bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative CFD Analyses of Particle Deposition on a Subsonic Axial Compressor Blade
Authors: Suman Alessio , Kurz Rainer , Aldi Nicola , Morini Mirko , Brun Klaus , Pinelli Michele , Spina Pier Ruggero
Published: August 2015

In literature there are some studies related to the fouling phenomena in transonic compressors, but, in industrial applications (heavy-duty compressor, pump stations, etc.) the subsonic compressors are widespread. It is of great interest to the manufacturer to discover the fouling phenomenon related to this type of compressor.

This paper presents three-dimensional numerical simulations of the micro-particle ingestion on a subsonic axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase.

The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface.

In this paper the particle impact pattern and the kinematic characteristics (velocity and angle) of the impact are shown. Both of the blade zones affected by particle impact and the blade zones affected by particle deposition are analyzed. The particle deposition is established by using the quantity called sticking probability. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon.

The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the leading edge. The suction side is affected only close to the leading edge and, at the hub, close to the trailing edge. Particular fluid-dynamic phenomena such as separation, stagnation and tip leakage vortex strongly influence the impact location of the particles. The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for smaller particles for which the fluid dynamic phenomena play a key role regarding particle impact velocity and angle.
Estimation of the Particle Deposition on a Transonic Axial Compressor Blade
Authors: Suman Alessio , Morini Mirko , Kurz Rainer , Aldi Nicola , Brun Klaus , Pinelli Michele , Spina Pier Ruggero
Published: August 2015

Solid particle ingestion is one of the principal degradation mechanisms in the compressor section of heavy-duty gas turbines. Usually, foulants in the ppm range, not captured by the air filtration system (0–2) μm cause deposits on blading and result in a severe performance drop of the compressor. It is of great interest to the industry to determine which areas of the compressor airfoils are interested by these contaminants as a function of the location of the power unit.

The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. The size of the particles, their concentrations and the filtration efficiency are specified in order to perform a realistic quantitative analysis of the fouling phenomena in an axial compressor. This study combines, for the first time, the impact/adhesion characteristic of the particles obtained through a CFD and the real size distribution of the contaminants in the air swallowed by the compressor.

The blade zones affected by deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface in terms of contaminant mass.

The analysis showed that particular fluid-dynamic phenomena such as separation, shock waves and tip leakage vortex strongly influence the pattern deposition. The combination of the smaller particles (0.15 μm) and the larger ones (1.50 μm) determines the highest amounts of deposits on the leading edge of the compressor airfoil.

From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn.
Impact of Turbine Blade Internal Cooling on Aerodynamic Loss
Authors: Vassiliev Vladimir , Granovskiy Andrey , Lomakin Nikolai
Published: August 2015

Modern gas turbines operate at high temperature, which exceed the endurance limit of material, and therefore the turbines components have to be cooled by the air taken from the compressor. The cooling providing positive impact on lifetime of GT has negative impact on its performance. Firstly because the cooling air bypasses combustor and its capacity is not fully utilized. This effect is usually accounted in thermodynamic calculations of gas turbine. Secondly the injection of cooling air in the turbine disturbs the main flow, and may lead to increased losses. In addition cooling requirements lead to limitation on the blade shape (e.g. limiting the minimal size of trailing edge) and thereby negatively affect the losses. These effects were already discussed in the literature, but further investigations for better understanding of flow physics and design improvement are still useful.

There is also additional impact of cooling - impact of heat transfer on near wall boundary layer and coolant properties. This effect was not sufficiently discussed in the open literature, where quite often the walls are considered as adiabatic.

The paper consists of two main parts. In the first part the results of experimental investigations of several linear cascades with and without trailing edge injection are presented and discussed.

In the second part the results of detailed numerical investigations of one of these cascades are presented. One set of calculations were done at the test rig conditions for comparison with measured data. These calculations were used for validation of CFD model. The next sets of calculations were done for engine typical conditions, including the simulation of blade material temperature. The calculations were performed for adiabatic wall and for surface with heat transfer, including the impact of heat transfer on coolant injection. This analysis provides split of losses caused by different factors, and offers the opportunities for efficiency and lifetime improvements of real engine designs/upgrades.
Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
Authors: Storgärds Erik , Saarimäki Jonas , Simonsson Kjell , Sjöström Sören , Gustafsson David , Månsson Tomas , Moverare Johan
Published: August 2015

In this paper scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550°C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provides for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analysing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other is of significant proportions.
Modal Characterization, Strain Gauge Setup and 1-Way FSI of a Low Pressure Turbine Rotor Blading
Authors: Schönleitner F. , Traussnig L. , Heitmeir F. , Marn A.
Published: August 2015

