bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Leading Edge Tubercles in an Annular Compressor Cascade With Different Hub-Tip Ratios and Aspect Ratios
Authors: Zheng Tan , Zhu Mingmin , Qiang Xiaoqing , Teng Jinfang , Feng Jinzhang
Published: August 2017

Humpback whale flippers’ scalloped tubercles on the leading edge are thought to enhance the whale’s underwater maneuverability. Inspired by the flippers, leading edge tubercles are applied in a low speed annular compressor cascade as a type of passive flow control techniques in this paper. A numerical study is performed to investigate the influence of tubercles on the aerodynamic losses and corner separation in the low speed cascades.

Different low speed cascades based on a CDA airfoil profile are built with several hub-tip ratios and aspect ratios. Steady RANS simulations are carried out for these cascades with and without leading edge tubercles. The aerodynamic performance and corner separation features are subsequently investigated in these cascades. The influence of tubercles under the variation of hub-tip ratio and aspect ratio is understood and concluded from the comparison of the performance attained by different cascades. Flow visualizations at a post-stall incidence angle show that the interaction between the tubercle-induced streamwise vortices and corner separation vortices plays a crucial role in attenuating the corner separation and reducing losses. By combining the performance analysis and flow visualizations, this paper discusses the mechanism of leading edge tubercles in a low speed annular compressor cascade with different hub-tip ratios and aspect ratios.
A Hybrid Free Wake Simulation Comparison of Turbine Wake Steering With Innovative Turbine Designs
Authors: Su Keye , Bliss Donald B.
Published: August 2017

Wake shielding in wind farms caused by the interaction of upstream energy-depleted wakes and down-stream turbines substantially reduces individual turbine efficiency and overall wind farm performance. A method is studied to alleviate this problem using shaft tilting to steer wakes upward and reduce the interaction with downstream turbines. Simulations have been conducted to verify this method and to assess its effectiveness. These simulations employ a specially developed hybrid free wake method that combines a Constant Circulation Contour Model, suitable for downwind far-wake evolution, with a Vortex Lattice Method, leading to accurate blade air-loads calculation, including unsteady effects, stall, and reduced complexity. The interaction of two inline tipped axis turbines has been analyzed to assess the advantages and challenges of wake steering in a system of turbines. Beyond the traditional HAWT, two unconventional turbine configurations have been studied with the intent to further increase wake ascent.
Arriving at the Optimum Overlap Ratio for an Elliptical-Bladed Savonius Rotor
Authors: Alom Nur , Saha Ujjwal K.
Published: August 2017

The Savonius rotor appears to be particularly promising for the small-scale applications because of its design simplicity, good starting ability, and insensitivity to wind directions. There has been a growing interest in recent times to harness wind energy in an efficient manner by developing newer blade profiles of Savonius rotor. The overlap ratio (OR), one of the important geometric parameters, plays a crucial role in the turbine performance. In a recent study, an elliptical blade profile with a sectional cut angle (θ) of 47.5° has demonstrated its superior performance when set at an OR = 0.20. However, this value of OR is ideal for a semicircular profile, and therefore, requires further investigation to arrive at the optimum overlap ratio for the elliptical profile. In view of this, the present study attempts to make a systemic numerical study to arrive at the optimum OR of the elliptical profile having sectional cut angle, θ = 47.5°. The 2D unsteady simulation is carried out around the elliptical profile considering various overlap ratios in the range of 0.0 to 0.30. The continuity, unsteady Reynolds Averaged Navier-Stokes (URANS) equations and two equation eddy viscosity SST (Shear Stress transport) k-ω model are solved by using the commercial finite volume method (FVM) based solver ANSYS Fluent. The torque and power coefficients are calculated as a function of tip speed ratio (TSR) and at rotating conditions. The total pressure, velocity magnitude and turbulence intensity contours are obtained and analyzed to arrive at the intended objective. The numerical simulation demonstrates an improved performance of the elliptical profile at an OR = 0.15.
DDES Analysis of Wake Vortex Related Unsteadiness and Losses in the Environment of High-Pressure Turbine Stage
Authors: Lin Dun , Su Xinrong , Yuan Xin
Published: August 2017

In this work, the flows inside the high pressure turbine (HPT) vane and stage are studied with the help of a high-fidelity delayed detached eddy simulation (DDES) code. This work intends to study the fundamental nozzle/blade interaction with special attention paid to the development and transportation of the vane wake vortex. There are two motivations for this work. On the one hand, the high pressure turbine operates at both transonic Mach numbers and high Reynolds numbers, which imposes a great challenge to modern computational fluid dynamics (CFD), especially for scale-resolved simulation methods. An accurate and efficient high-fidelity CFD solver is very important for a thorough understanding of the flow physics and the design of more efficient HPT. On the other hand, the periodic wake vortex shedding is an important origin of turbine losses and unsteadiness. The wake and vortex not only cause losses themselves, but also interact with the shock wave (under transonic working condition), pressure waves, and have a strong impact on the downstream blade surface (affecting boundary layer transition and heat transfer). Built on one of our previous DDES simulations of a HPT vane VKI LS89, this work further investigates the development and length characteristics of the wake vortex, provides explanations of the length characteristics and reveals the transportation of the wake vortex into the downstream rotor passage along with its impact on the downstream aero-thermal performance.
Renewable Energy Systems Integration for Efficiency Improvement of a CHP Unit
Authors: Ancona M. A. , Branchini L. , De Pascale A. , Melino F. , Di Pietra B.
Published: August 2017

