bluuebunny/crossref_metadata_2025 huggingface dataset:
Origami-Layer-Jamming Deployable Surgical Retractor With Variable Stiffness and Tactile Sensing
Authors: Banerjee Hritwick , Li Tai Kai , Ponraj Godwin , Kirthika Senthil Kumar , Lim Chwee Ming , Ren Hongliang
Published: November 2019

Origami-based flexible, compliant, and bio-inspired robots are believed to permit a range of medical applications within confined environments. In this article, we experimentally demonstrated an origami-inspired deployable surgical retractor with the controllable stiffness mechanism that can facilitate safer instrument–tissue interaction in comparison to their rigid counterparts. When controllable negative-pressure is applied to the jammed origami retractor module, it becomes more rigid, increasing its strength. To quantify origami-modules strength further, we demonstrated performances of retractor based on the Daler–Rowney Canford paper (38 grams per square meter (gsm)) and sandpaper of 1000 grit. Experiments on the proposed retractor prototype elucidated sandpaper-based retractor can outperform paper-38-gsm retractor for facelift incision with the width of more than 9 cm. Though 38 gsm Canford paper comprised of thin layers, 16 times lesser in thickness than sandpaper, experiments proved its comparable layer jamming (LJ) performance. We leverage the advantage of the LJ mechanism to tune retractor stiffness, allowing the instrument to hold and separate a facelift incision to mitigate the likelihood of surgical complications. The retractor is equipped with a custom-made printed conductive ink-based fabric piezoresistive tactile sensor to assist clinicians with tissue-retractor interaction force information. The proposed sensor showed a linear relationship with the applied force and has a sensitivity of 0.833 N−1. Finally, cadaver experiments exhibit an effective origami-inspired surgical retractor for assisting surgeons and clinicians in the near future.
Kinematic Geometry Description of a Line With Four Positions and Its Application in Dimension Synthesis of Spatial Linkage
Authors: Lin Song , Wang Hanchao , Zhang Yu , Jiang Jingyu
Published: November 2019

In the dimension synthesis of the spatial linkages, the geometric characteristics of floating links in mechanisms reveal the geometric relationship between the motion task and the dimensions of the mechanisms. In order to establish the kinematic geometry rules corresponding to the motion of the floating link, this paper transforms the kinematic problems of geometric elements on the floating link into geometric problems and uses the geometric procedure to solve the spatial linkages synthesis problem with four given positions. In a previous work, we have extracted the kinematic geometry rules of a line with two and three positions. However, as the number of task positions increases, the kinematic characteristics representing the position transformation become more complicated. The method proposed in this paper extends the previous work to four given positions and builds up the geometric relationships among the kinematic rules for two, three, and four positions. The establishment of this geometric relationship is helpful to unify the synthesis procedure of synthesis problems with different number of positions. After that, the two-plane projection system and the transformation of projection are introduced to establish a procedural graphical synthesis method.
Modelling the Effects of Reliability and Maintenance on Levelised Cost of Wind Energy
Authors: Dao Cuong D. , Kazemtabrizi Behzad , Crabtree Christopher J.
Published: November 2019

Levelised cost of energy is an important measure to evaluate the success of a wind energy project. It includes all the capital and operational expenditures of a wind turbine over its lifetime based on the expected power generated. In the literature, wind turbine reliability is largely neglected in levelised cost of energy estimation. This paper presents a model to evaluate levelised cost of energy while considering the reliability and maintenance of wind turbine subassemblies. The key concept behind this model is that the failure rate of a wind turbine subassembly depends on the preventive maintenance spending. The proposed model makes it possible to relate reliability data, such as failure rate and downtime of wind turbine subassemblies, to the operation and maintenance expenditure, as well as the annual energy production. The model is analysed using a sample set of recently published reliability data and it is observed that both the operation and maintenance expenditure and levelised cost of energy are convex functions of the subassembly’s failure rate and the preventive maintenance spending. This study can help wind turbine manufacturers and operators identify the level of reliability improvement and maintenance investment required to minimise the levelised cost of energy.
Determination of the Vibration Within a Squeeze-Film Damper Under Rotational Unbalance Conditions From Externally Mounted Sensors
Authors: Al-Ghazal Ghaith Ghanim , Bonello Philip , Torres Cedillo Sergio G.
Published: November 2019

Recently, there has been a focus on the use of inverse problem techniques in order to monitor rotor unbalance, and obtain a balancing solution, from vibration measurements on the casing and prior knowledge of the rotor-casing structure. In certain practical configurations that use nonlinear bearings like the squeeze-film damper (SFD) bearing, an inverse model of the bearing is an important part of the unbalance identification process. The inverse bearing model is used to estimate the journal vibration from casing vibration measurements, thus acting as a substitute for internal instrumentation in applications where the rotor is not accessible under operational conditions. Previous research has shown that an inverse bearing model can be identified using a trained Recurrent Neural Network (RNN) from experimental input/output data. However, the RNN was both trained and validated under simulated rotational conditions, wherein the motion was driven by two orthogonally-phased perpendicular shakers.

