bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Steady and Unsteady Coupled Heat-Transfer Simulations of a High-Pressure Turbine Blade
Authors: Schmidt Markus , Starke Christoph
Published: August 2015

This article presents results for the coupled simulation of a high-pressure turbine stage in consideration of unsteady hot gas flows.

A semi-unsteady coupling process was developed to solve the conjugate heat transfer problem for turbine components of gas turbines. Time-resolved CFD simulations are coupled to a finite element solver for the steady state heat conduction inside of the blade material. A simplified turbine stage geometry is investigated in this paper to describe the influence of the unsteady flow field onto the time-averaged heat transfer. Comparisons of the time-resolved results to steady state results indicate the importance of a coupled simulation and the consideration of the time-dependent flow-field.

Different film-cooling configurations for the turbine NGV are considered, resulting in different temperature and pressure deficits in the vane wake. Their contribution to non-linear effects causing the time-averaged heat load to differ from a steady result is discussed to further highlight the necessity of unsteady design methods for future turbine developments.

A strong increase in the pressure side heat transfer coefficients for unsteady simulations is observed in all results. For higher film-cooling mass flows in the upstream row, the preferential migration of hot fluid towards the pressure side of a turbine blade is amplified as well, which leads to a strong increase in material temperature at the pressure side and also in the blade tip region.
The Use of a New Fatigue Tool (ALBdeS) to Analyse the Effects of Vortex Generators on Wind Turbines
Authors: Castro Oscar , Lennie Matthew , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver
Published: August 2015

Wind turbines are classically designed for an extremely long lifetime in machinery design terms, for example, the Siemens SWT-6.0-154 was recently certified for 25 years [1]. The implication is that wind turbines accumulate damage via a number of mechanisms. A primary concern is naturally fatigue, exacerbated by a long life (high number of cycles); however, environmental effects such as bio-fouling and leading edge erosion damage the structure but also modify the Lift and Drag characteristics, particularly the stall behaviour. Vortex Generators (VGs), more commonly known from the aviation industry, have been demonstrated to delay stall and improve the stall region characteristics. This restoration of properties has been associated with reduced fatigue loading following the logic that the rotor blade will undergo stall less severely and less often. This hypothesis was tested in this study using a newly developed fatigue tool ALBdeS (named after W. Albert the first author to write a paper considering fatigue) to post-process aeroelastic simulations conducted in FAST (from NREL/NWTC) [2]. The post processing tool is an extension of the PMV custom section rotorblade analysis tool of SMART BLADE GmbH. The ALBdeS tool calculates the cumulative damage value in each individual layer of the blade section laminates and determines whether or not failure will occur over the course of 20 years, following the GL Guidelines [3]. Sensitivity studies showed that by de-constructing the main oscillation into 30 analysis points, the accumulated damage converges to a stable result, thus increasing confidence in the stability of the method. The FAST simulations were conducted with modified versions of the NREL 5MW reference turbine. The inboard lift and drag polars of the 5MW were modified in order to simulate the effect of adding VGs to the design. The polar modifications were made in the absence of 3D stall delay effects although literature does indicate the effects are somewhat additive. However, the resulting simulations did demonstrate that VGs did in fact change the fatigue characteristics of the rotor blades but by an inconsiderate amount.
Wake Analysis of a Finite Width Gurney Flap
Authors: Holst D. , Bach A. B. , Nayeri C. N. , Paschereit C. O. , Pechlivanoglou G.
Published: August 2015

The results of stereo Particle-Image-Velocimetry measurements are presented in this paper to gain further insight into the wake of a finite width Gurney flap. It is attached to an FX 63-137 airfoil which is known for a very good performance at low Reynolds numbers and is therefore used for small wind turbines and is most appropriate for tests in the low speed wind tunnel presented in this study. The Gurney flaps are a promising concept for load control on wind turbines but can have adverse side effects, e.g. shedding of additional vortices. The investigation focuses on frequencies and velocity distributions in the wake as well as on the structure of the induced tip vortices. Phase averaged velocity fields are derived of a Proper-Orthogonal-Decomposition based on the stereo PIV measurements. Additional hot-wire measurements were conducted to analyze the fluctuations downstream of the finite width Gurney flaps. Experiments indicate a general tip vortex structure that is independent from flap length but altered by the periodic shedding downstream of the flap.

