bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimizing Sampling Loss in Trace Gas Emission Measurements for Aircraft Engines by Using a Chemical Quick-Quench Probe
Authors: de la Rosa Blanco Elena , Peck Jay , Miake-Lye Richard C. , Hills Frank B. , Wood Ezra C. , Herndon Scott C. , Annen Kurt D. , Yelvington Paul E. , Leach Timothy
Published: January 2011

This paper describes the development and testing of a gas sampling probe that quenches chemical reactions by using supersonic expansion and helium dilution. Gas sampling probes are required for accurate measurement of exhaust emissions species, which is critical to determine the performance of an aircraft engine. The probe was designed through rounds of computational modeling and laboratory testing, and was subsequently manufactured and then tested at the University of Tennessee Space Institute (UTSI) behind a General Electric J85 turbojet engine at different power settings: idle, maximum military and afterburning. The experimental test results demonstrated that the Chemical Quick-Quench (CQQ) probe suppressed the oxidation of carbon monoxide (CO) inside the probe system and preserved more CO at afterburning conditions. In addition, the CQQ probe prevented hydrocarbons from being partially-oxidized to form CO at idle powers, and measured higher hydrocarbons and lower CO emission compared to a conventional probe at that low power condition. The CQQ probe also suppressed nitrogen dioxide (NO2) to nitric oxide (NO) conversion through all engine power settings. These data strongly support the conclusion that the CQQ probe is able to quench unwanted chemical reactions inside the probe for all engine power levels.
Dynamics Design of the Aero-Engine Rotor Joint Structures Based on Experimental and Numerical Study
Authors: Liu Shuguo , Wang Jun , Hong Jie , Zhang Dayi
Published: January 2011

This study investigated the rigidity and contact state of joint structures that influenced the rotor dynamic characteristics and imbalance response, and the curve for variable structure parameters and the external load. The consideration of rotor joint structures dynamics design was also discussed. The finite-element models were established by using 3D solid elements and surface-to-surface nonlinear contact elements between the interfaces for numerical analysis. The rotor dynamic characteristics were affected by the rigidity of joint structures, and the rotor imbalance response was affected by the contact state of the interfaces. The experimentation for measuring the static rigidity and dynamic contact state of bolted joints with different experimental cycles were performed. Both numerical simulation and experimental results showed that: Firstly, the stiffness of joint structures was not constant. There was a critical load Fcr, when the external load was less than Fcr, the stiffness of joint structures was K1; when the external load was more than Fcr, the bend stiffness of joint structures would drop to K2. The critical load Fcr was influenced by the length of interfaces and preload. Secondly, the contact state of joint structure interfaces varied after a long time of operating with alternating loads. The rotor imbalance was increased by fatigue damage accumulation and irreversible deformation. The study results show that the rigidity and contact state of joint structures vary with external loads and geometry structures, and would affect the rotor system operating. It is advisable to consider the influence of the position, structural parameter and external load of the rotor joint structures on aero-engine structure dynamics design.
Computational Modeling and Validation Testing of Dynamic Blade Stresses in a Rotating Centrifugal Compressor Using a Time Domain Coupled Fluid-Structure Computational Model
Authors: Lerche Andrew , Moore J. Jeffrey , Feng Yusheng
Published: January 2011

This work develops a time domain coupled fluid-structure computational model that predicts dynamic blade stresses in a rotating centrifugal compressor. Although, much research has been performed on axial flow turbomachinery, little has been published for radial machines such as centrifugal compressors and radial inflow turbines. This research develops a time domain coupled fluid-structure computational model using commercially available codes. The model couples the codes unidirectionally, where pressures are transferred to the structural code during the transient solution, and the fluid mesh remains unaffected by the structural displacements. Models are developed for the compressor at blade resonant conditions. The model is then validated with a rotating test of a centrifugal compressor instrumented with blade mounted strain gauges. The test rig is an open loop rig that utilizes an unshrouded centrifugal compressor with a vaneless diffuser. The strain gauge signals are passed through a high gain, low noise amplifier that is mounted on the compressor rotor. This work not only develops a unidirectionally coupled fluid-structure model capable of predicting dynamic strains, but also provides valuable experimental data that can be used for future research and validation cases of fluid-structure interaction (FSI) models.
An Automated Energy Conservation Decision Support System for Navy Gas Turbines
Authors: Roemer Michael J. , Palmer Carl A. , Bharadwaj Sudarshan P. , Savage Chris
Published: January 2011