In this paper, a RNN of an inverse bearing model that is identified from experimental data generated under simulated rotational conditions is validated under actual rotational (i.e. unbalance-driven) vibration conditions. The necessary modifications to the test rig are presented, together with the identification/training procedure. The results of the validation tests show that the RNN is capable of predicting the frequency spectrum of the dynamic nonlinear response of the journal with reasonable accuracy. This inverse SFD bearing model can be thus used in a future work to identify rotor unbalance.
Validation of an Advanced Diagnostic Methodology for the Identification and Classification of Gas Turbine Sensor Faults by Means of Field Data
Authors: Manservigi Lucrezia , Venturini Mauro , Ceschini Giuseppe Fabio , Bechini Giovanni , Losi Enzo
Published: November 2019

Sensor fault detection is a crucial aspect for raw data cleaning in gas turbine industry. To this purpose, a comprehensive approach for Improved Detection, Classification and Integrated Diagnostics of Gas Turbine Sensors (named I-DCIDS) was developed by the authors to detect and classify several classes of fault. For single-sensors or redundant/correlated sensors, the I-DCIDS methodology can identify seven classes of fault, i.e. Out of Range, Stuck Signal, Dithering, Standard Deviation, Trend Coherence, Spike and Bias.

Since the considered faults are detected by means of a methodology which relies on basic mathematical laws and user-defined parameters, sensitivity analyses are carried out in this paper on I-DCIDS parameters to derive some rules of thumbs about their optimal setting. The sensitivity analyses are carried out on four heterogeneous and challenging datasets with redundant sensors installed on Siemens gas turbines.
Thermomechanical Fatigue of Ceramic Matrix Composites
Authors: Longbiao Li
Published: November 2019

In this paper, the thermomechanical fatigue (TMF) of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the hysteresis-based damage parameter. The micro stress field of the damaged CMCs of matrix cracking and fiber/matrix interface debonding is obtained considering the temperature-dependent fiber/matrix interface shear stress. The fiber/matrix interface debonded length and unloading/reloading slip length are determined using the fracture mechanics approach. Based on the damage mechanisms of fiber sliding relative to the matrix in the interface debonded region, the TMF hysteresis loops models and hysteresis-based damage parameters are developed for the partially and completely debonding to analyze the damage evolution inside of fiber-reinforced CMCs. The effects of temperature, phase angle and loading sequences on the damage development of SiC/SiC composite are discussed. When TMF temperature range increases, the fatigue hysteresis loops area, residual strain increase, and the hysteresis modulus decreases, due to the increase of the fiber/matrix interface slip length. Under TMF loading, the phase angle affects the interface debonding and sliding range, and the hysteresis loops shape, location and area of the fiber-reinforced CMCs. The experimental TMF damage evolution of 2D SiC/SiC and cross-ply SiC/MAS composites are predicted.
A Numerical Investigation of Air/Mist Cooling Through a Conjugate, Rotating 3-D Gas Turbine Blade With Internal, External, and Tip Cooling
Authors: Abdelmaksoud Ramy , Wang Ting
Published: November 2019

This paper describes a numerical investigation to study the effect of injecting mist (tiny water droplets) into the cooling air used to cool down rotating gas turbine blades. In this study, the conjugate heat transfer method is employed which consists of the simulation of the air/mist fluid flow inside and outside the blades as well as the heat conduction through the blade body. The complete 3-D blade with internal cooling passages and external film cooling holes on the surface and blade tip is simulated in a rotating, periodic sector of the blade. The discrete phase model (DPM) is used to simulate and track the evaporation and movement of the tiny water droplets. The rotation effect of the turbine blade is included in the CFD simulation by using the moving reference frame method. The effects of different parameters such as the mist/air ratio (10–20%) and the mist droplets size (20–40μm) on mist cooling enhancement are investigated. The results show that the mist cooling enhancements are about 10% to 25% on the outer surface of the blade and reach 50% in some locations inside the blade on the internal cooling passages walls. Most of the liquid droplets completely evaporate inside the internal cooling passages; only a limited amount of mist is able to escape from the film cooling holes to enhance the blade outer surface and blade tip cooling. The effect of 10% mist on enhanced cooling is also converted to an equivalent of a 30% reduction in cooling air flow.
Fretting Induced Fatigue Failure in Steam Turbine Blades
Authors: Gowreesan Vamadevan , Grebinnyk Kyrylo
Published: November 2019

Fretting occurs when there is cyclic relative motion of extremely small amplitude between two tightly fit mating surfaces. In this process, the tight fitting load may lead to adhesion of mating surface. The subsequent relative movement breaks the adhesion and lead to local grooves and pits. The localized damage in conjunction with the stresses associated with the cyclic relative motion may lead to surface cracking. This crack subsequently may propagate by fatigue provided there is high enough cyclic stress at that location.

