bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficiency of methylene blue‐mediated photodynamic therapy vs intense pulsed light in the treatment of onychomycosis in the toenails
Authors: Alberdi Enrique , Gómez Clara
Published: August 2018

Background

Photodynamic therapy (PDT) or intense pulsed light (IPL) are efficient therapeutic methods in the treatment of superficial skin infections, and thus, they could be good options for onychomycosis treatment, the most common nail disorder.

Methods

Forty patients, affected with different diagnosed types of onychomycosis in nails of the first toe, were randomly divided into two groups of 20 patients to be treated by PDT or IPL. Nail plates were softened with urea 40% by occlusive dressing for 12 hours during 3‐7 days before treatments. Then, eight sessions separated by an interval of 2 weeks of a PDT protocol mediated by methylene blue (MB) and red laser diode (Periowave®, λ = 670 nm, 200 mW) or an IPL protocol based on 10 pulses/cm2 (Dye‐VL‐F module, Alma Lasers, λ = 500‐600 nm, 10 J) were applied.

Results

Both treatments reduced significantly the Onychomycosis Severity Index (OSI) (P < 0.05). In terms of complete cure: 70% (PDT) and 80% (IPL) of the patients reached it after 12 weeks post‐treatment. No patient reported any adverse effects or complications, although in the IPL Group, some referred pain sensation during light irradiation and hematomas apparition.

Conclusions

Photodynamic therapy and IPL were effective for onychomycosis cure of any etiology.
“Closer” or Context? Explaining Donald Trump’s Relations with Congress
Authors: Edwards George C.
Published: August 2018

Donald Trump entered office with aspirations for transformational policy change, much of which would have to be approved by Congress. Despite the president’s many unique characteristics, we can employ the framework of the president’s strategic position to explain his lack of success. The president’s opportunity structure was mixed. He lacked an electoral mandate but was fortunate enough to serve in a unified government. Nevertheless, Republican cohesion was imperfect, partisan polarization was high, and there was little public pressure for Democrats to abate their strong opposition. The structure of most of the choices before Congress did not favor the president. As a result, he has not been successful in obtaining congressional support for most of his major initiatives. Making strategic assessments by asking a few key questions about the president’s political environment provides us with crucial leverage for evaluating a president’s likely success in obtaining the support of Congress for his initiatives.
Missed Connections at the Junction of Sociolinguistics and Speech Processing
Authors: Docherty Gerard , Foulkes Paul , Gonzalez Simon , Mitchell Nathaniel
Published: August 2018

In recent years, significant momentum has built up in efforts to integrate the social with the cognitive in theoretical models of speech production/processing and phonological representation. While acknowledging these advances, we argue that what limits our ability to elaborate models of processing and representation in which social‐indexical properties of speech are effectively integrated is that we remain some way from fully understanding how these properties are manifested within spoken interaction in the first place. We explore some of these limitations, drawing on data from a study of sociophonetic variability in a population of speakers of Australian English. We discuss issues relating to methods for capturing variability in the realization of vowels and consonants, and we highlight the pivotal role of speech style and the challenges that this raises for models of production and processing.
Screening of red blood cells for extracellular vesicle content as a product quality indicator
Authors: Acker Jason P. , Almizraq Ruqayyah J. , Millar Daniel , Maurer‐Spurej Elisabeth
Published: August 2018

BACKGROUND

The controversy around the quality and clinical impact of stored and differentially manufactured red cell concentrates (RCCs) from different donor groups is ongoing. Current studies are limited by the lack of quality measures suitable for routine screening of RCCs. As extracellular vesicles (EVs) are markers of cellular activation or degradation, this study investigated the utility of EV screening to characterize the effects of RBCs production methods and storage.

STUDY DESIGN AND METHODS

RCCs were prepared by whole blood filtration or red blood cell (RBC) filtration methods, centrifuged to prepare a supernatant, and tested for EV content (dynamic light scattering or tunable resistive pulse‐sensing techniques), hemolysis, ATP, and RBC deformability on Days 7, 21, and 42 of storage. To simulate nondestructive quality control (QC) testing, 1 RBC unit was tested in parallel with six 10‐mL aliquots that were stored in small‐volume containers.

RESULTS

EV content showed a linear increase with storage time (p < 0.001) and correlated with supernatant hemoglobin and inversely with ATP or RBC deformability. The method of component manufacturing influenced the characteristics of the EVs during storage. A strong correlation between both EV testing methods' measure of total EV was observed. EV content in the six aliquots were consistent at each time point but statistically higher than in the original RCCs on and after 21 days of storage.

