bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Endwall Contours of a Turbine Blade Row Using an Adjoint Method
Authors: Luo Jiaqi , McBean Ivan , Liu Feng
Published: May 2012

This paper presents the application of a viscous adjoint method in the optimization of a low-aspect-ratio turbine blade through spanwise restaggering and endwall contouring. A generalized wall-function method is implemented in a Navier-Stokes flow solver coupled with Menter’s SST k-ω turbulence model to simulate secondary flow with reduced requirements on grid density. Entropy production through the blade row combined with a flow turning constraint is used as the objective function in the optimization. With the viscous adjoint method, the complete gradient information needed for optimization can be obtained by solving the governing flow equations and their corresponding adjoint equations only once, regardless of the number of design parameters. The endwall profiles are contoured alone in the first design case, while it is combined with spanwise restaggering in the second design case. The results demonstrate that it is feasible to reduce flow loss through the blade redesign while maintaining the same mass-averaged flow turning by using the viscous adjoint optimization method. The performance of the redesigned blade is calculated and compared at off-design conditions.
A Study on the Influence of Hole’s Diameter With Holed Casing Treatment
Authors: Xu Wei , Wang Tong , Gu Chuangang , Ding Liang
Published: May 2012

The holed casing treatment is a new type of casing treatment with self-adaptability for centrifugal compressor with unshrouded impellers. It is demonstrated experimentally and numerically that both of the stall margin and the choked margin of the compressor can be expanded by the treatment. Numerical results indicate that there is a reinjected flow in the holes when the compressor works at low flowrate conditions and a bypass flow at high flowrate conditions. Hole’s diameter is an important parameter for the holed casing treatment. Five cases of different diameter (1.0mm, 1.5mm, 2.0mm, 2.5mm and 3.0mm) were carried out to reveal its influence. Both the stall margin and efficiency are improving with increasing of the hole’s diameter in the cases of diameter below than 2.5mm. At diameter of 2.5mm, the stall margin increment and the efficiency of the compressor are the highest among all 5 cases. However, in the case of 3.0mm, the stable working range enhancing as well as the efficiency is weakened because the velocity magnitude of the reinjected flow decreases. Therefore a key principle of choosing the diameter and the radial position of the hole is presented in the paper to get the best self-adaptive effect: enhancing stable running range as much as possible and keeping higher efficiency.
Genetic Algorithm for Gas Turbine Blading Design
Authors: Cuciumita Cleopatra F. , Vilag Valeriu A. , Silivestru Valentin , Porumbel Ionut
Published: May 2012

Designing a gas turbine from scratch has always been an extremely laborious task in terms of obtaining the desired power output and efficiency. Theoretical prediction of the performances of a gas turbine has proven in time to be a compromise between accuracy and simplicity of the calculus. Methods such as the Smith chart are very easy to apply, but to make an exact prediction of the flow in a turbine would lead to an almost infinite number of variables to be considered. A quite precise method of determining total-loss coefficients for a gas turbine, based on a large number of turbine tests, was developed by D.G. Ainley and G.C.R. Mathieson, with an error of the calculated efficiency within 2%. The accuracy of the method has been validated by Computational Fluid Dynamics simulations, included in the paper. Even if it is not a novel approach, the method provides accurate numerical results, and thus it is still widely used in turbine blade design. Its difficulty consists of the large number of man-hours of work required for estimating the performances at each working regime due to the many interdependent variables involved. Since this calculus must be conducted only once the geometry of the turbine is determined, if the results are not satisfactory one must go back to the preliminary design and repeat the entire process. Taking into account all the above, this paper aims at optimizing the efficiency of a newly design turbine, while maintaining the required power output. Considering the gas-dynamic parameters used for determining the preliminary geometry of a turbine, and the influence of the geometry upon the turbine efficiency, according to the procedure stated above, a Monte Carlo optimizing method is proposed. The optimization method consists in a novel genetic algorithm, presented in the paper. The algorithm defines a population of turbine stage geometries using a binary description of their geometrical configuration as the chromosomes. The turbine efficiency is the fitness function and also acts as the mating probability criterion. The turbine energy output is verified for each member of the population in order to verify that the desired turbine power is still within acceptable limits. Random mutations carried on by chromosome string reversal are included to avoid local optima. Hard limits are imposed on optimization parameter variation in order to avoid ill defined candidate solutions. The approach presented here significantly reduces the time between design goal definition and the prototype.
Improvement on Ignition Performance for a Lean Staged Low NOx Combustor
Authors: Kobayashi M. , Ogata H. , Oda T. , Matsuyama R. , Horikawa A. , Kinoshita Y. , Fujiwara Hitoshi
Published: May 2012

