bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Assessment of Fan-Ducting Coupling for Gas Turbine Ventilation Systems
Authors: Corsini Alessandro , Delibra Giovanni , Minotti Stefano , Rossin Stefano
Published: August 2015

Gas turbines enclosures entail a high number of auxiliary systems which must be preserved from heat, ensuring therefore the long term operation of the internal instrumentation and of the data acquisition system. A dedicated ventilation system is designed to keep the enclosure environment sufficiently cool and dilute any gas coming from potential internal leakage to limiting explosion risks. These systems are equipped with axial fans, usually fed with air coming from the filter house which provides air to the gas turbine combustion system, through dedicated filters. The axial fans are embedded in a ducting system which discharges fresh air inside the enclosure where the gas turbine is housed. As the operations of the gas turbine need to be guaranteed in the event of fan failure, a backup redundant system is located in a duct parallel to the main one. One of the main requirements of a ventilation fan is the reliability over the years as the gas turbine can be installed in remote areas or unmanned offshore platforms with limited accessibility for unplanned maintenance.

For such reasons, the robustness of the ventilation system and a proper understanding of coupling phenomena with the axial fan is a key aspect to be addressed when designing a gas-turbine system. Here a numerical study of a ventilation system carried out with RANS and LES based methodologies will be presented where the presence of the fan is synthetized by means of static pressure discontinuity. Different operations of the fans are investigated by means of RANS in order to compare the different operating points, corresponding to 1) clean and 2) dirty filters operations, 3) minimum and 4) maximum pressure at the discharge section. Large Eddy Simulations of the same duct were carried out in the maximum loading condition for the fan to investigate the unsteady response of the system and validate its correct arrangement.

All the simulations were carried out using OpenFOAM, a finite volume open source code for CFD analysis, treating the filters as a porous medium and the fan as a static pressure discontinuity according to the manufacturer’s characteristic curve. RANS modelling was based on the cubic k-ε model of Lien et al. while sub-grid scale modelling in LES was based on the 1 equation model of Davidson.

Computations highlighted that the ventilation system was able to work in similarity for flow rates between 15 m3/s and 23.2 m3/s and that the flow conditions onto the fan suggest that the aerodynamic stress on the device could be reduced introducing in the duct flow straighteners or inlet guided vanes.
Vortices and Performance of Internal and External Volutes
Authors: Chen Hua , Tong Ding , Wang Xiaochun
Published: August 2015

In this paper, the cross flow in several internal and external volutes of a small centrifugal compressor is examined to highlight its effects on compressor performance. Different levels of the loss associated with shear stress related to the vortices in the volute cross section are shown to be the reason behind the diverse performance of internal volutes and external volutes. A numerical simulation is carried out to substantiate this and to further study this effect of cross sectional shape of volutes.
The Role of Alkali in Agglomeration During Combustion in Fluidised Beds
Authors: Akram Muhammad , Tan C. K.
Published: August 2015

Biofuels originating from process industries as by-products can be utilised to produce onsite power which can reduce their dependence on the National Grid. Beet Sugar industry by-products vinasse, raffinate and pressured sugar beet pulp are co-fired with Thoresby coal in a 25kW fluidised bed combustor. Agglomeration indices were used and muffle furnace tests were carried out before firing the materials in order to pre-assess the suitability of the materials for the firing tests as well as for finding out validity of indices and muffle furnace tests in relation to actual firing tests. The effect of the presence of alkali and its concentration in the fuel on the onset of agglomeration is investigated. Presence of Calcium in coal ash extends de-fluidization time which indicates that lime can be used as a bed material to increase operational times while firing these troublesome fuels. However, no signs of agglomeration were observed during prolonged tests with blends of coal and pressed pulp. Therefore, pulp can be used as fuel in fluidised bed without the use of alkali getters as long as operational parameters are properly controlled. But, vinasse and raffinate can’t be used without adapting measures such as addition of alkali getters to reduce agglomeration. It is found that accumulation of alkali as well as its feed rate in to fluidised bed are very important parameters in determining agglomeration behaviour of the bed.
Aeroacoustic Computational Analysis of a Steam Turbine Trip Valve
Authors: Bianchini C. , Da Soghe R. , Cosi L. , Imparato E.
Published: August 2015

The continuously growing request for high operational flexibility and extreme customization also for large scale steam turbine creates new challenges in the design of steam machineries. Most components in fact need to be operated, and hence verified, in conditions far from those they were originally designed for. Constant upgrade of selection tools for the assembly of the engine is thus required to extend correlations applicability range for both averaged aerodynamic performance and unsteady effects of critical components. In this context a trip valve of a medium sized steam turbine was analyzed by means of CFD analysis. The investigation had two principal objectives: the estimate of aerodynamic losses within the valve and the evaluation of fluctuating loads effects.

