bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling Methods for Matching Tasks in Turbocharged Engines
Authors: Njoya Thibaut , Nakhjiri Mehdi , Pelz Peter F. , Frase Robert
Published: September 2014

Specific turbocharger parameters are necessary to develop and match model based control strategies in the air path of a turbocharged engine. These parameters describe the turbocharger performance and are obtained from measurements on manufacturers’ standard test benches under steady state conditions and without taking into account the heat transfer between the components of the turbocharger or between the turbocharger and the surroundings. The latter falsifies the measured turbocharger efficiency which can be referred as “apparent efficiency”. The efficiency is a key parameter of the model based controls. Thus, the apparent efficiency increases the uncertainties (mismatching) and slows down the matching process considerably.

Due to the mismatching, manufacturers’ parameters themselves need to be calibrated. The calibration occurs on the basis of on-board measurements and offline analyses. However, this calibration procedure is not axiomatic and the results remain typical for a certain turbocharger and engine combination. Hence, it is usually not possible to apply the results when the same turbocharger should be matched with another engine.

A physically based scaling method has already been introduced in previous publications in order to obtain the “real” from the “apparent” efficiency, [1]. This work aims to show on the basis of a concrete example how the implementation of this method counteracts the mismatching without any further measurements. As a result, the matching process can be accelerated and enhanced. The reusability of the results leads to faster processes and lower costs.
Dynamic Analysis of Concentrated Solar Hybridised Gas Turbine
Authors: Traverso Alberto , Barberis Stefano , Lima Davide , Massardo Aristide F.
Published: September 2014

In this work the dynamic behaviour and the control strategy of a 12MWe size gas turbine hybridised with concentrated solar heat source has been investigated. Hybridised gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and because of their dispatchable power capability. An existing gas turbine model has been modified into a hybrid layout to incorporate high temperature heat from a concentrated solar field, through a high pressure air-cooled receiver. The system does not involve any hot air valve and includes a ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool developed at the University of Genoa. Initially, plant steady-state performance is analysed, identifying potential issues. Then, the different dynamic operations (storage charging, discharging and bypass) are simulated, showing the feasibility of the control strategy proposed. Eventually, design recommendations are drawn to improve the flexibility and the time response of such kind of plants.
Numerical Investigation of a Centrifugal Compressor for Supercritical CO2 as a Working Fluid
Authors: Kim Seong Gu , Ahn Yoonhan , Lee Jekyoung , Lee Jeong Ik , Addad Yacine , Ko Bockseong
Published: September 2014

The supercritical carbon dioxide (S-CO2) Brayton cycle is considered as a strong candidate for power conversion systems. This includes concentrated solar power, coal power, bottoming cycle to fuel cells, and the next generation nuclear systems. In the previous studies, it was identified that the compressor consumes very small compressing work as operating condition approaches to the critical point. Thus, smaller amount of input work contributes to the enhancement of overall cycle efficiency. To achieve an efficient S-CO2 cycle, one of the major technical challenges exists in the compressor design. At KAIST, a research team is conducting a S-CO2 compressor tests to obtain fundamental data for advanced compressor design and to measure the performance of the compressor near the critical point. The measurements reveal the S-CO2 fluid to have properties of gases and liquids at the same time, but in regards to compressibility and density variation, its behavior is much closer to the liquid rather than gas near the critical point. In this paper, a CFD analysis of S-CO2 centrifugal compressor with the full geometry including diffuser and volute is presented. The numerical results are compared to the experimental data from KAIST SCO2 Pressurizing Experiment facility. A 3D grid was generated starting from the model of the compressor full geometry provided by the manufacturer. Furthermore, a property table of CO2 was generated by an in-house code and implemented to the CFD code. Then the performance characteristic of S-CO2 compressor is investigated in terms of compressor efficiency and pressure ratio. Additional flow variables inside the compressor such as velocity, pressure and viscosity are also investigated to help understanding the main reason behind the relatively higher compressor efficiency near the critical point compared to other flow conditions far from this region. In general acceptable results in comparison to the experiment are obtained (order of error from 0.5 to 7% for the compressor efficiency). Hence, the current CFD results should be able to provide additional and detailed information to be used for design enhancements of the compressor for S-CO2 Brayton power cycle.
Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines: Part 1 — Numerical Validation of Wet Steam Models and Turbine Modeling
Authors: Grübel M. , Starzmann J. , Schatz M. , Eberle T. , Vogt D. M. , Sieverding F.
Published: September 2014

In this publication an overview of the current state of wetness modeling at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) is given. For the modeling an Euler-Euler method implemented in the commercial flow solver ANSYS CFX is used. This method is able to take into account the non-equilibrium state of the steam and models the interactions between the gaseous and liquid phases.

This paper is the first part of a two-part publication and deals with the numerical validation of wet steam models by means of condensing nozzle and cascade flows. A number of issues with regard to the quality of the CFD code and the applied condensation models are addressed comparing the results to measurements. It can be concluded, that a calibration of the models is necessary to achieve a satisfying agreement with the experimental results.