KHI (Kawasaki heavy industries Ltd, Japan) and JAXA (Japan Aerospace Exploration Agency) have been working together since 2004 to improve lean staged concentric fuel injector technologies. One of the weak points of a lean staged fuel injector is said to be ignition / light around performance. Ignition characteristics were assessed on several fuel injector configurations in burner tests. Laser diagnosis, CFD analysis and high-speed video camera recording were used to understand the effect of fuel injector geometry on fuel spray distribution and ignition characteristics. They showed a clear relationship between the burner geometry and ignition characteristics. Light around characteristics was evaluated with the burner configuration optimized in burner tests. Light around performance deteriorated in multi sector unit compared to that in burner test. CFD analysis and some ignition tests with different configuration of combustor gave a clue to restore the light around characteristics deteriorated in multi sector unit.
CFD Modeling Effects on Unsteady Multistage Simulation for a Transonic Axial Compressor
Authors: Yamagami Mai , Kodama Hidekazu , Kato Dai , Tsuchiya Naoki , Horiguchi Yasuo , Kazawa Junichi
Published: May 2012

Unsteady three-dimensional multistage calculations are performed for a highly loaded, high-speed axial compressor to investigate the impact of real geometry modeling and different numerical approaches on the accuracy of the performance prediction. First, two features of the real geometries are separately compared with the calculation which consists of a pure flow path model except that rotor tip clearances are considered. One treats leakage generated by part gaps between variable stator vanes and the annulus lines. Another incorporates seal cavities to model leakage underneath the shrouded stators. Then, the influence of different numerical approach with different turbulence models is also investigated. Discussion on the impact of the CFD modeling on the performance prediction focuses on the prediction accuracies of stage operating points and spanwise mixing. It is suggested that a realistic simulation of turbulent-type flow unsteadiness in a multistage machine is important for an accurate prediction of spanwise mixing phenomena.
Investigation of the Surge Behavior of a Multi-Stage Axial Compressor With a Multi-Sensor Probe
Authors: Waniczek P. , Jeschke P. , Schoenenborn H. , Metzler T.
Published: May 2012

The surge behavior of the first rotor of an eight-stage aero engine high pressure compressor has been investigated experimentally. For that purpose, a new multi-hole pressure probe was developed and adapted to the axial compressor test rig. Due to the high time resolution measurements (more than 45000 measuring points per surge cycle) it is possible to investigate the dynamic flow field of a surge cycle in a time-accurate manner. The results especially show the complex flow field structure at the surge inception. At the rotor leading edge the flow shows perturbations with high amplitudes and initiates the surge event, whereas the flow at the rotor trailing edge is less influenced. The inflow vector turns around the leading edge of the blade relatively slowly. During that turn around three different characteristic flow conditions have been identified. These are ‘zero rotor turning’, ‘turbine-like flow’ and ‘no flow’. ‘No flow’ means, that the absolute velocity vector reaches a flow angle where it consists of a pure tangential velocity component. That is the point where the reverse flow phase is initiated. A 180° shift of the flow direction at the rotor trailing edge is the consequence. After a quasi-steady reverse flow the acceleration of the flow starts. In total, this paper gives new and fundamental insights into the unsteady flow field phenomena during various surge cycles. Especially the transient velocity vector imparts a good idea of the flow field structure of a surging compressor.
DME as a Potential Alternative Fuel for Gas Turbines: A Numerical Approach to Combustion and Oxidation Kinetics
Authors: Glaude Pierre A. , Fournet Rene´ , Bounaceur Roda , Molie`re Michel
Published: May 2012

Many investigations are currently carried out in order to reduce CO2 emissions in power generation. Among alternative fuels to natural gas and gasoil in gas turbine applications, dimethyl ether (DME; formula: CH3-O-CH3) represents a possible candidate in the next years. This chemical compound can be produced from natural gas or coal/biomass gasification. DME is a good substitute for gasoil in diesel engine. Its Lower Heating Value is close to that of ethanol but it offers some advantages compared to alcohols in terms of stability and miscibility with hydrocarbons. While numerous studies have been devoted to the combustion of DME in diesel engines, results are scarce as far as boilers and gas turbines are concerned. Some safety aspects must be addressed before feeding a combustion device with DME because of its low flash point (as low as −83°C), its low auto-ignition temperature and large domain of explosivity in air. As far as emissions are concerned, the existing literature shows that in non premixed flames, DME produces less NOx than ethane taken as parent molecular structure, based on an equivalent heat input to the burner. During a field test performed in a gas turbine, a change-over from methane to DME led to a higher fuel nozzle temperature but to a lower exhaust gas temperature. NOx emissions decreased over the whole range of heat input studied but a dramatic increase of CO emissions was observed. This work aims to study the combustion behavior of DME in gas turbine conditions with the help of a detailed kinetic modeling. Several important combustion parameters, such as the auto-ignition temperature (AIT), ignition delay times, laminar burning velocities of premixed flames, adiabatic flame temperatures, and the formation of pollutants like CO and NOx have been investigated. These data have been compared with those calculated in the case of methane combustion. The model was built starting from a well validated mechanism taken from the literature and already used to predict the behavior of other alternative fuels. In flame conditions, DME forms formaldehyde as the major intermediate, the consumption of which leads in few steps to CO then CO2. The lower amount of CH2 radicals in comparison with methane flames seems to decrease the possibility of prompt-NO formation. This paper covers the low temperature oxidation chemistry of DME which is necessary to properly predict ignition temperatures and auto-ignition delay times that are important parameters for safety.
Experimental Study on a Notched Nozzle for Jet Noise Reduction
Authors: Ishii T. , Oinuma H. , Nagai K. , Tanaka N. , Oba Y. , Oishi T.
Published: May 2012