In the next years energy grids are expected to become increasingly complex, due to the integration between traditional generators (operating with fossil fuels, especially natural gas), renewable energy production systems and storage devices. Furthermore, the increase of installed distributed generation systems is posing new issues for the existing grids. The integration involves both electric grids and thermal networks, such as district heating networks. In this scenario, it is fundamental to optimize the production mix and the operation of each system, in order to maximize the renewable energies exploitation, minimize the economic costs (in particular the fossil fuel consumption) and the environmental impact.

The aim of this paper is the analysis of different solutions in terms of energy generation mix, in order to define the optimal configuration for a given network.

With this purpose, in this study a real district heating network served by a combined heat and power unit and four boilers has been considered. The current mode of operation of the selected network has been simulated, in order to individuate eventual criticism and/or improvement possibility. On the basis of the obtained results, several scenarios have been developed by considering the addition of thermal or electric energy production systems from renewable energy sources and/or heat pumps.

For a given scenario, a whole year of operation has been simulated with an in-house developed software, called EGO (Energy Grid Optimizer), based on genetic algorithms and able to define the load distribution of a number of energy systems operating into an energy grid, with the aim to minimize the total cost of the energy production. Further considered constraints have been the avoiding of thermal dissipations and the minimization of the electric energy sale to the national grid (in order to increase the grid stability).

The carried out analysis has allowed to evaluate the yearly fuel consumption, the yearly electric energy sold to the network and the yearly electric energy purchased from the network, for each of the developed configurations. In this study the obtained results have been discussed in order to compare the proposed scenarios and to define an optimal solution, which enables to reduce the yearly operation costs of the production plant.
Development and Validation of a Compressible Large-Eddy Simulation Code With Overset Mesh Method
Authors: Tateishi Atsushi , Watanabe Toshinori , Himeno Takehiro
Published: August 2017

This paper describes basic ideas for the design of a new computational fluid dynamics (CFD) code for large-eddy simulation (LES), as well as presenting fundamental validation and demonstration cases. The developed code combines highorder structured solver with overset mesh technique, which enables to control mesh density easily with keeping high mesh quality. The validations were conducted over two different flow regimes. The mesh size criteria for the present code were identified from the systematic mesh study of wall-bounded channel flow. In addition, the wake profile after the circular cylinder as a validation of free shear flow showed good agreement with the reference data. Then the validated code was applied to the flow field of highly loaded stator vane. The developed solver reproduced the position of separation bubble accurately however, the velocity profiles on the vane needed improvement by introducing free stream turbulence. From the sequence of validation and application studies, it was concluded that the present code can be used for the researches of fundamental turbulent flow field in turbomachinery.
Experimental Investigation of Rotating Rib Roughened Two-Pass Square Duct With Two Different Channel Orientations
Authors: Singh Prashant , Ekkad Srinath V.
Published: August 2017

Effects of rotation on heat transfer on leading and trailing sides of gas turbine blades has been extensively studied in the past. It has been established for typical two-pass channel that radially outward flow (first pass) has higher heat transfer on trailing side and lower heat transfer on leading side and vice versa for radially inward flow (second pass). Rotation induces three forces on the coolant flow — Coriolis, Centrifugal and Buoyancy forces. The direction of Coriolis force depends on the relative angle between the coolant flow and the rotation direction, because of which the direction of Coriolis force is different in individual passes — which in turn results in non-uniform distribution of high heat transfer regions on leading and trailing walls. The present study is focused on utilizing the Coriolis force favorably in both the passes by rotating the typical arrangement of two-pass channels by 90°. Firstly, smooth two pass duct (Model A-smooth) having typical arrangement of coolant flow and rotation direction is studied. The second configuration is the corresponding ribbed channel (Model A-ribbed) featuring V-shaped ribs on both leading and trailing walls. The rib-height-to-channel hydraulic diameter ratio was 0.125, rib pitch-to-rib height ratio was 8, and channel aspect ratio was unity. Model B was obtained by rotating the Model A by 90° and changing the coolant inlet port as well. Model B had three configurations — (a) smooth duct, (b) single sided ribbed duct, and (c) double sided ribbed duct. Detailed heat transfer coefficients were measured by transient liquid crystal thermography under rotating conditions. In order to match the direction of Buoyancy force as it exists in actual engines, colder air was passed during the transient experiment. The heat transfer experiments were carried out at a Reynolds number of 20000 and Rotation numbers of 0, 0.05 and 0.1. The Nusselt numbers have been reported in two forms, (a) normalized with respect to Dittus-Boelter correlation for developed turbulent flow in circular duct, (b) normalized with corresponding Nusselt number obtained from smooth channel experiments. The effects of Coriolis force and centrifugal force on heat transfer has been discussed in detail. A new model has been proposed based on the understanding and findings of the present study, which has positive effects of rotation on both leading and trailing walls.
Aerodynamic Performance of an Unlocated High Pressure Turbine Rotor With Worn Tip Seal Fins
Authors: Pawsey Lucas , Rajendran David John , Pachidis Vassilios
Published: August 2017

