bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Surface Curvature Effect Using LES for a Single Round Impinging Jet
Authors: Aillaud Pierre , Duchaine Florent , Gicquel Laurent , Didorally Sheddia
Published: August 2017

In this paper, wall resolved Large Eddy Simulation is used to study the effect of the surface curvature for two impinging jet configurations. The reference case is a single round jet impinging on a flat plate at a Reynolds number (based on the bulk velocity Ub and the pipe diameter D) Re = 23 000 and for a nozzle to plate distance H = 2D. The results on this configuration have been previously analyzed and validated against experimental results. This paper compares for the same operating point, the flat plate impingement to an impinging jet on a concave hemispherical surface with a relative curvature d/D = 0.089 where d is the concave surface diameter. Mean and Root Mean Square (RMS) quantities are compared to highlight differences and similarities between the two cases. In addition high order statistic such as Skewness of the temporal distribution of wall heat flux is analyzed. Probability density functions (PDF) are also built to further characterize the effect of surface curvature. It is shown that the surface curvature has a destabilizing effect on the vortical structures present in such a flow leading to a modification of the wall heat transfer compared to the flat plate case. The flow topology in the concave case is dominated by a large toroidal stationary vortex. This vortex generates a natural confinement that causes the increase of the mean temperature of the ambient air around the jet. The main effect is the reduction of the capacity of the vortical structures to enhance heat transfer. Finally, the confinement effect combined with the destabilization due to the concave curvature lead to an alleviation of the secondary peak in the Nusselt distribution and a reduction of the heat transfer at the wall.
Effects of Rotor Disc Growth on Flow and Heat Transfer Characteristics of Rim Seal
Authors: Jia Xingyun , Zheng Qun , Zhang Hai , Jiang Yuting
Published: August 2017

Under actual operating conditions of gas turbine, centrifugal and thermal growth of disc in radial direction result in dislocation of inflow boundary at the disc mid-radius height, and a radial step of platform at high radius height. In this paper, flow and heat transfer characteristics in dislocated rim seal region are analyzed by the conjugate and thermal mechanical numerical methods.

The calculated radial growths of turbine discs reach approximately 14–20 % of turbine platform structure thickness. Dislocation of rim seal structure directly affects the flow characteristic of externally-induced (EI) ingress and rotationally-induced (RI) ingress, and aggravates overheat of stator disc due to induced hot gas ingestion, further affects the loss of mixture of mainstream gas and cooling sealant air flow in rim-seal and wheelspace regions. Radial step between rotor and stator platforms exacerbates the area and depth of hot gas ingestion in seal clearance, along with a 2–7 % decrease in seal efficiency.
Prediction of Flammability Limits of Gas Mixtures Containing Inert Gases Under Variable Temperature and Pressure Conditions
Authors: Bounaceur Roda , Glaude Pierre-Alexandre , Sirjean Baptiste , Fournet René , Montagne Pierre , Vierling Matthieu , Molière Michel
Published: August 2017

Gas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations like maintenance, start-ups or fuel transfers, variable gas/air mixtures flow through the gas piping system and can cause damages in case of ignition. In order to properly control this risk of explosion and ensure safe operation, it is of the essence to have a good knowledge of the flammability limits of the gas mixtures involved, and to be in position to define safe inerting conditions every time it is required. While well-established methods are available in the engineering science to calculate flammability limits of fuel/air mixtures, no systematic methodology exists — to the authors’ knowledge — for the prediction of the Lower and Upper Flammability Limits (UFL-LFL) of gaseous blends containing variable amounts of inert components and over a large temperature and pressure range. The purpose of this study was then the evaluation of the LFL and UFL of multi-component fuels in air, in function of pressure, temperature and the concentrations of the most frequently used inerting gases, namely: nitrogen, carbon dioxide and steam. Different prediction criteria proposed in the literature were tested and eventually an original methodology based on the adiabatic flame temperature (Tad) was adopted as criterion and extended to gas mixtures and to high temperatures and pressures. Flame temperatures of different blends were calculated for different initial conditions assuming the access to the chemical equilibrium. Minimum temperature criteria corresponding to the Tad values reached at the LFL and UFL equivalence ratios were deduced from experimental data for each individual combustible molecule. It has been then possible to evaluate the minimum Tad values which ensure flame propagation of fuel blends on the lean and rich sides and to deduce the flammability limits. These calculations were repeated while adding various contents of the three selected inert gases. The methodology was validated by comparison against experimental data when available. The method proves to be simple, accurate, easy to use and applicable to large ranges of pressure, temperature and fuel compositions and to various diluents. The results confirm and quantify some well-known trends of flammability limits, e.g. their widening with increasing initial temperature and pressure, with a stronger effect on UFL than on LFL. The impact of the nature of the inerting gas was also successfully simulated for variable initial conditions and fuel compositions.
Comparison of Monte Carlo Methods Efficiency to Solve Radiative Energy Transfer in High Fidelity Unsteady 3D Simulations
Authors: Palluotto Lorella , Dumont Nicolas , Rodrigues Pedro , Koren Chai , Vicquelin Ronan , Gicquel Olivier
Published: August 2017