Moreover, the modeling of the low pressure model steam turbine operated at the ITSM is described focusing on the asymmetric flow field in the last stage caused by the axial-radial diffuser. Different simplified axisymmetric diffuser models are investigated in steady state simulations and the results and the arising issues for part-load, design-load and over-load conditions are discussed. Thereafter, a comparison between the equilibrium and non-equilibrium steam modeling approaches is performed and the advantage of the non-equilibrium model is highlighted.

The second part of the publication focuses on experimental investigations and compares the numerical results to wetness measurement data, see Schatz et al. [1]. For this purpose, also different load conditions are considered.
Experimental Investigation Into Thermal Behavior of Steam Turbine Components: Part 4 — Natural Cooling and Robustness of the Over-Conductivity Function
Authors: Marinescu Gabriel , Stein Peter , Sell Michael
Published: September 2014

Steam turbine transient maneuvers have a significant impact on the cyclic fatigue life. Modern steam turbines are operated at high temperatures for optimal efficiency, which results in high time and space temperature gradients. A low initial metal temperature after standstill results in a high temperature difference to be overcome during the next startup and consequently a low lifetime at critical locations. To achieve the fastest possible start-up time without reducing the lifetime of the turbine components, the natural cooling must be captured accurately in calculation and the start-up procedure optimized. At the past two ASME conferences we presented three papers [1], [2], [3], about a 2D numerical procedure for the thermal regime calculation during natural cooling and startup. The analysis included the rotor, casings, valves and pipes. The main concept was to replace the thermal effect of the fluid convectivity by a fluid function K(T) called “over-conductivity”, which is calibrated vs. experimental data. The paper below shows: (a) the theoretical background of the over-conductivity function K(T) and (b) the equation of the correlation function f(T,p) between the fluid velocity and fluid temperature gradient. Both K(T) and f(T,p) are applicable for the flow within the large turbine cavities with negligible pressure gradient. The robustness of the K(T) function is verified on three different turbine configurations. For each machine a separate transient thermal model was built and the calculated temperatures were compared with the corresponding measured temperatures. At the end of the paper conclusions about the natural cooling features are presented.
Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Rig for Testing Full Scale Burners
Authors: Laera Davide , Campa Giovanni , Camporeale Sergio M. , Bertolotto Edoardo , Rizzo Sergio , Bonzani Federico , Ferrante Antonio
Published: September 2014

This paper concerns the acoustic analysis of self–sustained thermoacoustic pressure oscillations that occur in a test rig equipped with full scale lean premixed burner. The experimental work is conducted by Ansaldo Energia and CCA (Centro Combustione Ambiente) at the Ansaldo Caldaie facility in Gioia del Colle (Italy), in cooperation with Politecnico di Bari. The test rig is characterized by a longitudinal development with two acoustic volumes, plenum and combustion chamber, coupled by the burner. The length of both chambers can be varied with continuity in order to obtain instability at different frequencies. A previously developed three dimensional finite element code has been applied to carry out the linear stability analysis of the system, modelling the thermoacoustic combustion instabilities through the Helmholtz equation under the hypothesis of low Mach approximation. The heat release fluctuations are modelled according to the κ-τ approach. The burner, characterized by two conduits for primary and secondary air, is simulated by means of both a FEM analysis and a Burner Transfer Matrix (BTM) method in order to examine the influence of details of its actual geometry. Different operating conditions, in which self–sustained pressure oscillations have been observed, are examined. Frequencies and growth rates of unstable modes are identified, with good agreement with experimental data in terms of frequencies and acoustics pressure wave profiles.
Endwall Contouring and Fillet Design for Reducing Losses and Homogenizing the Outflow of a Compressor Cascade
Authors: Reutter Oliver , Hemmert-Pottmann Stefan , Hergt Alexander , Nicke Eberhard
Published: September 2014

The following paper deals with the development of an optimized fillet and an endwall contour for reducing the total pressure loss and for homogenizing the outflow of a highly loaded cascade with a low aspect ratio. The NACA-65 K48 cascade profile without a fillet and without endwall contouring is used as a basis. Optimizations are performed using the DLR in-house tool AutoOpti and the RANS-solver TRACE. Three operating points at an inflow Mach number of 0.67 with different inflow angles are used to secure a wide operating range of the optimized design. At first only a fillet is optimized. The optimized fillet is small at the leading edge and rather high, wide and thick towards the trailing edge. It reduces the total pressure loss and homogenizes the outflow up to a blade height of 20 %. Following this a combined optimization of the endwall and the fillet is performed. The optimized contour leads to the development of a vortex, which changes the secondary flow in such a way, that the corner separation is reduced, which in turn significantly reduces the total pressure loss up to 16 % in the design operating point. The contour in the outflow region leads to a significant homogenization of the outflow in the near wall region.
Cross Validation of Multistage Compressor Map Generation by Means of Computational Fluid Dynamics and Stage-Stacking Techniques
Authors: Aldi Nicola , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio
Published: September 2014

