bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of Impingement Heat Transfer Characteristics in a Convergent Channel With Pin Fin
Authors: Xu Yang , Zhu Hui-ren , Xu Wei-jiang , Liu Cun-liang , Lu Hai-ying
Published: August 2017

The protection of the inlet components of an aircraft engine from the adverse effects of ice accretion has been a crucial design problem since the very early years of flight. Therefore, the configuration with efficient heat transfer is the focus on the design of a hot-air anti-icing system in an aeroengine. This paper studies experimentally on the heat transfer in a convergent channel with pin fin within the strut. Experiments are carried out by using a transient liquid crystal technique. The dimensionless lateral distance (S/d, where S is the distance between the leading edge and pin fin, d is the diameter of the impingement hole), the dimensionless vertical distance (S1/d, where S1 is the distance between pin fins) as well as the pitch ratio (D/d, where D is the diameter of the pin fin) of the pin fin and impingement hole are respectively investigated to study the heat transfer on the surface of convergent channel. The Reynolds number based on the hydraulic diameter of the impingement hole ranges from 6300 to 12700. Within the experimental range, the result shows that the Average Nusselt Number increases at first and then decreases as the dimensionless lateral distance S/d increases. The Average Nusselt Number has the highest value when S/d = 2.5;When the dimensionless vertical distance S1/d increases, the Average Nusselt Number goes up at first and then reduces .The Average Nusselt Number has the highest value when S1/d = 3;The increasing pitch ratio D/d leads to a lower Average Nusselt Number. The Average Nusselt Number has the highest value when D/d = 1/3. The Average Nusselt Number increases as the Reynolds number increases.
Validation Analysis of High Pressure Turbine Creep Deformation for Ultra-Supercritical Steam Turbine
Authors: Wu Shifang , Chen Yongzhao , Yang Yanlei , Zhu Yu , Liu Yang , Fan Yizhang
Published: August 2017

Ultra-supercritical (USC) coal-fired steam turbines, as the representative of fuel-efficient power generation technology, occupies a large portion of power generation capacity in China. During the design process of USC steam turbines, high temperature creep deformation is a focusing topic, usually predicted by finite element method (FEM). In-service test data of a specific USC power plant during nine-year operation are used to validate the predicted results based on FEM. Toward this end, the components in HP turbine of a specific USC steam turbine (600 °C/26.2MPa) is chosen for the FEM modeling. The measurement of the creep behavior inducing plastic deformation of the components was carried out during the major overhaul of the power plant. Comparison of the results between the simulation and the measurement disclosed an accepted agreement, and the accumulated test data and the experience of the simulation method would be of great help for the further design of the components and the operation of the power plant.
Measurement and Prediction of Centrifugal Compressor Axial Forces During Surge: Part 2 — Dynamic Surge Model
Authors: Munari Enrico , Morini Mirko , Pinelli Michele , Brun Klaus , Simons Sarah , Kurz Rainer
Published: August 2017

The force acting on centrifugal compressors is an important parameter to be considered throughout the operating life of these turbomachines. When the compressor is operating in surge conditions these forces can become highly dangerous for the mechanical and aerodynamic structures. This instability is usually avoided in industrial applications but the anti-surge system may not react in time when emergency shutdowns or power failures take place. During these rapid transients, surge can develop, generating unsteady forces which can harm the close clearance components of the compressor. Therefore, the capability to predict the characteristics and the dynamics of these surge forces would allow the estimation of the off-design fatigue cycles produced on these components by surge. Currently, no validated method exists to predict the frequency and amplitude of the surge forces and determine the potential damage of these components.

In this paper a lumped parameter model, developed by using the bond graph approach to predict the dynamic surge fluid-dynamic oscillations, is presented. The model requires the geometry and the steady-state performance maps of the compressor as inputs, together with the piping system configuration characteristics.

The simulator, is provided with a supplementary tool to estimate the axial force frequency and amplitude, taking into consideration all the contributions to the axial fluid-dynamic thrust, the stiffness-damping of the thrust bearing and the mass of the rotor.

The model was tuned and validated using the test case axial force data from the Southwest Research Institute facility. The model has shown good agreement with the experimental results which implies that it can offer significant information about the severity of a surge event and the quantification of the machine performance losses together with possible damage to the close clearance components. This study is a first important step that can lead to schedule optimization for maintenance and repair activities.
Dynamic Inlet Simulation Demonstration for Airframe-Propulsion Integration Using HPCMP CREATE™-AV Kestrel
Authors: Klepper Jason B. , Sirbaugh James R. , Davis Milt W.
Published: August 2017