The present work assesses different Monte Carlo methods in radiative heat transfer problems, in terms of accuracy and computational cost. Achieving a high scalability on numerous CPUs with the conventional forward Monte Carlo method is not straightforward. The Emission-based Reciprocity Monte Carlo Method (ERM) allows to treat each mesh point independently from the others with a local monitoring of the statistical error, becoming a perfect candidate for high-scalability. ERM is however penalized by a slow statistical convergence in cold absorbing regions. This limitation has been overcome by an Optimized ERM (OERM) using a frequency distribution function based on the emission distribution at the maximum temperature of the system. Another approach to enhance the convergence is the use of low-discrepancy sampling. The obtained Quasi-Monte Carlo method is combined with OERM. The efficiency of the considered Monte-Carlo methods are compared.
Reconstruction and Analysis of the Acoustic Transfer Matrix of a Reheat Flame From Large-Eddy Simulations
Authors: Bothien Mirko , Lauper Demian , Yang Yang , Scarpato Alessandro
Published: August 2017

Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are, however, also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. An important ingredient of this analysis is the characterization of the flame response to acoustic fluctuations, which is straightforward for lean-premixed flames that are propagation stabilized, since it can be measured atmospherically. Ansaldo Energia’s GT26 and GT36 reheat combustion systems feature a unique technology where fuel is injected into a hot gas stream from a first combustor, which is propagation stabilized, and auto-ignites in a sequential combustion chamber. The present study deals with the flame response of mainly auto-ignition stabilized flames to acoustic and temperature fluctuations for which a CFD system identification approach is chosen.

The current paper builds on recent works, which detail and validate a methodology to analyze the dynamic response of an auto-ignition flame to extract the Flame Transfer Function (FTF) using unsteady Large-Eddy Simulations (LES). In these studies, the flame is assumed to behave as a Single-Input Single-Output (SISO) or Multi-Input Single-Output (MISO) system. The analysis conducted in GT2015-42622 qualitatively highlights the important role of temperature and equivalence ratio fluctuations, but these effects are not separated from velocity fluctuations. Hence, this topic is addressed in GT2016-57699, where the flame is treated as a multi-parameter system and compressible LES are conducted to extract the frequency-dependent FTF to describe the effects of axial velocity, temperature, equivalence ratio and pressure fluctuations on the flame response.

For lean-premixed flames, a common approach followed in the literature assumes that the acoustic pressure is constant across the flame and that the flame dynamics are governed by the response to velocity perturbations only, i.e., the FTF. However this is not necessarily the case for reheat flames that are mainly auto-ignition stabilized. Therefore, in this paper we present the full 2 × 2 transfer matrix of a predominantly auto-ignition stabilized flame and hence describe the flame as a Multi-Input Multi-Output (MIMO) system. In addition to this, it is highlighted that in presence of temperature fluctuations the 2 × 2 matrix can be extended to a 3 × 3 matrix relating the primitive acoustic variables as well as the temperature fluctuations across the flame. It is shown that only taking the FTF is insufficient to fully describe the dynamic behavior of reheat flames.
Mixed Acoustic-Entropy Combustion Instabilities in a Model Aeronautical Combustor: Large Eddy Simulation and Reduced Order Modeling
Authors: Lacombe Florent , Mery Yoann
Published: August 2017

This article focuses on Combustion Instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, outlet nozzle) while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, circular nozzle at the outlet). A Large Eddy Simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, Dynamic Mode Decomposition (DMD) is used to visualize, analyze and model the complex phasing between the different processes affecting the reacting zones. Using these data, a 0D modeling of the premixed flame and of the diffusion flame is proposed. These models provides an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.
Physics Based Dynamic Models of Three SOFC/GT Emulator Test-Rigs
Authors: Rossi Iacopo , Traverso Alberto , Hohloch Martina , Huber Andreas , Tucker David
Published: August 2017

This paper presents the development, implementation and validation of a simplified dynamic modeling approach to describe SOFC/GT hybrid systems in three real emulator test-rigs installed at University of Genoa (UNIGE, Italy), German Aerospace Center (DLR, Germany) and National Energy Technology Laboratory (NETL, USA), respectively. The proposed modeling approach is based on an experience-based simplification of the physical problem to reduce model computational efforts with minimal expense of accuracy. Traditional high fidelity dynamic modelling requires specialized skills and significant computational resources. This innovative approach, on the other hand, can be easily adapted to different plant configurations, predicting the most relevant dynamic phenomena with a reduced number of states: such a feature will allow, in the near future, the model deployment for monitoring purposes or advanced control scheme applications (e.g. model predictive control). The three target systems are briefly introduced and dynamic situations analyzed for model tuning, first, and validation, then. Relevance is given to peculiar transients where the model shows its reliability and its weakness. Assumptions introduced during model definition for the three different test-rigs are discussed and compared. The model captured significant dynamic behavior in all analyzed systems (in particular those regarding the GT) and showed influence of signal noise on some of the SOFC computed outputs.
Evaluation of Numerical Methods to Predict Temperature Distributions of an Experimentally Investigated Convection-Cooled Gas-Turbine Blade
Authors: Findeisen E. , Woerz B. , Wieler M. , Jeschke P. , Rabs M.
Published: August 2017

