bluuebunny/crossref_metadata_2025 huggingface dataset:
Aero-Thermal Coupled Design Optimization of the Non-Axisymmetric Endwall for a Gas Turbine Blade
Authors: Liu Zhansheng , Yang Xing , Gao Chun , Liu Zhao , Feng Zhenping
Published: August 2018

Modern gas turbine endwall is operating in harsher conditions for the application of low NOx combustor. Non-axisymmetric endwall has been extensively studied for aerodynamic performance improvement, because endwall contouring can decrease the pressure gradient between the pressure side (PS) and the suction side (SS) in the blade passage. In addition to the influence of pressure gradient on aerodynamic losses, the vortical structures induced by pressure gradient are also the sources of high heat transfer regions in the passage. Consequently, thermal loads might be reduced by decreasing the pressure gradient thus weakening the strength of the secondary flows. In terms of engineering applications, distribution of thermal load is very important for the design of endwall cooling scheme, and it is necessary to take both aerodynamic and heat transfer performances into consideration for the endwall profile design. In this work, aero-thermal coupled design optimization of a turbine blade endwall was carried out. The endwall contour was obtained by multiplying heights of two curves in the streamwise and pitchwise directions. The streamwise curve was controlled by non-uniform B-spline (NUBS) and the pitchwise one was obtained by employing the sinusoidal function. The optimization method adopted in this research was the multi-objective genetic algorithm (MOGA) coupled with Kriging (KRG) model, which has been validated by benchmark functions. Numerical validation shows that static pressure coefficients on the blade surfaces and the Nusselt number (Nu) on the endwall agree well with the experimental results. The design variables were the endwall profile parameters, and the objective functions were maximizing total pressure recovery coefficient (ξ) at the blade outlet and minimizing the Nu on the endwall. Two optimal cases were selected from the Pareto front and analyzed in detail. It is indicated that the turbine blade aerodynamic performance can be improved while the heat transfer is restrained simultaneously. For the optimal Case I, mass flow-averaged ξ increases by 0.88%, and for Case II, area-averaged Nu reduces by about 7.78%.
Development and Material Characterization of an Additively Manufactured Nickel Alloy for Turbine Applications
Authors: Day David , Kawecki Edwin , McNally Joshua R. , Rosenbarger Thomas J.
Published: August 2018

The introduction of laser powder bed fusion, and other additive manufacturing processes, represents a disruptive force in the gas turbine industry. While LPBF provides opportunities to create geometries that were impossible with other techniques, a high potential exists to create designs which are also outside the experience of designers and analysts. Some of the most interesting opportunities for an LPBF application are components that would normally be investment cast superalloys. These materials present significant challenges due to their susceptibility to strain age cracking and the importance of creep capability in the final design. In order to minimize the risk of encountering unexpected failures during fabrication or operation, a systematic approach to material development and characterization was needed. This paper will discuss the development of a nickel-based LPBF process, from the selection of powder composition and material processing to optimization the material for its intended application. The formulation of material tests during and after material development will be discussed. Data from the material testing was used first to select required heat-treatments and then to create preliminary material models for use in the design and analysis of turbine hardware. The systematic development of a nickel LPBF manufacturing and material characterization presented in this paper facilitates the design innovative turbine hardware.
Turbofan Nose Cone Interactions With Inlet Swirl
Authors: Frohnapfel Dustin J. , Mack Elizabeth , Untaroiu Alexandrina , O’Brien Walter F. , Lowe K. Todd
Published: August 2018

With highly integrated airframe architectures emerging as the leading concept of next generation aviation vehicles, research is needed to understand the interactions between inlet swirl distortions and turbofan engines. To meet these research demands, a computational fluid dynamics investigation was conducted to monitor the streamwise development of a complex swirling velocity field in the inlet duct of a turbofan engine with and without the presence of the turbofan nose cone component. By modeling the two geometric setups, natural fluid development and forced fluid/nose cone interactions were distinguishable. To validate the model, computational results were compared to existing experimental data at the fan rotor inlet plane. With the nose cone included, flow angle and swirl intensity predictions from the computational approach agreed well with the experimental measurements. The computational results were expanded upstream to demonstrate the effects of the nose cone geometry on the incoming swirl distortion. Radial flow angles in the presence of the nose cone began to vary from natural swirl development at approximately 0.25 fan diameters upstream, reaching a maximum difference near the leading edge of the nose cone component. Results from this investigation provided a validated model for the prediction of swirl development in a turbofan inlet duct in the presence of a nose cone. Significant change in the swirl profile development was shown from natural vortex motion to induced fluid/solid interactions.
Study on Cooling Characteristics of an Internal Cooling Structure With a Sloping Sheet for Gas Turbine Blade
Authors: Wang Xiangyu , Xiao Kun , Feng Zhenping
Published: August 2018

