bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Expansion Sensitivity Studies During Steam Turbine Start-Up
Authors: Topel Monika , Jöcker Markus , Paul Sayantan , Laumert Björn
Published: August 2015

In order to improve the startup flexibility of steam turbines it becomes relevant to analyze their dynamic thermal behavior. In this work, the relative expansion between rotor and casing was studied during cold start conditions. This is an important property to monitor during start-up given that clearances between rotating and stationary components must be controlled in order to avoid rubbing. The investigation was performed using a turbine thermal simplified model from previous work by the authors. The first step during the investigation was to extend and refine the modeling tool in order to include thermo mechanical properties. Then, the range of applicability of the model was validated by a two-fold comparison with a higher order finite element numerical model and measured data of a cold start from an installed turbine.

Finally, sensitivity studies were conducted with the aim of identifying the modeling assumptions that have the largest influence in capturing the correct thermal behavior of the turbine. It was found that the assumptions for the bearing oil and inter-casing cavity temperatures have a large influence ranging between ± 25% from the measured values. In addition, the sensitivity studies also involved increasing the initial temperature of the casing in order to reduce the peak of differential expansion. Improvements of up to 30% were accounted to this measure. The studies performed serve as a base towards further understanding the differential expansion during start and establishing future clearance control strategies during turbine transient operation.
Flowfield and Temperature Profiles Measurements on a Combustor Simulator Dedicated to Hot Streaks Generation
Authors: Bacci Tommaso , Caciolli Gianluca , Facchini Bruno , Tarchi Lorenzo , Koupper Charlie , Champion Jean-Louis
Published: August 2015

In order to deepen the knowledge of the interaction between modern lean burn combustors and high pressure turbines, a real scale annular three sector combustor simulator has been assembled at University of Florence, with the goal of investigating and characterizing the generated aerothermal field and the hot streaks transport between combustor exit and the high pressure vanes location. To generate hot streaks and simulate lean burn combustors behavior, the rig is equipped with axial swirlers, fed by main air flow that is heated up to 531 K, and liners with effusion cooling holes that are fed by air at ambient temperature. The three sector configuration is used to reproduce the periodicity on the central sector and to allow to perform measurements inside the chamber, through the lateral walls.

Ducts of different length have been mounted on the swirlers, preserving the hot mainflow from the interaction with coolant. Such configurations, together with the one without ducts, have been tested, using different measurement techniques, in order to highlight the differences in the resulting flow fields.

First of all, isothermal PIV measurements have been performed on the combustion chamber symmetry plane, to highlight the mixing phenomena between the mainflow and cooling flows. Then a detailed investigation of the mean aerothermal field at combustor exit has been carried out, for nominal operating conditions, by means of a five hole pressure probe provided with a thermocouple, installed on an automatic traverse system. With the aim of analyzing the hot streaks transport and the flow field modification towards the vanes location, such measurements have been performed on two different planes: one located in correspondence of the combustor exit and the further one placed downstream, in the virtual location of the vanes leading edges.

Therefore, an experimental database, describing the evolution of the flow field in a combustor simulator with typical traits of modern lean burn chambers, for different injector geometries, has been set up.
A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow
Authors: Kolb Michael , Ahrens Denise , Hirsch Christoph , Sattelmayer Thomas
Published: August 2015

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multi-stage combustion to lower nitric oxide emissions and enhance turndown ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet lift-off depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K) and jet momentum ratio (6–210). The differences to existing lift-off studies are the high cross flow temperature and applying a premixed jet. The lift-off height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the lift-off height for similar staged combustion systems. A main outcome of this work is that the lift-off height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz number. Furthermore, the ignition delay time scale τign also misses part of the lift-off height mechanism. The presented model uses turbulent time scales, the ignition delay and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.
Shape Optimization of Multi-Stage Axial Compressor Blades Using Adjoint Method With Static Pressure Constraint at Blade Row Interface
Authors: Yu Jia , Ji Lucheng , Li Weiwei , Yi Weilin
Published: August 2015

Adjoint method is an important tool for design refinement of multistage compressors. However, the radial static pressure distribution deviates during the optimization procedure and deteriorates the overall performance, producing final designs that are not well suited for realistic engineering applications. In previous development work on multistage turbomachinery blade optimization using adjoint method and thin shear-layer N-S equations, the entropy production is selected as the objective function with given mass flow rate and total pressure ratio as imposed constraints. The radial static pressure distribution at the interfaces between rows is introduced as a new constraint in the present paper. The approach is applied to the redesign of a five-stage axial compressor, and the results obtained with and without the constraint on the radial static pressure distribution at the interfaces between rows are discussed in detail. The results show that the redesign without radial static pressure distribution constraint (RSPDC) gives an optimal solution that shows deviations on radial static pressure distribution, especially at rotor exit tip region. On the other hand, the redesign with the RSPDC successfully keeps the radial static pressure distribution at the interfaces between rows and make sure that the optimization results are applicable in a practical engineering design.
Shape Optimization of Axial Compressor Blades Using Adjoint Method With Emphasis on Thickness Distribution
Authors: Yu Jia , Ji Lucheng , Li Weiwei , Yi Weilin
Published: August 2015

