bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Studies on Flames Established in Reacting Film-Cooling Experiment
Authors: Katta Viswanath R. , Blunck David
Published: September 2014

Integration of turbine turning vanes into a combustor is needed for the development of ultra-compact combustors. A viable approach for protecting the combustor from the high-temperature fuel-rich environment is to inject air through the holes drilled on surfaces. However, it is possible that air intended to cooling may react with the fuel rich combustion products and increase the heat flux. Air Force Research Laboratory has initiated several experimental/numerical studies for investigating the flames that might develop between the injected air and fuel-rich flows in the combustor and their impact on film cooling. A time-dependent, detailed-chemistry computational-fluid-dynamics model is used in the present study for understanding the flames formed in reacting film cooling. Combustion of propane fuel with air is modeled using a chemical-kinetics mechanism involving 52 species and 544 reactions. Both laminar and turbulent flow simulations are performed. Effects of blowing ratio, equivalence ratio and sidewall cooling are investigated. Simulations have reproduced various flame characteristics observed in the experiments. Numerical results are used for explaining the non-intuitive shift in flame anchoring location to the changes in blowing ratio and equivalence ratio. The higher diffusive mass transfer rate of hydrogen in comparison to the local heat transport enhances cooling of cross-flow combustion products, which, in turn, affects the autoignition process. While increasing the blowing ratio abates the differences resulting from non-equal mass and heat transport rates, higher concentrations of hydrogen in the fuel-rich cross-flows accelerate those differences.
Analysis of Effect of Advanced Technique Configurations on Overall Performance of High Bypass Turbofan Engine
Authors: Jun Liu Jian
Published: September 2014

An analytical study was undertaken using the performance model of a two spool direct drive high BPR 300kN thrust turbofan engine, to investigate the effects of advanced configurations on overall engine performance. These include variable bypass nozzle, variable cooling air flow and more electric technique.

For variable bypass nozzle, analysis on performance of outer fan at different conditions indicates that different operating points cannot meet optimal performance at the same time if the bypass nozzle area kept a constant. By changing bypass nozzle throat area at different states, outer fan operating point moves to the location where airflow and efficiency are more appropriate, and have enough margin away from surge line. As a result, the range of variable area of bypass nozzle throat is determined which ensures engine having a low SFC and adequate stability.

For variable cooling airflow, configuration of turbine cooling air flow extraction and methodology for obtaining change of cooling airflow are investigated. Then, base on temperature analysis of turbine vane and blade and resistance of cooling airflow, reduction of cooling airflow is determined. Finally, using performance model which considering effect of cooling air flow on work and efficiency of turbine, variable cooling airflow effect on overall performance is analyzed.

For more electric technique, the main characteristic is to use power off-take instead of overboard air extraction. Power off-take and air extraction effect on overall performance of high bypass turbofan engine is compared. Investigation demonstrates that power offtake will have less SFC.
An Efficient Component Map Generation Method for Prediction of Gas Turbine Performance
Authors: Tsoutsanis Elias , Meskin Nader , Benammar Mohieddine , Khorasani Khashayar
Published: September 2014

Improving efficiency, reliability and availability of gas turbines have become more than ever one of the main areas of interest in gas turbine research. This is mainly due to the stringent environmental regulations that have to be met in such a mature technology sector; and consequently new research challenges have been identified. One of these involves the establishment of high fidelity, accurate, and computationally efficient engine performance simulation, diagnosis and prognosis technology.

Performance prediction of gas turbines is strongly dependent on detailed understanding of the engine component behaviour. Compressors are of special interest because they can generate all sorts of operability problems like surge, stall and flutter; and their operating line is determined by the turbine characteristic. Compressor performance maps, which are obtained in costly rig tests and remain manufacturers proprietary information, impose a stringent limitation that has been commonly resolved by scaling default generic maps in order to match the targeted off-design or engine degraded measurements. This approach is efficient in small range of operating conditions but becomes less accurate for a wider range of operations.

In this paper, a novel compressor map generation method, with the primary objective of improving the accuracy and fidelity of the engine model performance prediction is developed and presented. A new compressor map fitting and modelling method is introduced to simultaneously determine the best elliptical curves to a set of compressor map data. The coefficients that determine the shape of compressor maps’ curves have been analyzed and tuned through a multi-objective optimization algorithm in order to meet the targeted set of measurements. The proposed component map generation method is developed in the object oriented Matlab/Simulink environment and is integrated in a dynamic gas turbine engine model. The accuracy of this method is evaluated for off-design steady state and transient engine conditions. The proposed compressor map generation method has the capability to refine current gas turbine performance prediction approaches and to improve model-based diagnostic techniques.
Steady State Supercritical Carbon Dioxide Recompression Closed Brayton Cycle Operating Point Comparison With Predictions
Authors: Pasch Jim , Conboy Tom , Fleming Darryn , Carlson Matt , Rochau Gary
Published: September 2014