For the time averaged behavior, first pressure losses across the strainer band were evaluated through a detailed simulation of the filter geometry in a simplified configuration to characterize an equivalent distributed momentum loss in the complete domain. Steady state solutions of the flow within the valve and the diffuser were then obtained for the entire range of operations to evaluate the global valve loss coefficient.

The unsteady steam behavior is predicted by means of the Scale Adaptive Simulation principle to evaluate major characteristic frequencies and verify fluctuations amplitudes on critical points.

Finally an acoustic propagation analysis is performed to estimate possible interactions between aerodynamic forcing and proper acoustic modes both verifying sufficient decoupling between aerodynamic and acoustic proper frequencies and analysing the forced acoustic response when subjected to registered pressure fluctuations.
Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part B — Scale-Resolving Simulations
Authors: Drechsel Bastian , Müller Christoph , Herbst Florian , Seume Joerg R.
Published: August 2015

This paper examines the diffuser flow with consideration to turbine outflow conditions. The setup consists of a low-speed axial diffuser test rig, that represents a 1/10 scaled heavy-duty exhaust diffuser with an annular and a conical diffuser part. In part A of this paper it was shown through experimental investigation that the turbulent kinetic energy as well as the Reynolds shear stresses are the relevant physical parameters that correlate with diffuser pressure recovery. To complement the experimental investigations, unsteady scale-resolving CFD simulations are performed, applying the SST-SAS turbulence model. As a first step, the numerical approach is validated by means of the experimental data with regards to the diffuser’s integral parameters as well as the prediction of local flow characteristics. In a second step, the interaction of coherent vortices generated by the rotor and the diffuser’s boundary layer are analyzed by means of the validated SST-SAS results. These vortices are found to have a major impact on the boundary layer separation in the region immediately downstream of the rotor and at the diffuser inlet.
Optimization of Tilting-Pad Journal Bearings for Integrally Geared Compressors
Authors: Havlik Nico , Lutz Michael
Published: August 2015

Tilting-pad journal bearings (TPJBs) support highly loaded high speed rotors with high requirements on rotordynamic behavior. Typical applications therefore are integrally geared compressors, where the gear force of the high speed pinions (HSPs) is at least one magnitude higher than the gravity force.

A continuously rising demand for increasing the overall efficiency of integrally geared compressors leads to a necessity to expand TPJBs operation limits. Allowable limits of actual bearings often result in limitations for thermodynamical compressor design. In addition, bearings generate 20% to 40% of the mechanical power losses in integrally geared compressors. Improvements in the bearing design have to be performed in order to meet the challenges of rising loads and speeds.

This paper presents an optimization of TPJBs for integrally geared compressors to meet the further demand of higher operation limits.
Flowfield and Heat Transfer Numerical Analysis of a Stator Vane Endwall With High Freestream Turbulence
Authors: Andreini A. , Bianchini C. , Burberi E. , Facchini B. , Abram R. , Licata D. , Spataro G.
Published: August 2015

Among the different parts subjected to hot gas flow, endwall heat transfer evaluation is particularly challenging because the flow is strongly affected by secondary effects. Large three-dimensional flow structures introduce remarkable spatial variation of heat transfer, both along streamwise and spanwise directions, making the use of simplified modelling approaches questionable in terms of reliability, and at the same time increasing the challenge for high fidelity computational methods.

The aim of the present contribution is to describe the work done in the assessment of computational methods for the estimate of high pressure vane endwall heat transfer for industrial applications. Efforts were first devoted to the development and validation of an accurate computational procedure against a large set of aerodynamic and heat transfer data, available from literature, for both airfoil and endwall of a low-pressure linear cascade with low and high inlet turbulence levels.

The analysis, focused on steady state computations, is principally devoted to the turbulence modelling assessment, including non-linear turbulence closure as well as transition modelling.

Obtained results showed that the aerodynamics of both passage and endwall are well captured independently of the turbulence modelling while a large impact on both pattern and averaged value is verified for the heat transfer.
Turbulent Scale Resolving Modelling of Rotating Stall in Low-Pressure Steam Turbines Operated Under Low Volume Flow Conditions
Authors: Megerle Benjamin , Rice Timothy Stephen , McBean Ivan , Ott Peter
Published: August 2015

Non-synchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors.

Unsteady computational fluid dynamics (CFD) has been applied to simulate the rotating stall phenomenon in two model turbines. It is shown that the investigated flow field presents a challenge to conventional Reynolds-averaged Navier–Stokes equations simulations. The modelling has been enhanced by applying scale-resolving turbulence modelling, which can simulate large-scale turbulent fluctuations. With this type of simulation a qualitative and quantitative agreement between CFD and measurement for the unsteady and time averaged flow field has been achieved.