CONCLUSIONS

EV content correlates with measures of hemolysis and other RBC quality indicators and could be implemented as a routine screening tool for nondestructive QC testing of RCCs.
Real-Time Mechanical-Encoding of Needle Shape for Image-Guided Medical and Surgical Interventions
Authors: Abbass Mohamad , Fan Stacy , Barker Kevin , Fenster Aaron , Cepek Jeremy
Published: August 2018

Error and uncertainty in needle placement can drastically impact the clinical outcome of both diagnostic and therapeutic needle-based procedures. In this work, we aim to estimate the shape of a bent needle during insertion and provide a prototype design of a needle whose deflection is tracked in real time. We calculate slope along a needle by measuring the movement of fixed wires running along its length with a compact image-based sensor. Through the use of the Euler–Bernoulli beam theory, we calculate shape and trajectory of a needle. We constructed a prototype needle with two wires fixed along its length and measured wire-movement using a vertical-cavity surface-emitting laser (VCSEL) mouse sensor. This method was able to estimate needle tip deflection within 1 mm in a variety of deflection scenarios in real time. We then provide a design of a needle with real-time deflection tracking in 3D, providing the user with a simple display to convey needle deflection in tissue. This method could be applied to needle-based biopsy or therapy procedures to improve the diagnostic accuracy or treatment delivery quality.
Rotordynamic Characterization of Labyrinth Seals in Steam Turbines: Effects of Thermal and Mechanical Loads
Authors: Cangioli Filippo , Chatterton Steven , Pennacchi Paolo , Nettis Leonardo , Ciuchicchi Lorenzo , Vania Andrea , Vannini Giuseppe
Published: August 2018

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities.

Consequently, a more accurate estimation of the dynamic behavior of the machine has become mandatory as well as the stability assessment. Steam turbines are subjected to high temperatures, high pressures and centrifugal forces that could change the nominal geometry, especially the clearance profile in correspondence of the sealing components, occasionally generating a convergent or divergent annulus.

In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth.

By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different inlet pre-swirl ratios, as well as the stability of the seal are investigated in this paper. The model can be extremely useful for the dynamic characterisation of a wide class of labyrinth seals considering the effect of the surrounding environment on the rotordynamic coefficient prediction.
Large-Eddy Simulation of Turbine Rim Seal Flow
Authors: Pogorelov Alexej , Meinke Matthias , Schröder Wolfgang
Published: August 2018

The flow field in a complete one-stage axial-flow turbine with 30 stator and 62 rotor blades is investigated by large-eddy simulation (LES). To solve the compressible Navier-Stokes equations, a massively parallelized finite-volume flow solver based on an efficient Cartesian cut-cell/level-set approach, which ensures a strict conservation of mass, momentum and energy, is used. This numerical method contains two adaptive Cartesian meshes, one mesh to track the embedded surface boundaries and a second mesh to resolve the fluid domain and to solve the conservation equations. The overall approach allows large scale simulations of turbomachinery applications with multiple relatively moving boundaries in a single frame of reference. The relative motion of the geometries is described by a kinematic motion level-set interface method. The focus of the numerical analysis is on the flow inside the cavity between the stator and the rotor disks. Full 360° computations of the turbine stage with a single lip rim seal geometry are conducted. First, the impact of the mesh resolution on the LES results is analyzed. Second, the LES results are compared to experimental data, followed by a detailed analysis of the flow field inside the rotor-stator wheel space. A dominant mode unrelated to the rotor frequency and its harmonics is identified, which shows a major impact on the ingress of the hot gas into the rotor-stator wheel space.
Experimental Investigation of an Aerodynamically Mistuned Oscillating Compressor Cascade
Authors: Malzacher Leonie , Motta Valentina , Schwarze Christopher , Peitsch Dieter
Published: August 2018

In this paper, the effect of aerodynamic mistuning on stability of a compressor cascade is studied. The experiments have been carried out at a low speed test facility of the Technische Universität Berlin. The test section contains a linear cascade with compressor blades that are forced to oscillate in sinusoidal pitching motion. The aerodynamic mistuning is realized by a blade-to-blade stagger angle variation, three mistuning patterns have been investigated: one-blade mis-staggering, alternating mis-staggering and random mis-staggering. Mis-staggering can have stabilizing or destsabilizing effect, but depends strongly on the amount of the detuning that alters the flow passage. For positive stagger angle variation for the one-blade and alternating mis-staggering, the trend of the damping curve was maintained, in the sense that the unstable interblade phase angles (IBPA) remained unstable. For negative stagger angle variation, one IBPA shifted from stable to unstable. For the random pattern only very moderate changes are observed. The cascade stability was not noticeably effected by the aerodynamic mistuning.
Degradation Feature Extraction of Rolling Bearings Based on Optimal Ensemble Empirical Mode Decomposition and Improved Composite Spectrum Analysis
Authors: Wang Fengli , Chen Hua
Published: August 2018