The paper discusses a blade failure induced by such fretting related fatigue. The metallurgical evaluation of the fracture surfaces of the blades showed evidence of classical fatigue failure. However, the crack initiation location did not coincide with high stress location identified by the finite element analysis. This discrepancy along with the evidence of fretting at the crack initiation sites confirms that failures were induced by fretting. Finally, some methods to eliminate or minimize fretting damage are discussed.
Comparison of a Liquid Annular Seal for Pump Applications With and Without a Swirl Brake
Authors: Balke Nathan E. , Childs Dara W.
Published: November 2019

An annular seal is an annular clearance between a rotor and a stator within a turbomachine that restricts leakage flow, arising due to the seal’s pressure differential. Annular seals are important for consideration in turbomachinery in that they affect the rotodynamics and stability of the turbomachine. Data were available for a smooth liquid annular seal that had been previously tested with no swirl brakes. The seal was modified by adding slots at the inlet to produce a swirl brake seal. Tests produced static and dynamic data for the swirl brake seal. The swirl brake and unmodified seal data are compared to demonstrate how swirl brakes impact the seal’s rotordynamic performance.

Adding a swirl brake to a liquid annular seal increases direct stiffness, decreases cross-coupled stiffness, modestly increases direct damping, reduces cross-coupled damping, and decreases both the direct and cross-coupled virtual mass terms. The measured drop in cross-coupled stiffness via the addition of swirl brakes shows why swirl brakes are effective in remedying rotordynamic instabilities. Results show that varying inlet pre-swirl, or fluid rotation, on a swirl brake seal has little effect on the seal’s dynamic performance characteristics.

A notable phenomenon was observed with the direct stiffness. At certain test points the direct stiffness would abruptly increase and decrease when increasing either pressure or running speed. The behavior could be largely explained by transitioning the laminar/transitional/turbulent boundaries.
Secondary Flow Measurements in a Compressor Cascade Using 3D LDA/PDA: Part A — Flow Topology and its Numerical Representation
Authors: Geist Silvio , Harbeck Janneck , Joos Franz
Published: November 2019

A three-dimensional flow in a high speed (Main = 0.7) linear compressor cascade’s end wall region is presented in this paper. The attached blade geometry is of medium curvature with a deflection angle Δβ = 15°. To intensify the secondary flow structure the profiles were stalled deliberately and oil flow visualization was used to prove the presence of that hub-corner stall. Together with streamlines derived from velocities, measured by a three-channel laser Doppler anemometer (LDA), that allowed the identification of the secondary flow region’s key features and their extents into the flow field. A therefrom-derived topology is then compared to existing concepts. Moreover, an associated URANS simulation is set up using the k–ε model to verify its capabilities to reproduce the measured flow field. To confirm the previous observations the stall indicator is computed from the simulation results. It is further shown that the hub-corner stall dissolves when removing the side wall boundary layer. In summary, this paper combines elaborate laser Doppler measurements at both high Reynolds and Mach numbers combined with verified simulations allowing a detailed description of the end wall behavior within the cascade and further introduces a new flow topology concept.
Performance Informed Prognostics and its Implications
Authors: Slottner Pontus , Johansson Per
Published: November 2019

Gas turbine maintenance has historically been performed firstly to keep equipment safe and reliable to operate, and secondly to prevent performance loss. Component replacement plans have often been generic and therefore best suited for one set of ambient conditions and a few pre-defined operation profiles. Continuous development in materials and computerized analysis methods have resulted in much more well understood and robust designs than before, resulting in design induced failure rates dropping to levels where they can be considered as random and unexpected.

While gas turbine designs matured, market conditions changed. Deregulation, consumer energy efficiency improvements, emission reduction requirements and large-scale introduction of renewables have reduced both average electricity price and thus the average amount of gas turbine power needed, but has also increased the variability in demand, resulting in highly unit specific operation profiles. This requires operators to cut unnecessary costs wherever possible and optimize operation and maintenance strategy in a complex environment with a growing number of parameters to consider. Over the past years much focus has been put on cost reduction through extension of maintenance intervals. However, since less maintenance and longer intervals can mean lower reliability and higher degradation, it is not always cost efficient. This paper shows how costs of maintenance, operation, fuel and degradation can be analyzed together, resulting in improved decision support for choosing better operation and maintenance strategies.
Prediction of Premixed Flame Dynamics Using LES With Tabulated Chemistry and Eulerian Stochastic Fields
Authors: Avdonin Alexander , Javareshkian Alireza , Polifke Wolfgang
Published: November 2019

This paper demonstrates that a Large Eddy Simulation (LES) combustion model based on tabulated chemistry and Eulerian stochastic fields can successfully describe the flame dynamics of a premixed turbulent swirl flame. The combustion chemistry is tabulated from one-dimensional burner-stabilized flamelet computations in dependence of progress variable and enthalpy. The progress variable allows to efficiently include a detailed reaction scheme, while the dependence on enthalpy describes the effect of heat losses on the reaction rate. The turbulence-chemistry interaction is modeled by eight Eulerian stochastic fields. A LES of a premixed swirl burner with a broadband velocity excitation is performed to investigate the flame dynamics, i.e. the response of heat release rate to upstream velocity perturbations. In particular, the flame impulse response and flame transfer function are identified from LES time series data. Simulation results for a range of power ratings are in good agreement with experimental data.
Time-Volume Estimation of Velocity Fields From Non-Synchronous Planar Measurements Using Linear Stochastic Estimation
Authors: Butcher Daniel , Spencer Adrian
Published: November 2019

With increasing complexity of aerodynamic devices such as gas turbine fuel swirl nozzles (FSN) and combustors, the need for time-resolved full volume flow characterisation is becoming greater. Even with modern advancements in both numerical and experimental methods, this remains a challenging area.

