bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Validation of the Asymptotic Mistuning Model Using a High Fidelity Bladed Disk Model
Authors: Khemiri Oualid , Martel Carlos , Corral Roque
Published: January 2011

The Asymptotic Mistuning Model (AMM) is a recently introduced simplified method for the analysis of mistuning effects in the vibration characteristics of bladed disks. It is derived directly from the full mistuned bladed disk using an asymptotic expansion that exploits the smallness of the mistuning and the damping. The results from the AMM have been previously successfully verified using a simple 1-D mass-spring model. In this paper we validate the accuracy of AMM for the prediction of the effect of mistuning in realistic configurations. To this end, we perform a quantitative comparison between the AMM results and those from a detailed finite element method (FEM) numerical simulation of a complete mistuned bladed disk, for several mistuning patterns and forcing conditions. We also emphasize and comment the useful information provided by the AMM about the essential mechanisms involved in the mistuning effects on the vibration of cyclic structures.
Multi Stage Variable Speed Turbo Compressor for Enhancing Seasonal Energy Efficiency Ratio of Air Conditioners Using R718 as Refrigerant
Authors: Amibe Demiss A. , Li Qubo , Mu¨ller Norbert
Published: January 2011

An air conditioning system using water as refrigerant (R718) that compresses water vapor with multistage stage variable speed axial compressor with intercooling between stages by water injection is considered. Four stage compression with flash intercooling resulted in 50% improvement of coefficient of performance (COP) at full load compared to conventional refrigerants like R134a. The energy-efficiency of an air conditioning unit is specified by seasonal energy efficiency ratio (SEER). SEER is defined as the ratio of cooling output of an air conditioner measured and electrical energy consumption as per AHRI 210/240 during cooling season. The SEER is computed after determining the evaporator cooling capacity and the electrical energy demand of the compressor at each bin temperature using assumed compressor isentropic efficiency, mechanical efficiency and electrical efficiency and multiplying by the weight of each bin temperature to determine the total for the cooling season. As a result of multistage compression, best part load performance of water as a refrigerant and operation of compressor near design point at part load due to variable speed drive, 50–60% improvement in SEER is obtained compared to the best available in the market using conventional refrigerants such as R134a with single stage compression.
Extracting Two-Zone Model Parameters for Centrifugal Compressor Design
Authors: Gu Fahua , Thilges Chris , Cambio Matt
Published: January 2011

The two-zone model for the design and flow analysis for centrifugal compressor impellers, based on the observation of the jet-wake exit flow pattern, was initialized in 1980’s to avoid modeling each individual loss. The two-zone model introduced four model parameters, diffusion ratio MR2, secondary mass fraction Msec_M, and deviations for the primary and secondary zones, δp and δs. This paper aims at developing a methodology to extract values for the model parameters from CFD and test data. Four methods have been developed or assessed in this paper. The first method identifies the primary zone on the exit plane by setting a meridional velocity threshold; the regions with the meridional velocity higher than the pre-set value are the primary zone. We came to the conclusion this method is not consistent with the two-zone model. The other three methods deal with the selection of multiple solutions to the two-zone model parameters by introducing different assumptions to meet the impeller efficiency and total-to-total pressure ratio exactly. The last one, reduced model, is recommended. It sets the secondary deviation to 0 and decrements the primary static pressure from the exit total pressure until the second unique solution is reached. The impeller performance map indicates that this solution has the second highest diffusion ratio, and the primary deviation and secondary mass fraction are the second highest too. An example design shows that the diffusion ratio can be affected by the blade profiling, and the impeller performance can be referred from the primary deviation and secondary mass fraction when the diffusion ratios are similar for different designs.
Fault Isolation for an Industrial Gas Turbine With a Model-Based Diagnosis Approach
Authors: Larsson Emil , A˚slund Jan , Frisk Erik , Eriksson Lars
Published: January 2011

Model based diagnosis and supervision of industrial gas turbines are studied. Monitoring of an industrial gas turbine is important as it gives valuable information for the customer about service performance and process health. The overall objective of the paper is to develop a systematic procedure for modelling and design of a model based diagnosis system, where each step in the process can be automated and implemented using available software tools. A new Modelica gas media library is developed, resulting in a significant model size reduction compared to if standard Modelica components are used. A systematic method is developed that, based on the diagnosis model, extracts relevant parts of the model and transforms it into a form suitable for standard observer design techniques. This method involves techniques from simulation of DAE models and a model reduction step. The size of the final diagnosis model is 20% of the original model size. Combining the modeling results with fault isolation techniques, simultaneous isolation of sensor faults and fault tolerant health parameter estimation is achieved.
Experimental and Numerical Investigation on the Laminar Flame Speed of CH4/O2 Mixtures Diluted With CO2 and H2O
Authors: Mazas A. N. , Lacoste D. A. , Schuller T.
Published: January 2011

