bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unsteady Flow Physics and Performance Prediction of a 1-1/2 Stage Unshrouded High Work Turbine Using the Lattice Boltzmann Approach
Authors: Gonzalez-Martino Ignacio , Gautier Sébastien 
Published: September 2016

A comparison between experimental measurements and simulations of a 1-1/2 stage unshrouded high work turbine are presented. The experimental investigations were conducted by the Turbomachinery Laboratory of ETH Zurich. The data was obtained from steady and unsteady probe measurements that were performed in four axial planes between stator and rotor rows.
Simulations have be performed using the commercial CFD solver PowerFLOW based on the Lattice Boltzmann (LB) method to compute unsteady flow fields. The turbulent flow fluctuations are resolved up to a certain scale using a so-called Very Large Eddy Simulation (VLES) approach. One crucial aspect of the present study is the use a new non-isothermal version of the LB model that allows extending the Mach number range of the standard PowerFLOW scheme up to about 0.9. These unsteady simulations have been used to better understand the different flow structures observed in the experiments, and in particular the mechanisms of tip leakage across the blades of the unshrouded turbine rotor.
In the present work, the complete 1-1/2 stage turbine with time-accurate moving rotor geometry has been simulated using the LB solver. This means that no blade reduction technique or almost-periodic flow hypothesis have been used in the simulation. The geometry was modified in order to close the rotor tip gap and do not consider its effects. A thorough comparison of these two simulations with the experimental data has been conducted and presented in the paper: averaged quantities along the turbine stage such as pressure drop, the degree of reaction, the loading coefficient, and the flow coefficient; averaged midspan inlet and exit angles for each turbine blade rows; and flow distribution at four axial planes between the rotor and stator rows. Moreover, a deep analysis of the unsteady flows in the blade channel has been performed in order to better understand the flow features observed in the experimental measurements. Finally, it has been be possible to analyze the interaction modes between turbine rows thanks to the simulation of the full 360° geometry and its time-accurate approach.
Investigation on Jet Breakup of High-Viscous Fuels for Entrained Flow Gasification
Authors: Müller Thomas , Habisreuther Peter , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas 
Published: September 2016

The present study focuses on the atomization behaviour of liquids in external mixing twin fluid nozzles and investigates a wide range of viscosities as well as different nozzle geometries at a gas to liquid ratio (GLR) typically used in entrained flow gasification.
In a first stage experiments were performed using water and water-glycerol-mixtures as Newtonian model fuels with liquid viscosity up to 400 mPa s. Jet breakup was investigated qualitatively using a high speed camera as well as using a PIV and LDA-System for detailed quantitative investigation of the flow field. Two different primary instabilities flapping and pulsating mode were detected which are dependent on operating conditions of the nozzle (e.g. GLR) and rheological properties of the liquid phase (e.g. liquid viscosity) as well as nozzle geometry. For better interpretation of the phenomena occurring during jet breakup a frequency-analysis of the primary instabilities was performed using the pictures of the high speed camera.
In addition, compressible large eddy simulations (LES) were preformed to describe the experimental observations and to capture the morphology of the primary breakup as well as the important flow field characteristics. The numerical simulations were conducted by means of the open source CFD software OpenFOAM. A Volume of Fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Comparison of experimental and numerical results shows a good agreement concerning breakup frequency, velocity fields and morphology. The breakup frequency varied in a range of 430 to 757 Hz depending on operating condition and nozzle geometry.
Based on these results a more detailed understanding of the physics leading to liquid jet breakup and finally atomization process will be available.
LES Validation for a Rotating Cylindrical Cavity With Radial Inflow
Authors: Onori Michel , Amirante Dario , Hills Nicholas J. , Chew John W. 
Published: September 2016