Energy conservation measures currently employed by U.S. Navy surface combatants require labor-intensive, time-consuming data entry from which fuel curves are generated to drive each ship’s propulsion plant machinery alignment. From these rudimentary curves optimal transit speeds, configurations, and refueling requirements are determined for specific operational demands and mission profiles. This paper describes an automated process for optimizing shipboard fuel consumption rates by integrating advanced diagnostic and maintenance optimization techniques with the onboard data information system. The automated energy conservation decision support system described herein addresses fossil fuel propulsion (gas turbines, steam turbines, and diesel engines), power generation and auxiliary systems. The software tool consists of diagnostic, fuel management, and maintenance modules. The diagnostic module tracks and trends the health state of components that use fuel (and their supporting systems) to provide real-time information on the impact of their current condition on fuel consumption. The fuel management module automates data collection and the generation of fuel curves through open-systems architecture communication with ICAS. It also enables planning by recommending an optimal machinery configuration to minimize fuel consumption based on either speed or time to destination constraints. Additionally, a fuel management module provides real-time information on fuel consumption and optimizes the load of each component based on its health condition, operating requirements and the number and condition of similar components. Finally, overall decision support comes from the maintenance management module that tracks the maintenance actions being performed on fuel consuming systems and recommends future maintenance to be performed (from a fuel conservation standpoint) based on current health information.
Oil Mist Eliminator Vessel Modifications for GE 7EA Gas Turbine
Authors: Ingistov Steve , Cusack Roger , Bhargava Rakesh
Published: January 2011

With any rotating machinery as lube oil leaves bearings, a certain amount of lube oil is aerated resulting in formation of a mist of very small size (less than 1 micron diameter) particles. If oil mist elimination system is not sized and designed properly, it could cause various issues such as increased operation and maintenance cost, reentry of oily air into adjacent Gas Turbine (GT) units, fouling of surrounding atmosphere, and creation of oil slick on concrete floors, besides impacting environmental requirements and safety hazards. This paper presents a case study involving GE 7EA gas turbines operating at the Watson Cogeneration Plant and discusses issues with the existing oil mist elimination system and steps taken for a successful replacement of the Original Equipment Manufacturer (OEM) supplied mist elimination system with non-OEM designed and fabricated mist elimination system. The replaced system demonstrated significantly higher life expectancy than it was designed for.
Experimental Investigations of Laminar Separation Bubble for a Flow Past an Airfoil
Authors: Sharma Deepakkumar M. , Poddar Kamal
Published: January 2011

Wind tunnel experiments were carried out on NACA 0015 airfoil model to investigate the formation of laminar separation bubble on the upper surface of the airfoil by varying angle of attack from −5° to 25° with respect to the free stream velocity at constant Reynolds number varying from 0.2E06 to 0.6E06. Pressure signals were acquired from the pressure ports selected at the mid-span of the airfoil model along the chord. Static stall characteristics were obtained from the surface pressure distribution. The flow separation was found to be a trailing edge turbulent boundary layer separation preceded with a laminar separation bubble. Flow Visualizations were done by using Surface Oil flow Technique for qualitative analysis of the transition zone formed due to the presence of laminar separation bubble As the angle of attack is increased the separation bubble moves towards the leading edge of the airfoil and finally gets shredded or burst at a particular angle of attack resulting in leading edge turbulent flow separation which induces the static stall condition. The flow separation process is critically analyzed and the existence of laminar separation bubble is visualized and quantified with the increase in angle of attack and Re. Effect of Re and angle of attack on the various boundary layer and Separation bubble parameters are obtained and analyzed.
Performance of a Round Ejector With 22.5° Bent Entraining Diffuser
Authors: Chen Qi , Birk A. M.
Published: January 2011

This paper presents experimental data for the performance of a round ejector with a 22.5° bent entraining diffuser. The experiments were carried out on a hot gas wind tunnel that could provide primary mass flow rates up to 2.2 kg/s at ambient temperature and 1.8 kg/s at 500°C. Velocity, pressure and temperature were measured in the annulus upstream of the primary nozzle, on the mixing tube and diffuser walls, at the diffuser gap inlets and at the diffuser exit. The inlet flow swirl angle and flow temperature were varied to study their effect on ejector pumping, wall pressure, and wall temperature distribution. The data from bent ejectors were compared with similar data for a round straight ejector. The results showed that the 22.5° bent entraining ejector had better hot core cooling performance than the straight entraining ejector since the hot core was cooled by the tertiary flow more efficiently at the outer side of the bend.
Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Condition
Authors: Wang Ting , Dhanasekaran T. S.
Published: January 2011

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2-D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficultly in conducting experiments at elevated pressure and temperature working conditions, CFD simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviation from experimental results for the flows of steam only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number condition. The predicted results show an off-center cooling enhancement with a local maximum of 200% at s/d = 2 and an average cooling enhancement of about 150%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3-D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.
Heat Transfer Investigation of an Aggressive Intermediate Turbine Duct: Part 2—Numerical Analysis
Authors: Wallin Fredrik , Arroyo Osso Carlos
Published: January 2011