This paper describes an experimental study on a notched nozzle for jet noise reduction. The notch, a tiny tetrahedral dent formed at the edge of a nozzle, is expected to enhance mixing within a limited region downstream of the nozzle. The enhanced mixing leads to the suppression of broadband peak components of jet noise with little effect on the engine performance. To investigate the noise reduction performances of a six-notch nozzle, a series of experiments have been performed at an outdoor test site. Tests on the engine include acoustic measurement in the far field to evaluate the noise reduction level with and without the notched nozzle, and pressure measurement near the jet plume to obtain information on noise sources. The far-field measurement indicated the noise reduction by as much as 3 dB in terms of overall sound pressure level in the rear direction of the engine. The use of the six-notch nozzle though decreased the noise-benefit in the side direction. Experimental data indicate that the high-frequency components deteriorate the noise reduction performance at wider angles of radiation. Although the increase in noise is partly because of the increase in velocity, the penetration of the notches into the jet plume is attributed to the increase in sound pressure level in higher frequencies. The results of near-field measurement suggest that an additional sound source appears up to x/D = 4 due to the notches. In addition, the total pressure maps downstream of the nozzle edge, obtained using a pressure rake, show that the notched nozzle deforms the shape of the mixing layer, causing it to become wavy within a limited distance from the nozzle. This deformation of the mixing layer implies strong vortex shedding and thus additional noise sources. To improve the noise characteristics, we proposed a revised version of the nozzle on the basis of a computational prediction, which contained 18 notches that were smaller than those in the 6-notched nozzle. Ongoing tests indicate greater noise reduction in agreement with the computational prediction.
Thin Film Modelling for Aero-Engine Bearing Chambers
Authors: Wang C. , Morvan H. P. , Hibberd S. , Cliffe K. A.
Published: May 2012

This paper presents a dynamic mathematical model describing the thin film flow in aero-engine bearing chamber. By analyzing the depth averaged continuity equation and momentum equation term by term, the comprehensive physical mechanisms driving thin film flow are revealed. The terms that require extra modeling work are then identified. As a useful first approach, a thin film model based on presumed quadratic velocity profile is adopted. A preliminary study shows that this model can include the main film flow features in aero-engine bearing chamber, whilst maintain simple formulation and work efficiently. Finally, a converging computational strategy is obtained towards the numerical simulation of engine bearing chamber.
Highly Loaded LPC Blade and Non Axisymmetric Hub Profiling Optimization for Enhanced Efficiency and Stability
Authors: Lepot I. , Mengistu T. , Hiernaux S. , De Vriendt O.
Published: May 2012

The present contribution fits into the frame of the ongoing 7th Framework European Project DREAM (valiDation of Radical Engine Architecture systeMs). One of its main themes targets the development of contra-rotating open rotors with variable pitch blades which are known to provide 10 to 15% fuel burn reduction but are noisier than high by-pass turbofans. More specifically, the present research was conducted in the frame of work package 3.4 lead by Techspace Aero, dedicated for one part to the design of a high speed booster adapted to open rotor configurations, and for the second part, from which this paper is issued, to the investigation of 3D geometries to improve LPC efficiency. A reference rotor blade has first been designed, with high loading, especially at hub. To improve its efficiency, a backward sweep has then been applied as it tends to unload midspan sections. However, this performance gain came at the price of severe stall margin degradation, the criticality of the hub region being increased. Based on 1.5 stage 3D RANS simulations, automated surrogate-assisted optimization has then been exploited to respectively evaluate the potential benefit of tailored 2D contouring and 3D hub profiling a posteriori applied to the swept rotor blade and of joint 3D hub profiling and sweep optimization of the unswept baseline rotor blade. The potential benefit of 3D profiling will be demonstrated while the joint 3D profiling and blade stacking optimization shed light on the achievable interesting 3D effects combinations.
Validation and Analysis of Numerical Results for a Two-Pass Trapezoidal Channel With Different Cooling Configurations of Trailing Edge
Authors: Siddique Waseem , Shevchuk Igor V. , El-Gabry Lamyaa A. , Fransson Torsten H.
Published: May 2012