This study presents a cooling structure with a sloping sheet to improve the internal cooling of gas turbine blades, inspired by the concept of aircraft wing tip vortex. In this paper, the numerical simulation for the sloping sheet cooling structure has been carried out, which takes into account the heat conduction of the metallic material and the heat transfer of the external high temperature flow field. The results indicate that the structure utilizes the pressure difference between two sides of the sloping sheet to produce a strong vortex pair. The vortexes are led to the inner wall surface of the turbine blade by the downwash. Thanks to such a strong pair vortex, the high temperature air close to the inner wall is quickly blown out and the low temperature coolant is induced to impact on the internal surface, thus achieving an efficient cooling effect. Due to the strong vortex strength and the same vortex vector along the coolant flows, the pair vortex will travel a long distance in the cooling channel, and cool larger areas of the inner wall surface. According to the calculation results, such structure can make the overall temperature of the solid region decreased by 40K as compared to the smooth channel. The sloping sheet cooling structure can reduce the total pressure loss by 63% as compared to the array of pin fins which achieve the same cooling effect. Furthermore, the influence of the sloping sheet’s inclination angle, length and width on the cooling characteristics has also been studied. Through the strength analysis by FEM method, the maximum von Mises stress is 21.9 MPa and it verifies that the sloping sheet can work securely and firmly.
Numerical Flow Field Analysis in a Highly Bent Intake Duct
Authors: Haug Jakob P. , Rademakers Rudolf P. M. , Stößel Marcel , Niehuis Reinhard
Published: August 2018

In many modern aircraft concepts, civil as well as military ones, the engine is fully integrated into the fuselage. This integration often requires a highly bent intake duct. Due to the high degree of curvature and also the diffusive character of the intake duct, the inflow at the engine’s fan is non-uniform and may feature severe flow distortions. The size, strength, and pattern of these flow distortions may affect the engine’s compressor system and its safety margins. In this paper the flow through a short highly bent intake duct geometry is analysed by means of CFD. The numerical simulations are validated against experimental data, which are obtained in extensive investigations at the institute’s engine test facility. The setup for the numerical investigations is based on previous studies of the aerodynamics of intake ducts at the Institute of Jet Propulsion, where it is shown that the shape of the entrance cross-section of the intake duct has a strong influence on the flow field throughout the entire intake duct. In this paper the flow throughout the duct is analysed in order to gain information on the flow features which cause the flow distortion at the aerodynamic interface plane (AIP) and how these flow features interact. Two main flow distortion patterns exist at the AIP, one of them is a system of two twin vortices, one on each side in the lower part of the AIP. These are caused by the particular shapes of the cross-sections in the front part of the duct. The dominating flow distortion in the AIP is caused by a large flow separation in the rear part of the duct, which resides in the upper half of the AIP and results in a large total pressure loss and axial velocity deficit, combined with a twin swirl. Although no direct interaction between these two flow patterns is present, it was found that the small vortices in the lower part are influenced by the flow separation at the upper wall in the rear section of the intake duct.
A CFD Based Approach for Estimation of Rotor Dynamic Coefficients for Liquid Annular Seals in Turbomachinery
Authors: Krishna Bachanti , Premachandran B. , Darpe Ashish K.
Published: August 2018

Seals are used to control leakage across stages in pumps and other rotating machinery such as turbomachines. However, while acting to control leakage, the seals generate a reaction force on the rotating members. The rotordynamic forces produced by fluid impact the stability behaviour of the high-speed turbomachinery, therefore precise estimation of rotordynamic parameters is important to ensure vibrational stability and desired dynamic performance of rotors having annular seals. Studies on seals have so far mainly focused on bulk flow model based on Hirs turbulent lubrication theory for calculating leakage flow rate and rotordynamic coefficients. However, it is incapable to deal complex geometries and is less efficient in predicting precise rotor dynamic parameters for high speed rotating systems due to its basic assumptions. The experiments performed for calculating rotordynamic coefficients show their dependence on many physical and mechanical properties such as working fluid properties, pressure drop, seal clearance, rotor speed, eccentricity and misalignments. With the latest high performance computing facilities it is now relatively easy to simulate the flow in seal and evaluate the dynamic coefficients at high rotational speeds and with complex geometries. This paper proposes a 3-D CFD based transient stimulation method to capture the experimental conditions in virtual environment. The fluid force is calculated by integrating pressure to the rotor surface and the stiffness and damping coefficients are evaluated by appropriate curve fitting of fluid forces for various eccentricity values. The coefficients obtained from the present method show better correlation with experimental data compared to the existing steady state CFD and theoretical models. Variation of these rotordynamic coefficients with eccentricity helps in assessing the safe design of turbomachinery.
Investigation of a Passive Flow Control Device in an S-Duct Inlet of a Propulsion System With High Subsonic Flow
Authors: Asghar Asad , Sidhu Satpreet , Allan William D. E. , Ingram Grant , Hickling Tom M. , Stowe Robert
Published: August 2018