This paper describes Large-Eddy Simulations (LES) of the flow in a rotating cavity with narrow inter-disc spacing and a radial inflow introduced from the shroud.
Simulations have been conducted using a compressible, unstructured, finite-volume solver, and testing different subgrid scale models. These include the standard Smagorinsky model with Van Driest damping function near the wall, the WALE model and the implicit LES procedure. Reynolds averaged Navier-Stokes (RANS) results, based on the Spalart-Allmaras and SST k-ω models, are also presented. LES solutions reveal a turbulent source region, a laminar oscillating core with almost zero axial and radial velocity and turbulent Ekman type boundary layers along the discs.
Validations are carried out against the experimental data available from the study of Firouzian et al. [1]. It is shown that the tangential velocity and the pressure drop across the cavity are very well predicted by both RANS and LES, although significant differences are observed in the velocity profiles within the boundary layers.
Experimental and Numerical Investigations of Effusion Cooling for High Pressure Turbine Components: Part 1 — Experimental Study With PSP
Authors: Wang Guanghua , Ledezma Gustavo , DeLancey James , Wang Anquan 
Published: September 2016

Gas turbines overall efficiency enhancement requires further increasing of the firing temperature and decreasing of cooling flow usage. Multi-Hole (or effusion, full coverage) film cooling is widely used for hot gas path components cooling in modern gas turbines.
The present study focused on the adiabatic film effectiveness measurement of a round multi-hole flat plate coupon. The measurements were conducted in a subsonic open loop wind tunnel with a generic setup to cover different running conditions. The test conditions were characterized by a constant main flow Mach number of 0.1 with constant gas temperature. Adiabatic film effectiveness was measured by Pressure Sensitive Paint (PSP) through mass transfer analogy. CO2 was used as the coolant to reach the density ratio of 1.5. Rig CFD simulation was conducted to evaluate impact of inlet boundary layer on testing.
Experimental data covers blowing ratios (BR) at 0.4, 0.6, 0.8, 1.0 and 2.0. Both 2D maps and lateral average profiles clearly indicated that film effectiveness increases with increasing BR for BR<0.8 and decreases with increasing BR for BR>0.8. This observation agreed with coolant jet behavior of single film row, i.e. attached, detached then reattached, and fully detached. PSP data quality was then discussed in detail for validating Large Eddy Simulation in Part 2.
Experimental Investigation of Aspiration in a Multi-Stage High-Speed Axial-Compressor
Authors: Siemann Jan , Krenz Ingolf , Seume Joerg R. 
Published: September 2016

Reducing the fuel consumption is a main objective in the development of modern aircraft engines. Focusing on aircraft for mid-range flight distances, a significant potential to increase the engines overall efficiency at off-design conditions exists in reducing secondary flow losses of the compressor. For this purpose, Active Flow Control (AFC) by aspiration or injection of fluid at near wall regions is a promising approach.
To experimentally investigate the aerodynamic benefits of AFC by aspiration, a 4½-stage high-speed axial-compressor at the Leibniz Universitaet Hannover was equipped with one AFC stator row. The numerical design of the AFC-stator showed significant hub corner separations in the first and second stator for the reference configuration at the 80% part-load speed-line near stall. Through the application of aspiration at the first stator, the numerical simulations predict the complete suppression of the corner separation not only in the first, but also in the second stator. This leads to a relative increase in overall isentropic efficiency of 1.47% and in overall total pressure ratio of 4.16% compared to the reference configuration.
To put aspiration into practice, the high-speed axial-compressor was then equipped with a secondary air system and the AFC stator row in the first stage. All experiments with AFC were performed for a relative aspiration mass flow of less than 0.5% of the main flow. Besides the part-load speed-lines of 55% and 80%, the flow field downstream of each blade row was measured at the AFC design point. Experimental results are in good agreement with the numerical predictions. The use of AFC leads to an increase in operating range at the 55% part-load speed-line of at least 19%, whereas at the 80% part-load speed-line no extension of operating range occurs.
Both speed-lines, however, do show a gain in total pressure ratio and isentropic efficiency for the AFC configuration compared to the reference configuration. Compared to the AFC design point, the isentropic efficiency ηis rises by 1.45%, whereas the total pressure ratio Πtot increases by 1.47%. The analysis of local flow field data shows that the hub corner separation in the first stator is reduced by aspiration, whereas in the second stator the hub corner separation slightly increases. The application of AFC in the first stage further changes the stage loading in all downstream stages. While the first and third stage become unloaded by application of AFC, the loading in terms of the De-Haller number increases in the second and especially in the fourth stage. Furthermore, in the reference as well as in the AFC configuration, the fourth stator performs significantly better than predicted by numerical results.
Impact of Quarter Wave Tube Arrangement on Damping of Azimuthal Modes
Authors: Zahn Max , Schulze Moritz , Hirsch Christoph , Sattelmayer Thomas 
Published: September 2016

