bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical Understanding and Sensitivities of LPT Flutter
Authors: Waite Joshua J. , Kielb Robert E.
Published: September 2014

Successful, efficient turbine design requires a thorough understanding of the underlying physical phenomena. This paper investigates the flutter phenomenon of low pressure turbine (LPT) blades seen in aircraft engines and power turbines. CFD analysis will be conducted in a two-dimensional sense using a frequency domain RANS solver on a publicly available LPT airfoil geometry: EPFL’s Standard Configuration 4. An emphasis is placed on revealing the underlying physics behind the threatening LPT flutter mechanism. To this end, flutter sensitivity analysis is conducted on three key parameters: reduced frequency, mode shape, and Mach number. Additionally, exact two-dimensional acoustic resonance inter-blade phase angles (IBPAs) are analytically predicted as a function of reduced frequency. Made evident via damping vs. IBPA plots, the CFD model successfully captures the theoretical acoustic resonance predictions. Studies of the decay of unsteady aerodynamic influence coefficients away from a reference blade are also presented. The influence coefficients provide key insights to the harmonic content of the unsteady pressure field. Finally, this work explores methods of normalizing the work per cycle by the exit dynamic pressure.
The Semi-Closed Recuperated Cycle With Intercooled Compressors
Authors: Wettstein Hans E.
Published: September 2014

The Gas Turbine Combined Cycle (GTCC) is the best currently available choice, if gaps in the renewable electric power supply need being filled at short notice with power from fossil fuels. The GTCC manufacturers are in a fierce competition responding to these needs, especially for the best part load efficiency, the fastest load ramp capability and for the lowest low load power parking at an acceptable NOx and CO emission level.

But there is an option outperforming the GTCC technology for the above mentioned requirements, which is theoretically known since years but it has not yet been practically developed. It is the Semi-Closed Recuperated Cycle (SCRC). The author has described this recently in an article [1] with the title “The air breathing semi-closed recuperated cycle and its super chargeable predecessors”.

The SCRC does not require any component technology, which is not yet proven in operating commercial GTCC or GT plants. But of course the cycle integration is a different one, requiring a specific design of the components. An inherent side feature of the SCRC is the exhaust gas composition, which corresponds to a near-stoichiometric combustion gas. This allows comparing the SCRC with a (CO2-) capture ready GTCC having exhaust gas recirculation.

The above mentioned article [1] describes the thermodynamic performance analysis of a SCRC with an adiabatic compressor. But the cycle becomes even more attractive with an intercooling stage in each of the two compressors. Here this is quantified with another detailed thermodynamic analysis. Additionally also an ideal case with isothermal compression is analyzed. The latter is of course unrealistic for a practical realization. But it indicates the potential of using more than one intercooling stage per compressor. The aim of this paper is to quantitatively compare the three variants with adiabatic, intercooled and isothermal compressors. In all three cases the same turbine and recuperator temperature limitations are used while some other cycle data assumptions are adapted to the compressor technology in order to achieve an optimal performance level for each variant. The thermodynamic results have been cross-checked with a breakdown of the exergy losses in the three variants. The final results for base load operation indicate that the intercooled variant could become the best choice.
Numerical Investigation of VSVs Mal-Schedule Effects in a Three-Stage Axial Compressor
Authors: Li Yan-Ling , Sayma Abdulnaser
Published: September 2014

Variable Stator Vanes (VSVs) are commonly used in multi-stage axial compressors for stage matching at part load operations and during start up. Improper VSVs settings or malfunction of the controlling actuator system can lead to compressor instabilities including rotating stall and surge. It is important to be able to predict the aerodynamic behaviour of compressors in such events to either produce tolerant designs or incorporate diagnosis and recovery systems.

This paper presents a numerical study of a compressor operating near the stall boundary for a mal-scheduled VSVs case. A high-speed three-stage axial compressor with Inlet Guide Vanes (IGV) is used in the investigation because of its relative simplicity and availability of geometry and aerodynamic data. A 3D RANS viscous unsteady time-accurate flow solver was used to perform the full annulus simulation with a downstream variable nozzle to control outflow boundary conditions. The unstructured mesh contained about 25 million grid points and the simulation was performed on a high performance computing cluster for many engine rotations. Rotating stall with one single cell covering several passages in all three rotors was predicted which propagated at approximately half of the shaft speed. Full analysis of the flow features is presented in the paper.
Analysis of Using the M-Cycle Regenerative-Humidification Process on a Gas Turbine
Authors: Jenkins P. E. , Cerza M. , Al Saaid Mohammad M.
Published: September 2014