S-Ducts have wide application on air vehicles with embedded engines. The complex geometry is known to lead to separation downstream of curved profiles. This paper reports the influences on that flow of passive flow control geometries. In these experiments, stream-wise tubercles were applied in an effort to improve the internal performance of S-duct diffusers, parameters including pressure recovery, distortion and swirl. The test articles were tested with the high subsonic (Ma = 0.8) flow and were manufactured using 3D printing. Stream-wise static pressure and exit-plane total pressure were measured in a test rig using surface pressure taps and a 5-probe rotating rake, respectively; the baseline and variant S-ducts were simulated through computational fluid dynamics. The experiments showed that some subtle improvements to the S-Duct distortion could be achieved through careful selection of tubercle geometry. Generally, the recovered flow downstream of the inner radius of the second bend of the S-duct deteriorated, but overall pressure recovery improved. The simulations were useful in characterizing swirl, whereas experiments were not so equipped. Adjustments to the numerical approaches resulted in reasonable agreement with the experiments.
Numerical and Experimental Study on Bleed Impact on Intermediate Compressor Duct Performance
Authors: Siggeirsson Elias M. V. , Andersson Niklas , Wallin Fredrik
Published: August 2018

In this study, a comparison is done between an in-house experimental test rig at GKN Aerospace and simulations done using an in-house CFD solver at Chalmers University of Technology. The geometry represents an intermediate compressor duct of an aircraft engine. The main focus is on comparing the flow field at different operating conditions. Those conditions are controlled by extracted massflow through a bleed pipe, upstream of the intermediate compressor duct. The work presented in this paper is done using a RANS solver with the Spalart All-maras turbulence model. The CFD simulations compare well with measured data, for the lower bleed fraction, especially in terms of pressure coefficients in the intermediate compressor duct and at downstream locations. There are strong local effects due to instabilities in the bleed pipe for the higher bleed fraction, which caused the fluctuations in the pressure coefficient and resulted in degraded convergence. The difference in the flow field is also visible when comparing the operating points, where stronger total pressure wakes are noticed in the results for the lower bleed case.
Numerical and Experimental Investigation on Centrifugal Cooling Fan in a Traction Motor
Authors: Qu Xiaoyun , Tian Jie , Wang Tong
Published: August 2018

High-speed train is developing popular in China, which provides the convenient and fast transportation way, comparable to plane. The moving direction and speed of high-speed train is decided by the traction motor. Generally, a coaxial centrifugal fan is used to cool the motor and assemble in the motor casing. To ensure the reliability of the traction motor, more and more attention is paid to improve the performance of cooling fans in a wide range of rotating speed. As the train is designed to move in both directions, the traction motor is designed to rotate in both directions, so does the coaxial motor cooling fan. Symmetrical and straight blade structure is adopted to get the same performance of the fan in both forward and reverse moving directions. Therefore, the aerodynamic performance of the cooling fan is relatively not good enough, which results in relatively high aerodynamic noise. In order to analyze the cooling fan aerodynamic performance and aerodynamic noise, CFD method was performed on the full 3D model with the impeller-casing clearance. The acoustic analogy method was used to analyze the noise of the centrifugal cooling fan. In addition, the aerodynamic noise of the motor with the cooling fan was tested at different rotating speed in the semi-anechoic lab. The CFD method is verified and the results are in good agreement with the experimental results. The results show that it is necessary to consider the effects of impeller-casing leakage and the vacuum inlet condition in the simulated model to get its more accurate performance. Modified CFD model of the cooling fan was proposed here. It is suggested that the modified structure of the casing can be used to improve the performance of the cooling fan and reduce the corresponding aerodynamic noise.
Ansaldo Energia Gas Turbine Technology Developments
Authors: Ramaglia A. D. , Ruedel U. , Stefanis V. , Florjancic S.
Published: August 2018

The operating conditions of the gas turbine combined cycle (GTCC) power plants have significantly changed over the last few years and are directed towards an improved operational and fuel flexibility, increased GT power output and efficiency and improved component lifetime. The purpose of this paper is to provide an overview of the development, analysis and validation of modern gas turbine features, parts and components for the AE64.3, AE94.2, AE94.3A, the GT26 and GT36. The development of compressor blades with a low uncertainty using multidisciplinary optimization techniques is outlined while the lifetime of a welded rotor is quantified using a damage-tolerant lifetime assessment method based on experimental creep data. For the lateral dynamics of the shaft train a modal-based approach supported by elastic structures will be described. For the axial flow turbine, the aerodynamic and heat transfer related design and validation of film cooled vanes and blades will be introduced with a particular focus on the tip area, the platforms and the application of under-platform dampers. Furthermore, the impact of the combustor-turbine interface on the turbine vane aerodynamics and film cooling characteristics is shown. For the continued very successful operation of the Constant Pressure Sequential Combustion System (CPSC), the thermos-acoustic activities of can combustors as well as the rig-to-engine transferability are presented. Recent approaches to the development of SLM parts for turbine hardware, specifically the approach used to select process parameters and creation of preliminary material models will also be briefly summarized.
Numerical Study of Deterministic Fluxes in Compressor Passages
Authors: Wang Feng , Carnevale Mauro , di Mare Luca
Published: August 2018