Shape parameterization plays an important role in aerodynamic optimization design of axial compressor blades. Blade thickness is one of the most important parameters in blade design, which has strong influence on compressor aerodynamic performance. However, the previous adjoint-based optimization designs using the Hicks-Henne functions only parameterized the perturbations to the tangential coordinates of points on suction surface or meanline, and kept the tangential thickness of the blade constant during the optimization process. In previous development work of turbomachinery blade optimization using adjoint method and thin shear-layer N-S equations, a new shape parameterization is introduced, which uses Hicks-Henne functions to parameterize the perturbations to both the tangential coordinates of mesh points on suction blade surface and the tangential thickness of the blade. This new approach is applied to the redesign of NASA rotor 67 and the results obtained with and without the blade tangential thickness parameterization are discussed in detail. The results show the redesign with and without the blade tangential thickness parameterization can both improve the aerodynamic performance of the axial compressor. However, the redesign with the blade tangential thickness parameterization can produce a consistently better performance than that without it.
Effect of Air-Assist on Liquid Jet Penetration and Dispersion in a Cross-Flow of Hot, High-Pressure Air
Authors: Tan Zu Puayen , Lubarsky Eugene , Bibik Oleksandr , Shcherbik Dmitriy , Zinn Ben T.
Published: August 2015

This paper describes an experimental investigation of the effects of air-assist upon the penetration and dispersion of a liquid fuel jet that is injected into cross-flowing air. The spray patterns across the central longitudinal plane were investigated at flow conditions similar to those encountered at the combustor inlet of a modern gas turbine engine. Temperatures of the cross-flow and assist air were at 316 and 427°C, while test-channel pressures were set at 2.02 and 2.53MPa. Jet-A fuel was injected through a wall-recessed plain orifice into a rectangular test-channel where the cross-flow air velocity was Ucross-flow=75m/s. Assist air was injected from four slots surrounding the fuel orifice within the wall-recessed well. The air-assist jets impinged upon the fuel jet at a 45° angle. Pressure drops across the air-slots were limited to ≤4% of test-channel pressure to simulate the difference between stagnation and static pressures on a typical fuel-air mixer/injector. Thus, the assist-air-to-liquid fuel mass-flow ratios (ALR) were limited to 0.41, which was much lower than those used in traditional airblast atomizers with ALR in the range of 1 to 10. Momentum-flux ratios (J) of the fuel jet to cross-flow were varied between J=5 to 40. A 355nm planar laser was used to illuminate the spray’s central plane to capture images of liquid droplets Mie-scattering. An attempt was made at correlating the trajectories of the jet using an effective momentum-flux ratio Jeff that accounts for air-assist jets’ momentum. It was discovered that air-assist had limited influence on the spray’s outer-edge penetration, while it strongly enhances the penetration of the inner-edge and spray centerline. Air-assist’s effects were also found to be proportional to ALR. Contrary to the results of airblast jet-in-cross-flow researches, it was found that at J∼5, when the sprays’ inner-edges were close to the wall, air-assist enhanced the inner-edge penetration in a manner that was not well-captured by Jeff. Finally, it was also observed that sprays at 2.53MPa were more sensitive to J and air-assist variations than sprays at 2.02MPa.
Case Study: Dynamic Analysis of a Novel Vertical Axis Wind Turbine
Authors: Bennett Jeffrey A. , Coogan Shane , Lane Kenneth B.
Published: August 2015

An analytical model was developed for the dynamic evaluation of a novel vertical axis wind energy system. This study was conducted early on in the design process, so the goal was to create a low level tool to determine if the concept was feasible, to perform initial sizing of the turbine, to better understand the behavior of the unique furling mechanisms, and to predict the performance. In order to prevent damage at high rotational speeds, the novel concept integrates passive mechanisms into a drag driven vertical axis wind turbine with the intention that blades furl out of the wind once a critical wind speed is reached, and passively reopen. Established wind turbine aeroelastic codes were unable to represent this unique system, therefore, a standalone analytical model was developed in Python. A Lagrangian approach was taken to represent the interactions of the system’s degrees of freedom. To complete the model, mathematical representations of the furling mechanisms and interaction of the wind on the blades was developed. Basic structural calculations were also included to determine the initial size of the primary mechanical components. This case study focuses on the development of the low-level dynamic model and shares several results of the expected behavior.
Goal Driven Shape Optimisation for Conjugate Heat Transfer in an Effusion Cooling Plate
Authors: Savastano W. , Pranzitelli A. , Andrews G. E. , Biancolini M. E. , Ingham D. B. , Pourkashanian M.
Published: August 2015

