bluuebunny/crossref_metadata_2025 huggingface dataset:
Generalized Optimization of Counter-Rotating and Single-Rotating Fans
Authors: Lengyel-Kampmann Timea , Voß Christian , Nicke Eberhard , Rüd Klaus-Peter , Schaber Reinhold
Published: September 2014

On possible fan concept for future high and ultra-high bypass ratio turbofan engines is the counter-rotating (CR) fan. Several studies [1][2][3][4] dealt already with the optimization of CR fans, however the mass flow and the total pressure ratio were typically given and fixed for a specified application. The results of these studies showed a benefit of the CR fan compared to the conventional single-rotating (SR) fan, which strongly depended on the engine cycle. Following this experience, it was necessary to further specify the efficiency benefits more precisely in association with fan total pressure ratio and fan inlet axial Mach number. The results are discussed in this present paper. A special emphasis was given on determining the optimal pressure ratio, for which the CR-fan expectably achieves the maximal efficiency benefit.

The idea was to perform a global optimization study without any constraints for the operating point inside of a broad (ΠFan, Max) –range, for the rotational speeds and with only a few constraints for the geometry of the blades to avoid infeasible geometries. An adequate range for the fan pressure ratio (ΠFan) and for the axial Mach number (Max) was chosen for the global optimization covering the entire range from current to potential future ultra-high bypass ratio engine applications, also taking into account a reduced nacelle diameter and thus high axial fan inflow Mach numbers.

The focus of the present study was to develop a method for the global optimization of a fan stage.

As a result of this study, the maximal achievable efficiency is shown as a function of the fan pressure ratio and the axial Mach number. Thus the efficiency differences between the CR and SR fan can be calculated through the differences between the surfaces for any given set of parameters defining a potential engine. This allows for a generalized assessment of this particular fan concept over the entire range of relevant applications.
Hybrid Modeling of Heavy Duty Gas Turbines for On-Line Performance Monitoring
Authors: Palmé Thomas , Liard Francois , Cameron Dan
Published: September 2014

Due to their complex physics, accurate modeling of modern heavy duty gas turbines can be both challenging and time consuming. For online performance monitoring, the purpose of modeling is to predict operational parameters to assess the current performance and identify any possible deviation between the model’s expected performance parameters and the actual performance. In this paper, a method is presented to tune a physical model to a specific gas turbine by applying a data-driven approach to correct for the differences between the real gas turbine operation and the performance model prediction of the same. The first step in this process is to generate a surrogate model of the 1st principle performance model through the use of a neural network. A second “correction model” is then developed from selected operational data to correct the differences between the surrogate model and the real gas turbine. This corrects for the inaccuracies between the performance model and the real operation. The methodology is described and the results from its application to a heavy duty gas turbine are presented in this paper.
Dynamic Behavior of a Mistuned Air Turbine: Comparison Between Simulations and Measurements
Authors: Pohle Linus , Panning-von Scheidt Lars , Wallaschek Joerg , Aschenbruck Jens , Seume Joerg R.
Published: September 2014

Due to manufacturing tolerances, wear during operation or regeneration processes like maintenance operation, the structural properties of turbine blades deviate from design condition to reference blades. This deviation usually causes higher vibration amplitudes and as a consequence a lower service life expectation. Many different calculation methods can be used to simulate these increased amplitudes of mistuned blades. The major resulting problem is on the one hand to capture the occurring deviation of the eigenfrequencies from the reference blade and on the other hand to incorporate these real deviations in simulations. Solving these problems with a simplified experimental setup will make it possible to predict the maximum amplitude and to avoid costly experiments in a rotating turbine.

The aim of the paper is to verify a simulation of the vibration amplitude by experiments using a reduction method to calculate a mistuned system in reasonable time. The results of the chosen simulation are compared to experiments in a rotating turbine.

To reduce the number of degrees of freedom of the full finite-element model and the computational effort, a multi-step reduction method is used. In the simulation, the centrifugal force, the structural damping, the steady static pressure on the blades, and the mistuning are considered. To find the occurring deviations of each manufactured blade, an experimental modal analysis is performed for every single blade in a non-rotating setup with the eigenfrequencies of every single blade as an output. The single-stage results of the simulation are subsequently compared to experiments in a 5-stage air turbine in which the vibration amplitudes and the eigenfrequencies of every blade in the last rotor blade row are measured by a tip-timing system.
An Analytical Investigation on the Impact of Wall Cooling on the Development of Boundary Layers on the Suction Sides of Typical High Pressure Turbine Airfoils
Authors: Lin Ray-Sing , Sharma Om P.
Published: September 2014