The influence of Gurney flaps on a small wind turbine is investigated by simulating a small 40 kW turbine in Q-Blade. They can serve as power control without the need of an active pitch system and the starting performance is additionally improved. The application of Gurney flaps imply tonal frequencies in the wake of the blade. Simulation results are used to estimate the resulting frequencies. However, the solution of Gurney flaps is a good candidate for large scale wind turbine implementation as well. A FAST simulation of the NREL 5MW turbine is used to generate realistic time series of the lift. The estimations of control capabilities predict a reduction in the standard deviation of the lift of up to 65%. Therefore finite width Gurney flaps are promising to extend the lifetime of future wind turbines.
Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames
Authors: Watanabe Hirotatsu , Shanbhogue Santosh J. , Ghoniem Ahmed F.
Published: August 2015

Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.
Inlet Guide Vane Performance at Dry and Wet Gas Conditions
Authors: Vigdal Levi B. , Bakken Lars E.
Published: August 2015

As inlet properties of compressor stage deviates from design point, the compressor stage efficiency will be degraded. A change in properties typically affects the inlet volume flow and inlet Mach number. To maintain optimum performance a static stage called Variable Inlet Guide Vanes (IGV) is implemented before the compressor wheel to manipulate the inlet flow direction. The vanes are of airfoil type geometry, twisted in radial direction to compensate for compressor peripheral speed. The RMS radius has a geometrical flow turning of 20 degrees. Extensive research exists on vane performance in dry gas conditions, but there are however limited results on vane performance shift from dry to wet gas flow. This paper focuses on twisted VIGV performance with GMF down to 80 percent. The VIGV is mounted in front of a centrifugal compressor impeller operating at 9000 rpm. An outlet throttle valve is adjusted to allow for performance at constant gas volume flow. Increased liquid content shows a general reduction in continuity wave size. At low GVF the wave disappeared or was reduced drastically, only to reappear when the incidence angle was increased. This is presumably from the balance of momentum between the pressure side Horse Shoe Vortex and main flow. Flow separation was not observed at any incidence angles or GVF. A vortex at the trailing edge was observed which also allowed the movement of liquid in span-wise direction. Traces of several vortices were observed at all GVF. The general propagation of the vortices fits well with dry gas theory.
The Aerodynamic Response of Fuel Injector Passages to Incident Acoustic Waves
Authors: Su Jialin , Garmory Andrew , Carrotte Jon
Published: August 2015

Modern low emission combustion systems are more prone to combustion instabilities due to operation at lean conditions. The response of the airflow passing through the injector to incident acoustic waves is therefore of interest. Airflow fluctuations can initiate, for example, perturbations in stoichiometry and velocity that are subsequently delivered into the heat release region. In the case of liquid fuelled gas turbines the atomisation process will also be affected. Such effects can lead to further unsteady heat release and the generation of acoustic waves, thereby leading to combustion instability. This paper describes experimental measurements and the development of a numerical methodology by which the unsteady airflow response of complex, modern, low emission fuel injectors can be characterised.

Single and two passage injector configurations have been investigated which broadly capture many of the features associated with modern fuel injectors. Although targeted at low emission (lean burn) liquid fuelled injector geometries, the methodology developed is thought applicable to a wide range of injector configurations. Initially experimental measurements were used to characterise the overall acoustic impedance of each injector design over a range of frequencies. Such information is also required for the low order thermo-acoustic network models, as typically used in the design process, to predict the stability of the combustion system. In addition to the experimental measurements a methodology was developed using unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations in which acoustic boundary conditions were implemented to reproduce the experimental scenarios. Interrogation of the pressure field enabled similar data analysis techniques to be applied to the numerical data for determining the injector acoustic characteristics. Fidelity of the numerical simulations is confirmed by the excellent agreement between the experimental data and numerical simulations. Furthermore, the unsteady flow field within the passages is difficult to access experimentally, but can be examined in more detail from the simulation results. In this way an improved understanding of the passage flows and their individual responses to the incident acoustic pressure waves can be obtained. The numerical approach is aimed at providing a computationally efficient and economic tool for predicting the acoustic characteristics of the complex geometries typical of modern fuel injector designs. Using this tool injector designs with different acoustic response characteristics can be developed relatively quickly.
An Integrated Method for Propulsion System Conceptual Design
Authors: Becker R.-G. , Reitenbach S. , Klein C. , Otten T. , Nauroz M. , Siggel M.
Published: August 2015