An unlocated shaft failure in the high pressure turbine spool of an engine may result in a complex orbiting motion along with rearward axial displacement of the high pressure turbine rotor sub-assembly. This is due to the action of resultant forces and limitations imposed by constraints such as the bearings and turbine casing. Such motion of the rotor following an unlocated shaft failure, results in the development of multiple contacts between the components of the rotor sub-assembly, the turbine casing, and the downstream stator casing. Typically, in the case of shrouded rotor blades, the tip region is in the form of a seal with radial protrusions called ‘fins’ between the rotor blade and the turbine casing. The contact between the rotor blade and the turbine casing will therefore result in excessive wear of the tip seal fins, resulting in changes in the geometry of the tip seal domain that affects the characteristics of the tip leakage vortex. The rotor sub-assembly with worn seals may also be axially displaced rearwards, and consequent to this displacement, changes in the geometry of the rotor blade may occur because of the contact between the rotor sub-assembly and the downstream stator casing.

An integrated approach of structural analyses, secondary air system dynamics, and 3D CFD is adopted in the present study to quantify the effect of the tip seal damage and axial displacement on the aerodynamic performance of the turbine stage. The resultant geometry after wearing down of the fins in the tip seal, and rearward axial displacement of the rotor sub-assembly is obtained from LS-DYNA simulations. 3D RANS analyses are carried out to quantify the aerodynamic performance of the turbine with worn fins in the tip seal at three different axial displacement locations i.e. 0 mm, 10 mm and 15 mm. The turbine performance parameters are then compared with equivalent cases in which the fins in the tip seal are intact for the same turbine axial displacement locations.

From this study it is noted that the wearing of tip seal fins results in reduced turbine torque, power output and efficiency, consequent to changes in the flow behaviour in the turbine passages. The reduction in turbine torque will result in the reduction of the terminal speed of the rotor during an unlocated shaft failure. Therefore, a design modification that can lead to rapid wearing of the fins in the tip seal after an unlocated shaft failure holds promise for the management of a potential over-speed event.
A Combined Experimental and Numerical Investigation of the Flow and Heat Transfer Inside a Turbine Vane Cooled by Jet Impingement
Authors: Laroche Emmanuel , Fenot Matthieu , Dorignac Eva , Vuillerme Jean-Jacques , Brizzi Laurent Emmanuel , Larroya Juan Carlos
Published: August 2017

The present study aims at characterizing the flow field and heat transfer for a schematic but realistic vane cooling scheme. Experimentally, both velocity and heat transfer measurements are conducted to provide a detailed database of the investigated configuration. From a numerical point of view, the configuration is investigated using isotropic as well as anisotropic Reynolds-Averaged Navier-Stokes (RANS) turbulence models. An hybrid RANS/LES technique is also considered to evaluate potential unsteady effects. Both experimental and numerical results show a very complex 3D flow. Air is not evenly distributed between the different injections, mainly because of a large recirculation flow. Due to the strong flow deviation at the hole inlet, the velocity distribution and the turbulence characteristics at the hole exit are far from fully developed profiles.

The comparison between PIV measurements and numerical results shows a reasonable agreement. However, coming to heat transfer, all RANS models exhibit a major overestimation compared to IR thermography measurements. The Billard-Laurence model does not bring any improvement compared to a classical k-ω SST model. The hybrid RANS/LES simulation provides the best heat transfer estimation, exhibiting potential unsteady effects ignored by RANS models. Those conclusions are different from the ones usually obtained for a single fully developed impinging jet.
Fault Diagnosis of Gas Turbine Based on Complex Networks Theory
Authors: Cao Yunpeng , Yan Dongyang , Yang Qingcai , Li Shuying , Wu Minghao , Chen Lie
Published: August 2017