In a modern high pressure turbine, the first vane surface temperature has been lowered to below 70% of boundary-layer edge temperature. This highly cooled temperature ratio provides a stabilizing effect in addition to a favorable pressure gradient for maintaining laminar flow on turbine airfoil suction sides; this opens a potential opportunity to yield high cycle performance and reduced cooling air requirements. This paper will quantify the stabilizing effects of wall cooling on boundary layer development at moderate and high subsonic Mach numbers by using a linear boundary-layer stability theory. The delay of transition onset over a range of free-stream turbulence level, Tu = 0∼1.5%, is predicted by using well established eN correlation. Results indicate that on a wall cooled below 0.7Te, the transition Reynolds number, Rex, can be above 107 for M = 0.5, and the transition Reynolds numbers for M = 0.9 are even higher, almost reaching 108 due to additional stabilizing effects of compressibility. Results from simulations conducted on a typical high pressure turbine airfoil demonstrate a potential for an improved laminar run on the suction side of the first vane of a typical aero-engine. Note that overcoming laminar separation is a critical challenge in practical application.
Methods and Results in Remote Monitoring and Diagnosing a Fleet of Industrial Gas Turbines
Authors: Scheianu Dorin
Published: September 2014

The paper describes a set of analysis tools and the results obtained from applying them to remote monitoring a fleet of industrial gas turbines serviced under contract. It includes the following:

- The initial post overhaul acceptance test (performed in a specialized controlled environment facility) and the subsequent commissioning test (performed in the field at the end user)

- The object of monitoring service — data collection, transmission, organization, storage and access

- Data analysis and conversion into useful information

- Monitoring and analysis tools with results available and accessible in real time: statistics, trends, cloud points, estimators of engine health

- Development of malfunction indicators and their use

The purpose of such analysis is the development and implementation of proper quantitative tools and methods for correctly assessing when malfunctions of gas turbines develop and eventually to identify their causes, in order to help the operating personnel select the appropriate maintenance measures in a timely manner. The examples included are collected from actual applications, with engineering interpretation and resolution.
Numerical 3D Simulation of the Cavitating Flow in a Centrifugal Pump With Low Specific Speed and Evaluation of the Suction Head
Authors: Limbach Phillip , Kimoto Marius , Deimel Christian , Skoda Romuald
Published: September 2014

A numerical analysis is performed to assess the capability of common simulation methods, in particular Ansys CFX, to predict the performance and NPSH curve of a centrifugal pump at very low specific speed for both, design and off-design conditions.

In all cases, we use an entire numerical model containing the impeller, the volute casing, the side chambers as well as suction pipe and pressure pipe. A three-dimensional setup is used, testing the following numerical models: steady, i.e. frozen rotor model, unsteady model accounting for the impeller movement and the relative impeller-volute position, single-phase flow as well as cavitating flow conditions.

The global performance of the pump is assessed in terms of pressure head, power consumption and pump efficiency for single-phase flow. Furthermore, the drop of the pump head and Net Positive Suction Head (NPSH) characteristics are analyzed for cavitating flow conditions. Numerical results are validated against experimental data.

Regarding non-cavitating flow conditions, the trend of the characteristic curves is well predicted, while absolute performance values differ from measured data significantly. The results of steady and unsteady calculations deviate from each other by less than 2%. Concerning cavitating flow, unsteady simulations have to be performed in particular for overload conditions, in order to obtain convergence of the solver. The trend of the measured NPSH curve is well captured with default cavitation model parameters. For nominal and overload, the predicted NPSH curve underestimates the measured one significantly.
Effect of the Stator Hub Configuration and Stage Design Parameters on Aerodynamic Loss in Axial Compressors
Authors: Yoon Sungho , Selmeier Rudolf , Cargill Patricia , Wood Peter
Published: September 2014

The choice of the stator hub configuration (i.e. cantilevered versus shrouded) is an important design decision in the preliminary design stage of an axial compressor. Therefore, it is important to understand the effect of the stator hub configuration on the aerodynamic performance. In particular, the stator hub configuration fundamentally affects the leakage flow across the stator. The effect of the stator hub configuration on the leakage flow and its consequent aerodynamic mixing loss with the main flow within the stator row is systematically investigated in this study.

In the first part of the paper, a simple model is formulated to estimate the leakage loss across the stator hub as a function of fundamental stage design parameters, such as the flow coefficient, the degree of reaction and the work coefficient, in combination with some relevant geometric parameters including the clearance/span, the pitch-to-chord ratio and the number of seals for the shrouded geometry. The model is exercised in order to understand the effect of each of these design parameters on the leakage loss.

It is found that, for a given flow coefficient and work coefficient, the leakage loss across the stator is substantially influenced by the degree of reaction. When a cantilevered stator is compared with a shrouded stator with a single seal at the same clearance, it is shown that a shrouded configuration is generally favored as a higher degree of reaction is selected, whereas a cantilevered configuration is desirable for a lower degree of reaction. Further to this, it is demonstrated that, for shrouded stators, an additional aerodynamic benefit can be achieved by using multiple seals.