Demands on improved efficiency, reduced emissions and lowered noise levels result in higher by-pass ratio turbofan engines. The design of the intermediate turbine duct, connecting the high-pressure and low-pressure turbines in a two-spool engine, becomes thus more critical. The radial offset between the high-pressure core and the low-pressure system will increase, which leads to a higher aspect ratio (Δr/L) of the turbine duct. In order to improve the low-pressure turbine performance the turbine duct exit axial velocity could be reduced by increasing the duct area ratio (Aout/Ain). In order to keep the turbine frame weight as low as possible, it is also desirable to keep the duct short, i. e. keep the non-dimensional length (L/hin) as low as possible. Therefore, there is a need to improve the knowledge about the flowfield and heat transfer in aggressive (high aspect ratio/high area ratio) turbine ducts. The work presented here has been performed within the EU FP6 project AITEB-2, focusing on heat transfer in turbines. In a two-part paper the aerothermal behavior of a fairly aggressive intermediate turbine duct with nine non-lifting vanes has been studied. The flowfield and heat transfer data was acquired in the Chalmers Turbine Facility. The first part of the paper focuses on the experimental investigation and results. In this second part of the paper comparisons between experimental data and numerical results are made. The work highlights the challenges associated with numerical predictions of flowfield induced heat transfer in turbine ducts. The numerical analysis was performed using Chalmers in-house compressible flow solver. The experimental results are compared to CFD analyzes using two different turbulence models; k-ε with wall functions and low-Re k-ω SST, and using the measured inlet conditions to the duct as boundary conditions. Previously presented flowfield comparisons showed good agreement between experiments and CFD. The main flow features, such as vorticity and pressure gradients, are reasonably well reproduced by the CFD. The heat transfer results show reasonable agreement on the hub and on the downstream part of the shroud. The heat transfer agreement is, however, poor on the shroud in the region between the duct inlet and the leading edge of the vane.
An Analysis of Unstable Flow Dynamics and Flashback Mechanism Inside a Swirl-Stabilised Lean Burn Combustor
Authors: Wankhede Moresh J. , Bressloff Neil W. , Keane Andy J. , Caracciolo Luca , Zedda Marco
Published: January 2011

A modern lean burn combustor for propulsion application using a multi-swirler fuel injector system is studied under partially premixed combustion conditions. Combustion induced vortex breakdown (CIVB) plays an important role in establishing the near-field aerodynamic characteristics of lean burn fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms mainly consisting of a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. In the present study a numerical investigation is carried out with an unsteady Reynolds-averaged Navier Stokes (URANS) solver to capture the evolution of the PVC in the vicinity of the air blast atomizer of the injector and the helical vortex patterns inside the combustor. PVC suppression is captured causing upstream flame propagation and a sudden rise in the temperature near the injector end. The existence of hot-spots is reported near the injector end which can increase NOx production and also cause possible damage to the injector assembly itself. The unsteady dynamics of the PVC, which significantly influences fuel efficiency and emissions, are analyzed for a relatively long period of real time. The variation of velocity along the axis of the combustor confirming upstream flame propagation in to the injector is plotted. Mass weighted average temperatures across different planes in the combustor are monitored as target functions. The influence of different time-step sizes on the prediction of the temperature across these different planes is also presented. For this lean burn combustor using a complex multi-swirler fuel injector system, the results demonstrate the formation of a startup PVC in the vicinity of the air blast atomizer of the injector, its unstable mode of excitation, sustainment and suppression due to CIVB over a period of time and its strong influence on injector near-field aero-thermodynamics.
VeLoNOx™ Combustion System Operating Experience on Heavy Duty Gas Turbine
Authors: Bonzani Federico , Piana Carlo , Zito Domenico
Published: January 2011

In order to improve operability and flexibility, Ansaldo Energia has upgraded its top of the line AE94.3A gas turbine with a new combustion system called VeLoNOx™ (Very Low NOx) based on its own experience. This new combustion system meets the most stringent pollutant limitations (as of today) required by the governments all over EU, i.e. less than 15 ppm NOx emissions. The system has been first tested intensively on a single AE94.3A built by Ansaldo Energia. Due to the long term service agreement with the customer the whole operation has been constantly monitored and all most relevant operational conditions have been tested. Then has been installed on other engines. Up to now VeLoNOx™ combustion systems have been cumulating more than 25000 EOH on many sites, showing very good performances in line with expectations. Orders for many retrofit applications have been already awarded. This paper describes the performance of the system on the units of Ansaldo Energia fleet such as AE94.3A2 and AE94.3A4, focusing on the improvements carried out during commercial operation.
Modeling an Installation of Recuperative Heat Exchangers for an Aero Engine
Authors: Missirlis Dimitrios , Yakinthos Kyros , Seite Olivier , Goulas Apostolos
Published: January 2011