High inlet temperatures in a gas turbine lead to an increase in the thermal efficiency of the gas turbine. This results in the requirement of cooling of gas turbine blades/vanes. Internal cooling of the gas turbine blade/vanes with the help of two-pass channels is one of the effective methods to reduce the metal temperatures. Especially the trailing edge of a turbine vane is a critical area, where effective cooling is required. The trailing edge can be modeled as a trapezoidal channel. This paper describes the numerical validation of the heat transfer and pressure drop in a trapezoidal channel with and without orthogonal ribs at the bottom surface. A new concept of ribbed trailing edge has been introduced in this paper which presents a numerical study of several trailing edge cooling configurations based on the placement of ribs at different walls. The baseline geometries are two-pass trapezoidal channels with and without orthogonal ribs at the bottom surface of the channel. Ribs induce secondary flow which results in enhancement of heat transfer therefore for enhancement of heat transfer at the trailing edge, ribs are placed at the trailing edge surface in three different configurations: first without ribs at the bottom surface, then ribs at trailing edge surface in-line with the ribs at bottom surface and finally staggered ribs. Heat transfer and pressure drop is calculated at Reynolds number equal to 9400 for all configurations. Different turbulent models are used for the validation of the numerical results. For the smooth channel low-Re k-ε model, realizable k-ε model, the RNG k-ω model, low-Re k-ω model and SST k-ω models are compared, whereas for ribbed channel low-Re k-ε model and SST k-ω models are compared. The results show that the low-Re k-ε model, which predicts the heat transfer in outlet pass of the smooth channels with difference of +7%, underpredicts the heat transfer by −17% in case of ribbed channel compared to experimental data. Using the same turbulence model shows that the height of ribs used in the study is not suitable for inducing secondary flow. Also, the orthogonal rib does not strengthen the secondary flow rotational momentum. The comparison between the new designs for trailing edge shows that if pressure drop is acceptable, staggered arrangement is suitable for the outlet pass heat transfer. For the trailing edge wall, the thermal performance for ribbed trailing edge only, was found about 8% better than other configurations.
System Analysis of IGFC With Exergy Recuperation Utilizing Low-Grade Coal
Authors: Nomura Risa , Iki Norihiko , Kurata Osamu , Kawabata Masako , Tsutsumi Atsushi , Koda Eiichi , Furutani Hirohide
Published: May 2012

Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC) is expected to be the most efficient power generation system in coal fired power generation systems [1,2]. The Japanese project of the Strategic Technical Platform for Clean Coal Technology (STEP-CCT) aims a target efficiency of 65% (HHV) with exergy recuperation. We have been analyzing the processes of the exergy recuperated Integrated Coal Gasification Combined Cycle (IGCC) and the Advanced IGCC (A-IGCC) [3] which is expected to be realized in 2040. Previous studies have indicated a limitation of the quantity of high temperature steam in the case of auto-thermal reactions with the fluidized bed coal gasifier in the A-IGCC, in particular for TIT 1500 °C class gas turbine. The Advanced IGFC (A-IGFC) system can reduce the exergy loss resulting from combustion, and its ‘exergy recuperation’ is appealing. The waste heat exhausted from the fuel cells is recycled to the gasifier for steam reforming in an endothermic reaction with a low exergy loss and a high cold gas efficiency. Our current study focuses on the optimization of the unit configurations of the A-IGFC including gasifier, compressor, solid oxide fuel cell (SOFC), combustor, gas turbine, heat recovery steam generator (HRSG), and steam turbine. The process simulator HYSYS®.Plant (Aspen technology Inc.) is employed in order to express the gasifier, the SOFC and the other units. The optimum construction over the whole system by numerical simulation was examined for higher energy utilization efficiency. Under ideal conditions using bituminous coal, we verified the power generation efficiency to be 64.5% (HHV). However, utilizing low-grade coals, i.e., lignite and sub-bituminous coal, is deemed an important future energy resource to compensate for a decreasing supply of good-quality bituminous coal. For these low-grade coals, the power generation efficiency was as high as 53.6% (HHV) under the following conditions: Gasifier inlet: coal 23.6 Kg/s (667 MJ/s), steam 16.44 kg/s; Reactor reforming gas: 30.0, 8.7, 2.0, 0.8, 0.3, 0.05, 0.24, 0.14, 0.1 and 5.5 kg/s for CO, CO2, H2, CH4, C2H4, C2H6, C3H6, HCN, N2 and H2O respectively. The projected power outputs with this system were, SOFC: 214 MW; Gas turbine: 318 MW; Steam turbine: 86 MW.
Nonlinear Dynamic Analysis of a Multi-Gear Train With Time-Varying Mesh Stiffness Including Modification Coefficient Effect
Authors: Shiau T. N. , Chang J. R. , Huang K. H. , Cheng C. J. , Wang C. R.
Published: May 2012

The nonlinear dynamic analysis of a multi-gear train with time-varying mesh stiffness on account of the modification coefficient effect is in vestigated in this paper. The proposed application of the modification coefficient will revise the center distance of the gear pair, avoid undercut and raise the mesh stiffness of the designed gear system. In this study, the gear profile is generated from the relationship between the rack cutter and the gear work piece by using the envelope theory. The rack cutter with the modification coefficient increases the mesh stiffness and thus enhances the strength of the gear tooth. Then the time-varying mesh stiffness at the contact position of the gear pair is calculated from the tooth deflection analysis using the generated gear profile. With the obtained time-varying mesh stiffness, the nonlinear dynamic behavior of multi-gear train is investigated by using Runge-Kutta integration method. The numerical results of the studied examples show the harmonic motion, sub-harmonic motion, chaotic motion and bifurcation phenomenon of the gear train.
Experimental Investigation of Forced Response Impeller Blade Vibration in a Centrifugal Compressor With Variable Inlet Guide Vanes: Part 2—Forcing Function and FSI Computations
Authors: Zemp Armin , Abhari Reza S. , Schleer Matthias
Published: May 2012