Gas turbine operating state determination consists of the assessment of the modification, due to deterioration and fault, of performance and geometric data characterizing machine components. One of the main effects of deterioration and fault is the modification of compressor and turbine performance maps. In this paper, three-dimensional numerical simulations of a multistage axial compressor are carried out. As a case study, the axial sections (i.e. the first six stages) of the Allison 250-C18 axial-centrifugal compressor are considered for the numerical investigation. Simulations are performed by means of a commercial computational fluid dynamic code. A multistage numerical model is set up and validated against the experimental data, gathered from an in-house test rig. Computed performance maps and main flow field features show fairly good agreement with the experimental data. The model is then used to cross-validate the results of zero-dimensional stage-stacking procedures and the stage maps obtained by means of a multistage CFD calculation (i.e. to evaluate the mutual consistency of the two methods for the generation of multistage compressor maps). The stage-stacking procedure results adequately fit the behavior of the multistage compressor.
The Effects of Vane Showerhead Injection Angle and Film Compound Angle on Nozzle Endwall Cooling (Phantom Cooling)
Authors: Zhang Luzeng , Yin Juan , Moon Hee Koo
Published: September 2014

The effects of airfoil showerhead injection angle and film cooling hole compound angle on nozzle endwall cooling (second order film cooling effects, also called “phantom cooling”) was experimentally investigated in a scaled linear cascade. The test cascade was built based on a typical industrial gas turbine nozzle vane. Endwall surface phantom cooling film effectiveness measurements were made using a computerized pressure sensitive paint (PSP) technique. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness can be obtained by the mass transfer analogy. Two separate nozzle test models were fabricated, which have the same number and size of film cooling holes but different configurations. One had a showerhead angle of 45° and no compound angles on the pressure and suction side film holes. The other had a 30° showerhead angle and 30° compound angles on the pressure and suction side film cooling holes. Nitrogen gas (cooling air) was fed through nozzle vanes, and measurements were conducted on the endwall surface between the two airfoils where no direct film cooling was applied. Six cooling mass flow ratios (MFRs, blowing ratios) were studied, and local (phantom) film effectiveness distributions were measured. Film effectiveness distributions were pitchwise averaged for comparison. Phantom cooling on the endwall by the suction side film injections was found to be insignificant, but the pressure side airfoil film injections noticeably helped the endwall cooling (phantom cooling) and was a strong function of the MFR. It was concluded that reducing the showerhead angle and introducing a compound angle on the pressure side injections would enhance the endwall surface phantom cooling, particularly for a higher MFR.
Analysis of the Heat Transfer Driving Parameters in Tight Rotor Blade Tip Clearances
Authors: Lavagnoli S. , De Maesschalck C. , Paniagua G.
Published: September 2014

Turbine rotor tips and casings are vulnerable to mechanical failures due to the extreme thermal loads they undergo during engine operation. In addition to the heat flux variations during the transient phase, high-frequency unsteadiness occurs at every rotor passage, with amplitude dependent on the tip gap. The development of appropriate predictive tools and cooling schemes requires the precise understanding of the heat transfer mechanisms. The present paper analyzes the nature of the overtip flow in transonic turbine rotors running at tight clearances, and explores a methodology to determine the relevant flow parameters that model the heat transfer.

Steady-state three-dimensional Reynolds-Averaged Navier-Stokes calculations were performed to simulate engine-like conditions considering two rotor tip gaps, 0.1% and 1% of the blade span. At tight tip clearance, the adiabatic wall temperature is not anymore independent of the solid thermal boundary conditions. The adiabatic wall temperature predicted with the linear Newton’s cooling law was observed to rise to non-physical levels in certain regions within the rotor tip gap, resulting in unreliable convective heat transfer coefficients. This paper investigates different approaches to estimate the relevant flow parameters that drive the heat transfer. The present study allows experimentalists to retrieve information on the gap flow temperature and convective heat transfer coefficient based on the use of wall heat flux measurements. Such approach is required to improve the accuracy in the evaluation of the heat transfer data while enhancing the understanding of tight-clearance overtip flows.
Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators
Authors: Saddoughi S. , Bennett G. , Boespflug M. , Puterbaugh S. L. , Wadia A. R.
Published: September 2014