The work presented in this paper combines multiple non-synchronous planar measurements to reconstruct an estimate of a synchronous, instantaneous flow field of the whole measurement set. Temporal information is retained through the linear stochastic estimation (LSE) technique. The technique is described, applied and validated with a simplified combustor and FSN geometry flow for which 3-component, 3-dimensional (3C3D) flow information is known from published tomographic PIV[1]. Using the tomographic PIV data set, multiple virtual ‘planes’ may be extracted to emulate single planar PIV measurements and produce the correlations required for LSE. In this example, multiple parallel planes are synchronised with a single perpendicular plane that intersects each of them. As the underlying data set is volumetric, the measured velocity is known a priori and therefore can be directly compared to the estimated velocity field for validation purposes. The work shows that when the input time-resolved planar velocity measurements are first POD (proper orthogonal decomposition) filtered, high correlation between the estimations and the validation velocity volumes are possible. This results in estimated full volume velocity distributions which are available at the same time instance as the input field — i.e. a time resolved velocity estimation at the frequency of the single input plane. While 3C3D information is used in the presented work, this is necessary only for validation; in true application planar technique would be used. The study concludes that provided the number of sensors used for input LSE exceeds the number of POD modes used for pre-filtering, it is possible to achieve correlation greater than 99%.
Radial Inflow Turbine Geometry Generation Method Using Third Order Bezier Curves for Blade Design
Authors: Caldiño-Herrera U. , García J. C. , Sierra-Espinosa F. , Dávalos J. O. , Lira M. A.
Published: November 2019

Radial inflow turbines offer larger efficiency performance for small power applications due to its geometric configuration in which flow varies its radial position along the flow path.

The geometry configuration of radial-inflow turbines demands a careful and adequate design of the flow path, since a 90° change of direction occurs from the radial inflow to the axial outflow. The blade camberline also requires attention since it defines the tangential flow direction along the meridional coordinate and any variation in its geometry affects the turbine performance.

In this paper, a method for meridional profile and camberline geometry generation is proposed and tested through CFD. The method consists in using fourth order Bezier curves for defining the hub, shroud and mid-height blade meridional profile and third order Bezier curves for defining the relative flow velocity angle along the meridional coordinate, which leads to the camberline angular position in the rotor considering radial fibered blades. The blade thickness is set to vary linearly along the meridional coordinate and along the blade height. Different configurations of blade geometry are proposed and analyzed. These configurations are fixed to satisfy the design parameters.

The code is programed in Python and adjusts the geometry data in files that are readable by meshing software. Thereby numerical calculations are performed to verify which configuration of camberline results in better performance. The calculations are done in models with the same boundary conditions and geometric data except for the variation of relative flow velocity angle along the meridional coordinate but setting the inlet and outlet angle to a fixed value. This way, the most suitable camberline geometry can be selected. The CDF model used for this analysis was validated with the experimental results reported by Kang et al. [1]
Assessment of an Innovative Technique for the Robust Optimization of Organic Rankine Cycles
Authors: Serafino Aldo , Obert Benoit , Hagi Hayato , Cinnella Paola
Published: November 2019

After the extraordinary diffusion that we have observed over the last ten years, Organic Rankine Cycles (ORCs) are nowadays widely recognized as “the unrivalled technical solution for generating electricity from low-medium temperature heat sources of limited capacity” [1]. Despite the high level of confidence and know-how reached about ORCs, they still remain a delicate technology, hiding a great amount of technical difficulties which sometimes still make them a risky investment. Most of these complexities are originated from manifold sources of uncertainty which impact on almost the whole life of the ORC project, from their design to the commissioning and operation steps, with heavy consequences in terms of performance and costs. In this work we present the proof of concept assessing and validating an innovative technique for the robust design optimization (RDO) of ORC under uncertainty. The approach allows to deal with both aleatory and epistemic uncertainty in order to avoid an over-optimization of the system that can result in a high sensitivity to small changes. Because of the large number of sources of uncertainty, the design problem must be solved in a highly multi-dimensional space, spanned by the uncertain and design variables. In such a situation, the “brute-force” Monte-carlo approach [2] is not a viable technique, since it is limited to cheap and excessively simplified models. Consequently, in the present work we consider a more efficient design methodology relying on two nested Bayesian Kriging surrogates.
Object-Oriented Approach to Determine Effectiveness of Potential Gas Turbine Power Augmentation Methods
Authors: Krouse Charles R. , Delimont Jacob M.
Published: November 2019

