bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Effective Thermal Conductivity of Thermal Barrier Coatings Based on Microstructure
Authors: Wang Yuzhang , Wang Xing , Weng Yiwu
Published: September 2014

Due to different preparation processes, the microstructure of thermal barrier coatings can be varied. It is important to accurately calculate effective thermal conductivity for the design of thermal barrier. In this work, different microstructures of thermal barrier coatings were reconstructed using the four parameter stochastic growth method. The numerical calculation program was developed and used to analyze the heat conduction in composite materials at steady state. The performance of the coating with the layered, columnar and uniform structure was analyzed in detail. The results show the porosity of thermal barrier coating has a great influence on the thermal conductivity. The thermal conductivity reduces with increased coating porosity. Keeping the porosity constant, the pore diameter has no significant influence on the thermal conductivity of the coating. The thermal conductivity of layered structure with the porosity of 15% is 46% lower than that of columnar structure at this temperature.
Full-Annular Numerical Investigation of the Rim Seal Cavity Flows Using GPU’s
Authors: Basol A. M. , Raheem A. , Huber M. , Abhari R. S.
Published: September 2014

In high pressure turbines to prevent the ingestion of the hot gas into the disk cavity cold air is purged from the cavities in-between the blade rows into the main flow. This numerical paper investigates this unsteady interaction between the main flow and the purge flow on a full-annular computational model of the LEC’s in-house axial turbine facility “LISA” at ETH Zurich. The simulations have been conducted on the GPU accelerated in-house solver “MULTI3”. One complete revolution of the 360° model could be completed in 48h using 18 GPU’s.

Two injection rates have been considered. For the 0.9% injection rate a separation bubble has been captured at the cavity neck which triggered high frequency pressure fluctuations. The 20° model also predicted the high frequency fluctuations; however their amplitude was underestimated due to the forcing of the flow field to periodicity. On the other hand, at the low injection rate of 0.4% no considerable separation bubble was formed inside the cavity. The unsteady simulations have demonstrated the inherent unsteadiness in the purge flow - main flow interaction.
Analysis on Integrated Gasification Humid Air Turbine System With Air Blown Gasifier
Authors: Wang Yuzhang , Weng Yiwu
Published: September 2014

With the gradual scarcity of fossil fuels and the emergency demand of greenhouse gas emission reduction, coal, as the major energy source of China in a long time of future, should be used efficiently and cleanly. The integrated gasification humid air turbine (IGHAT) system is a promising clean coal utilization technology. In order to investigating the performance of IGHAT, the models of IGHAT system were developed based on Aspen Plus software. The effects of key parameters (such as air/coal ratio, humidifying capacity, air entering the compressor) on the optimal performance and efficiency of IGHAT system were studied in detail. The results show the efficiency of power generation of IGHAT system with air blown gasifier can arrive at 48.62%. The efficiency of IGHAT system and the inlet gas temperature of turbine arrive at the maximum value when the air/coal ratio is 2.7. The humidifying capacity has a great effect on the efficiency of IGHAT system, and there is a reasonable range for each system. These results will be useful for us to select the parameters of the IGHAT system and understand the essence of IGHAT system.
Numerical Estimation of the Unsteady Force on Rotor Blades in a Partial Arc Admission Stage of an Axial Turbine
Authors: Yoshida Takeshi , Sakai Naoto , Matsumoto Atsushi , Kitajima Yosuke
Published: September 2014

A study for numerical estimation about the unsteady blade force in a partial arc admission stage of an axial turbine is presented in this paper.

Firstly, in order to investigate the influence of modeling domains in CFD (Computational Fluid Dynamics) analysis upon unsteady blade forces and turbine performance in partial admission stages, CFD analyses of three models were carried out. The analysis models consist of “2D” model; only on a mean diameter, “Simple-3D” model; 3-Dimensional passages without a tip clearance and a disc cavity, and “Full-3D” model; 3-Dimensional passages with a tip clearance and a disc cavity.

It results in clear difference in unsteady blade forces among these models. And it was revealed that numerical estimations of unsteady blade forces in partial admission stages should be carried out with analysis models that include disc cavities and tip clearances. In a partial admission stage there is extremely large circumferential pressure distribution and it causes the typical leakage flow through the gaps around a blade row. The leakage flow affects the circumferential pressure distribution that is a dominant factor in the unsteady blade forces. Air turbine experiments were conducted to validate the accuracy of the CFD analyses. Turbine efficiency of the Full-3D model with the disc cavity and the tip clearance is the closest to that of the experiment among the three models. In addition, comparison of pressure histories on a blade surface between an experiment and a calculation of the Full-3D model shows remarkably good agreements.