Rolling bearing is a key part of turbomachinery. The performance and reliability of the bearing is vital to the safe operation of turbomachinery. Therefore, degradation feature extraction of rolling bearing is important to prevent it from failure. During rolling bearing degradation, machine vibration can increase, and this may be used to predict the degradation. The vibration signals are however complicated and nonlinear, making it difficult to extract degradation features effectively. Here, a novel degradation feature extraction method based on optimal ensemble empirical mode decomposition (EEMD) and improved composite spectrum (CS) analysis is proposed. Firstly, because only a few IMFs are expected to contain the information related to bearing fault, EEMD is utilized to pre-process the vibration signals. An optimization method is designed for adaptively determining the appropriate EEMD parameters for the signal, so that the significant feature components of the faulty bearing can be extracted from the signal and separated from background noise and other irrelevant components to bearing faults. Then, Bayesian information criterion (BIC) and correlation kurtosis (CK) are employed to select the sensitive intrinsic mode function (IMF) components and obtain fault information effectively. Finally, an improved CS analysis algorithm is used to fuse the selected sensitive IMF components, and the CS entropy (CSE) is extracted as degradation feature. Experimental data on the test bearings with single point faults separately at the inner race and rolling element were studied to demonstrate the capabilities of the proposed method. The results show that it can assess the bearing degradation status and has good sensitivity and good consistency to the process of bearing degradation.
Telemetric Heat Transfer Coefficient Measurements in an Open Rotor-Stator System Air Gap at up to 8500 rpm
Authors: Heinschke Benjamin , Uffrecht Wieland , Odenbach Stefan , Caspary Volker
Published: August 2018

This contribution presents the experimental results of telemetric heat transfer measurements on the rotor side of an open rotor-stator system air gap with various rotational speeds and rotor-stator distances. For the heat transfer measurements, the local over-temperature method is used, which is based on the analysis of the non-stationary temperature rise of small heated structures at the rotor surface. Additionally, experiments on a second test rig, a flat plate connected with an axial fan, are conducted for the streamwise calibration of the sensors. The measurement program is composed of eight rotational speeds n between 76 and 8,558 rpm at five gap distances s in the range from 1.5 mm to 25 mm at eight radial sensor positions r between 46 and 188 mm. Overall the test rig installation is equivalent to a rotational Reynolds number range Rer from 1,085 to 2,040,000. An evaluation and interpretation of the results shows that the characteristic correlation between the Reynolds number and the Nusselt number is similar to that used for the turbulent flow at a free rotating disc. The variation of the gap distance leads to a constant offset in the heat transfer coefficient, which becomes significantly higher with small distances.
A Numerical and Experimental Investigation of the Impact of Mixed Flow Turbine Inlet Cone Angle and Inlet Blade Angle
Authors: Leonard Thomas , Spence Stephen , Filsinger Dietmar , Starke Andre
Published: August 2018

Mixed flow turbines offer potential benefits for turbocharged engines when considering off-design performance and engine transient behaviour. Although the performance and use of mixed flow turbines is described in the literature, little is published on the combined impact of the cone angle and the inlet blade angle, which are the defining features of such turbines.

Numerical simulations were completed using a CFD model that was validated against experimental measurements for a baseline geometry. The mechanical impact of the design changes was also analysed. Based on the results of the numerical study, two rotors of different blade angle and cone angle were selected and manufactured. These rotors were tested using the QUB low temperature turbine test rig, which allowed for accurate and wide range mapping of the turbine performance to low values of velocity ratio. The performance results from these additional rotors were used to further validate the numerical findings.

The numerical model was used to understand the underlying physical reasons for the measured performance differences through detailed consideration of the flow field at rotor inlet, and to document how the loss mechanisms and secondary flow structures developed with varying rotor inlet geometry. It was observed that large inlet blade cone angles resulted in strong separation and flow blockage near the hub at off-design conditions, which greatly reduced efficiency. However, the significant rotor inertia benefits achieved with the large blade cone angles were shown to compensate for the efficiency penalties and could be expected to deliver improved transient performance in downsized automotive engine applications.
Evaluation of the Optimal Point Variation of the S-CO2 Cycle While Considering Internal Pinch in Recuperator
Authors: Son Seongmin , Heo Jin Young , Lee Jeong Ik
Published: August 2018

The Supercritical CO2 power cycle (S-CO2 cycle) is the power cycle that adopts CO2 as a working fluid and is designed to have a compression process near the critical point of CO2. Due to the non-linearity of CO2 pyhsical properties near the critical point, the S-CO2 cycle needs relatively less compression work. Therefore, the efficiency of the S-CO2 cycle is higher than traditional gas cycles. Furthermore, because of the relatively high system minimum pressure (near the critical point, ∼7.39 MPa), an S-CO2 cycle can be composed of smaller turbomachines. Considering these advantages, nowadays, there are many attempts to apply S-CO2 cycles to various fields, such as waste heat recovery, nuclear, coal, concentrated solar power plant and so on. These non-linear pyhsical properties become the cause of some unique issues. One of the most significant issues is the internal pinch point problem in a recuperator. Unlike the traditional gas-to-gas heat exchanger, each hot and cold side of the S-CO2 recuperator goes through the severe change of specific heat. This dramatic change of specific heat may cause the internal pinch point of the recuperator. When the internal pinch point phenomenon occurs, the performance of the recuperator may not able to be evaluated from the pre-fixed effectiveness. This can be an issue when the compressor inlet temperature decreases to transcritical or subcritical region. This may alter the optimal point of the S-CO2 power cycle. In this paper, optimal design points and optimal performance of the S-CO2 power cycle are tracked with the consideration of the internal pinch point phenomenon. While changing the system boundary conditions, the optimal point variation due to internal pinch point phenomenon is evaluated and compared with a traditional methodology. This research is progressed with an in-house integrated S-CO2 power cycle analysis code, which is named KAIST – ESCA (Evaluator for Supercritical CO2 Cycle based on Adjoint method). The target cycle layouts are Simple Recuperated, Intercooling, Recompression and Recompression with intercooling layouts. Both of the S-CO2 Rankine and Brayton cycles conditions are considered.
Conjugate Heat Transfer Analysis on Generic Rim Seal Configurations in Rotor-Stator System
Authors: Jia Xingyun , Wang Liguo , Zheng Qun , Zhang Hai , Jiang Yuting
Published: August 2018