The conceptual design of future, potentially highly integrated aircraft engines pose a variety of new design options to the propulsion system engineers. In order to find the best conceptual design, rapid evaluation of many design choices is essential. However, traditional, fast evaluation methods employing historical and empirical data can only be applied to novel engine concepts to a very limited degree. Thus, swift conceptual design methods based on physical approaches providing a sophisticated level of detail are needed. The current paper presents a methodology focused on conceptual engine design. The methodology is based on the gas turbine simulation framework GTlab, which integrates software tools for engine performance, component aerodynamics and structural design. For conceptual design a dedicated set of design tools exists — the so called GTlab-Sketchpad. Sketchpad tools have full access to the thermodynamic design data of the engine performance module. Based on cycle analysis, the tool set generates parametric representations of the propulsion system components and stores the results back to the frameworks data model. Computational time is limited to a few seconds, to ensure interactivity during the design process. The graphical user interface provides means to interactively modify the design parameters and to immediately evaluate their impact on the overall design. Since the internal data model facilitates three dimensional parameterizations of the engine components, 3D representations of the engine designs can be generated by interfacing an open source CAD-kernel. For the present paper, the conceptual design process of a commercial jet engine utilizing GTlab-Sketchpad is shown. The underlying computational methods are described and the resulting 3D-geometry is presented.
Enlarging Fuel Flexibility for Frame 5 DLN: Combustor Operability and Emissions With High C2+ Content
Authors: Zucca Alessandro , Forte Annalisa , Giannini Nicola , Romano Christian , Modi Roberto
Published: August 2015

Fuel flexibility is a key feature for Dry Low NOx (DLN) combustors, which shall be capable of accepting a wider range of fuel compositions to meet more and more challenging requests from the Oil and Gas market segment (upstream and downstream applications). Non-methane hydrocarbons (C2+) are one of the main targets of GE Oil & Gas efforts to enlarge the fuel flexibility of DLN combustors, as they are often present in high concentration in fuel gas streams that customers would like their gas turbine to be fed with. The main concerns with such fuel gases in DLN combustor are: the risks of flashback, hardware overheating, increased combustion dynamics and NOx emission, ignition in unexpected locations (with potential damage of the combustor, operability issues and impact on durability).

In order to assess the capability of the current Frame 5 DLN1 hardware design with high C2+ fuels, a single can full pressure test campaign was conducted on a full size DLN1 combustor at Sesta Combustion Lab (Italy).

The combustion chamber was successfully tested in premix mode up to 50%v. of ethane content, observing safe and reliable operation with regard to the above mentioned risks. Special tests were carried out in both Premix and Lean-Lean operating modes, in order to verify the ability of the combustor to maintain a stable and harmless flame and assess the operability margins in the different operating conditions of the combustor. Tests demonstrated a good margin already with the current design. After optimizing the air flow path, the expected performances also in terms of NOx and CO emissions and combustion dynamics were achieved in the investigated ethane content range. These tests outcomes allowed a paramount enlargement of the Frame 5 DLN1 capability in terms of acceptable C2+ concentration in fuel gas.
Experimental Study of Impingement Jet Cooling Above Pedestal Roughened Channels
Authors: Peacock G. L. , Thorpe S. J.
Published: August 2015

An experimental investigation has been conducted into the use of a combined impingement-pedestal cooling geometry to improve uniformity of surface heat transfer coefficient over traditional combustor liner impingement arrays. Various pedestal arrangements have been investigated by altering the height-to-diameter (H/D) and pitch-to-diameter (P/D) ratios and measurements have been made over a range of impingement jet Reynolds numbers between ∼20 and 40×103. The surface heat transfer coefficient has been determined using a transient liquid crystal thermography measurement technique and the data presented in terms of Nusselt number. A ‘shielded impingement’ concept has also been defined featuring full-height pedestals positioned upstream of each impingement jet and arranged to shield the impingement jets from the developing cross-flow. Aerodynamic measurements have also been made to evaluate the influence of changes to the pedestal geometry on the pressure drop incurred across the different cooling patterns. The analysis indicates superior heat transfer performance can be achieved for the shielded impingement arrangements, with the greatest improvement over equivalent geometries displayed towards the rear of the cooling channel.
Unsteady CFD Analysis of Erosion Mechanism in the Coolant Channels of a Rotating Gas Turbine Blade
Authors: Borello Domenico , Anielli Davide , Rispoli Franco , Salvagni Alessandro , Venturini Paolo
Published: August 2015

The two-phase flow in a rotating wedge mimicking the final portion of a blade turbine internal cooling channel is here presented and discussed focusing on unsteady motion and erosion mechanisms. The rotation axis is placed to properly reproduce a configuration with a very strong deviation (90°).

The flow field was modelled by using the well known k-ε-ζ-f unsteady-RANS model based on the elliptic-relaxation concept. The model was modified by some of the authors to take into account the influence of turbulence anisotropy as well as rotation. The model was applied to the well-established and fully validated T-FlowS code.

A systematic comparison of rotating and non-rotating case was carried out to show the influence of Coriolis force on flow and erosion mechanisms.