Next, CFD analyses with two different cascade setups (Cascade A and Cascade B) of partial admission stages were conducted in order to reveal the relationship between unsteady blade forces and cascade geometries such as a pitch of blades and a pitch of nozzles. These results show that there are clear differences in unsteady blade forces in an admission arc and those at leaving an admission arc. And some of trade-off relationships among the unsteady blade forces due to the geometries in partial admission stages are pointed out.
Investigation of Non-Axisymmetric Endwall Contouring and 3D Airfoil Design in a 1.5 Stage Axial Turbine: Part II — Experimental Validation
Authors: Niewoehner Jens , Poehler Thorsten , Jeschke Peter , Guendogdu Yavuz
Published: September 2014

This paper is the second part of a two-part paper reporting on the increase in efficiency of a 1.5 stage axial test rig turbine with the use of non-axisymmetric endwalls and 3D airfoil design. Contoured endwalls were developed for the inlet guide vane separately, as well as in combination with a bowed radial profile stacking. In addition, a contour endwall was applied to the hub of the unshrouded rotor. In part I the design of the profiled endwalls and 3D airfoils is presented, as well as a detailed analysis of the steady and unsteady CFD results. Part II reports on the experimental validation of the numerical results.

A distinct increase in mechanical efficiency for both new configurations in good agreement with the numerical results is observed. Additionally, performance map measurements demonstrate that the new designs are also beneficial under off-design conditions. Five- and three-hole-probes, as well as fast-response total pressure probes are used to investigate the new designs. The main effect is the homogenization of the yaw angle behind the first stator.
Numerical Simulation of the Flow Characteristics Within a Pressure-Swirling Atomizer
Authors: Xie Kaicheng , Mao Ronghai , Zhu Ying , Shang Mingtao , Wu Hao
Published: September 2014

The internal flow within a pressure swirl atomizer was numerically simulated and evaluated in the present investigation. To validate the numerical method, a large-scale atomizer with an orifice diameter 21mm has been simulated and compared with former experimental results in the literature. Then a production-scale atomizer with an orifice diameter 1mm was simulated and compared to the results of large-scale atomizer. The internal flow characteristics of the swirl chamber were evaluated mainly in terms of the film thickness at the exit of the orifice, the cone angle of the spray and the discharge coefficient of the nozzle. It was found that the numerical results of the large-scale atomizer with turbulent Reynolds Stress model yield more accurate solutions than the results with laminar flow model, which indicated that a turbulence flow has been formed within the large scale atomizer. Nevertheless, when the turbulent model was applied to a production-scale atomizer tested by Lacava (2004), its numerical results did not fit well with the experimental data any more. It was found that the Reynolds number of the flow in production-scale atomizer is about 2000, which is one order of magnitude lower than the Reynold’s number in the large-scale atomizer. As such a laminar flow model was successfully applied to its internal flow simulation and it is shown that the numerical results of the production-scale atomizer with laminar model yield more accurate solutions than the results with turbulent flow model. Finally, the effects of orifice contraction angle and mass flow rate were investigated in the production-scale pressure swirl atomizer using the laminar model. The numerical results showed that the discharge coefficient keeps almost constant with increasing orifice contraction angle, and the discharge coefficient, the film thickness at exit and the spray cone angle also almost keep constant with increasing the mass flow rate.
Full-Scale Tests on APU Noise Reduction
Authors: Knobloch Karsten , Fischer André , Bake Friedrich , Enghardt Lars , Busse-Gerstengarbe Stefan
Published: September 2014

The present paper describes an experimental investigation of the noise emission of a full-scale Garrett (Honeywell) GTCP 36-300 APU as installed on commercial airplanes like the Airbus A320. The APU exhaust noise emissions are measured in a well-controlled environment by 25 ground-based microphones arranged in a polar arc. Comparing a hard-wall reference case with different exhaust mufflers, special attention is given to the assessment of the noise reduction obtained. The performance of a newly designed muffler is compared to the standard device for the most relevant operating states ECS (environmental control system) and MES (main engine start). The paper concludes with a short examination of possibilities to improve the overall noise reduction.
Multi-Coupled Numerical Analysis of Advanced Lean Burn Injection Systems
Authors: Andreini Antonio , Bianchini Cosimo , Caciolli Gianluca , Facchini Bruno , Giusti Andrea , Turrini Fabio
Published: September 2014

Lean burn aero-engine combustors usually exploit advanced prefilming airblast injection systems in order to promote the formation of highly homogeneous air-fuel mixtures with the main aim of reducing NOx emissions. The combustion process is strongly influenced by the liquid fuel preparation and a reliable prediction of pollutant emissions requires proper tools able to consider the most important aspects characterizing liquid film evolution and primary breakup. This paper presents the numerical analysis of an advanced lean burn injection system using a multi-coupled two-phase flow three-dimensional solver developed on the basis of OpenFOAM modelling and numerics. The solver allows the coupled solution of gas-phase, droplets and liquid film exploiting correlation-based and theoretical models for liquid film primary atomization. A detailed analysis of the liquid film evolution is presented together with an investigation of the influence of film modelling and primary breakup on the combustion process at different operating conditions. The combustion field is strongly influenced by the characteristics of droplet population generated by the liquid film and this study proposes a computational setup, suitable for industrial calculations, able to account for all the main physical processes that characterize advanced prefilming airblast injection systems.
Laminar Burning Velocities and Emissions of Hydrogen-Methane-Air-Steam Mixtures
Authors: Göckeler Katharina , Krüger Oliver , Paschereit Christian Oliver
Published: September 2014