Blade tip losses represent a major performance penalty in low aspect ratio transonic compressors. This paper reports on the experimental evaluation of the impact of tip clearance with and without plasma actuator flow control on performance of an U.S. Air Force-designed low aspect ratio, high radius ratio single-stage transonic compressor rig. The detailed stage performance measurements without flow control at three clearance levels, classified as small, medium and large, are presented. At design-speed, increasing the clearance from small to medium resulted in a stage peak efficiency drop of almost 6 points with another 4 point drop in efficiency with the large clearance. Comparison of the speed lines at high-speed show significantly lower pressure rise with increasing tip clearance, the compressor losing 8 percent stall margin with medium clearance and an additional 1 percent with the large clearance. Comparison of the stage exit radial profiles of total pressure and adiabatic efficiency at both part-speed and design-speed and with throttling are presented. Tip clearance flow-control was investigated using Dielectric Barrier Discharge (DBD) type plasma actuators. The plasma actuators were placed on the casing wall upstream of the rotor leading edge and the compressor mapped from part-speed to high-speed at three clearances with both axial and skewed configurations at six different frequency levels. The plasma actuators did not impact steady state performance. A maximum stall margin improvement of 4 percent was recorded in this test series. The large clearance configuration benefited the most with the plasma actuators. Increased voltage provided more stall margin improvement. Plasma actuator power requirements were almost halved going from continuous operation to pulsed plasma. Most of the improvement with the plasma actuators is attributed to the reduction in unsteadiness of the tip clearance vortex near-stall resulting in additional reduction in flow prior to stall.
Performance of Multiple-Injection Dry Low-NOx Combustor on Hydrogen-Rich Syngas Fuel in an IGCC Pilot Plant
Authors: Asai Tomohiro , Dodo Satoschi , Karishuku Mitsuhiro , Yagi Nobuo , Akiyama Yasuhiro , Hayashi Akinori
Published: September 2014

Successful development of oxygen-blown integrated coal gasification combined cycle (IGCC) technology requires gas turbines capable of achieving dry low-nitrogen oxides (NOx) combustion of hydrogen-rich syngas for low emissions and high plant efficiency. The authors have been developing a “multiple-injection burner” to achieve the dry low-NOx combustion of hydrogen-rich syngas. The purposes of this paper are to present test results of the multi-can combustor equipped with multiple-injection burners in an IGCC pilot plant and to evaluate the combustor performance focusing on effects of flame shapes. The syngas fuel produced in the plant contained approximately 50% carbon monoxide, 20% hydrogen, and 20% nitrogen by volume. In the tests, the combustor that produced slenderer flames achieved lower NOx emissions of 10.9 ppm (at 15% oxygen), reduced combustor liner and burner plate metal temperatures, and lowered the combustion efficiency at the maximum load. The test results showed that the slenderer flames were more effective in reducing NOx emissions and liner and burner metal temperatures. These findings demonstrated that the multiple-injection combustor achieved dry low-NOx combustion of the syngas fuel in the plant.
Utilization of Modern Large Scale HAWT Blade Design Techniques for the Development of Small HAWT Blades
Authors: Pechlivanoglou G. , Weinzierl G. , Masmanidis I. T. , Nayeri C. N. , Philippidis T. P. , Paschereit C. O.
Published: September 2014

Lately the need for modern medium capacity wind turbines for self-consumption within urban and rural areas has risen again. The great majority however of the large wind turbine manufacturers are not interested in this small profit market. SMART BLADE GmbH in cooperation with the CORE Team of the University of Patras have decided to develop modern, sophisticated rotor blades with state of the art tools from the multi-MW wind turbine industry in order to boost the development of the upcoming modern small capacity wind turbines. The current paper presents the design of a modern 4m wind turbine blade with optimal aerodynamic design aimed at a variable speed hybrid stall operation.
Numerical Investigation of Film Cooling Performance With Different Internal Flow Structures
Authors: Luo Jianxia , Liu Cunliang , Zhu Huiren
Published: September 2014

Four coolant channel configurations, including supply plenum without crossflow, smooth channel with crossflow and ribbed channels with crossflow ( 135° and 45° angled ribs), are simulated to find out the effect of internal flow structures on the external film cooling performance. Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. Blowing ratios cover a range from 0.5 to 2.0. For the three cases with crossflow, a constant Reynolds number, ReDh, is fixed as 100000.

Particular attention has been paid to the flow structures and counter-rotating vortices. Helical motion of secondary flow is observed in the hole of the smooth case and the 45° ribs case, inducing strong velocity separation in the cooling hole and blocks at the entrance and exit. In the two cases, the cooling-air jet divides into two parts after being blown out of the hole and a pair of skewed vortices appears downstream. In the 135° ribs case, the vortex in the upper half region of the secondary flow channel rotates in the same direction with the hole inclination direction, the straight stream lines are generated and therefore lower loss and higher discharge coefficient. Experimental data of the smooth case and the 135° ribs case show the good agreement with the numerical results.
Development of Test Stand for Measuring Aerodynamic, Erosion, and Rotordynamic Performance of a Centrifugal Compressor Under Wet Gas Conditions
Authors: Bertoneri Matteo , Wilcox Melissa , Toni Lorenzo , Beck Griffin
Published: September 2014