The purpose of an aircraft inlet system is to capture airflow from the free-stream and deliver it to an engine at the appropriate Mach number for that system. To meet design constraints, modern fighter aircraft have complex inlets with multiple turns that generally lead to both total pressure and swirl distortion at the engine face. These flow distortions can lead to reduced system performance, operability, and durability introducing issues in the overall success of the weapons system performing its mission. Therefore the integration of the airframe, inlet, and propulsion system is a key design issue in the development of military aircraft. The purpose of this paper is to demonstrate the dynamic (hybrid RANS/DDES) simulation capabilities of the HPCMP CREATE™-AV Kestrel tools by application to a sub-scale airframe/inlet system for a current military aircraft. The computational results were compared to wind tunnel results at various Mach number, angles of attack, angles of sideslip, and corrected flow rates. The inlet pressure recovery and distortion intensities for each case compared well to wind tunnel results. By comparing the computational results and wind tunnel test results, the applicability of these tools to future weapon systems design and development can be assessed.
Foreign Object Damage Behavior of a SiC Fibrous Ceramic Composite
Authors: Kedir Nesredin , Faucett D. Calvin , Sanchez Luis , Choi Sung R.
Published: August 2017

The response of a SiC fibrous ceramic composite to foreign object damage was determined at ambient temperature and velocities ranging from 40 to 150 m/s. Target specimens were impacted, at a normal incidence angle and in a partially supported configuration, using 1.59 mm-diameter hardened steel ball projectiles. Qualitative analysis of the damage morphologies of targets and projectiles were made via scanning electron microscopy (SEM). In addition, the extent of impact damage was characterized by determining the post-impact strength of each target specimen as a function of impact velocity. Relative to the as-received strength, the fibrous composite showed limited strength degradation due to impact with the maximum reduction of 17 % occurring at 150 m/s. A quasi-static analysis of the impact force prediction was also made based on the principle of energy conservation and the results were verified via experimental data.
A Sensitivity Study of Gas Turbine Exhaust Diffuser-Collector Performance at Various Inlet Swirl Angles and Strut Stagger Angles
Authors: Siorek Michal P. , Guillot Stephen , Xue Song , Ng Wing F.
Published: August 2017

This paper describes studies completed using a quarter-scaled rig to assess the impact of turbine exit swirl angle and strut stagger on a turbine exhaust system consisting of an integral diffuser-collector. Advanced testing methods were applied to ascertain exhaust performance for a range of inlet conditions aerodynamically matched to flow exiting an industrial gas turbine. Flow visualization techniques along with complementary Computational Fluid Dynamics (CFD) predictions were used to study flow behavior along the diffuser endwalls. Complimentary CFD analysis was also completed with the aim to ascertain the performance prediction capability of modern day analytical tools for design phase and off-design analysis. The K-Epsilon model adequately captured the relevant flow features within both the diffuser and collector, and the model accurately predicted the recovery at design conditions. At off-design conditions, the recovery predictions were found to be pessimistic. The integral diffuser-collector exhaust accommodated a significant amount of inlet swirl without a degradation in performance, so long as the inlet flow direction did not significantly deviate from the strut stagger angle. Strut incidence at the hub was directly correlated with reduction in overall performance, whereas the diffuser-collector performance was not significantly impacted by strut incidence at the shroud.
NOx-Formation and CO-Burnout in Water Injected, Premixed Natural Gas Flames at Typical Gas Turbine Combustor Residence Times
Authors: Lellek Stephan , Sattelmayer Thomas
Published: August 2017

With the transition of the power production markets towards renewable energy sources an increased demand for flexible, fossil based power production systems arises. Steep load gradients and a high range of flexibility make gas turbines a core technology in this ongoing change. In order to further increase this flexibility research on power augmentation of premixed gas turbine combustors is conducted at the Lehrstuhl für Thermodynamik, TU München. Water injection in gas turbine combustors allows for the simultaneous control of NOx emissions as well as the increase of the power output of the engine and has therefore been transferred to a premixed combustor at lab scale. So far stable operation of the system has been obtained for water-to-fuel ratios up to 2.25 at constant adiabatic flame temperatures. This paper focuses on the effects of water injection on pollutant formation in premixed gas turbine flames. In order to guarantee for high practical relevance experimental measurements are conducted at typical preheating temperatures and common gas turbine combustor residence times of about 20 ms. Spatially resolved and global species measurements are performed in an atmospheric single burner test rig for typical adiabatic flame temperatures between 1740 and 2086 K. Global measurements of NOx and CO emissions are shown for a wide range of equivalence ratios and variable water-to-fuel ratios. Cantera calculations are used to identify non-equilibrium processes in the measured data. To get a close insight into the emission formation processes in water injected flames local concentration measurements are used to calculate distributions of the reaction progress variable. Finally, to clarify the influence of spray quality on the composition of the exhaust gas a variation of the water droplet diameters is done. For rising water content at constant adiabatic flame temperature the NOx emissions can be held constant, whereas CO concentrations increase. On the contrary, both values decrease for measurements at constant equivalence ratio and reduced flame temperatures. Further analysis of the data shows the close dependency of CO concentration on the equivalence ratio, however, due to the water addition a shift of the CO curves can be detected. In the local measurements changes in the distribution of the reaction progress variable and an increase of the flame length were detected for water injected flames along with changes of the maximum as well as the averaged CO values. Finally, a strong influence of water droplet size on NOx and CO formation is shown for constant operating conditions.
Characterization of Fuel Composition and Altitude Impact on Gaseous and Particle Emissions From a Turbojet Engine
Authors: Chan Tak W. , Canteenwalla Pervez , Chishty Wajid A.
Published: August 2017