This paper presents two different numerical methods to predict the thermal load of a convection-cooled gas-turbine blade under realistic operating temperature conditions. The subject of the investigation is a gas-turbine rotor blade equipped with an academic convection-cooling system and investigated at a cascade test-rig. It consists of three cooling channels, which are connected outside the blade, so allowing cooling air temperature measurements.

Both methods use FE models to obtain the temperature distribution of the solid blade. The difference between these methods lies in the generation of the heat transfer coefficients along the cooling channel walls which serve as a boundary condition for the FE model. One method, referred to as the FEM1D method, uses empirical one-dimensional correlations known from the available literature. The other method, the FEM2D method, uses three-dimensional CFD simulations to obtain two-dimensional heat transfer coefficient distributions. The numerical results are compared to each other as well as to experimental data, so that the benefits and limitations of each method can be shown and validated.

Overall, this paper provides an evaluation of the different methods which are used to predict temperature distributions in convection-cooled gas-turbines with regard to accuracy, numerical cost and the limitations of each method. The temperature profiles obtained in all methods generally show good agreement with the experiments. However, the more detailed methods produce more accurate results by causing higher numerical costs.
Unsteady Pressure Measurement on Oscillating Blade in Transonic Flow Using Fast-Response Pressure-Sensitive Paint
Authors: Watanabe Toshinori , Azuma Toshihiko , Uzawa Seiji , Himeno Takehiro , Inoue Chihiro
Published: August 2017

A fast-response pressure-sensitive paint (PSP) technique was applied to the measurement of unsteady surface pressure of an oscillating cascade blade in a transonic flow. A linear cascade was used, and its central blade was oscillated in a translational manner. The unsteady pressure distributions of the oscillating blade and two stationary neighbors were measured using the fast-response PSP technique, and the unsteady aerodynamic force on the blade was obtained by integrating the data obtained on the pressures. The measurements made with the PSP technique were compared with those obtained by conventional methods for the purpose of validation. From the results, the PSP technique was revealed to be capable of measuring the unsteady surface pressure, which is used for flutter analysis in transonic conditions.
Experimental and Computational Study of the Effect of Momentum-Flux Ratio on High Pressure NGV Endwall Cooling Systems
Authors: Ornano Francesco , Povey Thomas
Published: August 2017

High pressure nozzle guide vane endwalls are often characterized by highly three-dimensional flows. The flow structure depends on the incoming boundary layer state (inlet total pressure profile) and the (static) pressure gradients within the vane passage. In many engine applications this can lead to strong secondary flows. The prediction and design of optimized endwall film cooling systems is therefore challenging, and a topic of current research interest.

A detailed experimental investigation of the film effectiveness distribution on an engine-realistic endwall geometry is presented in this paper. The film cooling system was a fairly conventional axisymmetric double row configuration. The study was performed on a large-scale, low-speed wind tunnel using infrared thermography. Adiabatic film effectiveness distributions were measured using IR cameras and tests were performed across a wide range of coolant-to-mainstream momentum-flux and mass flow ratios. Complex interactions between coolant film and vane secondary flows are presented and discussed. A particular feature of interest is the suppression of secondary flows (and associated improved adiabatic film effectiveness) beyond a critical momentum flux ratio. Jet lift-off effects are also observed, and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to three-dimensional, steady-state CFD simulations.

This paper provides insights into the effects of momentum flux ratio in establishing similarity between cascade conditions and engine conditions, and gives design guidelines for engine designers in relation to minimum endwall cooling momentum flux requirements to suppress endwall secondary flows.
On the Combination of Large Eddy Simulation and Phenomenological Soot Modelling to Calculate the Smoke Index From Aero-Engines Over a Large Range of Operating Conditions
Authors: Lamouroux Jean , Richard Stéphane , Malé Quentin , Staffelbach Gabriel , Dauptain Antoine , Misdariis Antony
Published: August 2017

Nowadays, models predicting soot emissions are, neither able to describe correctly fine effects of technological changes on sooting trends nor sufficiently validated at relevant operating conditions to match design office quantification needs. Yet, phenomenological descriptions of soot formation, containing key ingredients for soot modeling exist in the literature, such as the well-known Leung et al. model (Combust Flame 1991). This approach indeed includes contributions of nucleation, surface growth, coagulation, oxidation and thermophoretic transport of soot. When blindly applied to aeronautical combustors for different operating conditions, this model fails to hierarchize operating points compared to experimental measurements.

