bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Agglomeration Affect Exports? Evidence from Italian Local Labour Markets
Authors: Cainelli Giulio , Di Maria Eleonora , Ganau Roberto
Published: September 2016

This paper analyses whether and how agglomeration economies – related variety, specialisation and urbanisation – affect the export performance of Italian local labour markets (LLM). Adopting spatial econometric techniques, and controlling for potential non‐linear effects, we find that related variety has a negligible effect on LLMs’ export intensity, while the effect of specialisation economies is negative. On the contrary, urbanisation economies positively affect export intensity. The robustness of these results is tested and confirmed using an alternative (institutional‐based) spatial weights matrix.
Degree bounds on homology and a conjecture of Derksen
Authors: Chardin Marc , Symonds Peter
Published: September 2016

Harm Derksen made a conjecture concerning degree bounds for the syzygies of rings of polynomial invariants in the non-modular case [Degree bounds for syzygies of invariants, Adv. Math. 185 (2004), 207–214]. We provide counterexamples to this conjecture, but also prove a slightly weakened version. We also prove some general results that give degree bounds on the homology of complexes and of $\text{Tor}\,$ groups.
On the Bateman–Horn conjecture for polynomials over large finite fields
Authors: Entin Alexei
Published: September 2016

We prove an analogue of the classical Bateman–Horn conjecture on prime values of polynomials for the ring of polynomials over a large finite field. Namely, given non-associate, irreducible, separable and monic (in the variable$x$) polynomials$F_{1},\ldots ,F_{m}\in \mathbf{F}_{q}[t][x]$, we show that the number of$f\in \mathbf{F}_{q}[t]$of degree$n\geqslant \max (3,\deg _{t}F_{1},\ldots ,\deg _{t}F_{m})$such that all$F_{i}(t,f)\in \mathbf{F}_{q}[t],1\leqslant i\leqslant m$, are irreducible is$$\begin{eqnarray}\displaystyle \biggl(\mathop{\prod }_{i=1}^{m}\frac{\unicode[STIX]{x1D707}_{i}}{N_{i}}\biggr)q^{n+1}(1+O_{m,\,\max \deg F_{i},\,n}(q^{-1/2})), & & \displaystyle \nonumber\end{eqnarray}$$where$N_{i}=n\deg _{x}F_{i}$is the generic degree of$F_{i}(t,f)$for$\deg f=n$and$\unicode[STIX]{x1D707}_{i}$is the number of factors into which$F_{i}$splits over$\overline{\mathbf{F}}_{q}$. Our proof relies on the classification of finite simple groups. We will also prove the same result for non-associate, irreducible and separable (over$\mathbf{F}_{q}(t)$) polynomials$F_{1},\ldots ,F_{m}$not necessarily monic in$x$under the assumptions that$n$is greater than the number of geometric points of multiplicity greater than two on the (possibly reducible) affine plane curve$C$defined by the equation$$\begin{eqnarray}\displaystyle \mathop{\prod }_{i=1}^{m}F_{i}(t,x)=0 & & \displaystyle \nonumber\end{eqnarray}$$(this number is always bounded above by$(\sum _{i=1}^{m}\deg F_{i})^{2}/2$, where$\deg$denotes the total degree in$t,x$) and$$\begin{eqnarray}\displaystyle p=\text{char}\,\mathbf{F}_{q}>\max _{1\leqslant i\leqslant m}N_{i}, & & \displaystyle \nonumber\end{eqnarray}$$where$N_{i}$is the generic degree of$F_{i}(t,f)$for$\deg f=n$.
Regression Models for Output Prediction of Thermal Dynamics in Buildings
Authors: Chasparis Georgios C. , Natschlaeger Thomas
Published: September 2016

Standard (black-box) regression models may not necessarily suffice for accurate identification and prediction of thermal dynamics in buildings. This is particularly apparent when either the flow rate or the inlet temperature of the thermal medium varies significantly with time. To this end, this paper analytically derives, using physical insight, and investigates linear regression models (LRMs) with nonlinear regressors (NRMs) for system identification and prediction of thermal dynamics in buildings. Comparison is performed with standard linear regression models with respect to both (a) identification error and (b) prediction performance within a model-predictive-control implementation for climate control in a residential building. The implementation is performed through the EnergyPlus building simulator and demonstrates that a careful consideration of the nonlinear effects may provide significant benefits with respect to the power consumption.
Performance Definitions for Three-Fluid Heat and Moisture Exchangers
Authors: Abdel-Salam Mohamed R. H. , Besant Robert W. , Simonson Carey J.
Published: September 2016