New designs of low pressure turbines show optimized geometries of stator and rotor blading as well as reduced axial spacing between stator and rotor due to the main target of saving weight which is directly related to the fuel consumption of the aero engine. An important step during the realization process is to investigate altered excitation mechanism. For this purpose aero elastic investigations will be performed at the test rig of Graz University of Technology. In general for a serious prediction of vibration characteristics under operating conditions of any structure a detailed knowledge of the dynamic behavior is essential. In preparation of upcoming strain gauge vibration measurements in combination with a telemetry system of the low pressure turbine rotor blading, modal characteristics as well as a realistic estimation of blade deformation are mandatory. Within this paper different methods of evaluating modal characteristic numerical as well as experimental such as impact hammer and shaker tests, respectively are presented. Numerical investigations show different models and mathematical contact formulation and should provide a better understanding for using correct contact models additionally. When comparing numerical with experimental results a prediction of an optimal strain gauge setup for vibration measurements as well as a simplified numerical model for further aero elastic investigations, such as fluid structure interaction analysis (FSI), complete previous investigations. In order to set up the telemetry system the knowledge of blade deformation at operating conditions is of particular importance. Therefore finally in this paper a 1-way FSI coupling is presented.
Analysis of Measured Flame Transfer Functions With Locally Resolved Density Fluctuation and OH-Chemiluminescence Data
Authors: Peterleithner Johannes , Stadlmair Nicolai V. , Woisetschläger Jakob , Sattelmayer Thomas
Published: August 2015

The goal of the study presented in this paper is to analyze flame transfer functions with a new approach based on the combination of-line-of sight OH*-chemiluminescence and density fluctuation data. The OH*-chemiluminescence is acquired with a photomultiplier and an intensified camera, the density fluctuations are measured with a Laser vibrometer on a two axis traverse. In flames with forcing the acoustic fluctuations can be extracted from the data by discrimination of all contributions from combustion noise, because it is not correlated with the excitation device. Assuming rotational symmetry of the fluctuations originating from excitation, planar phase-resolved and pseudo-local OH*-chemiluminescence and density fluctuation data is obtained from the measured line-of-sight integrated signals.

In the study this technique is applied to a swirl burner configuration with FTFs from known multi-microphone measurements (MMM). In the first step, the externally premixed mode without equivalence ratio fluctuations is studied and in the second step the fuel is injected in the swirler in order to generate equivalence ratio waves. At selected frequencies the planar fields of the OH*-chemiluminescence and density fluctuations are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. In addition to heat release the vibrometer data reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products. On the global scale the amplitudes and phases of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release if equivalence ratio fluctuations are present, because the amplitude of the FTF is significantly over-predicted due to the sensitivity of OH* on the local fuel-air mixture.
Investigation of Annular Jet Flows in a Subsonic Air-Air Ejector With Multi-Ring Entraining Diffuser
Authors: Namet-Allah A. , Birk A. M.
Published: August 2015

The current paper presents a cold flow simulation study of a low Mach number air-air ejector with a four ring entraining diffuser that is used in a variety of applications including infrared (IR) suppression of exhaust from helicopters and fixed wing aircraft. The main objectives of this investigation were to identify key issues that must be addressed in successful CFD modelling of such devices, and recognize opportunities to improve the performance of these devices. Two-dimensional CFD simulations were carried out using commercial software, Ansys14. Studies of mesh and domain size sensitivity were made to ensure the CFD results were independent of both factors. A turbulence model independence study using k-ε, k-ω and RSM turbulence models was performed to figure out the appropriate turbulence model that produced the best agreement with the experimental data for several of ejector performance criteria. The measured flow properties in the annulus were used as input boundary conditions for the CFD simulations. However, in the comprehensive turbulence model study, the measured flow parameters at the nozzle exit were also applied as inlet boundary conditions for the CFD simulations. The measured flow velocity at the nozzle exit, at one centerline section inside the mixing tube and at the diffuser exit and the system pressure recovery were compared with the CFD predictions. The ejector pumping ratios, back pressure coefficient and diffuser gap velocities were also compared.