The objective of this work is to propose an extension of the Leung model, including an identification of its constants over a wide range of condition relevant of gas turbines operation. Today, the identification process can hardly be based on laboratory flames since few detailed experimental data are available for heavy-fuels at high pressure. Thus, it is decided to directly target smoke number values measured at the engine exhaust for a variety of combustors and operating conditions from idling to take-off. A Large Eddy Simulation approach is retained for its intrinsic ability to reproduce finely unsteady behavior, mixing and intermittency.

In this framework, The Leung model for soot is coupled to the TFLES model for combustion. It is shown that pressure-sensitive laws for the modelling constant of the soot surface chemistry are sufficient to reproduce engine emissions. Grid convergence is carried out to verify the robustness of the proposed approach. Several cases are then computed blindly to assess the prediction capabilities of the extended model. This study paves the way for the systematic use of a high fidelity tool solution in design office constraints for combustion chamber development.
Heat Transfer Analysis Over a Film Cooled Platform of a Vane Cascade With a Non-Uniform Inlet Flow
Authors: Barigozzi G. , Ravelli S. , Abdeh H. , Perdichizzi A. , Henze M. , Krueckels J.
Published: August 2017

This paper reports on heat transfer measurements performed on the film cooled platform of a linear nozzle vane cascade, subject to non-uniform inlet flow conditions. An obstruction, installed upstream of the cascade at different tangential positions, was responsible for inlet flow distortion. The platform cooling system included both purge flow from a slot located upstream of the leading edge and coolant ejection from a row of cylindrical holes located upstream of the slot. Testing was performed at inlet Mach number of Ma1 = 0.12 with both slot and combustor holes blowing at nominal conditions. Measured values of adiabatic film cooling effectiveness on the platform were used to obtain a detailed map of the convective heat transfer coefficient. The final goal was to compute the net heat flux reduction (NHFR), due to film cooling, when varying the relative position between obstruction and airfoil. Aligning the inflow non uniformity with the vane leading edge leads to a detrimental increase in the heat flux into the platform, within the vane passage. Conversely, positive NHFR values are observed over most of the platform surface if the inlet flow distortion is moved toward the suction side of the adjacent vane.
Analysis of Micro-Slip Properties for Models of Bladed Disc Friction Joints
Authors: Chen Junjie , Zang Chaoping , Zhou Biao , Petrov E. P.
Published: August 2017

In the turbo-machinery structures with joints the contact pressures at contact interfaces are usually high enough to ensure that the contacting components stay joined and the gross slip does not occur. Nevertheless, the small relative slip over parts of the contact interface, i.e. the micro-slip, contributes significantly to the vibration damping. In the high-fidelity analysis of practical bladed discs the macro-slip model cannot provide sufficient accuracy for the predictive analysis of the properties of the friction damping in the contact interfaces. In this article, numerical studies of micro-slip damping effects is performed using 2D and 3D models of blade root joints. Analysis of hysteresis loops is performed to assess the influence of modelling parameters: choice of reference points, mesh configurations and other physical parameters. The impact of physical parameters, such as the contact geometry, friction coefficient, contact stiffness and tangential and normal loading, on the friction damping are numerically examined. The numerical results give a new insight in the micro-slip friction damping effects.
Review of Hybrid Emissions Prediction Tools and Uncertainty Quantification Methods for Gas Turbine Combustion Systems
Authors: Yousefian Sajjad , Bourque Gilles , Monaghan Rory F. D.
Published: August 2017

There is a need for fast and reliable emissions prediction tools in the design, development and performance analysis of gas turbine combustion systems to predict emissions such as NOx, CO. Hybrid emissions prediction tools are defined as modelling approaches that (1) use computational fluid dynamics (CFD) or component modelling methods to generate flow field information, and (2) integrate them with detailed chemical kinetic modelling of emissions using chemical reactor network (CRN) techniques. This paper presents a review and comparison of hybrid emissions prediction tools and uncertainty quantification (UQ) methods for gas turbine combustion systems. In the first part of this study, CRN solvers are compared on the bases of some selected attributes which facilitate flexibility of network modelling, implementation of large chemical kinetic mechanisms and automatic construction of CRN. The second part of this study deals with UQ, which is becoming an important aspect of the development and use of computational tools in gas turbine combustion chamber design and analysis. Therefore, the use of UQ technique as part of the generalized modelling approach is important to develop a UQ-enabled hybrid emissions prediction tool. UQ techniques are compared on the bases of the number of evaluations and corresponding computational cost to achieve desired accuracy levels and their ability to treat deterministic models for emissions prediction as black boxes that do not require modifications. Recommendations for the development of UQ-enabled emissions prediction tools are made.
Heat Transfer Coefficients of Forward and Backward Cylindrical Hole Film Cooling Using Transient IR Technique
Authors: Shi Bo , Li Xueyang , Ren Jing , Jiang Hongde
Published: August 2017