The effects of altitude and fuel composition on gaseous and particle emissions from a turbojet engine were investigated as part of the National Jet Fuels Combustion Program (NJFCP) effort. Two conventional petroleum based jet fuels (a “nominal” and a “worst-case” jet fuel) and two test fuels with unique characteristics were selected for this study. The “worst-case” conventional jet fuel with high flash point and viscosity resulted in reduced combustion efficiency supported by the reduced CO2 emissions and corresponding increased CO and THC emissions. In addition, increased particle number (PN), particle mass (PM), and black carbon (BC) emissions were observed. Operating the engine on a bimodal fuel, composed of heavily branched C12 and C16 iso-paraffinic hydrocarbons with an extremely low cetane number did not significantly impact the engine performance or gaseous emissions but significantly reduced PN, PM, and BC emissions when compared to other fuels. The higher aromatic content and lower hydrogen content in the C-5 fuel were observed to increase PN, PM, and BC emissions. It is also evident that the type of aromatic hydrocarbons has a large impact on BC emissions. Reduction in combustion efficiency resulted in reduced CO2 emissions and increased CO and THC emissions from this engine with increasing altitudes. PN emissions were moderately influenced by altitude but PM and BC emissions were significantly reduced with increasing altitude. The reduced BC emissions with increasing altitude could be a result of reduced combustion temperature which lowered the rate of pyrolysis for BC formation, which is supported by the NOx reduction trend.
Effects of Fluid Properties on Spray Characteristics of a Flow-Blurring Atomizer
Authors: Fisher Brian T. , Weismiller Michael R. , Tuttle Steven G. , Hinnant Katherine M.
Published: August 2017

In order to understand the reasons for the apparent benefits of using a flow-blurring (FB) atomizer in a combustion system, it is necessary to first examine fundamental spray characteristics under non-reacting conditions. Previous work on FB atomizers, however, has mostly involved only water and a relatively narrow range of parameters. In this study, a phase Doppler anemometry instrument was used to characterize FB atomizer sprays and determine the effects of varying surface tension and viscosity of the liquid. Operating at room pressure and temperature (i.e., a “cold spray”), droplet sizes and velocities were measured for water, a water/surfactant mixture (lower surface tension), a water/glycerol mixture (higher viscosity), and glycerol (much higher viscosity). For all of the tested fluids, with the exception of pure glycerol, the FB atomizer produced small droplets (below 50 μm) whose size did not vary significantly in the radial or axial direction, particularly above a characteristic distance from the atomizer exit. Results show that the spray is essentially unaffected by a 4.5x decrease in surface tension or a 7x increase in viscosity, and that Sauter mean diameter (SMD) only increased by approximately a factor of three when substituting glycerol (750x higher viscosity) for water. The results suggest that the FB atomizer can effectively atomize a wide range of liquids, making it a useful fuel-flexible atomizer for combustion applications.
Experimental Investigation of Dynamically Forced Impingement Cooling
Authors: Berthold Arne , Haucke Frank
Published: August 2017

The influence of dynamic forcing of a 7 by 7 impinging jet array on the cooling efficiency is investigated experimentally. Thereby, this work focused on determining the influence side wall induced cross flow has on the local convective heat transfer on an electrically heated target plate and on enhancing the local convective heat transfer. For the enhancement the main focus is on the influence of the impingement distance, the impingement frequency and the phaseshift between the individual rows of nozzles. Liquid crystal thermography is employed for measuring the local wall temperatures, which are used to calculate the local Nusselt numbers. The cooling efficiency of this dynamic approach is determined by comparing local Nusselt numbers with steady blowing conditions.
Turbine Vane Endwall Film Cooling From Cross-Row Configuration With Simulated Upstream Leakage Flow
Authors: Chowdhury Nafiz H. K. , Shiau Chao-Cheng , Han Je-Chin , Zhang Luzeng , Moon Hee-Koo
Published: August 2017

