bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity Analysis of Condensation Model Constants on Calculated Liquid Film Motion in Radial Turbines
Authors: Schuster Sebastian , Benra Friedrich-Karl , Dohmen Hans Josef , König Sven , Martens Uwe
Published: September 2014

In many technical processes, a mixture of gas and steam is used as the working fluid in radial turbines. When condensation occurs during expansion, a portion of the liquid droplets can hit the rotor blades and form a water film, which can move in a radial direction and even against the flow direction. Then, the liquid film separates in the rotor tip clearance or at the leading edge of the rotor and forms coarse water droplets. The presence of coarse water droplets in the gap between stator and rotor can cause damage to the turbine rotor. To design a radial turbine which works under condensation conditions, it is essential to know where and when condensation and film formation occur. With this information, it is possible to take action to remove the liquid or to adjust the required maintenance intervals. To examine the details of condensation and film motion, an existing flow solver is extended to capture condensation effects. Models describing nucleation and droplet growth are added to a particle-tracking algorithm. Droplets impinging on the rotor blades form a liquid film. The motion of this liquid film is calculated with a newly developed thin film solver. The calculation tool is validated against third party test rig experiments as well as numerical experiments. For many parameters, the agreement between the calculation tool and the experiments is quite satisfactory. Some results, however, show larger deviations. One of these parameters is the droplet diameter. The numerical results are generally reliable, but an experimental validation is necessary for detailed understanding of the mechanism. Before expensive experiments are conducted, it is recommended to perform a sensitivity study to emphasize important parameters. This sensitivity study is performed concerning a radial turbine for an operating point at which the liquid film travels into the tip clearance. In this paper it will be shown how the thickness and movement of the liquid film change with variation in influencing parameters. Finally, model constants that have the strongest influence on the calculated film motion are highlighted.
Redesign of a High-Pressure Compressor Blade Accounting for Nonlinear Structural Interactions
Authors: Batailly Alain , Legrand Mathias , Millecamps Antoine , Cochon Sèbastien , Garcin François
Published: September 2014

Recent numerical developments dedicated to the simulation of rotor/stator interaction involving direct structural contacts have been integrated within the Snecma industrial environment. This paper presents the first attempt to benefit from these developments and account for structural blade/casing contacts at the design stage of a high-pressure compressor blade. The blade of interest underwent structural divergence after blade/abradable coating contact occurrences on a rig test. The design improvements were carried out in several steps with significant modifications of the blade stacking law while maintaining aerodynamic performance of the original blade design. After a brief presentation of the proposed design strategy, basic concepts associated with the design variations are recalled. The iterated profiles are then numerically investigated and compared with respect to key structural criteria such as: (1) their mass, (2) the residual stresses stemming from centrifugal stiffening, (3) the vibratory level under aerodynamic forced response and (4) the vibratory levels when unilateral contact occurs. Significant improvements of the final blade design are found: the need for an early integration of nonlinear structural interactions criteria in the design stage of modern aircraft engines components is highlighted.
Compressible Direct Numerical Simulation of Low-Pressure Turbines: Part II — Effect of Inflow Disturbances
Authors: Michelassi Vittorio , Chen Li-Wei , Pichler Richard , Sandberg Richard D.
Published: September 2014

In the present paper, direct numerical simulation (DNS) studies of the compressible flow in the T106 linear cascade have been carried out. Various environmental variables, i.e. background turbulence level, frequency of incoming wakes and Reynolds number, and a combination of these were considered for a total of 12 fully resolved simulations. The mechanisms dictating the observed flow phenomena, including the mixing and distortion of the incoming wakes, wake/boundary layer interaction, and boundary layer evolution impact on profile loss generation are studied systematically. A detailed loss generation analysis allows the identification of each source of loss in boundary layers and flow core. Particular attention is devoted to the concerted impact of wakes distortion mechanics and the intermittent nature of the unsteady boundary layer. Further, the present study examines the validity of the Boussinesq eddy viscosity assumption, which invokes a linear stress-strain relationship in commonly used RANS models. The errors originating from this assumption are scrutinized with both time and phase-locked averaged flow fields to possibly identify shortcomings of traditional RANS models.
The Necessity of a Third Balance Plane for Generator Rotor Field Balancing
Authors: Yu John J.
Published: September 2014