The second part of the paper investigates the effect of the rotating surfaces. Traditionally, only the pressure loss has been considered for stators. However, the current advanced CFD generally includes the leakage path with associated rotating surfaces, which impart energy to the flow. It is shown that the conventional loss coefficient, based on considering only the pressure loss, is misleading when hub leakage flows are modeled in detail, because there is energy addition due to the rotation of the hub or the shroud seals for the cantilevered stator and the shrouded stator, respectively. The calculation of the entropy generation across the stator is a better measure of relative performance when comparing two different stator hub configurations with detailed CFD.
Turbulent Combustion Modeling Using Flamelet-Generated Manifolds for Gas Turbine Applications in OpenFOAM
Authors: Fancello A. , Panek L. , Lammel O. , Krebs W. , Bastiaans R. J. M. , de Goey L. P. H.
Published: September 2014

The continuous interest in reducing pollutions and developing both an efficient and clean combustion system require large attention in the design requirements, especially when related to industrial gas turbine application. Although in recent years the advancements in modelling have increased dramatically, combustion still needs a huge computational effort. The Flamelet-Generated Manifolds (FGM) method is considered a suitable solution with an accuracy that can be comparable with detailed chemistry simulations results. The full combustion system can be described by few controlling variables while the chemical details are stored in a database (manifold) as function of controlling variables. Transport equations are solved for the Navier-Stokes system and the controlling variables. The detailed chemistry code Chem1D is used to create the manifolds. Turbulence can be modeled using a PDF approach for the subgrid modeling of the chemistry terms. The OpenFOAM open source CFD package is used as CFD tool for the simulations. The aim of this work is to demonstrate the usage of FGM with OpenFOAM and figure out the status of the implementation. To achieve this goal, the work employs as test case a confined lean jet flame is used. For the case presented, an extensive experimental data set exist, including PIV and Raman data. Results are further compared with traditional methods, while FGM method might be easily extended to other scenarios.
Two Phase Computational Study of Flow Behaviour in a Region Within an Aeroengine Gearbox
Authors: Turner A. , Morvan H. P. , Simmons K.
Published: September 2014

Within large civil aeroengines a significant contributor to parasitic power loss (manifest as increased heat-to-oil) is the internal gearbox (IGB). An IGB typically contains high speed shafts, a spiral bevel gear pair, bearings and seals as well as the complex geometry of the stationary components. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems (UTC) has conducted experimental and computational projects to enhance understanding of two phase flow behaviour. Validated single phase modelling capability for an unmeshed shrouded crown gear has been established [1–3] and discrete phase modelling [3] has been applied to investigate the oil path under the shroud. Experimental work on shroud configurations [5] and two-phase flow [6] has also been conducted at the UTC using a rig with representative but simplified geometry relative to an aeroengine.

Recent modelling activity has focussed on the region behind the gear. In an aeroengine this region includes a large shaft location bearing that sheds oil into the rear chamber. This oil, combined with the high speed and complex airflows generated by proximity to the gear, makes this region particularly challenging to model. In the experimental test rig at the UTC this zone does not contain a bearing and so as yet no validation data exists.

In this paper an axisymmetric sector model of the rig back chamber is presented. Two phase flow behaviour was modelled using the Volume of Fluid (VOF) and Eulerian models within the CFD software ANSYS-Fluent. A comparison between these two multiphase models is made and their suitability to model the oil behaviour in the back chamber is discussed. Oil flow behaviour in this region is also reported.

The CFD results show that the VOF model is insufficient for predicting oil flows in this environment. Although there is a significant amount of liquid present as wall film, the liquid not on the walls appears important and is not adequately modelled by VOF, which is well-known as being most suitable where there is a definite interface between liquid and gaseous phases. The Eulerian model shows significantly more likely flow behaviour with results indicating a non-uniform distribution of oil across the axial length of the rear chamber with a bias towards the rear (bearing side). The air jet entering in the rear chamber from between the gear and shroud strongly influences flow behaviour in the rear chamber. The computed flow field is such that a full 360° model is recommended for future work of this nature.
3D CFD Compressor Map Computation Process Accounting for Geometry Changes due to Off-Design Operation Loads
Authors: Janke Christian , Karger Kai , Gaun Lilia , Bestle Dieter , Huppertz André
Published: September 2014