As the oil and gas industry addresses technology challenges for accessing gas reserves and enhancing the production of existing installations, wet gas compression becomes an important technology focus. When liquid is introduced into a compressor flow stream, the performance of the compressor is significantly influenced. Therefore, a concentrated effort is required to develop the tools to adequately predict the performance of the compressor when subjected to wet gas conditions. A series of tests were performed on a single stage compressor in a wet gas environment in order to provide empirical data for understanding how to predict wet gas performance. The compressor underwent aerodynamic, erosion, and rotordynamic performance testing. The tests were completed with a mixture of air and water at suction pressures of 10, 15, and 18.5 bar. The compressor was subjected to a multiphase flow with liquid volume fractions ranging from 0 to 3% (corresponding to a mass fraction of 73%) at three Mach numbers. Transient tests with liquid load variation were also done. This paper describes the test stand that was developed and operated for testing of the compressor in a wet gas environment. This includes a review of the overall test set-up, description of key test components and of the instrumentation installed on the compressor and the test loop. An overview of main test results is eventually shown.
Evaluation of Arabian Super Light Crude Oil for Use in a F-Class DLN Combustion System
Authors: Goldmeer Jeffrey , Symonds Richard , Glaser Paul , Mohammad Bassam , Nagel Zac , Perez-Diaz Peter
Published: September 2014

Global trends in natural gas and distillate oil prices and availability continue to influence decisions on power generation fuel choice. In some regions, heavy liquids are being selected as gas turbine fuels. One particular crude oil, Arabian Super Light (ASL), has the potential to be used as a primary or back-up fuel in F-class heavy duty gas turbines. This paper presents the results of a set of tests performed on ASL to determine the potential of using it in a Dry Low NOx (DLN) combustion system for operation in an F-class gas turbine.
A Comparison of RANS and LES of an Industrial Lean Premixed Burner
Authors: Goldin Graham , Montanari Federico , Patil Sunil
Published: September 2014

LES and RANS simulations of a Siemens scaled combustor are compared against comprehensive experimental data. The steady RANS simulation modeled one quarter of the geometry with 8M polyhedral cells using the SST-k-ω model. Unsteady LES simulations were performed on the quarter geometry (90°, 8M cells) as well as the full geometry (360°, 32M cells) using the WALE sub-grid model and dynamic evaluation of model coefficients. Aside from the turbulence model, all other models are identical for the RANS and LES. Combustion was modeled with the Flamelet Generated Manifold (FGM) model, which represents the thermo-chemistry by mixture fraction and reaction progress. RANS simulations are performed using Zimont and Peters turbulent flame speed (TFS) expressions with default model constants, as well as the kinetic rate from the FGM. The flame speed stalls near the wall with the TFS models, predicting a flame brush that extends to the combustor outlet, which is inconsistent with measurements. The FGM kinetic source model shows improved flame position predictions. The LES predictions of mean and rms axial velocity, mixture fraction and temperature do not show improvement over the RANS. All three simulations over-predict the turbulent mixing in the inner recirculation zone, causing flatter profiles than measurements. This over-mixing is exacerbated in the 900 case. The experiments show evidence of heat loss and the adiabatic simulations presented here might be improved by including wall heat-loss and radiation effects.
Full Load Stability Test (FLST) on LNG Compressor
Authors: Guglielmo Alberto , Mitaritonna Nicola , Catanzaro Michael , Libraschi Mirko
Published: September 2014

The present paper shows the results of a full pressure stability test on a centrifugal compressor for LNG application. The rotordynamic behavior of the compressor has been investigated during the full load test of the entire compression train. A Magnetic Exciter (ME) able to exert a constant rotating force was installed at shaft end (opposite to the coupling) in order to apply sub-synchronous excitation. In addition to bearings measurement location a measurement plane, equipped with vibration probes, has been introduced at compressor mid-span to gain a better understanding of the rotordynamic behavior (in particular for the first mode) of the machine during full load operations. A traditional stability test has been carried out at different compressor operating speeds exciting the rotor by mean of the ME, in order to identify frequency and logarithmic decrement of the first lateral mode the vibration data have been post-processed by a MDOF technique. Moreover Operational Modal Analysis (OMA) has been performed at the same operating speeds without any external excitation. Rotor was naturally excited by the gas flow inside compressor and the vibration signal has been recorded over proper measurement time windows. Power Spectral Density (PSD) of recorded signals shows a broad band excitation with several harmonic components superimposed while the analysis of coherence between different probes highlights the presence of excited modes in the spectrum. A state-space in time domain algorithm (Stochastic Subspace Identification) has been used to post-process the vibration signal. Natural frequency, damping properties and mode shapes at different speeds have been identified for the excited mode. A comparison between these two different identification techniques has been drawn and a confidence factor for OMA approach is defined disclosing new approaches to the compressor stability test.
Application of Optimisation Techniques for New High-Turning Axial Compressor Profile Topology Design
Authors: Komarov Oleg V. , Sedunin Viacheslav A. , Blinov Vitaly L.
Published: September 2014