The U.S. Department of Energy Office of Nuclear Energy (DOE-NE) supercritical carbon dioxide recompression closed Brayton cycle (RCBC) test assembly (TA) construction has been completed to its original design and resides at Sandia National Laboratories, New Mexico. Commissioning tests were completed in July 2012, followed by a number of tests in both the recompression CBC configuration, and in a bottoming cycle configuration that is proprietary to a current customer. While the test assembly has been developed and installed to support testing, a computer model of the loop, written in Fortran programming language, has also been developed. The purpose of this iterative model is to facilitate data interpretation, guide test assembly design modifications, develop control schemes, and serve as a foundation from which to develop a transient model. Of central utility is its modular nature, which has already been leveraged to develop a customer’s bottoming cycle configuration. Verification that the model uses appropriate physical representations of components and processes, is performing as intended, and validation that the model accurately reproduces test data, are necessary activities. Completion of the model’s verification and validation (V&V) supports the long-term goal of commercializing the RCBC for a sodium fast reactor. This paper presents verification results of certain subprocesses of the iterative computer model. Verification of these subprocesses was completed with positive results. While an adequate range of data for complete and thorough validation do not yet exist, comparison of subprocess predictions with data from a single, representative operating point are presented as are explanations for differences. Recommendations for activities necessary to complete subprocess and model validation are given. The RCBC iterative computer model V&V process should be revisited following completion of these recommended actions and the generation of steady state data while operating near the test assembly design point.
Comparative Analysis of Chemical Kinetic Models Using the Alternate Species Elimination (ASE) Approach
Authors: Peters Nathan D. , Akih-Kumgeh Ben , Bergthorson Jeffrey M.
Published: September 2014

A major thrust in combustion research is the development of chemical kinetic models for computational analysis of various combustion processes. Significant deviations can be seen when comparing predictions of these models against experimentally determined combustion properties over a wide range of operating conditions and mixture strengths. However, these deviations vary from one model to another. It would be insightful in such circumstances to elucidate the species and sub chemistry models which lead to the varying prediction ability in various models. In this work we apply the Alternate Species Elimination (ASE) method to selected mechanisms in order to analyze their predictive ability with respect to propane and syngas combustion. ASE is applied to a homogeneous reactor undergoing ignition. The ranked species of each model are compared based on their Normalized Change. We further provide skeletal versions of the various models for propane and syngas combustion analysis. It is observed that this approach provides an easy way to determine the chemical species which are central to predictive performance of a model in their order of importance. It also provides a direct way to compare the relative importance of chemical species in the models under consideration. Further development and in-depth analysis could provide more information and guidance for model improvement.
Influence of Liquid and Gaseous Fuel on Lifted Flames at Elevated Pressure Stabilized by Outer Recirculation
Authors: Sedlmaier Julia , Habisreuther Peter , Zarzalis Nikolaos , Jansohn Peter
Published: September 2014

Lifting a flame from the flow generating nozzle to some distance apart has a wide variety of effects on the properties of the resulting combustion phenomenon. The reason of this influence is the generation of a non-reacting flow domain where mixing takes place prior to the combustion reaction. It is obvious that the quality of premixing that can be achieved strongly depends on the time that is given to flow and the intensity of the turbulence that is mixing fuel and air. The most important parameter that is characterizing this time is the size of the premixing zone quantified by the so called lift-off height (LOH). Additionally, when employing liquid fuel the lift-off of a flame provides time to achieve better pre-evaporation of the fuel. As a consequence, better mixing of fuel and air helps to avoid high temperature regions that may be a result from an inhomogeneous equivalence ratio distribution. From safety considerations a major advantage of this method compared to the application of a premixing duct is that the risk of hardware destruction by flame flash back can be eliminated.

The current work extents the knowledge on lifted flames by the investigation of flames that are generated with an airblast atomizing nozzle that was designed to resemble systems close to application. Lifting of the flame is achieved applying a combination of swirling and non-swirling inflow ducts.