This paper presents performance definitions for calculating the overall effectiveness of three-fluid heat and moisture exchangers. The three-fluid heat and moisture exchanger considered in this paper is a combination of a liquid-to-liquid heat exchanger for heat transfer between a desiccant solution and a refrigerant and an energy exchanger for heat and moisture transfer between desiccant solution and air streams. The performance definitions presented in this paper are used to calculate the overall sensible and latent effectivenesses of a three-fluid heat and moisture exchanger, which has been tested under air cooling and dehumidifying operating conditions in a previous work (Abdel-Salam et al., 2016, “Design and Testing of a Novel 3-Fluid Liquid-to-Air Membrane Energy Exchanger (3-Fluid LAMEE),” Int. J. Heat Mass Transfer, 92, pp. 312–329). The effectiveness of this three-fluid heat and moisture exchanger is compared when calculated using the traditional energy exchanger effectiveness equations and the overall performance definitions. Results show that the overall performance definitions provide effectiveness values that are less sensitive to changes in the inlet refrigerant temperature and therefore are more generally applicable for energy exchanger design than the traditional effectiveness equations used in the literature.
Numerical Study on the Effect of Tandem Spacing on Flow-Induced Motions of Two Cylinders With Passive Turbulence Control
Authors: Ding Lin , Zhang Li , Wu Chunmei , Soo Kim Eun , Bernitsas Michael M.
Published: September 2016

The effect of tandem spacing on the flow-induced motions (FIM) of two circular cylinders with passive turbulence control is investigated using two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model. Results are compared to experiments in the range of Reynolds number of 30,000 < Re < 100,000. The center-to-center spacing between the two cylinders is varied from 2 to 6 diameters. Simulation results predict well all the ranges of FIM including vortex-induced vibrations (VIV) and galloping and match well with experimental measurements. For the upstream cylinder, the amplitude and frequency responses are not considerably influenced by the downstream cylinder when the spacing is greater than 2D. For the downstream cylinder, a rising amplitude trend in the VIV upper-branch can be observed in all the cases as is typical of flows in the TrSL3 flow regime (transition in shear layer 3; 2 × 104 < Re < 3 × 105). The galloping branch merges with the VIV upper-branch for spacing greater than three-dimensional (3D). Vortex structures show significant variation in different flow regimes in accordance with experimental observations. High-resolution postprocessing shows that the interaction between the wakes of cylinders results in various types of FIM.
On Vibration Suppression and Energy Dissipation Using Tuned Mass Particle Damper
Authors: Li Shilong , Tang J.
Published: September 2016

Particle damping has the promising potential for attenuating unwanted vibrations in harsh environments especially under high temperatures where conventional damping materials would not be functional. Nevertheless, a limitation of simple particle damper (PD) configuration is that the damping effect is insignificant if the local displacement/acceleration is low. In this research, we investigate the performance of a tuned mass particle damper (TMPD) in which the particle damping mechanism is integrated into a tuned mass damper (TMD) configuration. The essential idea is to combine the respective advantages of these two damping concepts and in particular to utilize the tuned mass damper configuration as a motion magnifier to amplify the energy dissipation capability of particle damper when the local displacement/acceleration of the host structure is low. We formulate a first-principle-based dynamic model of the integrated system and analyze the particle motion by using the discrete element method (DEM). We perform systematic parametric studies to elucidate the damping effect and energy dissipation mechanism of a TMPD. We demonstrate that a TMPD can provide significant vibration suppression capability, essentially outperforming conventional particle damper.
Vibration Analysis of Pipes Supported by a Flexible Tank Wall Considering the Support Clearances
Authors: Utsumi M.
Published: September 2016

The vibration of pipes supported by a flexible tank wall is analyzed taking into account the hydroelastic vibration of the tank and the nonlinearity caused by the support clearances. Because the support clearances increase the pipe displacement, it is important to examine whether the support clearances augment the pipe stress. We illustrate that the support clearances can cause an increase in the pipe stress not only due to the increase in pipe displacement but also to the difference between elastic behaviors of the tank wall and pipes. The tank wall and pipes are dominated by membrane and bending deformations, respectively. Furthermore, we illustrate that the support clearances render a stress reduction method ineffective. In this study, a semi-analytical method is applied, rather than a full finite element analysis. The semianalytical method is helpful not only for computationally efficient analysis but also for gaining physical insight into the clearance-nonlinearity-induced stress behaviors noted above.
Gas Dynamic Face Seal Tightness Under Non-Stationary Loading
Authors: Badykov Renat R. , Vinogradov Aleksandr S.
Published: September 2016