As the second part of a two-part paper, this paper presents an experimental investigation of forced response impeller blade vibrations in a centrifugal compressor stage caused by variable inlet guide vanes. Although it is common practice to experimentally test the forced response blade vibration behavior of new impeller designs in terms of strain gauge or tip-timing measurements, the impact of the unsteady blade pressure distribution acting as an unsteady load on the blade surfaces is still not known. A centrifugal compressor impeller was therefore instrumented with dynamic strain gauges and fast-response pressure transducers to measure the forcing of the impeller blades for different compressor operating points and various inlet guide vane angle settings. The results showed a decrease in the excitation amplitudes for reduced mass flow rates of the compressor stage. The inlet guide vane angle setting affected the convection speed of the distortion pattern along the blade surface. An increase in the negative inlet guide vane angle caused higher excitation amplitudes especially in the inducer part of the blade. However, the largest negative inlet guide vane setting caused the smallest excitation amplitudes as this setup introduced the smallest amount of inlet distortion to the inlet flow field. A series of unidirectional fluid structure interaction calculations was performed to show the limitations and requirements of today’s numerical tools.
Conceptual Design of a Mid-Sized Semi-Closed Oxy-Fuel Combustion Combined Cycle
Authors: Sammak Majed , Jonshagen Klas , Thern Marcus , Genrup Magnus , Thorbergsson Egill , Gro¨nstedt Tomas , Dahlquist Adrian
Published: May 2012

This paper presents the study of a mid-sized semi-closed oxy-fuel combustion combined cycle (SCOC-CC) with net power output around 108 MW. The paper describes not only the power balance and the performance of the SCOC-CC, but also the conceptual design of the SCOC turbine and compressor. A model has been built in the commercial heat and mass balance code IPSEpro to estimate the efficiency of semi-closed dual-pressure oxy-fuel combustion combined cycle using natural gas as a fuel. In order to obtain the real physical properties of the working fluids in IPSEpro, the code was linked to the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP). The oxy-fuel turbine was modeled with the in-house Lund University package LUAX-T. Important features such as stage loading, loss modeling, cooling and geometric features were included to generate more accurate results. The oxy-fuel compressor has been modeled using a Chalmers university in-house tool for conceptual design of axial compressors. The conceptual design of the SCOC-CC process has a net efficiency of 47%. The air separation unit and CO2 compression reduce the cycle efficiency by 10 and 2 percentage points, respectively. A single-shaft configuration was selected for the gas turbine simplicity. The rotational speed chosen was 5200 rpm and the turbine was designed with four stages. All stage preliminary design parameters are within ranges of established industrial axial turbine design limits. The main issue is the turbine exit Mach number; the stage must be lightly loaded in terms of pressure ratio to maintain the exit Mach number below 0.6. The compressor is designed with 18 stages. The current value of the product of the annulus area and the blade rotational speed squared (AN2) was calculated and found to be 40·106.
Numerical and Experimental Study of Polydispersed Acetone Spray Dispersion and Evaporation in Turbulent Flow
Authors: Chrigui M. , Sadiki A. , Gounder J. , Masri A.
Published: May 2012

Characteristics of acetone spray in a turbulent flow were numerically predicted and compared to experimental measurements. The focus was on the effect of polydispersity on the dispersion and evaporation of a relatively volatile fuel that featured a wide range of Stokes numbers in a turbulent two phase flow. Droplets were generated using an ultrasonic atomizer. It produced a relatively uniform velocity distribution with a moderate carrier to fuel velocities ratio. The simulations were performed in the framework of Reynolds Averaging Navier Stokes equations along with the Eulerian-Lagrangian approach where 12 different classes of the dispersed phase were tracked. Droplets differed in diameter, mean and rms velocities, and numbers density. The transport equations of the carrier phase were formulated in an Eulerian reference frame that included terms which accounted for the exchange of mass, momentum, energy and turbulence quantities with the spray, i.e. fully two way coupling. The phase transition was modeled by the Langmuir-Knudsen law that accounted for non equilibrium effects based on a consistent determination of the molar mass fraction on the droplet surfaces. Effects of turbulence modulation on the vaporization processes were resolved by a thermodynamically consistent model that determined the turbulence intensity at the droplet location, which affected the vapor concentration gradient near the droplet surfaces. For the droplet diffusion, the Markov sequence model was improved by adding a correction drift term to the fluid fluctuation velocity at the parcel position along the droplet trajectory. This correction term aimed at accounting for the non-homogeneity effects in the turbulent flow. The different sub-models for the prediction of multiphase flow characteristics were applied to a 3D configuration that consisted of a spray nozzle mounted in a 4 m/s coflowing air stream. A number of carrier phase jet velocities were used, thus denoting a variation of the fuel to air mass loading. Radial profiles of the axial and radial velocities and its corresponding rms fluctuations of the acetone spray were predicted and compared to the experimental measurements. Spray mass flux, which determined the degree of evaporation, was plotted at different axial location from the nozzle exit plane. The study aimed at assessing the combination of different models applied to a mono-component spray for the prediction of two-phase flow and at investigating what should be improved for the case of real fuel (eg. Kerosene) for industrial configurations.
Towards a Fully Coupled Component Zooming Approach in Engine Performance Simulation
Authors: Pilet Julien , Lecordix Jean-Loi¨c , Garcia-Rosa Nicolas , Bare`nes Roger , Lavergne Ge´rard
Published: May 2012