A vast amount of operating data, control data and log data are generated in the monitoring process of a gas turbine. This massive amount of data includes not only spatial distance features, but also related features. Currently, the analysis of data-related features based on data-driven diagnosis methods is challenging. In response to this limitation, a gas turbine fault diagnosis method based on network community detection is proposed in this paper. First, a gas turbine topology network model is established based on complex network theory. In the network model, gas turbine sampled-data are defined as the nodes; the similarity degree between the sampled-data is defined as the edge of the network; and the reciprocal function is selected as the similarity criterion function. Second, to reflect the community characteristics of the network, the topology network is converted to a training network by a threshold criterion that is designed based on the variation of the average path length and the average clustering coefficient. This method can establish a training network without prior knowledge of the number of clusters. Third, a fault detection algorithm is proposed based on community modularity, and fault reasoning is presented by calculating the probability based on the change in the community modularity which demonstrates the occurrence possibility of multiple faults. The effectiveness of the algorithm is verified by a three-shaft gas turbine fault simulation data-set. The results indicate that the proposed algorithm can be used to identify known faults, unknown faults and the graphical representation of a network can reflect the spatial distance and relationship among sampled-data.
A General Ply Design for Aero Engine Composite Fan Blade
Authors: Xiao Jiaguangyi , Chen Yong , Zhu Qichen , Lee Jun , Ma Tingting
Published: August 2017

Composite fan blade ply lay-up design, which includes ply drop-off/shuffle design and stacking sequence design, makes fan blade structures different from traditional composite structures. It gives designers more freedom to construct high-quality fan blades. However, contemporary fan blade profiles are quite complex and twisted, and fan blade structures are quite different from regular composite structures such as composite laminates and composite wings. The ply drop-off design of a fan blade, especially for a fully 3D fan blade, is still an arduous task. To meet this challenge, this paper develops a ply lay-up way with the help of a software called Fibersim. The fully 3D fan blade is cut into ply pieces in Fibersim. As a result, an initial ply sequence is created and ply shuffle could revise it. Because of the complexity of ply shuffling, the ply shuffle table developed in this paper mainly refers to the design experience gained from simple plate-like laminate structures and some criterion. Besides, the impact of different ply orientation patterns on the reliability of composite fan blade is studied through static and modal numerical analysis. The results show that this ply lay-up idea is feasible for aero engine composite fan blade. Under the calculated rotating speeds, the ply stacking sequence 4 (i.e.[−45°/0°/+45°/0°] with the outer seven groups are [−45°/0°/−45°/0°]) shows the greatest margin of safety compared with other stacking sequences. Modal analysis shows that plies with different angles could have relatively big different impacts on blades vibration characteristics. The composite fan blade ply design route this paper presents has gain its initial success and the results in this paper might be used as basic references for composite blade initial structural design.
Measurements of the Effect of Boundary Conditions on Upstream and Downstream Noise Arising From Entropy Spots
Authors: De Domenico Francesca , Rolland Erwan O. , Hochgreb Simone
Published: August 2017

Pressure fluctuations in combustors arise either directly from the heat release rate perturbations of the flame (direct noise), or indirectly from the acceleration of entropy, vorticity or compositional perturbations through nozzles or turbine guide vanes (indirect noise). In this work, the generation of synthetic entropy spots via the Joule effect produces direct noise, and their acceleration through orifice plates and nozzles produces indirect noise. These acoustic waves reverberate, reflecting several times at the boundaries to add up to the measured pressure. Single travelling pulses are isolated by the introduction of a semiinfinite tube that acts as an anechoic termination for a limited time-window. It is shown how the shape of the converging nozzle does not affect the reflection of the direct noise wave, confirming the hypothesis of a compact nozzle. Further, it is demonstrated that the assumption of an isentropic nozzle does not hold, but that an alternative theory which takes into account the partial acoustic energy dissipation offers good agreement with the experiments. Finally, it is shown that the reflected indirect noise is underpredicted by isentropic theories. An extension of the present work is indicated for the measurement of the transmissivity of indirect noise.
GT36 Turbine Aero-Thermal Development and Validation
Authors: Naik S. , Krueckels J. , Henze M. , Hofmann W. , Schnieder M.
Published: August 2017

This paper describes the aero-thermal development and validation of the GT36 heavy duty gas turbine. The turbine which has evolved from the existing and proven GT26 design, consists of an optimised annulus flow path, higher lift aerofoil profiles, optimised aerodynamic matching between the turbine stages and new and improved cooling systems of the turbine vanes and blades. A major design feature of the turbine has been to control and reduce the aerodynamic losses, associated with the aerofoil profiles, trailing edges, blade tips, endwalls and coolant ejection. The advantages of these design changes to the overall gas turbine efficiency have been verified via extensive experimental testing in high-speed cascade test rigs and via the utilisation of high fidelity multi-row computational fluid dynamics design systems.

The thermal design and cooling systems of the turbine vanes, blades have also been improved and optimised. For the first stage vane and blade aerofoils and platforms, multi-row film cooling with new and optimised diffuser cooling holes have been implemented and validated in high speed linear cascades. Additionally, the internal cooling design features of all the blades and vanes were also improved and optimised, which allowed for more homogenous metal temperatures distributions on the aerofoils. The verification and validation of the internal thermal designs of all the turbine components has been confirmed via extensive testing in dedicated Perspex models, where measurements were conducted for local pressure losses, overall flow distributions and local heat transfer coefficients.