The performance of a full coverage film cooling configuration called cross-row (CR) configuration including upstream inlet leakage flow was studied by measuring the adiabatic film cooling effectiveness distribution using PSP technique. Experiments were conducted in a blow-down wind tunnel cascade facility at the isentropic exit Mach number of 0.5 corresponding to inlet Reynolds number of 3.8 × 105, based on axial chord length. A free-stream turbulence level was generated as high as 19% with a length scale of 1.7 cm at the inlet. The results are presented as two-dimensional adiabatic film cooling effectiveness distributions on the endwall surface with corresponding spanwise averaged distributions. The focus of this study is to investigate the effect of coolant-to-mainstream mass flow ratio (MFR) and density ratio (DR) on the proposed endwall cooling design. Initially, increased MFR for the endwall cooling and upstream leakage levels up the local adiabatic cooling effectiveness and yields relatively uniform coverage on the entire endwall. However, in either case, highest MFR does not provide any improvement as endwall cooling suffered from the jet lift-off and leakage coolant coverage restricted by the downstream near-wall flow field. Results also indicated a density ratio of 1.5 provides the best performance. Finally, a fair comparison is made with another design called axial-row (AR) configuration from a companion paper.
Low-Order Modelling of Combustion Noise in an Aero-Engine: The Effect of Entropy Dispersion
Authors: Mahmoudi Yasser , Giusti Andrea , Mastorakos Epaminondas , Dowling Ann P.
Published: August 2017

The present work studies the effect of entropy dispersion on the level of combustion noise at the turbine outlet of the Rolls-Royce ANTLE aero-engine. A new model for the decay of entropy waves, based on modelling dispersion effects, is developed and utilised in a low-order network model of the combustor (i.e. LOTAN code that solves the unsteady Euler equations). The proposed model for the dispersion of entropy waves only requires the mean velocity field as an input, obtained by RANS computations of the demonstrator combustor. LOTAN is then coupled with a low order model code (LINEARB) based on the semi-actuator disk model that studies propagation of combustion noise through turbine blades. Thus, by combining LOTAN and LINERAB we predict the combustion noise and its counterparts, direct and indirect noise, generated at the turbine exit. In comparison with experimental data it is found that without the inclusion of entropy dispersion, the level of combustion noise at the turbine exit is over-predicted by almost two orders of magnitude. The introduction of entropy dispersion in LOTAN results in much better agreement with the experimental data, highlighting the importance of entropy wave dispersion for the prediction of combustion noise in real engines. In more detail, the agreement with the experiment for high and low frequencies was very good. At intermediate frequencies the experimental measurements are still over-predicted, however the predicted noise is much smaller compared to the case without entropy dispersion. This discrepancy is attributed to (i) the role of turbulent mixing in the overall decay of the entropy fluctuations inside the combustor, not considered in the model developed for the decay of entropy waves, and (ii) the absence of a proper model in LINEARB for the decay of entropy waves as they pass through the turbine blade rows. These are areas that still need further development to improve the prediction of low-order network codes.
Accurate Method to Reproduce Throughflow Results With a Meanline Solver
Authors: Chaquet Jose M. , Corral Roque , Fernandez Alfredo
Published: August 2017

A novel method to generate meanline models from through-flow results of low pressure turbines (LPT) is presented. Using a fast optimization approach, it is shown that it is possible to reproduce with the reduced fidelity model the main performance variables of the throughflow case, such as stage powers, pressure ratios, Mach numbers or Smith charts, with negligible errors in practical terms. Providing two throughflow models (a three-stage LPT rig and a six-stage plus an outlet guide vane LPT), it is discussed which variables should be matched in order to obtain a representative meanline model. It is studied as well the radial angle influence on the matching process. Using meanline models could have some benefits in the fast assessment of geometry and operation conditions changes due to their flexibility, robustness and easy setup compared with a throughflow simulation.
Working Fluid and Parametric Optimization of a Two-Stage ORC Utilizing LNG Cold Energy and Low Grade Heat of Different Temperatures
Authors: Sun Zhixin , Wang Shujia , Xu Fuquan , Wang Tielong
Published: August 2017

Natural gas is considered as a green fuel due to its low environmental impact. LNG contains a large amount of cold exergy and must be regasified before further utilization. ORC (Organic Rankine Cycle) has been proven to be a promising solution for both low grade heat utilization and LNG cold exergy recovery. Due to the great temperature difference between the heat source and LNG, the efficiency of one-stage ORC is relatively small. Hence, some researchers move forward to a two-stage Rankine cycle.

Working fluid plays a quite important role in the cycle performance. Working fluid selection of a two-stage ORC is much more challenging than that of a single-stage ORC. In this paper, a two-stage ORC is studied. Heat source temperatures of 100,150 and 200°C are investigated. 20 substances are selected as potential candidates for both the high and low Rankine cycles. The evaporating, condensing and turbine inlet temperatures of both Rankine cycles are optimized by PSO (Particle Swarm Optimization).