The effects of CO2 and H2O addition on premixed oxy-fuel combustion are investigated with experiments and numerical simulations on the laminar flame speed of CH4/O2/CO2/H2O(v) and CH4/O2/N2/H2O(v) mixtures, at atmospheric pressure and for a reactants inlet temperature Tu = 373 K. Experiments are conducted with steady laminar conical premixed flames over a range of operating conditions representative of oxy-fuel combustion with flue gas recirculation. The relative O2-to-CO2 and O2-to-N2 ratios, respectively defined as O2/(O2+CO2) (mol.) and O2/(O2+N2) (mol.), are varied from 0.21 to 1.0. The equivalence ratio of the mixtures ranges from 0.5 to 1.5, and the steam molar fraction in the reactive mixture is varied from 0 to 0.45. Laminar flame speeds are measured with the flame area method using a Schlieren apparatus. Experiments are completed by simulations with the PREMIX code using the detailed kinetic mechanism GRI-mech. 3.0. Numerical predictions are found in good agreement with experimental data for all cases explored. It is also shown that the laminar flame speed of CH4/O2/N2 mixtures diluted with steam H2O(v) features a quasi-linear decrease when increasing the diluent molar fraction, even at high dilution rates. Effects of N2 replacement by CO2 in wet reactive mixtures are then investigated. A similar quasi-linear decrease of the flame speed is observed for CH4/O2/CO2 H2O-diluted flames. For a similar flame speed in dry conditions, results show a larger reduction of the burning velocity for CH4/O2/N2/H2O mixtures than for CH4/O2/CO2/H2O mixtures, when the steam molar fraction is increased. Finally, it is observed that the laminar flame speed of weakly (CO2, H2O)-diluted CH4/O2 mixtures is underestimated by the GRI-mech 3.0 predictions.
TRANSIT Code for Unsteady Flows in Solar-Gravity Draught Turbine Towers
Authors: Cirligeanu Radu , Bogoi Alina , Rugescu Radu D.
Published: January 2011

Unsteady, non-isentropic, discontinuous flows with energy exchange, during solar heating transients of air turbine towers are approached through a proprietary computational front method, initially developed for the study of ignition in solid propellant rocket motors. Its application in the discontinuous flows with energy exchange also proves highly efficient. Computational efficiency is demonstrated by CFD simulation of transients in the air accelerator of the SEATTLER solar mirror, turbine tower. This is a typically unsteady flow simulation for slender channels. A 1-D computational scheme was developed to simulate the interference between zones with different flow conditions. Given values for the thermochemical properties of the working gas are considered and two zones of different flow characteristics are identified. The first zone is the heat exchanger, where a nonisentropic flow develops. At the aft end of this heating zone a second zone of the channel is encountered after a blunt passage, where an isentropic expansion of the gas begins and extends along the tower up to the upper exit. Into the 1-D, unsteady flow scheme of computation, the discontinuity of equations of motion at the interface between the two zones induces very specific precautions and this methodology is detailed into the paper. Consequently, the computational front scheme covers the dual behavior of the fully non-isentropic flow with mass addition and mixing in the heater and of the fully isentropic flow at the exhaust of the gravity draught tall tower, typical for the solar-gravity draught power plants. Small perturbations of the flow, in the form of developing weak shocks, and blunt discontinuities are simultaneously covered. Code robustness is demonstrated and revealed through diagrams. The 1-D numerical scheme is based on the enhanced method of the computational front with resolution of the expansion wave development.
Transmitted Power in a Structure Using the Effective Mass Parameters
Authors: Untaroiu Costin D. , Untaroiu Alexandrina , Wagner Matthew , Allaire Paul E.
Published: January 2011

To reduce the vibration levels in a complex structure, the designer often needs to know how the vibrations in one part of a structure are transmitted to other parts at each interface of the connected components. A lumped-mass method and component mode synthesis is used to evaluate the power flow for vibrations in low-frequency range. The model mass and stiffness matrices are portioned into substructures separated by the interfaces whose power flow should be evaluated. The vibration modes of the substructure are divided into constrained and fixed interface modes corresponding to the interface and interior degree of freedoms, respectively. The effective interface mass criterion is used to rank the most dynamic important modes at each interface. The most important modes are preserved in a reduced model for computing the power flow. A numerical example of a linear system is used to illustrate the application of the new technique.
Metallurgical Evaluation and Condition Assessment of FSX 414 Nozzle Segments in Gas Turbines by Metallographic Methods
Authors: Shejale Girish M.
Published: January 2011

