bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Chord Length and Inlet Boundary Layer on the Secondary Losses of Turbine Blades
Authors: Sauer Helmut , Schmidt Robin , Vogeler Konrad
Published: January 2011

In the present paper results concerning the influence of chord length and inlet boundary layer thickness on the endwall losses are discussed. The investigations were performed in a low speed cascade tunnel using the turbine profile T40. The deflection of 90 and 70 deg, the velocity ratio in the cascade from 1.0 to 3.5 as well as the chord length of 100,200 and 300 mm were predetermined. In a measurement distance behind the cascade of s2/l = 1, an approximate proportionality of endwall losses and chord length was observed in a wide range of velocity ratios. At small measurement distances (e.g. s2/l = 0.4), this proportionality does not exist. If aside from the flow path behind the cascade the flow path in the cascade is approximately incorporated, a proportionality to the chord length at small measurement distances can be obtained, too. Then to a large extent, the magnitude of the endwall losses is dependent on the length in main flow direction. At velocity ratios near 1.0, the influence of the chord length decreases rapidly, while at a velocity ratio of 1.0, the endwall losses are independent of chord length. By varying the inlet boundary layer thickness no correlation of displacement thickness and endwall losses was achieved. With a calculation method according to the modified integral equation by van Driest, the velocity gradient on the wall, the wall shear stress and the local friction coefficient were determined and their influence on the endwall losses analyzed.
Experimental Investigations of Pressure Losses on the Performance of a Micro Gas Turbine System
Authors: Zanger Jan , Widenhorn Axel , Aigner Manfred
Published: January 2011

Pressure losses between compressor outlet and turbine inlet are a major issue of overall efficiency and system stability for a SOFC/MGT hybrid power plant system. The goal of this work is the detailed analysis of the effects of additional pressure losses on MGT performance in terms of steady-state and transient conditions. The experiments were performed at the micro gas turbine test rig at the German Aerospace Centre in Stuttgart using a butterfly control valve to apply additional pressure loss. The paper reports electric power and pressure characteristics at steady-state conditions, as well as, a new surge limit, which was found for the Turbec T100 micro gas turbine. Furthermore, the effects of additional pressure loss on compressor surge margin are quantified and a linear relation between relative surge margin and additional pressure loss is shown. For transient variation of pressure loss at constant turbine speed time delays are presented and a compensation issue of the commercial gas turbine controller is discussed. Finally, bleed-air blow-off and reduction of turbine outlet temperature are introduced as methods of increasing surge margin. It is quantified that both methods have a substantial effect on compressor surge margin. Furthermore, a comparison between both methods is given in terms of electric power output.
A Probabilistic Secondary Flow System Design Process for Gas Turbine Engines
Authors: Ramerth D. L. , MirzaMoghadam A. V. , Kiratsingh A. , Banda G.
Published: January 2011

Gas turbine engine secondary flow systems are sensitive to variation in part dimensions, clearances, flow coefficients, swirl ratios, head loss factors, tolerances, boundary conditions, etc. This paper reveals a process and software application which embodies the process wherein both offer a measurable contribution to secondary airflow system reliability. The probabilistic methodology is empirically validated by (1) applying it to an engine component that failed in a validation test, and (2) demonstrating that a multiple order sensitivity analysis performed during detailed design was unable to detect a failure mode while a probabilistic analysis revealed a small yet significant risk of catastrophic failure. Therefore, a secondary flow analyst does not have a justifiable reason to be highly confident of a design qualified by a first, second, or higher order sensitivity analysis. The last example empirically demonstrates compatibility of optimization techniques with probabilistic methods (as part of the process) to quantify the likelihood of failure and reveal an optimized design space of key characteristics where risk is eliminated and the effects of variation are controlled. Trade study analysis is more valuable if it includes a quantitative evaluation of the effects of variation on alternate designs and the response to failure modes. A key feature of the software application is a relational database with the capability to configure and effectively manage flow networks in many forms including, a status model, failure modes of the status model, multiple alternative designs as well as failure modes specific to an alternative design.
Enhancement of Simple Gas Turbine System and Cogeneration Power Plant Using Dual Fueling of Combustion Chamber: Based on Endogenous and Exogenous Exergy Destruction Concepts
Authors: Razmara Nayyer , Khoshbakhti Saray Rahim
Published: January 2011