Ambient conditions have a significant impact on the performance of gas turbines. Higher ambient temperatures correlate with decreased power output and increased heat rate. These effects are undesirable for power generation plants, especially given that energy demand is highest during hot days. To replace some of the power lost on hot days, power augmentation methods, such as inlet fogging or inlet chilling, can be used. To determine the effectiveness and return on investment of potential power augmentation methods, economic impact studies are generally conducted. Among other things, these studies require theoretical models of the power augmentation systems. An object-oriented approach seems to be the most logical approach for modeling a gas turbine with potential power augmentation systems. This approach allows numerous power augmentation models to easily be added to, evaluated with, and removed from a gas turbine model. Existing literature focuses heavily on economic studies and complicated models, and there is a lack of fundamental information on how to simulate power augmentation methods. This paper will focus on the modeling and simulation of four primary gas turbine power augmentation techniques: inlet chilling, inlet fogging, air injection, and steam injection. The fundamental calculations associated with each object are discussed. Finally, the different techniques are modeling in a GE-7FA gas turbine to demonstrate a simple power augmentation case study.
A New Data-Driven Turbulence Model Framework for Unsteady Flows Applied to Wall-Jet and Wall-Wake Flows
Authors: Lav Chitrarth , Philip Jimmy , Sandberg Richard D.
Published: November 2019

The unsteady flow prediction for turbomachinery applications relies heavily on unsteady RANS (URANS). For flows that exhibit vortex shedding, such as the wall-jet/wake flows considered in this study, URANS is unable to predict the correct momentum mixing with sufficient accuracy. We suggest a novel framework to improve that prediction, whereby the deterministic scales associated with vortex shedding are resolved while the stochastic scales of pure turbulence are modelled. The framework first separates the stochastic from the deterministic length scales and then develops a bespoke turbulence closure for the stochastic scales using a data-driven machine-learning algorithm. The novelty of the method lies in the use of machine-learning to develop closures tailored to URANS calculations. For the walljet/wake flow, three different mass flow ratios (0.86, 1.07 and 1.26) have been considered and a high-fidelity dataset of the idealised geometry is utilised for the sake of model development. This study serves as an a priori analysis, where the closures obtained from the machine-learning algorithm are evaluated before their implementation in URANS. The analysis looks at the impact of using all length scales versus the stochastic scales for closure development, and the impact of the extent of the spatial domain for developing the closure. It is found that a two-layer approach, using bespoke trained models for the near wall and the jet/wake regions, produce the best results. Finally, the generalisability of the developed closures is also evaluated by applying a given closure developed using a particular mass flow ratio to the other cases.
Study on Leakage Loss Control Method of Circumferential Bending Clearance
Authors: Jiang Shuai , Chen Fu , Yu Jianyang , Chen Shaowen , Song Yanping
Published: November 2019

The concept of circumferential bending clearance based on Gauss Bimodal Function is proposed to suppress tip leakage flow (TLF) in a highly-loaded turbine cascade. In this method, a new vortex (BV) can be induced to mix with TLV in the middle of tip region and block the development of tip leakage vortex (TLV). Since the blocking effect divides the TLV into two parts, the tip leakage rate and loss of TLF can be reduced significantly. In order to reveal the mechanisms of blocking effect on leakage flow and its influencing factors, the research numerically investigates the effects of environmental conditions on the TLF development in a turbine cascade. The flow field analysis of the optimal bending clearance is in the first place, and then the effects of clearance heights (δ) and incidence angles (α) on the TLF characteristic and loss are investigated respectively.

Results indicate that the blocking effect has a close relationship with the TLF characteristic, which can be divided into the BV migration, TLV-2 location and blocking loss. The nearer distance to the leading edge (LE) and farther distance to the suction side (SS) of BV means a less loss of TLF in bending clearance cases. The further distance away from blade tip and SS of TLV-2 means a larger-scale vortex with more loss. The additional loss in blocking region expands constantly with the increase of clearance height and incidence angle. The bending clearance has limited control effect on TLF with the variation of clearance height, especially the loss increases in Case 2%H. However, it has a strong adaptability with the change of incidence angle, the relative total pressure loss drops up to 16% in Case −5°.
Numerical Investigations on the Sealing Effectiveness of Turbine Groove Radial Rim Seal
Authors: Chen Shuxian , Li Zhigang , Li Jun , Yan Xin , Song Liming
Published: November 2019