Performance of generic rim seal configurations, axial-clearance rim seal (ACS), radial-clearance rim seal (RCS), radial-axial clearance rim seal (RACS) are compared under realistic working conditions. Conjugate heat transfer analysis on rim seal is performed in this paper to understand the impact of ingestion on disc temperature.

Results show that seal effectiveness and cooling effectiveness of RACS are the best when compared with ACS and RCS, the minimum mass flow rate for seal of RACS is 75% of that of RCS, and 34.6% of ACS. Authors compare the disc temperature distribution between different generic rim seal configurations where the RACS seems to be favorable in terms of low disc temperature. In addition, RACS has higher air-cooled aerodynamic efficiency, minimizing the mainstream performance penalty when compared with ACS and RCS. Corresponding to the respective minimum mass flow rate for seal, the air-cooled aerodynamic efficiency of RACS is 23.71% higher than that of ACS, and 12.79% higher than the RCS.
Tilting-Pad Journal Bearing in Hybrid Operation: A Numerical and Experimental Investigation
Authors: Buchhorn Nico , Kukla Sebastian , Bender Beate , Neumann Marc
Published: August 2018

Large turbine bearings are usually equipped with hydrostatic jacking mechanisms to separate bearing and shaft during transient start-stop procedures. They are turned off once hydrodynamic operation is reached. In some cases, under severe operating conditions, the hydrostatic oil supply is kept running although the rotor already runs in full speed. The supplied amount of jacking oil is very small compared to the regular oil supply. However, experimental data of a large tilting-pad bearing shows that this hybrid operation has a considerable impact on the load carrying capacity in terms of lower pad temperature and larger film thickness.

In this paper, a theoretical investigation to analyse the effect of increased load carrying capacity of a large tilting-pad journal bearing in hybrid operation is presented. The increase is driven by three different aspects: 1) hydrostatic pressure component, 2) increase in lubricant viscosity due to the injection of cold oil, 3) decrease of temperature gradients and thus thermal pad deformation.

Subject of the approach is a ø500 mm five-pad, rocker-pivot tilting-pad journal bearing in flooded lubrication mode. The experiments are carried out on the Bochum test rig for large turbine bearings. The theoretical analyses are performed with a simulation code solving the Reynolds and energy equations for the oil film and calculating the thermomechanical pad deformations simultaneously. By considering each of the three above aspects separately and in combination, their share of load increase can be assessed individually. Contrary to expectations, the results indicate that the increase is not mostly based on the hydrostatic pressure component. Instead, the advantageously decreased pad deformations make the largest contribution to the increased load carrying capacity while the alteration in viscosity shows the least impact.
Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows: Part II — Effect of Axial Distance Between a Swirl Breaker and Rotor Shroud on Efficiency Improvement
Authors: Duan Chongfei , Fukushima Hisataka , Segawa Kiyoshi , Shibata Takanori , Fujii Hidetoshi
Published: August 2018

The basic principle of a distinct idea to reduce an aerodynamic mixing loss induced by the difference in tangential velocity between mainstream flow and rotor shroud leakage flow is presented in “Part I – Design Concept and Typical Performance of a Swirl Breaker” The design concept offers an effective geometry for improving steam turbine stage efficiency. When the swirl breaker is installed in the circulating region of leakage flow at the rotor shroud exit cavity, the axial distance between the swirl breaker and rotor shroud is a crucial factor to trap the leakage flow into the swirl breaker cavity. In this Part II of the study, five cases of swirl breaker geometry with different axial distances between the swirl breaker and rotor shroud, which covered a range for the stage axial distance of actual high and intermediate (HIP) pressure steam turbines, were investigated using computational fluid dynamics (CFD) analysis and tests. Compared to a conventional single-stage CFD analysis, by conducting an additional single-rotor analysis with the modified shear stress transport (SST) model coefficient, the prediction accuracy for typical improvements in stage efficiency was increased in comparison to the single-stage analysis with the default SST model. Based on CFD results, the verification tests were conducted in a 1.5-stage air model turbine. By decreasing the axial distance between the swirl breaker and rotor shroud, the tangential velocity and the mixing region in the tip side which is influenced by the rotor shroud leakage flow were decreased and the stage efficiency was increased. The case of the shortest axial distance between the swirl breaker and rotor shroud increased turbine stage efficiency by 0.7% compared to the conventional cavity geometry. In addition, the unsteady pressure was measured in the swirl breaker cavity to evaluate the structural reliability of the swirl breaker. These results showed the maximum pressure fluctuation was only 0.7% of the entire flow pressure. Consequently, both performance characteristics and structural reliability of swirl breaker were verified for application to real steam turbines.
Mission Analysis and Operational Optimization of Adaptive Cycle Micro-Turbofan Engine in Surveillance and Firefighting Scenarios
Authors: Palman M. , Leizeronok B. , Cukurel B.
Published: August 2018