Computational Fluid Dynamics (CFD) has been widely adopted at the compressor design process, but it remains a challenge to predict the flow details, performance and stage matching for multi-stage, high-speed machines accurately. The Reynolds Averaged Navier-Stokes (RANS) simulation with mixing plane for bladerow coupling is still the workhorse in the industry and the unsteady bladerow interaction is discarded. This paper examines these discarded unsteady effects via deterministic fluxes using semi-analytical and URANS calculations. The study starts from a planar duct under periodic perturbations. The study shows that under large perturbations, the mixing plane produces dubious mixed-out variables, e.g. whirl angle. The performance of the mixing plane can be considerably improved by including deterministic fluxes into the mixing plane formulation. This demonstrates the effect of deterministic fluxes at the bladerow interface. Furthermore the front stages of a 19-blade row compressor are investigated and URANS solutions are compared with RANS solutions. The magnitude of divergence of Reynolds stresses and deterministic stresses are compared. The effect of deterministic fluxes are demonstrated on whirl angle and radial profiles of total pressure and so on. The enhanced spanwise mixing due to deterministic fluxes are also observed. The effect of deterministic fluxes are confirmed via the non-linear harmonic method which includes the deterministic fluxes in the mean flow and the study of multistage compressor shows that unsteady effects, which are quantified by deterministic fluxes, are indispensable to have credible predictions of the flow details and performance of compressor even at its design stage.
A Parametric Study of the Effects of Inlet Distortion on Fan Aerodynamic Stability
Authors: Zhang Wenqiang , Vahdati Mehdi
Published: August 2018

The performance and aerodynamic stability of fan blades operating in a circumferentially non-uniform inlet flow is a key concern in the design of turbofan engines. With the recent trends in the design of civil engines with shorter inlet ducts (such as low-speed fans), or boundary layer ingesting engines, quick and reliable modelling of rotor/distortion interactions is becoming very important. The aim of this paper is to study the effects of inlet distortions on the aerodynamic stability of a fan blade and to identify the parameters that have a major impact on the stability of the blade. NASA rotor 67, for which a significant amount of measured data is available, was used for this study.

In the first part of this study, the behavior of the fan with inlet distortion at near stall condition is analyzed, and it is shown how rotating stall is triggered. In the second part of this study, unsteady simulations with inlet distortion were performed to study how parameters, such as exit duct length and distortion strength, influence the stall margin of the blade.
Tip Leakage Flow Reduction of a Linear Turbine Cascade Using String-Type DBD Plasma Actuators
Authors: Matsunuma Takayuki , Segawa Takehiko
Published: August 2018

Tip leakage flow through the small gap between the blade tip of a turbine and the casing endwall reduces the aerodynamic performance. String-type dielectric barrier discharge (DBD) plasma actuators made of silicone printed-circuit board were used for the active control of the tip leakage flow of a linear turbine cascade. Sinusoidal voltage excitation with amplitude varying from 4 kV to 6 kV (peak-to-peak voltage: 8 kVp-p to 12 kVp-p) and fixed frequency of 10 kHz was applied to the plasma actuators. The two-dimensional velocity field in the blade passage was estimated by particle image velocimetry (PIV) under the very low Reynolds number conditions of Re = 7.1 × 103 and 1.42 × 104. The tip leakage flow was reduced by the flow control using plasma actuators. The high turbulence intensity region caused by the tip leakage flow was also reduced. For the quantitative comparisons, the displacement thickness of the absolute velocity distributions was examined. By the flow control of the plasma actuators, the displacement thickness at tip-side gradually decreased as the input voltage increased. Although three types of plasma actuators were used, with thin, thick, and flat electrodes and different ratios of discharge area, the differences in their effect were negligible. The reason for these very small differences in effect is the wide spread of the plasma discharge from the encapsulated electrode in the plasma actuator to the exposed electrode of the blade tip. At the relatively high Reynolds number condition of Re = 1.42 × 104, the effect of the plasma actuator was smaller than that at the lower Reynolds number condition of Re = 7.1 × 103.
A Novel Experimental Technique for Investigating Natural Convective Heat Transfer in a Gas Turbine Annulus
Authors: Fahy Daniel D. , Ireland Peter T. , Lewis Leo V. , Raya Emile
Published: August 2018

When a gas turbine is shut down it cools asymmetrically due to natural convection. After some time, a thermal gradient develops across the rotor drum as the top section cools slower than the bottom. This induces a thermal stress that causes the shaft to deflect — a phenomenon known as rotor or thermal bow. In some cases, this can lead to compressor tip rubs. All engines are affected by rotor bow to some degree. However, the mechanisms of natural convective heat transfer and impact of design features on rotor bow is not well understood; thus, the issue is not identified until late in the design stage, hampering an engines development.

A novel experimental technique and facility has been developed that allows for accurate, detailed measurements of natural convective heat transfer in a gas turbine annulus to be made. The apparatus has the capacity to test circumferential and axial variations in temperature distribution, in addition to an isothermal wall boundary. An IR camera looking directly at the rotor surface is used to provide high-resolution heat transfer measurements. The test piece for this study consisted of a cylinder section and a conical section.