Exergy analysis provides useful information about the system optimization. An exergy analysis identifies the sources of thermodynamic inefficiencies by evaluating the exergy destruction within each system component. Splitting the exergy destruction into endogenous/exogenous parts represents a new development in the exergy analysis of energy conversion systems. The present work is an attempt to investigate the combustion process in a simple gas turbine and a cogeneration power plant based on the general concept of endogenous and exogenous exergy destruction. Therefore, using a graphical approach, the advanced exergy analysis is applied to both cycles with different fuels such as methane and diesel. Also, dual-fueling of combustion chamber is investigated based on the aforementioned approach in which 90% substitution of methane fuel for diesel one is considered. It is found that, in both cycles the combustion chamber has the largest value of the endogenous exergy destruction. The exergetic efficiency of combustion chamber increases when methane fuel is substituted for diesel fuel. Therefore, cycles efficiencies have been enhanced when fuel is substituted for diesel one. The results obtained here may provide some useful information for the optimal design and performance improvement of these cycles.
Propulsive Efficiency of Plane and Axisymmetric Nozzles With Non-Uniform Velocity Distributions
Authors: Kozˇulovic´ Dragan
Published: January 2011

The impact of non-uniform velocity distributions at the exit of plane and axisymmetric nozzles is investigated. For this aim, a general equation for the propulsive efficiency has been derived. Velocity profiles of trigonometric and quadratic form, which provide the same thrust force as constant velocity profiles, have been analysed. Only potential effects of the velocity distribution have been investigated. It is shown that the velocity non-uniformities reduce the propulsive efficiency. This reduction is negligible for small non-uniformities, but it can be up to 20% for large non-uniformities. The results indicate that the constant velocity profile is the optimum distribution for the propulsive efficiency.
A Preliminary Numerical Study on the Effect of High Freestream Turbulence on Anti-Vortex Film Cooling Design at High Blowing Ratio
Authors: Hunley Benson K. , Nix Andrew C. , Heidmann James D.
Published: January 2011

Researchers at NASA Glenn Research Center have developed and investigated a novel film cooling design, the anti-vortex hole (AVH), which has been shown to cancel or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low turbulence levels. This paper presents preliminary CFD results on the film effectiveness and net heat flux reduction at high blowing ratio and elevated freestream turbulence levels for the adjacent AVH. Baseline cases at low turbulence levels of 5% intensity and length scale of Λx/dm = 1 with a nominal blowing ratio of 2 and a density ratios of 1 and 2 were compared to previous results reported by Heidmann [1]. Higher freestream turbulence cases were investigated with a turbulence intensity and length scale of 10% and Λx/dm = 1 and 3, respectively. Results showed that higher freestream turbulence improves adiabatic effectiveness for the AVH design.
Development of Performance Deterioration Diagnosis Method for Gas Turbine Combined Cycle Power Plants
Authors: Takahashi Toru , Koda Eiichi , Nakao Yoshinobu
Published: January 2011

Recently, it is more necessary to maintain or improve the thermal efficiency of actual thermal power plants to reduce CO2 emission and energy consumption in the world, and it is also important to reduce the maintenance cost of commercial thermal power plants. Thus, it is crucial to investigate power plant performance deterioration factors and solve problems related to these factors promptly when the thermal efficiency decreases. However, it is difficult to understand the internal state of power plants sufficiently and to determine power plant performance deterioration factors only from operation data because actual thermal plants are composed of many components and are very complex systems. In particular, it is more difficult to understand performance deterioration in gas turbine combined cycle (GTCC) power plants than in steam power plants because the performance changes markedly in GTCC power plants depending on atmospheric conditions (temperature, pressure, humidity). In other words, when thermal efficiency changes, it is difficult to determine whether the cause is the change in external factors or that in the performance of the component. Therefore, we develop a method based on heat balance analysis to calculate the immeasurable quantity of state and the efficiency of each component in GTCC power plants, and to correct the performance of each component in a plant to a standard state using the performance function obtained from long-term operation data. Through the method, the analysis of the effects of deterioration factors on thermal efficiency becomes possible, and the performance of a plant can be simulated when the operation conditions are changed. Thus, we can determine the main factor that affects thermal efficiency using our method.
Experimental Methodology for Determining Turbomachinery Blade Damping Using Magnetic Bearing Excitation and Non-Contacting Optical Measurements
Authors: Provenza Andrew J. , Duffy Kirsten P.
Published: January 2011

Experiments to determine the effects of turbomachinery fan blade damping concepts such as passively shunted piezoelectric materials on blade response are ongoing at the NASA Glenn Research Center. A vertical rotor is suspended and excited with active magnetic bearings (AMBs) usually in a vacuum chamber to eliminate aerodynamic forces. Electromagnetic rotor excitation is superimposed onto rotor PD-controlled support and can be fixed to either a stationary or rotating frame of reference. The rotor speed is controlled with an air turbine system. Blade vibrations are measured using optical probes as part of a Non-Contacting Stress Measurement System (NSMS). Damping is calculated from these measurements. It can be difficult to get accurate damping measurements using this experimental setup and some of the details of how to obtain quality results are seemingly nontrivial. The intent of this paper is to present those details.
Unsteady Tip Leakage Flow Characteristics and Heat Transfer on Turbine Blade Tip and Casing
Authors: Rahman Md Hamidur , Kim Sung In , Hassan Ibrahim , El Ayoubi Carole
Published: January 2011