This investigation focused on the analysis of using the Maisotsenko Cycle (M-Cycle) to improve the efficiency of a gas turbine engine. By combining the Maisotsenko Cycle (M-Cycle) with an open Brayton cycle, a new cycle, is known as the Maisotsenko Combustion Turbine Cycle (MCTC), was formed. The MCTC used an Indirect Evaporative Air Cooler as a saturator with a gas turbine engine. The saturator was applied on the side of the turbine exhaust (M-Cycle#2) in the analysis. The analysis included calculations and the development of an Engineering Equation Solver (EES) code to model the MCTC system performance. The resulting performance curves were graphed to show the effects of several parameters on the thermal efficiency and net power output of the gas turbine engine. The models were also compared with actual experimental test results from a gas turbine engine. Conclusions and discussions of results are also given.
Broadband Combustion Noise Prediction With the Fast Random Particle Method
Authors: Grimm Felix , Ewert Roland , Dierke Jürgen , Noll Berthold , Aigner Manfred
Published: September 2014

A new highly efficient, hybrid CFD/CAA approach for broadband combustion noise modeling is introduced. The inherent sound source generation mechanism is based on turbulent flow field statistics, which are determined from reacting RANS calculations. The generated sources form the right-hand side of the linearized Euler equations for the calculation of sound fields. The stochastic time-domain source reconstruction algorithm is briefly described with emphasis on two different ways of spatial discretization, RPM (Random Particle Method) and the newly developed FRPM (Fast RPM). The application of mainly the latter technique to combustion noise (CN) prediction and several methodical progressions are presented in the paper.

(F)RPM-CN is verified in terms of its ability to accurately reproduce prescribed turbulence-induced one- and two-point statistics for a generic test and the DLR-A jet flame validation case. Former works on RPM-CN have been revised and as a consequence methodical improvements are introduced along with the progression to FRPM-CN: A canonical CAA setup for the applications DLR-A, -B and H3 flame is used. Furthermore, a second order Langevin decorrelation model is introduced for FRPM-CN, to avoid spurious high frequency noise. A new calibration parameter set for reacting jet noise prediction with (F)RPM-CN is proposed. The analysis shows the universality of the data set for 2D jet flame applications and furthermore the method’s accountance for Reynolds scalability. In this context, a Mach number scaling law is used to conserve Strouhal similarity of the jet flame spectra. Finally, the numerical results are compared to suitable similarity spectra.
Understanding Complexities in Underplatform Damper Mechanics
Authors: Gola Muzio M. , Gastaldi Chiara
Published: September 2014

All numerical models of friction damped bladed arrays require knowledge or information of contact-friction parameters, which are established either through direct frictional measurements, done with the help of single contact test arrangements, or by fine tuning the parameters in the numerical model and comparing the experimental response of damped blade against its computed response. Some critical assumptions are necessary to the purpose, such as the position and extension of the real contact areas and the values of local friction coefficients.

In the light of recent results from direct measurements on under-platform dampers [1–3] it became evident that a dedicated routine for the damper mechanics is a much more effective tool to capture those finer details which are essential to an appropriate description of damper behaviour. This was made possible by the successful effort of the present authors to accurately measure the forces transmitted between the platforms through the damper and to relate them with the relative platform movement [2].

Simulations, and the matching experiments which are here not described, are performed under so called out-of-phase (O-O-P) and in-phase (I-P) condition simulating the two basically important motion types. Damper forces and damper kinematics are discussed for two highly representative cases in the low frequency range. Diagrams are then used to show the sensitivity to contact parameters, input motion and initial conditions on damper behaviour, casting heavy doubts on the validity of oversimplified practices.
Setting Up and Managing a PEMS Mathematical Formula to Fully Respond to the Expectations of the Regulator
Authors: Bainier Francis , Havard Florian
Published: September 2014

Due to environmental regulations, Oxides of nitrogen (NOx) and carbon monoxide (CO) are important issues for gas turbine plants. Regulators are becoming more and more involved and they often require overall and real-time emission information. These measurements can easily be done with gas analyzers. This technology is called CEMS: Continuous Emissions Monitoring System. With CEMS, regulators easily understand proofs such as calibration and certificate. However, this technology is expensive to buy and to maintain. An alternative method is to use a calculation based on the turbine operation. This technology is called PEMS: Predictive Emissions Monitoring System. Although PEMS is less expensive than CEMS, setting up and managing a PEMS mathematical formula to fully respond to the expectations of the regulator is more complicated than using CEMS.

This paper describes an approach to set up an equation for PEMS which can be accepted by regulators.

Before starting PEMS research, expectations must be established. What are the expectations of the regulator? What are the users’ expectations? Yes, do not forget the goals of the unit operators. It is not sufficient to provide answers for regulator at the lowest cost. A responsible user is also concerned about the environmental aspect and this fact will help your in the future. GRTgaz, the main gas transmission company in France managing 44 turbines spread over 25 stations across France, has decided to answer these questions before starting research. The answers to these questions make up the first part of this 4-part paper.

The second part of the paper is a review of publications and literature. Since no applicable PEMS exist for all types of combustion turbines, analyzing empirical and theoretical formulas leads to the important parameters and the link between them.

The third part is dedicated to turbines. A lean premixed combustion system and its regulation are described. Also in this part, the available measured parameters are listed in regards to their combustion influence and their accuracy.

