bluuebunny/crossref_metadata_2025 huggingface dataset:
Three Dimensional Design and Optimization of a Transonic Rotor in Axial Flow Compressors
Authors: Okui Hidetaka , Verstraete Tom , Van den Braembussche R. A. , Alsalihi Zuheyr
Published: May 2012

This paper presents a 3-D optimization of a moderately loaded transonic compressor rotor by means of a multi-objective optimization system. The latter makes use of a Differential Evolutionary Algorithm in combination with an Artificial Neural Network and a 3D Navier-Stokes solver. Operating it on a cluster of 30 processors enabled the optimization of a large design space composed of the tip camber line and spanwise distribution of sweep and chord length. Objectives were an increase of efficiency at unchanged stall margin by controlling the shock waves and off-design performance curve. First, tests on a single blade row allowed a better understanding of the impact of the different design parameters. Forward sweep with unchanged camber improved the peak efficiency by only 0.3% with a small increase of the stall margin. Backward sweep with an optimized S shaped camber line improved the efficiency by 0.6% with unchanged stall margin. It is explained how the camber line control could introduce the forward sweep effect and compensate the negative effects of the backward sweep. The best results (0.7% increase in efficiency and unchanged stall margin) have been obtained by a stage optimization that also considered the spanwise redistribution of the rotor flow and loading to reduce the Mach number at the stator hub.
Film Cooling Effectiveness Distribution on First-Stage Vane Endwall With and Without Leading-Edge Fillets: Part I—Effect of Leading Edge Geometry
Authors: Zhang Yang , Yuan Xin
Published: May 2012

The paper is focused on the effect of leading edge airfoil geometry on endwall film cooling. Fillets placed at the junctions of the leading edge and the endwall are used in investigation. Three types of fillet profiles are tested, and the results are compared with baseline geometry without fillet. The design of the fillet is based on the suggestion by previous literature data indicating that sharp is effective in controlling the secondary flow. Three types of sharp slope fillet with the length to height ratio of 2.8, 1.2 and 0.5 are made using stereo lithography (SLA) and assessed in the experiment. Distributed with the approximately inviscid flow direction, four rows of compound angle laidback fan-shaped holes are arranged on the endwall to form full covered coolant film. The four rows of fanshaped holes are inclined 30 deg to the endwall surface and held an angle of 0, 30, 45 and 60 deg to axial direction respectively. The fanshaped holes have a lateral diffusion angle of 10 deg from the hole-centerline and a forward expansion angle of 10 deg to the endwall surface. The Reynolds number based on the axial chord and inlet velocity of the free-stream flow is 3.5*105, and the testing is done in a four-blade cascade with low Mach number condition (0.1 at the inlet) while the blowing ratio of the coolant through the discrete holes varies from 0.4 to 1.2. The film-cooling effectiveness distributions are obtained using the PSP (pressure sensitive paint) technique, by which the effect of different fillet geometry on passage induced flow and coolant is shown. The present paper compares the film cooling effectiveness distributions in a baseline blade cascade with three similar blades with different leading edge by adding fillets. The results show that with blowing ratio increasing, the film cooling effectiveness increases on the endwall. For specific blowing ratio, the effects of leading edge geometries could be illustrated as follows. The baseline geometry provides the best film cooling performance near leading edge pressure side. As for the leading edge suction side, the best leading edge geometry depends on the blowing ratio. The longfillet is the more effective in controlling horseshoe vortex at low blowing ratio, but for the high blowing ratio shortfillet and mediumfillet are better.
Heat Transfer and Friction Factor in the Rib Roughened Blade Leading Edge Cooling Passage
Authors: Khalatov Artem A. , Dashevskyy Yuriy Y. , Pysmennyi Dmytro M.
Published: May 2012

This paper presents the results of heat transfer and surface friction factor numerical simulation in the blade internal cooling passage with trip strip turbulators of different configurations and rib coverage. The passage cross section shape is the equilateral triangle with rounded apex simulating the leading edge area. The leading edge wedge angle is 30 degrees, inner radius to passage hydraulic diameter ratio is 0.30; channel hydraulic diameter is 10 mm. Such geometric parameters are typical to a leading edge cooling passage of an actual gas turbine blade or vane. Totally six basic rib configurations have been studied including the continuous transverse ribbing (normal to bulk flow direction), V-shaped ribbing, inverted V-shaped ribbing, broken transverse ribbing, broken V-shaped ribbing, as well as helical ribbing (angled to the bulk flow direction). Three cases of the passage partial ribbing for the widely used transverse and V-shaped rib configurations have been also analyzed, and the smooth cooling passage of the same configuration and cross section have been studied for the reference comparison as well. The ribs geometrical parameters for all configurations are the same: a square cross section, rib height to channel hydraulic diameter ratio (blockage ratio) is 0.10; rib pitch (rib-to-rib spacing) is 10, angle of attack for V-shaped, inverted V-shaped and helical ribs is 45°. All calculations were carried out at the constant Reynolds number of 100 000 using commercial software package ANSYS CFX 11.0. The results presented in this paper include the heat transfer, surface friction, vortex structure analysis and thermal hydraulic performance evaluation.
Probabilistic Analysis of Gas Turbine Disk Multi-Crack Propagation
Authors: Cui Wei , Wang Jianjun
Published: May 2012