This paper presents a numerical comparison of sealing performance between conventional radial rim seal and seven different kinds of groove radial rim seal with three coolant flow rates. Three-dimensional unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, coupled with a fully developed shear stress transport (SST) turbulent model from ANSYS-CFX, are utilized to investigate the sealing effectiveness of rim seal and flow characteristics in the wheel-space cavity of gas turbines. The numerical method for the pressure distributions on the vane hub and sealing effectiveness of rim seal is validated on the basis of published experimental data. The seven kinds of groove rim seals designed in this work include four circumferential groove structures, one axial groove structure and two oblique groove structures. The sealing effectiveness of conventional and seven different groove rim seals are compared. Then the flow field in the disc cavity of conventional and groove rim seals is simulated and analyzed. Compared with conventional radial rim seal, the groove rim seals can increase the sealing effectiveness obviously. It is shown that the groove structures improve the damping dissipation of invading gas. The number of grooves has an obvious effect on sealing effectiveness of circumferential groove rim seals. The axial groove case results in less minimum sealing flow rate than oblique groove cases. In addition, the flow pattern of rim seal and disc cavity is used to describe rim seal gas ingestion flow characteristics.
Tip Leakage Flow Instability in a Centrifugal Compressor
Authors: Cao Teng , Kanzaka Tadashi , Xu Liping , Brandvik Tobias
Published: November 2019

In this paper, an unsteady tip leakage flow phenomenon is identified and investigated in a centrifugal compressor with a vaneless diffuser at near-stall conditions. This phenomenon is associated with the inception of a rotating instability in the compressor. The study is based on numerical simulations which are supported by experimental measurements. The study confirms that the unstable flow is primarily driven by the Kelvin-Helmholtz instability inherent in the shear layer between the main-stream flow and the tip leakage flow. The shear layer instability induces large scale vortex shedding which propagates circumferentially, leading to pressure perturbations with short wavelength and high amplitude which rotates at about half of the blade speed. The shed vortex is also found to interact with the main blade leading edge, resulting in the reduction of the blade loading identified in the experiment. The paper also reveals that the downstream volute imposes a long wavelength circumferential non-uniform back pressure at the impeller exit, which is found to either excite or supress the vortex shedding within the blade passage depending on the relative circumferential position of the impeller and the volutes.
Study of the Tip Leakage Flow in a Compressor Cascade With Incidence Exceeding the Stability Limit
Authors: Leitner Markus W. , Staudacher Stephan , Rose Martin G.
Published: November 2019

In axial compressors, tip leakage flow is disadvantageous to efficiency and mass flow stability. We analyzed the tip leakage flow in a compressor cascade on a water table at various angles of incidence. When the angle of incidence is systematically increased, the flow rate is decreased and, finally, the stability limit is exceeded. To study the flow structures and vortex behavior, we installed Particle Tracking Velocimetry (PTV) on the water table. 3D-trajectories of the stable and unstable flow reveal significant effects. Increasing incidence generates a significant change in the nature of the flow. The tip leakage flow fluctuates and features unstable flow phenomena. A large blockage of the flow passage occurs, probably due vortex breakdown. Such a serious disturbance of the incoming flow may induce stall.
Quantification of Energy Transformation Processes Between Acoustic and Hydrodynamic Modes in Non-Compact Thermoacoustic Systems via a Helmholtz-Hodge Decomposition Approach
Authors: Hofmeister Thomas , Hummel Tobias , Schuermans Bruno , Sattelmayer Thomas
Published: November 2019

Solutions of the Linearized Euler Equations (LEE) are composed of acoustic, entropy and vortical perturbation types. The excitation of the latter can be provoked by a transformation of acoustic into rotational energy, which originates from the interaction between acoustics and a mean flow shear-layer. This is known as acoustically induced vortex shedding and represents the phenomenon of interest in this study. In the field of thermoacoustics, numerical eigenfrequency simulations with the LEE have moved into focus to determine the acoustic damping rates associated with vortex shedding to complete thermoacoustic stability analyses of gas turbine combustors. However, there is yet no fundamental investigation existent, which establishes the legitimation to consider these LEE damping rates for this purpose. This question arises due to the implicit presence of vortical disturbances caused by vortex shedding next to the acoustic ones in LEE eigensolutions. In conclusion, the corresponding damping rates are not expected to represent the pure acoustic damping rates, which are exclusively required for a thermoacoustic stability analysis. The main objective of this work comprises the clarification, whether damping rates obtained by straightforwardly performed LEE eigenfrequency simulations can be used for a thermoacoustic stability assessment, although their eigen-solutions are “polluted” by further disturbance types, i.e. the vortical one in this study. Therefore, a Helmholtz-Hodge decomposition approach is applied to LEE eigenmode shapes, which allows to explicitly access acoustic and vortical disturbance fields. These are used to extract the unambiguous, pure acoustic damping rates from LEE eigensolutions via evaluations of appropriate energy terms. The resulting damping rates are finally compared to the corresponding, original LEE damping rates and their experimental counterparts.
Concept Verification and Preliminary Design of Reversible Turbine for High Power Marine Gas Turbine Engine
Authors: Wen Xueyou , Niu Xiying , Li Yonglai , Yu Shunwang , Lin Feng , Li Dongming , Ge Bing
Published: November 2019