The results show that the best combination for heat source temperature of 100°C is R161/R218 with the maximum exergy efficiency of 35.27%. The best combination for 150°C is R161/RC318 with the maximum efficiency of 37.84% and ammonia/ammonia with the maximum efficiency of 39.15% for 200°C. Fluids with intermediate critical temperature, lower triple point temperature and lower normal boiling temperature are good candidates.
Fuel Cell Microturbine Hybrid System Analysis Through Different Uncertainty Quantification Methods
Authors: Abrassi Alessio , Cuneo Alessandra , Tucker David , Traverso Alberto
Published: August 2017

The analysis of different energy systems has shown various sources of variability and uncertainty; hence the necessity to quantify and take these into account is becoming more and more important. In this paper, a steady state, off-design model of a solid oxide fuel cell and turbocharger hybrid system with recuperator has been developed. Performances of such stiff systems are affected significantly by uncertainties both in component performance and operating parameters. This work started with the application of Monte Carlo Simulation method, as a reference sampling method, and then compared it with two different approximated methods. The first one is the Response Sensitivity Analysis, based on Taylor series expansion, and the latter is the Polynomial Chaos, based on a linear combination of different polynomials. These are non-intrusive methods, thus the model is treated as a black-box, with the uncertainty propagation method staying at an upper level. The work is focused on the application on highly non-linear complex systems, such as the hybrid systems, without any optimization process included. Hence, only the uncertainty propagation is considered. Uncertainties in the fuel utilization, ohmic resistance of the fuel cell, and efficiency of the recuperator are taken into account. In particular, their effects on fuel cell lifetime and some simple economic parameters are evaluated. The analysis distinguishes the specific features of each approach and identifies the strongest influencing inputs to the monitored output. Both approximated methods allow an important reduction in the number of evaluations while maintaining a good accuracy compared to Monte Carlo Simulation.
The Effect of Axial Flow Velocity on Annular Gap Windage Power Loss
Authors: Swanson Erik E. , Tsuei Hsin-Hua , O’Meara P. Shawn
Published: August 2017

As surface speeds of electrical machinery increase to meet ever more demanding application requirements, windage power losses due to shearing of air (or other process fluid) between the rotor and stator take on an increasingly significant role. Historically, these losses have not received a huge amount of research attention from the high speed motor community. Common approaches include making the rotor and stator surfaces as smooth as possible, keeping the rotor-stator gap as large as practical without compromising electrical efficiency, and simply accepting whatever losses are present. This paper presents a combined Computational Fluid Dynamics and experimental evaluation of the effect of axial flow on windage power loss in a rotor-stator gap. The results support other results in the literature suggesting that careful tuning of axial flow velocity in the gap can suppress the formation of turbulent Taylor vortices, and thereby reduce windage power loss. In specific cases, reductions in windage power loss of up to 30 percent have been predicted. The presence of an optimal axial flow velocity is confirmed experimentally.
Heat Exchanger Options for Dry Air Cooling for the sCO2 Brayton Cycle
Authors: Moisseytsev Anton , Lv Qiuping , Sienicki James J.
Published: August 2017

The capability to utilize dry air cooling by which heat is directly rejected to the air atmosphere heat sink is one of the benefits of the supercritical carbon dioxide (sCO2) energy conversion cycle. For the selection and analysis of the heat exchanger options for dry air cooling applications for the sCO2 cycle, two leading forced air flow design approaches have been identified and analyzed for this application; an air cooler consisting of modular finned tube air coolers; and an air cooler consisting of modular compact diffusion-bonded heat exchangers. The commercially available modular finned tube air cooler is found to be more cost effective and is selected as the reference for dry air cooling.
CAD-Based Aerodynamic Optimization of a Compressor Stator Using Conventional and Adjoint-Driven Approaches
Authors: Vasilopoulos Ilias , Flassig Peter , Meyer Marcus
Published: August 2017

This paper presents the results of a CAD-based aerodynamic optimization study conducted on the TU Berlin TurboLab Stator benchmark test case. Two different approaches are examined and compared: a conventional gradient-free optimization process which makes use of 2D and 3D CFD results and constructs a response surface to obtain the optimum solution; and an adjoint-driven optimization workflow, where the derivatives w.r.t. the design parameters are calculated by linking the adjoint surface sensitivity map with the model’s geometric sensitivities. Both methods are applied to the turbomachinery test case, where a multi-objective multi-point problem is considered. Moreover, manufacturing constraints are incorporated in the process chain, which makes the case even more challenging. Since the optimization output is already in CAD format, there is no requirement for a back-to-CAD step and the optimum blade can be straightforwardly manufactured.
Annular Gap Windage Loss Measurements for High Speed Electrical Machinery
Authors: Swanson Erik E. , O’Meara P. Shawn , Tsuei Hsin-Hua
Published: August 2017