The fourth part deals with the establishment of equations and their tests in regards to the goals.

The last part presents the implementation of the equations on the units.

If tools and knowledge are available, the conclusion point out that achieving a PEMS requires a good evaluation and understanding of the expectations of the regulator, not only in the present day but also what they will and could be.
Conjugate Heat Transfer CFD Predictions of Impingement Heat Transfer: The Influence of Hole Pitch to Diameter Ratio X/D at Constant Impingement Gap Z
Authors: El-Jummah Abubakar M. , Abdul Husain Reyad A. A. , Andrews Gordon E. , Staggs John E. J.
Published: September 2014

Conjugate heat transfer (CHT) computational fluid dynamic (CFD) predictions, were carried out for a 10 × 10 square array of impingement holes, for a range of pitch to diameter ratio X/D from 1.9 to 11.0 at a constant impingement gap Z of 10mm and pitch X of 15.24mm. The variation of X/D changes the impingement wall pressure loss for the same coolant mass flow rate and also changes the interaction with the impingement gap cross-flow. The experimental technique to determine the surface averaged heat transfer, used the lumped capacity method with Nimonic-75 metal walls with imbedded thermocouples and a step change in the hot wall cooling to determine the heat transfer coefficient h from the transient cooling of the metal wall. The test wall was electrically heated to about 80°C and then transiently cooled by the impingement flow and the lumped capacitance method was used to measure the locally surface average heat transfer coefficient. The predictions and measurements were carried out at an impingement jet mass flux of 1.93kg/sm2bar, which is a typical coolant flow rate for regenerative impingement cooling of low NOx gas turbine combustor walls. The computations were conducted for a fixed hot side temperature of 353K that was imposed at the hot face of the target wall. The wall temperatures as a function of distance along the gap were computed together with the impingement gap aerodynamics. Surface average heat transfer coefficient h and pressure loss predictions were in good agreement with the experimental measurements. However, there was less good agreement for the axial variation of the local surface averaged h for lower values of X/D. The surface averaged heat transfer to the impingement jet wall was also computed and shown to be roughly 70% of target wall impingement heat transfer.
Conjugate Heat Transfer Analysis of a Film Cooled High-Pressure Turbine Vane Under Realistic Combustor Exit Flow Conditions
Authors: Insinna Massimiliano , Griffini Duccio , Salvadori Simone , Martelli Francesco
Published: September 2014

In this paper conjugate heat transfer analysis of the cooled vane of the MT1 research high-pressure stage is presented. Inlet boundary conditions (including non-uniform total temperature, non-uniform total pressure, swirl, turbulence intensity and turbulence length scale) are obtained considering the exit flow field of a reactive annular combustor simulator. The combustor model has been designed in order to reproduce data available in literature about exit profiles of real combustion chambers and other combustor simulators. Steady simulations are performed on a hybrid unstructured grid obtained from a grid dependence study. The transitional kT-kL-ω model by Walters and Cokljat is used as turbulent closure. Thermal fields obtained from CHT analysis of the vane considering two different clocking positions with respect to the combustor are compared. Results, including film cooling parameters and High-Pressure Vane aerodynamics, are also compared with a uniform inlet case showing the crucial importance of considering realistic boundary conditions for thermal analysis of turbine components.
Techno–Economic Evaluation of Recuperated Gas Turbine Cogeneration Cycles Utilizing Animal Manure and Energy Crops for Biogas Fuel
Authors: Kontokostas Georgios , Goulos Ioannis , Stamatis Anastassios
Published: September 2014

This work presents the development of an integrated approach, targeting the techno-economic assessment of recuperated cogeneration gas turbine cycles, utilizing anaerobic digestion products of animal manure and energy crops for biogas fuel. The overall approach consists of a series of fundamental modeling theories applicable to; anaerobic digestion and biogas fuel yield, thermodynamic analysis of cogeneration gas turbine cycles, exergetic analysis of anaerobic digestion, and economic modeling of implementation and operation. The developed methodology is applied to the techno-economic analysis of a representative anaerobic digestion plant yielding biogas fuel which is supplied to a recuperated cogeneration gas turbine powerplant. The influence of employed thermodynamic cycle parameters along with the incorporated technology level, on the cycle performance parameters and economic sustainability of integrated digestion–cogeneration powerplant designs, is thoroughly investigated.