This work presents the complete effort to model the presence of an integrated system of heat exchangers mounted in the exhaust nozzle of an aero engine which uses an alternative but more efficient thermodynamic cycle. The heat exchangers are operating as heat recuperators exploiting part of the thermal energy of the turbine exhaust gas to preheat the compressor outlet air before combustion and to reduce pollutants and fuel consumption. The presence of the heat exchangers enforces a significant pressure drop in the exhaust gas flow which can affect the overall efficiency of the thermodynamic cycle and the potential benefit of this technology. For this reason it is important to optimize the operation of the system of heat exchangers. The main target of this optimization effort is the minimization of the pressure losses for the same amount of heat transfer achieved. The optimization is performed with the combined use of experimental measurements and CFD methods. Since the CFD modeling is taking into consideration the overall geometry of the exhaust nozzle of the aero engine where the heat exchangers are mounted, the presence of the latter is unavoidably modeled with the use of a porosity model for practical reasons, having to do with CPU and memory requirements. The porosity model is taking into account the pressure drop and heat transfer behaviour of the heat exchangers and was developed and validated with the use of detailed experimental measurements. For the validation of the CFD model, isothermal experimental measurements carried out for laboratory conditions in a 1:1 model of a quarter of the exhaust nozzle of the aero engine, including four full-scale heat exchangers, were used. The CFD results were in good agreement with the experimental measurements and the same flow structures and problematic regions were detected. Thus, a complete 3-D CFD model of the overall exhaust nozzle of the aero engine was created and validated which at the next step formed the basis for the optimization of the overall aero engine installation for real engine operating conditions. The improved design of the aero engine installation presented decreased pressure losses in relation to the initial design and a more balanced mass flow distribution, showing the applicability of the overall methodology and its advantages for producing efficient engineering solutions for similar setups.
3D Unsteady Computation of Stall Inception in Axial Compressors
Authors: Tu Baofeng , Hu Jun , Zhao Yong
Published: January 2011

Rotating stall is one of the unsteady phenomena in multistage axial compressors that will damage both of performance and service life of aero engines. Stall inception is a dynamic process including appearance of pre-stall disturbance, evolvement of disturbances into stall cells, and development of stall cells. The main purpose in researching stall inception is to reveal the origins of disturbances and stall cells, investigate the effects of aerodynamic design variations on stall inception, and find the effective ways to prevent engines from turning into rotating stall or surge. Numerical simulation is an economic, reliable and rapid tool to study stall inception. As stall inception is three-dimensional and unsteady, numerical simulation should be capable of describing these aspects. In this paper, a three dimensional unsteady computational model based on the three-dimensional unsteady Euler equations and the three dimensional multi actuator-disks model has been developed. The computational domain can be divided into two kinds. One is blade-free regions, which consist of upstream duct, the axial gaps among blade rows, and downstream duct. The other one is blade rows. The flows in blade-free regions considered inviscid, unsteady, and can be resolved using three-dimensional unsteady Euler equations. The blade rows are replaced by multi actuator-disks with different total-to-static characteristics. By added the correlation functions of inlet and outlet flow angles, we can compute the flow field by combining the Euler equations and the multi actuator-disks model. A two-stage low-speed compressor in NUAA has been investigated, and the predicted results indicates that the second stage comes out stall cell first, and the full developed stall cell rotates at about 40.4% rotor speed, which coincides with the experimental data.
A Numerical Study of an Impingement Array Inside a Three Dimensional Turbine Vane
Authors: Leo´n De Paz Marcel , Jubran B. A.
Published: January 2011

A simplified impingement high pressure turbine vane is modeled and solved via Fluent. A relatively flat section of the vane is fitted with 15 0.51mm diameter impingement holes — 5 rows of 3 jets. Results are then compared to known experimental data. Two different turbulence models are used to study this preliminary configuration: K-omega SST and the RNG k-epsilon model. The jet exit Reynolds numbers, cross flow velocity, and the average and local heat transfer distribution are analyzed with varying Reynolds numbers and jet to target spacing. It is observed that the static pressure decreases across the vane with the cross flow velocity increasing towards the trailing edge exit, thereby uniformly increasing the jet exit velocity at each row. Forced convection is seen in the downstream rows in-between span-wise jets due to high cross flow velocities. All numerical results were capable of replicating the higher heat transfer obtained with a higher Reynolds number, and conversely, a lower heat transfer with an increase in jet to target spacing. In its entirety, validating against all correlations, the RNG model obtained an average deviation of 15.7%, while the K-omega SST yielded only 7.8%.
Effect of Turning Vane Configurations on Heat Transfer and Pressure Drop in a Ribbed Internal Cooling System
Authors: Chen Wei , Ren Jing , Jiang Hongde
Published: January 2011