Gas turbine components such as nozzle segments, buckets, transition pieces and combustion liners experience damages such as creep, fatigue, high temperature oxidation and corrosion. The reliability, availability and efficiency of high temperature gas turbine parts is based on condition assessment and remaining life analysis. These gas turbine components are normally repaired, refurbished after stipulated operating hours. The decision on the extent of repairs is based on various inspection stages. Among various methodologies of condition assessment, metallography followed by microscopic evaluation has gained wide acceptance since it is cost effective, quick and reliable. Extensive in-house efforts have been put forth in this field in the development of improved techniques of metallography for accurate determination of material degradation and condition assessment. Experimental studies on Frame 6, 1st Stage Nozzle Segment (FSX 414 – cobalt based alloy) were conducted to assess the condition of the nozzle segment by using laboratory electropolishing technique for metallographic preparation. Sections taken from the nozzle segment were electropolished and examined in Light Optical Microscope (LOM) and Scanning Electron Microscope (SEM). It is concluded that the improved electropolishing technique is effective in assessing creep-fatigue, thermal fatigue and hot corrosion damage. Based on this the condition of the nozzle segment is assessed. Typical results of Frame 6, 1st Stage Nozzle Segment are presented and discussed.
The Cordier Line for Mixed Flow Compressors
Authors: Casey Michael , Zwyssig Christof , Robinson Chris
Published: January 2011

The specific speed and specific diameter of radial, mixed and axial flow compressors can be plotted in a Cordier diagram, and the best compressors then lie in a relatively narrow band, known as the Cordier or Balje line. This line exhibits a distinctive s-shape, and it is shown in this paper that this is due to the variation of the centrifugal effect on the pressure rise of the different compressor types. A new equation for the Cordier line in the mixed flow region based on the pressure rise coefficient is developed and calibrated with data from mixed flow pumps and ventilators. Together with other empirical relationships for the expected efficiency as a function of the specific speed this provides some useful new guidelines for the preliminary design of mixed flow compressors. These guidelines are then examined by carrying out a preliminary design of a high-speed mixed-flow micro-compressor that is analyzed using CFD and tested to justify the approach.
Understanding Ice Crystal Accretion and Shedding Phenomenon in Jet Engines Using a Rig Test
Authors: Mason Jeanne G. , Chow Philip , Fuleki Dan M.
Published: January 2011

The aviation industry has now connected a number of engine power-loss events to the ingestion of atmospheric ice crystals. Ice crystals are believed to penetrate to and eventually accrete on surfaces in the engine core where local air temperatures are warmer than freezing. Research aimed at understanding the accretion and shedding of ice crystals within the engine is being conducted industry-wide. Although this specific icing condition is readily produced inside an operating engine, rig testing is the preferred research tool because it has the advantage of good visibility of the ice accretion process and easy access for video documentation. This paper presents one of the first efforts to simulate the warm air/cold ice conditions occurring inside the engine core using a test rig. The test section contains geometry simulating the transition duct between the low and high compressors in a typical jet engine and an airfoil simulating the engine strut connecting the inner and outer surfaces. Test results showed ice formed on the airfoil and other surfaces in the test section at air temperatures warmer than freezing. However, when both the air and surface temperatures were held below freezing, the injected ice did not melt and no ice accretion was observed. Ice only formed on the airfoil when mixed phase conditions (liquid and ice) were produced, by introducing the ice into a warm airflow. This test concludes that a rig-level ice crystal icing test is feasible and capable of producing ice accretion in a simulated engine environment. As it was the first test of its kind, reporting of these preliminary test results are expected to benefit future experimenters.
Fluid Dynamics and Detailed Kinetic Modeling of Pollutant Emissions From Lean Combustion Systems
Authors: Frassoldati Alessio , Cuoci Alberto , Faravelli Tiziano , Ranzi Eliseo , Colantuoni Salvatore , Di Martino Pasquale , Cinque Giuseppe , Kern Matthias , Marinov Svetoslav , Zarzalis Nikolaos , Da Costa Isabel , Guin Christian
Published: January 2011

A methodology for computing steady turbulent reacting flows and the formation of pollutants in combustors for aeroengine applications is presented. The aim of this paper is to describe and to further validate the proposed computational approach. A 3-D computational fluid dynamics (CFD) proprietary code and a Kinetic Post-Processor (KPP) have been coupled and applied to calculate the gas temperature and pollutant emissions. The thermo-fluid dynamics results of the CFD code are post-processed by the KPP with the use of detailed kinetics for predicting pollutant emissions, with special emphasis on nitrogen oxides. A new application of the above calculation methodology has been carried out on an injection system based on Partial Evaporation and Rapid Mixing (PERM) concept, designed and developed in the frame of the EU program for NEW Aero engine Core concepts (NEWAC). This injection system was studied experimentally at Karlsruhe University and ONERA using a tubular combustor, in order to perform the first assessment in terms pollutant emissions at the outlet at different operating conditions. The model predictions are compared with experimental results and globally the agreement is satisfactory, especially for NOx emissions. The analysis of the data presented in this paper provides useful information for further improvements in both modeling and experimental activities.
Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control: Part I—Non-Axisymmetric Flow in Centrifugal Compressor
Authors: Yang Mingyang , Zheng Xinqian , Zhang Yangjun , Bamba Takahiro , Tamaki Hideaki , Huenteler Joern , Li Zhigang
Published: January 2011