An example of optimisation of high-turning outlet guide vanes for subsonic compressor stage is implemented in a new approach for blade profile topology. This topology includes types of curves on PS, SS, the number of control points and the distribution law, where several coefficients are implemented as function of the upstream flow. This functional law is defined during optimisation procedures for profiles with different parameters (Mach, inlet angle, turning angle, solidity) and further correlation analysis. As a result an 8 degree gain in turning angle for last stage guide vane is achieved. Also possible design is provided for a 12 degree gain in turning angle with higher pressure losses on 20% (relatively).
Turbomachinery Flowpath Design and Performance Analysis for Supercritical CO2
Authors: Moroz Leonid , Frolov Boris , Burlaka Maksim , Guriev Oleg
Published: September 2014

The development of Supercritical CO2 (S-CO2) power cycles is currently a major focus of the engineering and scientific community. The reason for such a growing interest in this type of power can be explained by the significant benefits in size and efficiency of power cycles, which use S-CO2 as a working fluid, as compared to conventional steam power generation. Many areas of application such as nuclear, solar, waste heat, energy storage, and clean coal combustion, are being studied for S-CO2 power production. Most of the publications discussing S-CO2 are concentrated on optimization of the cycle’s thermodynamic characteristics, topping and bottoming and have been conceptualized based on the heat source. At the same time, numerous aspects of turbomachinery design are often overlooked or are not well understood. This article discusses some specific engineering aspects of the design of turbine flow path which uses S-CO2 as a working fluid. The following design options have been studied to determine the best turbine configuration: number of stages, rotational speed, impulse versus reaction, types of stages, and radial clearance influence. The effect of larger bending loads, resulting from high power density on nozzles and blade chords size and, consequently, turbine length, has also been studied. The authors hope that the results presented in the article will help the engineering community design better S-CO2 turbomachinery.
The Influences of Thermal Effects Induced by the Light-Rub Against the Brush Seal to the Rotordynamics of Turbo Machines
Authors: Fay Robert , Kreuzer Daniel , Liebich Robert
Published: September 2014

Brush seals find increasing use in turbomachinery substituting conventional labyrinth seals thanks to their excellent leakage characteristics and convenient integration. Brush seals have very small clearances during operation. In case of contacts between rotor and brush seals, contact forces will be low due to the compliant behaviour of the bristles. While short term contacts between seal and rotor have no significant influence on the rotordynamics, longer-lasting rub can lead to thermally induced rotor-vibrations, also known as the Newkirk-effect. Light partial rub and the subsequently dissipated heat that enters into the shaft may yield a thermal bow performing spiral-vibrations regarding rotating coordinates. Depending on thermal coefficients and rotating speed, this thermal bow may effect instable behaviour with high amplitudes and a possible damage of the machine. At the Chair of Engineering Design and Product Reliability at Berlin Institute of Technology investigations of light partial rub of a rotor against a brush seal are conducted. A test rig is under construction in order to validate the numerically calculated parameters. Investigations are setting up on a thermoelastic model, developed by Kellenberger for a real rotor model. The goals of the investigations are to verify and to extend the model for brush seals and finally to formulate guidelines for the safe use of brush seals in turbomachinery concerning rotordynamics. The difficulty of defining stability statements is to quantify the required thermal parameters. Hence, the three dimensional temperature distribution inside the rotor, which depends on the rotating speed as well, must be known. In order to calculate this temperature distribution the three dimensional Laplace-Equation in cylindrical coordinates is solved for the different convection coefficients by means of Finite-Volume-discretization. Subsequently the required parameters are calculated by numerical integration of the 3-D-structure. The stiffness of the brush seal with respect to a partial rub is calculated using beam theory and continuous elastic support. This paper shows the numerical results of the 3-D temperature distribution, the numerically identified parameters that drive the thermal bow and stability charts regarding spiral vibrations for a chosen brush seal configuration.
A Test Rig for the Investigation of the Performance and Flow Field of Tesla Friction Turbines
Authors: Schosser Constantin , Lecheler Stefan , Pfitzner Michael
Published: September 2014

The paper summarizes the development and optimization of a flexible test facility for 3D tomographic PIV/PTV measurements of the flow field in the rotor gap of a Tesla friction turbine and performance evaluations. The main aim of the experiment will be the validation of CFD simulations. Another intention is to gain a deeper understanding of the flow phenomena in the gap. The extension of existing theoretical investigations lead to an improved knowledge of dimensioning such bladeless turbines with the goal of maximum power and efficiency. The mechanical design of the rotor, based on these equations, was optimized for a minimal deformation and low mechanical stress. Modal and harmonic response analyses due to imbalance forces have been performed to ensure low vibrations during operation. The design of the feed and guide vanes have been optimized for uniformity of the flow entering the Tesla disk’s gap. The rotor outlet is optimized to achieve minimal pressure loss at the intended exit swirl angle. For the demonstration of the measurement technique preliminary tomographic PIV/PTV tests have been carried out. The measurement, safety monitoring and feedback-control software was developed for running on a National Instruments compact RIO real-time target.
Pulsed LED Photography for Coarse Water Characterisation
Authors: Vernon Kris , Hann David , Rice Tim
Published: September 2014