Film cooling has been an effective method to protect the blade from hot gas. Recent studies have demonstrated that backward injection arrangement with cylindrical hole can achieve a much more uniform cooling effects under high blowing ratios, compared to forward injection which is commonly utilized. However, there has been relatively few results of heat transfer rate distribution with backward injections. The present experiment investigates a flat plate cooled with forward and backward coolant injection. Experiments are performed in a low speed wind tunnel. The test flat plate features cylindrical holes either along stream direction or reverse of it. Transient thermal measurements are carried out for the film cooling plate with IR camera. Detailed distributions of heat transfer coefficient are obtained. A series of blowing ratios from 0.25 to 2.0 are investigated. Effects of backward injection on the surface heat transfer distributions are studied, and the results are presented and explained in this investigation.
Correcting Turbocharger Performance Measurements for Heat Transfer and Friction
Authors: Schinnerl Mario , Ehrhard Jan , Bogner Mathias , Seume Joerg
Published: August 2017

The measured performance maps of turbochargers which are commonly used for the matching process with a combustion engine are influenced by heat transfer and friction phenomena. Internal heat transfer from the hot turbine side to the colder compressor side leads to an apparently lower compressor efficiency at low to mid speeds and is not comparable to the compressor efficiency measured under adiabatic conditions.

The product of the isentropic turbine efficiency and the mechanical efficiency is typically applied to characterize the turbine efficiency and results from the power balance of the turbocharger. This so-called ‘thermo-mechanical’ turbine efficiency is strongly correlated with the compressor efficiency obtained from measured data.

Based on a previously developed one-dimensional heat transfer model, non-dimensional analysis was carried out and a generally valid heat transfer model for the compressor side of different turbochargers was developed.

From measurements and ramp-up simulations of turbocharger friction power, an analytical friction power model was developed to correct the thermo-mechanical turbine efficiency from friction impact.

The developed heat transfer and friction model demonstrates the capability to properly predict the adiabatic (aerodynamic) compressor and turbine performance from measurement data obtained at a steady-flow hot gas test bench.
Development of the Supercritical Carbon Dioxide Power Cycle Experimental Loop With a Turbo-Generator
Authors: Cho Junhyun , Shin Hyungki , Cho Jongjae , Ra Ho-Sang , Roh Chulwoo , Lee Beomjoon , Lee Gilbong , Baik Young-Jin
Published: August 2017

KIER (Korea Institute of Energy Research) has developed three supercritical carbon dioxide power cycle test loops since 2013. After developing a 10 kWe-class simple un-recuperated Brayton cycle, a second sub-kWe small-scale experimental test loop was manufactured to investigate the characteristics of the supercritical carbon dioxide power cycle, for which a high speed radial type turbo-generator was also designed and manufactured. Using only one channel of the nozzle, the partial admission method was adopted to reduce the rotational speed of the rotor so that commercial oil-lubricated bearings can be used. This was the world’s first approach to the supercritical carbon dioxide turbo-generator. After several tests, operation of the turbine for power production of up to 670 W was successful. Finally, an 80 kWe-class dual Brayton cycle test loop was designed. Before completion of the full test loop, a 60 kWe axial type turbo-generator was first manufactured and our previous 10 kWe-class test loop was upgraded to drive this turbo-generator. Due to leakage flow through the mechanical seal, a make-up loop was also developed. After assembling all test loops, a cold-run test and a preliminary operation test were conducted. In this paper, the power generating operation results of the sub-kWe-class test loop and the construction of the tens of kWe-class test loop which drives an axial type turbo-generator are described.
Condition Monitoring of Combustion System on Industrial Gas Turbines Based on Trend and Noise Analysis
Authors: Zhang Yu , Martínez-García Miguel , Garlick Mike , Latimer Anthony , Cruz-Manzo Samuel
Published: August 2017

In this paper, a scheme of an ‘early warning’ system is developed for the combustion system of Industrial Gas Turbines (IGTs), which attains low computational workload and simple programming requirements, being therefore employable at an industrial level. The methodology includes trend analysis, which examines when the measurement shows different trends from the other measurements in the sensor group, and noise analysis, which examines when the measurement is displaying higher levels of noise compared to those of the other sensors. In this research, difficulties encountered by other data-driven methods due to temperature varying with load conditions of the IGT’s have also been overcome by the proposed approach. Furthermore, it brings other advantages, for instance, no historic training data is needed, and there is no requirement to set thresholds for each sensor in the system. The efficacy and effectiveness of the proposed approach has been demonstrated through experimental trials of previous pre-chamber burnout cases. And the resulting outcomes of the scheme will be of interest to IGT companies, especially in condition monitoring of the combustion system. Future work and possible improvements are also discussed at the end of the paper.
The Improvement of Air/Oil Separator Performance in the Aero-Engine Lubrication System
Authors: Yaguo Lyu , Jieyang Shen , Zhenxia Liu , Jianping Hu
Published: August 2017