This is the Part I of a two-part paper documenting the development of a novel asymmetric flow control method to improve the stability of a high-pressure-ratio turbocharger centrifugal compressor. Part I focuses on the non-axisymmetric flow in a centrifugal compressor induced by the non-axisymmetric geometry of the volute while Part II describes the development of asymmetric flow control method to avoid the stall on the basis of the characteristic of non-axisymmetric flow. To understand the asymmetries, experimental measurements and corresponding numerical simulation were carried out. The static pressure was measured by probes at different circumferential and stream-wise positions to gain insights about the asymmetries. The experiment results show that there is an evident non-axisymmetric flow pattern throughout the compressor due to the asymmetric geometry of overhung volute. The static pressure field in the diffuser is distorted at approximately 90° in rotational direction of the volute tongue throughout the diffuser. The magnitude of this distortion varies slightly with the rotational speeds. The magnitude of the static pressure distortion in the impeller is a function of the rotational speed. There is a significant phase shift between the static pressure distributions at the leading edge of the splitter blades and the impeller outlet. The numerical steady state simulation neglects the mentioned unsteady effects found in the experiments and can not predict the phase shift, but a detailed asymmetric flow field structure are obviously obtained.
Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control: Part II—Non-Axisymmetric Self Recirculation Casing Treatment
Authors: Zheng Xinqian , Zhang Yangjun , Yang Mingyang , Bamba Takahiro , Tamaki Hideaki
Published: January 2011

This is the Part II of a two-part paper involving the development of asymmetric flow control method to widen the operating range of a turbocharger centrifugal compressor with high-pressure-ratio. Non-axisymmetric Self Recirculation Casing Treatment (SRCT) as an instance of asymmetric flow control method is presented. Experimental and numerical methods were used to investigate the impact of non-axisymmetric SRCT on surge point of the centrifugal compressor. Firstly, the influence of the geometry of a symmetric SRCT on the compressor performance was studied by means of numerical simulation. The key parameter of the SRCT was found to be the distance from the main blade leading edge to the rear groove (Sr). Next, several arrangements of a non-axisymmetric SRCT were designed, based on flow analysis presented in Part I. Then, a series of experiments was carried out to analyze the influence of non-axisymmetric SRCT on the compressor performance. Results show that the non-axisymmetry SRCT has certain influence on performance and has a larger potential for stability improvement than the traditional symmetric SRCT. For the investigated SRCT, the surge flow rate of the compressor with the non-axisymmetric SRCT is about 10% lower than that of the compressor with symmetric SRCT. The largest surge margin (smallest surge flow rate) can be obtained when the phase of the largest Sr is coincident with the phase of the minimum static pressure in the vicinity of the leading edge of the splitter blades.
Extended Turndown, Fuel Flexible Gas Turbine Combustion System
Authors: Stuttaford Peter , Rizkalla Hany , Chen Yan , Copley Brian , Faucett Thomas
Published: January 2011

Flexibility is key to the future success of gas turbines for power generation. As renewable energy becomes more widely used the need for reliable, flexible standby power generation will increase. Gas turbines which are able to operate efficiently and in emissions compliance from extended low load to base load will have a significant advantage in meeting this need. Fuel costs and availability are of increasing concern. A gas turbine which is able to flexibly operate with a wide range of fuels, without the need for a diluent such as water or nitrogen, will provide added value to the operators of these machines. Carbon emissions are also of growing environmental concern, and the abatement of such emissions is likely to become of increasing monetary value. A fuel flexible combustor able to operate flexibly on both decarbonized fuel and natural gas will be well positioned to take commercial advantage of the situation. A combustion system is described and demonstrated which meets the goals set forth above. The system is simply retrofittable into existing E/F-class frame machines. The combustor is comprised of a dry lean premixed system without the need for diluents to control emissions. The operating principle of the new combustor is described. A full scale rig test program was undertaken to validate the new design and these results are presented. Results are shown with low emissions operation at 15–25% engine load. Combustor performance with a range of fuel blends up to 60% hydrogen, all with emissions below 9ppm of NOx and CO, is presented.
Multi-Objective Design Optimisation of a Diffuser-Ejector Exhaust Duct for Helicopter Engines
Authors: Gra¨sel J. , Demolis J. , Mohr H. , Schiffer H.-P.
Published: January 2011