The current work focuses on mission based evaluation of a novel engine architecture arising from the conversion of a micro turbojet to a micro turbofan via introduction of a variable speed fan and bypass nozzle. The solution significantly improves maximum thrust by 260%, reduces fuel consumption by as much as 60% through maintaining the core independently running at its optimum, and enables a wider operational range, all the meanwhile preserving a simple single spool configuration. Particularly, the introduction of a variable speed fan, enables real-time optimization for both high speed cruise and low speed loitering. In order to characterize the performance of the adaptive cycle engine with increased number of controls (engine speed, gear ratio, bypass opening), a component map based thermodynamic study is used to contrast it against other similar propulsion systems with incrementally reduced input variables. In following, a shortest path based optimization is conducted over the locally minimum fuel consumption operating points, based on a set of gradient driven connectivity constraints for changes in gear ratio and bypass nozzle area. The resultant state transition graphs provide global optimum for fuel consumption at a thrust range in a given altitude and Mach flight envelope. Then, the engine model is coupled to a flight mechanics solver supplied with a conceptual design for a representative multipurpose UAV. Lastly, the associated mission benefits are demonstrated in surveillance and firefighting scenarios.
A Machine Learning Based Approach of Performance Estimation for High-Pressure Compressor Airfoils
Authors: Marx Jonas , Gantner Stefan , Städing Jörn , Friedrichs Jens
Published: August 2018

In recent years, the demands of Maintenance, Repair and Overhaul (MRO) customers to provide resource-efficient after market services have grown increasingly. One way to meet these requirements is by making use of predictive maintenance methods. These are ideas that involve the derivation of workscoping guidance by assessing and processing previously unused or undocumented service data. In this context a novel approach on predictive maintenance is presented in form of a performance-based classification method for high pressure compressor (HPC) airfoils. The procedure features machine learning algorithms that establish a relation between the airfoil geometry and the associated aerodynamic behavior and is hereby able to divide individual operating characteristics into a finite number of distinct aero-classes. By this means the introduced method not only provides a fast and simple way to assess piece part performance through geometrical data, but also facilitates the consideration of stage matching (axial as well as circumferential) in a simplified manner. It thus serves as prerequisite for an improved customary HPC performance workscope as well as for an automated optimization process for compressor buildup with used or repaired material that would be applicable in an MRO environment. The methods of machine learning that are used in the present work enable the formation of distinct groups of similar aero-performance by unsupervised (step 1) and supervised learning (step 2). The application of the overall classification procedure is shown exemplary on an artificially generated dataset based on real characteristics of a front and a rear rotor of a 10-stage axial compressor that contains both geometry as well as aerodynamic information. In step 1 of the investigation only the aerodynamic quantities in terms of multivariate functional data are used in order to benchmark different clustering algorithms and generate a foundation for a geometry-based aero-classification. Corresponding classifiers are created in step 2 by means of both, the k Nearest Neighbor and the linear Support Vector Machine algorithms. The methods’ fidelities are brought to the test with the attempt to recover the aero-based similarity classes solely by using normalized and reduced geometry data. This results in high classification probabilities of up to 96 % which is proven by using stratified k-fold cross-validation.
Analysis of Performance of a Twin-Shaft Gas Turbine During Hot-End Damage in the Gas Generator Turbine
Authors: Cruz-Manzo Samuel , Maleki Sepehr , Panov Vili , Agbonzikilo Festus , Zhang Yu , Latimer Anthony
Published: August 2018

In this study, an analysis of the performance of a twin-shaft industrial gas turbine (IGT) during hot-end damage in the gas generator turbine (GGT) at high-power operation has been carried out using a validated Simulink IGT model. The Simulink model is based on fundamental thermodynamics and allows the implementation of correlation coefficients in the GGT module to predict the performance of the IGT system during a hot-end GGT damage incident. Measured field data from a twin-shaft IGT operated as a power generation unit denoting a reduction in performance due to hot-end GGT damage are considered for the analysis. Four hot-end GGT damage incidents across a range of measured field data have been identified and considered for the analysis. The results show that the Simulink model can predict the change of physical parameters (pressure, temperature) across the IGT system for each GGT damage incident. Hot-end damage increases the flow capacity and reduces the efficiency of the GGT. Future work will validate the dynamic change of flow capacity and efficiency during different GGT damage incidents.
Influence of Relative Velocity Ratio on Centrifugal Impellers Operating With Supercritical CO2
Authors: Liu Haiqing , Chi Zhongran , Zang Shusheng
Published: August 2018