The results of the numerical investigation allow for a detailed insight into the dynamic flow field and reveal information on the nature of the excitation mechanism. It is concluded that the CFD approach developed can be used to assess LSMB blade designs prior to model turbine tests to check whether they are subjected to vibration under LVF caused by rotating stall.
Transonic Turbine Cascade Measurements for a Variable Speed Power Turbine Blade at Low to Moderate Reynolds Numbers: Aerodynamic Loss Surveys
Authors: Long J. A. , Moualeu L. P. G. , Hemming N. J. , Ames F. E. , Suzen Y. B.
Published: August 2015

The influence of low to moderate Reynolds number and low to moderate turbulence level on aerodynamic losses is investigated in an incidence tolerant turbine blade cascade for a variable speed power turbine. This work complements midspan heat transfer and blade loading measurements which are acquired in the same cascade at the same conditions. The aerodynamic loss measurements are acquired to quantify the influence of Reynolds number and turbulence level on blade loss buckets over the wide range of incidence angles for the variable speed turbine. Eight discrete incidence angles are investigated ranging from +5.8° to −51.2°. Noting that the design inlet angle of the blade is 34.2° these incidence angles correspond to inlet angles ranging from +40° to −17°. Exit loss surveys, presented in terms of local total pressure loss and secondary velocities have been acquired at four exit chord Reynolds numbers ranging from 50,000 to 568,000. These measurements were acquired at both low (∼0.4%) and moderate (∼4.0%) inlet turbulence intensities. The total pressure losses are also presented in terms of cross passage averaged loss and turning angle. The resulting loss buckets for passage averaged losses are plotted at varied Reynolds numbers and turbulence condition. The exit loss data quantify the impact of Reynolds number and incidence angle on aerodynamic losses. Generally, these data document the substantial deterioration of performance with decreasing Reynolds number.
A Fully Coupled Aero, Thermal, and Structural Lifetime Model for Root Cause Failure Analysis and Robust Redesign of an Industrial F Class Gas Turbine Blade
Authors: Houck Lonnie , Sewell DeAnna , Burke Megan , Vogel Gregory
Published: August 2015

Modern large frame F, G, & J class gas turbine flow path component design requires the complex integration of multiple design disciplines that traditionally reside with distinct specialists. A traditional design system for an actively cooled gas turbine blade includes aerodynamicists, heat transfer engineers, structural engineers and a failure or lifetime prediction engineers passing information through a manual process with a small number of iterations between the disciplines. Design or manufacturing engineers can also be involved ensuring manufacturability and policing best practices in a predominantly deterministic design system. Over the past few decades robust design or probabilistic design philosophies along with cluster computing advancements have accelerated the release of commercial software that allows for the automation of multiple analytical evaluations at off design points. These software codes allow for process automation of several independent codes executed multiple times at various conditions for automated design of experiment (DOE), and reliability analysis using Monte Carlo or other advanced approximate probabilistic methods across the entire design system.

In this paper, the authors are presenting a novel approach of using a commercially available process integration tool to fully integrate a series of other commercially available tools for a root cause failure analysis of a F class turbine blade rather than a new make design. The analysis incorporated a computational fluid dynamics model (CFD) to define inlet temperatures and pressure profiles, a fully conjugate thermal analysis interacting with a finite element (FEA) solver linked to a proprietary creep lifetime prediction model. A DOE was executed to define the meaningful parameters and help rule out potential causes of failure such as loss of coating or compromised cooling system as a contributing factor of the failure which greatly reduced the amount of time and money needed for the investigation. A probabilistic failure analysis was then executed and surrogate models created for quick probabilistic assessment for different operating conditions. This allowed for validation against fleet history to explain the single engine failure not previously observed. Setting up the non-deterministic models initially allowed for rapid redesign in less than 1 month time with confidence that the true root cause was identified and mitigated. It further allowed for feedback and calibrations to the traditional design system methodology.
Rapid Airfoil Design for Uncooled High Pressure Turbine Blades
Authors: Moradi Niloofar , Vlasic Edward , Moustapha Hany
Published: August 2015

The aero-engine design process is highly iterative, multidisciplinary in nature and complex. The success of any engine design depends on best exploiting and considering the interactions among the numerous traditional engineering disciplines such as aerodynamics and structures. More emphasis has been placed lately on system integration, cross disciplines leveraging of tools and multi-disciplinary-optimization at the preliminary design phase. This paper investigates the automation of the airfoil generation process, referred to as Rapid Airfoil 3D (RAF 3D), for uncooled high pressure turbine blades at the preliminary design phase. This Matlab based program, uses the turbine aero meanline (TAML) in parallel with a database of previously designed P&WC airfoils, in-house design rules and best practices to define a pre-detailed airfoil shape which can be fed back to other analytical groups for pre-detail analyses, such as for structures and vibrations. Resulting airfoil shapes have been aerodynamically validated using an in-house 3D RANS code.