Compressor maps of aero engines show the relation between corrected inlet mass flow and total pressure ratio for various engine speeds. Different speed lines represent different operating conditions of the compressor, where especially operating bounds like surge and choke are important for the design process. Typically, 3D CFD compressor maps are computed with the so called hot geometry given for the aerodynamic design point. However, in reality airfoil shapes will change for different engine speeds and gas loads resulting in twisted airfoils and changed tip clearances. Thus, using the nominal hot geometry for the whole compressor map is not fully correct. In order to obtain higher quality performance maps these effects need to be considered. The paper shows a process for computing compressor maps with 3D CFD, where strucural deformations of the blade due to varying speeds and gas loads are taken into account by blade morphing. This process is applied to a 1.5-stage compressor showcase.
Aerodynamics Comparisons Between Two Typical Gas Turbine Combustion Swirlers
Authors: Kao Yi-Huan , Haseman Jacob B. , Tambe Samir B. , Jeng San-Mou
Published: September 2014

In this work, a series of tests have been conducted to study the aerodynamics of two typical gas turbine combustion swirlers, using Laser Doppler Velocimetry (LDV). The first swirler used is a coaxial counter-rotating, radial-radial swirler, designated as the R-R swirler. The primary swirler accounts for 40% of the total effective area of the R-R swirler. The second swirler employed consists of an inner dual-axial swirler assembly with only around 20% of total swirler effective area and an outer coaxial radial swirler, and is designated as the A-R swirler. The aim of this work is to compare the aerodynamics performance of these two different types of swirlers under similar boundary conditions, such as confinement effect, downstream exhaust nozzle, and chamber length.

The R-R swirler has a very high radial dispersing rate, and for the unconfined case, the swirling jet remained attached to the dome plate resulting in a very weak, unbound CTRZ. The swirling jet for the A-R swirler exited at a relatively low expansion angle. For confined cases, the swirling jet attached to the walls of the confinement at a certain distance downstream of the exit plane for both swirlers.

When the exhaust nozzle was applied as a downstream boundary condition, a spinning vortex core with high turbulent intensity was detected along the swirler axis for the A-R swirler, whereas the only difference for the R-R swirler was a slight reduction in the expansion angle of the swirling jet. The proximity of the exhaust nozzle to the swirlers was changed by changing the chamber length. For the R-R swirler, the effect of chamber length was only detected in the near-field region. For the A-R swirler, a reduction in chamber length caused the spinning vortex core to become more intense. Additionally, an annular CTRZ was observed for the shorter chamber lengths.
CFD Investigation Into Oil/Air Behaviour Near a Shrouded Spiral Bevel Gear
Authors: Simmons Kathy , Guymer Dan , Turner Adam
Published: September 2014

The capability to model an aeroengine internal gearbox in its entirety using CFD is currently hampered by the complexity of the two-phase, highly rotating system and the computational resource required. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems has established modeling capability for an unmeshed, shrouded spiral bevel gear and has conducted a number of experimental investigations for such a gear operating within a cylindrical chamber [1, 2].

In this paper a CFD model is created of an external chamber geometry comparable to that on the experimental test rig using the commercial CFD code Fluent. Droplets are introduced into this chamber at a range of diameters and their trajectories tracked. Small droplets (0.1 μm to 1μm) are representative of mist within the chamber and essentially follow the highly rotating air flow. Droplets in the range 1 μm to 100 μm travel to the chamber walls but interact with the flow such that they may be in the core flow some time before impact. Larger droplets in the range 100 μm to 5000 μm are largely undeflected, travelling directly to the walls.

The Fluent thin film model is used to generate wall films from droplet impacts and the simulation shows how film is likely to be driven away from the gear by the air flows within the chamber forming a thicker film away from the gear axial location.
Numerical and Experimental Investigation of Pulsating Flow Effect on a Nozzled and Nozzleless Mixed Flow Turbine for an Automotive Turbocharger
Authors: Padzillah M. H. , Yang M. , Zhuge W. , Martinez-Botas R. F.
Published: September 2014

To achieve better flow guidance into the turbine blades, nozzle vanes were added as an integral part of the stator design. However, the full investigation that directly addresses the comparison between the two turbine arrangements under pulsating flow conditions is still not available in literature. This work represents the first attempt to observe differences, particularly in the circumferential flow angle distribution between both volute arrangements under steady and pulsating flow operating conditions. Experimentally validated Computational Fluid Dynamics (CFD) simulations have been conducted in order to achieve this aim. As the experimental data within the Turbocharger Group at Imperial College are extensive, the simulation procedures are optimized to achieve the best compromise between the computational cost and prediction accuracy. A single operating pressure ratio is selected for the steady and pulsating environment in order to provide consistent comparison for both volute arrangements. The simulation results presented in this work are conducted at the turbine speed of 48000rpm and 60Hz flow frequency for the pulsating flow simulations. The results indicated that there are significant differences in the flow angle behavior for both volutes regardless of the flow conditions (steady or unsteady). It is also found that the differences in flow angle distribution between increasing and decreasing pressure instances during pulsating flow operation is more prominent in the nozzleless volute than its nozzled counterpart.
Vibration Reduction of a Centrifugal Compressor for Gas Transmission
Authors: Liu Zheji , Smith Raymond
Published: September 2014