An optical photography probe employing pulsed LED illumination has been developed for application to coarse water measurement in wet steam. High image resolution (1.38μm/px) and low exposure time (100ns) photographs capture details of micro-dynamic flow features with reduced motion blur. Camera and lens are held inside a 50mm O.D. cylindrical tube, with a custom designed titanium probe head allowing purging air to clear the front optical surface of stagnant liquid. Double exposure images are analyzed using standard image processing techniques to extract the size and velocity of liquid droplets. The accuracy and repeatability of the measurement probe has been verified on air-water sprays with direct comparison to Phase-Doppler Anemometry measurements, which show good agreement.
Numerical Study of Turbulent Flow Through Rib-Roughened Channels With Mist Injection
Authors: Elwekeel Fifi N. M. , Zheng Qun , Abdala Antar M. M.
Published: September 2014

This study investigated heat transfer characteristics on various shaped ribs on the lower channel wall using steam and steam/mist as cooling fluid. The lower wall is subjected to a uniform heat flux condition while others walls are insulated. Calculations are carried out for ribs with square ribs (case A), triangular ribs (case B), trapezoidal ribs (case C) and (case D) cross sections over a range of Reynolds numbers (14000–35000), constant mist mass fraction (6%) and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing three turbulence models: the standard k-ω, Omega Reynolds Stress (ωRS) and Shear Stress Transport (SST) turbulence models. The predicted results from using several turbulence models reveal that the SST turbulence model provide better agreement with available measurements than others. It is found that the heat transfer coefficients are enhanced in ribbed channels with injection of a small amount of mist. The steam/mist provides the higher heat transfer enhancement over steam when trapezoidal shaped ribs (38°, case C).
The Effect of Impurities on Ignition Delay Times and Laminar Flame Speeds of Syngas Mixtures at Gas Turbine Conditions
Authors: Mathieu Olivier , Hargis Joshua W. , Petersen Eric L. , Bugler John , Curran Henry J. , Güthe Felix
Published: September 2014

In addition to mostly H2 and CO, syngas also contains reasonable amounts of light hydrocarbons, CO2, H2O, N2, and Ar. Impurities such as NH3, HCN, COS, H2S, and NOx (NO, NO2, N2O) are also commonly found in syngas. The presence of these impurities, even in very low concentrations, can induce some large changes in combustion properties. Although they introduce potential design and operational issues for gas turbines, these changes in combustion properties due to the presence of impurities are still not well characterized. The aim of this work was therefore to investigate numerically the effect of the presence of impurities in realistic syngas compositions on some fundamental combustion properties of premixed systems such as laminar flame speed and ignition delay time, at realistic engine operating conditions. To perform this study, a state-of-the-art C0–C3 detailed kinetics mechanism was used. This mechanism was combined with recent, optimized sub-mechanisms for impurities which can impact the combustion properties of the syngas such as nitrogenous species (i.e., N2O, NO2, NH3, and HCN) and sulfur-based species such as H2S, SO2 and COS. Several temperatures, pressures, and equivalence ratios were investigated. The results of this study showed that the addition of some impurities modifies notably the reactivity of the mixture. The ignition delay time is decreased by the addition of NO2 and H2S at the temperatures and pressures for which the HO2 radical dominates the H2 combustion. However, while NO2 has no effect when OH is dominating, H2S increases the ignition delay time in such conditions for pressures above 1 atm. The amplitude of these effects is however dependent on the impurity concentration. Laminar flame speeds are not sensitive to NO2 addition but they are to NH3 and HCN, inducing a small reduction of the laminar flame speed at fuel rich conditions. H2S exhibits some inhibiting effects on the laminar flame speed but only for high concentrations. The inhibiting effects of NH3, HCN, and H2S are due to the OH radical consumption by these impurities, leading to the formation of radicals that are less reactive.
Calculation of Optimal Surface Roughness With Respect to Lift/Drag Forces Acting on Wind Turbine Blade
Authors: Mao Xuerui , Hogg Simon
Published: September 2014