It was found that the RANS-based CFD predictions were sensitive to the changes in the ejector domain size, mesh refinement and inlet boundary condition locations. With the annulus inlet boundary conditions, the tested turbulence models under predicted the size of the core separation downstream of the system, back pressure, pumping ratio and pressure recovery in the mixing tube and diffuser. However, the ability of the RNG turbulence model to predict the ejector performance parameters was better than that of the other turbulence models at all inlet flow conditions. Nevertheless, applying the inlet boundary conditions at the nozzle exit enhanced the capability of the RANS-based turbulence model particularly in predicting the ejector pumping ratios, pressure recovery and the size of the core separation. Finally, the acceptable agreement between the experimental data and the CFD predictions provides a valid tool to continue improving these devices using CFD techniques.
The Influence of Diluent Gases on Combustion Properties of Natural Gas: A Combined Experimental and Modeling Study
Authors: Ermel Jörn , Richter Sandra , Kick Thomas , Braun-Unkhoff Marina , Naumann Clemens , Riedel Uwe
Published: August 2015

Currently, new concepts for power generation are discussed, as a response to combat global warming due to CO2 emissions stemming from the combustion of fossil fuels. These concepts include new, low-carbon fuels as well as centralized and decentralized solutions. Thus, a more diverse range of fuel supplies will be used, with (biogenic) low-caloric gases such as syngas and coke oven gas (COG) among them. Typical for theses low-caloric gases is the amount of hydrogen, with a share of 50% and even higher. However, hydrogen mixtures have a higher reactivity than natural gas (NG) mixtures, burned mostly in today’s gas turbine combustors.

Therefore, in the present work, a combined experimental and modeling study of nitrogen-enriched hydrogen-air mixtures, some of them with a share of methane, to be representative for COG, will be discussed focusing on laminar flame speed data Su as one of the major combustion properties. Measurements were performed in a burner test rig at ambient pressure and at a preheat temperature T0 of 373 K. Flames were stabilized at fuel-air ratios between about φ = 0.5–2.1, depending on the specific fuel-air mixture.

This database was used for the validation of four chemical kinetic reaction models, including an in-house one, and by referring to hydrogen-enriched natural gas mixtures.

The measured laminar flame speed data of nitrogen-enriched methane-hydrogen-air mixtures are much smaller than the ones of nitrogen-enriched hydrogen-air mixtures. The grade of agreement between measured and predicted data depends on the type of flames and the type of reaction model as well as of the fuel-air ratio: good agreement was found in the fuel lean and slightly fuel rich regime; a large underprediction of the measured data exists at very fuel-rich ratios (φ > 1.4).

From the results of the present work, it is obvious that further investigations should focus on highly nitrogen-enriched methane-air mixtures, in particular for very high fuel-air ratio (φ > 1.4). This knowledge will contribute to a more efficient and a more reliable use of low-caloric gases for power generation.
DNS of Flow in a Low-Pressure Turbine Cascade Using a Discontinuous-Galerkin Spectral-Element Method
Authors: Garai Anirban , Diosady Laslo , Murman Scott , Madavan Nateri
Published: August 2015

A new computational capability under development for accurate and efficient high-fidelity direct numerical simulation (DNS) and large-eddy simulation (LES) of turbomachinery is described. This capability is based on an entropy-stable Discontinuous-Galerkin spectral-element approach that extends to arbitrarily high orders of spatial and temporal accuracy, and is implemented in a computationally efficient manner on a modern high performance computer architecture. A validation study using this method to perform DNS of flow in a low-pressure turbine airfoil cascade is presented. The results indicate that the method captures the main features of the flow.
Experimental Study of the Interactions Between Air Flow Rate Modulations and PVC in a Swirl-Stabilised Liquid Fuel Burner
Authors: Renaud Antoine , Ducruix Sébastien , Scouflaire Philippe , Zimmer Laurent
Published: August 2015

In a swirl-stabilised liquid fuel burner, the fuel spray response to the Precessing Vortex Core (PVC) and air flow rate modulations is analysed in non-reacting conditions. A siren-like device is used to modulate the air flow rate at a frequency corresponding to longitudinal combustion instability oscillations observed during reacting tests. Time-resolved Mie scattering images of the fuel spray are recorded and treated with multiple post-processing methods based on Dynamic Mode Decomposition. The spray velocity fluctuations induced by the PVC and the siren-generated modulations are extracted from noisy datasets and studied. The evolution of the PVC impact on the spray for different levels of flow rate fluctuations is followed and a nonlinear interaction mode is highlighted for several intensities of flow rate modulations. It is shown that increasing the flow rate modulations tend to weaken the PVC impact on the spray, progressively disturbing its structure, starting from the downstream part and progressing upstream. These observations on the fuel spray can be used to understand and interpret data obtained in reacting conditions, for example when competition between PVC and longitudinal combustion instabilities occurs.
Effect of Pad Flexibility on the Performance of Tilting Pad Journal Bearings: Benchmarking a Predictive Model
Authors: San Andrés Luis , Li Yingkun
Published: August 2015