The supercritical CO2 gas turbine is considered to achieve a high cycle efficiency by reducing compressor work near the critical point. But test loops made by international community show that the performance of the compressor is still quite far from the target at the design point. The paper focuses on the influence of relative velocity ratio on the performances of centrifugal impellers operating with real gas CO2 and ideal gas CO2. At the same time, comparisons between characteristic curves of impellers operating at near critical, supercritical, and subcritical inlet condition with real gas CO2 are also demonstrated. Relative velocity ratio demonstrates the same trend with real and ideal gas CO2 in the same impeller, but the specific value is different. Impellers with real gas CO2 could achieve a high isentropic efficiency when relative velocity ratio is in the range of 1.05∼1.5. The results show that relative velocity ratio plays an important role in compressor performance.
Investigation of Fan Blades Vibration due to Blade/Casing Rubbing Interactions Using In-Plane Two-Dimensional Model
Authors: Xiao Jiaguangyi , Chen Yong , Ouyang Hua , Wang Anjenq
Published: August 2018

Interactions between casings and bladed-disks of modern turbofan engines may occur through various mechanisms: casing distortions, rotor vibrations and casing vibrations to name a few. These interactions might lead to nonlinear blade vibrations, which could then induce severe damages to both structures. The impacts of casing vibrations on the vibration behaviors of engine blades are studied in this paper.

A two-dimensional in-plane model is established in this paper. Fan blade, disk and casing are modeled using beam element. Craig-Bampton model reduction is applied to simplify the model. Penalty method mixed with golden section method is created and used for contact treatments. The interaction is initiated by the external forces acting on the casing. The casing is excited to two-, three- and four-nodal diameter vibration patterns, respectively. In order to capture the core of the problem, contact forces applied to the casing, and casing damping are neglected. Steady casing vibrations could thus be generated. Blade vibrations are calculated in a wide rotating speed range, maximum amplitudes are recorded and studied. The results show that the bladed-disk will have several vibration peaks in the calculated rotating speed range. To figure out the physical mechanisms of these peaks, Fourier spectrums as well as different bladed-disk materials are introduced.

Almost all vibration peaks can be explained by three kinds of mechanisms found and summarized in this paper. Two of them are related to travelling waves and the third is related to harmonics. Speed and frequency margins that are related to blade-tip-rub induced vibrations are defined and analyzed. The findings and ideas shown in this paper can be used as a reference in engine preliminary structural design to avoid potential blade tip-rub induced damages.
Blowoff and Reattachment Dynamics of a Linear Multi-Nozzle Combustor
Authors: Kwong W. Y. , Steinberg A. M.
Published: August 2018

This paper describes the coupled flow and flame dynamics during blowoff and reattachment events in a combustor consisting of a linear array of five interacting nozzles using 10 kHz repetition-rate OH planar laser induced fluorescence and stereoscopic particle image velocimetry. Steady operating conditions were studied at which the three central flames randomly blew-off and subsequently reattached to the bluff-bodies. Transition of the flame from one nozzle was rapidly followed by transition of the other nozzles, indicating cross-nozzle coupling. Blow-off transitions were preferentially initiated in one of the off-center nozzles, with the transition of subsequent nozzles occurring in a random order. Similarly, the center nozzle tended to be the last nozzle to reattach.

The blowoff process of any individual nozzle was similar to that for a single bluff-body stabilized flame, though with cross-flame interactions providing additional means of re-stabilizing a partially extinguished flame. Subsequent to blowoff of the first nozzle, the other nozzles underwent similar blowoff processes. Flame reattachment was initiated by entrainment of a burning pocket into a recirculation zone, followed by transport to the bluff-body; the other nozzles subsequently underwent similar reattachment processes. Several forms of cross-nozzle interaction that can promote or prevent transition are identified. Furthermore, the velocity measurements indicated that blowoff or reattachment of the first nozzle during a multi-nozzle transition causes significant changes to the flow fields of the other nozzles. It is proposed that a single nozzle transition redistributes the flow to the other nozzles in a manner that promotes their transition.
Failure Assessment of Test Coupons: Comparison Between Model Predictions and Test Results
Authors: Roychowdhury Sushovan , Månsson Tomas , Hansson Thomas
Published: August 2018