Full coverage effusion cooling was numerically investigated by means of conjugate heat transfer (CHT) computational fluid dynamics (CFD) for an array of effusion cooling holes in order to maximise the overall cooling effectiveness for a fixed coolant mass flow rate G, kg/sm2. The baseline case study consisted of a 152×152×6.35mm perforated wall with a 300 K, 0.18 kg/sm2 coolant flow through a square array of 90° effusion holes. The plate was mounted in a 770 K duct crossflow. The numerical model was validated against the experimental work of Andrews et al. (1990) and showed a maximum disagreement between the prediction and the experimental data of 3%. The effects of three geometrical parameters, i.e. the inclination of the holes, the pitch in X direction and the pitch in Y direction, on the overall cooling effectiveness were investigated without varying the coolant flow rate. The inclination of the effusion holes was varied between −33° and +33° from the plane of the plate, while the pitch in both directions was varied between 10.64mm and 19.76mm. The numerical investigation was performed using the commercial software ANSYS Workbench following a design of experiments approach. The geometrical modifications were obtained automatically in the CFD solver ANSYS Fluent for each design point by means of the RBF Morph software. This avoided the manual modification of the geometry and the subsequent mesh generation. The optimised configuration was obtained considering the maximisation of the average overall cooling effectiveness as a goal and a chosen minimum value for the local cooling effectiveness of 0.4 as the constraint. The results showed that the inclination of the effusion holes and the pitch in the Y direction have a greater impact on the cooling effectiveness than the pitch in the X direction, up to 17%, 28% and 5% from the baseline, respectively, within the range of values considered. An optimal combination of the three parameters was determined.
Numerical Investigation of Two-Phase Wet Steam Flow With Spontaneous Condensation Based on Euler S2 Calculation Method
Authors: Li Deying , Chen Huanlong , Song Yanping , Cui Ke , Ooyama Hiroharu
Published: August 2015

The Euler equation suitable for the S2 stream surface calculation is derived in the arbitrary orthogonal coordinate system firstly. The numerical method for the two-phase wet steam flow with the spontaneous condensation is then developed on basis of the Euler S2 calculation code, the Eulerian/Eulerian multiphase model and the classic nucleation theory.

To adapt the complex geometry of the turbine blades, the Euler equations for the S2 stream surface calculation method are derived in the body-fitted coordinate system. The mathematical model for the third order TVD scheme with the non-conservative variables is also developed for the gas phase governing equation. The 2nd order NND and the VanLeer scheme are applied to the variable reconstruction and the numerical flux calculation respectively in the liquid equations solving process. The pressure and the droplet radii distribution fit well with the experimental data for both the high pressure nozzle and the low pressure nozzle. The S2 calculation method is also employed to predict the performance of a 3-stage low pressure steam turbine with spontaneous steam condensation, and the reasonable results are obtained.

The numerical method developed in the present work is able to predict the real wet steam flow with the spontaneous condensation and its impact on the flow field and the aerodynamic parameters distribution reasonably, supplying a fast and accurate technic and method to the steam turbine design.
Numerical Simulation of Ice Shedding From a Fan Blade
Authors: Chen Yong , Dong Wei , Wang Zhonglin , Fu Liang
Published: August 2015

In turbofan engine, ice accretion on the fan blade may block the flow path and disturbs the inlet flow, which will cause the decrease of the thrust and the increase of the vibration amplitude of the engine. More seriously, ice shedding can damage the compressor components, which may cause serious aircraft accidents. An understanding of the mechanisms responsible for ice shedding process is necessary in order to optimize the fan blade design to avoid hazardous ice shedding. In this paper, a numerical ice shedding model is developed by taking the coupling of the failure of the interface between ice and fan blade surface and the failure of ice itself into account. The ice shedding process is predicted and analyzed. Some factors that affect the break-up and shedding of the ice are discussed, which include the mechanical properties of the ice, centrifugal loading and vibration loading. This model could be used to further study on the ice debris trajectory prediction and ice impact analysis.
A Loosely Coupled Fluid/Solid Heat Transfer Method for Disc Cavities Including Mixing Planes and a Combination of 2D and 3D Cavities
Authors: Chaquet Jose M. , Corral Roque , Gisbert Fernando , Pastor Guillermo
Published: August 2015