Tilting pad journal bearings (TPJBs) supporting high performance turbomachinery rotors have undergone steady design improvements to satisfy ever stringent operating conditions that include large specific loads due to smaller footprints, and high surface speeds that promote flow turbulence and thus larger drag power losses. Simultaneously, predictive models continuously evolve to include minute details on bearing geometry, pads and pivots’ configurations, oil delivery systems, etc. In general, predicted TPJB rotordynamic force coefficients correlate well with experimental data for operation with small to moderately large unit loads (1.7 MPa). Experiments also demonstrate bearing dynamic stiffnesses are frequency dependent, best fitted with a stiffness-mass like model whereas damping coefficients are adequately represented as of viscous type. However, for operation with large specific loads (> 1.7 MPa), poor correlation of predictions to measured force coefficients is common. Recently, an experimental effort [1] produced test data for three TPJB sets, each having three pads of unequal thickness, to quantify the effect of pad flexibility on the bearings’ force coefficients, in particular damping, over a range of load and rotational speed conditions. This paper introduces a fluid film flow model accounting for both pivot and pad flexibility to predict the bearing journal eccentricity, drag power loss, lubricant temperature rise and force coefficients of typical TPJBs. A finite element pad structural model including the Babbitt layer is coupled to the thin film flow model to determine the mechanical deformation of the pad surface. Predictions correlate favorably with test data, also demonstrating that pad flexibility produces a reduction of up to 34% in damping for the bearing with the thinnest pads relative to that with the thickest pads. A parametric study follows to quantify the influence of pad thickness on the rotordynamic force coefficients of a sample TPJB with three pads of increasing preload, rp = 0, 0.25 (baseline) and 0.5. The bearing pads are either rigid or flexible by varying their thickness. For design considerations, dimensionless static and dynamic characteristics of the bearings are presented versus the Sommerfeld number (S). Pad flexibility shows a more pronounced effect on the journal eccentricity and the force coefficients of a TPJB with null pad preload than for the bearings with larger pad preloads (0.25 and 0.5), in particular for operation with a small load or at a high surface speed (S>0.8).
Effect of Machining Errors on the Gear Engagement Using Contact Finite Element Method
Authors: Zhang Tao , Wang Jianjun , Wu Yongjun , Zhang Haiying
Published: August 2015

Machining errors have a significant effect on the gear engagement, so it is necessary to learn the mechanism of action for the reduction of vibration. The contact finite element method was utilized to study the effect of machining errors on the gear pair’s vibration. The 3D shape deviation caused by machining errors was decomposed into pitch error, profile error and helix error, the precise modeling method was first presented, on this basis the dynamic engagement process of one spur gear pairs was simulated continuously using contact finite element method as an example. The time-domain response of various dynamic parameters was obtained, and the angular velocity, dynamic meshing force and stress distribution showed significant differences between the ideal gear pairs and the gear pairs with machining errors. Then the influence mechanism of profile error, pitch error and helix error on the gear vibration was researched respectively, quantitative analysis of meshing characteristics including dynamic transmission error and angular acceleration was done using the FFT. The results show that the proposed modeling method can simulate arbitrary form of machining errors even if in small order and reflected in the contact finite element analysis. It is not only effective to investigate how the machining errors impact the meshing process, but also to study the influence mechanism of individual machining error. Furthermore, the conclusions can be used to guide the anti-vibration design and accuracy design.
Application of a Creep Damage Constitutive Model for the Rotor of a 1000 MW Ultra-Supercritical Steam Turbine
Authors: Jiang Jishen , Wang Weizhe , Zhao Nailong , Wang Peng , Liu Yingzheng , Jiang Puning
Published: August 2015

A damage-based creep constitutive model for a wide stress range is applied to the creep analysis of a 1000 MW ultra-supercritical steam turbine, the inlet steam of which reaches 600°C and 35 MPa. In this model, the effect of complex multi-axial stress and the nonlinear evolution of damage are considered. To this end, the model was implemented into the commercial software ABAQUS using a user-defined material subroutine code. The temperature dependent material constants were identified from the experimental data of advanced heat resistant steels using curve fitting approaches. A comparison of the simulated and the measured results showed that they reached an acceptable agreement. The results of the creep analysis illustrated that the proposed approach explains the basic features of stress redistribution and the damage evolution in the steam turbine rotor over a wide range of stresses and temperatures.
The Effect of Wavy Leading Edge on Low Speed Turbine Cascade Aerodynamic and Acoustic Performance
Authors: Tong Fan , Qiao Wei-Yang , Wang Liang-Feng , Xu Kun-Bo , Chen Wei-Jie , Wang Xun-Nian
Published: August 2015