When balancing a generator rotor in the field, one often assumes that two balance planes at the drive end (DE) and non-driven end (NDE) fan rings would be sufficient to bring 1X vibration down. This paper, however, presents a case where a third balance plane must be utilized in order to reduce 1X vibration level below the alarm limit. Though this type of generator with rated speed of 3600 rpm appears to run just above the second couple mode from Bode and polar plots, couple weights (same weights placed at both DE and NDE with 180-degree out-of phase) have little effect on 1X vibration response. For vibration vectors at DE and NDE bearings presenting certain relative phase, it became impossible to further reduce vibration level at both ends from weights at DE and NDE fan ring planes only as indicated in obtained influence data. A third balance plane at the exciter end was attempted to change their relative phase, which proved to be successful. From the exciter end weights combined with the NDE fan ring weights, the generator rotor was balanced successfully. The purpose of this paper is to show in some cases ineffectiveness of couple weights to couple (pivotal mode) response and success of field balancing with a third balance plane on a generator rotor.
Study on Load Capacity and Dynamic Characteristics of the Wave Bearing at Infinite Compressibility Number
Authors: Yang Baisong , Geng Haipeng , Zhou Jian , Yu Lie , Qi Shemiao , Liu Xueyun
Published: September 2014

The wave bearing developed by Dimofte in the 1990’s features a continuous wave profile and presents numerous advantages compared to plain journal bearings. One of the main advantages of the wave bearing is that it has a higher degree of stability than the plain journal bearing and this load capacity is close to the load capacity of the plain journal bearing. Predicting these coefficients for the wave bearing with high bearing numbers is difficult, although there are many studies on the aerodynamic bearing. This paper presents an analytical method for calculating the limiting values of load capacity, dynamic stiffness and damping coefficients of the wave bearing for compressible fluids by simplifying the compressible Reynolds equation at high journal operation speed. A computational method is submitted which is derived from simple algebraic equations combined with infinitesimal perturbation method. The limiting characters of the wave bearing are compared with the plain journal bearing for all eccentricity ratios. Special emphasis is placed on investigating the effects of wave number, wave eccentricity ratio and wave starting angle on the limiting characteristics. Numerical results obtained indicate that the load capacity and stiffness of the wave bearing is better than the plain journal bearing at the same eccentricity ratio.
Simulations of Steady and Unsteady Flows Through a Twin-Entry Radial Turbine
Authors: Ghenaiet Adel , Cerdoune Mahfoudh
Published: September 2014

Radial inflow turbines have established their place in small power units and turbochargers which usually operate under highly unsteady gas flows. The present numerical study is an aerodynamic characterization of the steady and unsteady gas flows through the components of a twin-entry radial turbine with an asymmetrical volute, with an insight on the volute/rotor interactions and the effects of pulsatile flow. The details of the flow structures were possible to obtain by considering the full rotor blades simulations. Examination of the both sides of volute has revealed much more energy conversion with respect to the shroud side and the tongue influence is clearly depicted by a low momentum due to mixing till a tangential position. The rotor flow is characterized by intense secondary flows provoking migration of low energy fluid from hub to shroud and interacting with tip leakage flow. Spectral analysis of the pressure fluctuations recorded at different interfaces has revealed high unsteadiness which may be characterized by a space-time periodic behaviour and described by a double Fourier decomposition. This has led to the determination of different pressure fluctuation frequencies arising during the turbine working time and prevailing modes and their originating sources.
Effects of Sleeve Divergence Angle of Dual-Stage Swirl Cup on the Ignition Performance
Authors: Kang Yao , Lin Yuzhen , Wang Xiaofeng , Zhang Chi , Song Shuangwen
Published: September 2014

Due to the effective decrease on the exhaust smoking, pollutant emission and lean blowout limit, the swirl cup has a wide application in the combustor design. The flow field and two-phase atomizing field downstream of the swirl cup are greatly affected by the sleeve. To investigate the influence of the variation of the sleeve geometry on the ignition performance of the combustor used in jet engine with Chinese aviation kerosene RP-3, three dual-stage swirl cup with different sleeve divergence angles, namely 60°, 70°, and 80°, were examined under normal inlet temperature and normal inlet pressure. The first-stage of the swirl cup uses oblique holes as swirler which is in the anticlockwise direction, while that of the second-stage employs radial blades as swirler in the clockwise direction. High speed imaging was used to obtain the transient process of the combustor ignition. Numerical simulation was used to assist the analysis on the experimental results. It was found that the ignition process in the single dome combustor can be divided into four stages, namely 1) the formation of a flame kernel, 2) the upstream propagation of the flame kernel to the swirl cup exit, 3) the flame stabilization in the swirl cup, and 4) the flame spread from the swirl cup to the primary combustion zone. With the sleeve divergence angle increased from 60° to 80°, the size of the central recirculation zone, the divergence angle of the swirl flow, and the spray angle at the swirl cup exit increased, and the lean ignition fuel/air ratio was reduced by 38%.
CFD Analysis of Swirling Flows in Premixers
Authors: Nazukin Vladislav A. , Avgustinovich Valery G.
Published: September 2014