RAF 3D will shorten the turnaround time for P&WC’s turbine aerodynamics group to provide a preliminary 3D airfoil shape to turbine structures group by up to a factor of ten. Additionally, the preliminary assessments of stress and vibration specialists will be more accurate as their assessments will be based on an airfoil that has had inputs from all functional groups even though it is “first pass” design.
Flame Area Fluctuation Measurements in Velocity-Forced Premixed Gas Turbine Flames
Authors: De Rosa Alexander J. , Samarasinghe Janith , Peluso Stephen J. , Quay Bryan D. , Santavicca Domenic A.
Published: August 2015

Fluctuations in the heat release rate that occur during unstable combustion in lean premixed gas turbine combustors can be attributed to velocity and equivalence ratio fluctuations. For a fully premixed flame, velocity fluctuations affect the heat release rate primarily by inducing changes in the flame area. In this paper, a technique to analyze changes in flame area using chemiluminescence-based flame images is presented. The technique decomposes the flame area into separate components which characterize the relative contributions of area fluctuations in the large scale structure and the small scale wrinkling of the flame. The fluctuation in the wrinkled area of the flame which forms the flame brush is seen to dominate its response in the majority of cases tested. Analysis of the flame area associated with the large scale structure of the flame resolves convective perturbations that move along the mean flame position. Results are presented that demonstrate the application of this technique to both single-nozzle and multi-nozzle flames.
Experimental and Numerical Study of Return Channel Flow Influence on Surge Margin of a Multi-Stage Centrifugal Compressor
Authors: Nishida Yoshifumi , Nishida Hideo , Kobayashi Hiromi , Nishioka Takahiro
Published: August 2015

Experimental and numerical studies were performed to investigate influences of the return channel flow on the surge margin of a multistage centrifugal compressor. Two return channels, which were named RCH-A and RCH-B, were designed and evaluated in a two-stage centrifugal compressor. The measured performance of the compressor suggested that the surge margin of this compressor was dominated by the operating limit of the second stage and that the surge margin of RCH-B was 5% larger than that of RCH-A. The outlet flow of RCH-A and RCH-B swirled in a counter-rotating direction near the shroud region, and the flow angle at the outlet of RCH-A was larger than that of RCH-B. CFD was conducted to investigate the internal flow in the return channel. The CFD results of both RCH-A and RCH-B showed that the flow separation occurred on the suction surface of the return vanes near the operating limit. This separation induced the velocity difference between the suction and pressure sides, and the swirl flow in the counter-rotating direction was generated by this velocity difference. The swirl flow in the counter-rotating direction increased the blade loading of the second stage impeller at the operating limit. It was considered that the blade loading of RCH-B was lower than that of RCH-A at the operating limit, because the swirl flow in the counter-rotating direction of RCH-B was weaker than that of RCH-A. Therefore, the surge margin of the second impeller with RCH-B seemed to be larger than that with RCH-A. It was conclude from the experimental and numerical results that the locally swirl flow in the counter-rotating direction at the outlet of the return channels near the shroud side influenced the surge margins of the downstream impeller and the multi-stage centrifugal compressor.
A New Melting Model in Electrothermal De-Icing Simulation
Authors: Lei Guilin , Dong Wei , Zhu JianJun , Zheng Mei
Published: August 2015

A melting model which is based on the Enthalpy-Porous Medium method is applied to study the transient heat transfer and ice melting process in a multi-layered body which was covered by ice and heated by electrothermal de-icing system. Three typical cases including one-dimensional, two-dimensional and three-dimensional model are studied. The liquid fraction is computed based on the enthalpy balance. The mushy zone is modeled as a pseudo-porous medium in which the porosity ranges from 0 (solid) to 1 (liquid) as the ice melting. The melting time and process are both investigated as well as the ice-water interface profiles and water thickness for the three typical geometries. The computational results show that the melting model is valid for simulating the process of transient heat transfer and ice-melting. The Enthalpy-Porous Medium method can be used to study thermal de-icing systems of aircraft or aeroengine inlet. The method can also be used to judge the ice shedding. A parallel interface is introduced at the position of 0.2 mm away from the ice/abrasion shield interface to simulate ice shedding. The computational results show that the new melting model is effectiveness and can be used to provide detailed information for de-icing system design.
Failure of a Test Rig Operating With Pressurized Gas Bearings: A Lesson on Humility
Authors: San Andrés Luis , Rohmer Michael , Park Sangshin
Published: August 2015