LES and acoustic analogy are performed to investigate the effect of wavy leading edge on a linear low pressure turbine cascade aerodynamic performance and the turbulence cascade interaction noise. One straight leading edge cascade and two different wavy leading edge cascades are studied. In each case a rod with a diameter of 2.05mm is placed upstream of the cascade to produce wake which will then interact with the cascade leading edge. Results show that the wavy leading edge can reduce the turbulence cascade interaction noise peak by up to about 6∼8dB in narrow band and attenuate interaction broadband noise by about 3dB in the frequency range below 4000Hz. However, wavy leading edge can lead to a self noise increase in some frequency and increase cascade total pressure loss. Wavy leading edge can change the flow field near the leading edge while the further downstream flow field is altered only a little. The mechanism of noise reduction is also investigated. It is shown that wavy leading edge can reduce blade surface pressure fluctuation near the leading edge. In addition, the spatial-temporal correlation coefficient of pressure fluctuation near the blade leading edge is also decreased. These factors may work jointly and contribute to the final noise reduction.
Large Eddy Simulations of a Liquid Fuel Swirl Burner: Flame Characterization for Pilot and Multipoint Injection Strategies
Authors: Cheneau Benoit , Vié Aymeric , Ducruix Sébastien
Published: August 2015

A laboratory-scale swirling burner fueled with dodecane is studied numerically using large eddy simulations. The burner is composed of two stages, allowing the use of two different injector types (namely pilot and multipoint) in order to study the influence of droplet size and initial position with fixed geometry and delivered power. For a chosen lean operating point, the two liquid injection types are tested, highlighting a dramatic influence on the flame stabilization process. When fuel is injected through the multipoint stage, evaporation and mixing are enhanced and a partially premixed mixture enters the combustion chamber. The flame then takes an ‘M’ shape, mainly controlled by the large inner and outer recirculation zones associated with this highly swirling flow and in which trapped burnt gases guarantee permanent ignition of the fresh mixture entering the chamber. The situation is much more complex when fuel is solely injected through the pilot nozzle. Due to the large amount of liquid fuel present in the pilot zone, premixing is not achieved and the flame must stabilize itself mainly in a hybrid combustion regime. This is only possible thanks to a very complex situation in this region, where hot evaporated fuel is trapped in front of the nozzle and oxygen is mainly coming from the large central recirculation zone. In that case, the flame takes a ‘tulip’ shape, with a stabilization point inside the injection device. Both flame shapes are compared using scatterplots and flame dynamics are analyzed.
3D Flame Measurements at 5 kHz on a Jet Fueled Aviation Combustor
Authors: Ma Lin , Li Xuesong , Kang MinWook , Lamont Warren G. , Venkatesan Krishnakumar , Wehe Shawn
Published: August 2015

This paper describes the measurements of three-dimensional (3D) flame measurements at 5 kHz from an optically accessible, atmospheric combustor burning Jet A. The measurements were performed by 3D tomography of flame chemiluminescence emissions. Such measurements resolve the instantaneous flame topography generated by the combustor in all three spatial directions and at a temporal resolution of 5 kHz (0.2 ms), essentially providing 4D information about the combustor. This paper reports the measurement technique, the experimental implementation, the results and their expected use for the continued development of future combustor concepts.
An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in Confined and Non-Confined Environment
Authors: Dossena Vincenzo , Persico Giacomo , Paradiso Berardo , Battisti Lorenzo , Dell’Anna Sergio , Brighenti Alessandra , Benini Enrico
Published: August 2015

This paper presents the results of a wide experimental study on an H-type Vertical Axis Wind Turbine (VAWT) carried out at Politecnico di Milano in the frame of the national founded project PRIN 2009. The experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where real-scale wind turbines for micro generation can be tested in full similarity conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor.

The machine was tested in both confined and non-confined environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio λ = 2.5. Detailed flow measurements, performed in three conditions for λ equal to 1.5, 2.5 and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a non-symmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlight the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of a non-symmetric dynamic stall for λ lower than 2.
Optimization of Compressor Variable Geometry Settings Using Multi-Fidelity Simulation
Authors: Reitenbach S. , Schnös M. , Becker R.-G. , Otten T.
Published: August 2015

Variable geometry blade rows are a common instrument to avoid compressor instabilities which occur especially at low- and full-speed operation of gas turbines. The operating settings of variable stator vanes (VSVs) are typically obtained from expensive and time consuming performance rig tests and are not known during the early design phase of a gas turbine.