The effect of mixing plane boundary condition in conjugate heat transfer analysis is studied. The vehicle is a 1.5 stage warm turbine rig solved using a loosely coupled fluid/solid heat transfer method. To reduce the elapsed time, two and three dimensional CFD cavities are solved simultaneously in a Graphics Processing Units (GPU) cluster. The experimental data are compared against a coupled model with mixing plane distributions obtained from an adiabatic case. A moderate influence of the mixing plane on the results is observed, with non-dimensional temperature differences around 2% in some locations.
An Implicit Harmonic Balance Method in Graphics Processing Units for Vibrating Blades
Authors: Crespo Javier , Corral Roque , Pueblas Jesus
Published: August 2015

An implicit harmonic balance method for modeling the unsteady non-linear periodic flow about vibrating airfoils in turbomachinery is presented. As departing point, an implicit edge-based three-dimensional Reynolds Averaged Navier-Stokes equations solver for unstructured grids that runs both on central processing units (CPUs) and graphics processing units (GPUs) is used. The harmonic balance method performs a spectral discretization of the time derivatives and marches in pseudo-time a new system of equations where the unknowns are the variables at different time samples.

The application of the method to vibrating airfoils is discussed. It is shown that a time spectral scheme may achieve the same temporal accuracy at a much lower computational cost than a Backward Finite Difference method at the expense of using more memory.

The performance of the implicit solver has been assessed with several application examples. A speed-up factor of 10 is obtained between the spectral and finite difference version of the code whereas and an additional speed-up factor of 10 is obtained when the code is ported to GPUs, totalizing a speed factor of 100. The performance of the solver in GPUs has been assessed using the 10th standard aeroelastic configuration and a transonic compressor.
Detuning the Natural Frequencies of a Compressor Impeller Blade Through the Design Optimization
Authors: Pugachev Alexander O. , Sheremetyev Alexander V. , Tykhomirov Viktor V. , Petrov Alexey V.
Published: August 2015

This paper describes a theoretical approach to shift individual natural frequencies of centrifugal compressor impeller blades. The approach applies sizing optimization of blade’s geometry using a gradient-based optimization method. Calculation of gradients is carried out by the finite-difference method. A new centrifugal compressor blade profile generator incorporating a blade parametrization procedure is developed. The blade’s geometry is parametrized using intuitive geometric parameters. Five design parameters related to the length of the sectional profile generator line, profile thicknesses and rotation angles at hub and shroud are defined for each of the blade sectional profiles. In addition, two global design parameters are defined to control rigid rotation of the blade hub and shroud sections in circumferential direction. Four nonlinear optimization problems containing multiple frequency constraints and constraints on the static equivalent stresses are considered. The optimization aims are either shifting a particular natural frequency of a blade or minimization of blade’s mass. For instance, one of the considered optimization problems is to decrease the 1st natural frequency of an impeller blade by 5%, while the 2nd and the 3rd natural frequencies must be simultaneously increased by 5%. The analysis is applied to the centrifugal compressor of a small-size turboprop engine. A three-dimensional finite element model of the impeller blade is developed in ANSYS Mechanical software package to perform static and modal analyses. The results of the optimization show that the code can meet defined objectives and constraints with reasonable accuracy. A detailed comparison of optimized profiles with the baseline geometry is provided.
Numerical Modeling of an Aero-Engine Bearing Chamber Using the Meshless Smoothed Particle Hydrodynamics Method
Authors: Wieth Lars , Lieber Christian , Kurz Wolfram , Braun Samuel , Koch Rainer , Bauer Hans-Jörg
Published: August 2015

The prediction of the two-phase flow in an aero-engine bearing chamber using the meshless Lagrangian Smoothed Particle Hydrodynamics (SPH) method is presented in this paper. The prediction of the prevailing flow types, like shear-driven wallfilms, droplet-wall- and droplet-film-interactions require an accurate numerical method, which is robust and efficient. Therefore, a code based on the SPH method was developed and validated to numerically predict such technical relevant multi-phase flows in gas turbines.

The simulations to be presented in this paper are focused on an aero-engine bearing chamber configuration, which was experimentally investigated previously. For time saving reasons, the bearing chamber is modeled as two-dimensional problem. This requires special boundary conditions for the oil- and sealing-air flow inlet and outlet, which must physically reflect those of the experiments. In the experiments different operating regimes at different boundary conditions could be identified.

The major objective of the simulations is to investigate if those different flow regimes can be captured by the numerical method. The simulations do reproduce the different flow regimes highly accurate and demonstrate the ability of this new approach.
Experimental Verification of Friction Behaviors Under Periodically-Varied Normal Force by Developing a Two-Directional Friction Test System
Authors: Asai Kunio , Gola Muzio M.
Published: August 2015

In order to achieve more accurate friction damping of turbine blades equipped with shroud covers and under-platform dampers, it is necessary to clarify such friction behaviors as tangential contact stiffness, micro-slips, and dissipated energy, under periodically varied normal force instead of constant normal force. Although some analytical studies were reported on the contact mechanics under alternating normal force, only minimal research has been conducted on the experimental verification of such behaviors, as friction tests were commonly done under constant normal force. In this study, we developed an original two-directional friction test system that can apply any combination of alternating normal and tangential forces by changing the displacement-controlled loading direction. In this system, relative displacement and contact force were measured simultaneously by using a laser Doppler displacement sensor and force transducers of the strain gage type.