Roughness on the surface of turbine blades induced by icing, dirt, erosion or manufacturing imperfections changes the aerodynamic configurations of wind turbines and reduces the power generation efficiency. In this work, a modified NACA0024 aerofoil is adopted to study effects of surface roughness on lift/drag forces. Three Reynolds numbers, 1000, 2000 and 5000 and a range of angles of attack [0°,20°] are studied. Since the magnitude of the roughness is small, it can be modelled as non-zero velocity boundary conditions imposed on the smooth surface without roughness. The flow with surface roughness can be therefore decomposed as the sum of a flow without roughness and a flow induced by roughness (or the velocity boundary conditions). The first flow can be obtained by solving the Navier-Stokes (NS) equation while the second one is governed by the linearized NS equation. Correspondingly the lift and drag forces acting on the aerofoil can be also decomposed as the sum of a force without considering roughness and a force induced by roughness. Instead of studying a particular type or distribution of roughness, we calculate the optimal roughness, which changes aerodynamic forces most effectively. This optimal roughness is obtained through a sensitivity study by solving an adjoint equation of the linearized NS equation. It is found that the optimal roughness with respect to both drag and lift forces is concentrated around the trailing edge and upper leading edge of the aerofoil and the lift is much more sensitive to roughness than the drag. Then the optimal roughness with a small magnitude is added to the smooth aerofoil geometry and this new geometry is tested through direct numerical simulations (DNS). It is found that the optimal roughness with a small magnitude (e-norm, defined as the square integration of the roughness around the surface, 0.001) induces over 10% change of the lift. Comparing the forces acting on the smooth surface and on the rough surface, it is noticed that the roughness changes the pressure force significantly while has little influence on the viscous forces. The pressure distribution is further inspected to study mechanisms of the effects of roughness on forces.
Assessment of Fracture Toughness and Fatigue Crack Growth Threshold of a Welded Joint Constituent of a Steam Turbine LP Rotor
Authors: Herman Shen M.-H. , Akanda Sajedur , Liu Xia , Wang Peng
Published: September 2014

In order to ensure safety and reliability of steam turbine welded rotors, the present investigation focuses on evaluation of crack initiation, growth, and resistance parameters of base metal (BM), weld metal (WM) and heat affected zone (HAZ) of a steam turbine rotor welded joint constituent. The experimental part consists of three-point bending conducted on single edge notch bend specimens to induce stable crack propagation. The crack size was calculated by incorporating the crack opening displacement measured by a clip-gage, in a compliance method. The fatigue crack threshold was obtained from a crack growth rate curve according to ASTM E647 and the fracture toughness was determined from a J-based resistance curve according to ASTM E1820. From the experimental results the fatigue crack threshold is found to be a function of loading ratio rather than a single material parameter. From the fracture toughness results, the WM and the BM are found to have similar KIc values whereas HAZ is found to have slightly better KIc values although HAZ had little crack extension during the experiments.
Simulation of Combustor/NGV Interaction Using Coupled RANS Solvers: Validation and Application to a Realistic Test Case
Authors: Insinna Massimiliano , Salvadori Simone , Martelli Francesco
Published: September 2014

Numerical techniques are commonly used during both design and analysis processes, mainly considering single components. Technological progress asks for advanced approaches that include real-machine conditions and analyze components interaction, especially considering the combustor/turbine coupling. Modern combustors operate with strong swirl motions in order to obtain an adequate flame stabilization, generating a very complex flow field characterized by high turbulence level. These aspects affect performance of downstream components which are subjected to very aggressive inlet flow conditions: non-uniform total temperature, non-uniform total pressure, swirl and high turbulence intensity. For these reasons coupled analysis of combustor and turbine is necessary to accurately predict aero-thermal aspects that influence performance and reliability of these two components.

From a numerical point of view the simulation of a single domain characterized by a reactive flow with very different Mach number regimes (from low-Mach flow in combustion chamber to transonic flow in turbine) is problematic due to the different numerical requirements needed, especially concerning stability and accuracy. These problems could be overcome using coupled methods to simultaneously simulate combustor and turbine in separated domains which are managed by different solvers that communicate with each other.

A coupling method for the study of combustor/turbine interaction using the RANS methodology is proposed. In the first part of the paper the method is described and validated. The second part is dedicated to the application of the proposed coupling methodology to a realistic test case consisting of a model annular combustor and the Nozzle Guide Vane (NGV) of the MT1 high-pressure turbine stage. A commercial solver and an in-house code are respectively used for the simulation of combustor and NGV.

Results are presented and analyzed highlighting the importance of such type of simulations in understanding aero-thermal phenomena that characterize combustor/vane interaction.
Determination of Particle Penetration Factors in a Particle Transfer Line for Aero Gas Turbine Engine Exhaust Particle Measurement
Authors: Altaher Mohamed A. , Li Hu , Williams Paul , Johnson Mark , Blakey Simon
Published: September 2014

There is a need to develop a reliable and standard PM (Particulate Matter) measurement method for aircraft engines. Due to safety and practicability of such measurements, a distance is required for the transportation of the exhaust samples from the aircraft engine exhaust exit to particle measurement instruments. The particle line loss during the transportation is therefore a critical issue for the accurate and reliable determination of particle emissions from aircraft engines. The work in this paper investigated the particle penetration/loss along a 25 meters ARP proposed particle sample transfer line by measuring the particle emissions from an aircraft auxiliary power unit (APU) at idle and full power. Two SMPS instruments were used to simultaneously measure exhaust particle size distributions at the entrance and exit of the 25 m transfer line. A catalytic stripper was used to remove volatile particles so that non-volatile particles can be measured. The particle penetration factors for the 25 m transfer line were found to be 0.6∼0.7 in general, excluding particles smaller than 10 nm. For the particles smaller than 10nm, particle penetrations were very poor and about 70–100% of parcel losses were observed. The volatile factions were roughly 20∼30% of the total concentrations.