The turbine is currently being tested and undergoing validation in the GT36 Test Power Plant in Birr, Switzerland. The gas turbine is heavily instrumented with a wide range of validation instrumentation including thermocouples, pressure sensors, strain gauges and five-hole probes. In addition to performance mapping and operational validation, a dedicated thermal paint validation test will also be performed.
HEEDS Optimized HyChem Mechanisms
Authors: Goldin Graham , Ren Zhuyin , Gao Yang , Lu Tianfeng , Wang Hai , Xu Rui
Published: August 2017

Transportation fuels consist of a large number of hydrocarbon components and combust through an even larger number of intermediates. Detailed chemical kinetic models of these fuels typically consist of hundreds of species, and are computationally expensive to include directly in 3D CFD simulations. HyChem (Hybrid Chemistry) is a recently proposed modeling approach for high-temperature fuel oxidation based on the assumptions that fuel pyrolysis is fast compared to the subsequent oxidation of the small fragments, and that, although their proportions may differ, all fuels pyrolyse to similar sets of these fragment species. Fuel pyrolysis is hence modeled with a small set of lumped reactions, and oxidation is described by a compact C0-4 foundation chemistry core. The stoichiometric coefficients of the global pyrolysis reactions are determined to match experimental or detailed mechanism computational data, such as shock-tube pyrolysis products, ignition delays and laminar flame speeds. The model is then validated against key combustion properties, including ignition delays, laminar flame speeds and extinction strain rates. The resulting HyChem model is relatively small and computationally tractable for 3D CFD simulations in complex geometries. This paper applies the HEEDS optimization tool to find optimal pyrolysis reaction stoichiometric coefficients for high-temperature combustion of two fuels, namely Jet-A and n-heptane, using a 47 species mechanism. It was found that optimizing on experimental ignition delay and laminar flame speed targets yield better agreement for ignition delay times and flame speeds than optimizing on pyrolysis yield targets alone. For Jet-A, good agreement for ignition delays and flame speeds were obtained by using both ignition delay and flame speeds as targets. For n-heptane, a trade-off between ignition delay and flame speed was found, where increased target weights for ignition delay resulted in worse flame speed predictions, and visa-versa.
A Processing Method for Combined Fatigue Accelerated Test Data
Authors: Zheng Songwang , Chen Cao , Han Lei , Zhang Xiaoyong , Yan Xiaojun
Published: August 2017

To carry out combined low and high cycle fatigue (CCF) test on turbine blades in a bench environment, it is imperative to simulate the vibration loads of turbine blades in the field. Due to the low vibration stress of turbine blades in the working state, the test time will be very long if the test vibration stress is equal to the real vibration stress in working state. Therefore, an accelerated test will be used when the test life reach the target value (typically 107). During the accelerated test, each blade is tested at two or more times than the real vibration stress. That means some specimens are tested under two vibration stress levels. In this case, a reasonable data processing method becomes very important. For this reason, a data processing method for the CCF accelerated test is proposed in this paper. These test data are iterated on the basis of S-N curve. Finally, ten real turbine blades are tested in a bench environment, one of them is tested under two vibration stress levels. The test data is processed using the method proposed above to obtain the unaccelerated life data.
An Experiment-Based Sticking Model for Heated Sand
Authors: Barker Brett , Hsu Kwen , Varney Bruce , Boulanger Andrew , Hutchinson John , Ng Wing F.
Published: August 2017

A hot sand model has been developed to predict the rebounding and sticking behavior of environmental particulates in the hot section of a gas turbine. This paper will focus on the sticking part of the model with rebounding effects to be discussed in a future paper.

The key element of the model is determining the probability of the particle sticking to the surface when it comes into contact. Recent studies have suggested this sticking probability is a function of temperature, particle size, normal and tangential velocities of the impacting particle. Previous studies have predicted the sticking probability using theories for mechanical properties of the particles. These methods rely on idealized particle shapes and compositions which does not match the variable nature of sand in the environment. The current model attempts to take this randomness into account and ensure prediction accuracy by matching the model to results of a series of controlled coupon tests. The framework for the modeling approach and validation results of the developed predictive model are both presented.
The Effects of Third Substances at the Particle/Surface Interface in Compressor Fouling
Authors: Aldi Nicola , Casari Nicola , Dainese Devid , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio
Published: August 2017

Since the beginning of the 1950s, manufacturers and operators have struggled to understand, reduce and eliminate compressor fouling and its effects on gas turbine operation. Several devices (inertial separators, barriers, filters, etc.) and strategies (on-line and off-line washing, manual cleaning, etc.) have been adopted in order to limit and/or eliminate the foulants which stick to the compressor blade and vane surfaces.