Humidified gas turbines using steam generated from excess heat feature increased cycle efficiencies. Injecting the steam into the combustor reduces NOx emissions, flame temperatures and burning velocities, promising a clean and stable combustion of highly reactive fuels, such as hydrogen or hydrogen-methane blends. This study presents laminar burning velocities for methane, and hydrogen-enriched methane (10 mol% and 50 mol%) at steam contents up to 30% of the air mass flow. Experiments were conducted on prismatic Bunsen flames stabilized on a slot-burner employing OH planar laser-induced fluorescence for determining the flame front areas. The experimental burning velocities agree well with results from one dimensional simulations using the GRI 3.0 mechanism. Burning velocities are increased with hydrogen enrichment, and reduce non-linearly with ascending steam mole fractions, showing the potential of steam dilution for a stable combustion of these fuels over a wide flammability range. Additionally measured NOx and CO emissions reveal a strong reduction in NOx emissions for an increasing dilution with steam, whereas CO curves are shifted towards higher equivalence ratios.
Aerodynamic and Aeroacoustic Optimization of a Transonic Centrifugal Compressor
Authors: Wang Peng , Zangeneh Mehrdad
Published: September 2014

The performance of transonic compressors can be characterized aerodynamically and aeroacoustically. In this paper, the DLR SRV2 compressor without vaned diffusers and its redesigned version are studied. The redesign strategy (Zangeneh et al. 2011 [1]) utilized the 3D inverse design and CFD analysis. Both compressors were analyzed in ANSYS CFX 11, and the computational results show that the predicted pressure-ratio and efficiency of the original compressor have good agreement with experimental results. The simulations have also revealed that the redesigned one is superior at both design and off-design points at different rotating speeds.

This work applies a convective FW-H method to further investigate the noise radiation from these two compressors. As the blade tip speed is supersonic, the permeable integral surface scheme must be adopted. The flow quantities needed as the inputs to the FW-H solver were extracted from the CFD solutions. The numerical predictions of the noise SPLs at blade passing frequency and its harmonics match the experimental measurements reasonably well. It is found that the original compressor has significant variations of SPLs as the operating mass flow rate changes whereas the redesigned one has much slighter variations. At peak efficiency the redesigned compressor has a lower noise level.

This study provides insights for the optimal design of a transonic compressor when good aerodynamic and aeroacoustic performance are both required.
Non-Linear Dynamics of a Simplified Model of an Overhung Rotor Subjected to Intermittent Annular Rubs
Authors: Zilli Andrea , Williams Robin J. , Ewins David J.
Published: September 2014

The dynamic forced response of a two-degrees-of-freedom model of an unbalanced overhung rotor with clearance and symmetric piecewise-linear stiffness is examined in the time domain. The stiffness nonlinearity is representative of the contact between the rotor and a concentric stator ring. This rubbing interaction comes as a result of the rotor transient motion initiated by the sudden application of a static unbalance, such as in a blade loss scenario. The focus of this study is on the range of rotor speeds above resonance, where the contact between rotor and stator is characterised by a “bouncing” or intermittent type of behaviour. Brute-force numerical bifurcation analysis on the long-term forced response revealed ranges of rotation frequency for which there is bi-stability between non-impacting synchronous equilibrium and impacting sub-synchronous motion. It is found that, for sufficiently high levels of transient energy in the rotor, there exists the possibility for the solution to jump into a stable limit cycle characterised by three non-harmonically related frequencies, namely the synchronous response frequency and the forward and backward whirl frequencies. A simple relationship defining the point of synchronisation between these three components is proposed as an explanation to the region of bi-stability detected. The stiffening effect induced by the contact non-linearity enables this synchronisation to be maintained over a range of forcing frequencies rather than just at the single condition determined from the nominal whirl mode frequencies.
Design and Off-Design Optimization of a Low Pressure Steam Turbine Radial Diffuser Using an Evolutionary Algorithm and 3D CFD
Authors: Verstraete Tom , Prinsier Johan , Cosi Lorenzo
Published: September 2014

The design of the radial exhaust hood of a low pressure (LP) steam turbine has a strong impact on the overall performance of the steam turbine. A higher pressure recovery of the diffuser will lead to a substantial higher power output of the turbine. One of the most critical aspects in the design of such devices is the steam guide, which guides the flow near the shroud from axial to radial direction and has a high impact on the pressure recovery.