Windage loss in small, high speed electrical machinery is often predicted using fairly simple quasi-empirical correlations. Many of the correlations used are primarily based on testing performed with larger test articles, at lower speeds, and often with liquid lubricants. This paper presents a new set of air gap windage loss test data for test articles that are more nearly representative of small, high speed electrical machinery. These data were obtained using a unique new test rig. This rig was designed around test articles that are representative of 50 to 200 kW machinery operating up to 60 krpm with air as the fluid in the rotor-stator clearance. This paper describes the new test facility and presents data for a smooth surface 72.4 mm rotor with both a smooth stator and a stator with simulated winding slots, for a range of clearances. The smooth surface results are shown to be in reasonable agreement with previously published results for annular gap windage power loss.
Classification of Fluid Dynamic Loss in Aeroengine Transmission Gears: Experimental Analysis and CFD Validation
Authors: Arisawa Hidenori , Shinoda Yuji , Tanaka Mitsuaki , Goi Tatsuhiko , Akahori Hirofumi , Yoshitomi Mamoru
Published: August 2017

Reducing fluid dynamic power loss as speed increases is crucial to developing highly efficient high-speed aircraft engine gearing. Therefore, in this study, experiments were conducted using a precise friction-loss management technique and a vacuum pump in the gearbox for experimentally classifying fluid dynamic loss. Consequently, it was found that fluid dynamic loss could be classified into “oil-jet acceleration loss and oil reacceleration loss based on the momentum conservation of point mass” and “oil churning loss and windage loss based on the momentum conservation of an incompressible continuum”. Furthermore, the simulation results obtained via appropriate computational fluid dynamics (CFD) modeling of the resultant mechanisms agreed with the experimental results. The results of the present study are expected to improve the efficiency of mechanical systems, e.g., the fan drive gear system of Geared Turbofan™ and the accessory gearbox.
Development of Compression System Dynamic Simulation Code for Testing and Designing of Anti-Surge Control System
Authors: Mohajer Abbas , Abbasi Eshagh
Published: August 2017

As cost of damages to the compression systems in oil and gas industry can lead to significant capital cost loss and plant downtime, these valuable assets must be carefully protected to achieve a high level of production and operational reliability. In recent years, several research activities have been conducted to develop knowledge in analysis, design and optimization of compressor anti surge control system. Since, the anti-surge control testing on a full scale compressor are limited for possible consequences of failure and also the experimental facility can be expensive to set up control strategies and logics, design process often involves analyses using compression system dynamic simulation. Such Simulator enables the designer to test the new control logic and see the results before implementing it on governor system. This would increase the reliability and prevents undesirable costs resulting from practical trial and error process. Taking into account its own requirements and market demand, a high fidelity compression system dynamic simulation environment has developed by MAPNA Turbine (TUGA) to verify the anti-surge control system design and test the control logic across the all operating range of the compressor performance. Typical control scenarios that have to be considered are process control, starting and stopping, and emergency shutdowns. Having such simulator is also deemed to be essential to serve other applications during all stages of system life cycle, including but not limited to the educational tool for operators training, Site Acceptance Test (SAT) and Factory Acceptance Test (FAT) and compression plant design optimization.

This research focuses on developing and validating a physics-based, modular, non-linear and one-dimensional dynamic model of a compression system: centrifugal compressor and its surrounding process equipment like scrubber, cooler, a recycle line with a control valve and check valve. The mathematical approach of the model is based on laws of conservation and the included ordinary differential equations (ODEs) which describe the system dynamics, is solved by using advanced computational method in an in-house FORTRAN code. Compressor characteristics maps generated from company compressor test bench are used to determine compressor pressure ratio and efficiency. All equipment and inlet/outlet accessories as well as test instructions follow the requirements of PTC10. The simulation within a wide range of operating conditions allows a parametric study to be performed and the optimal values of the control parameters to be selected. In order to check the validity of the model, the simulation results are then compared with experimental data taken on the company industrial compressor test facility and also with operational field measurement.
Numerical Investigation on Loss Mechanism and Performance Improvement for a Zero Inlet Swirl Turbine Rotor
Authors: Zhao Wei , Zhao Qingjun , Sui Xiuming , Luo Weiwei , Xu Jianzhong
Published: August 2017