An unsteady numerical investigation was performed to examine time dependent behaviors of the tip leakage flow structures and heat transfer on the rotor blade tip and casing in a single stage gas turbine engine. A transonic, high-pressure turbine stage was modeled and simulated using a stage pressure ratio of 3.2. The rotor’s tip clearance was 1.2 mm in height (3% of the rotor span) and its speed was set at 9500 rpm. Periodic flow is observed for each vane passing period. Tip leakage flow as well as heat transfer data showed highly time dependent behaviors. A stator trailing edge shock appears as the turbine stage is operating at transonic conditions. The shock alters the flow condition in the rotor section, namely, the tip leakage flow structures and heat transfer rate distributions. The instantaneous Nusselt number distributions are compared to the time averaged and steady-state results. The same patterns in tip leakage flow structures and heat transfer rate distributions were observed in both unsteady and steady simulations. However, the unsteady simulation captured the locally time-dependent high heat transfer phenomena caused by the unsteady interaction with the upstream vane trailing-edge shock and the passing wake.
An Analysis of the Merits of CFD for the Performance Prediction of a Low Pressure Steam Turbine Radial Diffuser
Authors: Beevers Adam , Congiu Francesco , Pengue Fabio , Mokulys Thomas
Published: January 2011

The performance of the last stage and the diffuser of a low pressure steam turbine module are inherently linked. Design alterations in one part must take into consideration the subsequent effects imposed upon the other. Through a linked design system, including both the last stage and the exhaust, the last stage performance can be predicted more accurately and hence further performance improvements are possible. The importance of a valid prediction for the effects of the diffuser upon last stage power and efficiency become even more important when considering retrofit applications. In a retrofit project, a new flow path including modernised blades are installed in an existing older steam turbine casing. In these cases, the exhaust geometry does not lend itself to allowing the last stage to perform to its originally predicted level, but an optimization has to be established for a diffuser design, that links the last stage blade to the exhaust. This paper presents the coupled CFD design system, used by Alstom Power, to highlight the importance of including the 3D exhaust geometry, coupled to the last stage, when conducting last stage performance calculations. The test case is of a typical retrofit application. A comparison with measured test data shows the significance of the fidelity of any CFD system claiming to predict last stage performance, especially when used during the optimisation process of the diffuser.
Non-Linear Forced Response Analysis of Mistuned Bladed Disk Assemblies
Authors: Yu¨mer M. Ersin , Cig˘erog˘lu Ender , O¨zgu¨ven H. Nevzat
Published: January 2011

Forced response analysis of bladed disk assemblies plays a crucial role in rotor blade design, and therefore has been investigated by researchers extensively. However, due to lack of computation power, several studies in the literature utilize either linear mistuned models which are short of capturing nonlinear effects, or non-linear tuned models which do not catch the effects of mistuning. Studying the combined effect of the two, namely non-linearity and mistuning, is relatively recent and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom related with the non-linear elements. In this paper, a new approach is proposed to predict forced response of frictionally damped mistuned bladed disk assemblies in modal domain. A friction element, which enables normal load variation and separation of the contact interface, is utilized to determine the non-linear contact forces in three-dimensional space, and harmonic balance method is used to obtain a relationship between the non-linear contact forces and the relative motion. As mistuning phenomenon destroys the cyclic symmetry, modeling the whole assembly rather than a sector of it is necessary, which increases the number of non-linear elements required considerably. In the proposed approach, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is proportional to the number of modes retained, rather than the number of degrees of freedom related with the nonlinear elements. Therefore, the proposed approach can be applied to realistic bladed disk models without increasing the number of non-linear equations. Moreover, to accomplish this it is not required to use a reduced order model in the method suggested. Two case studies are presented to illustrate the implementation of the method: a lumped parameter bladed disk model and an academic bladed disk model with shrouds.
Disturbance Field Characteristics of a Transversely Excited Annular Jet
Authors: O’Connor Jacqueline , Natarajan Shweta , Malanoski Michael , Lieuwen Tim
Published: January 2011