A wide range of operating conditions as well as gaseous and liquid fuels are used to investigate their influence on the lift-off height. The lift-off height and location of the reaction zone was determined by means of chemiluminescence of OH* and it is shown, that the impact of pressure drop and preheating temperature on the LOH is different for gaseous and liquid fuels.
A CFD Methodology for Assessment and Improvement of Aerodynamic Stability of a Premixed Swirler Burner
Authors: Geng Weiqun , Magni Fulvio , Ruck Thomas
Published: September 2014

A methodology is presented in this paper how to assess and to improve burner aerodynamic stability of a premixed swirl burner by means of CFD. Steady-state RANS has been widely used for complex industrial applications for decades because of its good reproducibility of mean flow and acceptable turn-around time. With affordability of high performance cluster it becomes feasible to extend steady-state RANS to unsteady-state LES for industrial applications. It is especially beneficial for swirl burners to assess burner stability directly because swirling flow is in fact an unsteady-state phenomenon, which RANS cannot fully capture. This paper shows an industrial practice for how to improve burner design using both RANS and LES. The former helps find potential problems in the flow field, e.g. flow separation. The latter quantifies their impact on flow stability/turbulent fluctuations, e.g. helical modes generated by coupling of flow disturbances and swirling flow. Improvement measures were worked out to supress such flow fluctuations and to enhance stability of burner aerodynamics.

Another critical issue for burner design, reverse flow within the burner, was also discussed because it is a potential risk. When a flame instantaneously enters the burner backwards it can be stabilized in the recirculation zone and damage hardware. The risky region was eliminated by enhancing axial momentum of the air inflow.

The strong turbulent fluctuations within the burners interfere with burner stability significantly and lead to a bad flashback resistance in macroscopic view [1]. In the second part of the paper, atmospheric tests verify the improvement of burner stability via improved flashback resistance and show an upgrading of aerodynamic behaviour via reduced burner pressure drop.
Thermodynamic Analysis and Optimization for an IGCC Power Plant
Authors: Zhang Huisheng , Huang Di , Lu Zhenhua , Su Ming
Published: September 2014

IGCC system has been revealed to be a very attractive power generation system based on coal, promising highly efficient electricity generation and very low environmental impact. The integration of gasifier and power island will be a system engineering. This paper will investigate the influence of IGCC system configuration on system performance. Especially the exhaust heat utilization of syngas from gasifier will be discussed in detail. As the example, one E class gas turbine will be utilized as the core subsystem, the gasifier and HRSG system will be matched. A steady state thermodynamic model for IGCC system is developed on IPSEpro simulation platform and applied to a performance analysis. The characteristics under off-design and design condition for IGCC system were also analyzed.
Time-Linearized Forced Response Analysis of a Counter Rotating Fan: Part II — Analysis of the DLR CRISP2 Model
Authors: Gómez Fernández Io Eunice , Blocher Michael
Published: September 2014

Over the last 3 years, several Institutes of the German Aerospace Center (DLR) investigated the possible gains of a counter rotating fan arrangement manufactured from CFRP designed with an automated optimization tool chain. While counter rotating fans promise aerodynamic efficiency improvements, they might suffer from aerodynamic exitation phenomena as well. The wakes, potential fields and shocks on the blade suction sides might cause blade vibrations leading to high cycle fatigue. Therefore, numerical investigations into aerodynamic excitation are necessary to estimate the amplitude of induced vibrations. At the Institute of Aeroelasticity, a time-linearized loosely coupled approach was used to determine the aerodynamic forcing of the blade rows of this counter rotating fan arrangement.

A finite element model consisting of shell elements was created for the blades in order to be able to model the CFRP material properties. Subsequently, nonlinear finite element load calculations (inertia and blade surface pressure) with a modal analysis in the last step were performed to generate a Campbell diagram of the rotor blades. Critical operating points were identified from the Campbell diagram. Nonlinear steady CFD simulations of these operating points were performed. Based on these calculations, time-linearized unsteady simulations at the crititcal inter-blade phase angle were performed with forced blade motion to determine the aerodynamic damping. Similarly, time-linearized unsteady simulations were performed with gust boundary conditions to determine the aerodynamic forcing. The results of aerodynamic damping and aerodynamic forcing simulations were combined to yield the predicted forced response amplitude of the eigenmode shape that is going to be excited at the respective critical operating point.

As a last step, a nonlinear finite element displacement simulation is conducted to determine the static and dynamic stresses and strains during a forced response vibration. These static and dynamic stresses and strains are then compared to the material properties of the CFRP material to determine if the blades will keep their structural integrity over time. The results of these calculations are presented and discussed.
Numerical Simulation on Ice Shedding Phenomena in Turbomachinery
Authors: Hayashi Ryosuke , Yamamoto Makoto
Published: September 2014