A zero inlet swirl turbine rotor (ZISTR) is originally presented as the first stage in a multistage vaneless counter-rotating turbine (MVCT), which only consists of 4 rotors without any vanes. The vanes upstream of a ZISTR are removed to reduce the turbine weight and length, as well as the viscous losses and coolants associated with vanes. However, due to the lack of inlet swirl the stagger angles for ZISTR blade profiles are high and the blade deflections are very small, resulting in almost straight cambers and very thin airfoils. The motivation of this paper is to reveal the overall performance and key loss sources of a ZISTR associated with its special blade profile, and provide corresponding optimization approaches for its practical usages. The 3D viscous numerical results show that the wake, the suction side trailing edge shock and the tip leakage flow have substantial influence on the rotor performance. To optimize the performance of a ZISTR, reducing blade solidity is proposed to decrease the viscous and shock losses by increasing the portion of the inviscid mainstream. Leaned blade is also presented to restrict the tip leakage flow by adjusting the axial position of stagnation points on the blade profile, obtaining an increase in efficiency of 0.9%. The off-design performance of the optimized rotor is also presented to show the effect of the blade lean on efficiency at various rotating speeds and back pressures.
A New Temperature Based Method for Determination of Lifetime Consumption of Turbo-Machinery Components During Operation
Authors: Sistaninia M. , Ugel D. , Olmes S.
Published: August 2017

In order to operate the turbo-machineries more flexibly, a lifetime counting method was developed which enables estimating lifetime consumption of high thermal-inertia components based on the temperature history of the components. It can account for consumed fatigue life at the locations of temperature measurement during the turbo-machine operation. By considering the operation history, the structural component can be operated closer to its lifetime limits, to increase the intervals between inspections, and therefore to extend the operational lifetime of the turbo-machine.

In this method the cold start (CS) to full load cycle, with the number of cycles to crack initiation Ncs, is defined as reference load cycle. The damage weighting factor Ni/NCS for cyclic event i is then calculated based on a semi-empirical correlation between Ni/NCS and the temperature history of the part. The semi-empirical correlation can be determined for each component or each location depending on the required precision. It is determined based on the Low Cycle Fatigue (LCF) life calculated for different Gas Turbine (GT) operation scenarios. The damage weighting factors are then employed to calculate the lifetime consumption using Miner’s rule.

The predictions of this method for the turbine housings of several Gas Turbines (GTs) were evaluated against finite element (FE) results. Multiple load cases were considered for each GT. It is shown that this approach can account for the lifetime consumption using the minimum required number of GT operation parameters.
CFD Analysis of the Combustion Chamber of a Commercial Aircraft Engine of Medium Thrust Class From a Maintenance Perspective
Authors: Kuntzagk Stefan , Kraft Jörn , Esemann Ina
Published: August 2017

The combustion chamber of aircraft engines plays an important role in achieving the optimum performance during an engine overhaul. For long decades, it has been common understanding in the MRO business that a well overhauled compressor and turbine are required to get an engine with low SFC and high EGT margin. In recent work at Lufthansa Technik AG, a comprehensive CFD analysis of the combustion chamber showed that, in contrast to this, small geometrical features influence the mixing process in the combustion chamber and can have an effect on the exit temperature profile. This in turn can reduce the accuracy of the EGT measurement significantly and create measurement errors and misinterpretations of the real engine performance.

In order to get insight into the flow topology, a very detailed digital model has been created using scans of the hardware available in the shop. Important geometrical features such as the cooling provisions and swirl creating components have been included in a very detailed manner with an efficient hexahedral mesh. The model includes the HPT vanes and the cooling flow extraction from the secondary cold flow. CFD results have been generated using the flow solver Ansys CFX 17.1, which is able to predict all relevant physical effects such as injection of liquid fuel, evaporation, and combustion of Jet A1 fuel using the Burning-Velocity combustion model. The flow in the combustion chamber shows large natural fluctuations. Subsequently, for each case a transient calculation has been carried out in order to allow an evaluation of the time-averaged flow field. Different geometrical features are investigated to predict the effect of geometry deviations on the exit temperature profile, e.g. the shape and size of the dilution holes.

Finally along the example of two CFM56 engines it will be shown how the data obtained by the detailed CFD model is used to optimize work-scoping and maintenance procedures. On the two cases put forward the combination of extended test-cell instrumentation and detailed modeling enabled not only the identification but also the rectification of combustion chamber deviations. This in turn minimized the necessary work, whereas in the past combustion chamber issues often went unnoticed and consequently resulted in extensive additional work.
Influence of Carrier Air Preheating on Autoignition of Inline-Injected Hydrogen-Nitrogen Mixtures in Vitiated Air of High Temperature
Authors: Schmalhofer Christoph A. , Griebel Peter , Aigner Manfred
Published: August 2017

Gas turbines will play a significant role in future power generation systems because they provide peak capacity due to their fast start-up capability and high operational flexibility. However, in order to meet the COP 21 goals, de-carbonization of as turbine fuels is required. Compared to natural gas operation, autoignition and flashback risks in gas turbines operated on hydrogen-rich fuels are higher which has to be taken into account for a proper gas turbine design. From investigations of these phenomena at relevant operating conditions with appropriate measurement techniques, e.g. high-speed imaging, the understanding of the non-stationary processes occurring during autoignition can be improved and design guidelines for a safe and reliable gas turbine operation can be derived.