This paper presents an extension of a design activity previously reported for the design optimization of the steam guide of a steam turbine for industrial power generation and mechanical drive of centrifugal compressors. Whereas this previous work only focused at peak efficiency, this paper will look into the off-design aspect. Peak performance, as usually used as design criteria, will now be replaced by proper off-design criteria guaranteeing a high performance level at both design and off-design conditions. On the basis of these considerations a multi-objective optimization of the steam guide has been performed keeping the exhaust outer casing unchanged.

The maximization of the objective functions is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with a CFD solver. The profile of the steam guide is parameterized by a Bezier curve. This allows for a wide variety of shapes respecting the manufacturability constraints of the design. The pressure recovery coefficient is computed over a wide operating range through several RANS computations including the last stage but introducing a mixing plane between the rotating blade and the diffuser inlet to reduce the computational burden. Steam tables are used for the accurate prediction of the steam properties.

Finally, the optimized design is analyzed by a frozen rotor computation to validate the approach. Also off-design characteristics of the optimized diffuser are shown.
Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part I — Compressor Performance Analysis
Authors: Ubben Stefan , Niehuis Reinhard
Published: September 2014

The combination of variable speed control and adjustable diffuser vanes offers an attractive design option for centrifugal compressors applied in industrial applications where a wide operating range at high efficiency level and a favorable surge line is required. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall which is mandatory since the diffuser geometry adjustment has to take place during operation, is still not satisfying.

This two-part paper summarizes results of investigations performed at the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen with an industrial-like centrifugal compressor, featuring a design pressure ratio of 4 and a design speed of 35200 rpm. Particular attention was directed to the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed.

Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency.

The flow phenomena responsible for this detected performance behavior are exposed in Part II [28], where the results of detailed measurements with pressure probes at diffuser exit and Particle Image Velocimetry (PIV) measurements conducted inside the diffuser channel, revealing the complex and unsteady flow leaving the impeller and passing the diffuser channel, are discussed.

The experimental results are published as an open CFD testcase “Radiver 2” [26], extending the experimental data base of the testcase “Radiver” published in 2003 by Ziegler [31].
A Study on Maximizing Power Output of IGCC Plants Considering Operating Limitations of Gas Turbine
Authors: Kang Do Won , Kim Chang Min , Kim Tong Seop , Sohn Jeong L.
Published: September 2014

This study aims to provide a systematic overview of the relations between IGCC performance and major design and operating parameters such as integration degree, nitrogen dilution, and ambient temperature. A unique feature of this study is that allowable maximum values of both the gas turbine power ouput and the turbine blade temperature were considered. For this purpose, a simulation tool to predict operation and performance of a syngas turbine, which was modified from a base gas turbine model, was set up using off-design models. Then, an entire integrated gasification combined cycle using the syngas turbine was modeled. The power block (i.e. the combined cycle) was modeled in detail and mass and energy interactions of the power block with a gasifier block and an air separation unit were included. Variation in syngas turbine power output according to varying nitrogen dilution was simulated and operating conditions where gas turbine power needs to be suppressed to the allowable maximum value were found out. Maximum net IGCC power output under the limitations of gyngas turbine power and blade temperature was predicted for various integration degrees in a wide ambient temperature range. The influence of steam dilution on plant performance was also investigated.
Investigations on a Test Bench for Integrated ORC-FC Micro-CHP Energy Systems
Authors: Bianchi M. , De Pascale A. , Melino F. , Peretto A. , Branchini L.
Published: September 2014

Micro-CHP (Combined Heat and Power) energy systems are potentially suitable for residential and tertiary utilities, typically characterized by low-grade heat demand and limited electric-to-thermal energy demand ratio values. Different innovative and under development CHP technologies are currently investigated in small scale units, but a standard has not been identified till now. Moreover, depending on the load request, the produced electricity can be used, stored in electric accumulator or in the external net, or integrated with other external sources. Contextually, the available heat can be used, accumulated inside the system or dissipated. The actual convenience of small size CHP systems depends on the demand profiles and the operation management logic.

A test facility is being developed, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies: a Micro Rankine Cycles (MRC), a Proton Exchange Membrane (PEM) Fuel Cells (FC), a battery and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles.

This report describes the main characteristics of the implemented test bench, the selection procedure of the adopted micro-CHP unit and expected performance.