The paper demonstrates the successful application of an optimisation methodology for the design of a diffuser-ejector exhaust duct. Maximising simultaneously pressure recovery and the entrainment ratio are diverging objectives which could hardly be achieved by a conventional manual trial-and-error approach relying on the designer’s experience. This multi-objective design problem has been solved for the axis-symmetric exhaust duct with a given characteristic length, inlet section and minimal standoff distance by coupling a parametric method with 2D CFD analysis. Open cubic B-splines have been employed to generate the contoured duct shape, for which the control-point vertices have been defined by a total of 17 engineering parameters. A bell mouth inlet has been chosen for the ejector inlet. The parameter constraints result from weight and integration requirements. Three characteristic engine operating points have been chosen for the multi-point and multi-objective shape optimisation. The entire process of model building, meshing, performing the 2D CFD calculation and post-processing to extract the required metrics has been fully automated. A commercial process integration software package is used to link the different tools together in a unified environment. The design space exploration is carried out via a latin-hypercube sampling technique. This random space filling method has been chosen because of its considerable lower number of experiments compared to factorial sampling techniques. Parameter ranking is obtained by a weighted average of the correlation coefficients for each objective. The parameter hierarchy is slightly different for the engine operating points. However, there exists a clear threshold separating the influential parameters from the insignificant ones. A subsequent DOE is performed for the reduced parameter set for which the minimum number of experiments has been chosen as twice the number of experiments to generate a quadratic response surface. The Normal-Boundary Intersection method is applied to find the Pareto front based on the response surface model as surrogate model. The results show that a gain of 20% for the pressure recovery for a given entrainment ratio could be achieved compared to a configuration defined by a manual trial-and-error approach. The great benefit of the present method is its capability to handle easily geometrical constraints and the weight of the different design objectives which may change even during the detailed design phase.
Combustor Configuration Influence on Combusion Instabilities Performance
Authors: Vedeshkin Georgy K. , Sverdlov Evgeniy D. , Doubovitsky Alexey N.
Published: January 2011

The paper describes the results of calculations and experimental investigations of combustor configurations. It is shown that combustor configuration effects high frequency and low frequency combustor instabilities, gas dynamics of the flow, recirculation zones dimensions and lean flame out limits. Combustion instability modes had been investigated in two versions of combustor configurations: with the abrupt divergence of the channel and with an inlet conical diffuser. Gas flow instabilities had been investigated in the central recirculation zone without any chemical reactions. As a result the combustion instability model in which a role of a feed back mechanism is performed by hydrodynamic gas flow instability in the combustor is suggested. Modification of the combustor with a conical diffuser with the suggested model of the hydrodynamic combustion instability taken into account made it possible to settle the instability problem for the given combustor.
Complex Secondary Flow and Associated Loss Generation in Ultra-Highly Loaded Turbine Cascade
Authors: Tsujita Hoshio , Yamamoto Atsumasa
Published: January 2011

An increase of turbine blade loading decreases the numbers of blades and stages, and results in the improvement of the performance characteristics of gas turbines. However, in such highly loaded turbine cascade with high turning angle, the secondary flow becomes much strong due to the steep pressure gradient across the blade-to-blade passage and deteriorates the performance of turbine enormously. In this study, the computations were performed for the flow in the ultra-highly loaded turbine cascade in order to clarify the effects of the inlet boundary layer thickness and the incidence angle which strongly influence the secondary flow structure in a turbine cascade. Moreover, the experimental oil flow visualization was conducted on the blade surface and the endwall, and the measurements of blade surface static pressure were performed at the midspan. The computed results agreed well with the oil flow visualization and the measured blade surface static pressure. The effects of the incidence angle and the inlet boundary layer thickness on the secondary flow structure, the total pressure loss, the secondary flow kinetic energy and the blade loading distributions were examined in detail. The positive incidence angle induced the characteristic vortex released from the endwall. Moreover, it was revealed that the interactions among the horseshoe vortex, the passage vortex and the characteristic vortex strongly increase the secondary loss in the cascade passage.
Heat Transfer in a Rotating Rectangular Channel With Two Opposite Walls Roughened With Spherical Protrusions at High Rotation Numbers
Authors: Chang S. W. , Liou T.-M. , Chen W. C.
Published: January 2011

Detailed heat transfer distributions over two opposite leading and trailing walls roughened by spherical protrusions were measured from a rotating rectangular channel at rotation number up to 0.6 to examine the effects of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers on local and area averaged Nusselt numbers (Nu and Nu) using the infrared thermography. A set of selected heat transfer data illustrates the Coriolis and rotating-buoyancy effects on the detailed Nu distributions and the area-averaged heat transfer performances of the rotating channel. The Nu for the developed flow region on the leading and trailing walls are parametrically analyzed to devise the empirical heat transfer correlations that permit the evaluation of the interdependent and individual Re, Ro and Bu effect on Nu.
Wet Gas Impeller Test Facility
Authors: Gru¨ner Trond G. , Bakken Lars E.
Published: January 2011

The development of wet gas compressors will enable increased oil and gas production rates and enhanced profitable operation by subsea well-stream boosting. A more fundamental knowledge of the impact of liquid is essential with regard to the understanding of thermodynamic and fluid dynamic compressor behavior. An open-loop impeller test facility was designed to investigate the wet gas performance, aerodynamic stability, and operation range. The facility was made adaptable for different impeller and diffuser geometries. In this paper, the wet gas test facility and experimental work concerning the impact of wet gas on a representative full-scale industrial impeller are presented. The centrifugal compressor performance was examined at high gas volume fractions and atmospheric inlet conditions. Air and water were used as experimental fluids. Dry and wet gas performance was experimentally verified and analyzed. The results were in accordance with previous test data and indicated a stringent influence of the liquid phase. Air/water tests at atmospheric conditions were capable of reproducing the general performance trend of hydrocarbon wet gas compressor tests at high pressure.
Further Computational Investigations Into Aero-Engine Bearing Chamber Off-Take Flows
Authors: Robinson Adam , Eastwick Carol , Morvan Herve´
Published: January 2011