Results from the isothermal cylinder test cases agreed quite well with previously published data, which gives confidence to the method that has been employed. The addition of a conical section had a profound effect on the results; however, more work is required before a method can be developed which will accurately predict the heat transfer coefficients based on initial temperature distribution. A 2D concentric cylinder methodology has also been developed that gives results in strong agreement with previously published data. Going forward, this new facility and the CFD method will be further developed to help quantify the effect of various design features on the natural convective heat transfer performance of a large civil gas turbine.
Effects of Rotating Inlet Distortion on Two-Stage Compressor Stability With Stall Precursor-Suppressed Casing Treatment
Authors: Sun Dakun , Li Jia , Dong Xu , Gu Benhao , Sun Xiaofeng
Published: August 2018

Experimental research about rotating inlet distortion is carried out on a two-stage compressor with emphasis on the compressor stability as well as the stall margin improvement with a kind of stall precursor-suppressed (SPS) casing treatment in this paper. The wire mesh screen is placed at the upstream of the IGV and can rotate at various speeds in co- and counter-direction of the compressor rotor to simulate the rotating inlet distortion in different levels. The results show that the rotating inlet distortion can deteriorate the compressor stall margin and the SPS casing treatment can extend the compressor stall margin (1.95%–7.90%) without additional efficiency loss. The pre-stall behavior of compressor is also analyzed to uncover the mechanism of the stall margin improvement with such casing treatment. Results show that casing treatment of this configuration can weaken the unsteady disturbances in compression system.
Forced Response Sensitivity Analysis Using an Adjoint Harmonic Balance Solver
Authors: Engels-Putzka Anna , Backhaus Jan , Frey Christian
Published: August 2018

This paper describes the development and initial application of an adjoint harmonic balance solver. The harmonic balance method is a numerical method formulated in the frequency domain which is particularly suitable for the simulation of periodic unsteady flow phenomena in turbomachinery. Successful applications of this method include unsteady aerodynamics as well as aeroacoustics and aeroelasticity. Here we focus on forced response due to the interaction of neighboring blade rows.

In the CFD-based design and optimization of turbomachinery components it is often helpful to be able to compute not only the objective values — e.g. performance data of a component — themselves, but also their sensitivities with respect to variations of the geometry. An efficient way to compute such sensitivities for a large number of geometric changes is the application of the adjoint method. While this is frequently used in the context of steady CFD, it becomes prohibitively expensive for unsteady simulations in the time domain. For unsteady methods in the frequency domain, the use of adjoint solvers is feasible, but still challenging. The present approach employs the reverse mode of algorithmic differentiation (AD) to construct a discrete adjoint of an existing harmonic balance solver in the framework of an industrially applied CFD code. The paper discusses implemen-tational issues as well as the performance of the adjoint solver, in particular regarding memory requirements. The presented method is applied to compute the sensitivities of aeroelastic objectives with respect to geometric changes in a turbine stage.
Influence of Upstream Geometry on Pulsatile Turbocharger Turbine Performance
Authors: Lim Shyang Maw , Dahlkild Anders , Mihaescu Mihai
Published: August 2018

Unlike conventional turbomachinery, an automotive turbocharger’s turbine is operated under unsteady hot and pulsatile flow due to the inherent nature of reciprocating engine. Although the turbine is integrated with exhaust manifold in real application, some experiments and numerical studies ignore its presence. In this study, we aimed to investigate the effects of upstream complex exhaust manifold on the prediction of pulse flow turbine performance via Detached Eddy Simulation (DES). Heat transfer was incorporated and the exergy based approach was used to quantify the heat transfer associated losses. Our primary results showed that under the investigated turbine stage, although the presence of exhaust manifold influences the prediction of heat transfer and internal irreversibilities in the scroll significantly, it does not significantly affect the prediction of turbine power, heat transfer and irreversibilities at the downstream components.
Experimental Study on Acoustic Performances of Notched Nozzle Using a Subscale Turbofan Engine
Authors: Ishii Tatsuya , Nagai Kenichiro , Oinuma Hideshi , Kagaya Ryo , Oishi Tsutomu
Published: August 2018

This paper describes an experimental study on the acoustic performance when mixer nozzles were applied to the core of a subscale turbofan engine. The primary concern of the mixer nozzle is how to satisfy both less jet mixing noise emission and minimum impact on engine performance parameters such as thrust and fuel consumption. A notched nozzle, a nozzle with tiny dents on the trailing edge, initiates small disturbances in the shear layer, weakens the shear stress, and suppresses jet noise. The Japan Aerospace Exploration Agency (JAXA) and IHI Corporation have studied notched nozzles and found that finer and more notches are preferable for both acoustic and aerodynamic performance.