This paper describes an investigation of transverse acoustic instabilities in premixed, swirl-stabilized flames. Additional measurements, beyond the scope of the current work, are described in O’Connor et al. [1]. Transverse excitation of swirling flow involves complex interactions between acoustic waves and fluid mechanic instabilities. The flame’s response to transverse acoustic excitation is a superposition of both acoustic and vortical disturbances that fluctuate in both the longitudinal and transverse direction. In the nozzle near field region, the disturbance field is a complex superposition of convecting vortical disturbances, as well as longer wavelength transverse and longitudinal acoustic disturbances. Farther downstream, the disturbance field is dominated by the transverse acoustic field. The phasing between the disturbances on the inside and outside of the burner annulus, as well as the left and right sides of the burner annulus is a strong function of the transverse disturbance field characteristics. For cases where the burner centerline is an approximate pressure node and velocity anti-node, the mass flow out of the left and right sides of the burner actually oscillates out-of-phase with respect to each other. In contrast, for cases where the centerline is a pressure anti-node, the burner responds symmetrically about the burner and annulus centerlines. These results show that the burner response characteristics strongly depend upon their location in the acoustic mode shape.
An Experimental Study of Heat Transfer and Pressure Drop on the Bend Surface of a U-Duct
Authors: Salameh Tareq , Sunden Bengt
Published: January 2011

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct. Such duct geometries can be found in many engineering applications where cooling air extracts heat from hot internal walls of the duct, e.g., passage cooling inside gas turbine blades. Both friction factors and convective heat transfer coefficients were measured inside a U-duct for three different cases, namely (a) the smooth straight part, (b) the smooth bend (turn) part, and (c) a rough (ribbed) bend (turn) part. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2, the inside length of the bend part 240 mm, the cross section area of the rib was 5×5 mm2 and the rib height-to-hydraulic diameter ratio, e/Dh, was 0.1. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configuration can be changed. Both the U-duct and the rib were made from plexiglass material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The rib was placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The friction factor ratio and the heat transfer enhancement ratio for case (c) at a Reynolds number of 20,000 were 48.75 and 2.66, respectively. It is found that the presence of the rib increases the heat transfer coefficient on the outer wall of the bend part (tip of side U-duct). The uncertainties were 3% and 6% for the Nusselt number and friction factor, respectively.
Numerical Investigation Into the Unsteady Aerodynamics of a Ducted Helicopter Tail Rotor Under Side-Wind Conditions
Authors: Kainz Marc , Danner Florian , Kau Hans-Peter , Le Chuiton Fre´de´ric
Published: January 2011

A numerical study into the unsteady aerodynamics of a ducted helicopter tail rotor is presented. Computations were carried out for ideal hover flight conditions and under the influence of side-wind. The results are validated against existing experimental performance data. The investigated numerical model incorporates the full annulus turbomachinery components as well as the entire tail boom including non-axis-symmetric casing contour, drive shaft fairing, fin and stabilisers. The rotor is characterised by an uneven azimuth-wise blade distribution, while the stator vanes complemented by the drive shaft fairing are distributed evenly. For the computational fluid dynamics analysis the fully turbulent three-dimensional Favre-averaged Navier-Stokes equations were solved on a Chimera grid system with 24.7 million cells. Besides thrust and shaft power characteristics, the varying blade loading due to the azimuth-wise position and the side-wind effect is analysed.
Avoidance of Gas Turbine Failure Using Metallurgical Analysis and Engine Health Monitoring as Predictive Tools
Authors: Canteenwalla Pervez , Ingistov Steve , Nagy Douglas
Published: January 2011

Combining metallurgical analysis with performance analysis is a powerful tool for engine health monitoring and can aid in determining the root cause of component failure. A case study is presented for an industrial gas turbine engine operating at BP Watson Cogeneration Company in Carson, California where accelerated material aging and coating depletion were found in the first-stage turbine buckets after an engine up-rate to an increased firing temperature. After the material degradation was discovered, the engine was intended to be derated back to its original firing temperature, however, the performance analysis found the engine was still operating in a higher firing condition which would have continued to cause accelerated damage to the turbine buckets if not detected. Through combined analysis efforts, the error was found and corrected before the units failed from overheating.
Experimental and Analytical Investigations of a Low Pressure Model Turbine During Forced Response Excitation
Authors: Heinz Christoph , Schatz Markus , Casey Michael V. , Stu¨er Heinrich
Published: January 2011

To guarantee a faultless operation of a turbine it is necessary to know the dynamic performance of the machine especially during start-up and shut-down. In this paper the vibration behaviour of a low pressure model steam turbine which has been intentionally mistuned is investigated at the resonance point of an eigenfrequency crossing an engine order. Strain gauge measurements as well as tip timing analysis have been used, whereby a very good agreement is found between the methods. To enhance the interpretation of the data measured, an analytical mass-spring-model, which incorporates degrees of freedom for the blades as well as for the rotor shaft, is presented. The vibration amplitude varies strongly from blade to blade. This is caused by the mistuning parameters and the coupling through the rotor shaft. This circumferential blade amplitude distribution is investigated at different operating conditions. The results show an increasing aerodynamic coupling with increasing fluid density, which becomes visible in a changing circumferential blade amplitude distribution. Furthermore the blade amplitudes rise non-linearly with increasing flow velocity, while the amplitude distribution is almost independent. Additionally, the mechanical and aerodynamic damping parameters are calculated by means of a non-linear regression method. Based on measurements at different density conditions, it is possible to extrapolate the damping parameters down to vacuum conditions, where aerodynamic damping is absent. Hence the material damping parameter can be determined.
Performance Study for the Benefits of a Variable Pitch Composite Fan
Authors: Mazzawy Robert S.
Published: January 2011