Within an aero-engine bearing chamber oil is provided to components to lubricate and cool. This oil must be efficiently removed (scavenged) from the chamber to ensure it does not overheat and degrade. Bearing chambers typically contain a sump section with an exit pipe leading to a scavenge pump. In this paper a simplified geometry of a sump section, here simply made of a radial off-take port on a walled inclined plane, is analysed computationally. This paper follows on work presented within GT2008-50634. In the previous paper it was shown that simple gravity draining from a static head of liquid cold be modelled accurately, for what was akin to a deep sump situation fond in integrated gear boxes for example. The work within this paper will show that the draining of flow perpendicular to a moving film can be modelled. This situation is similar to the arrangements found in transmission bearing chambers. The case modelled is of a walled gravity driven film running down a plane with a circular off-take port, this replicates experimental work similar to that reported in GT2008-50632. The commercial computational fluid dynamics (CFD) code, Fluent 6 [1] has been employed for modelling, sing the Volume of Fluid (VOF) approach of Hirt and Nichols [2, 3] to capture the physics of both the film motion and the two phase flow in the scavenge pipe system. Surface tension [4] and a sharpening algorithm [5] are used to complement the representation of the free surface and associated effects. This initial CFD investigation is supported and validated with experimental work, which is only depicted briefly here as it is mainly sued to support the CFD methodology. The case has been modelled in full as well as with the use of a symmetry plane running down the centre of the plane parallel to the channel walls. This paper includes details of the meshing methodology, the boundary conditions sued, which will be shown to be of critical importance to accurate modelling, and the modelling assumptions. Finally, insight into the flow patterns observed for the cases modelled are summarised. The paper further reinforces that CFD is a promising approach to analysing bearing chamber scavenge flows although it can still be relatively costly.
Performance Analysis of a Wind Powered Gas Storage System
Authors: Arnulfi Gianmario L. , Marini Martino
Published: January 2011

All over the world huge masses of gas are compressed in a number of storage stations to compensate seasonal fluctuations of the users’ demand versus the methane extraction from geological deposits. In the great majority of such plants, turbo-compressors are used, namely centrifugal machines. Since in this kind of machines compression is essentially adiabatic, gas temperature rises up even to dangerous values. Natural gas cannot be injected into the reservoirs too hot without risk of geological damage, so often an after-cooler has to be provided. Natural gas compressors are driven by gas turbines (GT), fuelled by part of the gas flowing through the station; otherwise electric motors connected to the general grid are used. In the paper the exploitation of the renewable energy of the wind to drive the compressors of the system is proposed. The matching with the driving wind turbine is different from the matching with a gas turbine or an electric motor. However whereas the stochastic character of the wind source affects power generation seriously, in the proposed use it is not a real problem: the only constraint consists of having enough wind energy to complete a charge all over a season. An in-house code, based on the lumped parameter approach and a quasi-steady dynamics, has been developed in order to simulate the system performance during a complete charge for a known wind distribution. The turbo-compressor is modeled through its characteristic maps. Similarly the wind turbines, that drive the storage station, and the fans, that counterbalance the friction losses of the after-cooler, are replaced with their characteristic curves. The after-cooler, which is a gas-air compact heat exchanger, is modeled by means of the overall heat transfer coefficient and the total pressure losses. Finally the reservoir is supposed omothermal and isothermal. In order to investigate the plant performance, different kinds of wind distributions have been considered and the corresponding operation paths as well as power and pressure evolutions are shown and discussed.
Investigation of Coriolis Forces Effect of Flow Structure and Heat Transfer Distribution in a Rotating Dimpled Channel
Authors: Elyyan Mohammad A. , Tafti Danesh K.
Published: January 2011

Large-eddy simulations are used to investigate Coriolis forces effect on flow structure and heat transfer in a rotating dimpled channel. Two geometries with two dimple depths are considered, δ = 0.2 and 0.3 of channel height, for a wide range of rotation number, Rob = 0.0–0.70, based on mean bulk velocity and channel height. It is found that the turbulent flow is destabilized near the trailing side and stabilized near the leading side, with secondary flow structures generated in the channel under the effect of Coriolis forces. Higher heat transfer levels are obtained at the trailing surface of the channel, especially in regions of flow reattachment and boundary layer regeneration at the dimple surface. Coriolis forces showed a stronger effect on the flow structure for the shallow dimple geometry (δ = 0.2) compared to the deeper dimple where the growth and shrinkage of the flow recirculation zone in the dimple cavity with rotation were more pronounced than the deep dimple geometry (δ = 0.3). Under the action of rotation, heat transfer augmentation increased by 57% for δ = 0.2 and by 70% for δ = 0.3 on the trailing side and dropped by 50% for δ = 0.2 and by 45% for δ = 0.3 on the leading side from that of the stationary case.
Study of Flow Control Using a Slotted Blade for a Compressor Airfoil at Low Reynolds Numbers
Authors: Zhou Min , Zhu Junqiang , Lu Xingen , Ge Zhihui , Yan Kexue , Huang Rong
Published: January 2011