As a next step, it is necessary to maintain the tradeoff between noise suppression and impact on engine performance. To evaluate both the acoustic and aerodynamic performance with the notched nozzle, a subscale turbofan engine, DGEN380, was adopted as a demonstration engine. Experiments with this engine were conducted both in a test cell and in an open test site. The notched nozzle, together with a baseline conical nozzle and a referential serrated nozzle, i.e., a chevron nozzle, was applied to the core exhaust of the engine.

The experiment in the test cell clarified that the notched nozzle possibly provides better thrust specific fuel consumption than the referential chevron nozzle. The acoustic measurement in the open environment confirmed that the notched nozzle has the noise suppression characteristics expected from previous test results. The perceived noise levels are attenuated by 1.5 dB, which is the same as or better than the referential mixer nozzle.
Numerical Simulation of the Blade Aging Process in an Induced Draft Fan due to Long Time Exposition to Fly Ash Particles
Authors: Castorrini Alessio , Corsini Alessandro , Rispoli Franco , Venturini Paolo
Published: August 2018

Erosion issues usually affect fans used for the extraction of exhaust gas in fluid power plants. Because of the presence of fly ash within the exhaust flow, fan blades are subjected to material wear at the leading edge, trailing edge and blade surface, and this may cause a modification of the blade aerodynamic profile, a reduction of blade chord and effective camber. All these effects results in a deterioration of the aerodynamic performance of the blade.

Prediction of erosion process in industrial applications helps to better schedule the maintenance and predict the blade life. To this aim, we report a numerical simulation of the blade aging process due to particle erosion in an induced draft fan. This is done using in-house numerical tools able to iteratively simulate the flow field, compute the particle tracking/dispersion/erosion, and modify the geometry (and mesh) according to the predicted erosion rate. A scale factor is introduced to align the simulation time and particle concentrations to a real application, and compare the results with the on-field observation.
Challenges and Solutions for Utilization of Bioliquids in Microturbines
Authors: Seljak Tine , Pavalec Klemen , Buffi Marco , Valera-Medina Agustin , Chiaramonti David , Katrašnik Tomaž
Published: August 2018

Increased public concerns and stricter regulatory frameworks promote the role of bioliquids (liquid fuel for energy purposes other than for transport, including electricity and heating and cooling, produced from biomass). This is a driving force for development and employment of micro-gas-turbines (MGTs) due to their ability to combust bioliquids with less favorable properties in a decentralized manner. Gas turbines are characterized by relatively high combustion efficiency at relatively low concentrations of harmful emissions, relatively high effective efficiency and durability when utilizing a common portfolio of gas turbine approved fuels. It is thus desired to preserve these advantages of gas turbines also while burning bioliquids and further relying on their scalability that is crucial to efficient support of decentralized energy production at small scales. To support these objectives, MGT technology needs to allow for utilization of bioliquids with much wider spectrum of physical and chemical properties compared to common commercially available MGTs in a single MGT based plant. In this view, the present study is providing the first thorough overview of challenges and solutions encountered by researchers across the wide area of bioliquids in MGTs.
A New Model Approach for Convective Wall Heat Losses in DQMoM-IEM Simulations for Turbulent Reactive Flows
Authors: Emmi Yeshaswini , Fiolitakis Andreas , Aigner Manfred , Genin Franklin , Syed Khawar
Published: August 2018

A new model approach is presented in this work for including convective wall heat losses in the Direct Quadrature Method of Moments (DQMoM) approach, which is used here to solve the transport equation of the one-point, one-time joint thermochemical probability density function (PDF). This is of particular interest in the context of designing industrial combustors, where wall heat losses play a crucial role. In the present work, the novel method is derived for the first time and validated against experimental data for the thermal entrance region of a pipe. The impact of varying model-specific boundary conditions is analysed. It is then used to simulate the turbulent reacting flow of a confined methane jet flame. The simulations are carried out using the DLR in-house Computational Fluid Dynamics (CFD) code THETA. It is found that the DQMoM approach presented here agrees well with the experimental data and ratifies the use of the new convective wall heat losses model.
Robust Multiphysics Optimization for Fan Blade Aerodynamic Efficiency, Structural Properties and Flutter Sensitivity
Authors: Vinogradov Kirill A. , Kretinin Gennady V. , Leshenko Igor A. , Otriakhina Kseniia V. , Fedechkin Konstantin S. , Vinogradova Olga V. , Bushmanov Vyacheslav V. , Khramin Roman V.
Published: August 2018

A fan blade is a complicated object and obviously it is subjected to geometrical uncertainties from manufacture tolerances and other production deviations. In spite of all uncertainties a fan blade should provide stable aerodynamic efficiency and strength properties. That is why it is considered to solve a multidimensional and multidisciplinary optimization task (aerodynamics, strength and flutter sensitivity) in robust statement under geometrical uncertainties. In the proposed test case geometrical uncertainties from the fan blade manufacture tolerances and deviations are considered. The probability density function (pdf) was obtained as a result of statistical operation upon the results of blade coordinate measurements. Approximately 2500 fan blades were measured by means of CMM process to reconstruct the pdf for more than 40 geometrical uncertainties (there are blade thicknesses for different airfoil locations in several cross-sections). CFD and FEM calculations were carried out in NUMECA FINE/Turbo and ANSYS software, correspondingly.