Centrifugal compressors used in gas transmission produce strong pressure pulsations, piping vibration, and noise. These are undesirable by-products of the compressor operation that is inherently an unsteady process. This is particularly true for compressors that use a vane diffuser, rather than a vaneless scroll type of diffuser. High vibration levels can potentially cause structural damage in the piping, particularly instrumentation connections, which can cause unnecessary machine down-time and production loss, and is a potential safety hazard.

This paper discusses a unique technique to reduce centrifugal compressor piping vibration. This technique reduces aeroacoustics excitation by mounting a duct resonator array inside a compressor diffuser. The effectiveness of this technique is demonstrated by a recent field application to address a noise and vibration concern of a compressor installed in a pipeline station. This compressor had run successfully for several years with a high (but not excessive) level of high frequency vibration in the unit piping. Recent changes in pipeline operating conditions resulted in a significant increase in vibration and associated problems including failure of thermowells and resistance temperature detectors (RTDs).

A preliminary measurement of gas pressure pulsations and piping vibration revealed a severe level of high frequency vibration that could lead to a fatigue failure of the unit piping, if operation continued under these conditions. Additional vibration data were measured from the compressor to characterize the noise and vibration and to establish the baseline for future comparison. The baseline vibration data are characterized with a dominant component at the blade passing frequency that makes the duct resonator array an ideal solution. Consequently, a resonator array was designed, manufactured, and installed to reduce the compressor piping vibration and noise.

A final test was conducted to verify the effectiveness of the resonator array. Comparing the data acquired before and after the resonator array shows that the dominant vibration level at the blade passing frequency was reduced by 93% on average. The compressor is now able to operate safely at the new pipeline conditions, and it runs much quieter over the full operating range.
Response of Soot Temperature to Unsteady Inlet Airflow Under Modulated Condition and Naturally-Occurring Combustion Dynamics
Authors: Knadler Michael , Cakmakci Arda , Lee Jong Guen
Published: September 2014

The response of soot temperature to unsteady inlet airflow is characterized using pyrometry. The unsteady inlet airflow is achieved by either modulating inlet air or naturally-occurring unstable flame, running on a jet fuel at fuel-rich conditions. The inlet air is modulated by a siren device running at frequencies between 150 and 250 Hz and up to 60% of modulation level (u’/um) is achieved. Also, the combustor can be run naturally unstable at the same inlet operating condition by changing the combustor length. For the pyrometry, the emission from whole flame at 660 nm, 730 nm and 800 nm is recorded and the three-color pyrometry is used to measure soot temperature. The effect of non-isothermal distribution of soot in flame on the measured temperature is also considered. The level of overall temperature fluctuation under inlet flow modulation (Trms/Tmean) is about an order of magnitude lower than that of flame emission fluctuation (Irms/Imean). Under naturally occurring instability the measured soot temperature is in phase with the pressure measured in the combustor, indicating that the measured soot temperature can be used as a quantity related to combustion dynamics for fuel-rich sooty flames.
Flame Dynamics in a Multi-Nozzle Staged Combustor During High Power Operation
Authors: Dolan Brian , Villalva Rodrigo , Munday David , Zink Gregory , Pack Spencer , Gutmark Ephraim
Published: September 2014

Periodic behavior in the reaction zone of a multiple nozzle combustor undergoing self-sustaining combustion oscillations is examined. This combustor has three stages: a high-swirl pilot stage, a lower-swirl intermediate stage, and a low-swirl outer stage. The high-power conditions reviewed in this paper have fuel supplied to all three stages. Four conditions are examined in which thermoacoustic coupling is observed at a well-defined frequency. The highest overall equivalence ratio case displays a significantly higher oscillation amplitude than the other cases. Changes to the fuel distribution (with constant overall equivalence ratio) results in smaller effects on the oscillation strength. Phase averaged images of the OH* chemiluminescence emission show dramatic changes in the OH* distribution and intensity over an average period of the oscillation. This variation in chemiluminescence is dominated by recurrent quenching and reignition downstream of the intermediate and outer fuel stages. The pilot stage reaction zone also displays periodic variation in intensity which is out-of-phase and precedes the intermediate and outer fuel stages. Proper orthogonal decomposition is used to extract the most energetic spatial components which form the periodic behavior in the OH* distribution. The POD modes allow direct field visualization of fluctuation location and magnitude. For all four cases, the phase and location of the OH* emission variations are generally similar with small differences in the location and rates of periodic changes in the reaction oscillation.
Effects of Burner Interaction on NOx Emission From Swirl Premix Burner in a Gas Turbine Combustor
Authors: Cho Cheon Hyeon , Sohn Chae Hoon , Cho Ju Hyeong , Kim Han Seok
Published: September 2014