By using our original test system, we examined the dissipated energy under constant normal force and periodically-varied normal force whose amplitude is the same as that of tangential force with no phase difference. We then obtained a new finding that dissipated energy depends on alternating normal force under the same mean normal force and alternating tangential force. More specifically, when the tangential force coefficient, defined as the ratio of the amplitude of alternating tangential force to mean normal force, is large enough to cause a macro-slip, dissipated energy under variable normal force is smaller than that under constant normal force. Conversely, when tangential force coefficient is small in the micro-slip region, dissipated energy under variable normal force is larger than that under constant normal force. This behavior was successfully reproduced by FE analysis based on a macro-slip model, where an array of macro-slip elements was used to describe micro-slip behavior. It was found that alternating normal force makes it easier to cause a micro-slip in a certain area of the contact surface under variable normal force, resulting in higher dissipated energy than at constant normal force when tangential force coefficient is small.

In this study, basic friction data were also obtained regarding the tangential contact stiffness with variations in contact pressure, as well as the relation between a micro-slip and the tangential force coefficient. Tangential contact stiffness increases as contact pressure increases. In addition, tangential contact stiffness increases with the nominal contact area, but is not proportional to the area. The non-dimensional slip range (corresponding to the ratio of slip range to stick displacement) was confirmed as being described in a unified form against different contact area (6 and 18 mm2) and contact pressure ranging from 3 to 40 MPa.
Numerical and Experimental Investigation of Thermo–Acoustic Combustion Instability in a Longitudinal Combustion Chamber: Influence of the Geometry of the Plenum
Authors: Laera Davide , Gentile Andrea , Camporeale Sergio M. , Bertolotto Edoardo , Rofi Luca , Bonzani Federico
Published: August 2015

This paper concerns the study of self–sustained combustion instabilities that occur in a test rig characterized by a single longitudinal combustion chamber equipped with a full scale industrial burner and a longitudinal plenum. The length of both plenum and combustion chamber can be continuously varied. During tests, at a fixed value of the length of the combustion chamber, a sensibility of the amplitude of pressure oscillations to the length of the plenum has been registered, while the frequency remained constant. To investigate this behavior, a linear stability analysis has been performed evaluating the influence of the length of the plenum on the frequency and growth rate of the registered unstable mode. The analysis has been performed by means of a finite element method (FEM) code with a three–dimensional distribution of the n-τ Flame Transfer Function (FTF) computed by means of computational fluid dynamics (CFD) simulations. According to the Rayleigh criterion, the distribution of the local Rayleigh index has been computed in order to evaluate the acoustic energy production, while the scattering matrix of the entire system has been used to evaluate the acoustic energy losses. Numerical results show that the reduction of the plenum length induces an increase of acoustic energy losses while the energy production remains almost constant. This result is in agreement with the reduction of the pressure oscillations amplitude observed during tests.
Design Considerations of Rotor Cone Angle for Downwind Wind Turbines
Authors: Kress Christian , Chokani Ndaona , Abhari Reza S.
Published: August 2015

Due to their potential to use light, flexible blades, downwind turbines are well suited for offshore floating platforms, for which there is a need to substantially lower the cost of wind-generated electricity. However, downwind rotors must operate in the presence of the tower’s wakes with which are associated strong changes in flow incidence, and thus high fatigue loads. In order to guide the development of design rules for multi-megawatt downwind turbines, a comprehensive experimental study has been conducted to better understand the characteristics of the unsteady rotor torque on downwind turbines. High frequency measurements of the unsteady rotor torque on a model turbine that can be configured with rotors of different cone angles, and operated either downwind or upwind in well-controlled flow conditions are conducted. The measurements show that in the case of the downwind turbine, the blade’s passage through the tower’s wake accounts for 56% to 61% of the variance of the rotor torque; the proportion of this unsteadiness is independent of the cone angle. For non-optimum tip speed ratios, the increase in unsteadiness is consistently less for downwind configurations than for upwind configurations. For the 5°-cone downwind configuration, the increase in rotor torque unsteadiness is 13%–18% of the increase observed for the 5°-cone upwind configuration for non-optimum tip speed ratios. Thus from a design perspective, downwind rotor configurations offer above or below rated wind speed, a smaller increase in unsteadiness of the rotor torque compared to upwind turbine configurations. These characteristics differ from upwind turbines, on which broadband vortex shedding from the blade is the primary source of the unsteadiness, which may be reduced by increasing the rotor-tower clearance. It is suggested that given the strong periodic character of the blade’s passage through the tower’s wake, the turbine control system may be designed to reduce fatigue loads and there is a broader design space on downwind turbines that can be exploited for peak load mitigation by moderately adjusting the blade’s stiffness.
Nacelle Aerodynamic Optimization and Inlet Compatibility
Authors: Chen Jingjing , Wu Yadong , Wang Zhonglin , Wang Anjenq
Published: August 2015