An approach of predicting probabilistic life of multi-source surface crack growth problem is described in the paper. Multi-source circumferential surface cracks occur occasionally on aircraft engine turbine disk. A serious of semi-elliptical cracks which located in a certain radius but different circumferential position on turbine disk was caused by low-cycle fatigue. The residual life should be predicted according to the damage tolerance design theory. A typical turbine disk was studied as a numerical example by using finite element method. The existing experimental result in literature shows that the surface crack propagates faster on circumferential direction than on axial direction, and the surface cracks are going to merge on circumferential direction, which made the multi-crack a closed ring crack. The experiment shows that the multi-cracks would merge into a 2/3 circle crack after certain number cycles which agrees the numerical simulation. Then the crack model was reasonable simplified to axial direction 2-D crack problem in meridian plane of turbine disk. This 2-D axisymmetric simplification significantly reduces the probabilistic analysis computational time. The randomness of materials, load and geometric imperfection is considered in sensitivity analysis by using response surface method. Then the probabilistic life is predicted by considering the major random variables of initial crack length and engine speed. The probabilistic life analysis result is also compared with the existing experimental results.
Limits on Morrow Mean Stress Correction of Manson-Coffin Life Prediction Models
Authors: Day W. David
Published: May 2012

Accurate prediction of crack initiation life is of critical importance in designing turbo-machinery. To improve this accuracy, more sophisticated prediction techniques are required. A large number of materials have shown a correlation between low cycle fatigue initiation life and strain range, as represented by the well-known Manson-Coffin equation. Testing has shown that tensile mean stress has a negative impact on life. This effect has been noted for many years when applied to high-cycle fatigue, resulting in the use of Goodman or Haigh diagrams to account for the impact of both stress range (and therefore strain range) and mean stress. Morrow proposed a methodology for accounting for mean stress in low cycle fatigue. Noting that as plasticity increases, the effect of mean stress decreases, the correction was applied only to the elastic strain versus life line. Use of the Morrow mean stress corrections improves the accuracy of life predictions, but there are limitations. The most significant of these limitations are situations in which the correction may be non conservative for high compressive mean stresses or very high tensile mean stresses. While a benefit from compressive mean stress is to be expected, at some point further increasing the compressive mean stress should have a negative impact on life. At very high tensile mean stresses near the material yield, the calculated impact of mean stress on life is non conservative. To overcome these limitations, the analyst may place limits on the acceptable range of R-ratios used based on actual test data, but this would do little more than highlight when the user is outside of his database limits. Alternatively a life system may be made in which mean stresses are conservatively expected to be tensile. Neither of these methods are useful for calculating different lives in compressive or tensile regimes. This difficulty is especially seen in bolted joints, which are subjected to high mean stresses and small stress amplitudes. A technique is proposed here in-which limits are placed on the mean stress correction, directly analogous to those used in the creation of so-called modified Goodman diagrams. This technique has been successfully applied at PSM to improve the accuracy of life prediction without increasing the risk of non conservatism. A review of some literature is made to show examples where this effect may be taking place. A small number of tests provide additional validation.
A Numerical Method for Turbulent Flows in Highly Staggered and Low Solidity Supersonic Turbine Cascades
Authors: Senoo Shigeki , Sakakibara Kazuya , Kudo Takeshi , Shibashita Naoaki
Published: May 2012

Two main problems are associated with conventional numerical methods for simulating turbulent flows in high-reaction-type supersonic turbine cascades near the tip of the last stage blade in a steam turbine: the large skewness of computational grids and treatments of boundary conditions when the shock waves hit boundaries. This paper presents a numerical method to deal with these issues. A grid generation technique which uses five-block structured grids has been developed. The orthogonality of the grid is good even for highly staggered and low solidity cascades. In addition, the grids are completely continuous at the boundary between the blocks and at the periodic boundaries. Both the gradient of the grid lines and the change rate of the grid widths connected smoothly. As a result, shock waves can be captured accurately and stably. The inflow and outflow boundary conditions based on the two-dimensional characteristic theory have been applied and diminished the spurious reflections and fluctuations of shock waves at both the inlet and outlet boundaries. Therefore the non-physical reflection does not affect the flow in the cascades. A low Reynolds number k-ε turbulent model has been proposed. Distance from a wall is not used as the characteristic length of turbulent flows so that the turbulent model can be applied to a wake and a separation flow. The validity of the numerical method was verified by comparisons of the pressure distributions on the blade, the loss coefficients, and flow angles with linear cascade experiments of transonic compressor cascades.
Film Cooling on Highly Loaded Blades With Main Flow Separation: Part 1—Heat Transfer
Authors: Gomes Reinaldo A. , Niehuis Reinhard
Published: May 2012