Flame interaction between neighboring burners in a gas turbine combustor is investigated numerically for pursuit of its effect on NOx emission from the burners. In a model chamber or liner, EV burners with double cone are installed. Two burners with the same rotating direction of air stream are adopted and the distance between them is variable from 74.2 mm to 222.6 mm by the step size of 37.1 mm. Gaseous methane and air are adopted as fuel and oxidizer, respectively. From steady-state numerical analyses, flow, temperature, and NO concentration fields are calculated in all computational cases to find their correlation with NOx formation. NOx emission is evaluated at the exit of the model chamber with two burners as a function of burner distance and compared with that from a single burner. In all cases of two-burner calculations, NOx emission is higher than that of a single burner, which results from flow interactions between neighboring burners as well as between a burner and a liner wall. NOx emission is affected significantly by flow and flame interactions between them and strongly depends on burner distance. Burner interaction is divided into two regimes of a burner-burner interaction and a burner-wall interaction depending on the distance. In the former regime, NOx emission is reduced as flame interaction between burners is enhanced and in the latter regime, it is also reduced as interaction between the burner and the liner wall is enhanced.
Study on the Stiffness Loss and its Affecting Factors of the Spline Joint Used in Rotor Systems
Authors: Zhang Qicheng , Li Weixi , Liang Zhichao , Hong Jie
Published: September 2014

The spline joint is a kind of widely used joint structures in the rotor system. Its discontinuous mechanical characteristics results from the contact surface. The surface will slide and deform when the spool deforms. As a consequence, the joint stiffness is always smaller than that of the integral configuration. This affects the rotor stiffness distribution and the rotor dynamics further. The objective of this study is to investigate the stiffness mechanical characteristics of the spline joint and their affecting factors. Based on the characteristics of structure and mechanical state, a spline joint stiffness mechanical model is built to explain the stiffness loss and its affecting factors. The cylindrical coordinate contact model is used to describe the contact of the cylindrical centering surface. And then a spline joint simulation model, taking the characteristics of the contact into account, is built by the nonlinear finite element method. At last, in the static stiffness experiment, the displacement of the spline joints is measured in different assembling and loading conditions. The results show that, the linear and angular stiffness loss of spline joint is significant and has a close relationship with the load and assembling condition. The study shows the effectiveness in controlling the mechanical properties of the rotor with spline joints by carefully adjusting structural design, load and assembling parameters.
An Investigation of Real Gas Effects in Supercritical CO2 Centrifugal Compressors
Authors: Baltadjiev N. , Lettieri C. , Spakovszky Z.
Published: September 2014

This paper presents a comprehensive assessment of real gas effects on the performance and matching of centrifugal compressors operating in supercritical CO2. The analytical framework combines first principles based modeling with targeted numerical simulations to characterize the internal flow behavior of supercritical fluids with implications for radial turbomachinery design and analysis. Trends in gas dynamic behavior, not observed for ideal fluids, are investigated using influence coefficients for compressible channel flow derived for real gas. The variation in the properties of CO2 and the expansion through the vapor-pressure curve due to local flow acceleration are identified as possible mechanisms for performance and operability issues observed near the critical point.

The performance of a centrifugal compressor stage is assessed at different thermodynamic conditions relative to the critical point using CFD calculations. The results indicate a reduction of 9% in the choke margin of the stage compared to its performance at ideal gas conditions due to variations in real gas properties. Compressor stage matching is also impacted by real gas effects as the excursion in corrected mass flow per unit area from inlet to outlet increases by 5%. Investigation of the flow field near the impeller leading edge at high flow coefficients shows that local flow acceleration causes the thermodynamic conditions to reach the vapor-pressure curve. The significance of two-phase flow effects is determined through a non-dimensional parameter that relates the time required for liquid droplet formation to the residence time of the flow under saturation conditions. Applying this criterion to the candidate compressor stage shows that condensation is not a concern at the investigated operating conditions. In the immediate vicinity of the critical point however, this effect is expected to become more prominent. While the focus of this analysis is on supercritical CO2 compressors for carbon capture and sequestration, the methodology is directly applicable to other non-conventional fluids and applications.
Large Eddy Simulation of a Thermoacoustic Instability Within a Swirl-Stabilized Burner Using Impedance Boundary Conditions
Authors: Lourier Jean-Michel , Noll Berthold , Aigner Manfred
Published: September 2014

A thermoacoustic instability observed within a lean swirl-stabilized burner is analyzed by means of numerical calculations. As extension to previously reported numerical data for the considered test case, the numerical domain is extended to include the fuel plenum and the acoustic outlet impedance is modeled by time domain impedance boundary conditions.