At present, the key element of lean low NOx combustors is a premixer where swirlers are often used for intensification of mixing processes and further formation of required flow pattern in combustor liner. Swirling flow leads to significant effect of some parts of hardware on stream features and mixing quality, emergence of flashback and flame blowout, formation of complex eddy structures causing flow perturbations. Therefore, at design phase, it is necessary to pay great attention to aerodynamics of premixers. The most effective method of swirling flow analysis in real combustor design is computational fluid dynamics (CFD). The present work is dedicated to study the effect of some computational model parameters, such as a turbulence model, grid size on calculation results as well as the analysis of the flow pattern in real swirler. Comparison between the analysis and experimental data showed that use of Detached Eddy Simulation (DES) allows to defining flow structure more accurately rather than use of RANS (URANS) with SST turbulence model also the size of computational grid elements influences stability of vortex structures. Analysis of swirling flow in production combustor swirler showed presence of large number of different eddy structures that can be conditionally divided into three types relative to its location of origin and a propagation path. Further, features of each eddy type were subsequently defined. Comparison of calculated and experimental pressure fluctuations spectrums verified correctness of computations. It was also noted that for the studied construction there is not even qualitative agreement between the steady and the time-averaged results of unsteady computations.
Humidity Effects on Experimental Compressor Performance: Corrected Conditions for Real Gases
Authors: Berdanier Reid A. , Smith Natalie R. , Fabian John C. , Key Nicole L.
Published: September 2014

The effects of humid air on the performance of a multistage research compressor and new methods of humidity accounting to ensure appropriate representation of performance parameters are investigated in this paper. Turbomachinery textbooks present methods of correcting speed and mass flow rate using perfect gas assumptions, but these methods can reduce the ability to achieve repeatable compressor performance when using unconditioned air in a climate where absolute humidity may vary. Instead, a new method is introduced which models humid air as a real gas and circumvents the need for assumptions in the correction process. In the area of compressor research, the ability to measure small changes in performance parameters and ensure repeatable results is essential. Errors of more than 0.5% can result from using perfect gas assumptions to calculate corrected speed, which can lead to misrepresented performance parameters beyond the uncertainty of the measurements. Multiplicative correction factors based on analytical data are also introduced as an alternate method of applying the new real-gas method, and these correction factors are compared to those derived by previous authors applying ideal gas methods for humidity accounting. This is the first time in open literature that experimental results for a component of a gas turbine engine are presented comparing a humid air correction method with traditional correction methods.
Relationship Between Optimum Curved Blade Generate Line and Cascade Parameters in Subsonic Axial Compressor
Authors: Ling Jing , Du Xin , Wang Songtao , Wang Zhongqi
Published: September 2014

Curved blade has been widely used to reduce the endwall loss, but there is no criterion for curved blade design. Relationship of the optimum curved blade generate line (stack line) and the inlet Mach number, solidity, aspect ratio and camber angle in a linear compressor cascade were researched by optimization method in present paper. The stack line is vertically symmetrical, composed of two third-order Bezier curves and a straight line. The results show that total pressure loss coefficient decreases with the curved height increasing in the present calculate conditions at the same curved angle, and the optimum curved height is 0.5. The total pressure loss coefficient variation with curved angle presents a approximate parabola line type at the same curved height, there is an optimum curved angle, at which the total pressure loss coefficient is minimal. The optimum curved angle variation with the cascade parameters. Optimum curved angle increases with the inlet Ma and camber angle increasing, optimum curved angle variation with inlet Ma shows a polynomial curve type, optimum curved angle varied linearly with camber angle increasing. Optimum curved angle has little changes with solidity and aspect ratio increasing, optimum curved angle is about 6.5° in present conditions, but optimum curved angle will change with the blade loading. The benefit of the optimum curved blade increases with the inlet Mach number and camber angle increasing, and it has little change with solidity and aspect ratio increasing.
A Study on Integrated Milling Process of Shrouded Impeller
Authors: Hu ChuangGuo , Zheng JunJun , Zuo PingYing , Huo HaiYan , Cai Ying
Published: September 2014

Impeller is the key component of centrifugal compressor, which affects the operating efficiency and safety of centrifugal compressor greatly with its manufacturing level. This paper presents some key manufacturing technique issues on integrated milling of shrouded impeller, which relates to the following: determination of machinability of the shrouded impeller flow passage by checking visibility of intersecting line position of blades with disk & shroud; increasing of cutting system rigidity by machining region dividing; increasing of flow passage roughing efficiency by combination of plunge & side roughing; achieving the shortest tool length and maximum tool rigidity by determination of optimal tool orientation; etc. And the proposed methods have been applied in programming and machining process and have been verified successfully.
An Adjustment Method of Axial Force on Marine Multi-Shaft Gas Turbine Rotor
Authors: Wen Xue-You , Zhang Li-chao , Kou Dan , Xiao Dong-ming , Zhang Han
Published: September 2014

During the research and development of marine multi-shaft gas turbine, the axial force on the thrust ball bearing of the rotor is required to be measured under actual operating conditions, and then the axial force would be adjusted to a predetermined range with a predetermined method, so as to assure the bearing’s long-term and reliable operation.