The impact of quarter wave tube (QWT) arrangements in terms of axial location, circumferential distribution and number of cavities on damping of azimuthal modes is investigated both experimentally and numerically in an atmospheric annular test rig under isothermal conditions. Well-established measurement techniques are applied to characterize the damping potential for azimuthal modes of different quarter wave tube (QWT) arrangements. For additional insight into the considered configurations eigenfrequency studies are conducted using linearized Euler equations (LEE). Measured boundary conditions are used for inlet and outlet. The reflection coefficient of a single quarter wave tube (QWT) is measured on an impedance rig using longitudinal wave excitation. It is shown that this reflection coefficient can be used for the eigenfrequency analysis of the annular rig in which the QWT is mounted in radial direction.
The effects of different quarter wave tube configurations on the spatial mode shape of the first azimuthal mode and the corresponding change in modal dynamics are analyzed. This provides guidance for the circumferential and axial arrangement of damping devices to most effectively attenuate an annular acoustic system. It is illustrated that the complete acoustic system including the resonators has to be considered to properly dimension the acoustic characteristics of a damping device.
Powerful Interpolation Method Demonstrated on Experimental Data From Fast Response Pressure Transducers in a Turbofan Engine
Authors: Kern Felix , Bindl Stefan , Stößel Marcel , Aberle Svenja , Niehuis Reinhard 
Published: September 2016

Interpolation is a common procedure in scientific practice. In many cases, linear interpolation is tacitly applied in order to present measurements or numerical results. The application of sophisticated interpolation methods is rather rare, even though they can help to extract more information from a measurement, especially if the resolution is relatively low. This paper presents an interpolation method and a validation procedure, which is demonstrated on experimental data from a low pressure compressor of a twin spool turbofan engine.
As a research test vehicle the Larzac 04 turbofan engine is used, which is equipped with extensive instrumentation and control systems. This publication focuses on the high speed pressure transducers mounted directly above the tip of the first LPC rotor blades. Besides the installation of those sensors in a jet engine, the processing, the storage, and the analysis of the data is challenging, as the sampling rate is extraordinary high (1 MHz). Those sampling rates result in a high circumferential resolution (1 MHz ≙ 2.69 samples per mm at 90% rel. spool speed) compared to the relatively low geometrical resolution of the nine axial sensors (0.23 samples per mm). Therefore, sophisticated interpolation methods are applied on the data points in axial direction, aiming to get the best possible result from the acquired data. A major part of this paper is the discussion and validation of several different interpolation methods. Especially with the Akima sub-spline interpolation, very promising results were obtained.
Finally, some of the results from the fast response pressure transducers are presented. The casing wall pressure distribution and some flow phenomena at the design operating point are compared to the corresponding near stall conditions.
Wake and Loss Analysis for a Double Bladed Swept Propeller
Authors: Capitao Patrao Alexandre , Avellán Richard , Lundbladh Anders , Grönstedt Tomas 
Published: September 2016