The surrogate model technique (the response surface and the Monte-Carlo method implemented to RSM results) was applied for the uncertainty quantification and the robust optimization process for the task under consideration. APPROX software was used for surrogate model construction. The IOSO technology was employed as one of the robust optimization tools. This technology is also based on a widespread application of the response surface technique.

As a result, robust optimal solutions (the Pareto set) for all 4 considered criteria (aerodynamic efficiency, structural properties, stall margin and flutter sensitivity) were obtained. The probabilistic criteria were assessed based on the results obtained. The robust optimization results were compared with the deterministic optimization results.
Torsional Response of Additively Manufactured Steel Under Monotonic and Cyclic Conditions
Authors: Siddiqui Sanna F. , Fasoro Abiodun A. , Gordon Ali P.
Published: August 2018

The value of additively manufactured (AM) components with application in the aerospace industry can be assessed by subjecting them to realistic operational service conditions. While there is considerable knowledge about the tensile response of AM materials, minimal studies have considered the torsional and torsional-fatigue response of AM materials. A comprehensive understanding of the effect of both axial and torsional conditions of AM parts can allow for improvements in manufacturing design of components to effectively meet or exceed service requirements. This study is the first study to date, to investigate the torsional and torsional-fatigue response of as-built direct metal laser sintered (DMLS) stainless steel (SS) GP1, through monotonic torsion and completely reversed torsional fatigue experiments, for samples built at varying orientations in the horizontal xy build plane. Experimental results include monotonic torsional shear properties, torsional cyclic response, and fracture surfaces, which will be used to assess the torsional material response with regards to build orientation. Findings will be used to contribute to a much needed and comprehensive framework of the material behavior of AM components when subjected to axial/torsional loading conditions.
Constituent Development for Higher-Temperature Capable Ceramic Matrix Composites
Authors: Cinibulk M. K. , Apostolov Z. D. , Boakye E. E. , Key T. S. , King D. S.
Published: August 2018

This paper highlights research that is addressing the need for improved high-temperature-capable CMCs, with a focus on CMC constituents and an understanding of their processing, microstructure, and behavior in relevant service environments. The most pervasive lifetime and temperature limitations for SiC/SiC CMCs are related to oxidation, creep and stress rupture of the fibers, oxidation-induced instability of the fibermatrix interface, and instability of the matrix at temperatures > 1400°C. Consequently, we are addressing these shortcomings by developing technologies to enable higher-temperature capable SiC fiber, oxidation-resistant fiber-matrix interfaces, and improvements in processing of refractory matrices for both turbine engine and hypersonic applications.
Stability and Limit Cycles of a Nonlinear Damper Acting on a Linearly Unstable Thermoacoustic Mode
Authors: Bourquard Claire , Noiray Nicolas
Published: August 2018

The resonant coupling between flames and acoustics is a growing issue for gas turbine manufacturers. They can be reduced by adding acoustic dampers on the combustion chamber walls. Nonetheless, if the engine is operated out of the stable window, the damper may be exposed to high-amplitude acoustic levels, which may trigger unwanted nonlinear effects. This work aims at providing an overview of the dynamics associated with those limit cycles using a simple analytical model, where a perfectly tuned damper is coupled to the combustion chamber. The damper, crossed by a purge flow in order to prevent hot gas ingestion, is modeled as a non-linearly damped harmonic oscillator, with vortex shedding as the main dissipation mechanism. The combustion chamber featuring a linearly unstable thermoacoustic mode is modelled as a Van der Pol oscillator. The fixed points of the coupled system and their stability can be determined by analyzing the averaged amplitude equations. This allows the computation of a fixed point topology map as function of the growth rate of the unstable mode and the mean velocity through the damper neck. Simulink simulations are also performed and compared to the analytical predictions. Finally, experiments are performed on a simple rectangular cavity, where the thermoacoustic instability resulting from the interaction between heat release and acoustic pressure is mimicked by an electro-acoustic instability. A feedback loop is built, where the signal from a microphone is filtered, delayed, and amplified before being sent to a loudspeaker placed inside the rectangular cavity. The delay and gain of the feedback loop can be modified to change the growth rate of the instability. One Helmholtz damper can be added to the cavity and tuned to the unstable mode of interest. The growth rate reduction capabilities of the damper and the amplitude of the limit cycle in the unstable cases are in good agreement with the analytical and numerical predictions, underlining the potentially dangerous behavior of the limit cycles which should be taken into account for real engine cases.
Combustion Characteristics of Isolated Free-Falling Droplets of Jet A Blended With Ethanol and Butanol
Authors: Muelas Álvaro , Remacha Pilar , Ballester Javier
Published: August 2018

Recent studies on experimental gas turbines suggest that the addition of ethanol or butanol to Jet A are viable alternatives for reducing CO and NOx emissions while maintaining similar performance to that of pure Jet A. In light of this potential, experimental data regarding the burning characteristics of Jet A/ethanol and Jet A/butanol blends are required in order to better understand their combustion process.