The obtained results suggest that, the dominant thermodynamic cycle variables that affect the electrical performance of integrated digestion-cogeneration systems, are the gas/air temperatures at the combustor outlet and recuperator air side exit, respectively. It is shown that the profitability of the investment is highly depended on the electrical power output and the feed–in tariff for electrical energy. Optimization of the employed co-generation cycle for maximum electrical power output, is shown to be a crucial element in terms of securing investment sustainability. A general review of the results indicates that, anaerobic treatment of animal manure and energy crops may constitute a sustainable investment, primarily for cases that substantial volumes of substrates are available in order to secure biogas yield and stable operation of the AD–gas turbine power plant.
Performance Prediction and Analysis of a Three-Shaft Gas Turbine Supported by Turbine Cooling Model
Authors: Ji Xingxing , Gu Chunwei , Song Yin , Xie Weihong
Published: September 2014

Performance prediction method of the modern gas turbine is an important tool for the engine design and performance analysis. This paper integrates a hybrid cooling model to the previous research of gas turbine performance prediction method which is applied to predict the multi-shaft gas turbine performance. The cooling model, combined with the semi-empirical model and analytical model, had been originally proposed for the investigation of turbine convective cooling or film cooling performance. The aim of the work is to apply the hybrid model to effectively estimate the coolant requirement in the gas turbine performance prediction, therefore to improve the reliability of the analysis in the innovative gas turbine cycle.

The analysis involved a three-shaft gas turbine. Experiments were carried out on the engine, and the effectiveness of the prediction method is validated by the experiment. Consequently detailed performance characteristic of the engine is investigated under different stagger angles of the variable-angle nozzle, revealing how the stagger angle of the variable-angle nozzle and the turbine inlet temperature affect the gas turbine performance. The analysis is considered valuable for the engine operation and components optimization.
Selecting Cavity Geometries for Improving the Aerodynamic Performance of an Axial Compressor
Authors: Flores Diego , Seume Joerg R.
Published: September 2014

Designers and researchers have traditionally sought to minimize aerodynamic losses in turbomachinery without considering the influence of fillets, seals and cavities. The validity of this assumption is investigated in the present paper. Three different cavity geometries have been implemented in the third stage of a four-stage high-speed axial compressor. To better understand the interaction between the main flow path and the secondary flow caused by leakage through labyrinth seals, three different cavity outlet angles have been investigated: 90°, 45°, and 135° with respect to the main flow path direction. Moreover, three different clearances between the seal tips and the stator have been used in order to investigate the leakage mass flow inside the cavity. Three-dimensional steady RANS simulations with two different turbulence models using the TRACE solver by DLR have been performed in all cases. The SST turbulence model showed higher fidelity when compared to experimental data and proved more sensitive to variations of parameters studied. A comparison of aero-thermodynamic results in the main flow path for the different configurations at the inlet and outlet of the cavities shows that the radial profiles are strongly influenced by clearance height H and cavity outlet angle a in the third stator as well as rotor. A cavity outlet directed against the main flow direction gives the best results in terms of compressor overall efficiency.

The results also reveal some modeling limitations in that neither of the two turbulence models can precisely predict the progressive temperature rise noticed in the experimental data above of 55% blade height in the third stator and rotor, pointing at deficiencies in modeling the tip clearance vortex.
Comparison of Ni-Based 625 Alloy and ATI 20-25+Nb™ Stainless Steel Foils After Long-Term Exposure to Gas Turbine Engine Exhaust
Authors: Bender M. D. , Klug R. C.
Published: September 2014

A field test program to validate the high temperature oxidation resistance of the ATI 20-25+Nb™ alloy in a Solar Turbines Incorporated Mercury™ 50 gas turbine engine has exceeded 66,000 operating hours. The primary goal of this program is to assess the effect of the actual recuperator operating environment on the high temperature degradation of primary surface recuperator (PSR) materials. As PSRs are generally fabricated from thin foil materials, excessive degradation can cause perforation or collapse, leading to decreased performance or failure. To avoid such issues, PSRs are generally fabricated from highly-alloyed austenitic stainless steels or nickel-base superalloys.

This field test program evaluates and compares the long-term performance of the iron-based austenitic ATI 20-25+Nb™ stainless steel (UNS S35140) with the more highly alloyed nickel-based 625 alloy (UNS N06625) in an in-situ turbine exhaust environment.

Sub-size air cell samples of alloy 625 and ATI 20-25+Nb™ alloy, exposed for 66,000 hours (running time) in turbine exhaust, were removed and tested for materials characterization. Analysis showed that both alloys exhibit excellent long-term resistance to environmental degradation, even after service exposures equivalent to over 7.5 years.
Steady-State Power Operation of a Supercritical Carbon Dioxide Brayton Cycle
Authors: Clementoni Eric M. , Cox Timothy L.
Published: September 2014

Bechtel Marine Propulsion Corporation (BMPC) is testing a supercritical carbon dioxide (S-CO2) Brayton system at the Bettis Atomic Power Laboratory. The Integrated System Test (IST) is a two shaft recuperated closed Brayton cycle with a variable speed turbine driven compressor and a constant speed turbine driven generator using S-CO2 as the working fluid designed to output 100 kWe. The main focus of the IST is to demonstrate operational, control and performance characteristics of an S-CO2 Brayton power cycle over a wide range of conditions.