The state of the power plant design and installation and environmental conditions determine the rate of fouling and, in turn, gas turbine performance losses. The types of contaminant (organic or inorganic), their concentration and their ability to stick are variable depending on the weather conditions. Desert, tropical, rural, and off-shore conditions are characterized by different foulants with different characteristics which determine compressor fouling.

In this paper, an analysis of the influence of third substances at the particle/surface interface is presented. The analysis is carried out on two different compressor rotors, transonic and subsonic. Firstly, a sensitivity analysis is proposed related to the particle diameter and foulant mixture in order to highlight the influence of air humidity due to environmental conditions or the pressure drop after the filtration stages. The effects of a water electrolytic solution (generated by the presence of inorganic matter) and a water surfactant solution (used in the case of washing) are also considered. In this case, the properties of the mixture substance (solid particles bound by a liquid film) are considered. Secondly, using previous numerical analyses (particle-laden flow with a Eulerian-Lagrangian approach) as a starting point, the variation in particle sticking ability is evaluated against the presence of third substances (water solutions and oily substances) and the particle kinematic characteristics using a sticking model based on an energy balance equation.

The results show the influence of the third substance on particle sticking capability using a susceptibility-to-fouling criterion. Particularly in the presence of humid conditions, sticking capability increases with respect to dry conditions, even though the major effects are due to the mixture viscosity and not only to the presence of liquid water. The sticking capability of the mixture varies according to particle diameter as a function of the particle normal velocity. The results are presented in order to easily quantify the effects of the presence of a third substance at the particle/surface interface according to the type of liquid phase involved in the sticking process.
A New Modified Contrast Method for Life Prediction in Combined Cycle Fatigue Test
Authors: Han Lei , Chen Cao , Zhang Xiaoyong , Yan Xiaojun
Published: August 2017

The combined high and low cycle fatigue (CCF) test on full scale turbine blade in the laboratory is an important method to evaluate the life. In fact, the low cycle fatigue which is usually caused by the centrifugal force can be confirmed easily. While, the high cycle fatigue which is usually caused by the vibration and aerodynamic force is often hard to determine. So the previous scholar has proposed the contrast method to determine the high cycle load in the field. This method utilizes the new and used blades to determine the high cycle within certain limits. While it can’t be applied effectively in the whole life range with the low cycle-high cycle-ultra high cycle fatigue theory raised. So this paper put forward the modified contrast method to realize the optimization. Firstly, the CCF tests are carried out on the turbine blade systematically. Then, the CCF damage properties, including the crack propagation, the fracture morphology and the dynamic characteristic are analyzed. Lastly, the new modified contrast method is proposed with the new coordinate axes, new fitting criterions and amend method. Through comparisons we conclude that: the new method is slightly complicated, but the evaluate precision has significantly increased. So it could be used to deal with data for CCF tests on full scale turbine blade in the future.
A Study of Spontaneous Transition in Swirl-Stabilized Flames
Authors: Boxx Isaac , Carter Campbell D. , Geigle Klaus Peter , Meier Wolfgang , Akih-Kumgeh Benjamin , Lewalle Jacques
Published: August 2017

The goal of this study was to select and test some analysis tools to identify and characterize precursors to the onset of thermo-acoustic pulsation in a gas turbine combustor. The target flame was a turbulent, swirl-stability ethylene-air flame operated at ϕ = 0.91, and 5 bars pressure. 3-component stereo-particle image velocimetry (PIV) measurements, acquired at 9.3 kHz over periods of approximately 4 seconds were used to characterize the flow-field near the exit plane of the combustor. Acoustic measurements and OH*-chemiluminescence images were acquired synchronously, with OH* images acquired at every third cycle of the PIV measurement system.

Analysis revealed the presence of two characteristic frequencies in the data for the stable flame; a 475 Hz oscillation associated with the shear-layer dynamics and a weak thermo-acoustic oscillation 610 Hz. In the excited state, a 720 Hz self-excited thermo-acoustic oscillation dominated combustor dynamics. A possible precursor event was identified in the form of a 635 Hz oscillation that appeared in the data 0.15s prior to transition. Bandpass filtering of the velocity data at this frequency showed this oscillation originates in the outer recirculation zone of the combustor.
Development of a Jet-Stabilized Combustion System for the Use of Low-Caloric SOFC Off-Gas
Authors: Bücheler S. , Huber A. , Aigner M.
Published: August 2017