Flow control using a blade which is slotted from pressure surface to suction surface was studied. The effects of a slotted blade for a compressor airfoil at low Reynolds numbers were studied with the help of a linear cascade wind tunnel and a state-of-the-art multi-block flow solver. Measurements were taken in a low-speed linear cascade. The compressor cascade with a steady inflow was examined based on blade chord length at low Reynolds numbers. The experimental results showed that the slotted blade could effectively reduce the loss wake width and depth. The maximum relative reduction of wake width and depth were 48% and 45%, respectively. The numerical results at Reynolds numbers ranging from 1.2×105 to 2.1×105 showed that the airfoil aerodynamics of cascade are substantially improved by a slotted blade within this Reynolds number regime. This yields less total pressure loss and a greater flow turning angle and static pressure rise. The extensive numerical results showed that the slot inlet could capture the high pressure flow from the pressure surface, bring it into the slot, and discharge it onto the suction surface of the blade. This then blows off the boundary layer separation flow and accelerates the low energy flow, reducing the size of the separation region, or even eliminating the separation entirely on the trailing edge of blade.
A Numerical Study of the Flow Fields in a Highly Off-Design Variable Geometry Turbine
Authors: Walkingshaw Jason , Spence Stephen , Ehrhard Jan , Thornhill David
Published: January 2011

Conventionally, radial turbines have almost exclusively used radially fibred blades. While issues of mechanical integrity are paramount, there may be opportunities for improving turbine efficiency through a 3D blade design without exceeding mechanical limits. Off-design performance and understanding of the secondary flow structures now plays a vital role in the design decisions made for automotive turbocharger turbines. Of particular interest is extracting more energy at high pressure ratios and lower rotational speeds. Operating in this region means the rotor will experience high values of positive incidence at the inlet. A CFD analysis has been carried out on a scaled automotive turbine utilizing a swing vane stator system. To date no open literature exists on the flow structures present in a standard VGT system. Investigations were carried out on a 90 mm diameter rotor with the stator vane at the maximum, minimum and 25% mass flow rate positions. In addition stator vane endwall clearance existed at the hub side. From investigation of the internal flow fields of the baseline rotor, a number of areas that could be optimized in the future with three dimensional blading were identified. The blade loading and tip leakage flow near inlet play a significant role in the flow development further downstream at all stator vane positions. It was found that tip leakage flow and flow separation at off-design conditions could be reduced by employing back swept blading and redistributing the blade loading. This could potentially reduce the extent of the secondary flow structures found in the present study.
Thermo-Mechanical FEA/CFD Coupling of an Interstage Seal Cavity Using Torsional Spring Analogy
Authors: Amirante Dario , Hills Nicholas J. , Barnes Christopher J.
Published: January 2011

The optimisation of heat transfer between fluid and metal plays a crucial role in gas turbine design. An accurate prediction of temperature for each metal component can help to minimise the coolant flow requirement, with a direct reduction of the corresponding loss in the thermodynamic cycle. Traditionally, in industry fluid and solid simulations are conducted separately. The prediction of metal stresses and temperatures, generally based on finite element analysis, requires the definition of a thermal model whose reliability is largely dependent on the validity of the boundary conditions prescribed on the solid surface. These boundary conditions are obtained from empirical correlations expressing local conditions as a function of working parameters of the entire system, with validation being supplied by engine testing. However, recent studies have demonstrated the benefits of employing coupling techniques, whereby computational fluid dynamics (CFD) is used to predict the heat flux from the air to the metal, and this is coupled to the thermal analysis predicting metal temperatures. This paper describes an extension of this coupling process, accounting for the thermo-mechanical distortion of the metal through the engine cycle. Two distinct codes, a finite element analysis (FEA) solver for thermo-mechanical analysis and a finite volume solver for CFD, are iteratively coupled to produce temperatures and deformations of the solid part through an engine cycle. At each time step, the CFD mesh is automatically adapted to the FEA prediction of the metal position using efficient spring analogy methods, ensuring the continuity of the coupled process. As an example of this methodology, the cavity flow in a turbine stator well is investigated. In this test case, there is a strong link between the thermo-mechanical distortion, governing the labyrinth seal clearance, and the amount of flow through the stator well, which determines the resulting heat transfer in the stator well. This feedback loop can only be resolved by including the thermo-mechanical distortion within the coupling process.
Sensor and Actuator Needs for More Intelligent Gas Turbine Engines
Authors: Garg Sanjay , Schadow Klaus , Horn Wolfgang , Pfoertner Hugo , Stiharu Ion
Published: January 2011