The ribbed serpentine blade cooling system is a typical configuration in the modern gas turbine airfoil. In this study, the experimental and the numerical efforts were carried out to investigate the local heat transfer and pressure drop distribution of a ribbed blade cooling system with different configurations in the turn region. A test rig containing a ribbed rectangular U-duct with a 180° round turn was built in Tsinghua University for this study. Transient liquid crystal method was applied to get the heat transfer distribution. Nine test cases with three turn configurations under three Reynolds numbers were carried out in the experiment. Pressure was measured along the duct in order to determine the influence of turning vane configurations on pressure drop. The test cases were also analyzed numerically based on RANS with three different turbulence models: the k-ε model, the SST reattachment model, and the Omega Reynolds Stress turbulence model. Both the experimental and the numerical results showed a significant influence of the turning vane configuration on the heat transfer and pressure drop in the convective cooling channel. Among the three configurations, the loss coefficient of turn in configuration 2 was lowest, due to the introduction of turning vane. Even the ribs were added in turn region of configuration 3, the loss coefficient and friction factor are reduced by 23% and 17.5%, respectively. Meanwhile, the heat transfer in baseline configuration is still the highest. As the introduction of turning vane, the heat transfer in the region after turn was reduced by 35%. In configuration 3, the heat transfer in the turn region was enhanced by 15% as the ribs installed in the turn region. In the before turn region, the pressure drop and heat transfer was not influenced by the turn configuration. All the turbulence models captured the trend of heat transfer and pressure drop distribution of three test sections correctly, but all provide overpredicted heat transfer results. Among the models, the ORS turbulence model provided the best prediction. While aiming at high heat transfer level and low pressure drop, it is suggested that, a suitable turn configuration, especially with the turning vane and/or the ribs, is a promising way to meet the conflicted requirements of the heat transfer and pressure drop in the convective cooling system.
Experimental Investigation of Laminar Flame Speeds for Medium Calorific Gas With Various Amounts of Hydrogen and Carbon Monoxide Content at Gas Turbine Temperatures
Authors: Sigfrid Ivan R. , Whiddon Ronald , Collin Robert , Klingmann Jens
Published: January 2011

It is expected that, in the future, gas turbines will be operated on gaseous fuels currently unutilized. The ability to predict the range of feasible fuels, and the extent to which existing turbines must be modified to accommodate these fuels, rests on the nature of these fuels in the combustion environment. Understanding the combustion behavior is aided by investigation of syngases of similar composition. As part of an ongoing project at the Lund University Departments of Thermal Power Engineering and Combustion Physics, to investigate syngases in gas turbine combustion, the laminar flame speed of five syngases (see table) have been measured. The syngases examined are of two groups. The first gas group (A), contains blends of H2, CO and CH4, with high hydrogen content. The group A gases exhibit a maximum flame speed at an equivalence ratio of approximately 1.4, and a flame speed roughly four times that of methane. The second gas group (B) contains mixtures of CH4 and H2 diluted with CO2. Group B gases exhibit maximum flame speed at an equivalence ratio of 1, and flame speeds about 3/4 that of methane. A long tube Bunsen-type burner was used and the conical flame was visualized by Schlieren imaging. The flame speeds were measured for a range of equivalence ratios using a constrained cone half-angle method. The equivalence ratio for measurements ranged from stable lean combustion to rich combustion for room temperature (25°C) and an elevated temperature representative of a gas turbine at full load (270°C). The experimental procedure was verified by methane laminar flame speed measurement; and, experimental results were compared against numerical simulations based on GRI 3.0, Hoyerman and San Diego chemical kinetic mechanisms using the DARS v2.02 combustion modeler. On examination, all measured laminar flame speeds at room temperature were higher than values predicted by the aforementioned chemical kinetic mechanisms, with the exception of group A gases, which were lower than predicted.
Aerodynamic Optimization System Development for Low Pressure Exhaust Hood of Steam Turbine
Authors: Wang Hongtao , Zhu Xiaocheng , Du Zhaohui , Yang Hong
Published: January 2011