The rotational effects strongly changed the flow behaviour within the channel, affecting both the unsteady flow and the particles trajectories. In the rotating case, there is no recirculation on the tip region; besides, position of the small recirculation regions above each pedestals change. These, and other minor effects, affect the particle motion thus resulting in a different erosion pattern.
Experimental and Numerical Analysis of Geometrical Induced Mistuning
Authors: Popig Frederik , Hönisch Peter , Kühhorn Arnold
Published: August 2015

The application of high pressure compressor (HPC) rotors manufactured as blisk (Blade Integrated Disk) is ever-expanding in modern jet engine designs. Despite the major advantages of less mass and higher efficiency, the most challenging problem is lower mechanical damping due to the loss of damping between blades root’s and the disk. Mistuning is induced by material inhomogeneities, manufacturing tolerances or wear during use and leads to amplitude magnification and mode localization. From the experimental point of view mistuning can be evaluated via experimental vibration analysis in terms of frequency deviations. Furthermore optical measurements can be evaluated in terms of geometrical deviations between the real and designed geometry. From the structural point of view a mistuned blisk model can be obtained by morphing the nodes of the geometrical tuned FE model or by performing blade individual stiffness mistuning due to modification of Young’s modulus. The following work is focused on the numerical prediction of mistuned blisk vibrations. Therefore, the research blisk of the 4 stage research compressor, manufactured as job-production, is analyzed. For this research blisk optical measurement data as well as experimentally obtained frequency patterns are available. In a first part mistuning identification in terms of experimental vibration analysis and Proper Orthogonal Decomposition of the geometrical deviations is presented. In a second part mistuning modeling in terms of stiffness mistuning and geometrical mistuning is applied to the tuned FE-model and the numerical results are evaluated against experimental data regarding accuracy. Furthermore, the impact of geometrical deviations on mistuning is analyzed.
Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage
Authors: Lynch Stephen P. , Thole Karen A.
Published: August 2015

Turbine blade components in an engine are typically designed with gaps between parts due to manufacturing, assembly, and operational considerations. Coolant is provided to these gaps to limit the ingestion of hot combustion gases. The interaction of the gaps, their leakage flows, and the complex vortical flow at the endwall of a turbine blade can significantly impact endwall heat transfer coefficients and the effectiveness of the leakage flow in providing localized cooling. In particular, a platform gap through the passage, representing the mating interface between adjacent blades in a wheel, has been shown to have a significant effect. Other important turbine blade features present in the engine environment are non-axisymmetric contouring of the endwall, and an upstream rim seal with a gaspath cavity, which can reduce and increase endwall vortical flow, respectively. To understand the platform gap leakage effect in this environment, measurements of endwall heat transfer and film cooling effectiveness were performed in a scaled blade cascade with a non-axisymmetric contour in the passage. A rim seal with a cavity, representing the overlap interface between a stator and rotor, was included upstream of the blades and a nominal purge flowrate of 0.75% of the mainstream was supplied to the rim seal. Results indicated that endwall heat transfer coefficients increased as platform gap net leakage increased from 0% to 0.6% of the mainstream flowrate, but net heat flux to the endwall was reduced due to high cooling effectiveness of the leakage flow.
Effects of Blade Count Ratio on Aerodynamic Forcing and Mode Excitability
Authors: Li Jing , Kielb Robert E.
Published: August 2015

The effects of blade count ratio (BCR) on both the steady and unsteady blade loading and the sensitivity of generalized force to a change in mode shape (mode excitability) are studied numerically on two 2D configurations: a subsonic research compressor stage and a turbine stage with supersonic exit. Using the Harmonic Balance method, only a single passage is modeled to represent the actual blade count in a row at a high level of computational efficiency. BCR variation is achieved by scaling the downstream airfoils with a fixed chord-to-pitch ratio, thus preserving the steady-state aerodynamics. It is found that the interaction among potential-, wake-, and shock-related excitations, and the relative strength of harmonic contents are dependent on BCR, resulting in a non-monotonic correlation between unsteady loading and BCR in the downstream row. It is also found that the mode excitability can be sensitive to BCR variation in both up- and downstream rows in some cases. To the best of authors’ knowledge, this is the first work on BCR study involving supersonic flow and a discussion of mode excitability patterns.
Aeroelastic Investigation of an Annular Transonic Compressor Cascade: Experimental Results
Authors: Chenaux Virginie Anne , Zanker Achim , Ott Peter
Published: August 2015

A reliable determination of the unsteady aerodynamic loads acting on the blades is essential to predict the aeroelastic stability of vibrating compressor cascades with accuracy. At transonic flow conditions, the vibration of the shock may change the blade aeroelastic behavior. Numerical tools still have difficulties to capture the physics associated to this effect. In order to increase the prediction’s accuracy, high quality experimental data at high spatial resolution is therefore required to enable the calibration and validation of these tools.

Within the frame of the European project FUTURE, experimental aeroelastic investigations were performed on a transonic compressor cascade in the Non-Rotating Annular Test Facility at EPFL. Associated to the measurements, the numerical flutter prediction procedure was applied.