A promising technology solution to meet the demands for highly efficient and clean CHP systems with the highest load and fuel flexibility is the SOFC/MGT hybrid power plant concept (HPP). In this concept, a solid oxide fuel cell (SOFC) is combined with a micro gas turbine (MGT) to use the hot and low-caloric SOFC off-gases for further energy production. In this study, the focus is set on the development of a suitable single-stage jet-stabilized combustor which combines the functionality of a gas turbine combustor and a SOFC off-gas burner for low-caloric SOFC off-gases at combustor inlet temperatures up to 1073 K. To experimentally characterize the newly developed SOFC off-gas combustion system beyond the turbine operating conditions in the HPP, atmospheric tests were carried out. The anode and cathode flows within the test series are provided without the SOFC being in place. Reflecting the resulting SOFC off-gas conditions at different possible HPP operating points, the results from variations of the cathode and anode mass flow rates, the O2 content and the LHV were carried out and are presented. The off-gas burner proves a wide operational stability of the combustion concept with CO emissions below 10 ppm and NOx emissions below 3 ppm. The shape and location of the flame is investigated using the OH* signal detected by an ICCD camera.
Influence of Detailing on Aerodynamic Forcing of a Transonic Axial Turbine Stage and Forced-Response Prediction for Low-Engine-Order (LEO) Excitation
Authors: Müller Tobias R. , Vogt Damian M. , Vogel Klemens , Phillipsen Bent A. , Hönisch Peter
Published: August 2017

The effects of detailing on the prediction of forced-response in a transonic axial turbine stage, featuring a parted stator design, asymmetric inlet and outlet casings as well as rotor cavities, is investigated. Ensuring the mechanical integrity of components is of paramount importance for the safe and reliable operation of turbomachines. Among others, flow induced resonance excitation can lead to high-cycle fatigue (HCF) and potentially to damage of components unless properly damped. This numerical study is assessing the necessary degree of detailing in terms of spatial and temporal discretization, boundary conditions of the pre-stressed rotor geometry as well as geometrical detailing for the reliable prediction of the aerodynamic excitation of the structure. In this context, the sensitivity of the aerodynamic forcing is analyzed by means of the generalized force criterion, showing a significant influence for some of the investigated variations of the numerical model.

Moreover, the origin and further progression of several low-engine-orders (LEO) within the flow field, as well as their interaction with different geometric details has been analyzed based on the numerical results obtained from a full 360° CFD-calculation of the investigated turbine stage. The predicted flow induced vibration of the structure has been validated by means of a full forced-response analysis, where a good agreement with tip-timing data has been found.
Numerical Characterization of Flow and Heat Transfer in Pre-Swirl Systems
Authors: Da Soghe Riccardo , Bianchini Cosimo , D’Errico Jacopo
Published: August 2017

This paper deals with a numerical study aimed at the validation of a computational procedure for the aerothermal characterization of pre-swirl systems employed in axial gas turbines. The numerical campaign focused on an experimental facility which models the flow field inside a direct-flow pre-swirl system. Steady and unsteady simulation techniques were adopted in conjunction with both a standard two-equations RANS/URANS modelling and more advanced approaches such as the Scale-Adaptive-Simulation principle, the SBES and LES. The comparisons between CFD and experiments were done in terms of swirl number development, static and total pressure distributions, receiving holes discharge coefficient and heat transfer on the rotor disc surface. Several operating conditions were accounted for, spanning 0.78·106<Reφ<1.21·106 and 0.123<λt<0.376. Overall the steady-state CFD predictions are in good agreement with the experimental evidences even though it is not able to confidently mimic the experimental swirl and pressure behaviour in some regions. Although the use of unsteady sliding mesh and direct turbulence modelling, would in principle increase the insight in the physical phenomenon, from a design perspective the tradeoff between accuracy and computational costs is not always favourable.
Design of a Single Stage Variable Pitch Axial Fan
Authors: Bonanni Tommaso , Corsini Alessandro , Delibra Giovanni , Volponi David , Sheard Anthony G. , Bublitz Mark
Published: August 2017

The European Union imposed minimum industrial fan efficiency levels in 2013 and then increased them in 2015. In the USA, the Department of Energy (DoE) is also developing regulations aimed at eliminating inefficient industrial fans from the market by 2023. A consequence of this regulatory activity is a need to apply design methods originally developed within the aerospace community to the design of high efficiency industrial fans.

In this paper, we present a process used to design, numerically verify and experimentally test a high-pressure single-stage axial fan. The goal was a fan design capable of working over a range of blade angles in combination with a single fixed cambered plate stator. We present the process used when selecting blade airfoil sections and the vortex distribution along the blade span. The selected methodology is based on a coupling between the aerodynamic response of each blade profile and the chosen vortex distribution, creating a direct link between the load distribution and the aerodynamic capability of the blade profile section. This link is used to develop radial distributions of blade twist and chord for the selected blade profiles that result in the required radial work distribution.

The design method has been enhanced through intermediate verifications using two different numerical methodologies. The methodologies are based on different approaches, in so doing providing confidence in the verification process. The final blade design has been analyzed using a three-dimensional computational fluid dynamic (CFD) code. Results of the CFD analysis indicate that performance of the final blade design is consistent with the design specifications.