Inspired by Prandtl’s theory on aircraft wings with minimum induced drag, the authors introduced a double-bladed propeller, the Boxprop, intended for high-speed flight. The basic idea is to join the propeller blades pair-wise at the tip to improve aerodynamics and mechanical properties compared to the conventional propeller. The rather complex geometry of the double blades gives rise to new questions, particularly regarding the aerodynamics.
This paper presents a propeller wake energy analysis method which gives a better understanding of the potential performance benefits of the Boxprop and a means to improve its design.
CFD analysis of a five bladed Boxprop demonstrated its ability to generate typical levels of cruise thrust at a flight speed of Mach 0.75. The present work shows that the near tip velocity variations in the wake are weaker for this propeller than a conventional one, which is an indication that a counter rotating propeller designed with a Boxprop employed at the front may exhibit lower interaction noise.
Aerodynamic and Acoustic Performance of a Single Stage Axial Fan With Extensive Blade Sweep Designed to Limit Noise Emissions
Authors: Giesecke Daniel , Friedrichs Jens , Stark Udo , Dierks Maik 
Published: September 2016

Not only the aerodynamic performance of axial flow fans is important but also the acoustic behaviour plays a vital role. It is to be expected that in the future noise limits will be more regulated by legislation. The aim of this project is to develop a very versatile tool for efficient and noise reduced axial flow fans in rotor / stator configuration.
This paper describes the design, numerical verification and tests of a highly loaded single stage axial flow fan making use of extensive blade sweep in rotor and stator for acoustic reasons. The tests include aerodynamic and acoustic investigations.
The stage is a conventional free vortex design with unconventional blades of a special planform. The blade sections of both rotor and stator are NACA 65-sections on circular arc mean lines. Sectional diffusion factors and de Haller numbers are close to their respective limits, especially for the sections next to the rotor and stator hubs.
The rotor is characterised by a forward-swept leading edge with increasing sweep angle towards hub and tip and an unswept trailing edge. The leading edge of the stator blades is forward-swept as before but this time at an almost constant sweep angle between the hub and the two-thirds position of the blade span. The trailing edge is straightened for reducing the previously mentioned aerodynamic loadings.
The study shows that the numerical results are consistent with the experimental outcome. It concludes that the advanced design features show potential aerodynamic and acoustic benefits by sweeping the blade in the described manner. This is particularly the case when comparing to single row designs.
The Optimization of a Centrifugal Impeller Based on a New Multi-Objective Evolutionary Strategy
Authors: Li Xiaojian , Zhao Yijia , Liu Zhengxian , Chen Hua 
Published: September 2016

Centrifugal compressors with high aerodynamic performance are widely used in turbochargers, aero-engines and petrochemical engineering. The impeller is the core component and plays a key role in determining the compressor performance.
This paper reports the optimisation of the aerodynamic performance of an industrial centrifugal impeller by a multi-objective evolutionary strategy. Firstly the 3-D modeling method for parameterisation of impeller’s geometry was described. Secondly the traditional NSGA-II method was modified to improve its ability and efficiency. Employed CFD code was first validated using the experimental data of an existing impeller. The optimisation was applied to the industrial centrifugal impeller through a two-step optimization process to allow for significant variations of the impeller geometry and speedy finding of the optimum. The optimisation was completed within 53 hours on a workstation with two 24-core processors (Xeon(R) E5-2670 v3 2.3GHz). The results indicated that the isentropic efficiency of the impeller increased by 5.3 percents and the total pressure ratio by 20.5 percents at design condition.
Developing Additive Manufacturing Technology for Burner Repair
Authors: Andersson Olov , Graichen Andreas , Brodin Håkan , Navrotsky Vladimir 
Published: September 2016