In the jet engine, icing phenomena occur primarily on the fan blades, the fan exit guide vanes (FEGVs), the splitter, and the low-pressure compressor. Accreted ice disturbs the inlet flow and causes large energy losses. In addition, ice accreted on a fan rotor can be shed from the blade surface due to centrifugal force and can damage compressor components. This phenomenon, which is typical in turbomachinery, is referred to as ice shedding. Although existing icing models can simulate ice growth, these models do not have the capability to reproduce ice shedding. In the present study, we develop an icing model that takes into account both ice growth and ice shedding. Furthermore, we validated the proposed ice shedding model through the comparison of numerical results and experimental data, which includes the flow rate loss due to ice growth and the flow rate recovery due to ice shedding. The simulation results for the time at which ice shedding occurred and that were obtained using the proposed ice shedding model were in good agreement with the experimental results.
Experimental Study of the Effect of Fuel Properties on Spray Performance of Alternative Jet Fuel
Authors: Kannaiyan Kumaran , Sadr Reza
Published: September 2014

Increase in energy demand and stringent emission norms lay emphasis on the need for cleaner, alternative fuels. Application of Gas-to-Liquid (GTL) fuel, a synthetic fuel obtained from Fischer-Tropsch synthesis, as an alternate aviation fuel has been the subject of attention in recent years. This is mainly due to its cleaner combustion characteristics when compared to conventional jet fuel and the reduction of dependence on the crude oil supply. However, chemical and physical properties of the GTL are different from conventional jet fuels owing to the difference in their production methodology. The change in GTL fuel physical properties could potentially alter the atomization characteristics, which, in turn affects the evaporation, mixing, combustion, and finally the pollutant formation processes. Therefore, it is important to have a thorough understanding of the combustion precursors of GTL fuel to better understand the combustion and emission processes. A comprehensive evaluation of the microscopic spray characteristics of GTL and Jet A-1 fuels are carried out using a point-wise laser diagnostic technique, Phase Doppler Anemometry at atmospheric condition. The spray characteristics are investigated at several axial and radial locations of the spray. Results obtained clearly show that the influence of fuel properties on the spray characteristics at atmospheric condition is mostly observed near the nozzle exit, rather than in regions further downstream.
Experimental and Numerical Investigation of Confined Jets in Hot Co-Flow
Authors: Tautschnig G. , Haner E.-M. , Hirsch C. , Sattelmayer T.
Published: September 2014

Sequential staged combustion with an expansion turbine between both stages is an efficient way of extending the low emission regime of gas turbines towards very low loads. The dominating combustion regime in the second stage is auto-ignition. A confined natural gas jet in hot vitiated co-flow is investigated to obtain deeper insights in the parameters effecting auto-ignition. A generic pressurized combustion experiment is presented. Optical measurement techniques are applied to determine lift-off height and air excess ratio of the flame in the ignition region. Oxygen content of the co-flow, momentum flux ratio and pressure are varied in the experiments. Cold flow measurements are used to analyze the mixing behavior for different momentum flux ratios. Tendencies observed in the experiments are successfully simulated by a numerical method wherein the flow-, mixture- and temperature-fields are acquired using a non-reacting Realizable k-ε RANS simulation in Fluent. Mixture-PDFs obtained from water-channel measurements are used to take mixture-fluctuations into account. In a post-processing step the combustion-process is calculated with unsteady flamelet equations evaluated in Matlab. By using a progress variable approach with tabulated chemistry only two partial differential equations need to be solved. Hence the computational cost is low. With this study a low-cost numerical model for auto-ignition is demonstrated and the effect of temperature gradients in the co-flow on self-ignition is highlighted.
Thermal Modeling and Mechanical Integrity Based Design of a Heat Shield on a High Pressure Module Solar Steam Turbine Inner Casing With Focus on Lifetime
Authors: Stein Peter , Marinescu Gabriel , Born Dominik , Lerch Michael
Published: September 2014

As part of the renewable energies and because of their low environmental impact, solar thermal power plants enjoy a wide acceptance in the public. In the past years, several projects have been launched to install plants even with a total power output level beyond 200 MW, which require large size steam turbines. Steam turbines of solar power plants face much more start-ups and shutdowns, compared to typical fossil type baseload machines. In order to provide the required lifetime of steam turbine components, i.e. in high- and intermediate-pressure modules, accurate calculation methods of temperatures and heat transfer coefficients are essential for natural cooling and start-up assessment. Beside rotors, also turbine inner casings face high thermal stresses, especially close to the inlet spiral. At these conditions high thermal stress occurs, which prevents the part to meet the technical requirements.

The paper below gives a solution how to avoid this high stress and a calculation method for inner casings. A heat-shield introduced around the inlet spiral separates the active cooling domain of the turbine cavity relative to a narrow domain around the inlet spiral, where the fluid velocity is negligible. A method on how to simplify heat transfer calculations below the heat shield region is investigated and discussed. The results are verified vs. a CFD based sensitivity analysis. Finally a reduction of the peak stress on the configuration with heat-shield is demonstrated relative to the peak stress calculated without heat-shield.
Numerical Study on Increased Energy Density for the DLN Micromix Hydrogen Combustion Principle
Authors: Haj Ayed A. , Kusterer K. , Funke H. H.-W. , Keinz J. , Kazari M. , Kitajima J. , Horikawa A. , Okada K. , Bohn D.
Published: September 2014

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for Dry Low NOx (DLN) hydrogen combustion. Thus, the development of DLN hydrogen combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.