A common requirement for engine structures designed in the aviation industry is the ability to withstand the limit and ultimate loads with a flaw of certain size. Thus, reliable prediction of failure load is of utmost importance. In this paper, predictions from several applicable failure criteria are compared with test results. The tests are carried out on simple coupons with a rectangular cross-section and containing a surface crack. Majority of the tests are carried out under tensile loads and a few under bending loads. The tests correspond to two titanium alloys and two nickel-based super-alloys. The tests span a wide range of temperature (room temp to 700° C), and two forms, namely, cast and forged. In total over 200 test results are obtained and compared with predictions. The predictive models include (i) elasto-plastic J-integral analysis through FEA (ii) Failure Assessment Diagram (R6v3 and SINTAP) (iii) elastic stress intensity factor (LEFM) and (iv) average stress over remaining cross-section. The comparisons demonstrate that the R6v3 FAD method provide a reasonable estimate of the failure load for the test coupon geometry with surface cracks. The average stress approach, though works well for purely tensile loading, cannot cope with bending-dominated loads. On the other hand, predictions from LEFM approach can be non-conservative by up to a factor of two.
Reverse Thrust Aerodynamics of Variable Pitch Fans
Authors: Williams Tim S. , Hall Cesare A.
Published: August 2018

Variable pitch fans are of interest for future low pressure ratio fan systems since they provide improved operability relative to fixed pitch fans. If they can also be re-pitched such that they generate sufficient reverse thrust they could eliminate the engine drag and weight penalty associated with bypass duct thrust reversers. This paper sets out to understand the details of the 3D fan stage flow field in reverse thrust operation.

The study uses the Advanced Ducted Propulsor variable pitch fan test case, which has a design fan pressure ratio of 1.29. Comparison with spanwise probe measurements show that the computational approach is valid for examining the variation of loss and work in the rotor in forward thrust. The method is then extended to a reverse thrust configuration using an extended domain and appropriate boundary conditions.

Computations, run at two rotor stagger settings, show that the spanwise variation in relative flow angle onto the rotor aligns poorly to the rotor inlet metal angle. This leads to two dominant rotor loss sources: one at the tip associated with positive incidence, and the second caused by negative incidence at lower span fractions. The second loss is reduced by opening the rotor stagger setting, and the first increases with rotor suction surface Mach number. The higher mass flow at more open rotor settings provide higher gross thrust, up to 49% of the forward take-off value, but is limited by the increased loss at high speed.
Probabilistic Design of Radial Pins Constraint System in a Gas Turbine Annular Combustion Chamber
Authors: Funghi Federico , di Sisto Paolo
Published: August 2018

One of the possible constraint configuration of an annular combustion chamber in a gas turbine is by means of radial pins. Radial pins usually connect the outer turbine casing to the combustor dome and fix combustor axial and circumferential displacements while allowing combustor free radial deformation, under thermal loads. In the typical mounting scheme, radial pins are screwed on the outer casing and then inserted into dedicated housing holes on the dome. Because of this arrangement the force (introduced by mechanical, thermal and dynamic loads) reacted by each pin is inherently not deterministic since it depends on the actual gap between the pin itself and the housing bush on the dome, which, in turn, is not explicitly known, being a function of the overall tolerance stack up. The scope of this study was to develop a method to design the radial pins of NovaLT™16 (*) combustion chamber, applicable since the conceptual phase, using a probabilistic approach [7]. Actual pin-bush gap distribution is calculated from stack up analysis and then used as input for a numerical simulation which computes the distribution of the reaction force on each pin, as a function of number of pins, stiffness of the pin, gap between pin and bush. Two different arrangements have been considered: the classic scheme and the floating pin configuration. The new probabilistic design approach allowed to have a robust understanding of the force distribution within the whole set of pins, to compute the optimal combination of pin number, pin stiffness, and gap and ultimately to select the floating pin configuration as the one to be implemented in NovaLT16 combustor. Test results revealed pin contact distribution was in line with predictions.
Hydrodynamic Journal Bearings Optimization Considering Rotor Dynamics Restrictions
Authors: Moroz Leonid , Romanenko Leonid , Kochurov Roman , Kashtanov Evgen
Published: August 2018

In this study, optimal designs of hydrodynamic journal bearings for 13.5 MW induction motor prototype is developed based on the design of experiment approach and best sequences method which involves entire rotor-bearing system multidisciplinary simulations. These simulations consist of bearing hydrodynamic characteristics calculation and optimization and rotor dynamics analyses for a rotor-bearing system. The results of rotor dynamics analyses are taken into account as the constraints during optimization.

Several journal bearings such as plain cylindrical with a different configuration of pockets, elliptical type, and 4-lobe fixed pad have been considered to select the most appropriate design for the application. The bearing clearance, length, diameter, pockets positions, lobe width, oil viscosity, are applied as design input variables. To find the bearing optimal design, following objective functions were considered:

1) Minimum oil film thickness. Optimal bearing clearance is designed to produce the maximum possible level of minimum oil film thickness in order to avoid or reduce possible metal-to-metal contact;

2) Maximization of the performance is done by minimization of friction power loss.