Air/oil separator plays an important role in the aero-engine lubricating oil system, and connects oil cavity and atmospheric environment, where it is used to separate oil from oil-gas two-phase flow and reduce the consumption of lubricating oil. Oil-gas separation efficiency and flow resistance are two key performance parameters of the separator. This paper focuses on how to improve the separation efficiency of one certain air/oil separator, which has many venting holes, under the condition of keeping the stability of flow resistance. Based on the mathematical model, a large number of numerical calculations were carried out using the ANSYS-Fluent. The characteristics of oil-gas separation efficiency, flow resistance were achieved firstly, although the venting holes number changes from 4 to 15, but the holes total flow area is constant, under the same operate condition. In addition, the separation efficiency for single diameter oil droplet was also calculated when the venting holes number changes. The results show that increase the venting holes can effectively reduce the minimum oil droplets diameter which could be separated, improve the separation efficiency and maintain steady flow resistance at the same time. The result of this study may provide an idea or method for the optimization and improvement of Air/oil separator with similar structure.
A Comparison of Small-Scale Gas Turbine Control Schemes
Authors: Jaatinen-Värri Ahti , Backman Jari , Honkatukia Juha , Malkamäki Matti
Published: August 2017

Throughout the world there is pressure to increase distributed energy generation. Driving factors include for example political and environmental concerns in developed countries and reliability in places where centralized grid does not either exist or is too unreliable. The energy generation based on renewable fuels such as biogas is also usually decentralized. To answer this demand, the number of small-scale gas turbine combined heat and power (CHP) installations have increased. Due to its nature, the required power output of distributed generation is highly variable. The power output of decentralized power plant needs to follow the local consumption power need and thus it needs to be efficiently controlled. Therefore, the requirement for variable output necessitates that small-scale gas turbines are often run at part-loads.

Previously, most of the installed small-scale gas turbines have been single-spool units with either fixed or variable speed shafts. Control schemes and part-load performance are somewhat different for the two setups. Recently, a two-spool gas turbine where the spools can be controlled independently has been proposed as a feasible alternative. The possibility to produce the desired power output with two spools, both having their own generator, which can be controlled independently of each other, offers significantly more possibilities for the control. Therefore, it might also offer better part-load performance.

In this paper, the control schemes of three different small-scale gas turbines are compared. Especially, the part-load electrical efficiency is studied. The studied gas turbines are: a single-spool fixed speed, a single-spool variable speed driven, and a two-spool variable speed driven gas turbine. The part-load performance of different machines is studied and then compared against each other. Furthermore, some estimations are given on how the part-load performance of each machine fares against certain load profiles.
Two-Phase CFD-Calculations for the Design of Water-Based Turbine Cleaning Systems for Turbochargers
Authors: Fischer Magnus , Weickgenannt Ansgar
Published: August 2017

Turbochargers operated with heavy fuel oil are subjected to deposition of combustion residues on stator vanes, the turbine rotor and turbine casing. Without appropriate measures the turbine stage efficiency drops. Moreover, in severely contaminated turbine stages clogging of whole stator channels can occur, which results in unwanted turbine excitation and ultimately failure. To assure a constantly high level of efficiency and mechanical integrity turbochargers operated with critical fuels are equipped with an online turbine cleaning system that is based on the injection of water. The water is injected such that the whole stator is evenly wetted with water and ultimately cleaned.

The design of modern cleaning systems is based on two-phase computational fluid dynamics (CFD) simulations, where water-jets are tracked throughout the computational domain, commonly in a Lagrangian way. Multiple physical phenomena are considered, e.g. turbulent interaction with the gas phase and droplet break-up within the liquid spray, where the latter has a direct influence on spray penetration depth and finally the proper design of the cleaning system. This paper presents a validation of spray modeling in the relevant Weber and Reynolds number regime, with emphasis on the droplet break-up model. The numerical results are compared with LIF and laser diffraction measurements of the water spray in cross flow in terms of concentration and droplet size distribution. Finally, the validated and improved model is applied to re-calculate a real world application: the state-of-the-art cleaning system of a turbocharger again thoroughly validated against the test bench measurements.
Partial Admission, Axial Impulse Type Turbine Design and Partial Admission Radial Turbine Test for SCO2 Cycle
Authors: Shin Hyungki , Cho Junhyun , Baik Young-Jin , Cho Jongjae , Roh Chulwoo , Ra Ho-Sang , Kang Youngseok , Huh Jaesung
Published: August 2017