Basing on the theoretical analysis and engineering practice, we propose a practical method for the analysis and adjustment of the axial force. The method features combining the analysis of the air system and the small deviation analysis for the gas turbine engineering, with the typical experimental verifications.

According to this method and the first measurement results of the axial force, the adjustment measures, which would locate the axial force value in a predetermined range, can be given. Since the proposed adjustment measures are based on the theoretical analysis, the component tests and the actual measurement for the whole engine, the result is of engineering accuracy.

The engine delivery tests also show that the adjusting workload of axial force can be reduced significantly by use of the above method.
Experimental Evaluation of Small GTE Test Bed
Authors: Pečinka Jiří , Jílek Adolf , Bugajski Gabriel T.
Published: September 2014

Staff at the University of Defence in Brno, Czech Republic, designed and constructed a test cell for small gas turbine engines as detailed in GT2012-69419. Once construction was completed, the test cell was instrumented and put through a series of tests to confirm the design suitability, calibrate data acquisition channels, establish correction parameters for measurement values, and examine real operating conditions. This paper details the methodology of those tests with a focus on used equipment, noise emissions, air and gas flow and the associated impact on engine thrust. Lastly, measurement results are presented and compared with the design predictions.
Blade Shape Optimization of Transonic Axial Flow Fan in Terms of Sectional Profiles and Stacking Line
Authors: Song Peng , Sun Jinju , Wang Ke
Published: September 2014

Transonic axial flow fan has relatively high blade tip speed and produces higher pressure ratio than the subsonic. However, considerable losses are brought about by the shock waves close to blade tip and over part of span, leading to deteriorated overall efficiency and operating flow range. It is generally acknowledged that modifications of blade stacking line (axially sweep and tangentially lean) and sectional profiles can help to control spanwise distribution of blade loading, reduce shock loss and secondary flow, and extend the operating flow range.

The present study is to maximize the comprehensive benefits of simultaneously optimizing the sectional profiles and stack line by means of a global optimization method with reduced cost. In contrast with previous studies, it is of two distinguished features. First, in blade geometry parameterization, both sectional profiles and stacking line are varied to provide more flexible blade shape variation and subsequently permit more optimization performance gains. Secondly, with simultaneous variation of sectional profiles and stacking line, number of optimization variables and nonlinearity of optimization problem will increase largely. How to obtain a global optimal solution and also reduce the computation become the major concerns. For this purpose, a global optimization method proposed by us is used. It includes an improved CCEA (Cooperative Co-Evolution Algorithm) optimizer, adaptively updated kriging surrogate model, and one-stage Expected Improvement (EI) approach that permits adaptive sampling. At initial stage, a coarse surrogate model is constructed with small number of samples. During the optimization process, some new samples are identified, evaluated, and then used to refine the model and conduct further optimal searching. In the optimization process, the accuracy of the surrogate model is improved based on its own characteristics of optimization problem and this permits the optimizer to conduct the aim-oriented optimal searches. In such a manner, the surrogate model sustains high-level of accuracy while uses fewer samples, thus the blade optimization and computations are significantly reduced.

The optimization is conducted for NASA Rotor67 at design flow rate with a single workstation of DELL 7500. It is demonstrated that the optimized blade design produces significant performance gains at design condition (where the overall efficiency and pressure ratio are increased respectively by 1.27 and 6.53 points) and also at off-design conditions.
Numerical Investigation of the Aerodynamic Behaviour of a Compressor Bleed-Air System
Authors: Peltier V. , Dullenkopf K. , Bauer H.-J.
Published: September 2014

In this paper the aerodynamic behaviour of two bleed off-take configurations is numerically investigated. Steady RANS simulations were performed and validated with detailed experimental results, thereby improving the understanding of the flow phenomena in the bleed-air system. Bleed air for cooling purposes is usually taken from the main gas path at several locations inside the compressor. This bleed air system must be designed to extract up to 30% of the primary air mass flow of the core engine. In most of the engine designs bleed air is collected by holes or slots, then led through a manifold and distributed by one or more tubes to the components. The design of the bleed air system is usually facing two competing purposes: (1) a high static pressure recovery through the bleed air system and (2) a low interaction with the main gas path. In this study, two bleed off-take configurations are investigated at several operating points, exit tube numbers and positions. Both designs are axisymmetric slots. The first one is inclined at 90° with respect to the main flow path direction representing the simplest design. The second one is inclined at 45° with a radius on its upstream side to improve the bleeding performance. Inserting a radius and a chamfer in the off-take increases the bleed static pressure but also has a negative effect on the main gas path stagnation pressure losses as it disturbs the corner separation on the suction side of the blade.
Influence of Cavity Flows Modeling on Centrifugal Compressor Stages Performance Prediction Across Different Flow Coefficient Impellers
Authors: Guidotti Emanuele , Toni Lorenzo , Rubino Dante Tommaso , Tapinassi Libero , Naldi Giovanni , Koyyalamudi V. V. N. K. Satish , Prasad Sridhar
Published: September 2014