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and it reattaches at about half of the axial chord. In this zone film cooling rows are placed among others for reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses but increases in general heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to stronger heating of the blade. Film cooling should therefore take into account both: firstly a proper protection of the surface and secondly reduce aerodynamic losses diminishing the extension of the main flow separation. While experimental results of the adiabatic film cooling effectiveness were shown in previous publications, the local heat transfer is analyzed in this paper. Emphasis is also put in analyzing in detail the flow separation process. The tests comprise furthermore the analysis of the effect of different outlet Mach and Reynolds numbers and film cooling. In part two of this paper the overall film cooling effectiveness is addressed. Local heat transfer is still difficult to predict with modern numerical tools and this is especially true for complex flows with flow separation. Some numerical results with RANS and LES show the capability of a commercial solver in predicting the heat transfer.
Film Cooling on Highly Loaded Blades With Main Flow Separation: Part 2—Overall Film Cooling Effectiveness
Authors: Gomes Reinaldo A. , Niehuis Reinhard
Published: May 2012

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main targets of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and it reattaches at about half of the axial chord. In this zone film cooling rows are placed among others for reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses but increases in general heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to stronger heating of the blade. Film cooling should therefore take into account both: firstly a proper protection of the surface and secondly reduce aerodynamic losses diminishing the extension of the main flow separation. The overall effectiveness of film cooling for a real engine has to combine heat transfer with film cooling effect. In this paper the overall effectiveness of film cooling, combining results from measurements of the adiabatic film cooling effectiveness and the local heat transfer coefficient are shown. The tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers at engine relevant values and film cooling ratio. A new parameter is introduced which allows to evaluate the effect of film cooling accounting at the same time for the change of local heat transfer coefficient. To the authors’ opinion this parameter allows a better, physically based assessment than the strategy using the so-called heat flux ratio. A parameter study is carried out in order to benchmark the effect of changes of the blade design.
Experimental and Numerical Research of Fan Bypass Duct Flows in Japanese Environmentally Compatible Engine for Small Aircraft Project
Authors: Ooba Yoshinori , Murooka Takeshi , Yamane Takashi , Nozaki Osamu , Ishiyama Takeshi
Published: May 2012

This research aims at developing fan integration technologies to improve the installation loss due to the fan/OGV/strut/pylon interaction of gas-turbine engines for small aircraft on Small Aircraft Project in Japan (the ECO Engine Project). Researches on experimental measurement using fan rig testing and numerical prediction using unsteady CFD analysis are conducted. The UPACS code which is developed by JAXA is used in order to accurately simulate the phenomena which occur in the interaction between a rotating fan and its downstream obstacles like strut/pylon in the fan duct. The accuracy of the CFD simulation is also validated by the measured data acquired in the rig testing. Through the investigations, its interaction mechanisms are clarified and the reducing technologies of such interaction for small aircraft engines are created. In the paper, the achievement of the improved aerodynamic performance by introducing the new concept of the long nose shaped fat pylon L/E are demonstrated.
Simulation of Blade Casing Interaction Phenomena in Gas Turbines Resulting From Heavy Tip Rubs Using an Implicit Time Marching Method
Authors: Williams Robin J.
Published: May 2012

Severe rubs between gas turbine blades and engine casings can in extreme cases result in damaging blade vibration levels and rapid loss of casing lining material. Even for more minor rubs, the wear in the lining material will result in increase tip gaps and a consequent loss in efficiency. Major rub events are extremely rare in practice, and there is seldom any useful diagnostic evidence of the root cause of the behaviour. Moreover, traditional analysis methods are not suitable for exploring the wide range of potential conditions under which an unstable vibration response might be initiated. A new modelling technique has been developed for modelling blade casing rubs which includes a detailed model of the interaction with liner wear. The method is time based, but is very efficient, enabling a wide range of initiating conditions to be explored. A series of examples have been developed to firstly: demonstrate the method is robust and reliable, and secondly: to investigate potential interaction phenomena under representative simulated conditions. The method has been applied to a real blade example, for which severe wear is known to have occurred. The method predicts that instability may occur above a threshold level of tip rub severity, and also demonstrates the improvement in an alternative blade design for which rub tolerance is known to be superior.
An Optimization Procedure for the Aerodynamic Model Tuning of Centrifugal Compressor Stages
Authors: Svensdotter Susanne , El Shamy Omar , Ghizawi Nidal , Michelassi Vittorio , Sankaran Sivasubramaniyan
Published: May 2012