During preliminary design of the overall engine it is common practice to use default component characteristics based on considerable engineering experience. These can deviate substantially at off-design and often do not properly account for the impact of changes in component geometry. As a solution, multi-fidelity simulation often referred to as zooming or variable complexity analysis is applied. This proceeding facilitates a transfer of single component performance characteristics obtained in mid- or high-fidelity analysis to a full gas turbine system analysis based on lower resolution level.

The purpose of this study is to present a multidisciplinary numerical optimization methodology to define ideal blade row staggering of variable compressor stator vanes during the early preliminary design phase using multi-fidelity simulation. The objective of the resultant multi-dimensional constraint optimization is to find the best solution for the entire gas turbine system for a set of discrete operating points.

For the assessment a generic turbofan engine model is designed by taking into account top level engine requirements from an assumed airframe and flight mission scenario. Based on the performance calculation a full 3-D axial multistage high pressure compressor (HPC) is designed. The assumed design considerations are summarized and the modelling techniques are presented.

The optimization of VSV staggering mentioned above is carried out by re-staggering the variable geometry blade rows of the high-fidelity HPC and run a full 2-dimensional through-flow calculation. Results are then automatically transferred to the 0-dimensional engine model to calculate the engine overall performance. A Pareto optimized blade row staggering is found by taking into account the surge margin and the specific fuel consumption of the entire engine system as objective functions of the optimization process. Simultaneously several constraints such as DeHaller numbers and diffusion factors are considered. The optimization process chain and the tool coupling are summarized and described in detail. The resulting VSV staggering for a set of discrete operating points is shown.
Integrated Modelling and Multi-Objective Optimization of Organic Rankine Cycle Based on Radial Inflow Turbine
Authors: Rahbar K. , Mahmoud S. , Al-Dadah R. K. , Moazami N.
Published: August 2015

This paper presents the integrated modelling and multi-objective optimization of ORC based on radial inflow turbine. With this approach it is possible to replace the constant turbine efficiency with a dynamic efficiency that is unique for each set of cycle operating conditions and working fluid properties. This allows overcoming any arbitrary assumption of the turbine efficiency, unlike the previous literature, and providing a more realistic estimation of the cycle performance. Parametric studies were conducted utilizing the developed model to identify the key input variables that have significant effects on the critical turbine-ORC performance indicators. These variables were then included in the optimization process using DIRECT algorithm to optimize two objective functions as the cycle thermal efficiency and the turbine overall size for five organic fluids. Optimization results predicted that isobutane exhibited the best performance with the maximum cycle thermal efficiency of 13.21% and turbine overall size of 0.1434m while having relatively high turbine isentropic efficiency of 77.03%.
Aerodynamic and Heat Transfer Characterization of a Nozzle Vane Cascade With and Without Platform Cooling
Authors: Barigozzi G. , Perdichizzi A. , Henze M. , Krueckels J.
Published: August 2015

In the present paper, aerodynamic and thermal performance of a linear nozzle vane cascade is fully assessed. Tests have been carried out with and without platform cooling, with coolant ejected through a slot located upstream of the leading edge. Cooling air is also ejected through a row of cylindrical holes located upstream of the slot, simulating a combustor cooling system. The cascade was tested at a high inlet turbulence intensity level (Tu1 = 9%) and at variable cooling injection conditions. Aero-thermal characterization of vane platform was obtained through 5-hole probe measurements, oil & dye surface flow visualizations, measurements of end wall adiabatic film cooling effectiveness and heat transfer coefficient. The platform cooling scheme operated at nominal injection rate was shown to effectively reduce the heat load over most of the platform surface, with only a small increase in secondary flows loss. Combustor holes injection resulted beneficial in controlling momentum of coolant approaching the cascade, thus limiting the secondary flows growth and resulting in an increase of the coolant film length inside of the passage.
Applying Hollow Blades for Small Wind Turbines Operating at High Altitudes
Authors: Pourrajabian Abolfazl , Ebrahimi Reza , Mirzaei Masoud , Ahmadizadeh Mehdi , Wood David
Published: August 2015