This paper describes the installed performance potential for a recently patented new design concept for a variable pitch composite fan blade [1,2]. The unique characteristic of this design is the compactness and light weight of the assembly of fan plus variable pitch mechanism. This design enables turbofan engine cycles with higher propulsive efficiency that previously were not viable due to high installation weight and performance penalties. As part of its mandate to support new technology that improves fuel efficiency, the Connecticut Coalition for the Advancement of Technology (CCAT) sponsored a study to quantify the potential savings. A comparison is made between a current high bypass ratio engine and an advanced very high bypass ratio engine both configured to deliver approximately 30,000 lbs of thrust at the sea level static takeoff (SLTO) power setting. These engines are evaluated to determine the installed thrust and fuel consumption characteristics over the full spectrum of flight operation, enabling fuel burn to be evaluated for any aircraft mission. For a nominal mission profile considered in this paper, the advanced engine cycle enabled by the use of the variable pitch composite fan blade provided more than 12% reduction in fuel burn.
Interest for Liquid Fuels in Power Generation Gets Renewed
Authors: Moliere Michel , Vierling Matthieu , Symonds Rich
Published: January 2011

As investments in power additions are under scrutiny, the viability and sustainability of generation projects are increasingly challenged by planners, and the debate about the most appropriate primary energy and prime mover is renewed with a sharper focus. Faced with limited forecasts on future growth, today’s power generators are looking cautiously at power addition blueprints and placing increased emphasis on equipment versatility and fuel flexibility in a move to eliminate single fuel reliance. Heavy duty gas turbines (HDGTs) can mitigate the uncertainty about operation factor and plant capacity thanks to versatile and modular installation schemes; in addition, they open the door to large clusters of alternative primary energies. In this context, it is important to note that liquid fuels are making a comeback in the power generation scene. This is due to the tactical advantages inherent to liquid fuels such as multiple sourcing, ease of transportation, and existing infrastructures. Liquid fuels as primary energies cover a wide product range from Super Light Hydrocarbons (naphtha, gas condensates and natural gas liquids) to ash forming fuels through aromatic cuts (BTEX, C9+), heavy distillates, synfuels, gasification derivatives (methanol & dimethyl ether: DME) and biogenic fuels (ethanol, biodiesel). This paper stresses the importance of fuel flexibility as a requirement for plant versatility and offers a review of the main liquid fuels that are accessible to gas turbines.
Characteristics of Multi-Cavity Trapped Vortex Combustors
Authors: Briones Alejandro M. , Sekar Balu
Published: January 2011

This research is motivated towards improving and optimizing the performance of AFRL’s Inter-Turbine Burner (ITB) in terms of greater combustion efficiency, reduced losses and exit temperature profile requirements. The ITB is a minicombustor concept, situated in between the high and low pressure turbine stages and typically contains multiple fueled and non-fueled Trapped Vortex Combustor (TVC) cavities. The size, placement, and arrangement of these cavities have tremendous effect on the combustor exit temperature profile. The detailed understanding of the effect of these cavities in a three-dimensional ITB configuration would be very difficult and computationally prohibited. Therefore, a simple but somewhat similar conceptual axi-symmetric burner is used here the design variations of Trapped Vortex Combustor (TVC) through modeling and simulation. The TVC can be one single cavity or can be represented by multi-cavity combustor. In this paper, both single cavity TVC and multi-cavity TVCs are studied. The single cavity TVC is divided into multiple cavities while the total volume of the combustor remains constant. Four combustors are studied: Baseline, Staged, Three-Staged, and Interdigitated TVC. An extensive computational investigation on the characteristics of these multi-cavity TVCs is presented. FLUENT is used for modeling the axisymmetric reacting flow past cavities using a global eddy dissipation mechanism for C3H8-air combustion with detailed thermodynamic and transport properties. Calculations are performed using Standard, RNG, and Realizable k-ε RANS turbulence models. The numerical results are validated against experimental temperature measurements on the Base TVC. Results indicate that the pressure drag is the major contributor to total drag in the Base TVC. However, viscous drag is still significant. By adding a concentric cavity in sequential manner (i.e. Staged TVC), the pressure drag decreases, whereas the viscous drag remains nearly constant. Further addition of a secondary concentric cavity (i.e. Three-Staged TVC), the total drag does not further decrease and both pressure and viscous drag contributions do not change. If instead a non-concentric cavity is added to the Base TVC (i.e. Interdigitated TVC), the pressure drag increases while the viscous drag decreases slightly. The effect of adding swirl flow is to increase the fuel-air mixing and as a result, it increases the maximum exit temperature for all the combustors modeled. The jets and heat release contribute to increase pressure drag with the former being greater. The fuel and air jets and heat release also modify the cavity flow structure. By turning off the fuel and air jets in the Staged TVC, lower drag (or pressure loss) and exit temperature are achieved. It is more effective to turn off the fuel and air jets in the upstream (front) cavity in order to reduce pressure losses. Based on these results, recommendations are provided to the engineer/designer/modeler to improve the performance of the ITB.
An Investigation of Compressor Map Width Enhancement and the Inducer Flow Field Using Various Configurations of Shroud Bleed Slot
Authors: Sivagnanasundaram Subenuka , Spence Stephen , Early Juliana , Nikpour Bahram
Published: January 2011