Low pressure exhaust hood of steam turbine is used to connect the last stage turbine and the condenser. To further improve the recovery capability of low pressure turbine exhaust hood, an aerodynamic optimization system has been developed with Matlab platform. The system includes four modules: parametric geometry modeling, structured meshes generator, commercial aerodynamic simulator and Kriging surrogate based optimizer. The diffuser geometry profile in the exhaust hood is parameterized using cubic Bezier curve, and the control points of these curves are considered as design variables. The exhaust hood performance is optimized by changing those design variables to maximizing the average static pressure coefficient. The block-structured meshes are generated with ICEM-CFD Hexa. Aerodynamic performance evaluations of the hood are carried out by the three dimensional Reynolds-averaged Navier-Stokes computational fluid dynamics solver-CFX. Mesh generation and aerodynamic analysis are done automatically, which are driven by script commands in batch mode. Kriging model is used as surrogate, which establishes a global mapping between design variables and objective variable. In order to balance the exploration and exploitation with Kriging surrogate, Expected Improvement (EI) sample criteria is adopted to update Kriging surrogate. The proposed optimization framework drastically reduces the number of calling time-consuming CFD. Two aerodynamic optimization test cases are performed with the system. The aerodynamic performance of the original and optimal exhaust hood will be compared, while the flow filed in the both exhaust hood will be illustrated.
Effect of Impeller Blade Loading on Compressor Stage Performance in a High Specific Speed Range
Authors: Shibata Takanori , Yagi Manabu , Nishida Hideo , Kobayashi Hiromi , Tanaka Masanori
Published: January 2011

The authors previously found that compressor stage efficiency in a high specific speed range was significantly improved by employing an increased relative velocity diffusion ratio coupled with a high backsweep angle. In spite of such a high relative velocity diffusion ratio, the same surge margin as with a conventional design could be achieved by using a special front loading distribution with a lightly loaded inducer. In the present study, the blade loading distribution was further optimized in order to achieve a larger surge margin than previously. Four types of fully shrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the developed impeller achieved 3.8% higher stage efficiency and 11% larger surge margin than the conventional design without reducing the pressure coefficient and choke margin. It was concluded that aft loading coupled with a high degree of reaction was a very effective way to improve surge margin as well as stage efficiency. Stator matching was also investigated by changing the design incidence angle which was shown to have little influence on surge margin in the present test results.
Non-Linear Multiple Points Gas Turbine Off-Design Performance Adaptation Using a Genetic Algorithm
Authors: Li Y. G. , Abdul Ghafir M. F. , Wang L. , Singh R. , Huang K. , Feng X.
Published: January 2011

Accurate gas turbine performance models are crucial in many gas turbine performance analysis and gas path diagnostic applications. With current thermodynamic performance modelling techniques, the accuracy of gas turbine performance models at off-design conditions is determined by engine component characteristic maps obtained in rig tests and these maps may not be available to gas turbine users or may not be accurate for individual engines. In this paper, a non-linear multiple point performance adaptation approach using a Genetic Algorithm is introduced with the aim to improve the performance prediction accuracy of gas turbine engines at different off-design conditions by calibrating the engine performance models against available test data. Such calibration is carried out with introduced non-linear map scaling factor functions by ‘modifying’ initially implemented component characteristic maps in the gas turbine thermodynamic performance models. A Genetic Algorithm is used to search for an optimal set of non-linear scaling factor functions for the maps via an objective function that measures the difference between the simulated and actual gas path measurements. The developed off-design performance adaptation approach has been applied to a model single spool turboshaft aero gas turbine engine and demonstrated a significant improvement in the performance model accuracy at off-design operating conditions.
Experimental Investigation of the Dynamic Performance of a Micro Gas Turbine Recuperator Including Innovative Cycle Configurations
Authors: Ferrari Mario L. , Sorce Alessandro , Pascenti Matteo , Massardo Aristide F.
Published: January 2011

The aim of this work is the experimental analysis of steady-state and transient behavior of a primary surface recuperator installed in a 100 kW commercial micro gas turbine. The machine is integrated in an innovative test rig for high temperature fuel cell hybrid system emulation. It was designed and installed by the Thermochemical Power Group (TPG), at the University of Genoa, within the framework of the Felicitas and LARGE-SOFC European Integrated Projects. The high flexibility of the rig was exploited to perform tests on the recuperator operating in the standard cycle. Attention is mainly focused on its performance in transient conditions (start-up operations and load rejection tests). Start-up tests were carried out in both electrical grid-connected and stand-alone conditions, operating with different control strategies. Attention is focused on system response due to control strategy and on boundary temperature variation because of its influence on component life consumption. Further tests were carried out using the valves installed on the test rig to bypass the air side of the unit. Different operative conditions were analyzed to show the effect of different mass flow rates on recuperator behavior. Attention is mainly focused on recuperator performance when it operates in unbalanced flow rate conditions (i.e. different mass flow rate values in recuperator sides), as well as during advanced cycle start-up and shutdown operations.
Performance of JP-8 Surrogates and Parent Species in a Swirl Combustor
Authors: Katta Viswanath R. , Roquemore William M.
Published: January 2011