Further the development of a calculation code able to simulate the performance of the considered systems will be described. This calculation code has been applied to design the components of the test bench. More in details, in this paper the sizing of the electrical energy storage system, and of the thermal and H2 storage tanks will be presented and discussed.
Synchrotron XRD Measurements Mapping Internal Strains of Thermal Barrier Coatings During Thermal Gradient Mechanical Fatigue Loading
Authors: Knipe Kevin , Manero Albert C. , Sofronsky Stephen , Okasinski John , Almer Jonathan , Wischek Janine , Meid Carla , Karlsson Anette , Bartsch Marion , Raghavan Seetha
Published: September 2014

An understanding of the high temperature mechanics experienced in Thermal Barrier Coatings (TBC) during cycling conditions would be highly beneficial to extending the lifespan of the coatings. This study will present results obtained using synchrotron x-rays to measure depth resolved strains in the various layers of TBCs under thermal mechanical loading and a superposed thermal gradient. Tubular specimens, coated with Yttria Stabilized Zirconia (YSZ) and an aluminum containing nickel alloy as a bond coat both through Electron Beam - Physical Vapor Deposition (EBPVD), were subjected to external heating and controlled internal cooling generating a thermal gradient across the specimen’s wall. Temperatures at the external surface were in excess of 1000 °C. Throughout high temperature testing, 2-D high-resolution XRD strain measurements are taken at various locations through the entire depth of the coating layers. Across the YSZ a strain gradient was observed showing higher compressive strain at the interface to the bond coat than towards the surface. This behavior can be attributed to the specific microstructure of the EB-PVD-coating, which reveals higher porosity at the outer surface than at the interface to the bond coat, resulting in a lower in plane modulus near the surface. This location at the interface displays the most significant variation due to applied load at room temperature with this effect diminishing at elevated uniform temperatures. During thermal cycling with a thermal gradient and mechanical loading, the bond coat strain moves from a highly tensile state at room temperature to an initially compressive state at high temperature before relaxing to zero during the high temperature hold. The results of these experiments give insight into previously unseen material behavior at high temperature which can be used to develop an increased understanding of various failure modes and their causes.
Elevation of Heat Rejection Temperature in Transcritical Condensing Cycles Using CO2+Propane Mixtures
Authors: Garg Pardeep , Kumar Pramod , Srinivasan Kandadai , Dutta Pradip
Published: September 2014

In this paper, a detailed thermodynamic performance analysis of a transcritical condensing (TC) cycle is performed with pure CO2 and a blend of 48.5 % propane with 51.5 % CO2 as working fluids. A realistic thermodynamic model is used incorporating irreversibilities in turbo-machineries and heat exchangers. The Key finding is that the addition of propane elevates the heat rejection temperature, but does not impair any of the performance indicators. Such a fluid may be useful for power generation in concentrated solar power applications by using which a hike of up to 2 % can be realized in the thermal efficiency of a power plant.
Aerodynamic Design and Optimization of a Small Scale Wind Turbine
Authors: Kröger G. , Siller U. , Dabrowski J.
Published: September 2014

Small scale wind turbines can meet a substantial part of the electricity demand of residential buildings and facilities in isolated areas. It is a curious fact, however, that for many of these systems the actual power output has been dramatically overestimated. This can be partially explained by the very high rated wind speeds at which the design power output applies. The current work depicts the pathway to an aerodynamically optimized design of a small scale horizontal axis wind turbine in the 1kW class, optimized for wind speeds between 3.5 m/s and 5.5 m/s, a typical range of the energetic average of urban wind speeds. The aerodynamic stability of the blade has been a particular focus leading to a nearly constant efficiency over a range of wind speeds. The rotating speed of the system is adjusted to the optimal tip speed ratio at wind speeds up to maximum power via active control of the aerodynamic torque of the rotor blades. This is realized by adapting the generator torque to the current wind speed guaranteeing optimal efficiency and power output. The rotor blade optimization has been conducted unconventionally, in a turbomachinery-inspired 3D-blade design optimization campaign, using high-fidelity compressible CFD. This approach is described in detail, focussing on geometry parametrization and the numerical model with reasonable boundary conditions. Finally, the aerodynamic performance of the rotor blade is assessed at different wind speeds and pitching angles.
High Velocity Impact Damage Assessment in SiC/SiC Composites
Authors: Baker Christopher R. , Maillet Emmanuel , Morscher Gregory N. , Gyekenyesi Andrew L. , Choi Sung R. , Abdi Frank
Published: September 2014

Foreign object damage in gas turbines presents serious safety and financial concerns. As the aerospace industry draws closer to implementing ceramic matrix composites (CMCs) in gas turbines, the corresponding behavior in these materials after such events needs to be understood. To address this requirement, several silicon infiltrated fiber reinforced SiC/SiC coupons were impacted with high speed projectiles with velocities up to 360 m/s with an impact rig built at the University of Akron and NAVAIR. The resulting damage states were assessed using several non-destructive evaluation (NDE) techniques and compared to actual damage condition observed through the sectioning of impacted coupons. Ultimately, the true consequence of the damage was revealed by measuring the post-impact, residual strengths via uniaxial tensile tests to failure at both room and elevated temperatures. Lastly, the NDE results revealed a complicated damage morphology consisting of in-and-out-of plane damage that significantly affected the retained mechanical properties.
Numerical Computation of the Performance Map of a Supercritical CO2 Radial Compressor by Means of Three-Dimensional CFD Simulations
Authors: Rinaldi Enrico , Pecnik Rene , Colonna Piero
Published: September 2014