Process fluid lubrication of rotating machinery offers advantage of compactness and efficiency while dispensing with complicated oil lubricant supply systems. Prior work in a dedicated test rig demonstrated the performance of water lubricated radial and thrust bearings into high speed and high load conditions. The application related to a high performance rocket engine turbo pump. The test rig was revamped to operate with gas bearings in a program aiming to measure the performance of gas thrust bearings. The gas bearings for lateral support of the rotor are of hybrid type (hydrostatic/hydrodynamic) with flexure pivots and multiple ports for inlet gas pressurization. The paper details the design of the flexure pivot bearings and predictions of the lateral rotordynamics of the rotor supported on the hybrid gas bearings. Troubleshooting operation of the test rotor supported on the novel gas bearings followed with preliminary runs with the bearings supplied with air at 7.9 bar, then 6.5 bar and at 5.1 bar, and shaft speeds to 25 krpm (surface speed=50 m/s). The data recorded showed a very lightly damped system with a critical speed at ∼6 krpm, and susceptible to excite sub synchronous whirl motions when operating above the first critical speed. Ignoring the initial warnings, the operator persisted in operating the rotor to a high speed of 28 krpm while lowering the air supply pressure to 5.1 bar into the bearings. Suddenly, the shaft experienced large amplitude sub synchronous whirl motions, contacted the bearings, and produced a catastrophic failure. The incident produced much damage including a broken coupling, a twisted rotor, sheared covers, and welded pads into the bearing casing. Post-mortem analysis shows the failure is due to a sub synchronous whirl instability of the first rigid body rotor-bearing mode also exacerbated by the rotor approaching second natural frequency of the rotor-bearing system. The rotordynamics model includes the rotor rigidly connected to a long quill shaft and coupling produces results in agreement with the last vibration data set acquired prior to the incident. The experience demonstrates the need for following proper operating procedures while also paying attention to early evidence that could have prevented the mishap.
3D Blade Stacking Strategies and Understanding of Flow Physics in Low Pressure Steam Turbines: Part I — 3D Stacking Mechanisms
Authors: Havakechian Said , Denton John
Published: August 2015

Optimization of blade stacking in the last stage of Low Pressure (LP) steam turbines constitutes one of the most delicate and time consuming parts of the design process. This is the first of two papers focusing on the stacking strategies applied to the last stage guide vane (G0). Following a comprehensive review of the main features that characterize the LP last stage aerodynamics, the 3D CFD code used for the investigation and options related to modeling of wet steam are described. Aerodynamic problems related to the LP last stage and the principles of 3D stacking are reviewed in detail. In this first paper the results of a systematic study on an isolated LP stator row are used to elucidate the effects of stacking schemes such as lean, twist, sweep and hub profiling. These results show that stator twist has the most powerful influence on the reaction variation but it also produces undesirable spanwise variations in angular momentum at stator exit. These may be compensated by introducing a positive stagnation pressure gradient at entry to the last stage.
Assessment of Unsteady Pressure Measurement Uncertainty: Part 1 — Single Sensor Probe
Authors: Dell’Era Giulia , Mersinligil Mehmet , Brouckaert Jean-François
Published: August 2015

With the advancements in miniaturization and temperature capabilities of piezo-resistive pressure sensors, pneumatic probes — which are the long established standard for flow-path pressure measurements in gas turbine environments — are being replaced with unsteady pressure probes. Any measured quantity is by definition inherently different from the ‘true’ value, requiring the estimation of the associated errors for determining the validity of the results and establishing respective confidence intervals. In the context of pressure measurements, the calibration uncertainty values, which differ from measurement uncertainties, are typically provided. Even then, the lack of a standard methodology is evident as uncertainties are often reported without appropriate confidence intervals. Moreover, no time-resolved measurement uncertainty analysis has come to the attention of the authors.

The objective of this paper is to present a standard method for the estimation of the uncertainties related to measurements performed using single sensor unsteady pressure probes, with the help of measurements obtained in a one and a half stage low pressure high speed axial compressor test rig as an example. The methodology presented is also valid for similar applications involving the use of steady or unsteady sensors and instruments.

The static calibration uncertainty, steady measurement uncertainties and unsteady measurement uncertainties based on phase-locked and ensemble averages are presented in this contribution. Depending on the number of points used for the averaging, different values for uncertainty have been observed, underlining the importance of having greater number of samples. For unsteady flows, higher uncertainties have been observed at regions of higher unsteadiness such as tip leakage vortices, hub corner vortices and blade wakes.

Unfortunately, the state of the art in single-sensor miniature unsteady pressure probes is comparable to multi-hole pneumatic probes in size, preventing the use of multi-hole unsteady probes in turbomachinery environments. However, the angular calibration properties of a single sensor probe obtained via an aerodynamic calibration may further be exploited as if a three-hole directional probe is employed, yielding corrected total pressure, unsteady yaw angle, static pressure and Mach number distributions based on the phase-locked averages with the expense of losing the time-correlation between the virtual ports. The aerodynamic calibration and derivation process are presented together with the assessment of the uncertainties associated to these derived quantities by the authors in [1]. In the virtual three-hole mode, similar to that of a single-sensor probe, higher uncertainty values are observed at regions of higher unsteadiness.
Aerothermodynamic Design and Numerical Investigation of Supercritical Carbon Dioxide Turbine
Authors: Zhang Hanzhen , Zhao Hang , Deng Qinghua , Feng Zhenping
Published: August 2015

Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in power conversion systems, as SCO2 power cycle has several advantages of the modest turbine inlet temperature, smaller compression work and more compact layout compared with some traditional cycle. For SCO2 turbines, the main challenge is to achieve a design scheme to meet the aerothermodynamics request, geometry restriction, structural strength, and component functionality requirements while in consideration of the applicable materials. This paper conducts the selection and verification of SCO2 turbine types and rotational speeds when the required power outputs are 15MW and 1.5MW. The type of turbine for the 15MW is an axial one and for the 1.5MW is a radial one, respectively. A numerical investigation on the aerothermodynamics design, geometrical design, and overall performance prediction of the two different SCO2 turbines are performed. Actual properties of the SCO2 are input to the model from the Refprop database provided by the US National Institute of Standards and Technology (NIST). The detailed aerodynamic analysis is carried out based on a complete three-dimensional model of the whole passages of nozzle vane and rotor flow field by the commercial CFD software-NUMECA. In addition, the strength analysis of the turbine is performed using the commercial software ANSYS/Mechanical, and the effect of the working fluid pressure load is taken into consideration.
Effects of Inlet Swirl on Hot Streak Migration Across Tip Clearance and Heat Transfer on Rotor Blade Tip
Authors: Liu Zhaofang , Wang Zhiduo , Feng Zhenping
Published: August 2015

This paper presents an investigation on the hot streak migration across tip clearance and heat transfer on blade tip in a high pressure (HP) gas turbine with different inlet swirl directions and clocking positions. The geometry is taken from the first stage of GE-E3 turbine engine. Two swirl directions (positive and negative) and two circumferential clocking positions (aligning with S1 nozzle leading edge and mid passage) for inlet hot streak and swirl have been employed and investigated, respectively. Two cases with only hot streak at different inlet circumferential positions are adopted as the baseline in this study. By solving the unsteady compressible Reynolds-averaged Navier-Stokes equations, the time dependent solutions were obtained. The results indicate that the influence of inlet swirl on pressure distribution focuses on the suction side. Positive swirl attracts more hot fluid to the upper endwall, when it aligns with nozzle stator leading edge. Because of the squeezing mechanism between positive swirl and leakage flow, the heat transfer on rotor blade tip is more uniform. While negative swirl increases tip leakage flow and the heat load at the first half on tip surface. In all cases with swirl, the heat load at the second half on blade tip is effectively reduced, which is good for cooling rotor blade tip. If the stator is cooled effectively, inlet positive swirl aligning with nozzle vane leading edge will be the best choice for protecting rotor blade tip. By comparing with the results of previous literature, it is concluded that whatever arrangement the blade rows locate, the swirl direction which is opposite to the leakage flow should be chosen for protecting not only blade surface but also blade tip when the inlet swirl exists.
Investigation of the Dynamics of an Ultra Low NOx Injection System by POD Data Post-Processing
Authors: Berrino M. , Lengani D. , Satta F. , Ubaldi M. , Zunino P. , Colantuoni S. , Di Martino P.
Published: August 2015

The present paper is focused on the investigation of the dynamics of the flow downstream of an Ultra Low NOx (ULN) injection system, designed to reduce NOx emissions and combustor axial length. Two rectangular flame tubes have been experimentally investigated: one aimed at simulating an unconfined exit flow, and another with the same transverse dimensions of the combustor annular sector, to simulate the confined flow field. The effects induced by the realistic flame tube presence are investigated comparing the flow field with that generated in the unconfined case. Particular attention is paid to the vortex breakdown phenomena associated with the flow generated by the two co-rotating swirlers constituting the injection system.

Two different and complementary measurement techniques have been adopted to characterize the aerodynamics of the vortex breakdown. The hot-wire investigation results reveal the frequencies associated with the precession motion due to the vortex breakdown. The Particle Image Velocimetry technique has been coupled with Proper Orthogonal Decomposition (POD) for data post-processing in order to reconstruct the swirling motion generated by the injection system. The property of POD, which consists of splitting temporal from spatial information of the flow field in analysis, allows the distinction between deterministic and random fluctuations without the need of an external trigger signal. This feature is fundamental for the better understanding of an highly-swirling flow.
Experimental Investigation of Circumferential Groove Casing Treatments for Large Tip Clearances in a Low Speed Axial Research Compressor
Authors: Rolfes Matthias , Lange Martin , Vogeler Konrad
Published: August 2015

In high pressure compressors large tip clearances can occur in the rear stages especially during transient operation. This can lead to a reduced operating range and performance of the compressor. One simple means to reduce the negative effects of a rotor tip clearance increase can be circumferential groove casing treatments. Their ability to improve the operating range of a compressor is well-known for several decades.