Aircraft engines have multiple operation modes for different flight conditions. However, each element of an engine is generally designed for one particular operating mode (maximum load or maximum duration). Mode alteration leads to the variation of pressure and temperature in sealing cavities. Therefore, it is important to consider the full load range into the design process of separate units. This paper presents an original technique of leakage calculation for the spiral-grooved mechanical gas face seal on the different operation modes of the aircraft engine. This type of seal has never used in aircraft engine design. However it has a history of excellent performances in comparison with the traditional type of seals, such as labyrinth or face contact seals. The value of sealing rings deformation must be determined for all operation modes. The flow model of the gas face seal is used to define heat transfer coefficients of seal ring surfaces. Using transient analysis, the influence of the load change rate on the sealing rings can be determined. The developed technique investigates the effect of the engine operating mode alteration on the temperature loads and deformations. Results of the simulation are compared with the experimental data.
Rapid Close of a Butterfly Valve Placed in a Curved Channel: A Computational Study of Unsteady Steam Flow and Aerodynamic Torque
Authors: Wang Peng , Liu Yingzheng , Hu Zhiqiang , Xu Sihua
Published: September 2016

The transient steam flow inside a curved channel, which is embedded with dual butterfly valves (stop valve & throttle valve), was numerically simulated when the throttle valve was rapidly closed. Two cases with different closing time were particularly compared in terms of the instantaneously varying flow pattern and aerodynamic torque, i.e., 0.5 s and 1.0 s; as the benchmark cases, the flows at different opening angles of the valve disk were also simulated for comparison. To accurately capture the transient flow, a total of 30 meshes corresponding to different opening angles of the throttle valve’s disk were preliminarily built by using ANSYS ICEM CFD 14.0, while mesh deformation and remeshing methods were used as Dynamic Mesh model to get the consecutively updated mesh. The SST model was chosen as turbulence model and ANSYS CFX 14.0 Software Package was used to solve the flow field. The results showed that rapid close of the throttle valve would lead to an overall flow imbalance between the inlet and the outlet, which was deteriorated with the decrease in the closing time.
Experimental Investigation of the Upstream Effect of Different Low Pressure Turbine Exit Guide Vane Designs on Rotor Blade Vibration
Authors: Schönleitner F. , Selic T. , Schitter C. , Heitmeir F. , Marn A.
Published: September 2016

Exit guide vanes of turbine exit casings are designed to meet aerodynamic, structural and acoustic criteria. New low pressure turbine architectures of aero engines try to optimize components weight in order to decrease the fuel consumption and reduce noise emissions. For this purpose different designs of turbine exit guide vanes (TEGV) exist which vary geometry as well as the number of vanes in the casing. In the subsonic test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics of Graz University of Technology, which represents a 1 ½ low pressure turbine stage, the upstream effect of these innovative turbine exit casings (TEC) designs is under investigation. Up to now the influence of the turbine exit casing in relation to the aerodynamic vibration excitation of the rotor blading is not well known. For rotor blade vibration measurements a telemetry system in combination with strain gauges is applied. The present paper is a report of blade vibration measurements within a rotating system in the area of low pressure turbines under engine relevant operating conditions. Within the test phase different turbine exit casings are under investigation at two different operating points (OP). These turbine exit casings represent different design goals, e.g. aerodynamically optimization was performed to reduce losses at the aero design point or an acoustically optimization was done to reduce noise emission at the operating point approach. All these different design intents lead to a changed upstream effect, thus changing rotor blade vibrations. To identify parameters affecting blade vibration attention is paid to aerodynamic measurements as well. Selected results of steady and unsteady flow field measurements are analyzed to draw conclusions. The upstream effect of different turbine exit casings can be quantified at OP1. Depending on the vane number both the potential effect of the TEGV increase and the upstream effect as well. Aerodynamic as well as acoustic improvements as wanted with H-TEC and inverse-cut-off TEC lead to unfavorable conditions and higher blade loading in comparison to the referenced TEC. OP2 provides additional information of downstream effects. Due to the stator vane number the rotor blading is excited in its 4th eigenfrequency. The comparison between all investigated turbine exit casings with respect to the referenced configuration provides a basis for numerical code validation and future developments.
Vibration Absorbers for a Mistuned Bladed Disk
Authors: Sinha Alok
Published: September 2016