This paper presents an automated optimization procedure for tuning and optimizing the performance parameters of centrifugal compressor stages in order to improve the accuracy of a 1D performance prediction tool and performance database. An in-house, well-validated 1D tool is used to predict the performance of centrifugal compressor stages. The stages are usually tested under similitude conditions in order to verify the predicted performance with the experimental data. Continuous improvements have been done on the tool to improve its accuracy, but the tuning to test data is still done manually and separately for each tested design flow coefficient. As a further leap in this activity, an in-house developed optimization code (PEZ) is interfaced with the 1D prediction tool to provide the best possible solution within the given tuning limits. This provides the possibility to use an extended number of tuning parameters and to tune the entire design family simultaneously, thereby ensuring a smooth evolution of the tuning parameters within the database. The optimization plan consists of a Differential Evolution (DE) genetic algorithm followed by a simplex-based optimization method (AMOEBA) with an objective of reducing the Root Mean Square (RMS) value of the error with the specified constraints. The procedure was successfully challenged with several families of similar stages but with various design corrected mass flows, by setting different objective/constraints combinations. The Optimizer was able to reduce the total RMS value of the error by approximately 80% with respect to the baseline for one of the recently tuned families. The result is a minimal deviation between predicted and experimental data for entire families, as well as a significant time reduction compared to the previous tuning methodology.
Numerical Predictions of Rotating Stall in an Axial Multi-Stage-Compressor
Authors: Peng Caetano
Published: May 2012

This paper describes a numerical investigation of rotating stall in an axial multi-stage compressor using an in-house CFD (Computational Fluid Dynamics) based aeroelasticity code. This study investigates the effects of VSV (variable stator vanes) schedule on the occurrence of rotating stall at engine part-speed. Moreover, the effects of VSV circumferential mis-stagger angles (e.g. vane stagger angle variation) on the inception of rotating stall are also investigated. Virtual pressure probes are used here in the CFD models to extract unsteady pressure levels at locations of interest. These numerical studies have also enabled to evaluate the blade peak displacements due to rotating stall and hence to predict the blade vibration levels. In general, the numerical results would appear to be in line with past experience from rig and development engine data.
Effects of Orientation and Position of the Combustor-Turbine Interface on the Cooling of a Vane Endwall
Authors: Thrift A. A. , Thole K. A. , Hada S.
Published: May 2012

First stage, nozzle guide vanes and accompanying endwalls are extensively cooled by the use of film cooling through discrete holes and leakage flow from the combustor-turbine interface gap. While there are cooling benefits from the interface gap, it is generally not considered as part of the cooling scheme. This paper reports on the effects of the position and orientation of a two-dimensional slot on the cooling performance of a nozzle guide vane endwall. In addition to surface thermal measurements, time-resolved, digital particle image velocimetry (TRDPIV) measurements were performed at the vane stagnation plane. Two slot orientations, 90° and 45°, and three streamwise positions were studied. Effectiveness results indicate a significant increase in area averaged effectiveness for the 45° slot relative to the 90° orientation. Flowfield measurements show dramatic differences in the horseshoe vortex formation.
Power Output Increase due to Decreasing Gas Turbine Inlet Temperature by Mist Atomization
Authors: Agata Yukiko , Akabayashi Shinichi , Ishikawa Shinya , Matsumura Yuji
Published: May 2012

Decreases in inlet mass flow due to rises in ambient temperature during the summer lead to a decrease in the power output of gas turbines. In order to recover lost output, this study employed a mist atomization system using efficient spray nozzles, developed mainly as a technology for urban heat-island mitigation, installing the system in an inlet air flow path of a gas turbine at Higashi-Niigata thermal power station No.4 train, a commercial plant. The nozzles can efficiently decrease inlet air temperature of gas turbines because of their minute atomized mist size and highly-efficient evaporation properties. A flow path in the upstream of the inlet filter was used for mist evaporation by the system. This path is unique to the power plant, and is intended to prevent snow particles from direct entry. Model and field tests to confirm safe and effective operation of the system developed were performed in order to address possible concerns associated with the introduction of this system. As a basic consideration, wind tunnel experiments using nozzles were performed. Through the experiments, the most suitable nozzles were chosen, and effectiveness of the mist atomization was evaluated. The basic specifications of the system were determined from the evaluation results. At the same time, flow-field in the inlet air channel of the intended gas turbine was analyzed, and positioning of the atomization devices optimized. The mist atomization system that was developed was installed in a gas turbine at the power plant. To prevent excessive atomization from possibly causing erosion, a target value of 95% humidity at the compressor inlet was set, and a thermo-hygrometer was installed downstream of the inlet silencer to monitor humidity. As a result of the operation, no signs of erosion were detected in a major inspection conducted about one year following the introduction of the system. Another concern had to do with immediate changes in the state of the gas turbine due to mist atomization stoppages. To evaluate effects of the stoppages, field tests in the plant were performed, resulting in no significant changes in turbine inlet temperature and exhaust gas temperature. Combustion pressure oscillations was also not observed. From these results, it has been confirmed that the system can be operated safely. After activating the atomization system, inlet temperature decreased by up to about 7.5 degrees Celsius and power output increased by up to 13 MW in the gas turbine.
The NEKOMIMI Cooling Technology: Cooling Holes With Ears for High-Efficient Film Cooling
Authors: Kusterer Karsten , Elyas Anas , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo , Kazari Masahide
Published: May 2012