In order to verify that a high-power marine gas turbine engine can be redesigned to be a reversible one, concept verification was done on a reversible turbine test rig. The reversible power turbine test pieces were designed, which are transformed to be capable of rotating reversely. And more than 100 times of operational tests were done for the switching devices. Based on the reversible turbine test rig, 50 times of switching tests between normal and reverse rotational direction were done by compressed air under low temperature condition. While more than 100 times of operational tests were done with hot gas at temperature of 400–500 °C. The tests results show that the switching devices could operate flexibly and the output power reached over 40% of rated power condition. During the switching tests between the normal and reverse rotational direction, the propeller could stop running. All of these verify the concept feasibility of reversible gas turbine engine. Based on this concept, preliminary design was completed for a high-power marine gas turbine engine redesigned into a reverse one, which laid solid foundation for the following detailed design, experimental verification and application.
Conceptual Fan Design for Boundary Layer Ingestion
Authors: Mennicken M. , Schoenweitz D. , Schnoes M. , Schnell R.
Published: November 2019

Aircraft concepts using boundary layer ingestion (BLI) are promising future flight systems aiming at reduced mission fuel burn. In this scenario the fan operates at inhomogeneous inflow conditions around the circumference. The accurate calculation of the resulting flow phenomena using uRANS approaches is highly time-consuming and therefore not suitable for fan design at early stages of the design process. In this paper, we introduce a throughflow based design methodology for BLI. The methodology includes the detailed design of the annulus geometry, the design of rotor and stator blades as well as the performance assessment in the BLI scenario. The throughflow approach is extended and calibrated to cover major BLI flow physics. The calibration data set consists of 12 fans with different fan pressure ratios (FPR) and meridional Mach numbers. The new design methodology is applied to design three specific fans and the effect of radial FPR is investigated. All designs are verified using 3D CFD uRANS approaches and the results indicate that either ascending or constant radial FPR should be favored. In addition an exploration study is conducted using the design methodology. This study covers 72 fan stages in the parameter space tip speed and meridional Mach number. The results suggest that there is a favorable tuple of design parameters to design a distortion tolerant fan by trading tip speed and meridional Mach number. In the end the newly gained knowledge is transferred to the DLR UHBR fan in order to improve the tolerance to BLI.
Estimation of Forcing Function, Mistuning and Modal Damping in a Bladed Rotor
Authors: Chauhan Arjun Singh , Sinha Alok
Published: November 2019

This paper deals with the estimation of forcing function, modal damping and mistuned modal stiffnesses in a bladed rotor. Previous research on parameter estimation in a mistuned bladed rotor relies on the knowledge of the forcing function as well as the vibration data. This paper presents two novel approaches. The first approach relies on knowledge of both the forcing and vibration data. The parameters are treated as states of the system and an augmented state space model is created. Unscented Kalman Filter is then used on the steady state data to estimate the parameters. The second approach eliminates the dependence on forcing data. Both the forcing and parameters are now treated as states of the system to construct an augmented state space model. Unscented Kalman Filter is then used on transient vibration data for estimation. Numerical results are presented for a simple model of a mistuned bladed rotor which considers a single mode of vibration per blade.
A New OpenFOAM Solver Capable of Modelling Oil Jet-Breakup and Subsequent Film Formation for Bearing Chamber Applications
Authors: Nicoli Andrew , Jefferson-Loveday Richard , Simmons Kathy
Published: November 2019

To create an adequate computational model of oil behaviour in an aeroengine bearing chamber previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) suggests it is necessary to be able to model oil shedding from bearings, breaking up into droplets/ligaments and forming thin and thick films driven by gravity and shear. Our previously published work using Fluent successfully coupled volume of fluid with the Eulerian thin film model (ETFM) and identified the challenges coupling the ETFM with the discrete phase modelling (DPM). For this latter work comparison was made to published experimental and modelling data in which a jet is injected into a duct breaking up into droplets before forming a wall film.

In this paper the use of the open-source CFD code OpenFOAM is investigated for this application recognising that such an approach eliminates some of the restrictions in a commercial product. A transient solver for spray particle cloud modelling and thin liquid film transport (sprayParcelFilmFoam) has been developed and incorporated within OpenFOAM. Fully coupled DPM-ETFM is presented, capable of modelling both primary atomization and secondary breakup. In addition two new film sub-models have been implemented for film stripping and edge separation. In order to achieve accurate statistical representation of droplets, modifications to the DPM particle injector code were implemented.

CFD results are validated against published high speed imaging and phase Doppler experimental data and in addition there is a comparison to computational results obtained using ANSYS Fluent. The fidelity of both the solver and the novel surface film sub-models are evaluated against average film thickness measurements along the duct centreline. With the inclusion of both film stripping and edge separation, a normalized root mean squared deviation of 5.1 % was achieved when compared to film thickness measurements, improving significantly on the results obtained with Fluent. A comparison with experimental data of particle diameters and velocities downstream of the expansion edge gives good qualitative agreement. Future work is recommended to provide a better formulation for the edge-separated droplet diameters. Analysis of film momentum source terms highlights the necessity for including both the gas and hydrostatic pressure source terms within the film momentum transport equation.