Computational Fluid Dynamics (CFD) is becoming fundamental to predict turbomachinery performance. However, only using advanced numerical models coupled with high fidelity grid generation is possible to reach a very good matching with test data. In this regard, secondary flow modeling plays a critical role in the accuracy of performance prediction for centrifugal compressor stages. This study analyses the effects of cavity models on centrifugal compressor stages performance across the full range of impeller flow coefficients used in common industrial applications. Both bi-dimensional low flow coefficients with splitter and non splitter blades and three-dimensional high flow coefficients stages have been used as test cases to compare the numerical prediction with test data. Furthermore the effects of secondary flows modeling have been assessed when comparing detailed flow features with advanced experimental data both in terms of 1D profiles and 2D maps.

The effects of cavity flows modeling is growing, as expected, moving to very low flow coefficients, reaching several points of difference in efficiency calculation with respect to simpler models. Furthermore, the agreement with experimental data is very good both in terms of overall performance and detailed flow features. Finally, the high fidelity CFD is capable to give deep in-sides into the flow evolution inside the machine allowing aero designers to design centrifugal compressor stages with higher performance. It should be remarked here that a good matching of CFD prediction with test data is possible only by using high fidelity models.
Impact of Turbulator Design on the Heat Transfer in a High Aspect Ratio Passage of a Turbine Blade
Authors: Naik S. , Retzko S. , Gritsch M. , Sedlov A.
Published: September 2014

The trailing edge region of gas turbine blades is generally subjected to extremely high external heat loads due to the combined effects of high mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfils both the part mechanical integrity and turbine performance, highly efficient and reliable cooling of the trailing edges is required without increasing the coolant consumption.

In this paper, the heat transfer and pressure drop characteristic of three different turbulator designs in a very high aspect ratio passage have been investigated. The turbulator designs included angled and tapered ribs, broken discrete ribs and V-shaped small chevrons ribs.

The heat transfer and pressure drop characteristics of all the turbulator configurations was initially investigated via numerical predictions and subsequently in a scaled experimental perspex model. The experimental study was conducted for a range of operational Reynolds numbers and the TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients on all surfaces of the passage. Pressure taps were located at several locations within the perspex model and both the local and average heat transfer coefficients and pressure loss coefficients were determined.

The measured and predicted results show, that for all cases investigated, the local internal heat transfer coefficient, which is driven by the highly three dimensional passage flows, is highly non-uniformly within the passage. The highest overall average heat transfer was obtained for the angled and tapered turbulator. Although the average heat transfer coefficient of the discrete broken turbulator and the small chevron turbulator were slightly lower than the baseline case, they had much higher pressure losses. In terms of the overall non-dimensional performance index, which incorporates both the heat transfer and the pressure drop, it was found that the angled and tapered turbulator gave the best overall performance.
An Aggressive S-Shaped Compressor Transition Duct With Swirling Flow and Aerodynamic Lifting Struts
Authors: Walker A. D. , Barker A. G. , Mariah I. , Peacock G. L. , Carrotte J. F. , Northall R. M.
Published: September 2014

In a multistage intermediate pressure compressor an efficiency benefit may be gained by reducing reaction in the rear stages, and allowing swirl to persist at the exit. This swirl must now be removed within the transition duct that is situated between the intermediate and high pressure compressor spools, in order to present the downstream compressor with suitable inlet conditions. This paper presents the numerical design and experimental validation of an initial concept which uses a lifting strut to remove tangential momentum from the flow within an S-shaped compressor transition duct. The design methodology uses an existing strut profile with the camber line modified to remove a specified amount of the inlet tangential momentum. A linear strut loading was employed in the meridional direction with a nominally constant loading in the radial direction. This approach was applied to an existing aggressive S-duct configuration in which approximately 12.5° of swirl remains at OGV exit. 3D CFD predictions were used for preliminary assessment of duct loading and to determine how much swirl could be removed. Consequently, a fully annular test facility incorporating a 1½ stage axial compressor was used to experimentally evaluate four configurations; an unstrutted duct, a non-lifting strut and lifting struts designed to remove 50% and 75% of the inlet tangential momentum. Despite the expected large increase in loss caused by the introduction of struts there was not a significant additional loss measured with the inclusion of turning. No evidence of flow separation was observed and the data suggested that it may be possible to remove more swirl than was attempted. Although the turning struts did not remove the entire targeted swirl due to viscous deviation the data still confirm the feasibility of using a lifting strut/duct concept which has the potential to off-load the rear stages of the upstream compressor.
Numerical Simulation on Ice Growth in High-Temperature Environment
Authors: Furuta Koharu , Yamamoto Makoto
Published: September 2014