This paper focuses on the experimental results. The experimental database gained during the project is presented and aims at helping the aeroelastic community to develop and improve their flutter prediction capabilities.

The test model consists of twenty prismatic blades. Each blade of the cascade assembly was mounted on an elastic spring element enabling harmonic bending vibrations in the twenty possible cascade’s travelling wave modes. Large efforts were made to improve the measuring techniques and to provide high quality data at relatively high spatial resolution. For various sub- and transonic flow conditions, steady-state and unsteady blade surface pressure distributions were measured to evaluate the local contributions to the blade stability in terms of local aerodynamic work. The blade global aerodynamic stability is determined applying an integration of all unsteady pressure signals measured over the airfoil.
Competing 3D Mechanisms in Compressor Flows
Authors: Taylor James V. , Miller Robert J.
Published: August 2015

Even though three-dimensional design is central to all modern compressor design systems, many of these methods still rely, at the their core on a two-dimensional, sectional, view of blade aerodynamics. This paper argues that this view fundamentally limits design by not correctly considering the way in which pressure gradient transverse to the flow direction affects both separation and loss.

The first part of the paper details how 3D blade stacking and the transverse pressure gradient fundamentally alters the behaviour of the corner separations and trailing edge separations. By controlling this design parameter it is possible to switch between the two. The transverse pressure gradient is also shown to be responsible for a substantial increase in profile loss.

In the second part this understanding is used to explore the uncertainty of the design space by simultaneously varying pitch-chord ratio and 3D stacking. It is shown that the design space is split in half by two different levels of risk.
Improved Methodologies for Time Resolved Heat Transfer Measurements, Demonstrated on an Unshrouded Transonic Turbine Casing
Authors: Collins Matthew , Chana Kam , Povey Thomas
Published: August 2015

The HP rotor tip and over-tip casing are often life-limiting features in the turbine stages of current gas turbine engines. This is due to the high thermal load, and high temperature cycling both at low and high frequency. In the last few years there have been numerous studies of turbine tip heat transfer. Comparatively fewer studies have considered the over-tip casing heat transfer. This is in part, no doubt, due to the more onerous test facility requirements to validate computational simulations. Because the casing potential field is dominated by the passing rotor, to perform representative over-tip measurements a rotating experiment is an essential requirement.

In this paper we describe improved methodologies for time resolved heat transfer measurements. Specifically we show that:

1. Changes in driving temperature (within limits) can be accounted for in both time-resolved and steady heat transfer measurement processing. This allows useful data to be extracted even under varying inlet temperature.

2. Superposition of several runs with different starting wall temperatures can be used to improve the accuracy of time resolved regressions by extending the wall temperature range over which the unsteady regressions are conducted.

3. A new time-resolved data processing technique that can be applied to data sets involving changes in wall temperature has been developed and is applied to experimental measurements to compute time resolved TAW and Nu.

These improvements are demonstrated using unsteady heat transfer measurements conducted on the stationary casing above an unshrouded transonic turbine. The measurements were taken in the Oxford Turbine Research Facility (OTRF), an engine-scale rotating turbine facility which replicates engine-representative conditions of Mach number, Reynolds number, and gas-to-wall temperature ratio. High density arrays of miniature thin-film heat-flux gauges were used with a spatial resolution of 0.8 mm and temporal resolution of ∼120 kHz. The small size of the gauges, the high frequency response, and the improved processing methods allowed very detailed measurements of the heat transfer in this region. Time-resolved measurements of TAW and Nu are presented for the casing region (−30 % to +125% CAX) and compared to other results in the literature. The results provide an almost unique data set for calibrating CFD tools for heat transfer prediction in this highly unsteady environment dominated by the rotor over-tip flow.
A Diagnostic Technique for Particle Characterization Using Laser Light Extinction
Authors: Barboza Kris , Ma Lin , Lowe K. Todd , Ekkad Srinath , Ng Wing
Published: August 2015

Increased operations of aircraft, both commercial and military in hostile desert environments has increased the risk of micro sized particle ingestion into engines. The probability of increased sand and dust ingestion results in increased life cycle costs in addition to increased potential for performance loss. Thus the ability to accurately assess the amount of inlet debris would be useful for engine diagnostics and prognostic evaluation. Previous engine monitoring studies were based on particle measurements performed a posteriori. Thus there exists a need for in situ quantification of ingested particles. This paper describes the initial development of a line-of-sight optical technique to characterize the ingested particles at concentrations similar to those experienced by aircraft in brownout conditions using laser extinction with the end goal of producing an onboard aircraft diagnostic sensor. By measuring the amount of light that is transmitted due to the effects of scattering and absorption in the presence of particles over a range of concentrations, a relationship between particle diameters and the laser light extinction was obtained. This relationship was then used to obtain information on diameters and number densities of ingested particles. The particle size range of interest was chosen to be between 1–10 μm and the size distribution function was assumed to be lognormal. Tests were performed on polystyrene latex spheres of sizes 1.32 μm, 3.9 μm and 5.1 μm in water dispersions to measure diameters and concentrations. Measurements were performed over multiple wavelengths to obtain information on the size distribution and number density of particles. Results of tests presented in this paper establish the validity of the laser extinction technique to provide real time information of ingested particles and will serve as an impetus to carry out further research using this technique to characterize particles.
Experimental Identification of Cutting Force Coefficients for Finish-Milling Operations Considering the Sensor’s Transmissibility
Authors: Rekers S. , Adams O. , Veselovac D. , Klocke F.
Published: August 2015