This paper presents a fully-coupled zooming approach for the performance simulation of modern very high bypass ratio turbofan engines developed by Snecma. This simulation is achieved by merging detailed 3D simulations and map component models into a unified representation of the whole engine. Today’s state-of-the-art engine cycle analysis are commonly based on component mapping models which enable component interactions to be considered, while CFD simulations are carried out separately and therefore overlook those interactions. With the methodology discussed in this paper, the detailed analysis of an engine component is no longer considered apart, but directly within the whole engine performance model. Moreover, all links between the 3D simulation and overall engine models have been automated making this zooming simulation fully-integrated. The simulation uses the PROOSIS propulsion object-oriented simulation software developed by Empresarios Agrupados for whole engine cycle analysis and the computational fluid dynamics (CFD) code CEDRE developed by ONERA for the high fidelity 3-D component simulations. The whole engine model is created by linking component models through their communication ports in a graphical user-friendly interface. CFD simulated component models have been implemented in PROOSIS libraries already providing mapped components. Simple averaging techniques have been developed to handle 3D-to-0D data exchange. Boundary conditions of the whole engine model remain the same as for the typical 0-D engine cycle analysis while those of the 3-D simulations are automatically given by PROOSIS to CEDRE. This methodology has been applied on an advanced very high bypass ratio engine developed by Price Induction. The proposed zooming approach has been performed on the fan stage when simulating Main Design Point as well as severe case of off-design conditions such as wind-milling. The results have been achieved within the same time frame of a typical CFD fully-converged calculation. A detailed comparison with upcoming test results will provide a first validation of the methodology and will be presented in a future paper.
Computational and Experimental Analysis of an Industrial Gas Turbine Compressor
Authors: Wiedermann Alexander , Frank Dirk , Orth Ulrich , Beukenberg Markus
Published: May 2012

Test rig results and their comparison with computational analyses of a highly-loaded 11-stage compressor for a newly developed industrial gas turbine will be presented in this paper. The scope of the tests has been validation of aerodynamic and mechanical features of the bladed flow path to meet both the demands for single- and dual-shaft operation of the gas turbine. The test was carried out in three phases using extensive instrumentation. In phase 1 the front stages have been tested, and in phase 2 the test of the full 11-stage compressor was performed including numerous aerodynamic and structural check-outs. Vane and blade vibration modes were measured in all rows with numerous strain gauges using a telemetry system and Tip Timing, which additionally was applied to the front stage rotors. Concerning the mechanical design, finite element predictions of the vibration modes of all blades and vanes were carried out in the design phase to guarantee safe and resonance-free operation for a wide range of operational speeds which could be verified by the test data up to higher modes. Flow field computations were carried out with both a through flow solver and full 3-D viscous multistage solver based on Denton’s TBLOCK, where all rotor and stator flow fields had been solved simultaneously and compared with experiments. The effects of tip clearance and stator cavities on compressor performance have been taken into account by the computational analysis. Effects of inlet distortion were examined in phase 3. Comprehensive comparisons of computed and measured results will be presented. The extensive instrumentation gave also insight into flow details as vane pressure distributions and total pressure profiles in span wise direction. It will be shown that the agreements of predicted and measured data were excellent.
Heavy-Duty Gas Turbines Axial Thrust Calculation in Different Operating Conditions
Authors: Bozzi Luca , Malavasi Francesco , Garotta Valeria
Published: May 2012

Several types of forces give a contribution to the axial thrust of gas turbines shafts: flow-path forces (due to blades, endwalls and shrouds of compressor and turbine rows), forces acting on the surfaces of rotor-stator cavities, disks forces (due to the different pressure levels in the rotating cavities inside the rotor), etc. As a rule, the estimation of the rotor thrust needs the handling of a large amount of output data, resulting from different codes. This paper presents a calculation tool to estimate the rotor axial thrust from the results of compressor, turbine and secondary air system calculations. Applications to heavy-duty gas turbines of different classes and sizes (namely two models of AEx4.3A F-class family, AE64.3A and AE94.3A, and the AE94.2 E-class gas turbines) are presented. On the basis of calculation results, in base load and part load operating conditions, guidelines to determine the rules of variation of axial bearing thrust and the relating scatter band are given. Pressure transducers were installed on the bearing pads of different gas turbines, in order to provide experimental data for the calibration of the calculation procedure. Comparison of experimental data with numerical results proves that the proposed calculation tool properly evaluates gas turbines rotor thrust and the axial bearing load.
Tip Clearance Investigation of a Ducted Fan Used in VTOL UAVS: Part 1—Baseline Experiments and Computational Validation
Authors: Akturk Ali , Camci Cengiz
Published: May 2012