Power generation cycle — typically Brayton cycle — to use CO2 at supercritical state as working fluid have been researched many years because this cycle increase thermal efficiency of cycle and decrease turbomachinery size. But small turbomachinery make it difficult to develop proto type Supercritical Carbon dioxide (S-CO2) cycle equipment of lab scale size. KIER (Korea Institute of Energy Research) have been researched S-CO2 cycle since 2013. This paper is about 60kWe scale and sub-kWe class turbo generator development for applying to this S-CO2 cycle at the lab scale. A design concept of this turbo-generator is to use commercially available components so as to reduce development time and increase reliability. Major problem of SCO2 turbine is small volume flow rate and huge axial force. High density S-CO2 was referred as advantage of S-CO2 cycle because it make small turbomachinery possible. But this advantage was not valid in lab-scale cycles under 100kW because small amount volume flow rate means high rotating speed and too small diameter of turbine to manufacture it. Also, high inlet and outlet pressure make huge axial force. To solve these problem, KIER have attempt various turbines. In this paper, these attempts and results are presented and discussed.
Development of Efficient Compressors for Turbochargers
Authors: Ramachandran Dhinagaran , Mayandi Balamurugan , Krishnamoorthy Seran , Mani Gopalakrishnan , Ramesh Vasudevan , Lakshmanan Swathi Chitra
Published: August 2017

Automotive turbochargers play an important role in improving fuel economy, reducing emissions and improving drivability. Key to the improvement of the turbocharger performance is compressor efficiency. Compressors used in turbochargers are typically operated in a wide range of speed and flow. This wide operating range is a challenge to the design and improving the performance is often a fine balance between required efficiencies towards the surge, choke regions apart from having a comfortable speed margin for high altitude operations. In this study an existing compressor that best matched a 180hp commercial diesel engine application is chosen and its performance is further improved towards the lower flow region. Improvement is carried out through a set of designed experiments using a combination of Preliminary Design (PD) and Computational Fluid Dynamics (CFD) tools. Mechanical integrity of the wheel is ensured using Finite Element Analysis. A prototype is made out of the improved design and tested in an in-house gas stand. Predicted efficiency improvements are reflected in gas stand tests. Efficiency improvements in the lower flow range are observed over 7% while there is an acceptable drop (3.7%) near the peak power side. The improved compressor also shows higher part load efficiencies.
Aerodynamic Optimization Process for Turbocharger Compressor Impellers
Authors: Lotz R. D.
Published: August 2017

This paper presents the progression at BorgWarner Turbo Systems of the aerodynamic optimization process for radial turbocharger compressor impellers used in commercial vehicle applications. The design process was refined over several years, starting from relatively simple, single objective optimizations and moving to increasingly higher complexity with multiple operating points and objectives. CFD and numerical optimization techniques are used extensively with the aim of reducing costly gas stand testing with prototype hardware. Commercial software packages are used throughout for geometry definition, flow field evaluation, as well as an optimization scheduling providing genetic and gradient based algorithms. Design outcomes of the various developments were prototyped and tested at the BorgWarner Technical Center in Arden, NC. CFD predictions are compared with test data and discrepancies quantified. The resulting impeller designs show steady improvements with each design and methodology iteration, to the point that significant improvements in performance over conventional designs can be achieved consistently.
Wet Gas Compression: Test Conditions and Similitude
Authors: Mæland Dagfinn , Bakken Lars E.
Published: August 2017

Wet gas compression of gas/condensate/water provides a business opportunity for oil and gas producers. There are several opportunities of particular note: 1) As well tail-end production commences, the installation of sub-sea compressors will provide enhanced oil recovery and, if the subsea compressor is capable of handling liquids, the subsea process complexity can be dramatically reduced, thus decreasing capital investments and possibly operational costs. 2) Topside and Onshore projects can also be dramatically simplified. This is the case for both new installations and modification projects for which wet gas compression is a suitable solution.

However, there are several challenges that need to be addressed before wet gas compression, by means of centrifugal compressors, can be considered as a robust commercial solution for future projects. This relates to the robustness of the mechanical design, effects on electrical systems, and issues related to performance. This paper will focus on challenges related to performance prediction and testing.

For conventional dry gas compressor design, performance prediction is usually undertaken by the compressor manufacturer, utilising in-house know-how in impeller design and selection. This specialised knowledge is potentially unsuitable for predicting wet gas performance in the design phase; hence, a wet gas compressor design may not meet design requirements specified by the customer.

It is typical that agreements on performance testing of centrifugal compressors state that these are to be conducted according to an international standard such as ASME PTC10 or ISO 5389. These standards require that the compressed gas is dry.