The performance map of a radial compressor operating with supercritical CO2 is numerically computed by means of three dimensional steady state Reynolds-averaged Navier–Stokes simulations. The results concern a 250 kW prototype. An in-house fluid dynamic solver is coupled with a thermodynamic library which ensures the highest accuracy of the thermophysical properties evaluation. Look-up table interpolation is used in order to reduce the computational cost, while keeping the desired level of accuracy in the fluid characterization. The compressor map is calculated considering three different rotational speeds (45 krpm, 50 krpm, and 55 krpm). For each speed-line several mass flow rates are simulated. Numerical results are compared to experimental data to prove the potential of the methodology.
Calculation of Heat Transfer Coefficient Distribution on 3D Geometries From Transient Liquid Crystal Experiments
Authors: Ryley J. C. , McGilvray M. , Gillespie D. R. H.
Published: September 2014

A valuable new technique to provide spatially resolved heat transfer coefficient (HTC) measurements over geometrically complex surfaces has been developed. The method is generally applicable, for use with conventional transient liquid crystal experiments, and uses the capability of commercially available finite element analysis (FEA) software. This technique has many potential applications where lateral conduction effects are significant, and can provide measurements in areas where data have not previously been possible. In the current study it has been applied to a section of a stationary internal cooling passage containing engine realistic features. The technique couples experimental data from transient liquid experiments and FEA, in an iterative procedure, to generate the solutions.

Spatially resolved maps of heat transfer have been determined over the surface of the ribs for five Reynolds number conditions (18,000–105,000) for two aspect ratio passages, 1:2 and 1:3. The results are compared to conventionally processed experimental and numerical data. Where the 1D application is applicable results agree within experimental uncertainty (∼6%) at the majority of locations. Typical 1D based methods are unable to provide reliable spatial measurements over ribbed surfaces and to the authors best knowledge this is the first time distributions of HTC have been reported for engine representative rib geometry.
A New Experimental Facility to Investigate Combustor-Turbine Interactions in Gas Turbines With Multiple Can Combustors
Authors: Luque S. , Kanjirakkad V. , Aslanidou I. , Lubbock R. , Rosic B. , Uchida S.
Published: September 2014

This paper describes a new modular experimental facility that was purpose-built to investigate flow interactions between the combustor and first stage nozzle guide vanes of heavy duty power generation gas turbines with multiple can combustors. The first stage turbine nozzle guide vane is subjected to the highest thermal loads of all turbine components and therefore consumes a proportionally large amount of cooling air that contributes detrimentally to the stage and cycle efficiency. It has become necessary to devise novel cooling concepts that can substantially reduce the coolant air requirement but still allow the turbine to maintain its aerothermal performance. The present work aims to aid this objective by the design and commissioning of a high-speed linear cascade which consists of two can combustor transition ducts and four first stage nozzle guide vanes. This is a modular non-reactive air test platform with engine realistic geometries (gas path and near gas path), cooling system, and boundary conditions (inlet swirl, turbulence level and boundary layer). The paper presents the various design aspects of the high pressure blow down type facility, and the initial results from a wide range of aerodynamic and heat transfer measurements under highly engine realistic conditions.
Unsteady Aerodynamics and Forced Response Studies on Aeroderivative Gas Turbine Exhaust System
Authors: Di Mare Luca , Thirumurthy Deepak , Green Jeffrey S. , Myers John
Published: September 2014

Industrial and aeroderivative gas turbines use exhaust systems for flow diffusion and pressure recovery. These processes result in a three-dimensional, unsteady, turbulent, and complex flow in the exhaust diffusers. The downstream balance-of-plant systems such as heat recovery steam generators or selective catalytic systems require, in general, a steady, uniform flow out of the exhaust system.

Aeroderivative gas turbines for power generation application have a wide operational envelope. Even though the exhaust systems are designed for 70% load to 110% load, its performance is significantly altered at low power operations. Application of gas turbines at low power can increase exhaust diffuser vibrations because of diffuser flow separations and wakes from the last stage of the power turbine. Aerodynamic excitations which result in excessive structural vibration can cause the units to trip and the power plant to stop, resulting in customer revenue loss.

The primary motivation for this research is to investigate an aerodynamic mechanism to ensure reliable operation of the exhaust system by identifying the regimes where aerodynamic instabilities can occur. In-house and university supported initiative to predict unsteady aerodynamics at low power conditions shows the presence of turbulent and time dependent flow.