Swirl-stabilized combustor utilizes recirculation zones for stabilizing the flame. A numerical study is conducted for understanding the effect of recirculation zones on the combustion of practical fuels in this burner. A time-dependent, detailed-chemistry CFD model UNICORN is used. JP-8 fuel is modeled using two independently proposed surrogate mixtures. A semi-detailed chemical-kinetics model involving 161 species and 1538 reactions is incorporated into UNICORN code for describing the combustion of these surrogate mixtures. Calculations are performed for fuel-lean, stoichiometric, and fuel-rich conditions. Flames simulated with different surrogate mixtures in all three equivalence-ratio cases yielded nearly the same structures even though the two surrogate mixtures are very different in chemical composition. For understanding the role of individual parent species in the surrogate mixtures, calculations for the swirl combustor are repeated after replacing the surrogate fuel with one of its parent species. Detailed comparisons of flames generated with different parent species revealed significant variations in flame structures. However, the flames generated by the surrogate mixtures are nearly similar—suggesting that these mixtures are formulated for representing the same JP-8 fuel.
Methane Oxy-Combustion for Low CO2 Cycles: Blowoff Measurements and Modeling
Authors: Amato Alberto , Hudak Robert , Noble David R. , Scarborough David , D’Carlo Peter A. , Seitzman Jerry M. , Lieuwen Tim C.
Published: January 2011

Increasing concerns about climate change have encouraged interest in zero-CO2 emission hydrocarbon combustion techniques. In one approach, nitrogen is removed from the combustion air and replaced with another diluent such as carbon dioxide or steam. In this way, formation of nitrogen oxides is prevented and the exhaust stream can be separated into concentrated CO2 and water by a simple condensation process. The concentrated CO2 stream can then be sequestered or used for enhanced oil recovery. Burning fuels in an O2/CO2 diluent raises new combustion opportunities and challenges for both emissions and operability: this study focuses on the latter aspect. CH4/O2/CO2 flames are known to be characterized by slower chemical kinetics than methane-air flames and as such, flame stability is more problematic as they are easier to blow off. This issue was investigated experimentally by characterizing the stability boundaries of a swirl stabilized combustor. Near stoichiometric CO2 and N2 diluted methane/oxygen flames were considered and compared with baseline methane/air flames. Numerical modeling of chemical kinetics was also performed to analyze the dependence of laminar flame speeds and extinction strain rates upon dilution by different species and to develop correlations for blowoff boundaries. Finally, blowoff trends at high pressure were extrapolated from atmospheric pressure data to simulate conditions closer to those of gas turbines.
Parametric Analysis of a New CCHP System Utilizing Liquefied Natural Gas (LNG)
Authors: Wang Jiangfeng , Dai Yiping , Sun Zhixin , Ma Shaolin
Published: January 2011

Liquefied natural gas (LNG) contains considerable cold energy because a significant amount of energy is consumed to produce low-temperature LNG. So, finding a good way to utilize the LNG effectively, particularly its cold energy, is an important issue to solve the problem of energy crisis. In the present study, a new CCHP system utilizing liquid natural gas is proposed to provide cooling, heat and electricity output simultaneously to meet user’s different energy requirements. This CCHP system consists of a gas/steam combined cycle and an ejector refrigeration cycle. For cold energy utilization, LNG is firstly considered as a heat sink to condense the steam turbine exhaust in Rankine cycle, then cools down the suction air of compressor in Brayton cycle, and finally enters the combustion chamber after preheated by HRSG exhaust. The steam turbine has two streams of extraction steam. One is used to drive an ejector refrigeration cycle to produce the cooling effect, and the other is used to provide the heat. To evaluate the system performance, the exergy efficiency is selected as an evaluation criterion to eliminate the difference of energy quality. A thermodynamic simulation of the new CCHP system utilizing LNG is achieved using a simulation program. A parametric analysis is conducted to examine the effects of several key thermodynamic parameters on the performance of the proposed CCHP system. The results indicate that as gas turbine inlet temperature, pressure ratio of compressor and steam turbine inlet pressure increase, the exergy efficiency increases. In addition, as steam turbine back pressure, extraction mass rate ratio for heat, extraction mass rate ratio and extraction pressure for refrigeration increase, the exergy efficiency decreases.
The Predicted and Measured Effects of Increasing Back Pressure on the Performance of a Turboshaft Engine
Authors: Attia Marco S. , Eustace Richard W. , Favaloro Shane C.
Published: January 2011