However, for wet gas compressors, no such internationally established standards exist for performance evaluation. Several of the requirements stipulated in the standards are challenging to apply to wet conditions and they do not ensure similar conditions. Such parameters including the maximum permissible deviation in the specific volume ratio, Mach number and Reynolds number. It is clear that the path towards a standard for wet gas performance testing will require a substantial amount of effort in order to establish new requirements related to wet gas similarity. Based on wet gas compressor test experience, challenges and requirements related to low pressure inert fluid, compared with full pressure actual fluid tests, are analysed and discussed.
A Study of Power Production and Noise Generation of a Small Wind Turbine for an Urban Environment
Authors: Hays Andrew , Van Treuren Kenneth
Published: August 2017

Wind energy has had a major impact on the generation of renewable energy. While most research and development focuses on large, utility-scale wind turbines, a new application is in the field of small wind turbines in the urban environment. A major design challenge for these urban wind turbines is the noise generated during operation. This study examines the power production and the noise generated by two small-scale wind turbines tested in a small wind tunnel. Both rotors were designed using the Blade-Element Momentum Theory and either the NREL S823 or the Eppler 216 airfoils. Point noise measurements were taken using a 1/4” microphone at three locations downstream of the turbine: 16% of the diameter (two chord lengths), 50% of the diameter, and 75% of the diameter. At each horizontal location downstream of the turbine, a vertical traverse was performed to analyze the sound pressure level from the tip of the turbine blades down to the hub. The rotor designed with the Eppler 216 airfoil showed a 9% increase in power production and decrease of up to 7 dB(A).
Process Analysis of Selective Exhaust Gas Recirculation for CO2 Capture in Natural Gas Combined Cycle Power Plants Using Amines
Authors: Diego Maria Elena , Bellas Jean-Michel , Pourkashanian Mohamed
Published: August 2017

Post-combustion CO2 capture from natural gas combined cycle (NGCC) power plants is challenging due to the large flow of flue gas with low CO2 content (∼3–4%vol.) that needs to be processed in the capture stage. A number of alternatives have been proposed to solve this issue and reduce the costs of the associated CO2 capture plant. This work focuses on the selective exhaust gas recirculation (S-EGR) configuration, which uses a membrane to selectively recirculate CO2 back to the inlet of the compressor of the turbine, thereby greatly increasing the CO2 content of the flue gas sent to the capture system. For this purpose, a parallel S-EGR NGCC system (53% S-EGR ratio) coupled to an amine capture plant using MEA 30%wt. was simulated using gCCS (gPROMS). It was benchmarked against an unabated NGCC system, a conventional NGCC coupled with an amine capture plant (NGCC+CCS), and an EGR NGCC power plant (39% EGR ratio) using amine scrubbing as the downstream capture technology. The results obtained indicate that the net power efficiency of the parallel S-EGR system can be up to 49.3% depending on the specific consumption of the auxiliary S-EGR systems, compared to the 49.0% and 49.8% values obtained for the NGCC+CCS and EGR systems, respectively. A preliminary economic study was also carried out to quantify the potential of the parallel S-EGR configuration. This high-level analysis shows that the cost of electricity for the parallel S-EGR system varies from 82.1–90.0 $/MWhe for the scenarios considered, with the cost of CO2 avoided being in the range of 79.7–105.1 $/tonne CO2. The results obtained indicate that there are potential advantages of the parallel S-EGR system in comparison to the NGCC+CCS configuration in some scenarios. However, further benefits with respect to the EGR configuration will depend on future advancements and cost reductions achieved on membrane-based systems.
Simplified Ingestion Model Assessment for 1D Gas Turbine Engine Secondary Flow Network
Authors: Negi Ashish , Mirzamoghadam A. V. , Thamke Sushilkumar , Thangavel Balakrishnan
Published: August 2017

Modeling of hot gas ingestion in a gas turbine engine is critical because its accuracy directly affects performance as well as turbine durability. In this paper, ASU ingestion test rig data accompanied by its published ingress/egress discharge coefficients (Cdi and Cde , formulation) are used to propose a simplified 1D ingestion model embedded in the secondary air system software (Network). The proposed externally induced ingress model includes separate boundary nodes with equal static pressure in the annulus hub, and distinct circumferential pressure variation in the form of normalized annulus pressure at the hub (P1 – P1avg)/(P1max – P1min). The corresponding Cdi and Cde for the engine conditions are scaled based on rig-to-engine non-dimensional minimum purge, Cwmin where engine Cwmin uses the actual (P1 – P1avg)/(P1max – P1min) derived from previously published CFD data along with the effective rim-seal overlap clearance. The vane pitch integrated driving pressure difference at the hub for the ingestion used in the orifice model comes from an embedded saw-tooth assumption on the circumferential pressure profile. Recirculation of ingested hot gas from the upper rim cavity to the lower wheel space is considered by comparing the supplied purge flow to the rotating disc entrainment requirement. The proposed model is compared with another model based on constant Cdi / Cde ratio of 0.14 published by the University of Bath. Engine test data from a previously published engine configuration is used to assess the appropriate model for engine. The probability of failure in violating the lower rim cavity sealing effectiveness limit based on analysis of variation (AOV) was conducted under both formulations and the results are presented.