The predicted thermoacoustic frequency is in excellent agreement with experimental findings. Furthermore, the thermoacoustic feedback loop is discussed by means of phase resolved data which show that a variation of the equivalence ratio within the swirler is the driving mechanism of the instability. Finally, the Rayleigh criterion is shown to be satisfied within the combustion chamber. Hence, a closed thermoacoustic feedback loop is observed.
Methods for Generating Rotordynamic Models in Retrofits of Large Steam Turbines From On-Site Measurements
Authors: Hiss Florian C. , Zimmer Gerta
Published: September 2014

In turbine modernization projects accurate knowledge about the existing configuration and the prediction of the retrofitted configuration is vital for the success of the retrofit. Great progress has been made in recent years with laser-scanning techniques to capture the geometry of the existing configuration and convert it into CAD models for further design work. Equally important are proper structural dynamics models which are vital for reliably predicting the behavior of the new configuration at an early project stage. This paper discusses the application of on-site experimental modal analysis and vibration measurements during turbine operation from which the rotordynamic model of the turbine-generator including its supports and residual unbalance can be derived. Frequency response data and identification techniques are applied in combination with finite-element modeling to update the rotordynamic model based on measurements. The capabilities and limitations of the presented methods for predicting the vibration behavior by means of the established model are shown for the example of a large steam turbine unit retrofit.
Comparison of Two Widely-Used Frequency-Time Domain Contact Models for the Vibration Simulation of Shrouded Turbine Blades
Authors: Herzog Anna , Krack Malte , Panning-von Scheidt Lars , Wallaschek Jörg
Published: September 2014

Friction damping is often used in turbomachinery to reduce the vibration amplitudes of turbine blades in operation. Different approaches can be used to simulate the friction contact in the design process. For nonlinear steady state simulations, the Multi-Harmonic Balance Method (MHBM) is often used in combination with an Alternating Frequency Time (AFT) Method. The friction contact can be modeled by introducing normal and tangential stiffnesses and a Coulomb friction law. However, it is difficult to identify these contact stiffnesses experimentally. Alternatively, a formulation with Dynamic Lagrangians can be chosen. This contact model can be formulated without the need for contact stiffnesses. Both widely-used approaches are applied to a model bladed disk with nonlinear shroud contact and compared with a special focus on the predicted vibrational behaviour, numerical convergence, and their sensitivity towards changes in the input parameters.
Effects of Curvature on the Film Cooling Effectiveness of Double-Jet Film Cooling
Authors: Liao Gaoliang , Wang Xinjun , Li Jun , Zhang Feng
Published: September 2014

The effect of curvature on the film cooling characteristics of Double-Jet Film Cooling (DJFC) was numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS). The low-Reynolds number shear stress transport (SST) model was employed as the turbulence closure model. Six different curved surfaces and a flat surface were tested numerically. The blowing ratios were from 0.66 to 1.99, and the compound injection angle with respect to the cooled surface was 30 degree. The blowing ratios and the curvature of cooled surface have crucial effects on the film cooling effectiveness. The numerical results show that there are two peek value of the averaged film cooling effectiveness along the mainstream direction. The results also indicate that the film cooling effectiveness of a specified curved surface depends on the reasonable selection of the slope of curved surface and blowing ratios.
Leakage Performance and Rotordynamic Characteristics of Bump Floating Ring Seals for Turbopump
Authors: Lee Yong-Bok , Kim Kyoung-Wook , Ryu Sol-Ji , Chung Jin Taek
Published: September 2014

Floating ring seal with bump foil (BFRS) was newly proposed and tested. BFRS which has a thickness of bump (0.076, 0.1 and 0.12 mm) are separately tested for pressure-drops of 3.0, 5.0 and 7.0 MPa and rotor-speed up to 24,800 rpm. The measured data included leakage performance, attitude angle, lock-up eccentric ratio, and rotordynamic coefficients such as stiffness, damping and equivalent whirl frequency ratio to decide the whirling stability of seal were compared with floating ring seal.