Since the air density reduces as the altitude increases, operation of Small Wind Turbines (SWTs) which usually have no pitch mechanism, remains as a challengeable task at high altitudes due largely to the reduction of starting aerodynamic torque. By reducing the blades moment of inertia through the use of hollow blades, the study aims to mitigate that issue and speed up the starting. A three-bladed, 2 m diameter small horizontal axis wind turbine with hollow cross-section was designed for operating at two sites with altitude of 500 and 3,000 m. The design variables consist of distribution of the chord, twist and shell thickness along the blade. The blade-element momentum theory was employed to calculate the output power and starting time and, the beam theory was used for the structural analysis to investigate whether the hollow blades could withstand the aerodynamic and centrifugal forces. A combination of the starting time and the output power was included in an objective function and then, the genetic algorithm was used to find a blade for which the output power and the starting performance, the goals of the objective function, are high while the stress limitation, the objective function constraint, is also met. While the resultant stresses remain below the allowable stress, results show that the performance of the hollow blades is far better than the solid ones such that their starting time is shorter than the solid blades by approximately 70%. However, in the presence of the generator resistive torque, the algorithm could not find the blade for the altitude near to 3000 m. To solve that problem, the tip speed ratio of the turbine was added to other design variables and another optimization process was done which led to the optimal blades not only for the lower altitude but also for the higher one.
Influence of Channel Geometry and Flow Variables on Cyclone Cooling of Turbine Blades
Authors: Bruschewski Martin , Scherhag Christian , Schiffer Heinz-Peter , Grundmann Sven
Published: August 2015

The presented study deals with the internal cooling of turbine blades by swirling flow. The sensitivity of this flow type is investigated towards Reynolds number, swirl intensity and the common geometric features of cooling ducts. The flow system consists of a straight and round channel that is attached to a tangential-type swirl generator. The channel outlet features various orifices and 180-degree-bends. The investigated Reynolds number range is Re = 2000…32000 and the geometric swirl numbers are S* = 1,3,5. The experiments were carried out with Magnetic Resonance Velocimetry for which water was used as flow medium. As the main outcome, it was found that the investigated flows are highly sensitive to the conditions at the outlet of the channel. But it was also discovered that for some channel outlets the flow field remains the same. The associated flow type features a favorable topology for heat transfer: The majority of mass is transported in the annular region close to the channel walls. Together with its high robustness, it is regarded as an applicable type for the internal cooling of turbine blades. A Large Eddy Simulation was conducted to analyze the heat transfer characteristic of this flow. For S*=3 and Re=20000, the simulation showed an averaged Nusselt number increase of factor 4.7 compared to fully-developed flow. However, a pressure loss increase of factor 43 must be considered as well. The presented measurements and simulations have led to a further understanding of swirling flows and proved these flows advantageous for the internal cooling of turbine blades.
Risk Assessment of Gas Turbines Rotors That Have Exceeded Their Design End of Life
Authors: Di Sisto Paolo , Benericetti Daniele
Published: August 2015

The paper will describe the main outcomes of a risk assessment performed by General Electric O&G (GE O&G) in 2013 on a large number of gas turbine rotors that had exceeded their design end of life (EOL).

The assessment involves a large number of medium frames (e.g. MS3002J, MS5002C) plus small industrial gas turbines (e.g. MS1002, PGT10).

The design end of life is the lifespan inside which the risk of uncontained failure is expected to be improbable and this means the failure has a probability of occurrence of 0.12 total events or less during the life of five hundred gas turbines operating 8000 hours per year for 30 years [1].

GE gas turbine rotors are designed to operate with no need of inspection and maintenance till their design EOL (alias serviceable life).

The gas turbines end users may exceed EOL, provided the rotors have been subjected to a specific investigation that includes teardown and a full inspection.

The disregard of this recommendation may have catastrophic consequences on the gas turbines and on surrounding equipment and personnel.

Such recommendation was provided to customers the first time in 2005 through GETIL 1576 [2], the recommendation was renewed in 2013 with a new communication NIC 13.16 [3].

The risk assessment has essentially focused on rotating parts, because rotors (i.e. shaft, wheel, spacer) are the highest gas turbine energy components, that even if designed with high safety margins, they are not immune from time (e.g. creep) and/or cyclic dependent damage (e.g. fatigue).

The assessment has been carried out by following MIL-STD-882C [1] guidelines and in accordance to the principles defined by ISO 12100-2010 [4].

The failure risks have been estimated with the help of specific tools by using field data and life calculations performed with physics-based models.

The paper describes the methodology used to support the risk assessment and this means the “rotor life management methodology” that was developed by GE more than ten years ago, and was subsequently improved by including statistical assessments.
Combustor Heat Shield Impingement Cooling and its Effect on Liner Convective Heat Transfer for a Model Annular Combustor With Radial Swirlers
Authors: Gomez-Ramirez David , Dilip Deepu , Viswanath Ravi Bharath , Deshpande Samruddhi , Pandit Jaideep , Ekkad Srinath V. , Moon Hee-Koo , Kim Yong , Srinivasan Ram
Published: August 2015