Due to lightweight construction numerous parts in turbomachinery industry with aerodynamic properties exhibit thin-walled features. Typical examples are compressor blades or turbine blades. Finish-milling depicts a stage of the manufacturing process of these parts with significant value creation. A major limitation of productivity is process stability in terms of self-excited or forced vibration. Different simulation approaches attempt determining a priori the process stability to avoid a bad surface quality, accelerated tool wear, tool breakage or scrapped parts. One distinctive part of these simulations is a cutting force model which incorporates material and tool dependent coefficients. The simulation accuracy directly depends on the exactness of these coefficients. Usually, these coefficients are identified experimentally from cutting force measurements with piezoelectric sensors, whose transmissibility is nonlinear. In this paper a multidimensional stationary inverse filter for compensating the influence of the nonlinear transmissibility of force sensors is presented. In a subsequent step, a Levenberg–Marquardt algorithm is used to identify cutting force coefficients from filtered force measurements. The functionality of the filter is validated by comparing highly nonlinear and almost linear piezoelectric force measurement sensors connected in series during finish-milling experiments. The accuracy of the identified cutting force coefficients is assessed by comparing cutting force simulations to measurements.
Effects of Inlet Air Distortion on Gas Turbine Combustion Chamber Exit Temperature Profiles
Authors: Maqsood O. , LaViolette M. , Woodason R.
Published: August 2015

Localized damage to turbine inlet nozzles is typically caused by non-uniform temperature distributions at the combustion chamber exit. This damage results in decreased turbine performance and can lead to expensive repair or replacement. A test rig was designed and constructed for the Rolls-Royce Allison 250-C20B dual-entry combustion chamber to investigate the effects of inlet air distortion on the combustion chamber’s exit temperature fields. The rig includes a purposely built water cooled thermocouple rake to sweep the exit plane of the combustion chamber. Test rig operating conditions simulated normal engine cruise conditions by matching the quasi-non-dimensional Mach number, equivalence ratio and Sauter mean diameter. The combustion chamber was tested with an even distribution of inlet air and a 4% difference in airflow at either combustion chamber inlet.

An even distribution of inlet air to the combustion chamber did not produce a uniform temperature profile and varying the inlet distribution of air exacerbated the profile’s non-uniformity. The design of the combustion chamber promoted the formation of an oval-shaped toroidal vortex inside the combustion liner, causing localized hot and cool sections separated by 90° that were apparent in the exhaust. Uneven inlet air distributions skewed the oval vortex, increasing the temperature of the hot section nearest the side with the most airflow and decreasing the temperature of the hot section on the opposite side.
Design and Assessment of a Fuel-Flexible Low Emission Combustor for Dry and Steam-Diluted Conditions
Authors: Kuhn Phoebe , Terhaar Steffen , Reichel Thoralf , Paschereit Christian Oliver
Published: August 2015

In the present study a new combustor design for swirl-stabilized premixed combustion is presented and analyzed. By means of axial air injection into the mixing tube, the flow field inside the mixing tube and combustion chamber is altered for the purpose of increasing flame stability, resulting in low lean blow-out limits and flashback safety. For this reason, the combustor design is suited for fuel-flexible combustion over a wide range of reactivities including those of pure hydrogen and natural gas. Furthermore, the combustor design is suitable for high amounts of steam injection, significantly decreasing NOx emissions. The assessment of the flow field properties is conducted under isothermal and reacting conditions and the results are in good agreement. The fuel-air-mixing quality is examined by water tunnel experiments using laser induced fluorescence and show low levels of unmixedness. Flame properties are assessed by means of OH planar laser induced fluorescence and OH*-chemiluminescence. Emission probing of major combustion species was also conducted.
Comparison Between Linear and Non-Linear Fracture Mechanics Analysis of Experimental Data for the Ductile Superalloy Haynes 230
Authors: Ewest Daniel , Almroth Per , Sjödin Björn , Leidermark Daniel , Simonsson Kjell
Published: August 2015