Ducted fans that are popular choices in vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) offer a higher static thrust/power ratio for a given diameter than open propellers. Although ducted fans provide high performance in many VTOL applications, there are still unresolved problems associated with these systems. Fan rotor tip leakage flow is a significant source of aerodynamic loss for ducted fan VTOL UAVs and adversely affects the general aerodynamic performance of these vehicles. The present study utilized experimental and computational techniques in a 22″ diameter ducted fan test system that has been custom designed and manufactured. Experimental investigation consisted of total pressure measurements using Kiel total pressure probes and real time six-component force and torque measurements. The computational technique used in this study included a 3D Reynolds-Averaged Navier Stokes (RANS) based CFD model of the ducted fan test system. RANS simulations of the flow around rotor blades and duct geometry in the rotating frame of reference provided a comprehensive description of the tip leakage and passage flow. The experimental and computational analysis performed for various tip clearances were utilized in understanding the effect of the tip leakage flow on aerodynamic performance of ducted fans used in VTOL UAVs. The aerodynamic measurements and results of the RANS simulations showed good agreement especially near the tip region.
A Correlation Between Vibration Stresses and Flow Features of Steam Turbine Long Blades in Low Load Conditions
Authors: Shibukawa Naoki , Tejima Tomohiro , Iwasaki Yoshifumi , Murakami Itaru , Saito Ikuo
Published: May 2012

The vibration stress of long steam turbine blades during low load operating conditions is examined in this paper. A series of experiments has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressure fluctuation. It is found that a steady pressure distribution over the blade tip is much to do with the unsteady pressure and fluctuation of the vibration stress. A precise investigation of unsteady wall pressure near blade tip explains the relationship between pressure fluctuation and the vibration stress, and reveals the existence of particular frequency which affects blade axial modes. Blade to blade flow mechanisms and aerodynamic force and properties during low load operating condition were investigated by a steady CFD simulation. FFT of aerodynamic force by another steady full arc CFD simulation provides various pattern of harmonic excitation which account for the behavior of vibration stresses well. The mechanism of the rapid stress increase and a step drop were examined by considering CFD results and measured unsteady pressure data together.
Influence of Surface Roughness on the Profile and End-Wall Losses in Low Pressure Turbines
Authors: Va´zquez Rau´l , Torre Diego , Partida Fernando , Arman˜anzas Leyre , Antoranz Antonio
Published: May 2012

The influence of surface roughness on the profile and end-wall total pressure losses in Low Pressure Turbines was investigated experimentally in a turbine high-speed rig. The rig consisted of a rotor-stator configuration. Both rows of airfoils are high lift, high aspect ratio and high turning blades that are characteristic of state of the art Low Pressure Turbines. The stator airfoils (both vanes and platforms) were casted and afterwards they were barreled to improve their surface finish up to 1.73 μm Ra. Then they were assembled in the rig and tested. The stator was traversed upstream and downstream with miniature pneumatic probes to obtain total pressure, flow angle and static pressure flow fields. Once this test was completed the rig was disassembled and the stator airfoils were polished to achieve a roughness size of 0.72 μm Ra, characteristic of Low Pressure Turbine polished airfoils. Once again, the stators were assembled in the rig and tested to carry out a back-to-back comparison between the two different surface roughnesses. The total pressure profile and end-wall losses were measured for a wide range of Reynolds numbers, extending from 8×104 to 2.4×105, based on suction surface length (Res∼1.5 ReCx) and exit Mach number of 0.61. Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses, flow angles and helicity. The results agree with previous studies of roughness in Turbines, a beneficial effect of surface roughness was found at very low Reynolds numbers, in stagnation pressure losses.
Experimental Investigation of the 4th Generation DLE Burner Concept: Emissions and Fuel Flexibility Performance at Atmospheric Conditions
Authors: Carrera Arturo Manrique , Andersson Mats , Na¨svall Henrik
Published: May 2012

The “4th Generation DLE” (4G-DLE) gas turbine burner has been developed at Siemens Industrial Turbomachinery AB in Finspong, Sweden (SIT). The present document describes the design concepts of the 4G-DLE burner; emission performance and fuel flexibility capacity. These features were explored at atmospheric conditions at SIT. High concentrations of H2 and N2 mixed with natural gas were used in the experiments. Emissions (NOx, Unburned hydrocarbons, CO), combustion dynamics and temperature operation range were evaluated. Moreover, operation characteristics of the burner were investigated through forced flashback, flameouts and unfavorable ignition situations. The fuel flexibility concerning H2 stretched up to 90% vol. in a mixture with natural gas. In the case of N2 it was possible to use over 50% vol. mixed with natural gas. The operation was stable in all cases. The 4G-DLE burner showed good NOx emission performance that was linearly dependent on the flame temperature, while CO levels were also low. This fact reveals the high mixing level achieved in the burner. Finally; the burner operated over in a wide flame temperature range (approximately 200 K), showing both good stability and good emission levels.
A New Hex-8 Finite Element for Gas Turbine Engine Fatigue Life Prediction
Authors: Tarar Wasim , Shen M.-H. Herman
Published: May 2012