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter-rotating vortices (CRV) in the cooling jets and lead to jet lift-off effects. Thus, the film-cooling effectiveness is reduced soon behind the cooling air ejection through the holes. Due to that basic understanding, different technologies for improving film cooling have been developed. Some of them focus on establishing anti-counter-rotating vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the double-jet film cooling (DJFC), invented by the authors, where the special arrangement of two cylindrical holes lead to a cooling jet with such an anti-vortex system. However, beside the advantage that the holes are simple cylindrical holes, one disadvantage is that appropriate supply with cooling air for both holes is sometimes difficult to be established in real configurations. Thus, the authors have followed the idea to transfer the original double-jet film cooling principle to a special configuration with merged holes. Thus, in that case only one air supply is necessary but the anti-vortex effect has been preserved. The derived cooling technology has been named NEKOMIMI technology. The paper explains the principle of that technology. Results from experimental investigations including film cooling effectiveness measurements for the new technology are presented. The results are compared to conventional cooling hole configurations showing the tremendous positive effect in reaching highest film cooling effectiveness for the new configuration at M = 1.5 and partly for M = 1. Numerical investigations for the M = 1.5 case indicate that the existence of the ACRV is the likely reason for the enhanced cooling performance of the new configuration.
Real-Time Simulation of an Experimental Rig With Pressurized SOFC
Authors: Pezzini Paolo , Caratozzolo Francesco , Traverso Alberto
Published: May 2012

The availability of reliable simulation models can reduce the time required for commissioning test rigs as well as preventing components from suffering serious damage during testing. The aim of this study is to set up and validate, against experimental data, a real-time model referring to the Rolls-Royce Fuel Cell System Limited (RRFCS) hybrid system concept, based on SOFCs. The dynamic model of the SOFC “block” has been developed, run in real-time, and successfully validated against experiments. Initially, the dynamic evolution of the model is considered under constant inputs at steady-state and is compared against experimental data; secondly, transient behaviour is also considered. Step variations of the main air flow, main fuel flow, syngas flow and electrical current were performed. The model can now be employed to carry out the following: performance analysis, design verification, development of control strategies, on-line analysis and integration with Human Machine Interface.
Evaluation of the Performance of a Sirocco Fan Driven by a Diesel Engine in Mist Sprayer Applications
Authors: Bettocchi Roberto , Morini Mirko , Pinelli Michele
Published: May 2012

The coupling of a sirocco fan, used to supply air to a mist sprayer, and a Diesel engine is studied in order to enhance the performance of the integrated system. In this case, the main problem for the correct design of the fan arises from the fact that it is not possible to define a priori the operating point. In fact, the rotational speed is not fixed as in the case of an electric motor driven fan, but is determined as an equilibrium of the power supplied by the engine and the power absorbed by the fan to recover the pressure drops of the mist sprayer system. In this paper, the experimental campaign performed to characterize the existent fans is presented. Moreover, the sprayer duct is characterized by using literature correlations and by performing numerical simulations. Then, the collected data are elaborated in order to scale the fans in order to enhance the performance of the system.
A High Performance Low Pressure Ratio Turbine for Engine Electric Turbocompounding
Authors: Mamat Aman M. I. , Padzillah Muhamad H. , Romagnoli Alessandro , Martinez-Botas Ricardo F.
Published: May 2012