This paper describes an investigation of various shroud bleed slot configurations of a centrifugal compressor using CFD with a manual multi-block structured grid generation method. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. The baseline numerical model has been developed and validated against experimental performance measurements. The influence of the bleed slot flow field on a range of operating conditions between surge and choke has been analysed in detail. The impact of the returning bleed flow on the incidence at the impeller blade leading edge due to its mixing with the main through-flow has also been studied. From the baseline geometry, a number of modifications to the bleed slot width have been proposed, and a detailed comparison of the flow characteristics performed. The impact of slot variations on the inlet incidence angle has been investigated, highlighting the improvement in surge and choked flow capability. Along with this, the influence of the bleed slot on stabilizing the blade passage flow by the suction of the tip and over-tip vortex flow by the slot has been considered near surge.
Study of a Two-Phase Flow Pump and Separator System
Authors: Gruselle Franc¸ois , Steimes Johan , Hendrick Patrick
Published: January 2011

The Aero-Thermo-Mechanics (ATM) Department of ULB (Universite´ Libre de Bruxelles) is developing an original system to pump and separate a two-phase flow. Many applications need to extract a certain phase of a multiphase flow: oil extraction, flow in nuclear pumps, flow in aircraft lubrication systems, pulp and paper processing, etc. The main objective of this study is to obtain a lightweight, compact and efficient system that can both extract the gas of a two-phase flow and increase the pressure of the liquid phase. Prototypes with different designs were first tested at ULB on a specific test bench using water and air. The current prototype is a kind of axial-centrifugal pump. The axial part is used to separate the two phases of the flow and to collect, in the centrifugal part, the liquid phase only. The test results of the water-air prototypes have allowed to identify the key design and working parameters for efficient separation and pumping. A theoretical model has also been developed to describe the behavior of these prototypes. After successful tests with water-air mixtures, the technology has been implemented for a hot oil-air mixture. The tests with oil-air mixtures are performed on the aeroengine lubrication system test bench that the ATM Department developed and continues developing for other projects. At the same time, the flow field in the pump and separator system is being studied with commercial CFD (Computational Fluid Dynamics) software packages. Several two-phase flow models are considered for this particular application.
Computational Analysis of Droplet Motion in Industrial Compressor Intakes
Authors: Payne Robin C. , Rick Wilfried , Lo¨tzerich Michael
Published: January 2011

Water droplets enter compressors for a number of reasons, such as rain ingestion in aero engines; inlet fogging, and online washing for industrial engines. Several methods have been developed to examine their behaviour within compressors for a number of these applications, particularly of relevance for industrial engines, for wet compression. To further the understanding of the behaviour of compressors with water ingestion, it is important to establish the means by which water droplets are entering the compressor, so that appropriate inlet boundary conditions can be applied within the compressor, and so that droplet spray systems can be optimised. In this paper, Lagrangian droplet tracking methods have been applied to droplet motion within compressor intakes to model the flow of droplets from spray to compressor first stage. It is found that, due to the geometry of the intake and the gas flow patterns found, the droplets enter the compressor with significant non-uniformity, and the distribution of droplets is strongly dependent on droplet size, for all droplet sizes considered. The technique has been applied to two sample cases: one that is typical of a high fogging type application and one that is typical of an online washing application. In each case, the way in which the method can be used to optimise the positions of water sprays is examined.
Probabilistic Creep Life Prediction of Turbine Discs
Authors: Koul Ashok K. , Tiku Ajay , Shankar Srinivasan Shanks , Zhao Jun
Published: January 2011