This paper discusses a fundamental study on icing phenomena in a high-temperature environment. Generally, ice accretion is a phenomenon to form ice layer on a body due to impingement of super-cooled water droplets. In recent years, it is known that ice accretion occurs in the engine core such as the low pressure compressor and the first stage of the high pressure compressor, where the temperature is about 30 degree C. The ice accretion in the engine core is called as “ice crystal accretion”. Some scenarios are given for the ice crystal accretion, but the mechanism has not been sufficiently clarified yet. Moreover, the current icing model is not available in the environment where the temperature is above the freezing point. In this paper, we develop a new icing code which is applicable to a warm environment. The new icing model consists of four iterative computations for turbulent flow, droplet/ice trajectory, thermodynamics of icing, and heat conduction within a wall. First, we validate our new icing model with a flat plate instead of a compressor stator blade as the fundamental study of ice crystal accretion. Then, we simulate ice accretion on a two-dimensional compressor stator blade in a high-temperature environment, in order to clarify the ice-crystal physics.
Impact of Low Load Operation on Plant Lifetime
Authors: Vogt Jan , Schaaf Thomas , Sun Hongtao , Helbig Klaus
Published: September 2014

In the past steam turbines were designed to operate on a certain load level. However, plant operators are often forced to operate their steam turbines on various load levels depending on the fluctuating demand of the grid. Due to the influence of renewable energies on the electricity market, these fluctuations significantly increased in the last decade.

One possibility to increase a plant’s flexibility and adapt to these altered conditions is to operate it in low load during periods of reduced electricity demand, instead of shutting the plant down. Doing so, the plant can provide power very quickly, if demanded from the grid and it saves the costs for start-up.

However, like all transient events, the transition to Low Load Operation (LLO) can cause temperature differences in the rotor and thick-walled components resulting in deformations and thermal stresses which increase the lifetime consumption of the turbine or might even damage the turbine. Since LLO was mostly only a secondary criterion in the design of the turbine and installed turbine protection systems (e.g. stress controllers) do not offer sufficient protection in many cases, the possible risks of LLO should be investigated before the implementation of LLO for a plant.

This paper analyses the lifetime consumption and damaging mechanisms at different components of the steam turbine that can be caused by LLO. Therefore, test runs in LLO (down to 15% of nominal load) performed by a hard-coal fired plant are investigated. In a first step the thermal stresses occurring in the rotor during transition to LLO are evaluated. Therefore, the rotor is modeled with Finite-Element-Method and the thermal boundary conditions during transient operation are derived from measurement data recorded during the test runs. The influence of these additional stress cycles on the overall lifetime consumption is analyzed.

In a second step operation data is examined with regard to critical operation regimes (e.g. elevated temperatures at HP and IP outlet caused by windage effects).

The results show that certain components can be exposed to increased lifetime consumption during a start-stop cycle containing LLO phases. Moreover, the analysis of operation data indicates that a close monitoring of steam temperatures and pressures is necessary to avoid operation in critical regimes which might cause damage to turbine components.
Training Future Engineers on Gas Turbine Gas Path Diagnostics Using PYTHIA
Authors: Li Y. G.
Published: September 2014

Technology on gas turbine gas path diagnostics has become more and more mature over the years and the demand of the technology in industrial applications, training and education is increasing. To make the technology more accessible to gas turbine users in different areas, including gas turbine design, operation, condition monitoring, maintenance, education, training, etc., comprehensive software to support an easy, fast and user friendly application of the technology has become highly desirable. In this paper, gas turbine thermodynamic performance and diagnostics software, PYTHIA, and a training model on gas turbine gas path diagnostics have been introduced. The objective of the training is to provide trainees the knowledge and an opportunity to effectively learn how to set up gas turbine thermodynamic performance models, understand degradation effects on engine performance, improve the accuracy of engine performance models, pre-process measurement data, detect sensor faults and carry out engine diagnostic analysis. Four tutorial exercises are provided to demonstrate how to use the PYTHIA software to support the training and education. As the gas path diagnostic technology and the software have been developed for industrial applications, particular for gas turbine condition monitoring and diagnostics, it is user friendly and has a high level of flexibility to be used for different gas turbine engines and can be accessed remotely via internet. Therefore it provides a useful tool and a virtual environment to enhance the effectiveness of the training and education of the technology. Such technology and training model is suitable for professional engineers and postgraduate students.
Energy Analysis of Pulsating Coolant Ejection
Authors: Saracoglu Bayindir H. , Paniagua Guillermo , Salvadori Simone
Published: September 2014