This CFD investigation has successfully established a fully coupled two-way DPM-ETFM approach. This work illustrates an advance in bearing chamber modelling capability and has established a necessary foundation for future aeroengine bearing chamber film modelling.
Numerical Analysis and Optimization of Syngas Flow Rates for Gas Turbine for Low Heating Value Fuel
Authors: Zhang Bo , Qin Ye , Yanfei Mu , Shi Shaoping
Published: November 2019

An engineering thermodynamic model has been developed to study the phenomena that large discrepancies found among the different temperature sensors monitoring the exhaust of the gas turbine designed for syngas. The mathematical model utilized large amounts of industrial operation data at different typical power loads for validation and good agreements were found between the measured and calculated exhaust temperature using input boundary conditions not in the training sets. The reason for the large temperature discrepancies of exhaust corresponding to different combustion chambers has been attributed to the deviation between the flow rates of the compressed air from single compressor to different combustion chambers through analysis with the mathematic model. Finally, a method to reduce the temperature discrepancies has been proposed with the mathematic model using industrial operation data from various power loads. The proposed method can quickly calculate the required syngas flow rates to different combustion chambers based on measured differences of exhaust temperatures. The scheme of varying syngas flow rates to different combustion chambers according to the proposed method has been verified by simulation. The impacts to the stability of combustion and NOx emission by the scheme of varying syngas flow rates to different combustion chambers according to the proposed method have also been studied via computational fluid dynamics (CFD) simulations and found that there is little impact on the stability of combustion and it may lead to slightly lower NOx emission for all power loads.
Experiments on a Large Flexure Pivot Journal Bearing: Summary of Test Results and Comparison With Predictions
Authors: Vannini Giuseppe , Cangioli Filippo , Ciulli Enrico , Nuti Matteo , Forte Paola , Kim Jongsoo , Livermore-Hardy Richard
Published: November 2019

Flexure Pivot® Journal Bearings (FPJBs) have typically been used in small high-speed applications such as Integrally Geared Compressors (IGCs) and multistage high-speed compressors, where the temperature management and the rotordynamic stability of the machine are the main targets. Nevertheless, the need for high-speed applications may also be applicable to large compressors and for this reason a large 280mm diameter four-pad FPJB with L/D = 0.7 has been designed, built and tested by the Authors.

The test facility is a novel rig, set up at the University of Pisa, that includes a floating test bearing and a rigid rotor supported by two stiff rolling element bearings. Both static and dynamic loads are applied through hydraulic actuators, capable of 270kN static and 40kN overall dynamic load.

The instrumentation can measure all the relevant test boundary conditions as well as the static and dynamic quantities that characterize the bearing performance.

This paper presents the results from a test campaign conceived to explore not only the design conditions (7000rpm rotational speed and 0.75MPa unit load) but also the sensitivity to the unit load (from 0.2MPa minimum load up to 2.2MPa maximum load) as well as the oil flow. The results are discussed and compared with predictions from an existing numerical code.
Aeroacoustical and Aerodynamical Investigations of Riblets Applied on Low Pressure Turbine Exit Guide Vanes for Two Different Operating Points
Authors: Zenz M. , Hafizovic A. , Simonassi L. , Leitl P. , Heitmeir F. , Marn A.
Published: November 2019

One of the main goals for modern aircrafts is to lower the fuel consumption and noise emissions without worsening the aerodynamic performance. One possibility to lower the fuel consumption is to reduce the skin-friction losses of vanes and blades inside the engine. Therefore, this paper is about the aeroacoustical as well as the aerodynamical effects of a riblet foil applied on the suction side surface of turbine exit guide vanes (TEGVs) of a 1½ stage low pressure turbine (LPT). There have been numerous studies concerning riblets but none using them in a LPT. In general, if riblets are applied on the suction side of vanes or blades, they lower the drag and increase the lift.

Test runs were performed under two different operating points in a subsonic test turbine facility for aerodynamic, aeroacoustic, and aeroelastic investigations (STTF-AAAI) located at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. One operating point was the design point of the riblets and the second one an off-design point. During the test campaign, two different set-ups have been investigated. One configuration with riblets applied on the suction side of the TEGVs, and one configuration with a smooth foil on the vanes to achieve the same thickness as the first set-up. This smooth configuration serves as a reference case. The tested riblet structure was of trapezoid type with 45 μm tip distance and a height to tip distance ratio of 0.45.

The acoustical data has been obtained by using flush mounted condenser microphones, rotated over 360 deg around the flow channel. The aerodynamical data was obtained by using an aerodynamic five-hole-probe as well as a trailing edge probe. Measuring in planes up- and downstream of each TEGV allowed the comparison of a rough pressure loss estimation between the two studied set-ups.

The present work gives a closer insight into the change of the acoustical and aerodynamical behaviour by applying riblets to LPT vanes.