The present study investigates the influences of elevated carrier-air preheating temperatures and hydrogen fuel volume fractions on autoignition at hot gas temperatures higher than 1100 K and pressures of 15 bar. An in-line co-flow injector is used to inject the hydrogen-nitrogen fuel mixtures. The formation, temporal and spatial development of autoignition kernels at high-temperature vitiated air conditions, e.g. relevant to reheat combustor operation, are studied. The experiments were conducted in an optically accessible mixing section of a generic reheat combustor. The hydrogen-nitrogen fuel mixtures of up to 70 vol. % hydrogen are injected in-line into the mixing section along with the carrier-air which was preheated to temperatures between 303 K and 703 K. High-speed imaging was used to detect the autoignition kernels and their temporal and spatial development from luminescence signals. Particle Image Velocimetry measurements were conducted to obtain the velocity distribution in the mixing section at autoignition conditions.

The influences of vitiated air temperatures and carrier preheating temperatures on autoignition and flame stabilisation limits are shown, alongside the spatial distribution of different types of autoignition kernels, developing at different stages of the autoignition process. The development of autoignition kernels could be linked to the shear layer development derived from global experimental conditions.
A Fault Diagnosis Approach for Rolling Element Bearing Based on S-Transform and Artificial Neural Network
Authors: Zhao Ningbo , Zheng Hongtao , Yang Lei , Wang Zhitao
Published: August 2017

The condition monitoring and fault diagnosis of rolling element bearing is a very important research content in the field of gas turbine health management. In this paper, a hybrid fault diagnosis approach combining S-transform with artificial neural network (ANN) is developed to achieve the accurate feature extraction and effective fault diagnosis of rolling element bearing health status. Considering the nonlinear and non-stationary vibration characteristics of rolling element bearing under stable loading and rotational speeds, S-transform and singular value decomposition (SVD) theory are firstly used to process the vibration signal and extract its time-frequency information features. Then, radical basis function (RBF) neural network classification model is designed to carry out the state pattern recognition and fault diagnosis. As a practical application, the experimental data of rolling element bearing including four health status are analyzed to evaluate the performance of the proposed approach. The results demonstrate that the present hybrid fault diagnosis approach is very effective to extract the fault features and diagnose the fault pattern of rolling element bearing under different rotor speed, which may be a potential technology to enhance the condition monitoring of rotating equipment. Besides, the advantages of the developed approach are also confirmed by the comparisons with the other two approaches, i.e. the Wigner-Ville (WV) distribution and RBF neural network based method as well as the S-transform and Elman neural network based one.
Influence of Non-Equilibrium Fluid Properties During Fogging on Intake Duct and Compressor Characteristics
Authors: Günther Christoph , Joos Franz
Published: August 2017

This study reports on numerically calculated thermophysical properties of air passing through a gas turbine compressor after passage through an intake duct affected by wet compression. Case of reference is unaffected ambient air (referenced to as dry scenario) passing through intake duct and compressor. Furthermore, ambient air cooled down by (overspray) fogging (referenced to as wet scenarios) was considered. Acceleration at the end of intake duct causing reduction of static temperature and pressure results in supersaturated fluid properties at inlet to gas turbine compressor. These supersaturated fluid properties are non-equilibrium with saturation level above relative humidity of φ = 1. Entrance of supersaturated fluid into gas turbine compressor can result in condensation within first compressor stage. At the same time delayed impact of evaporative cooling influences compression process.
Influence of a Cylindrical Exhaust Hood Installation on the Last Stage Rotor Blades of a Low Pressure Model Steam Turbine
Authors: Müller Fabian F. , Schatz Markus , Vogt Damian M. , Aschenbruck Jens
Published: August 2017

The influence of a cylindrical strut shortly downstream of the bladerow on the vibration behavior of the last stage rotor blades of a single stage LP model steam turbine was investigated in the present study. Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood. To capture the influence of such an installation on the flow field characteristics, extensive flow field measurements using pneumatic probes were conducted at the turbine outlet plane. In addition, time-resolved pressure measurements along the casing contour of the diffuser and on the surface of the cylinder were made, aiming for the identification of pressure fluctuations induced by the flow around the installation. Blade vibration behavior was measured at three different operating conditions by means of a tip timing system.

Despite the considerable changes in the flow field and its frequency content, no significant impact on blade vibration amplitudes were observed for the investigated case and considered operating conditions. Nevertheless, time-resolved pressure measurements suggest that notable pressure oscillations induced by the vortex shedding can reach the upstream bladerow.
Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings
Authors: Mahner Marcel , Li Pu , Lehn Andreas , Schweizer Bernhard
Published: August 2017

A detailed elasto-gasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The 2D pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the bearing stiffness (in particular for moderate shaft displacements) and the bearing damping.