In order to enhance energy extraction from the exhaust gases of a highly boosted downsized engine, an electric turbo-compounding unit can be fitted downstream of the main turbocharger. The extra energy made available to the vehicle can be used to feed batteries which can supply energy to electric units like superchargers, start and stop systems or other electric units. The current research focuses on the design of a turbine for a 1.0 litre gasoline engine which aims to reduce the CO2 emissions of a “cost-effective, ultra-efficient gasoline engine in small and large family car segment”. A 1-D engine simulation showed that a 3% improvement in brake specific fuel consumption (BSFC) can be expected with the use of an electric turbocompounding. However, the low pressure available to the exhaust gases expanded in the main turbocharger and the constant rotational speed required by the electric motor, motivated to design a new turbine which gives a high performance at lower pressures. Accordingly, a new turbine design was developed to recover energy of discharged exhaust gases at low pressure ratios (1.05–1.3) and to drive a small electric generator with a maximum power output of 1.0 kW. The design operating conditions were fixed at 50,000 rpm with a pressure ratio of 1.1. Commercially available turbines are not suitable for this purpose due to the very low efficiencies experienced when operating in these pressure ranges. The low pressure turbine design was carried out through a conventional non-dimensional mixed-flow turbine design method. The design procedure started with the establishment of 2-D configurations and was followed by the 3-D radial fibre blade design. A vane-less turbine volute was designed based on the knowledge of the rotor inlet flow direction and the magnitude of the absolute speed. The overall dimensions of the volute design were defined by the area-to-radius ratios at each respective volute circumferential azimuth angle. Subsequently, a comprehensive steady-state turbine performance analysis was performed by mean of Computational Fluid Dynamics (CFD) and it was found that a maximum of 76% of total-static efficiency ηt-s can be achieved at design speed.
Experimental Investigation of Lubrication Oil Film Dynamics in a Typical Aero-Engine Bearing Chamber Environment
Authors: Hashmi Amir A. , Dullenkopf Klaus , Bauer Hans-Jo¨rg , Klingsporn Michael
Published: May 2012

This paper deals with the wall film dynamics of lubrication oil in the vicinity of the scavenge port of a typical aero engine bearing chamber. Based on the major driving forces influencing the film dynamics, shear forces and gravity, two film flow regimes namely co & counter-current can be identified. The film flow in the bearing chambers is influenced by several factors which results in an undeveloped film thus making a comprehensive analysis of the flow field extremely difficult. A profound knowledge of the individual factors is required before a superposition can be performed. A simple test rig was designed and built to isolate and investigate the influence of major factors affecting the wall film dynamics in a typical bearing chamber environment. For the quantitative analysis, a parameter determined from the single phase pressure drop measurements (only in gas) is introduced to effectively analyze the undeveloped multiphase flow regime. It is shown that the momentum losses occurring in the counter-current regime become considerably greater than in the co-current regime when the shearing gas flow rate is increased beyond a certain value. For high gas flow rates (high shaft speeds in engine) the losses on the counter-current side (churning losses) can be several magnitudes larger than on the co-current side (no churning losses). It is also shown that for the conditions investigated and relevant to the bearing chamber, the possibility of waveforms leading to the droplet shedding on the co-current side is very unlikely. Significant droplet shedding occurs in the counter-current regime. Based on the results obtained, the possible characteristics of the near scavenge oil film in the absence of coexisting phenomena e.g. droplet interaction, offtake disturbances etc are outlined.
Development and Strategy for A-USC Steam Turbine Cycle
Authors: Okita Nobuo , Sasaki Takashi , Suga Takeo , Iwai Shogo
Published: May 2012

Efficiency improvement of thermal power plants is one of the key technologies to protect the global environment because of lower emission gas. There are many approaches in this regard, which are investigated and developed around the world. Thermal efficiency of fossil power plants has been improved by raising steam temperature as high as 620 C in a realization of Ultra Super Critical (USC) steam turbine system. In order to enhance the thermal efficiency further, we are developing the Advanced Ultra Super Critical (A-USC) steam turbine system using high pressure and high temperature steam of 700 C or over 700 C. The main focus of the Research & Development of A-USC steam turbine is the verification of the alloys for the large rotor, casing and valve components, and the main issue for application to the power plant is an economical aspect and field of technology for the realization of such steam conditions with cost-effectiveness, for instance, optimization of cycle heat balance, turbine design, welding technology and so on. This paper describes briefly about R&D results of A-USC steam turbine and suggests an economical strategy in order to make it possible to be realized sooner.
Numerical Analysis of a Microturbine Combustion Chamber Modified for Biomass Derived Syngas
Authors: Laranci Paolo , Bursi Edoardo , Fantozzi Francesco
Published: May 2012