IST operation has reached the point where the system can be operated with the turbine-compressor thermal-hydraulically balanced so that the net output of the system is equal to the turbine-generator output. In this operating mode, power level is changed by using the compressor recirculation valve which changes the fraction of compressor flow that goes to the turbines. Steady-state operation with the turbine-compressor thermal hydraulically balanced at near zero net system power is presented.
Comparison of Carbon Dioxide Property Measurements for an Operating Supercritical Brayton Cycle to the REFPROP Physical Property Database
Authors: Clementoni Eric M. , Cox Timothy L.
Published: September 2014

Supercritical carbon dioxide (S-CO2) power cycles have been gaining interest in recent years due to their high efficiency and compact components. As interest in CO2 cycles grows, work is being done to test the operation and control of these cycles and model individual component and system performance. A key aspect in this work is the accuracy of the physical properties of the fluid used in the design, system operation, and model validation efforts. A commonly used physical property database is the NIST REFPROP database which implements correlations developed for CO2 by Span and Wagner.

Bechtel Marine Propulsion Corporation (BMPC) is testing an S-CO2 Brayton system at the Bettis Atomic Power Laboratory. The Integrated System Test (IST) is a two shaft recuperated closed Brayton cycle with a variable speed turbine-driven compressor and constant speed turbine-driven generator using S-CO2 as the working fluid designed to output 100 kWe. The IST utilizes coriolis mass flow meters to measure system flow rates as well as CO2 density at various points in the loop. Operational test data for CO2 temperature, pressure, and density are presented and comparisons made on the ability to accurately calculate the density of CO2 using REFPROP with temperature and pressure measurements for an operating Brayton loop. An uncertainty analysis using vendor specified instrument accuracy was performed to show that the calculated and measured properties of CO2 for the operating conditions examined are in good agreement.
Blade-Row Interactions in an LP Turbine at Design and Strong Off-Design Operation
Authors: Lipfert Martin , Habermann Jan , Rose Martin G. , Staudacher Stephan , Guendogdu Yavuz
Published: September 2014

In a joint project between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines a two-stage low pressure turbine is tested at design and strong off-design conditions. The experimental data taken in the altitude test-facility aims to study the effect of positive and negative incidence of the second stator vane. A detailed insight and understanding of the blade row interactions at these regimes is sought. Steady and time-resolved pressure measurements on the airfoil as well as inlet and outlet hot-film traverses at identical Reynolds number are performed for the midspan streamline. The results are compared with unsteady multi-stage CFD predictions. Simulations agree well with the experimental data and allow detailed insights in the time-resolved flow-field. Airfoil pressure field responses are found to increase with positve incidence whereas at negative incidence the magnitude remains unchanged. Different pressure to suction side phasing is observed for the studied regimes. The assessment of unsteady blade forces reveals that changes in unsteady lift are minor compared to changes in axial force components. These increase with increasing positive incidence. The wake-interactions are predominating the blade responses in all regimes. For the positive incidence conditions vane 1 passage vortex fluid is involved in the midspan passage interaction leading to a more distorted three-dimensional flow field.
Conjugate Heat Transfer Measurements and Predictions of a Blade Endwall With a Thermal Barrier Coating
Authors: Mensch Amy , Thole Karen A. , Craven Brent A.
Published: September 2014

Multiple thermal protection techniques, including thermal barrier coatings (TBCs), internal cooling and external cooling, are employed for gas turbine components to reduce metal temperatures and extend component life. Understanding the interaction of these cooling methods, in particular, provides valuable information for the design stage. The current study builds upon a conjugate heat transfer model of a blade endwall to examine the impact of a TBC on the cooling performance. The experimental data with and without TBC are compared to results from conjugate CFD simulations. The cases considered include internal impingement jet cooling and film cooling at different blowing ratios with and without a TBC. Experimental and computational results indicate the TBC has a profound effect, reducing scaled wall temperatures for all cases. The TBC effect is shown to be more significant than the effect of increasing blowing ratio. The computational results, which agree fairly well to the experimental results, are used to explain why the improvement with TBC increases with blowing ratio. Additionally, the computational results reveal significant temperature gradients within the endwall, and information on the flow behavior within the impingement channel.
Effects of Geometry on Sealing Effectiveness of a Rim Seal
Authors: Moon Mi-Ae , Lee Chung-Suk , Kim Kwang-Yong , Kim Jun-Hee
Published: September 2014

A parametric study has been performed to find the effects of geometric parameters on sealing effectiveness of a rim seal, which is used to prevent the hot gas ingestion into the gas turbine component and to cool the turbine disk. The flow and temperature fields in the reference rim seal which was tested by Popović and Hodson have been investigated using three-dimensional Reynolds-averaged Navier-Stokes equations. The one-equation Spalart-Allmaras turbulence model has been selected as turbulence closure. Computational results for the area-averaged sealing effectiveness have been validated compared to the experimental data at the specified values of rim seal inlet velocities (Vc,in = 11.50m/s and 16.10m/s) and leakage fractions (0.50%, 0.75% and 1.00%). Best shape of the rim seal has been found among ten different shapes of the rim seal.
Experimental Study on Local Heat Transfer in a Rotating, Two-Pass Cooling Channel With Dense Array of Turbulence Promoters With Naphthalene Sublimation Method
Authors: Hagari Tomoko , Ishida Katsuhiko , Takeishi Kenichiro , Komiyama Masaharu , Oda Yutaka
Published: September 2014

Detailed heat transfer coefficient distributions in a rotating, two-pass, square channel with densely arranged rib turbulators on the leading and trailing walls are investigated. Rib turbulators have been used in a cooling channel of turbine airfoils. The dense arrangement of the ribs is one of the potential candidates to improve heat transfer performance because of its surface area enlargement effect.