3) Rotor dynamics simulation for the rotor-bearing system is embedded in the optimization process in order to avoid resonances by providing sufficient critical speeds separation margins from operating speed.

The methodology for the bearing simulation is based on the mass-conserving mathematical model, proposed by Elrod & Adams and numerical solution for the equations is generated using finite difference method. Rotor dynamics analyses are performed using finite element method.

As the result of the study, optimized bearing designs for 13.5 MW induction motor were generated. Optimized bearings provide sufficient frequency margins for critical speeds for the rotor-bearing system and, at the same time, improved hydrodynamic bearing characteristics: maximized oil film thickness and increased efficiency compared to the starting design.

Through the considered bearings examples, the study shows how different parameters, such as bearing clearance, length, diameter, and etc., influence key performance characteristics like bearing minimum oil film thickness, friction power losses, rotor-bearing system critical speeds.
Thermoacoustics of Can-Annular Combustors
Authors: Ghirardo G. , Di Giovine C. , Moeck J. P. , Bothien M. R.
Published: August 2018

Can-annular combustors consist of a set of independent cans, connected on the upstream side to the combustor plenum, and on the downstream side to the turbine inlet, where a transition duct links the round geometry of each can with the annular segment of the turbine inlet. Each transition duct is open on the sides towards the adjacent transition ducts, so that neighbouring cans are acoustically connected through a so called cross-talk open area. This theoretical, numerical and experimental work discusses the effect that this communication has on the thermoacoustic frequencies of the combustor. We show how this communication gives rise to axial and azimuthal modes, and that these correspond to particularly synchronised states of axial thermoacoustic oscillations in each individual can. We show that these combustors typically show clusters of thermoacoustic modes with very close frequencies and that a slight loss of rotational symmetry, e.g. a different acoustic response of certain cans, can lead to mode localization. We corroborate the predictions of azimuthal modes, clusters of eigenmodes and mode localization with experimental evidence.
Demonstration of Bleed Air Recirculation System to Improve Part Load Efficiency of Solar Mars® 100 DLE Industrial Gas Turbine
Authors: Cowell Luke , Reynolds Simon , Caron Tim , Zhang Donghui
Published: August 2018

On two-shaft DLE (Dry Low Emissions) gas turbines compressor air is often bled off the combustor housing to control the combustor flame temperature for part load emissions management. The bleed air is typically directed into the exhaust ducting, bypassing the turbine, causing engine efficiency to decrease. A prototype bleed air recirculation system was fitted onto a compressor package in the field that redirects bleed flow from the engine exhaust to the air inlet to raise the air temperature entering the engine. This system is designed to reduce the amount of bleed air required at a given ambient operating condition, while not compromising emissions, to increase part load efficiency.

The bleed air recirculation system was designed, built, installed, and tested on a Mars 16000S compressor package at a station in northern Pennsylvania. A control algorithm was developed and validated to control bleed air recirculation so that package durability was not impacted. Over an evaluation period of 12 months, no significant durability issues or degradation were noted.

The on-site evaluation indicated that the engine’s heat rate is significantly improved by using bleed air recirculation. The heat rate was reduced by as much as 7% during testing at site with a strong dependency on the engine operating load and ambient temperature. As predicted the best case was demonstrated at 50% load and at colder ambient conditions. The NOx emissions were also improved with bleed air recirculation. In addition, using this system extended the range of low emissions operation to lower loads. No effects on compressor surge or sound emissions were detected.
Vibration Control for Rotor Mounted on a Novel Active Bump Type Foil Bearing With Controllable Mechanical Preloads
Authors: Guan Hanqing , Liu Tianyu , Zhang Tao , Feng Kai , Guo Zhiyang
Published: August 2018

A novel active bump type foil bearing (ABFB) is put forward aims at demonstrate the feasibility of applying active lubrication control of the aerodynamic gas bearing. The proposed active structure consists of (1) piezoelectric actuators (PZTs) amounted in the bearing housing to produce control forces, (2) flexure hinges machined in the bearing housing to produce pivot for the lever amplifier, (3) lever amplifier machined in the bearing housing to amplify the deformation of PZTs. The mechanical preloads of the ABFB can be actively adjusted by using lever amplifiers which is actuated and controlled by the controlling the driving voltage on PZTs to create variable multiple lobe clearance and realizing the real time shape changing of the lubricate gas film. The static load-deformation test of the ABFB is done to demonstrate that the preload of the bearing is significantly adjusted by changing the driving voltage on PZTs. The lift-off tests versus different driving voltages of the ABFB are done to illustrate that the change of the preloads can significantly affect the drag torque of the ABFB and illustrate the significance of the active control. Rotordynamic tests of the ABFB with different driving voltages have been conducted. Subsynchronous vibrations of the rotor have been suppressed significantly by increasing the driving voltage. The coast-down time increases with the increase of the driving voltage on PZTs. At the rotational speed of 33krpm, the amplitude of the whip motion can be suppressed timely and actively by controlling the driving voltage on PZTs.