The DLN Micromix combustion principle for hydrogen fuel is being developed since years to significantly reduce NOx-emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flashback and the low NOx-emissions due to a very short residence time of reactants in the flame region of the micro-flames.

For the low NOx Micromix hydrogen application the paper presents a numerical study showing the further potential to reduce the number of hydrogen injectors by increasing the hydrogen injector diameter significantly by more than 350% resulting in an enlarged diffusion-type flame size. Experimental data is compared to numerical results for one configuration with increased hydrogen injector size and two different aerodynamic flame stabilization design laws.

The applied design law for aerodynamic stabilization of the miniaturized flamelets is scaled according to the hydrogen injector size while maintaining equal thermal energy output and significantly low NOx emissions. Based on this parameter variation study the impact of different geometric parameters on flow field, flame structure and NOx formation is investigated by the numerical study.

The numerical results show that the low NOx emission characteristics and the Micromix flame structure are maintained at larger hydrogen injector size and reveal even further potential for energy density increase and a reduction of combustor complexity and production costs.
A Novel Transonic Fan Swept Outlet Guide Vane Using 3D Design Optimization
Authors: Sonoda Toyotaka , Endicott Giles , Arima Toshiyuki , Olhofer Markus
Published: September 2014

In our previous work on a transonic fan swept outlet guide vane (OGV) for a small turbofan engine (GT2011-46363), we showed a novel oscillatory casing profile that leads to approximately 20% loss reduction, using a numerical design optimization method. In this paper we analyze the resulting geometry of an optimization based on a blade representation which is able to realize significantly larger surface modifications. The final optimized design displays a novel blade geometry that has its maximum blade thickness at around 80% blade chord (located between the blade’s mid-chord and trailing edge) especially in the mid-span region. The flow physics explaining why this blade geometry without the oscillatory casing profile has the same loss reduction level of more than 20% at the peak efficiency point are discussed, focusing on the secondary flow and span-wise static pressure gradient on the blade suction side.
Effects of Air Jets Through Combustor Liner Holes on Emissions of Lean Staged Combustor
Authors: Yamamoto Takeshi , Shimodaira Kazuo , Kurosawa Yoji , Nakamura Naoki
Published: September 2014

In JAXA, combustion technologies have been developed with a target that is an 80% NOx reduction of the CAEP/4 standard. A lean staged fuel nozzle with a pilot mixer and a main one in a coaxial arrangement has been developed by single-sector combustor tests under LTO cycle conditions of the target engine with a total pressure ratio of 25.8.

In this study, effects of air jets through combustion liner holes on combustion characteristics was investigated. Combustion tests were conducted by using four single-sector combustor liners with different air holes, no air holes, six air holes with short distance from the fuel nozzle, six air holes with long distance from the fuel nozzle, and one air flow path with three swirlers. From these results, air jets affect NOx emissions and combustion efficiency. Numerical analyses are also conducted by using a commercial large eddy simulation code, Front Flow Red. Quench of high temperature of pilot burned gas and NOx generation by air jets are captured by numerical simulations.
Optical Methods for Studies of Self-Excited Oscillations and the Effect of Dampers in a High Pressure Single Sector Combustor
Authors: Meier U. , Lange L. , Heinze J. , Hassa C. , Sadig S. , Luff D.
Published: September 2014

Self-excited periodic instabilities in a staged lean burn injector could be forced by operating the combustor at off-design conditions. These pressure oscillations were studied in a high pressure single sector combustor with optical access. Two damper configurations were installed and tested with respect to their damping efficiency in relation to the configuration without dampers.

For a variety of test conditions, derived from a part load case, time traces of pressure in the combustor were measured, and amplitudes were derived from their Fourier transformation. These measurements were performed for several combinations of the operating parameters, i.e., injector pressure drop, air/fuel ratio, pilot/main fuel split and preheat temperature. These tests “ranked” the respective damper configurations and their individual efficiency with respect to the configuration without dampers. Although a general trend could be observed, the ranking was not strictly consistent for all operating conditions.

For several test cases, preferably with pronounced self-excited pressure oscillations, phase-resolved planar optical measurement techniques were applied to investigate the change of spatial structures of fuel, reaction zones and temperature distributions over a period of an oscillation. A pulsating motion was detected for both pilot and main flame, driven by a pulsating transport of the liquid fuel. This pulsation, in turn, is caused by a fluctuating air velocity, in connection with a prefilming airblast type atomizer. A phase shift between pilot and main injector heat release was observed, corresponding to a shift of fuel penetration.