When the thickness of bump floating ring seals is increasing, leakage flow rate somewhat increases. Also, the lock-up eccentric ratio of the bump floating ring seal with large thickness is lower than that of the floating ring seal or small thickness of bump foil. The attitude angle increases linearly with the operating speeds in both cases. The direct damping coefficients increase significantly with the increments in bump-foil thickness and hydrostatic pressure-drop, but diminish with the rising rotor-speed. Especially, Coulomb friction damping force between the bump foil and housing surface contributes to the enhancement of direct damping coefficient value. Whirl frequency ratio of the floating ring seal without bump shows somewhat small in low speed ranges. When bump foil thickness is 0.074mm or 0.1mm, WFR is insensitive in rotating speed and pressure. But BFRS (0.12mm) shows up more stable tendency according to decreasing whirl frequency ratio in high speed ranges. The design parameters determined from these test results will be used to enhance the stability in high pressure and high speed turbomachinery seals.
Development of the Electric Fuel System for the More Electric Engine
Authors: Morioka Noriko , Oyori Hitoshi , Gonda Yukinori , Takamiya Kenji , Yamamoto Yasuhiko
Published: September 2014

This paper describes the experimental rig test result of the electric motor-driven fuel pump system for the MEE (More Electric Engine). The MEE is an aircraft engine system concept, which replaces conventional mechanical/hydraulic driven components with electric motor-driven components. Various MEE approaches have been studied since the early 2000s and one of its key concepts is an electric motor-driven fuel pump [1–4]. The authors commenced a feasibility study of the electric motor-driven gear pump system for what was assumed to be a small-sized turbofan engine. The concept study and system design were conducted, whereupon technical issues for the electric fuel pump system, which both supplies and meters fuel via the motor speed control, were clarified [5, 6]. Since one of the key issues is fuel-metering accuracy, the electric fuel system, including a flow feedback closed-loop control, was designed to ensure accurate fuel-flow metering for aircraft engine applications.

To verify the rig system, an experimental model of the electric fuel pump system is assumed for a small-sized turbofan engine. The hardware of the motor-driven fuel pump and flow measurement mechanism, including an FPV (Fuel-Pressurizing Valve) and orifice, were designed, manufactured and fabricated and a differential pressure sensor for flow feedback was selected. Other equipment was also prepared, including a motor controller, power source and measurement devices, and the entire rig set-up was constructed.

A bench test using the rig test set-up was conducted to verify the fuel-metering accuracy, response and system stability. Data, including the static performance and frequency response, were obtained for the electric motor, motor-driven fuel pump and entire fuel system respectively. The rig test results indicate the feasibility of the system, which will provide an accurate engine fuel flow (Wf) measurement and frequency response required for actual engine operation, via an electric motor speed control and fuel-flow feedback system, as proposed in the MEE electric fuel system.
Numerical Conjugate Heat Transfer Study of a Cooled Compressor Rear Cone
Authors: Bleier Fabian , Hufnagel Max , Pychynski Tim , Bauer Hans-Jörg , Eichler Christian
Published: September 2014

The paper presents the setup of a conjugate heat transfer study of an annular conical gap, its validation and a parameter study. The main goal of the work is to identify effects of gap width and swirl ratio on the local and global heat transfer in the annular conical gap. The validation of the numerical model is done by a comparison against experimental data from literature. It is shown that the non-axisymmetric flow in the gap can be well reproduced by a three-dimensional axisymmetric model. To identify influences of geometric and operational parameters on the cooling efficiency, a RANS parameter study of the cooling concept is performed. The parameter study includes variations of the gap width and the pre-swirl of the inlet air.

The results are used to evaluate the quality of the cooling concept and to identify the effect of geometry on frictional effects and on heat transfer coefficients. In this respect it is important to separate frictional heating and convective heat transfer effects.
Numerical Investigations on the Conceptual Design of a Ducted Contra-Rotating Fan
Authors: Huo Chao , Gonzalez Diez Nestor , Rao Arvind Gangoli
Published: September 2014

The Advisory Council for Aeronautics Research in Europe (ACARE) has set an ambitious array of objectives to be accomplished by 2050. It is often claimed that complying with those targets will not require evolution but, rather, revolution. If the growth in aviation has to be sustained in the future then we must come up with radical aircraft and engine configurations which can meet the demands of future aviation.

The contra-rotating fan is one such system which can play an important role in the future engine configurations, such as the hybrid engine configuration that is being investigated in the EU cofounded AHEAD project.

In order to design a CRF system, a 1-D code has been developed based on the inverse Blade Element Method (BEM) to design a contra rotating fan. The CRF design obtained from this methodology is then analyzed with a full 3D RANS simulation.

The numerical analysis revealed that the performance of the first rotor satisfies with the given design requirements in terms of both pressure ratio and isentropic efficiency, thus proving the efficacy of using the 1-D code for designing the CRF. However, the performance of the rear rotor does not reach the design demands. It was observed that there is a strong flow separation around the root and a strong normal shock in the blade passage near the tip. It was found that there is a great difference between the blade metal inlet angles and the relative flow inlet angles near the root of the rear rotor. One of the main reasons for this is the calculation of the axial velocity depending on the vortex design and the resolution of the radial equilibrium. Based on the CFD simulations, the design code could be further modified to improve the design of CRF.