This paper presents a comparison between the predicted effect of an increase in backpressure on a turboshaft helicopter engine and the actual results measured in an experimental test program. A generic engine performance program was used to perform a sensitivity study to identify the effect of increases in power turbine exit pressure (backpressure) on other engine performance parameters. The analysis showed that as the backpressure increases the engine increases fuel flow to produce a constant shaft torque (or horsepower), until the maximum power turbine entry temperature is reached. Once this occurs, fuel flow can no longer increase and thus further increases in backpressure cause a decrease in output torque. These predicted results are then compared with the actual effect as measured on a T55-GA-714A engine in a static test facility. The tests involved replacing the standard engine tail pipe with one of three shorter stub ducts which increased the backpressure by employing straight and convergent flow passages instead of the divergent passage on the standard tail pipe. The test-cell data identified that the stub ducts increase specific fuel consumption by between 0.016 and 0.039 lb/hr/hp, while the turbine inlet temperature increased by up to 108 deg F. This temperature increase means that the power output will become turbine temperature limited at a lower ambient temperature than would otherwise occur. Results showed that when temperature limiting exists the power output will be reduced by between 115 and 400 SHP depending on the choice of stub duct.
Assessment of URANS and DES for Prediction of Leading Edge Film Cooling
Authors: Takahashi Toshihiko , Funazaki Ken-ich , Bin Salleh Hamidon , Sakai Eiji , Watanabe Kazunori
Published: January 2011

This paper describes assessment of CFD simulations for the film-cooling on the blade leading edge with circular cooling holes in order to contribute durability assessment of the turbine blades. Unsteady RANS (URANS) applying a k–ε–v2–f turbulence model and the Spallart and Allmaras turbulence model, and Detached-Eddy Simulation (DES) based on the Spallart and Allmaras turbulence model are addressed to solve thermal convection. The CFD calculations were conducted by simulating a semi-circular model in the wind tunnel experiments. The DES and also the k–ε–v2–f model evaluate explicitly unsteady fluctuation of local temperature by the vortex structures, so that the predicted film cooling effectiveness comparatively in agreement with measurements. On the other hand, the predicted temperature fields by the Spallart and Allmaras model are less diffusive than the DES and the k–ε–v2–f model. In the present turbulence modeling, the DES only predicts penetration of main flow into the film cooling hole, but the Spallart and Allmaras model is not able to evaluate the unsteadiness and the vortex structures clearly, and over-predict film cooling effectiveness on the partial surface.
Establishment of a High Quality Database for the Modelling of Perforated Liners
Authors: Heuwinkel Claus , Enghardt Lars , Bake Friedrich , Sadig Sermed , Gerenda´s Miklo´s
Published: January 2011

Perforated liners, especially in combination with a bias flow, are very effective sound absorbers. Applied to gas turbine combustors they can suppress thermoacoustic instabilities and thus allow the application of new combustion concepts concerning higher efficiency and lower emissions. While the successful application of such a damping concept has been shown, it is still not possible to accurately predict the damping performance of a given configuration. This paper provides a comprehensive database of high quality experimental data. Variations of geometric, fluid mechanic and acoustic parameters have been studied, including realistic engine configurations. The results demonstrate each parameters influence on the damping performance. A low order thermo-acoustic model is used to simulate the test configurations numerically. The model shows a good agreement with the measurements for a wide range of geometries, Strouhal and bias flow Mach numbers.
Film Cooling Performance of the Embedded Holes in Trenches With Compound Angles
Authors: Li Jia , Ren Jing , Jiang Hongde
Published: January 2011

Film cooling performance for a row of cylindrical holes can be enhanced by embedding the row in a suitable transverse slot. The compound angle of the holes can even more affects the cooling performance at downstream of the injections. In this study the cooling performance of the embedded holes in transverse trenches with different compound angles are explored both by pressure sensitive paint (PSP) experiment technology and RANS algorithm. A film cooling test rig was built up in Tsinghua University, which contains an accelerating free stream section to model the surface of a turbine airfoil. The PSP technology is applied in the tests to obtain the film cooling effectiveness. The experiments are performed for a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 4000. Considering three compound angles, 0°, 45° and 90°, and with or without transverse trenches. All six cases are tested at three different coolant-to-mainstream blowing ratios of 0.5, 1.0, and 1.5. Meanwhile, the test cases are numerically simulated based on RANS with k-ε turbulence model to show the detail of the flow patterns. Both the experimental and numerical results show that the adiabatic film effectiveness is relative insensitive to the blowing ratio in the case of holes with trenches. Moreover, it could be improved with a more uniform spanwise distribution. It is mainly due to the blockage of the ejected coolant at the downstream edge of the trench, which forces a portion of the cooling air to spread laterally within the trench prior to issuing onto the upper surface. Both 45° and 90° compound angles can further enhance the film cooling effectiveness over the axial ejection, this is mainly due to the lateral momentum component of the ejection. A lateral passage vortex is formed inside the trench which strengthens the lateral spreading of the jets. The 45° compound angle gives a higher film cooling effectiveness overall.