Local Rayleigh indices were calculated qualitatively, based on phase-resolved OH chemiluminescence used as marker for heat release, and corresponding pressure values. This identified regions, where a local amplification of pressure oscillations occurred. These regions were largely identical to the reaction regions of pilot and main injector, whereas the recirculation zone between the injector flows was found to exhibit a damping effect.
Development of a Conjugate Heat Transfer Simulation Methodology for Prediction of Steam Turbine Cool-Down Phenomena and Shell Deflection
Authors: Mukhopadhyay Debabrata , Brilliant Howard M. , Zheng Xiaoqing
Published: September 2014

Shell deflection during shutdown, cool-down process is a phenomenon well known to the steam turbine community. The main reason for this phenomenon is slower cooling of the top half shell and a relative faster cooling of the bottom half shell. There are multiple reasons for such thermal behavior of the two half casings, including natural heat convection from the bottom half to the top half, asymmetrical distribution of mass, dissimilar behavior of thermal insulation over the top and the bottom halves, etc. Shell deflection poses considerable challenge to the clearance engineer in terms of configuring operating clearance which ensures rub free operations. Understanding the cool-down process for the rotor is also equally important as the allowable steam inlet temperature during the hot or warm restart will depend on prevailing local temperature of the rotor.

This paper describes an exemplary physics-based cool-down prediction methodology capable of accurately capturing the rotor cool-down process. The methodology involves development of a full 3D rotor casing thermal model, integrated conjugate heat transfer FE model and validated with measured field data.
Transient Thermal Stress Analysis of the Typical Structures in Turbine Rotor Based on Thermomechanical Analysis
Authors: Xu Ning , Liu Zhansheng , Peng He
Published: September 2014

Thermal stress is one of the most important monitoring parameters in turbine rotors during the transition of work conditions. It has significant influence on the safety and life of turbine rotors. In order to obtain the thermal stress in turbine rotors during the transition process conveniently, the transient heat conduction process in typical structures of turbine rotors is analyzed based on heat conduction equation and finite element simulation. According to thermomechanical principle, thermal stress distributions in the typical structures of turbine rotor are investigated. The solutions of thermal stress in a solid cylinder are derived. A corner formed by shaft and disc is modeled and analyzed by finite element method, and the influences of structure parameters on thermal stresses are studied. The results on thermal stresses in cylinder and corner structures could provide a continent method to estimate thermal stress of turbine rotor on early design stage.
The Influence of Coolant Unsteadiness on Impingement Heat Transfer
Authors: Zimmer Victor J. , Rutledge James L. , Knieriem Chris , Ou Shichuan
Published: September 2014

Interest in impingement jet cooling and the associated convection phenomena has grown in the past few decades due in part to the desire for higher operating temperatures and reduced coolant flow in turbines. This study utilizes an array of 55 impingement jets to explore both steady and unsteady impingement flow conditions to evaluate the impact of the inherent unsteadiness present in engines compared to traditional steady experiments. Although unsteadiness occurs naturally in engines, intentional pulsation of coolant flow has also been proposed for flow control purposes, further underscoring the need for examination of the impact of pulsation on the heat transfer. Flow unsteadiness of varying amplitudes was induced at Strouhal numbers of magnitude 10−3 to 10−4. Infrared thermography was used to determine high spatial and temporal resolution Nusselt numbers. Time-resolved Nusselt number and mass flow characteristic waveforms were found to differ substantially as a function of the fluctuation amplitude relative to the mean. In some cases, transient coolant flow increases were associated with non-monotonic behavior in the time resolved Nusselt number. Although with certain configurations unsteady flow demonstrated time-averaged Nusselt numbers equivalent to steady flow with equivalent average mass flux, those with the greatest fluctuation in the amplitude of flow unsteadiness relative to the mean resulted in lower average Nusselt numbers.
A Holistic Approach to GTCC Operational Efficiency Improvement Studies
Authors: Boksteen Sowande Z. , van Buijtenen Jos P. , van der Vecht Dick
Published: September 2014