In this paper, an experimental study to investigate the influence of three different circumferential groove casing treatments on a low speed axial research compressor with very large rotor tip clearances (5% of annulus height) is presented. Two single-groove and one double-groove casing treatments have been tested. The grooves are positioned from 31% to 69% axial chord. The compressor characteristics of the smooth wall and the three groove configurations are discussed as well as selected five-hole probe measurements of the flow field downstream the rotor. It can be shown that all grooves are able to improve the operating range of the compressor. Furthermore, an improvement of efficiency due to the casing grooves can also be observed in certain operating points.
An Evaluation of Vaneless Diffuser Modelling Methods as a Means of Improving the Off-Design Performance Prediction of Centrifugal Compressors
Authors: Stuart Charles , Spence Stephen , Filsinger Dietmar , Starke Andre , Kim Sung In , Harley Peter
Published: August 2015

An evaluation of existing 1-D vaneless diffuser design tools in the context of improving the off-design performance prediction of automotive turbocharger centrifugal compressors is described. A combination of extensive gas stand test data and single passage CFD simulations have been employed in order to permit evaluation of the different methods, allowing conclusions about the relative benefits and deficiencies of each of the different approaches to be determined. The vaneless diffuser itself has been isolated from the incumbent limitations in the accuracy of 1-D impeller modelling tools through development of a method to fully specify impeller exit conditions (in terms of mean quantities) using only standard test stand data with additional interstage static pressure measurements at the entrance to the diffuser. This method allowed a direct comparison between the test data and 1-D methods through sharing common inputs, thus achieving the aim of diffuser isolation.

Crucial to the accuracy of determining the performance of each of the vaneless diffuser configurations was the ability to quantify the presence and extent of the spanwise aerodynamic blockage present at the diffuser inlet section. A method to evaluate this critical parameter using CFD data is described herein, along with a correlation for blockage related to a new diffuser inlet flow parameter ⚡, equal to the quotient of the local flow coefficient and impeller tip speed Mach number. The resulting correlation permitted the variation of blockage with operating condition to be captured.
Turbine Stator Well Cooling: Improved Geometry Benefits
Authors: Pohl Julien , Dixon Jeffrey A. , Fico Vincenzo
Published: August 2015

Nowadays, it is common practice to expose engine components to air temperatures exceeding the thermal material limit in order to increase the overall engine performance and to minimise the engine specific fuel consumption (SFC). To avoid the overheating of the materials and thus the reduction of the component life, an internal flow system is designed to cool the critical engine parts and to protect them. As the coolant flow is bled from the compressor and not used for the combustion the amount of coolant is aimed to be minimised as much as possible to preserve the overall engine performance. Experiments as well as numerical simulations have shown that with the use of a deflector plate, the cooling flow is fed more directly into the disc boundary layer, allowing more effective use of less cooling air, leading to an improved engine efficiency. In this paper, the benefits of the use of a stationary deflector plate inside a turbine stator well (TSW) are presented. So far unpublished experimental data obtained from tests carried out in a two-stage turbine rig are presented. The main objective of this research has been to produce reliable methods for predicting the effects of geometry changes in this type of engine cavity, with a view to optimising the cooling flows required to maintain component integrity and life. Therefore, a numerical methodology is presented and validated against the experimental data. Steady and unsteady computational fluid dynamics (CFD) calculations of a sector model are used to determine whether fluid side flow distributions and heat transfer can be adequately represented, as well as to expose the limits of these approaches. The main annulus geometry is meshed with a multi-block structured mesh using the in-house code PADRAM. The cavity geometry is meshed once with a multi-block structured mesh using the commercial tool ANSYS ICEM and once with an unstructured mesh using the in-house code PADRAM. The CFD calculations are carried out with the commercial code FLUENT from ANSYS as well as the in-house code HYDRA. Finally, for the cavity with the deflector plate and no net ingestion, the steady state solution of the CFD is coupled to a finite element analysis (FEA) model created in the in-house code SC03 in order to take the conjugate effects into account. With this method the final non-adiabatic flow field inside the cavity as well as the final metal temperatures are obtained, which again are compared against thermocouple measured data in order to evaluate the accuracy of the numerical prediction method.
Parametric and Comparative Assessment of Navier-Stokes CFD Methodologies for Darrieus Wind Turbine Performance Analysis
Authors: Balduzzi Francesco , Bianchini Alessandro , Gigante Fabio Antonio , Ferrara Giovanni , Campobasso Michele Sergio , Ferrari Lorenzo
Published: August 2015

Navier-Stokes computational fluid dynamics simulations are expected to provide the basis for a deeper understanding of the real behavior of vertical-axis wind turbines. The prediction of the flow field past Darrieus rotors, a popular turbine of this type, requires a good resolution of both the unsteadiness caused by the periodic variation of the modulus and direction of the relative velocity perceived by the blades, and the interaction between the wakes shed by the blades in the upstream region of the rotor and the downstream blades traveling through such wakes.