Increasing pressure to reduce pollutant emissions such as NOx and CO, while simultaneously increasing the efficiency of gas turbines, has led to the development of modern gas turbine combustors operating at lean equivalence ratios and high compression ratios. These modern combustors use a large portion of the compressor air in the combustion process and hence efficient use of cooling air is critical. Backside impingement cooling is one alternative for advanced cooling in gas turbine combustors. The dome of the combustor is a primary example where backside impingement cooling is extensively used. The dome directly interacts with the flame and hence represents a limiting factor for combustor durability. The present paper studies two aspects of dome cooling: the impingement heat transfer on the dome heat shield of an annular combustor and the effect of the outflow from the spent air on the liner heat transfer. A transient measurement technique using Thermochromic Liquid Crystals (TLCs) was used to characterize the convective heat transfer coefficient on the backside of an industrial heat shield design provided by Solar Turbines, Inc. for Reynolds numbers (with respect to the hole diameter) of ∼ 1500 and ∼ 2500. Reynolds-Averaged Navier Stokes (RANS) calculations using the k-ω SST turbulence model were found to be in good agreement with the experiment. A standard heat transfer correlation for impingement hole arrays overestimated the mean heat transfer coefficient compared to the experiment and computations, however this could be explained by low biases in the results.

Steady state IR measurements were performed to study the effects that the spent air from the heat shield impingement cooling had on the liner convective heat transfer. Measurements were taken for three Reynolds numbers (with respect to the hydraulic diameter of the combustor annulus) including 50000, 90000, and 130000. A downstream shift in the flow features was observed due to the secondary flow introduced by the outflow, as well as a significant increase in the convective heat transfer close to the dome wall.
Aerodynamic Redesign of a 5-Stage Axial Compressor by Re-Stagger and Bow
Authors: Ning Tao , Gu Chun-wei , Li Xiao-tang , Liu Tai-qiu , Xiao Yao-bing
Published: August 2015

The paper is a preliminary methodology research of the aerodynamic redesign of a 5-stage axial compressor by re-stagger and bow with multistage CFD methods, with the purpose of developing the next upgrade version of this type of compressor. Prior to aerodynamic redesign, the validation study is carried out for overall performance, casing static pressure and spanwise total pressure profiles based on full-scale test data, proving that the multistage CFD applied is a relatively reliable tool for the analysis of the follow-up redesigning. Furthermore, at the near stall point, aerodynamic analysis demonstrates that significant separation exits in the last stator, which leads to the aerodynamic redesign focused on the last stator.

To explore the potential of aerodynamic improvement, it is focused on the aerodynamic redesign by re-stagger and bow. Multi-stage CFD methods are applied in the whole redesign process. Two steps of redesigning are applied for aerodynamic optimization. Upgrade 1 by re-stagger is used to adjust the operating points to more reasonable region, which contributes about 9 percent stall margin increase. Based on upgrade 1, an unconventional asymmetric bow configure is employed in upgrade 2 to reduce the high loss region dominated by mainstream. The redesigning exploitation by re-stagger and bow in this research produces a total 16% increase in stall margin.
Numerical Comparison of Rotordynamic Characteristics for a Fully-Partitioned Pocket Damper Seal and a Labyrinth Seal With High Positive and Negative Inlet Preswirl
Authors: Li Zhigang , Li Jun , Feng Zhenping
Published: August 2015

Pocket damper seals are used as replacements for labyrinth seals in high-pressure centrifugal compressors at the balance piston location or center seal location to enhance rotordynamic stability. A concern exists that this enhanced stability will be lost at high positive inlet preswirl.

Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for a fully-partitioned pocket damper seal (FPDS) and a labyrinth seal at high positive and negative inlet preswirl, using a proposed transient CFD method based on the multi-frequency elliptical orbit whirling model. The negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation at seal inlet. Both seals have identical diameter and sealing clearance. The full 3D concentric CFD model and mesh were built for the labyrinth seal and FPDS, respectively. The accuracy and availability of the present transient CFD numerical method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the labyrinth seal and FPDS at zero and high positive preswirl conditions. The numerical boundary conditions include two high positive preswirl, two high negative preswirl and a zero preswirl. Numerical results show that the effect of inlet preswirl on the direct force coefficients is weak, but the effect on the cross-coupling stiffness and effective damping is dramatic. Both two seals possess negative effective damping at lower excitation frequencies due to positive preswirl, and the crossover frequency of effective damping term increases with increasing positive preswirl. Negative preswirl produces negative cross-coupling stiffness and positive effective damping over the whole excitation frequency range. Increasing negative preswirl is a stabilizing factor for annular gas seals which results in a significant increase in the effective damping and a decrease in the crossover frequency. It is desirable to reduce the inlet preswirl to zero or even negative through applications of negative-swirl brakes and negative injection devices.