A CFD analysis was carried out to study the performance of a modified combustion chamber of a micro gas turbine with the objective to change its fuelling from natural gas to biomass pyrolysis gas. The micro gas turbine is a component of a pilot IPRP (Integrated Regenerated Pyrolysis Plant), a distributed energy system, based on a rotary kiln reactor for the pyrolysis of biomass. This paper describes the combustion process occurring inside the combustion chamber of the micro gas turbine. In particular, a new, revised kinetic scheme was implemented in the RANS analysis to better reproduce CO oxidation and flue gases temperature, for both methane and pyrolysis gas combustion; further investigation was undertaken on NOx formation mechanisms, which are now modeled through a non-adiabatic PPDF approach, also taking into account the effects of turbulence interaction. CFD simulations for natural gas and pyrolysis gas combustion were performed for two different annular rich-quench-lean combustion chamber configurations, one with the original design for natural gas and one with a modified design optimized for syngas, in order to quantify the advantage of using a dedicated design. Furthermore, through the numerical analysis, the hot spots of the combustor have been identified and monitored the to study the possible effects of material corrosion due to high temperatures.
Rotordynamic Force Coefficients for Three Types of Annular Gas Seals With Inlet Preswirl and High Differential Pressure Ratio
Authors: Ertas Bugra H. , Delgado Adolfo , Vannini Giuseppe
Published: May 2012

The following paper presents and compares rotordynamic force coefficients for three types of non-contact annular gas seals, which include a labyrinth (LABY), honeycomb (HC), and a fully partitioned damper seal (FPDS). These three annular seals represent the typical seal types used in process gas centrifugal compressors at the balance piston location or center seal location to limit internal leakage and ensure a robust rotordynamic design. Tests were conducted on 170.6mm (6.716 in) diameter seals for rotor speeds up to 15kprm, inlet air pressure of 6.9 bar (100 psi), ambient back pressure, and with inlet gas preswirl. The three seals were designed to have the same nominal clearance and similar axial lengths. Testing was conducted on a controlled motion test rig possessing non-synchronous excitation capability up to 250Hz. Three different test methods were employed to give confidence in the rotordynamic coefficients, which include static force deflection tests, mechanical impedance tests, and dynamic cavity pressure tests. Results from experiments compare force coefficients for all seal configurations while paying special attention to the cross-over frequencies of the effective damping term. All seals possessed negative effective damping at lower excitation frequencies with inlet preswirl, where the straight-through FPDS possessed the lowest cross over frequency of 40Hz at 15krpm. The testing also revealed that the preswirl parameter had significantly more influence on effective damping levels and cross-over frequencies when compared to rotor speed.
A High Temperature High Bandwidth Fast Response Total Pressure Probe for Measurements in a Multistage Axial Compressor
Authors: Mersinligil Mehmet , Brouckaert Jean-Franc¸ois , Courtiade Nicolas , Ottavy Xavier
Published: May 2012

Over the last decades, fast response aerodynamic probes have been recognized as a robust measurement technique to provide time-resolved flow field data in turbomachinery environments. Still, most of the existing probe designs are restricted to low temperature applications (< 120 °C) either because of sensor temperature range limitations or packaging issues. Measurements in turbomachines also require a small probe size often with a very high bandwidth which are conflictual constraints difficult to satisfy simultaneously. This contribution therefore presents the development of a novel miniature (O̸ 2.5 mm) high temperature single sensor total pressure probe, designed for operation up to 250 °C with a very high bandwidth of 250 kHz. The probe main element is a 1.7 mm diameter commercial piezoresistive transducer placed in a Pitot type arrangement with a flush mounted sensor to provide the highest bandwidth. The details of the probe design are presented as well as the probe calibrations in pressure and in temperature. The effects of using a thermal compensation module or a sense resistor to monitor the temperature drift are described in the context of measurement uncertainty. The probes were characterized in terms of aerodynamic characteristics versus flow angle and Mach number. Shock tube tests have shown a dynamic response of the probe with sensor resonance frequencies well over 300 kHz, with a flat frequency range up to 250 kHz. Two probe prototypes were manufactured and first used in the 3 1/2-stage high speed axial compressor CREATE of the LMFA at E´cole Centrale de Lyon in France. The probes were traversed at each inter blade row plane up to temperatures of 180 °C and absolute pressure of 3 bar. The probe was able to resolve the high blade passing frequencies (∼16 kHz) and several harmonics including rotor-stator interaction frequencies up to 200 kHz. Besides the average total pressure distributions from the radial traverses, phase-locked averages and random unsteadiness are presented. The probe spatial and temporal resolutions are discussed in the context of those results.
Evaporation of Volatile Liquid Pools Under Forced Convection: Experimental Approach for Multi-Component Liquids and Validation of a Vaporization Model
Authors: Alonso Dominique , Genin Ghislain , Heller David , Chabrier Brice , Molie`re Michel
Published: May 2012