The design of air induction system is targeting to balance the internal and external flow characteristics as well as the structure and aerodynamic integrity. An optimized air intake design that providing velocity and pressure distributions with least drag and maximum pressure recovery could end up at the expense of higher inlet flow distortion and lower stability margin. Indeed, design requirements and considerations at different operating conditions, such as takeoff, and high AOA maneuvers, could be significantly different from that of cruise and level flight. One of the most challenged operating conditions to be certified for FAR33 & FAR25 requirements is ground crosswind condition, when “Engine” is operating statically on the ground with high crosswind presented. It could accommodate inlet separation or distortion resulted from crosswind, and triggers fan or core stall, as well as induces high fan and/or engine vibrations. Studies of engine inlet compatibility become one of the major tasks required during the engine developing phase.

This research is a parametric study of using CFD to evaluate operational characteristics of the air induction system. Comparisons of various inlet designs are made and characterized into four categories, i.e., i) Inlet pressure loss, ii) Nacelle drag, iii) Inlet flow distortion, and iv) Inlet Mach distribution. The objective is to assess the impact of air induction design of turbofan upon inlet compatibility.

The research introduces the Kriging model and weighting coefficients to optimize internal total pressure loss and external drag using the isolated nacelle model. Bezier equation was used to fit the optimized curves obtained by changing several control points of the baseline configuration of nacelle. To study the impact of asymmetric lip on flow separation in ground crosswind condition, the paper built crosswind model which introduce a inlet boundary as fan face. Comparisons are then made between the original and optimal nacelle, to show correlation between inlet compatibility and air intake profile.
Effects of Heat-Treatment Residual Stress on Low Cycle Fatigue Life of a Turbine Disk in PM Superalloy
Authors: Wang Rongqiao , Li Da , Hu Dianyin , Hai Yang , Song Jun
Published: August 2015

Turbine disks in powder metallurgy (PM) superalloy have been widely used in advanced aeroengines. The production of PM superalloy turbine disks involves a series of heat treatment processes, which would inevitably create residual stresses. It has been proved that the low cycle fatigue (LCF) life of the turbine disk is affected by the residual stresses. The computational simulation of heat treatment is considered as an effective way to evaluate the residual stresses in a turbine disk. A finite element software was used to simulate the heat-treatment processes of a FGH95 turbine disk to obtain the residual stress field.

To investigate the relaxation of residual stress in FGH95, smooth bar specimens were measured by X-ray diffraction before and after being loaded. Modified by the residual stresses, SWT model is used to predict the low cycle fatigue life of the turbine disk modified by the residual stress field obtained from the simulation of heat treatment.

By the comparison between the prediction modified by the residual stress and the prediction without modification, a considerable decrease in low cycle fatigue life is indicated.
Thermoeconomic Evaluation of a Novel Utility-Scale Hybrid Solar Dish Micro Gas-Turbine Power Plant
Authors: Spelling James , Aichmayer Lukas , Laumert Björn
Published: August 2015

A novel solar power plant concept is presented, based on the use of a coupled network of hybrid solar-dish micro gas-turbines, driving a centralized heat recovery steam generator and steam-cycle, thereby seeking to combine the high collector efficiency of the solar dish with the high conversion efficiency of a combined-cycle power block. To explore the potential of the concept, its performance has been compared against a more conventional solar dish farm based on recuperated micro gas-turbines. Multi-objective optimization has been used to identify Pareto-optimal designs and examine the trade-offs between minimizing capital costs and maximizing performance. The micro gas-turbine combined-cycle layout has been shown to be promising for utility-scale applications, reducing electricity costs by 5–10%, depending on the degree of solar integration; this novel power plant layout also reduces emissions through increased conversion efficiency of the power block. However, at smaller plant sizes (outputs below 18 MWe), more traditional recuperated solar dish farms remain the most viable option.
Numerical Investigation of a Non-Confined Spray Flame Exposed to Acoustic Forcing
Authors: Fratalocchi Virginia , Kok Jim B. W.
Published: August 2015