High-pressure turbines are subjected to high expansion ratios which may result in supersonic vane or rotor outlet. In the supersonic regime, shock waves are formed at the vane trailing edges that periodically impact on the downstream rotor blades and the neighboring vane. Pulsating cooling was proposed to modulate the trailing edge shocks to diminish the detrimental efficiency abatement and structural problems. A large test section equipped with three airfoils, replicated the actual loading of a transonic vane. Tests were performed in a short duration compression tube facility at four Mach numbers (0.8, 0.95, 1.1 and 1.2) and two different Reynolds numbers (4 and 6 million). Coolant was fed to the trailing edge of the central airfoil through a siren valve, that allowed to study four different coolant blowing cases: no-blowing, continuous blowing at three pressure levels and a pulsating coolant blowing condition. Unsteady numerical simulations of the flow over the airfoil model were performed using ANSYS 14 (Fluent) flow solver. In order to understand the impact of the different steady and unsteady cooling schemes on the efficiency of high pressure turbine bladings, the individual contribution of trailing edge and profile losses were calculated. The coolant ejection generated a significant reduction of the trailing edge loss. The overall losses also diminished by the introduction of cooling as compared to no blowing case. Improvements in loss levels owing to pulsating cooling observed to be more pronounced for the engine representative cooling rates (∼3%). The trends in loss variation with respect to cooling scheme show that pulsating cooling may become superior for high blowing cases.
Implementation of a CFD-Based Aeroelastic Analysis Toolbox for Turbomachinery Applications
Authors: Romanelli G. , Mangani L. , Casartelli E.
Published: September 2014

The understanding of aeroelastic phenomena is fundamental for the structural integrity of many applications in aerospace and mechanical engineering and even in some other disciplines (e.g. civil engineering) where flexible structures possibly undergo unsteady fluid-dynamic loads. Therefore the availability of accurate analysis tools for the study of the aeroelastic interaction between aerodynamic and elastic forces is an important asset for the design of modern, high performance turbomachinery.

Together with the more and more powerful computing resources, current trends pursue the adoption of high-fidelity tools and state-of-the-art technology within the research fields of Computational Structural Dynamics (CSD) and Computational Fluid Dynamics (CFD). This choice is somehow obliged when dealing with highly non-linear aeroservoelastic phenomena.

The approach typically used for turbomachinery aeroelastic analysis features the so-called “one-way coupling”, i.e. the loads predicted by the aerodynamic model are transferred to the structural model to evaluate relevant stresses and displacements.

The objective of the present work is to illustrate the design and implementation of a platform for solving multidisciplinary non-linear Fluid-Structure Interaction (FSI) problems with a “two-way coupling” or fully coupled approach, that is linking together high-fidelity state-of-the-art CSD and CFD tools by means of a robust, flexible aeroelastic interface scheme.

The credibility of the proposed aeroservoelastic analysis toolbox is assessed by tackling a set of aeronautical and turbomachinery-oriented benchmark test problems such as: the evaluation of the fully coupled non-linear aeroelastic trim of HIRENASD (HIgh REynolds Number AeroStructural Dynamics) wing and the identification of the aerodynamic damping coefficient of Standard Configuration 10, high subsonic/transonic, 2D/3D compressor cascade. The results are compared with reference experimental and numerical data available in literature.
Modified Transient Infrared Methodology for Leading Edge Impingement Measurements
Authors: Helmer David B.
Published: September 2014

Modifications to the energy balance based transient IR methodology for measuring heat transfer coefficients (HTCs) are presented in this work. Improvements are shown to increase the accuracy of the method and to allow quantitative testing of complex and/or highly curved geometries. Thin-walled test articles are manufactured via rapid prototyping processes, allowing for rapid quantitative concept screening. The methodology is demonstrated with a transient heating test for two distinct leading edge impingement configurations. The gage repeatability and reproducibility is shown to be approximately 2%, providing a strong ability to resolve trends in the data. This is demonstrated with a measurement of the impact of altered gill flows and relatively small variations in the jet Reynolds number on the leading edge HTC fields. Detailed uncertainty quantification of the method is shown and uncertainty mitigation techniques are discussed. The impact of un-corrected conduction effects is also demonstrated via a comparison of corrected and uncorrected results.
Analysis of Azimuthal Thermoacoustic Modes in Annular Gas Turbine Combustion Chambers
Authors: Bothien Mirko , Noiray Nicolas , Schuermans Bruno
Published: September 2014