The paper presents the results of a probabilistic creep life study on F5001P turbine discs and demonstrates the importance of using physics based probabilistic damage modeling techniques to deal with life prediction uncertainty in forged components. In physics based modeling, the influence of individual microstructural or thermal-mechanical loading factors on metallurgical crack initiation can also be studied with relative ease. In a previous study, Life Prediction Technologies Inc.’s (LPTi’s) prognosis tool known as XactLIFE™ was successfully used to conduct deterministic analysis to establish the fracture critical location of F5001P first stage discs under steady state loads. In this paper, the variability in life is further established as a function of prior austenite grain size. The analysis used typical engine operating data from the field in terms of engine speed and average exhaust gas temperature (EGT). The primary objectives of the case study are to show how prognosis can allow a user to assess fleet reliability for engine specific operating conditions. The lower bound deterministic creep life and probabilistic creep life at 0.1% cumulative probability of failure are very close in magnitude.
Development and Application of a Membrane-Based Thermodenuder for Measurement of Volatile Particles Emitted by a Jet Turbine Engine
Authors: Cheng Meng-Dawn
Published: January 2011

Measurement of volatile particles emitted by modern jet engines is a daunting task. Besides the complexity in sampling jet aircraft exhaust, the main difficulty lies at how to faithfully capture the phase-partition dynamics of volatile particles as they travel downstream from the engine exhaust nozzle. As a result, the physico-chemical properties of the exhaust are also transformed. We have developed a sampling instrument that aims at enabling study of the phase-partition dynamics. The objective of this research project was to design and evaluate a new thermodenuder for performing phase separation of the engine-emitted volatile particles. The backbone of the new thermodenuder is a thin metallic membrane. The membrane enables extraction of molecules that can be thermally desorbed from the condensed particulate phases and collected for subsequent chemical analysis. Toward realization of the technique in the future field aircraft emissions measurement we tested this new thermo-denuding device using laboratory-generated particles that were made of non-volatile or semi-volatile chemicals. The particle penetration efficiency, a measure of the device performance, of this thermodenuder was found to be better than 99%. Results obtained from the tests executed at a number of operating temperature conditions show reasonably good thermal separation. We have scheduled to apply this new device to characterize emissions from a T63 turboshaft engine in the spring of 2010 and are expecting to show the engine results at the conference. The test results based on the laboratory-generated particles were encouraging for the intended application. With excellent particle transmission efficiency and an ability to simultaneously measure the composition in the gas and particle phases of the engine particles, we believe the new technology will make a great contribution to measurement research of engine emissions.
Ad-Hoc Boundary Conditions for CFD Analyses of Turbomachinery Problems With Strong Radial Flow Gradients at Farfield Boundaries
Authors: Campobasso M. Sergio , Baba-Ahmadi Mohammad H. , McLelland Grant
Published: January 2011

This paper reports on the improvements of flux enforcement and auxiliary state farfield boundary conditions for Euler and Navier-Stokes Computational Fluid Dynamics codes. The new conditions are based on 1D characteristic data and also on the introduction in the boundary conditions of certain numerical features of the numerical scheme used for the interior of the domain. In the presence of strong radial gradients of the flow field at the farfield boundaries, the new conditions perform significantly better than their conventional counterparts, in that they a) preserve the order of the space-discretization, and b) greatly reduce the error in estimating integral output. A coarse-grid CFD analysis of the compressible flow field in an annular duct for which an analytical solution is available yields a mass flow error of 62% or 2%, depending on whether the best or the worst farfield BC implementation is used. The presented BC enhancements can be applied to structured, unstructured, cell-centered and cell-vertex solvers.
Methodology to Identify the Unsteady Flow Field Associated With the Loss of Acoustic Energy in the Vicinity of Circular Holes
Authors: Rupp Jochen , Carrotte Jon , Spencer Adrian
Published: January 2011

Thermo-acoustic instabilities in lean gas turbine combustors have been well reported over the past decade. One option by which the generation of potentially damaging, large scale, pressure amplitudes can be avoided is to increase the amount of damping within the combustion system using passive damping devices. Common to these devices is the absorption mechanism by which acoustic energy, associated with incident pressure fluctuations onto an orifice, generates an unsteady flow that cannot be converted back into acoustic energy. This paper is concerned with providing a greater understanding of this fundamental process. Experimental results are presented for a single orifice that is exposed to plane acoustic waves within a rectangular duct. Measurements of unsteady pressure enable the acoustic power absorbed by the orifice to be determined, whilst Particle Image Velocimetry (PIV) is used to measure the unsteady flow field. A method is outlined for identifying those features within the measured unsteady flow field that are responsible for absorption of the acoustic energy. This is based on a Proper Orthogonal Decomposition (POD) analysis of the velocity field and identification of the relevant modes. The method is validated for the non-linear and linear absorption regimes by comparing the energy of the relevant velocity field features with the energy absorbed from the acoustic field. The good agreement obtained indicates the success of the technique presented. The improved understanding of the mechanisms by which energy is transferred out of the acoustic field, and into the unsteady velocity field, explains many of the observed absorption characteristics. This improved understanding should lead to the design of optimized damping systems. The presented methodology is also thought to be the basis by which numerical, CFD based, predictions relating to the absorption of acoustic waves should be analyzed and validated.
Rotor-Tip Flow Fields Near Inception Point of Modal Disturbance in an Axial-Flow Fan
Authors: Nishioka Takahiro , Kanno Toshio , Hayami Hiroshi
Published: January 2011