A numerical investigation of the interaction between a spray flame and an acoustic forcing of the velocity field is presented in this paper. The test-case which is the focus of this work is a non-confined flame1,2 burning at atmospheric pressure and therefore the velocity fluctuations play a key role. Acoustic waves will eventually affect the rate of combustion, and the oscillating fluctuation of the heat released by the flame might be increased by the evaporation process. The dynamic interaction between the evaporating fuel spray and the velocity fluctuations induced by an acoustic perturbation is investigated to understand the impact of the acoustic waves on the droplet dispersion and on the evaporation rate. The influence of the initial droplet diameter has been observed to be irrelevant, when two monodispersed sprays of 20 μm and 80 μm were numerically simulated. In this work the main question to address is how the interphase heat and mass transfer, and the momentum exchange are influenced, at low amplitude velocity fluctuations, by the forcing frequency, under two different imposed velocity profiles of the liquid fuel. A fast decay of the slip velocity is predicted under both steady and perturbed conditions. Thus, slip velocity fluctuations do not have a significant influence on the solved spray field. Finally, the impact of the forcing frequency and of the pilot are the main effects acting on the forced flame response. At low frequency, the entrainment of hot gases into the spray results in a clearly visible stretching of the flame which causes a high level of temperature fluctuation. At high frequency, despite the weak response of the gas velocity field, the dynamics of the combustion show a faster evaporation rate than the acoustic–free case.
Heat Transfer Measurements Downstream of Trenched Film Cooling Holes Using a Novel Optical Two-Layer Measurement Technique
Authors: Schreivogel Peter , Pfitzner Michael
Published: August 2015

A new approach for steady state heat transfer measurements is proposed. Temperature distributions are measured at the surface and a defined depth inside the wall to provide boundary conditions for a three-dimensional heat flux calculation. The practical application of the technique is demonstrated by employing a superposition method to measure heat transfer and film cooling effectiveness downstream of two different 0.75D deep narrow trench geometries and cylindrical holes. Compared to the cylindrical holes, both trench geometries lead to an augmentation of the heat transfer coefficient supposedly caused by the highly turbulent attached cooling film emanating from the trenches. Areas of high heat transfer are visible, where recirculation bubbles or large amounts of coolant are expected. Increasing the density ratio from 1.33 to 1.60 led to a slight reduction of the heat transfer coefficient and an increased cooling effectiveness. Both trenches provide a net heat flux reduction superior to that of cylindrical holes, especially at the highest momentum flux ratios.
Combined Experimental and Numerical Study of Showerhead Film Cooling in a Linear Nozzle Vane Cascade
Authors: Barigozzi G. , Ravelli S.
Published: August 2015

In this paper showerhead film cooling performance measured on a first stage nozzle guide vane within a linear cascade are presented and compared against steady and unsteady CFD simulations. A showerhead cooling scheme was tested at blowing ratios of BR = 2 to 4 under engine-like conditions (i.e. nominal exit Mach number of Ma2is = 0.42 and high mainstream turbulence level). Adiabatic film cooling effectiveness in the leading edge region was measured by means of wide banded Thermochromic Liquid Crystals. A borescope was used to overcome the constraints to the optical access imposed by the turbulence generator. Moreover, exit surveys detailing total pressure downstream of the cooled vane were acquired using a five-hole miniaturized aerodynamic pressure probe. In view of qualitative/quantitative validation purposes, numerical modelling based on steady RANS and Detached Eddy Simulation (DES) approach was performed for the lowest investigated BR of 2.0, which provided the best film coverage. Nevertheless the dilution of the coolant jets from the showerhead was predicted by DES, agreement with the measured cooling effectiveness in the leading edge region was still far from being achieved. Instead, the steady approach was enough to capture aerodynamic features such as vane load, wake loss and plenum to mainstream pressure ratio.
Experimental Investigation of Fuel Composition Effects on Syngas Combustion
Authors: Bouten Thijs , Beran Martin , Axelsson Lars-Uno
Published: August 2015

The OPRA OP16 gas turbine is an all radial single-shaft gas turbine rated at 1.9 MW with a successful track record from oil and gas applications as well as industrial and commercial CHP applications. To meet the growing demand for alternative fuels, OPRA Turbines has developed a new tubular combustor for the OP16 gas turbine fleet. The combustor has been successfully tested on a wide variety of (ultra-) low-calorific gaseous fuels in an atmospheric combustion test rig.

This paper presents an experimental investigation of syngas combustion in the low-calorific fuel combustor. The effect of the variation in fuel composition on the combustion characteristics has been investigated extensively. This includes the effect of variable heating values and variations in the ratio between hydrogen and carbon monoxide and between syngas and hydrocarbons. The effects of these variations on the combustor performance, emissions and lean blowout limits will be discussed and compared to the results obtained from the combustion of propane. Major differences in emissions have been found, mainly influenced by the flame temperature and presence of hydrogen in the fuel. Lean blowout of the combustor is largely determined by the presence of hydrogen, whereas other components are found to have less influence.