Because of the increasing share of renewables in the energy market, part load operation of gas turbine combined cycle (GTCC) power plants has become a major issue. In combination with the variable ambient conditions and fuel quality, load variations cause these plants to be operated across a wide range of conditions and settings. However, efficiency improvement and optimization studies are often focused on single operating points. The current study assesses efficiency improvement possibilities for the KA26 GTCC plant, as recently built in Lelystad, The Netherlands, taking into account that the plant is operated under frequently varying conditions and load settings. In this context, free operational parameters play an important role: these are the process parameters, which can be adjusted by the operator without compromising safety and other operational objectives. The study applies a steady state thermodynamic model with second-law analysis for exploring the entire operational space. A method is presented for revealing correlations between the exergy losses in major system components, indicating component interactions. This is achieved with a set of numerical simulations, in which operational conditions and settings are randomly varied, recording plant efficiency and exergy losses in major components. The resulting data is used to identify distinct operational regimes for the GTCC. Finally, the free operational parameters are used as decision variables in a genetic algorithm, optimizing plant efficiency in the operational regimes identified earlier. The results show that the optimal settings for decision variables depend on the regime of operation.
Detailed Heat Transfer Distributions of Narrow Impingement Channels With Varying Jet Diameter
Authors: Terzis Alexandros , Cochet Magali , von Wolfersdorf Jens , Weigand Bernhard , Ott Peter
Published: September 2014

The development of integrally cast turbine airfoils allows the production of narrow impingement channels in a double-wall configuration, where the coolant is practically injected within the wall of the airfoil providing increased heat transfer capabilities. This study examines the cooling performance of narrow impingement channels with varying jet diameters using a single exit design in an attempt to regulate the generated crossflow. The channel consist of a single row of five inline jets tested at two different channel heights and over a range of Reynolds numbers. Detailed heat transfer coefficient distributions are evaluated over the complete interior surfaces of the channel using the transient liquid crystal technique. Local jet discharge coefficients are determined by probe traversing measurements for each individual jet. A 10%-increasing and a 10%-decreasing jet diameter pattern is compared with a baseline geometry of uniform jet size distribution indicating a considerable effect of varying jet diameter on the heat transfer level and the development of the generated crossflow.
U. S. Navy Ship Service Gas Turbine Generator Thermocouple Logic Enhancements to Improve Reliability
Authors: Viercinski John , Hoffman Matthew , Pineiro Ivan , Russom Dennis , Kozuhowski Helen , Connery Brian
Published: September 2014

The U. S. Navy uses Rolls-Royce gas turbines for ship service power on the DDG-51 class destroyer and the CG-47 class cruiser. Both engines have duplex thermocouples (T/Cs) and redundant T/C harnesses for turbine temperature monitoring and control. One harness provides an average of all the installed T/Cs, while the other provides the full authority digital control (FADC) with an individual signal from each. The legacy FADC algorithm allows up to four T/Cs to be out of average on the individual harness. Any additional T/C failures will cause the control to ignore the entire individual harness and rely on the averaging harness alone. This logic has inadvertently led to multiple over-temp conditions and subsequent engine removals. A change to control logic has been developed that aims to prevent these over-temp scenarios and is currently being introduced to the fleet. This paper will discuss in depth the cause of the over-temp, the examination of the control logic and the correction that is designed to prevent it from recurring.
A Low Order Model for Predicting Turbocharger Turbine Unsteady Performance
Authors: Cao Teng , Xu Liping
Published: September 2014

In this paper, a low order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three dimensional CFD method with multiple one-dimensional meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential non-uniformity. It also still maintains the desirable properties of being easy to set up and fast to run.

The model has been validated against a experimentally validated full three-dimensional URANS solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed up ratio of about four orders of magnitude (∼104) for the low order model.

The low order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle averaged turbine power output and the cycle averaged mass flow capacity while it has a large influence on the cycle averaged ideal power output and cycle averaged efficiency. This is related to the wave dynamics inside the volute and the detailed mechanisms responsible are discussed in this paper.
Turbulent Premixed LES Combustion Models Based on Fractal Flame Surface Density Concepts
Authors: Allauddin Usman , Keppeler Roman , Pfitzner Michael
Published: September 2014

With increasing computational power, Large Eddy Simulation (LES) is being widely used to study and develop a better understanding of turbulent combustion. A variety of subgrid combustion models have been proposed to investigate premixed combustion in LES. One of the physical aspects that can be exploited, are the fractal characteristics of premixed flames which have been confirmed in several experimental works. In this work the performance of a simplified version of an already established sub-grid flame surface density combustion model, which is based on the fractal characteristics of the flame surface is investigated. The original model was derived on the basis of theoretical models, experimental and direct numerical simulations databases and its performance was validated with data from the available literature. The simplifications to the established flame surface density model are discussed, and its performance is validated in comparison to the original model. Secondly numerical simulations with both models at conditions typical for spark-ignition engines and industrial gas turbines are validated against experimental data. It is found that both original and simplified models are suitable for LES of low to high turbulent premixed combustion in ambient and elevated pressure conditions.
Acoustic Design and Validation of Radial Inflow Turbine
Authors: Nordwall G. , Demeulenaere A. , Ferrante P.
Published: September 2014

A radial inflow turbine installed in a large extraction facility in Canada has shown to be a significant contributor to the noise generated in that facility. These high sound pressure levels have led to the expenditure of millions of dollars in sound abatement measures over the last 20 years, and pose a health danger to employees.