With increasing use of renewable energy sources, an industrial gas turbine is often a competitive solution to balance the power grid. However, life robustness approaches for gas turbine components operating under increasingly cyclic conditions, is a challenging task. Ductile superalloys, as Haynes 230, are often used in stationary gas turbine hot parts such as combustors. The main load for such components is due to non-homogeneous thermal expansion within or between parts. As the material is ductile there is considerable redistribution of stresses and strains due to inelastic deformations during the crack initiation phase. Therefore, the subsequent crack growth occurs through a material with significant residual stresses and strains. In this work, fatigue crack propagation experiments, including the initiation phase, have been performed on a single edge notched specimen under strain controlled conditions. The test results are compared to fracture mechanics analyses using the linear ΔK and the nonlinear ΔJ approaches, and an attempt to quantify the difference in terms of a life prediction is made. For the tested notched geometry, material and strain ranges, the difference in the results using ΔKeff or ΔJeff are larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The ΔJ approach clearly shows better agreement with the experimental results in this regime.
Quantification of Combined Operational and Geometrical Uncertainties in Turbo-Machinery Design
Authors: Wunsch Dirk , Hirsch Charles , Nigro Rémy , Coussement Gregory
Published: August 2015

The NASA rotor 37 is investigated accounting for as many as 9 simultaneous operational and geometrical uncertainties. The combined influence of uncertainties on input quantities such as the total inlet pressure, static outlet pressure, tip gap or leading and trailing edge angles on output quantities is studied. These simulations provide results which go far beyond the standard deterministic simulation. A probabilistic collocation method in combination with a sparse grid quadrature is introduced into the software suite FINE™ propagating combined operational and geometrical uncertainties in complex 3D CFD simulations. The modification of the parameterized geometry and the consequent re-meshing is provided by a fully automatic tool, which also couples with the flow solver and provides post-treatment routines. It is this automation, which makes this kind of study feasible. A manual modification of geometry, manual meshing and simulation set-up accounting for a multitude of simultaneous uncertainties is simply unfeasible for as many as hundreds of complex 3D turbo-machinery simulations. This work represents thus a break-through in the uncertainty management towards the application of uncertainty propagation in the daily engineering practice.
Utility Scale Wind Turbine Yaw From a Flow Visualization View
Authors: Vey Stefan , Lang Henning M. , Nayeri Christian N. , Paschereit Christian O. , Pechlivanoglou Georgios , Weinzierl Guido
Published: August 2015

Results from a quantitative tuft flow visualization of a utility scale wind turbine undergoing a yaw movement are presented. Based on the turbine’s SCADA data suitable pre- and post-yaw timeframes were defined and the surface flowfields were analysed. A distinct asymmetry between the surface flow patterns of the 90° and 270° azimutal blade positions was observed in the pre-yaw timeframe. After the turbine yawed back into the wind the symmetry was restored. Yaw-misalignment is a source of dynamic loads which limit a turbine’s life time. The characterization of the involved flow structures and their dynamics is an essential step towards possible future load alleviation techniques. The quantitative tuft flow visualization technique is a measurement tool that can be used to assess the surface flow field.
Aerodynamic Quenching and Burning Velocity of Turbulent Premixed Methane-Air Flames
Authors: Nivarti Girish V. , Cant R. Stewart
Published: August 2015

Industry-relevant turbulent premixed combustion models continue to rely on empirical expressions for turbulent flame speed in closure modelling for the mean turbulent reaction rate. To date, an accurate sub-model for turbulent flame speed has not been proposed for flows with high turbulence intensities. Experimental studies in the pertinent combustion regime, known as the Thin Reaction Zones (TRZ) regime, are limited by the existing techniques of turbulence generation whereas, until recently, the high computational expense involved in solving such problems has restricted theoretical studies.

We investigate the behaviour of premixed flames in the TRZ regime by conducting a parametric 3D Direct Numerical Simulation (DNS) study of stoichiometric methane-air mixtures using single-step chemistry in an inflow-outflow configuration. Inflow turbulence intensity is varied while keeping the integral length scale constant across six separate simulations which span altogether a significant portion of the TRZ regime. The resulting variation of turbulent flame speed with turbulence intensity demonstrates the well-known bending phenomenon and conforms with recent experimental observations of freely-propagating premixed flames in this regime.