The paper concludes with a comparison between predicted and experimentally measured performance. The need is clarified for balance between computational and empirical approaches. When used together the development effort results in a lower cost and higher efficiency design than would have been possible using either approach in isolation.
Radial Mode Analysis of Broadband Noise in Flow Ducts Using Azimuthal Sensor Array
Authors: Xu Kunbo , Qiao Weiyang , Tong Fan , Wei Renke
Published: August 2017

For the evaluation and improvement of fan noise reduction notions and the verification of broadband sound power measurement in flow ducts, special interest was given to the analysis of the broadband noise fields in duct. Two axial sensor arrays were wall-flush mounted upstream of a single-stage axial fan in the circular duct section of the fan inlet, staggered by 180° in the circumferential direction. During the tests, the rotating drum was rotated by step of 6 degrees to give a total 840 measurement points. There are two static reference microphones mounted upstream of rotating measurement section. Time-series of 12 seconds duration were recorded at each of the 30 azimuthal positions of the rotating duct in order to allow for a statistically accurate cross-correlation data analysis. This method is able to discriminate the sound waves propagating in upstream and downstream directions. Special attention was given to the blade passing frequencies of the axial fan. Rotor-stator interaction mode dominates the incident sound field, while modes with low azimuthal order play an important role in the reflected sound field. The reflected broadband sound power is almost 10dB lower than the transmitted sound field in a broad-frequency range. On the whole, this method behaves robustly in decomposition of broadband noise in flow duct and delivers physically meaningful broadband mode amplitudes.
Turbomachinery Active Subspace Performance Maps
Authors: Seshadri Pranay , Shahpar Shahrokh , Constantine Paul , Parks Geoffrey , Adams Mike
Published: August 2017

Turbomachinery active subspace performance maps are 2D contour plots that illustrate the variation of key flow performance metrics with different blade designs. While such maps are easy to construct for design parameterizations with two variables, in this paper maps will be generated for a fan blade with twenty-five design variables. Turbomachinery active subspace performance maps combine active subspaces — a new set of ideas for dimension reduction — with fundamental turbomachinery aerodynamics and design spaces. In this paper, contours of (i) cruise efficiency, (ii) cruise pressure ratio, (iii) maximum climb flow capacity and (iv) sensitivity to manufacturing variations, are plotted as objectives for the fan. These maps are then used to infer pedigree design rules: how best to increase fan efficiency; how best to desensitize blade aerodynamics to the impact of manufacturing variations? In the present study, the former required both a reduction in pressure ratio and flow capacity — leading to a reduction of the strength of the leading edge bow wave — while the latter required strictly a reduction in flow capacity. While such pedigree rules can be obtained from first principles, in this paper these rules are derived from the active subspaces. This facilitates a more detailed quantification of the aerodynamic trade-offs. Thus, instead of simply stating that a particular design is more sensitive to manufacturing variations; or that it lies on a hypothetical ‘efficiency cliff’, this paper seeks to visualize, quantify and make precise such notions of turbomachinery design.
Development of Direct-Driven and Geared Fan Stages With Reduced Tip Speeds
Authors: Pankov S. V. , Mileshin V. I. , Orekhov I. K. , Fateev V. A.
Published: August 2017

This work presents the latest results of aeromechanical design of two large-scale fan model stages (Dr = 700 mm) for low-noise high-performance single-stage fan prototypes designed for advanced civil aircraft geared and direct-driven turbofans with reduced and ultra-low rotor tip speeds, high specific capacity, and high bypass ratios. They are designed with account of all features of blades made of polymer composite materials (PCM) or titanium alloy. Metal and composite blades have a similar shape in hot state at the design point. The stages are intended for tests in the anechoic chamber of the CIAM’s C-3A special acoustic test facility with the aim of verification new optimal design methods for similar fans to achieve maximum performance.

Performances of the fans and parameters of viscous steady flows are calculated. The calculations show that both fan models can provide a high specific capacity along with a high efficiency and sufficient stall margins. For example, calculated max. efficiency level of the bypass duct in the geared model fan with ultra-low tip speed (Ucor. = 313.4 m/s) is equal to 94%.

Data measured by tests of an ungeared bypass fan model with solid metal rotor blades developed earlier by the authors are used for the mathematical model verification. Tip speed of rotor blades at the design point is Ucor. = 400m/s, bypass ratio — m = 8.4. Four booster stages are installed in the core duct. From first test results it is clear that required values of key parameters are achieved. Comparison of measured and calculated data gives evidence of their good agreement. At present, detailed tests of this fan and a similar fan with 3 booster stages are under way in the anechoic chamber of the CIAM’s C-3A acoustic test facility.

The new direct-driven fan model described in this paper has quite different design values of parameters, geometry of the meridian contours, and shapes of outer and inner ducts. Tip speed of its rotor blades is reduced by 30 m/s, the hub diameter is decreased, and bypass ratio is higher (m = 11).

In the near future, these two new models of non-geared and geared fans can be manufactured and tested.