The frequency spectrum results are discussed for low power and high power gas turbine operating conditions. The numerical predictions are in good agreement with test results.
Heat Recovery Steam Generator Health Assessment Basing on Reconciled Measurement
Authors: Sorce Alessandro , Martini Alessio , Traverso Alberto , Torelli Giorgio
Published: September 2014

Long-term monitoring and diagnostic of power plants is a permanent issue for the energy companies. In particular with the increase of flexible operation (e.g. daily start-up and shutdown cycles, part load operations) the definition of proper diagnostic indicators becomes mandatory. Different monitoring strategies were developed, implemented and tested for the main components of a combined cycle power plant (e.g. Gas Turbine, Heat Recovery Steam Generator, Steam Turbine, Pumps) to prevent fault/failure or to plan/evaluate the maintenance activities.

This work focuses on the first principles health assessment of the Heat Recovery Steam Generator (HRSG). The impact of ambient conditions on the gas turbine outlet temperature and mass flow rate and thus on the HRSG behavior is presented referring to the control strategies of the Gas Turbine (GT). To validate the measurements a preprocessing phase basing on Data Reconciliation was performed, aimed at improving the accuracy of the estimation of exhaust mass flow rate entering the HRSG. Gas Turbine and HRSG nergy balances are exploited to reduce the uncertainties of the results, eliminate the outlier data sets and obtain consistent data. Moreover an evaluation of the sensitivity of the indicator will be made basing on field measurements before and after a maintenance intervention.
CFD Assessment of Rotordynamic Coefficients in Labyrinth Seals
Authors: Sreedharan Sai S. , Vannini Giuseppe , Mistry Hiteshkumar
Published: September 2014

Seals used in high speed centrifugal compressors are prone to generate rotordynamic (RD) instabilities. To further understand their influence, a CFD based approach is developed. The objective of the current study is to numerically investigate and characterize the RD coefficients, representative of the dynamic seal forces. Experiments were carried out at high pressure test rig (up to 200 bar seal inlet pressure) which runs at 10000 RPM and has a high pre-swirl (about 0.9) along the same direction of rotor rotation. The rotor shaft in the experiment was instrumented with active magnetic bearings (AMBs) to linearly excite the rotor at three different frequencies: 28 Hz, 70 Hz and 126 Hz. Each frequency is characterized by amplitude of vibration and a phase. CFD simulations were carried out using commercial flow solver, using similar boundary conditions as that of experiments. The paper describes details of CFD model and its comparison against experiments. Numerical results show reasonable agreement of RD coefficients with test results. This job has to be considered as a first approach to CFD methodology applied to annular seals for the authors.
Predictive Capability of CFD Models for Transonic Compressor Design
Authors: Ellbrant Lars , Eriksson Lars-Erik , Mårtensson Hans
Published: September 2014

The primary focus of this work is to validate a CFD model intended to be used for transonic compressor design purposes. This design model includes a coarse grid using wall functions and mixing planes at interfaces connecting the compressor components. The computations are compared with experimental data from the transonic highly loaded 1.5 stage compressor test case Hulda. Additional comparisons are done with higher complexity CFD models accounting for the rotor-stator interaction. The performance of Hulda has been measured with both a small and a large tip clearance. These two configurations are used to investigate the necessity of resolving the tip clearance gap in the design model. The comparison is presented in terms of the overall performance at two rotational speeds as well as radial distribution of total pressure and total temperature at stations downstream of the rotor. The predictive capability at these speeds is assessed in terms of mass flow, pressure ratio and efficiency. Furthermore, the response of the predicted radial flow distributions with respect to the throttle setting along the two rotational speeds is qualitatively compared with the measurements.

The validation of the small tip clearance test shows that the design model, with or without tip gap modeling, is in good agreement with the measurements at both speeds. As for the large tip clearance test a design model resolving the tip clearance was able to predict trends but the penalty related to the increased tip gap was overestimated compared to the measured.
Energetic and Environmental Analysis of Partial Repowering of a Coal Fired Power Plant Through Upstream GT Integration and Employing Waste Heated Feed Water Heaters
Authors: Samanta S. , Ghosh S.
Published: September 2014