This paper provides an overview of the controls and diagnostics technologies, that are seen as critical for more intelligent gas turbine engines (GTE), with an emphasis on the sensor and actuator technologies that need to be developed for the controls and diagnostics implementation. The objective of the paper is to help the “Customers” of advanced technologies, defense acquisition and aerospace research agencies, understand the state-of-the-art of intelligent GTE technologies, and help the “Researchers” and “Technology Developers” for GTE sensors and actuators identify what technologies need to be developed to enable the “Intelligent GTE” concepts and focus their research efforts on closing the technology gap. To keep the effort manageable, the focus of the paper is on “On-Board Intelligence” to enable safe and efficient operation of the engine over its life time, with an emphasis on gas path performance.
Experimental Heat Transfer Investigation in a Multisplitter LP Vane Architecture
Authors: Pinilla V. , Solano J. P. , Paniagua G. , Lavagnoli S. , Yasa T.
Published: January 2011

This paper reports the external convective heat transfer in an innovative low pressure vane with multisplitter configuration. Three small aerodynamic blades are positioned between each structural vane, providing a novel architecture for ultra-high by-pass ratio aero-engines, with increased LP vane radius and swan-neck diffuser to link the HP turbine. The measurements have been performed in the compression tube test rig of the von Karman Institute, using single layered thin film gauges. Time-averaged and time-resolved heat transfer distributions are presented for the three aerovanes and for the structural blade, at three pressure ratios tested at representative conditions of modern aeroengines, with M2,is ranging from 0.87 to 1.07 and a Reynolds number of about 106. This facility is specially suited to control the gas-to-wall temperature ratio. Accurate time-averaged heat transfer distributions around the aerovanes are assessed, that allow characterizing the boundary layer status for each position and pressure ratio. The heat transfer distribution around the structural blade is also obtained, depicting clear transition to turbulence, as well as particular flow features on the pressure side, like separation bubbles. Unsteady data analysis reveals the destabilizing effect of the rotor left-running shock on the aerovanes boundary layer, as well as the shift of transition onset for different blade passing events.
Evaluating the Machinability of Inconel 718 Using Polar Diagrams
Authors: Avdovic Pajazit , Xu Linhong , Andersson Mats , Sta˚hl Jan-Eric
Published: January 2011

The use of a polar diagram method for describing and evaluating the machinability of Inconel 718 was explored. Five key parameters of the work material, representing the mechanical and physical properties which have strongest influence on its machinability, were employed in the diagrams. These five parameters were integrated into a single polar diagram, used to describe the machinability of Inconel 718. Variations in the machinability of Inconel 718 products or components of a given type produced in different batches were analyzed. Industrial experiments were conducted to test the relationship between the polar diagram of the work material, its carbon content, and tool wear of the ceramic cutting tools used in machining it. Work materials of Inconel 718 in which the polar diagrams of machinability were similar in size and shape exhibited very similar behavior during the cutting process. The polar diagram method employed appeared to be useful for selecting suitable cutting data for the machining of new materials.
Modeling of Aerodynamic Noise Using Hybrid SAS and DES Methods
Authors: Rulik Sebastian , Dykas Slawomir , Wroblewski Wlodzimierz
Published: January 2011

The purpose of the presented studies is to compare simple and fast CFD methods based on the unsteady Reynolds-Averaged Navier-Stokes equations (uRANS) with the so called hybrid uRANS/LES methods like Detached Eddy Simulation (DES) and Scale Adaptive Simulation (SAS) implemented in the commercial code ANSYS CFX. The goal of this comparison is to find an efficient and relatively fast method for both the flow dynamic and aerodynamic noise prediction in the near and far field, which would be suitable for engineering applications. The CFD calculations were carried out using the commercial code ANSYS CFX 11. The non-reflective boundary conditions and grid stretching were used to avoid the reflections of the acoustic waves from the outer boundaries. The different boundary conditions and turbulence models were used in the calculations. For the acoustic calculations the Fast Fourier Transformation (FFT) was applied to obtain the sound spectrum. The CFD results were compared with the experimental data obtained in references.
Short and Long Range Mission Analysis for a Geared Turbofan With Active Core Technologies
Authors: Alexiou A. , Aretakis N. , Roumeliotis I. , Mathioudakis K.
Published: January 2011

A novel engine concept, for reducing the environmental impact of gas turbines, is the Geared Turbofan with Active Core technologies (GTAC), investigated in the context of the European program NEWAC (New Aero Engine Core Concepts). Two performance models of this engine are created for short and long range aircraft applications and matched to manufacturer specifications. The engine performance data are used in a mission analysis module simulating typical aircraft applications. Compared to missions using Year 2000 in service engines, the results show a significant reduction in fuel consumption and noise levels. A significant reduction in NOx emissions requires the application of new technology combustor designs as developed e.g. in NEWAC.