High cycle fatigue is the major governing failure mode in aerospace structures and gas turbine engines. Different design tools are available to predict number of cycles to failure for a component subjected to fatigue loads. An energy-based fatigue life prediction framework was previously developed in recent research for prediction of axial, bending and torsional fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. A 1-D ROD element for unixial fatigue, a BEAM element for bending fatigue and a QUAD-4 element for biaxial fatigue were developed by authors based on this constitutive law. In this study, the energy expressions that construct the new constitutive law are integrated into minimum potential energy formulation to develop a new HEX-8 BRICK finite element for fatigue life prediction. The newly developed HEX-8 BRICK element has 8 nodes and each node has 3 degrees of freedom (DOF) in x, y and z directions. This element is further modified to add the rotational and bending DOFs for application to real world three dimensional (3D) structures and components. HEX-8 BRICK fatigue finite element has capability to predict the number of cycles to failure for 3-D objects subjected to multiaxial stresses. The new HEX-8 element is benchmarked with previously developed uniaxial tension/compression finite element in order to verify the new development. The comparison of finite element method (FEM) results to existing experimental fatigue data, verifies the new finite element development for fatigue life prediction. The final output of this finite element analysis is in the form of number of cycles to failure for each element in ascending or descending order. Therefore, the new finite element framework can predict the number of cycles to failure at each location in gas turbine engine structural components. The new finite element provides a very useful tool for fatigue life prediction in gas turbine engine components as it provides a complete picture of fatiguing process. The performance of the HEX-8 fatigue finite element is demonstrated by comparison of life prediction results for A16061-T6 to previously developed multiaxial fatigue life prediction approach by the authors. Another set of comparison is made to results for type 304 stainless steel data.
Thrust Reverser for a Separate Exhaust High Bypass Ratio Turbofan Engine and its Effect on Aircraft and Engine Performance
Authors: Mahmood Tashfeen , Jackson Anthony , Sethi Vishal , Pilidis Pericles
Published: May 2012

This paper discusses thrust reversing techniques for a separate exhaust high bypass ratio turbofan engine and its effect on aircraft and engine performance. Cranfield University is developing suitable thrust reverser performance models. These thrust reverser performance models will subsequently be integrated within the TERA (Techno-economic Environmental Risk Analysis) architecture thereby allowing for more detailed and accurate representations of aircraft and engine performance during the landing phase of a typical civil aircraft mission. The turbofan engine chosen for this study was CUTS_TF (Cranfield University Twin Spool Turbofan) which is similar to the CFM56-5B4 engine and the information available in the public domain is used for the engine performance analysis along with the Gas Turbine Performance Software, ‘GasTurb 10’ [1]. The CUTEA (Cranfield University Twin Engine Aircraft) which is similar to the Airbus A320 is used alongside with the engine model for the thrust reverser performance calculations. The aim of this research paper is to investigate the effects on aircraft and engine performance characteristics due to the pivoting door type thrust reverser deployment. The paper will look into the overall engine performance characteristics and how the engine components get affected when the thrust reversers come into operation. This includes the changes into the operating point of fan, booster, HP compressor, HP turbine, LP turbine, bypass nozzle and core nozzle. Also, thrust reverser performance analyses were performed (at aircraft/engine system level) by varying the reverser exit area by ± 5% and its effect on aircraft deceleration rate, deceleration time and landing distances were observed.
Numerical Simulation and Full Scale Landing Test of a 12.5MW Vertical Motorcompressor Levitated by Active Magnetic Bearings
Authors: Masala Andrea , Vannini Giuseppe , Ransom David , Moore Jeff , Baudelocque Luc
Published: May 2012

The development of a hermetically sealed, high speed, high performance motor-compressor for subsea application was started by GE Oil & Gas in 2006. The bearings consist of Active Magnetic Bearings (AMBs) as primary bearings and angular contact ball bearing pairs as auxiliary bearings, both provided by S2M. To mitigate the risk of rotor or stator component damage in case of a rotor emergency landing from full speed/full load conditions, a new numerical tool for predicting rotor and stator dynamics during the drop phase was developed in 2007 by GE Oil & Gas jointly with the Southwest Research Institute. In addition, a scaled vertical rotor drop test rig was built to validate the numerical tool, to perform endurance tests on the auxiliary bearings and to identify failure modes and relevant predictors. The numerical tool was extended to predict the transient rotor drop dynamics of the full-scale prototype machine during field operation. As a conclusion of the extensive factory acceptance test performed on the prototype machine, a rotor drop test with five drops on auxiliary bearings from full speed/full load was performed. This paper presents the results of the experimental activity in terms of rotordynamic and auxiliary bearing performance. In addition, a comparison between measured and predicted parameters (i.e., rotor whirl frequency and amplitude) is discussed, highlighting the strong interaction between the axial and radial dynamics of the rotor on auxiliary bearings during coast-down. Finally, a detailed description of the post-test inspection of the auxiliary bearings and compressor internals is given.