This paper presents a theoretical study of partial repowering scheme for an existing 210MW coal fired power plant and reports predicted performance improvement obtainable from the repowering by using Cycle Tempo software. In this method old boiler is used as it is, only modifying its air heater and forced flow sections. Out of four operating coal mills, one mill is considered to be taken out. A new natural gas fired gas turbine (GT) block is considered to be integrated with the existing plant whose exhaust is fed to the existing boiler. The GT size is selected such that its exhaust provide heat input equivalent to the replaced coal mill. The burners associated with that coal mill are assumed to be modified to handle hot exhaust gas from the GT block. It is noticed that a substantial amount of energy is available in the flue gas, coming out from the boiler, after the air preheater which can partially meet the heat loads of feed water heaters. This helps in saving of intermediate pressure (IP) and low pressure (LP) bleed steam and consequent increase in the output of the steam cycle. The partial repowering results in nearly 40% increase in capacity of the plant (from 210MW to 284MW). It also results in substantial increase in overall efficiency of the repowered plant by 28%, and consequent decrease in plant heat rate by 22%. The specific CO2 emission of the plant decreases about 31% after repowering.
Tri-Generation Systems Optimization: Comparison of Heuristic and Mixed Integer Linear Programming Approaches
Authors: Bischi Aldo , Campanari Stefano , Castiglioni Alberto , Manzolini Giampaolo , Martelli Emanuele , Silva Paolo , Macchi Ennio
Published: September 2014

This work compares two optimization approaches for combined cooling, heating and power (CCHP or Tri-generation) energy systems scheduling. Both approaches are developed through dedicated software codes and are based on simulation models capable of evaluating of the best operating strategy (both economically and energy-wise) to run a given trigeneration plant while dealing with time-variable loads and tariffs. The simultaneous use of different prime movers operating in parallel is taken into consideration as well as their part load performance, the influence of ambient temperature and the usage of a heat storage system. Cooling may be generated through absorption chillers or electrically driven compression cycles. One of the models is heuristic and adopts an optimization strategy based on a multi-step approach: it simulates several cases according to a pre-defined number of paths, exploring the most reasonable operational modes and comparing them systematically. The other relies on a mathematical approach, based on a Mixed Integer Linear Programming (MILP) optimization model which has been developed in order to deal with more complex systems without the need of predefining a too large variety of operation paths.

Results of the two models are compared against a test case based on real plant specifications, discussing their performance by the point of view of simulation capabilities, quality and accuracy of the optimization results (in terms of differences in energy and economic performance) and computational resources.
Pressure Activated Leaf Seal Technology Readiness Testing
Authors: Bowsher Aaron , Crudgington Peter , Grondahl Clayton M. , Dudley James C. , Kirk Tracey , Pawlak Andrew
Published: September 2014

This paper continues the evaluation of Pressure Actuated Leaf Seals (PALS) technology readiness for shaft and shroud sealing in power generation and aerospace applications. Seal designs tested are prototypical and constructed using processes appropriate for volume production. Results include both static and dynamic seal leakage measurements running against a 5.1 in (129.54mm) diameter smooth surface test rotor and another that simulates sealing against turbine blade shrouds. A further test was undertaken using a 2D static rig that determined acoustic noise experienced during testing was attributed to leaves vibrating at their natural frequency as a result of inter-leaf gaps. The dynamic simulated shroud test includes steps, duplicating small discontinuities of adjacent shroud sealing surfaces and slots to inject air radially under the seal leaves as may occur between shrouds on blades with a high degree of reaction. Consistent seal performance over 15 hours confirms suitability for turbine blade tip applications. Controlled deflection of PALS leaves with operating differential pressure is effective for startup rub avoidance in service as well as conformal wear-in sizing of leaf tips with the rotor. Tested leaf tip wear-in of approximately 0.010in (0.25mm) against rotor discs without hard-face coating, shows potential to eliminate seal misalignment and run-out contributions to operating seal clearance. PALS design features prevent further rubbing contact with the operating rotor after initial wear-in sizing thereby sustaining a small effective seal clearance and prospects for long seal life. Measurements of rotor surface wear tracks from the wear-in process and endurance runs are included as well as rotor and leaf tip photos. Test results support the technology readiness of the PALS concept as a viable, robust, low leakage dynamic seal for select commercial application.
About the Negative Direct Static Stiffness of Highly Eccentric Straight Annular Seals
Authors: Arghir Mihai , Mariot Antoine
Published: September 2014

Experimental results indicating negative direct static stiffness of highly eccentric straight gas annular seals were very recently presented in [1] by Childs and Arthur. This instability occurred at zero rotation speed and at high eccentricities. Up to then only gas annular seals with zero rotation speed, operating in centered position and with choked exit section were known as being susceptible of developing negative direct static stiffness. The seals and the working conditions presented in [1] had clearly no choked exit section. The present work advances a theoretical explanation of results reported in [1]. The analysis is based on the numerical solution of the bulk flow equations of the flow in the annular seal. Theoretical results show a negative static stiffness at high eccentricities and zero rotation speeds. Other seal geometries and working conditions were tested and showed that the decrease of the direct static stiffness at high eccentricities and zero rotation speeds is a characteristic of all straight annular seals whether the fluid is compressible or not. Nevertheless with increasing rotation speed, the static stiffness becomes again positive and may increase with increasing eccentricity. The negative static stiffness is then limited to very specific working conditions: high eccentricities and zero rotation speed.