Theoretical calculation, based on le Chatelier’s rule and a method based on heat release, of the lean blowout limit has been compared to the experiments. It was found that the heat release method predicts the flammability limit more accurately than le Chatelier’s rule. This is caused by the inaccuracy of the latter to handle fuels with a large amount of hydrogen.
Aerodynamic Implications of Reduced Vane Count
Authors: Saha Ranjan , Fridh Jens , Annerfeldt Mats
Published: August 2015

Given the shortage of fossil fuels and the growing greenhouse effect, one strive in modern gas turbines is to make maximum usage of the burnt fuel. By reducing the number of vanes or blades and thereby increasing the loading per vane (or blade) it is possible to spend less cooling air, which will have a positive impact on the combined cycle efficiency. It also reduces the number of components and usage of metal and thereby also the cost of the engine. These savings should be achieved without any efficiency deficit in aerodynamic efficiency. Based on the fact, aerodynamic investigations were performed to see the aerodynamic implications of reduced vane number in a transonic annular sector cascade. The number of new nozzle guide vane was reduced with 24% compared to a previous design with higher vane count. The investigated vanes were two typical high pressure gas turbine vanes. Results regarding the loading indicated an expected increase with the reduced vane case. The minimum static pressure at the suction side is lower and at an earlier location for the reduced vane case and therefore, an extension of the trailing edge deceleration zone is observed for the reduced vane case. Results regarding losses indicate that even though the losses produced per vane significantly increases for the reduced vane case, a comparison of mass averaged losses between the reduced vane case and previous vane case show similar spanwise loss distributions. Assessing results leads to a conclusion that the reduction of the number of vanes in the first stage seems to be a useful method to save cooling flow as well as material costs without any significant deficit in overall efficiency.
Novel Turbulators to Enhance Turbine Blade Internal Heat Transfer Rates
Authors: Bommisetty Venkata Naga Ramakumar , Murari Sridhar , Liu Jong S. , Malak Malak F.
Published: August 2015

Turbine blades are driven by hot gases from the combustor. The heat transfer from the hot gases produces substantial thermal load and can affect the performance of the turbine blades. In previous designs, cavities inside the blades were created to pass the coolant. Such cooling designs helped to increase the thermal performance of the blades by taking away the turbine blades’ heat. The cooling effect was further enhanced by increasing the turbulence in the flow of coolant. To increase the turbulence in the cavities, various turbulator designs were proposed. However, most of the designs have also introduced wake area while increasing the turbulence. This reduces the heat exchange between the coolant and the blade. The current paper discusses new designs of tabulators for turbine blades that increase the heat transfer rates of the cooling surface by increasing the turbulence of the coolant flow while minimizing the wake area.
Generalized Thermodynamic Assessment of Concepts for Increasing the Efficiency of Civil Aircraft Propulsion Systems
Authors: Schmidt Florian , Staudacher Stephan
Published: August 2015

It is known from thermodynamics that intercooling, recuperation, sequential combustion and constant-volume combustion increase the efficiency of thermal engines. Although these concepts are already analyzed at a high level of detail, no comparative and structured assessment of the theoretic and realistic efficiency increase for long-range turbofan engines is given. In light of this a generalized thermodynamic assessment of the mentioned technologies is conducted. First, current technological limits are ignored and the propulsive power is completely utilized. Theoretic efficiency improvements of over 24% are obtained. Second, the modelling is refined to include a ducted fan, turbine blade cooling and account for minimum blade height and maximum temperature at HPC outlet. Realistic efficiency improvements of still over 10% are identified. It is shown that significant increases in efficiency necessitate new engine architectures, outlining the restrictions of the current engine architecture. Intercooling is identified as the driving technology for high efficiency.
Experimental Investigation on Dynamical Response of an Overhung Rotor due to Sudden Unbalance
Authors: Ma Yanhong , Liang Zhichao , Zhang Dayi , Yan Wenzhong , Hong Jie
Published: August 2015

Blade loss is a typical extreme load in the turbo machinery, which can cause intense vibration in rotor and huge loads in supporting system due to the sudden unbalance applied on the disk. An overhung rotor-support system is built to study the dynamic characteristics of rotor and support experimental system under the sudden unbalance excitation. The responses due to a mass loss are tested respectively both in subcritical state and in supercritical state, further the orbits of the rotor and load transmitting process on the stator are obtained and investigated. Moreover, the impact effect of response achieved by a mechanical model is presented to compare with the test result. The results show that sudden unbalance can induce an impact effect on the rotor system with response containing rotational speed frequency and natural frequency in frequency domain. The impact effect is more evident for flexible rotor than the rigid rotor, and the vibration response exhibits local effect. As a consequence the paper provides a reference and basis for the dynamical design and analysis for flexible overhung rotor system suffering sudden unbalance.