The evaporation of pools of volatile liquids under dynamic conditions is gaining interest as an engineering subject. Indeed there is an increasing need to optimize the control of thermal or chemical processes and to cope with more and more stringent Environmental, Health and Safety (EHS) regulations applicable to the handling of hazardous liquids, especially those relating to stationary gas turbine installations. A specific issue, tied with flammable substances, comes from the fact that the transition from a flame to an explosion is not sufficiently well controlled due to the difficulty in modeling complex installations. Therefore, the current approach used to address explosion risks consists in quantifying the flux of vapors emitted by the pool and evaluating the mechanical effect entailed by a potential ignition of the flammable cloud generated. It is therefore of paramount importance to accurately know, under variable vaporizing conditions, how much of the volatile matter is extracted by the ventilation stream from the liquid pool and how these vapors get diluted downstream of the source. A survey of the literature shows that while pool evaporation of water has been extensively covered by experimentation, most organic liquids including hydrocarbons, alcohols, ethers, etc. have been insufficiently studied. In order to fill this gap, the authors have combined an experimental approach enabling to quantify the source of vapors with a dedicated Computational Fluid Dynamics (CFD) approach describing the mixing/dilution phenomena in the gas phase. This dual approach has proved very fruitful as it leads to realistic spatial distributions of the species downstream of the source. Therefore it has been utilized to develop experimentally verified data for the evaporation rate of single and multicomponent liquids. This paper presents the original experimental rig developed to quantify the vaporization rates. The elaboration of the CFD model and the results obtained when coupling both approaches will be the matter of a next paper.
Operating Experience on Advanced Technology AE64.3A Gas Turbine
Authors: Bonzani Federico , Silingardi Andrea , Traversone Laura , Di Pasquale Luigi
Published: May 2012

The growth of power markets stresses the importance of optimizing power plant performance and boosts the need to improve and upgrade the existing power generation plants. In this framework, Gas Turbine with medium power output are regarded as strategic asset to gain competitiveness in energy business. In such a challenging scenario, the current version of the 50/60 cycles AE64.3A Gas Turbine has been upgraded by Ansaldo Energia, enhancing performances, operational and dynamic features. Therefore the unit is rated now 75 Mwe power output and 35.9% efficiency. The upgraded AE64.3A along with the relevant generator and auxiliary systems in single shaft configuration, has been installed in the combined cycle generation plant of Vlore, on the Adriatic coast of Albania. The gas turbine has been supplied in accordance to the standard and proven design of the manufacturer, optimizing the need for burning fuel oil in continuous operation. The paper will report the main feature of the engine highlighting the upgrade and present the operational experience gained during the commissioning phase.
CFD Aerodynamic Performance Validation of a Two-Stage High Pressure Turbine
Authors: Sridhar Murari , Sunnam Sathish , Goswami Shraman , Liu Jong S.
Published: May 2012

In the continual effort to improve analysis and design techniques, Honeywell is investigating on the use of CFD to predict the aerodynamic performance of a high pressure turbine. The present study has a two fold objective. The first objective is to validate the commercially available CFD codes for aerodynamic performance prediction of a two-stage high pressure turbine at design and off-design points. The other objective is to establish guidelines to help the designer to successfully.set-up and execute the suitable CFD model analysis. The validation to model the stage interfaces is performed with three different types of approaches such as Mixing Plane approach, Frozen Rotor approach and NonLinear Harmonic approach. The film holes on the blade surface, hub and the shroud walls are modeled by using source term cooling and actual film hole modeling techniques for all the analysis. The validation is accomplished with the test results of a two-stage high pressure turbine, Energy Efficient Engine (E3). The aerodynamic performance data at a design point and typical off-design point are taken as test cases for the validation study. One dimensional performance parameters such as corrected mass flow rate, total pressure ratio, cycle efficiency along with two dimensional spanwise distribution of total pressure, total temperature which are obtained from CFD results are compared with test data. Flow field results are presented to understand the aerodynamic behavior.
Imbalance Response of a Rotor Supported by Hybrid Air Foil Bearings
Authors: Kim Daejong , Shetty Prajwal , Lee Donghyun
Published: May 2012

Air foil bearings (AFB’s) are widely used in small to midsized turbomachinery. They are simple in construction, offer very low drag friction, and have very high reliability at high speed operations. This paper presents experimental imbalance response of a 4.84 kg rigid rotor (operating below bending critical speed) supported by two hybrid air foil bearings with 50 mm in diameter. The concept of “hybrid” in this paper utilizes the hydrostatic augmentation of the load capacity during the start up and shut down. The hybrid air foil bearings were designed with three top foils for enhanced stability. Imbalance responses in cylindrical mode are presented up to 44,000rpm with different supply pressures. As the supply pressure is increased from 2.67 to 4 bar, the bearing stiffness increases slightly, resulting in slightly larger vibration (and reduced damping ratio) during the trans-critical speed operation. Hydrodynamic instability was observed with whirl frequency ratios of about 0.17∼0.2 depending on the supply pressures. Tests were also conducted to investigate the effect of supply pressure on the rotordynamic stability. The test results show that the hybrid operation is very effective to suppress the subsynchronous vibrations at high speeds.