The ribs are arranged with a rib height to channel hydraulic diameter ratio (e/Dh) of 0.13, angles of attack to the mainstream of 60 and 90deg, and rib pitch-to-height ratios (P/e) of 3, 6 and 10. Both rib and floor surfaces are coated with naphthalene to measure their local mass transfer rate, which is correlated with heat transfer coefficient through heat/mass transfer analogy. Combination of a laser displacement sensor and a precision auto-traverse system enables detailed measurement of local heat transfer distribution on the floor surface between the ribs. Overall heat transfer coefficient including the effect of the rib is obtained by measuring the decrease in weight of the naphthalene test piece. Reynolds number is set at 50,000 and rotation numbers are up to 0.05.

The results show that the effect of rotation on local heat transfer behavior depends on the rib spacing and orientation. Compared the overall heat transfer coefficients with the local ones on the floor surface, they showed different trend in some cases. This suggests that variation of rib heat transfer characteristics due to rotation might determine the overall heat transfer coefficient. Such tendency would be stronger for smaller rib spacing because surface area of the rib has large portion of the total heat transfer area. Further investigation on this effect is expected by measuring heat transfer of rib itself under rotating condition.
Influence of Fuel-Air Mixing on Flame Dynamics of Premixed Swirl Burners
Authors: Bade Stefanie , Wagner Michael , Hirsch Christoph , Sattelmayer Thomas , Schuermans Bruno
Published: September 2014

The influence of fuel-air mixing on the flame dynamics of premixed swirl flames is investigated comparing flame transfer functions determined for perfectly premixed (PP) and technically premixed (TP) operation. In PP operation fuel and air are mixed far upstream of the burner so no equivalence ratio fluctuations appear during thermo-acoustic oscillation. In TP operation the fuel is injected in the swirler slots so equivalence ratio fluctuations occur. The employed swirl burner is a modular system that consists of a swirler and a mixing tube with three different lengths. It was investigated in an atmospheric single burner test rig equipped for flame transfer matrix measurements. Flame transfer function data are presented for both the PP and the TP operation for a variation of power at fixed equivalence ratio and a variation of equivalence ratio for constant power. The unforced flame shapes corresponding to these operation points were acquired and analyzed for scaling parameters of the flame response. It was found that a basic frequency scaling can be achieved for both operation modes using the nominal burner velocity and the flame stand-off distance. A detailed comparison of the PP and TP flame transfer functions is performed for the three different mixing tubes at one operation point. Finally the difference between the PP and the TP flame transfer function is presented and discussed. It is shown that the influence of equivalence ratio fluctuations exhibits a generalized delay time behavior.
Off-Design Performance of a Highly Loaded LP Turbine Cascade Under Steady and Unsteady Incoming Flow Conditions
Authors: Berrino Marco , Simoni Daniele , Ubaldi Marina , Zunino Pietro , Bertini Francesco
Published: September 2014

The off-design performance of a highly loaded LP turbine cascade has been experimentally investigated, at the Aerodynamics and Turbomachinery Laboratory of Genova University, under steady and unsteady incoming flow conditions. Tests have been performed for different Reynolds numbers (Re = 70000 and Re = 300000), in order to cover the typical LP turbine working range. The incidence angle has been varied between i = −9° and +9°, in order to test off-design conditions characterizing the engine. For the unsteady case upstream wake periodic perturbations have been generated by means of a tangential wheel of radial rods. The cascade and the moving bars system have been located over a common bearing in order to make them rigidly rotating. This solution allows a proper comparison of the cascade robustness at the incidence angle variation under steady and unsteady incoming flows, since all the other operating parameters have been kept the same. In order to survey the variation of the unsteady boundary conditions characterizing the off-design operation of the downstream cascade, time-mean and time-resolved wake structures have been analyzed in detail.

For what concerns the cascade performance, profile aerodynamic loadings and total pressure loss coefficients at the cascade exit have been surveyed for the different incidence angles under both steady and unsteady inflows. Different total pressure loss sensitivity at the incidence angle variation has been observed for the steady and the unsteady inflow conditions.