The rotor-tip flow fields in two rotors of a low-speed axial-flow fan were experimentally and numerically investigated to clarify the mechanism behind modal stall inception. A NACA 65 wing section and a controlled diffusion airfoil were applied to the two rotors. At the small stagger-angle setting for both rotors, which is ten degrees smaller than the design value, the modal disturbance is observed near the peak pressure-rise point, and the rotor blades at the tip stall before the modal disturbance is observed. In the modal stall inception, the interface between the incoming flow and the reversed tip-leakage flow does not become parallel to the leading edge plane, although backflow from the trailing edge initiates near the stall condition. The reversed tip-leakage flow does not spill from the leading edge at the stall condition. Moreover, the tip-leakage vortex breakdown does not occur near or at the stall condition. A three-dimensional separation vortex is induced by secondary flow on the suction surface near the stall condition and develops at the stall condition. It is concluded from these results that the rotor-tip flow fields in the modal stall inception differ from those in the spike stall inception and that the three-dimensional separation vortex induced by the secondary flow influences the initiation of modal disturbance.
Analysis and Comparison of Reactivity and CO2 Capture Capacity of Fresh Calcium-Based Sorbents and Samples From a Lab-Scale Dual Fluidized Bed Calcium Looping Facility
Authors: Sivalingam Senthoorselvan , Gleis Stephan , Spliethoff Hartmut , Hawthorne Craig , Charitos Alexander , Scheffknecht Guenter
Published: January 2011

Naturally occurring limestone and samples from a lab scale dual fluidized bed (DFB) calcium looping (CaL) test facility were analysed in a thermo gravimetric analyser (TGA). The reactivity of the samples evaluated at typical carbonation conditions prevailed in the carbonator was compared with raw samples. Carbonations were carried out at 600, 650 &700°C and 5, 10 &15 vol-% CO2 atmosphere using a custom designed sample holder that provided ideal conditions for solid gas contact in a TGA. The rate of carbonation and carbonation capacity of the samples were compared with respect to the following three categories: number of calcination-carbonation cycles, carbonation temperature and CO2 concentration. Notable differences in total conversion (XCaO) and the rates of conversions were observed between the raw and DFB samples in all three cases. It is suspected the much lower activity of the DFB sample is attributed to the differences in experimental conditions: ie., partial carbonation of the DFB particles, fast heating rate in the calciner and thus a rapid calcination reaction, and particle attrition in the CFB calciner riser. These harsh conditions lead sintering and thus a loss of surface area and reactivity. Sintered DFB samples showed low (nearly 1/3 of the raw samples) but stable conversions with increasing number of cycles. The sorbent taken from the DFB facility did not decrease with respect to carbonation rate or maximum conversion over 4 cycles whereas the fresh limestone changed significantly over 4 cycles. Hydration was used as an attempt to regenerate the lost capture capacity of partially carbonated DFB sample. Hydration of the sintered DFB sample was successful in increasing the maximum capture capacity in the fast reaction regime to values almost as high as that of a fresh sample in its first carbonation cycle. Although more investigation is required to investigate the effect of hydration on the CaO particle morphology, a process modification to enhance the CO2 capture efficiency of the carbonator via particle hydration was proposed.
Demonstration of an Aerodynamic Design Process for Turbomachines Using Open Source Software Tools
Authors: Borm Oliver , Balassa Balint , Barthmes Sebastian , Fellerhoff Julius , Ku¨hrmann Andreas , Kau Hans-Peter
Published: January 2011

This paper demonstrates an aerodynamic design process for turbomachines for compressible flows, using exclusively open source software tools. Some relevant software already existed and few additional components were required, which have been developed mainly by students and are available at ftp.lfa.mw.tum.de. The geometry of turbomachine blades is described with a newly developed NURBS based blade designer. One-dimensional preliminary analysis is done with OpenOffice.org Calc and an extended mean line program, where loss models are already included. For two-dimensional through-flow computations a compressible streamline curvature method was implemented. Two-dimensional blade-to-blade and three-dimensional simulations are performed with the CFD toolbox OpenFOAM. The two- and three-dimensional results are visualized and analyzed using the open source postprocessing tool ParaView. The presented tools are regularly used in student projects. A generic one stage axial compressor was created with the workflow as a showcase in order to demonstrate the capabilities of the open source software tools.