Based on shop testing and field data, it was believed that a new rotor design could dramatically reduce the noise generated. It was further believed that Computational Fluid Dynamics with Aeroacoustic analyses was capable of predicting this improvement. Such a process can allow parts to be designed and installed quickly, when time and budget does not allow for detailed factory testing.

This paper describes this turbine redesign procedure and the details of the analyses performed throughout the process.

This new rotor has now been installed on-site, and measurements have been made before and after the replacement. This offers a unique opportunity to validate the numerical work performed through this redesign, which is also presented in the paper.
Prediction of Gas Thrust Foil Bearing Performance for Oil-Free Automotive Turbochargers
Authors: San Andrés Luis , Ryu Keun , Diemer Paul
Published: September 2014

Green technologies are a mandate in a world concerned with saving resources and protecting the environment. Oil-free turbocharger systems for passenger and commercial vehicles dispense with the lubricant in the internal combustion engine, hence eliminating not just oil coking, but also suppressing nonlinear behavior, instability and excessive noise; all factors to poor reliability and premature mechanical failure. The work hereby presented is a stepping stone in a concerted effort towards developing a computational design tool integrating both radial and thrust foil gas bearings for oil-free automotive turbochargers. The paper presents the physical analysis and numerical model for prediction of the static and dynamic forced performance of gas thrust foil bearings (GTFBs). A laminar flow, thin film flow model governs the generation of hydrodynamic pressure and a finite element plate model determines the elastic deformation of a top foil and its support bump strip layers. For a specified load, the analysis predicts the minimum gas film thickness, deformation and pressure fields, the drag torque and power loss, and the axial stiffness and damping force coefficients, respectively. Open-source archival test data on load capacity and drag torque serves to benchmark some of the model predictions. Next, predictions are obtained for a GTFB configuration designed for an oil-free turbocharger operating at increasing gas temperatures, axial loads, and shaft rotational speeds. The largest drag torque occurs at the highest temperature since the gas viscosity is also highest, whereas the largest load determines operation with a minute film thickness that sets a limit for the manufacturing tolerance. While airborne, the drag friction factor for the bearing is small, ranging from 0.009 to 0.015, thus demonstrating the advantage of an air bearing technology over engine oil lubricated bearings. The synchronous speed axial stiffness increases with operating speed (and load), whereas the axial damping coefficient remains nearly invariant. The operating gas temperature plays an insignificant role on the variation of the force coefficients with frequency whereas the operating speed and the ensuing applied thrust load determine the largest changes. The model predicts, as an excitation frequency (ω) increases, a GTFB axial stiffness (Kz) that hardens and a damping coefficient (Cz) that quickly vanishes. The most important finding is that CzΩ/Kz ≈ γ = the material loss factor for the bearing. Hence, the success of foil bearing technology relies on the selection of a metal underspring structure that offers the largest mechanical energy dissipation characteristics.
A Simplified and Consistent Nonlinear Transient Analysis Method for Gas Bearing: Extension to Flexible Rotors
Authors: Hassini Amine , Arghir Mihai
Published: September 2014

A simplified, new method for evaluating the nonlinear fluid forces in air bearings was recently proposed in [1]. The method is based on approximating the frequency dependent linearized dynamic coefficients at several eccentricities, by second order rational functions. A set of ordinary differential equations is then obtained using the inverse of Laplace Transform linking the fluid forces components to the rotor displacements. Coupling these equations with the equations of motion of the rotor lead to a system of ordinary differential equations where displacements and velocities of the rotor and the fluid forces come as unknowns. The numerical results stemming from the proposed approach showed good agreement with the results obtained by solving the full nonlinear transient Reynolds equation coupled to the equation of motion of a point mass rotor. However the method [1] requires a special treatment to ensure continuity of the values of the fluid forces and their first derivatives. More recently, the same authors [2] showed the benefits of imposing the same set of stable poles to the rational functions approximating the impedances. These constrains simplified the expressions of the fluid forces and avoided the introduction of false poles. The method in [2] was applied in the frame of the small perturbation analysis for calculating Campbell and stability diagrams. This approach enhances also the consistency of the fluid forces approximated with the same set of poles because they become naturally continuous over the whole bearing clearance while their increments were not. The present paper shows how easily the new formulation may be applied to compute the nonlinear response of systems with multiple degrees of freedom such as a flexible rotor supported by two air bearings.