Low emission combustion is one of the most important requirements for Industrial gas turbines. Siemens Industrial gas turbines SGT-800 and SGT-700 use DLE (Dry Low Emission) technology and are equipped with 3rd generation of DLE burners. These burners demonstrate high performance and reliable operation for the duration of their design lifetime. The design and shape of the burner tip is of great importance in order to achieve a good fuel/ air mixture and at the same time a resistance to the fatigue created by heat radiation input. This gives a requirement for a tip structure with delicate internal channels combined with thicker structure for load carrying and production reasons. It was found that the extension of the burner lifetime beyond the original design life could be accomplished by means of repair of the burner tip.
Initially the tip repair has been done by conventional methods — i.e. cutting off the tip and replacing it with a premanufactured one. Due to the sophisticated internal structure of the burner the cuts have to be made fairly high upstream to avoid having the weld in the delicate channel area.
Through the use of AM (Additive Manufacturing) technology it has been possible to simplify the repair and only replace the damaged part of the tip.
Special processes have been developed for AM repair procedure, including:
a) machining off of the damaged and oxidized tip,
b) positioning the sintered model on the burner face,
c) sintering a new tip in place,
d) quality assurance and inspection methods,
e) powder handling,
f) material qualification including bonding zone,
g) development of methods for mechanical integrity calculation,
h) qualification of the whole repair process.
This paper describes how we have developed and qualified SGT-800 and SGT-700 DLE burners repair with the help of additive manufacturing technology and our research work performed. In addition, this paper highlights the challenges we faced during design, materials qualification and repair work shop set-up.
Assessment of RANS Against LES for the Aero-Thermal Behavior of High Pressure Turbine Stages Under Realistic Inlet Conditions
Authors: Vagnoli Stefano , Verstraete Tom , Koupper Charlie , Bonneau Guillaume 
Published: September 2016

Modern Lean Burn combustors generate a complex field at the High Pressure turbine (HPT) inlet, characterized by non-uniform velocity and temperature distributions, together with very high turbulence levels (up to 25%). For these extreme conditions, classical numerical methods employed for the HPT design, such as Reynolds Averaged Navier Stokes (RANS) simulation, suffer from a lack of validation. This leads to a reduced confidence in predicting the combustor-turbine interactions, which requires to use extra safety margins, to the detriment of the overall engine performance.
Within the European FACTOR project, a 360° non reactive combustor simulator and a 1.5 HPT stage are designed to get more insight into the mutual interaction of these two components. A first experimental and numerical campaign has demonstrated the potential of Large Eddy Simulations (LES) to accurately reproduce the turbulent flow field development at the combustor outlet.
The aim of the present paper is to exploit the accuracy of LES to validate less time-consuming RANS models in predicting the hot streak migration in the turbine stage. In this sense, LES results are used as a reference to discriminate the different RANS simulations in terms of turbulence modeling and aerothermal predictions.
The current investigations clearly indicate that turbulence and hot streak diffusion within the HPT are strongly linked. In this sense, the choice of the RANS turbulence model and the inlet turbulent conditions plays a major role in modeling the thermal behavior for the stator and rotor blades.
Accounting for Uncontrolled Variations in Low-Speed Turbine Experiments
Authors: Evans K. R. , Longley J. P. 
Published: September 2016

It is common to assume that the performance of low-speed turbines depend only on the flow coefficient and Reynolds number. As such the required operating point is achieved by controlling the values of these two non-dimensional quantities by, for example, appropriate choices for the mass flow rate and applied brake torque. However, when the turbine has an atmospheric inlet and uses unconditioned air, variations in ambient pressure, temperature and humidity are introduced. Whilst it is still possible to maintain the required values for the flow coefficient and Reynolds number, the ambient variations affect additional non-dimensional quantities which are related to the blade speed and gas properties. Generally, the values of these additional non-dimensional quantities cannot be controlled and, consequently, they affect the turbine performance. In addition, thermal effects, which are exacerbated by the use of plastic blades, can cause changes in the blade row seal clearance and these also affect the performance. Therefore to obtain measurements with greater accuracy and repeatability, the changes in the uncontrolled non-dimensional quantities must be accounted.
This paper contains four parts. Firstly, it is described how suitable data acquisition parameters can be determined to eliminate short time scale facility unsteadiness within the measurements. Secondly, by the analysis of models, the most appropriate forms for the additional non-dimensional quantities that influence turbine performance are obtained. Since the variations in the uncontrolled non-dimensional quantities affect repeatability the size of the effect on the turbine performance is quantified. Thirdly, a best-fit accounting methodology is described which reduces the effects of the uncontrolled non-dimensional quantities on turbine performance provided sufficient directly related measurements are available. Finally, the observations are generalised to high-speed turbomachines.