This paper presents a comparative assessment of the predictive capabilities of two substantially different time-dependent Navier-Stokes Reynolds-averaged-based approaches to the analysis of Darrieus turbines. One is based on a commercial code, and the other on an academic research code. A Darrieus rotor configuration previously analyzed by other researchers was selected for this study, which focused on the turbine flow at a tip-speed ratio of 3.3. Aggregate power coefficient comparisons at other regimes are also provided. Solution sensitivity analyses to spatial and temporal grid refinement, domain size and boundary condition modeling aspects for each of the two approaches are provided in the study. A very good agreement is obtained between the two simulation sets, and a fairly good agreement is found between both simulations and available measured data.
Towards Multiple Operating Point Axial Fan Design
Authors: Semel Matthias , Haag Viktor , Delgado Antonio , Grilliat Julien
Published: August 2015

The dimensionless performances of an axial fan are derived analytically from an arbitrary work distribution. The formulation is illustrated using five different work distributions at a selected operating point and comparing the resulting hydraulic characteristics. A first validation of the formulation is brought by means of RANS and URANS of an axial fan with free vortex work distribution. It is shown that a single RANS prediction at the design point allows predicting the hydraulic characteristic up to 20% off the design flow rate with very good accuracy. Based on these results, a strategy for axial fan design at multiple operating points is proposed.
Ring Vane Evaluation in Short Annular Diffusers With Swirling Flow
Authors: Cerantola D. J. , Birk A. M.
Published: August 2015

Ring vanes were recognized as being beneficial for increasing pressure recovery and reducing stall in wide-angled diffusers. Augmentation devices can also reduce swirl-induced flow distortion. A three-point ring vane was inserted into a short annular diffuser with a length-to-inlet-height ratio of 14.5 and area ratio of 4. Numerical optimization studies were completed using the realizable k-ε turbulence model at zero and 12 deg inlet swirl that established a preferential location of the ring vane leading edge. Parametric computational fluid dynamics studies evaluated the influence of the dominant variables — overall length and angle — at 0 to 12 deg inlet swirl. Performance was dependent on the ability of the ring vane to reduce outer wall stall without swirl or the central toroidal recirculation zone with swirl and the ring vane wake. Shorter vanes angled towards the centre reduced back pressure with no swirl whereas longer outward-angled vanes were preferred with 12 deg swirl.
Evaluation of Thermomechanical Fatigue Crack Initiation in a Single-Crystal Superalloy
Authors: Leidermark Daniel
Published: August 2015

In this study the thermomechanical fatigue (TMF) crack initiation of the single-crystal nickel-base superalloy MD2 is investigated and evaluated. A series of experiments are performed of smooth specimens loaded in the nominal [001] and [011] crystal orientations, subjected to both in-phase and out-of-phase TMF loading conditions. Considering the inherent internal structure of crystallographic slip planes in single-crystals, a number of critical-plane approaches are evaluated to enable a good description of the TMF crack initiation. These are evaluated using finite element simulations and a post-process, in which crystallographic entities are extracted and compared to the experimental TMF life. A good correlation is achieved for two of the critical-plane approaches. These are able to predict the TMF crack initiation taking into account the elastic and plastic anisotropy, the tension/compression asymmetry and the creep relaxation present in the material.
Snecma’s Viewpoint on the Numerical and Experimental Simulation of Blade-Tip/Casing Unilateral Contacts
Authors: Millecamps Antoine , Batailly Alain , Legrand Mathias , Garcin François
Published: August 2015

Aircraft engine manufacturers are developping a new generation of turbojet engines featuring a lower impact on the environment, increased performances as well as reduced gas consumption. The efficiency of an engine is mostly driven by the operating clearance between the rotating parts and the stator. Accordingly, modern designs focus on the minimization of these clearances. In this context, unavoidable rotor imbalances or mistuning stemming from manufacturing processes as well as distortions resulting from thermal expansion or assembly conditions may generate blade-tip/casing contacts that are now considered as non-accidental operating conditions. In order to minimize the consequences of such events, an abradable coating is sprayed along the inner surface of the casing and acts as a fuse when the blade and the casing are in contact. However, even when an abradable coating is used, significant structural damages and wear as well as blade failures have been witnessed experimentally. The understanding of the physical phenomena at play called, on one hand, for throrough experimental investigations of rotor/stator contacts on full-scale stages of compressors and underlined that blade failure is mainly due to vibratory fatigue although the abradable coating is worn. On the other hand, numerical simulations have been performed to better understand the blade dynamics: over the last decade Snecma and its academic partners jointly developed a code for the simulation of contacts between rotor and stator: COROS. This code allows for the simulation of contacts — with a Lagrange multiplier contact treatment procedure — between full 3D models of engine components and accounts for abradable coating material removal. In particular, the simulation of experimental set-ups with COROS highlighted the correlation between the blade vibratory response and the abradable material removal. Yet still an experimental code, this paper addresses the integration of COROS within the design process of aircraft engine blades at Snecma. The paper focuses on on-going research for the identification of critical parameters in the arising of interactions as early as the design stage of components. A particular attention is paid to the mechanical properties of the abradable coating for which both experimental and numerical investigations are detailed.