Hot-wire anemometer has been employed to obtain the time-mean pressure and suction side boundary layer velocity profiles at the blade trailing edge for the different conditions. The integral parameters at the cascade exit plane help to justify the different loss trend vs incidence angle found for the steady and the unsteady cases, explaining the different sensibility of the blade profile when this operates under realistic unsteady inflow condition.
Introduction of an Universal Scale-Up Method for the Efficiency of Axial and Centrifugal Fans
Authors: Pelz Peter F. , Stonjek Stefan S.
Published: September 2014

Acceptance tests on large fans to prove the performance (efficiency and total pressure rise) to the customer are expensive and sometimes even impossible to perform. Hence there is a need for the manufacturer to reliably predict the performance of fans from measurements on down-scaled test fans. The commonly used scale-up formulas give satisfactorily results only near the design point, where inertia losses are small in comparison to frictional losses. At part- and overload the inertia losses are dominant and the scale-up formulas used so far fail. In 2013 Pelz and Stonjek introduced a new scaling method which fullfills the demands ( [1], [2]). This method considers the influence of surface roughness and geometric variations on the performance. It consists basically of two steps: Initially, the efficiency is scaled. Efficiency scaling is derived analytically from the definition of the total efficiency. With the total derivative it can be shown that the change of friction coefficient is inversely proportional to the change of efficiency of a fan. The second step is shifting the performance characteristic to a higher value of flow coefficient. It is the task of this work to improve the scaling method which was previously introduced by Pelz and Stonjek by treating the rotor/impeller and volute/stator separately. The validation of the improved scale-up method is performed with test data from two axial fans with a diameter of 1000 mm/250mm and three centrifugal fans with 2240mm/896mm/224mm diameter. The predicted performance characteristics show a good agreement to test data.
Emergency Shutdown Management in Fuel Cell Gas Turbine Hybrid Systems
Authors: Lambruschini Fabio , Ferrari Mario L. , Traverso Alberto , Larosa Luca
Published: September 2014

A real-time dynamic model representing the pressurized fuel cell gas turbine hybrid system emulator test rig at Thermochemical Power Group (TPG) laboratories of the University of Genoa has been developed to study the fuel cell behavior during different critical operative situations like, for example, load changes (ramp and step), start-up and shut-down and, moreover, to implement an emergency shutdown strategy in order to avoid any damage to the fuel cell and to the whole system: focus has been on cathode/anode differential pressure, which model was validated against experimental data. The real emulator plant (located in Savona University campus) is composed of a 100 kW recuperated micro gas turbine, a modular cathodic vessel (4 modules of 0.8 m3 each) located between recuperator outlet and combustor inlet, and an anodic circuit (1 module of 0.8m3) based on the coupling of a single stage ejector with an anodic vessel.

Different simulation tests were carried out to assess the behavior of cathode-anode pressure difference, identifying the best control strategies to minimize the pressure stress on fuel cell stack.
Experimental Study of Aero-Mechanical Damping of Full-Scale Wind Turbines
Authors: Zendehbad M. , Chokani N. , Abhari R. S.
Published: September 2014

An opto-mechanical system has been developed to measure the dynamic behaviour of multi-megawatt wind turbines. This portable system is easier and less expensive to use than previously used methods. Thus it is feasible to use the system to develop a large database of the modal damping characteristics of operational full-scale wind turbines for the development of the improved fatigue life prediction tools that are needed in the rapidly growing global wind industry. The opto-mechanical system and a 3D scanning pulsed Doppler LIDAR system are used to make simultaneous measurements of the dynamic response and wind field in three different utility-scale wind farms. The wind farms are located in different types of terrain, ranging from the flat terrain through to highly complex terrain. The measurements are made on five different multi-megawatt wind turbines (1.8MW Vestas V90; 2.0MW Vestas V80; 2.3MW Enercon E70; 3MW Vestas V90; and 3.6MW Siemens SWT). A single-degree-of-freedom dynamic model is used to determine the modal damping parameters from the measured spectra of the tower deflections. It is shown that the aeromechanical damping ratios range from 0.4% to 0.8%. Measurements in the operating and idling phases of a turbine are used to show that the aerodynamic damping, which arises from the interaction between the rotor and wind, is the dominant damping mechanism for an operating wind turbine, and accounts for two-thirds of the overall damping; the material damping accounts for one-third of the overall damping. The 3.6MW Siemens SWT wind turbine has the smallest overall damping, whereas the 3MW Vestas V90 has the largest damping as well as the largest dynamic deflections. However, an assessment of the Goodman diagram shows that in its location of flat terrain, the 3MW Vestas V90 wind turbine may likely meet its 20-year design life. Nevertheless, for other locations, such as in complex terrain, in-situ measurements should be made to verify the suitability of the wind turbine for wind farms in such locations. This work demonstrates the feasibility of using the opto-mechanical system to develop a large database of the modal damping characteristics of operational full-scale wind turbines.
Detection and Monitoring of Shaft Misalignment in Rotors Using Hilbert Huang Transform
Authors: Chandra N. Harish , Sekhar A. S.
Published: September 2014