As turbulence intensity is increased, the calculated flame surface exhibits an increasing degree of wrinkling and pocket-formation. In addition, the internal thermo-chemical structure of the flame is greatly affected when the turbulence intensity is more than an order of magnitude higher than the laminar flame speed. These qualitative observations establish the present DNS framework as a powerful tool for capturing turbulence-chemistry interactions that influence the bending phenomenon. Hence, this work forms the basis for further analysis using a detailed chemical description to investigate these interactions and, thereby, improve combustion models of industrial relevance.
Study of a Highly Loaded Centrifugal Compressor With Pipe Diffuser at Design and Off-Design Operating Conditions
Authors: Han Ge , Lu Xingen , Zhang Yanfeng , Zhao Shengfeng , Zhu Junqiang
Published: August 2015

This present work is aimed at providing detailed understanding of the flow mechanisms in a highly loaded centrifugal compressor with different diffusers. Performance comparison between compressor stages with pipe diffuser and its original wedge diffuser was conducted by a validated state-of-the-art multi-block flow solver at different rotating speeds. Stage with pipe diffuser achieved a better performance above 80% rotating speed but a worse performance at lower rotating speeds near surge, than that of stage with wedge diffuser. Four operating points including the design point were analyzed in detail. The inherent diffuser leading edge of pipe diffuser could alleviate the flow distortion upstream diffuser throat and created a better operating condition for the downstream diffusion, which reduced the possibility of flow separation in discrete passages at design rotating speed. At 60% rotating speed operating point, there was a misalignment between the leading edge absolute flow angle and the metal angle of diffuser, resulted in an acceleration near diffuser leading edge due to the large negative incidence angle. The sharp leading edge of pipe diffuser could largely accommodate this negative incidence as comparison of the round leading edge of wedge diffuser. As a result, the flow separation was depressed and a better performance was achieved in the pipe diffuser. At 60% rotating speed near surge, performance of the pipe diffuser dropped below wedge diffuser. Total pressure loss of pipe diffuser exceeded that of the wedge diffuser due to the larger friction loss near wall at throat and cone, meanwhile ineffective static pressure recovery for pipe diffuser was triggered by the strong boundary layer blockage in the front of pipe diffuser cone.
Experimental Modal Identification of Mistuning in an Academic Blisk and Comparison With the Blades Geometry Variations
Authors: Nyssen Florence , Arnst Maarten , Golinval Jean-Claude
Published: August 2015

In the field of turbomachinery, the assumption of cyclic symmetry of rotor stages is usually made to lower the required computational resources. However, in reality, small random blade-to-blade variations, known as mistuning, appear due to manufacturing tolerances, etc. and disturb the dynamic behavior of bladed disks. In this work, an experimental modal analysis is performed on a mono-stage and monobloc academic bladed structure. The frequency response function (FRF) is measured using a base excitation with an electrodynamic shaker and one measurement point per blade. The mistuning of the structure is identified. Then, an optical geometry measurement system is used to obtain the exact geometry of each blade. Based on these optical data, a finite element model of the structure is constructed and the FRF of this model is compared to the experimental FRF. The accurate measurement of the geometry allows to compare the level of geometry mistuning of the academic structure with the identified frequency mistuning.
Orbit-Model Force Coefficients for Fluid Film Bearings: A Step Beyond Linearization
Authors: San Andrés Luis , Jeung Sung-Hwa
Published: August 2015

High performance turbomachinery demands high shaft speeds, increased rotor flexibility, tighter clearances in the flow passages, advanced materials, and increased tolerance to imbalances. Operation at high speeds induces severe dynamic loading with large amplitude shaft motions at the bearing supports. Typical rotordynamic models rely on linearized force coefficients (stiffness K, damping C, and inertia M) to model the reaction forces from fluid film bearings and seal elements. These true linear force coefficients are derived from infinitesimally small amplitude motions about an equilibrium position. Often, however, a rotor-bearing system does not reach an equilibrium position and displaces with motions amounting to a sizable portion of the film clearance; the most notable example being a squeeze film damper (SFD). Clearly, linearized force coefficients cannot be used in situations exceeding its basic formulation. Conversely, the current speed of computing permits to evaluate fluid film element reaction forces in real time for ready numerical integration of the transient response of complex rotor-bearing systems. This approach albeit fast does not help to gauge the importance of individual effects on system response. Presently, an orbit analysis method estimates force coefficients from numerical simulations of specified journal motions and predicted fluid film reaction forces. For identical operating conditions in static eccentricity and whirl amplitude and frequency as those in measurements, the computational physics model calculates instantaneous damper reaction forces during one full period of motion and performs a Fourier analysis to characterize the fundamental components of the dynamic forces. The procedure is repeated over a range of frequencies to accumulate sets of forces and displacements building mechanical transfer functions from which force coefficients are identified. These coefficients thus represent best fits to the motion over a frequency range and dissipate the same mechanical energy as the nonlinear mechanical element. More accurate than the true linearized coefficients, force coefficients from the orbit analysis correlate best with SFD test data, in particular for large amplitude motions, statically off-centered. The comparisons also reveal the fallacy in representing nonlinear systems as simple K-C-M models impervious to the kinematics of motion.