Following a previous study on Jet A/butanol droplet combustion, the scope has been extended in order to also include ethanol and a Jet A/ethanol mixture as well as to perform a more detailed characterization. In this work the combustion characteristics of Jet A, butanol, ethanol and their mixtures (20% vol. alcohol in kerosene) are presented for different test conditions. The evaluated combustion characteristics include droplet, flame and soot shell size evolutions, burning rates and image-based soot estimations. The influence of oxygen availability is also ascertained.

The evolution of droplet diameter and burning rates for Jet A and its blends with both alcohols are very similar, whereas pure ethanol and butanol display more distinct behaviors. Soot indices are found to be quite different, with a clear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. These results support the feasibility of kerosene-alcohol mixtures as promising alternative fuels with similar combustion characteristics, but with much lower sooting propensity than pure kerosene.
Numerical and Experimental Investigation of Aerodynamic Characteristics of Model Ultra High Bypass Ratio Counter Rotating Fan
Authors: Druzhinin Iaroslav , Mileshin Victor , Korzhnev Vladimir
Published: August 2018

One of the perspective schemes of air breathing engine is a scheme with Ultra High Bypass Ratio (BPR 16...25) Counter Rotating Fan. This solution potentially allows significant increase of fuel efficiency compared to modern conventional turbofans.

The model UHBR counter rotating fan named COBRA-1 was developed by CIAM within the framework of European Project COBRA (Innovative Counter rOtating fan system for high Bypass Ratio Aircraft engine). The fan was designed using up-to-date 1D, 2D and 3D methods. COBRA-1 is a 0.7 m diameter model of counter rotating fan driven by a planetary reduction gearbox. The bypass ratio of COBRA-1 is 20. The R2/R1 torque ratio was chosen to obtain 1.42-muliple prevalence in power for 2nd row. The blade numbers are 8/12 for R1/R2 correspondingly. Final geometry of airfoils was defined by 3D profiling process to achieve required aerodynamics and acoustic parameters. Application of control-diffusion airfoils allows reaching high integral performances: specific mass flow equals 211 kg/(s*m^2) and isentropic efficiency at design point is higher than 0.93.

The paper presents results of computational simulation of the flow in UHBR fan COBRA-1 based on 3D steady RANS method, 3D URANS and Non-Linear Harmonic method for different operation conditions in comparison with experimental data. Numerical simulation was carried out using Numeca FINE TURBO software package. Steady RANS approach was used during design process to make quick estimation of performances at different rpm. 3D URANS simulation was conducted to analyze unsteady wake-blade and shock-wave interaction and to make a decision about sufficient value of axial gap between rotors.

The COBRA-1 fan was tested in CIAM at C3-A test facility which allows conducting a wide range of measurements of local and integral parameters including acoustics of ducted counter rotating fan at different operating conditions.

Experimental results demonstrate a high level of integral performances and good agreement with computed values.

Significant part of numerical and experimental investigation is devoted to effect of gear-box requirements on aerodynamics. C3-A rig allows to set rotational speed of rotors independently and measure torques at each shaft to achieve required torque ratio and study the influence of small (3–5%) deviation in rpm on aerodynamic characteristics.
A Benchmarking Analysis of a Data-Driven Gas Turbine Diagnostic Approach
Authors: Loboda Igor , Pérez-Ruiz Juan Luis , Yepifanov Sergiy
Published: August 2018

In an effort to better compare particular gas turbine diagnostic solutions and recommend the best solution, the software tool called Propulsion Diagnostic Method Evaluation Strategy (ProDiMES) has been developed. This benchmarking platform includes a simulator of the aircraft engine fleet with healthy and faulty engines. The platform presents a public approach, at which different investigators can verify and compare their algorithms for the diagnostic stages of feature extraction, fault detection, and fault identification.

Using ProDiMES, some different diagnostic solutions have been compared so far. This study presents a new attempt to enhance a gas turbine diagnostic process. A data-driven algorithm that embraces the mentioned three diagnostic stages is verified on the basis of ProDiMES. At the feature extraction stage, this algorithm uses a polynomial model of an engine baseline to compute deviations of actual gas path measurements from the corresponding values of a healthy engine. At the fault detection and fault identification stages, a common classification for fault detection and fault identification is firstly constructed using deviation vectors (patterns). One of the three chosen pattern recognition techniques then performs both fault detection and fault identification as a common process.

Numerous numerical experiments have been conducted to select the best configurations of the baseline model, a pertinent structure of the fault classification, and the best recognition technique. The experiments were accompanied by a computational precision analysis for each component of the proposed algorithm. The comparison of the final diagnostic ProDiMES metrics obtained under the selected optimal conditions with the metrics of other diagnostic solutions shows that the proposed algorithm is a promising tool for gas turbine monitoring systems.