Precise detection of the misalignment can reduce maintenance cost, power loss and improve life of rotating machinery. In this paper, Hilbert Huang Transform (HHT) of the run-up response of a rotor is used to detect coupling misalignment. A finite element analysis is carried out to simulate desirable level of possible parallel and angular misalignment. All the best conventional detection techniques like Fourier spectrum analysis, Continuous Wavelet Transform are compared with results obtained by HHT. The effect of Signal to Noise Ratio and angular acceleration on all the methods to detect misalignment is discussed. The comparison of the methods is oriented towards detecting least possible misalignment level. Finally, experiments are performed on a test rotor rig to detect induced misalignment using the proposed method. It is observed that this method is sensitive to low misalignment, and consumes less testing time.
Minimum Environmental Load Reduction in Heavy Duty Gas Turbine by Bleeding Lines
Authors: Cioffi Marco , Piola Stefano , Puppo Enrico , Silingardi Andrea , Bonzani Federico
Published: September 2014

The power generation and energy market scenarios are requiring the power generation plants to fulfill more flexible operations respect to the recent past. One of the main concerns of plant operators is the lowering of minimum load at which the machines can be exercised while respecting the pollution limits. A strategy to improve minimum turndown capability by reducing the minimum environmental load of heavy duty axial gas turbines is here presented: it is based on the use of the compressor air bleeding lines (blow-off lines).

The described technical development activities are based on the numerical modeling of blow-off lines and bleeding compressor sections; these preliminary tasks have been followed by on-field plant testing.

The blow-off lines modeling reserves a particular regard, due to the somehow non-usual fluid dynamics involved. A Fanno flow 1D approach has been adopted to properly model the bleeding lines fluid flow whereas full 3D numerical solutions have been developed to get a better insight of the bleeding plenums and of the line sector including the valve. In addition, the gas turbine components off-design behavior and the overall performances are computed by the Ansaldo modular simulation code. Numerical analysis and performed field tests are here presented and results are compared, showing a good agreement, in accord to the simplified model adopted. Additional comparisons with different alternative strategies are finally presented in terms of gas turbine power and excess air variation.

The described technique by blow-off lines opening shows to be able to fulfill the required task by incrementing the plant operative flexibility and guaranteeing safe plant operation. The technique drawbacks are a gas turbine slightly lower efficiency and the lower output flue gas temperature, whose relative importance have to evaluate by the plant operators. At present the long term sustainability of the new operative condition is the object of a deeper and longer field testing phase.
Substrate Effect on the Lifetime of EB-PVD TBC Systems With 7YSZ and GDZ as Ceramic Top Coat Materials
Authors: Munawar Ahmed Umar , Schulz Uwe , Cerri Giovanni , Lau Hendrik
Published: September 2014

Thermal barrier coatings (TBCs) consist of a multi-layered system where the different layers are deposited to improve the high temperature capability of the underlying substrate material. Substrate materials are usually made of Ni-based superalloys which have an outstanding combination of high-temperature strength, toughness and resistance to degradation in corrosive or oxidizing environments. In this study, the effect of different substrate materials on cyclic TBC lifetime has been studied by using two different superalloys, IN100 and CMSX-4, as the substrate materials. Two different ceramic topcoat materials, 7wt. % yttria partially stabilized zirconia (7YSZ) and Gadolinium Zirconate (GdZ), have been deposited on NiCoCrAlY bond coats. All depositions in this study have been carried out by Electron Beam Physical Vapor Deposition (EB-PVD). Lifetime measurements have been done by holding the systems at 1100°C for 50mins and then reducing the temperature to ambient level by forced air cooling for 10mins. The TBC lifetime in case of IN100 substrates is higher than on CMSX-4. The use of GdZ as topcoat material improves the lifetime for both IN100 and CMSX-4 based TBC systems, however, the lifetime for CMSX-4 based TBC system is still shorter than its IN100 counterpart. In this study, lifetime comparisons, changes in the microstructure and diffusion of different elements in the system are investigated.
Secondary Flows and Fillet Radii in a Linear Turbine Cascade
Authors: Mank Sebastian , Duerrwaechter Lukas , Hilfer Michael , Williams Richard , Hogg Simon , Ingram Grant
Published: September 2014

Most large scale cascade experiments and the corresponding computational fluid dynamics are conducted on geometries without fillet radii, that is with sharp edges. Despite that the fact that all real machines have a fillet radii there has not so far been a detailed examination of the influence of fillet radii on the secondary flow structures in turbines.

This paper presents detailed measurements on a large scale, low speed cascade with significant secondary flows. A series of detailed traverses inside the blade row were obtained allowing the influence of fillet radii on the formation of secondary flows to be examined. The experimental campaign is backed up by RANS computations.

The fillets were found to increase loss by around 10% compared to the base case. This loss could not be accounted for by a simple model of boundary layer behaviour and an accounting of the complex secondary flow interactions is required to explain the observed changes in performance. The secondary flow interactions include a larger radial migration of secondary flows from the endwall and the elimination of the corner vortex. The potential to improve performance by varying the fillet radii around the blade was identified.