of droplets. This approach has been validated on a benchmark quality dataset with an average SMD (Sauter Mean Diameter) error of ∼6 microns and is being used on Gas Turbine combustor fuel-air mixing devices employing liquid jet in cross flow atomizers.
Heat Transfer Enhancement for a Turbine Blade Leading Edge Passage Using Various Turbulator Geometries
Authors: Saxer-Felici H. , Naik S. , Gritsch M. , Sedlov A.
Published: September 2014

The leading edge regions of first stages blades and vanes of heavy-duty gas turbines are subjected to high thermal loads. Efficient cooling allows the reduction of the coolant mass flow required to drive the metal temperatures to a range satisfying mechanical integrity requirements.

This paper investigates the heat transfer and pressure loss behavior for the internal cooling channel of a leading edge of a gas turbine blade. The geometrical profile of the blade leading edge and the operating conditions considered are representative of that normally found in a heavy-duty gas turbine.

The geometries investigated cover angled turbulators of various angles, pitches and heights. Partial and full length rib coverage as well as broken ribs are also considered. In addition, the impact of including fillets in the geometry is assessed.

The experimental and numerical studies are conducted at passage Reynolds numbers ranging from 7.5·104 to 1.3·105.

Experiments are performed using Perspex models at atmospheric conditions. The internal heat transfer coefficients on all internal surfaces are measured via thermochromic liquid crystal method and the pressure drop is measured via pressure taps distributed along the channel.

The predicted and experimental heat transfer enhancements are compared on the leading-edge, pressure, suction and web surfaces. The overall non dimensional cooling performance numbers are also compared for the various geometries.

The results show a large variation of heat transfer enhancement and pressure loss over the various turbulator geometries investigated. Also, the complex flow structures lead to highly differentiated results for leading edge, pressure, suction and web surfaces. Although some configurations with higher ribs lead to increased heat transfer, the associated pressure losses are also shown to increase substantially.
Hydrogen Fueled Dry Low NOx Gas Turbine Combustor Conceptual Design
Authors: Cerutti Matteo , Cocchi Stefano , Modi Roberto , Sigali Stefano , Bruti Gualtiero
Published: September 2014

Conceptual design of a hydrogen fueled dry low NOx combustor for heavy duty gas turbine is presented in this paper, including a complete experimental validation, with focus on both NOx emissions and operability. Effort was first provided in the identification of viable conceptual solutions: a technology screening has been carried out, balancing both innovation content and proven experience of each concept. A look to alternative solutions coming from literature has been given too. Three burner concepts have been selected, designed and procured to be tested into a reduced scale rig, arranged to mimic main features of a small size gas turbine combustor, in terms of combustion air inlet temperature, hot gases residence times and amount of cooling: atmospheric pressure operation was considered a proper approximation to actual operating conditions for a conceptual design phase. The three solutions have been first characterized in terms of emissions against equivalence ratio, pilot percentage and burner pressure drop. At the same time, safe operation margins to both flashback and combustion instabilities onset have been identified for both pure hydrogen and pure natural gas feeding options. Results, while recommending different development paths for each of the investigated concepts, clearly indicate the most mature among them, allowing authors to address specific operability detailed investigations on it: flashback and flame holding resistance tests were thus performed, demonstrating that such a solution is mature for a preliminary full scale arrangement design and experimental characterization.
An Application of Metal Plasticity in Finite Element Modeling to Predict the Low-Cycle Fatigue Life of a High-Pressure Steam Turbine Casing
Authors: Dyer Zachary , Altland George C.
Published: September 2014

In the current market for large steam turbines, customers increasingly want to aggressively cycle their equipment to accommodate electrical grids that include fluctuating supplies of green energy. Increased and aggressive cycling leads to higher probability of low-cycle-fatigue cracking and provides motivation for the design of new steam turbines that are robust enough to withstand this demanding working environment yet still meet the operational and cost expectations of potential customers.

ASME BPVC Section III Subsection NH provides a calculation for fatigue damage assessment using either an elastic method or an inelastic method. This paper describes how the inelastic method can be applied to large steam turbines — calculating low-cycle fatigue damage by using commercial finite element software and plastic material models to directly determine elastic-plastic strains throughout the cycle, rather than approximating them using the results of an elastic analysis. The inelastic method is applied to a steam turbine casing during startup cycles — the total strain through the cycle is calculated directly by the elastic-plastic finite element analysis (FEA) then the delta equivalent total strain is calculated using equations in Subsection NH. For comparison, an elastic method is applied to the same analysis — the maximum elastic stress is calculated by the linear-elastic FEA then the delta equivalent total strain is approximated using Neuber’s rule.

The inelastic method calculates a smaller delta equivalent total strain, which leads to significantly increased fatigue life. This more sophisticated method could lead to steam turbine components with less cost, more durability, and better performance. This paper also discusses some issues in using the inelastic method, such as shakedown and ratcheting.
Aerodynamics of Boundary Layer Ingesting Fans
Authors: Gunn E. J. , Hall C. A.
Published: September 2014

Boundary Layer Ingesting (BLI) turbofan engines could offer reduced fuel burn compared with podded engines, but the fan stage must be designed to run continuously with severe inlet distortion. This paper aims to explain the fluid dynamics and loss sources in BLI fans running at a cruise condition. High-resolution experimental measurements and full-annulus unsteady CFD have been performed on a low-speed fan rig running with a representative BLI inlet velocity profile. A three-dimensional flow redistribution is observed, leading to an attenuation of the axial velocity non-uniformity upstream of the rotor and to non-uniform swirl and radial angle distributions at rotor inlet. The distorted flow field is shown to create circumferential and radial variations in diffusion factor with a corresponding loss variation around the annulus. Additional loss is generated by an unsteady separation of the casing boundary layer, caused by a localised peak in loading at the rotor tip. Non-uniform swirl and radial angles at rotor exit lead to increased loss in the stator due to the variations in profile loss and corner separation size. An additional CFD calculation of a transonic fan running with the same inlet profile is used to show that BLI leads to wide variations in rotor shock structure, strength and position and hence to loss generation through shock-boundary layer interaction, but otherwise contained the same flow features as the low-speed case. For both fan geometries, BLI was found to reduce the stage efficiency by around 1–2% relative to operation with uniform inlet flow.
Influence of Volute Cross-Sectional Shape of a Nozzleless Turbocharger Turbine Under Pulsating Flow Conditions
Authors: Yang Mingyang , Martinez-Botas Ricardo , Rajoo Srithar , Yokoyama Takao , Ibaraki Seiichi
Published: September 2014

This paper presents an experimental and computational investigation of the influence of volute cross-sectional shape on the performance of a radial turbocharger turbine under pulsating conditions. Two volute configurations (denoted volute A and B) with the same area-to-radius ratio (A/R) distribution but different aspect ratios are rapid prototyped and tested with a same radial rotor. Experimental results show that the turbine with smaller aspect ratio volute (volute A), which has a squarish shape, shows consistently better cycle averaged efficiency at different loadings and frequencies, and the magnitude of improvement is influenced by the operational conditions. In consequent to experiments, a reduced order unsteady computational fluid dynamics (CFD) method was employed to investigate the mechanism of the performance discrepancies between volute A and B. Computational results show a stronger flow angle distortion in both circumferential and spanwise direction for volute B. Furthermore, compared with the volute A, the flow distortion near the shroud at the rotor inlet is evidently amplified by the volute B under pulsating conditions compared with the corresponding steady condition. Results in this paper, in general, demonstrate a direction for desired volute cross-sectional shape to be used in a turbocharger radial turbine.