Modern gas turbine combustors operating in lean-premixed mode are prone to thermoacoustic instabilities. In annular combustion chambers, usually azimuthal acoustic modes are the critical ones interacting with the flame. In case of constructive interference, high amplitude oscillations might result. In this paper, the azimuthal acoustic field of a full-scale engine is investigated in detail. The analyses are based on measurements in a full-scale gas turbine, analytical models to derive the system dynamics, as well as simulations performed with an in-house 3d nonlinear network model. It is shown that the network model is able to reproduce the behaviour observed in the engine. Spectra, linear growth rates, as well as the statistics of the system’s dynamics can be predicted. A previously introduced algorithm is used to extract linear growth rates from engine and model time domain data. The method’s accuracy is confirmed by comparison of the routine’s results to analytically determined growth rates from the network model. The network model is also used to derive a burner staging configuration resulting in the decrease of linear growth rate and thus an increase of engine operation regime; model predictions are verified by full-scale engine measurements. A thorough investigation of the azimuthal modes statistics is performed. Additionally, the network model is used to show that an unfavorable flame temperature distribution with an amplitude of merely 1% of the mean flame temperature can change the azimuthal mode from dominantly rotating to dominantly standing. This is predicted by the network model that only takes into account flame fluctuations in axial direction.
Comparison Between Long and Short Blade Vibration Using Shaft Instantaneous Angular Speed in Rotating Machine
Authors: Gubran Ahmed A. , Sinha Jyoti K.
Published: September 2014

The blade failure normally occurs as a result of blade cracking due to unforeseen operating conditions and variable loads. Therefore, the early detection of damage in the blades is critical to reduce machine down time, maintenance costs and to maintain overall safety. Earlier studies indicate that the shaft instantaneous angular speed (IAS) representing the shaft torsional vibration is a good approach for the blade vibration. Hence, the shaft IAS is extracted from the measured encoder data during machine run-up to understand the blade vibration. A number of experiments on an experimental rig with a bladed disk were conducted using 2 types of blades (long and short blades) with healthy but mistuned blades and with different faults simulation in the blades. The paper presents the experimental setup, simulation of blade faults, experiments conducted, observations and comparison of results between the long and short blades with and without faults.
LES and Hybrid RANS/LES of a Fundamental Trailing Edge Slot
Authors: Ivanova Elizaveta , Laskowski Gregory M.
Published: September 2014

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer, mean velocity, and turbulence in a fundamental trailing edge slot. The geometry represents a landless slot (two-dimensional wall jet) with adjustable slot lip thickness. The reference experimental data taken from the publications of Kacker and Whitelaw [1] [2] [3] [4] contains the adiabatic wall effectiveness together with the velocity and the Reynolds-stress profiles for various blowing ratios and slot lip thicknesses. The simulations were conducted at three different lip thickness and several blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against unsteady RANS. The predictive capability of the tested LES models (dynamic ksgs-equation [5] and WALE [6]) was comparable. The Improved Delayed Detached Eddy Simulation (IDDES) hybrid method [7] also shows satisfactory agreement with the experimental data. In addition to the described baseline investigations, the influence of the inlet turbulence boundary conditions and their implication for the initial mixing layer and heat transfer development were studied for both LES and IDDES.
Investigation of the Suction Side Boundary Layer Development on Low Pressure Turbine Airfoils With and Without Separation Using a Preston Probe
Authors: Stotz Stephan , Wakelam Christian T. , Niehuis Reinhard , Guendogdu Yavuz
Published: September 2014

Characterizing the transition process of airfoils can be very challenging and requires often extensive measurement methods. Frequently at low Reynolds numbers the suction side separation often occurs close to the trailing edge so that asserting reattachment of the flow to form a closed separation bubble from the profile pressure distributions becomes uncertain. In the current work the suction side transition process is investigated more precisely with a convenient method to determine the dynamic pressure close to the suction surface using a Preston probe (flattened Pitot tube). Therefore four low pressure turbine airfoils, which show different characteristics of the transition process in the static pressure distribution have been investigated at the High-Speed Cascade Wind Tunnel at the Universität der Bundeswehr München at constant Mach number and under a wide range of Reynolds numbers (40 000 to 400 000). It is shown that this method is appropriate to determine transition start and end as well as the separation and reattachment point of a separated flow as long as the probe height is small enough compared to the boundary layer thickness. The measurement results are compared to profile pressure distributions and hot-wire boundary layer profiles. Also the influence of periodic unsteady inflow conditions on the dynamic pressure near the wall is revealed in the time average. Limitations due to the probe geometry are discussed and a method to estimate the influence of the probe geometry on the measured dynamic pressure coefficient is suggested.