Mistuning refers to variations in modal properties of blades due to manufacturing tolerances. This can result in the amplification of a blade vibratory amplitude. This paper deals with the design of vibration absorbers for a mistuned bladed disk. First, the basic theory is established for undamped vibration absorbers using a single mode model for each blade. Then, it is extended to include a multiple mode model of each blade and disk dynamics. The impact of mistuning on the bladed disk vibration is examined in the presence of undamped absorbers via Monte Carlo simulations. It is found that vibration absorbers can be an effective method to counter the detrimental effects of mistuning.
Unsteady Flow Phenomena in Turbine Rim Seals
Authors: Beard Paul F. , Chew John , Gao Feng , Chana Kam S.
Published: September 2016

While turbine rim sealing flows are an important aspect of turbomachinery design, affecting turbine aerodynamic performance and turbine disc temperatures, the present understanding and predictive capability for such flows is limited. The aim of the present study is to clarify the flow physics involved in rim sealing flows and to provide high quality experimental data for use in evaluation of CFD models. The seal considered is similar to a chute seal previously investigated by other workers, and the study focuses on the inherent unsteadiness of rim seal flows, rather than unsteadiness imposed by the rotating blades. Unsteady pressure measurements from radially and circumferentially distributed transducers are presented for flow in a rotor-stator disc cavity and the rim seal without imposed external flow. The test matrix covered ranges in rotational Reynolds number, Reø, and non-dimensional flow rate, Cw, of 2.2–3.0×106 and 0–3.5×103 respectively. Distinct frequencies are identified in the cavity flow and detailed analysis of the pressure data associates these with large scale flow structures rotating about the axis. This confirms the occurrence of such structures as predicted in previously published CFD studies and provides new data for detailed assessment of CFD models.
Profile Loss Prediction for High Pressure Steam Turbines
Authors: Cheon J. H. , Milčák P. , Pacák A. , Kang C. R. , Šťastný M.
Published: September 2016

A method is presented for predicting the energy loss for a 2D turbine cascade blade operating in subsonic regions where the exit Mach number ≤ 0.8. A prediction method based on entropy creation was used to analyze the cascade profile loss mechanism. The basic profile loss model was introduced from the isentropic Mach number distribution along the blade surface and the trailing edge loss model was introduced from available test data, CFD results and available loss models. In addition, the Reynolds number correction curve was applied from previous research. Linear cascade test datasets which represent hub, mid-span and tip sections were used to validate this loss model.
Evaluation of the SST-SAS Model for Prediction of Separated Flow Inside Turbine Internal Cooling Passages
Authors: Zacharzewski Piotr , Simmons Kathy , Jefferson-Loveday Richard , Capone Luigi
Published: September 2016

The flow and heat transfer over a three-dimensional axisymmetric hill and rectangular ribbed duct is computed in order to evaluate the Shear Stress Transport - Scale Adaptive Simulation (SST-SAS) turbulence model. The study presented here is relevant to turbine blade internal cooling passages and the aim is to establish whether SAS-SST is a viable alternative to other turbulence models for computations of such flows. The model investigated is based on Menter’s modification to Rotta’s k-kL model and comparison is made against experimental data as well as other models including some with scale resolving capability, such as LES, DES & hybrid LES-RANS.

For the hill case the SAS model dramatically overpredicts the size of the separation bubble. The LES on the other hand proved to be more accurate even though the mesh is courser by LES standards. There is little improvement of SST-SAS compared with RANS. Broadly speaking all models predict streamwise velocity profiles for the ribbed channel with reasonable accuracy. The cross-stream velocity is underpredicted by all models. Heat transfer prediction is more accurately predicted by LES than RANS, DES & SST-SAS on a mesh that is slightly coarser than required by LES standard, however it still exhibits significant error. It is concluded that more investigation of the SST-SAS model is required to more broadly assess its viability for industrial computation.
Material Selection Issues for a Nozzle Guide Vane Against Service Induced Failure
Authors: Wu Xijia , Zhang Zhong , Jiang Leiyong , Patnaik Prakash
Published: September 2016

Nozzle guide vanes (NGV) of gas turbine engines are the first components to withstand the impingement of hot combustion gas, and therefore often suffer thermal fatigue failures in service. A lifing analysis is performed for the NGV of a gas turbine engine using the integrated creep-fatigue theory (ICFT). With the constitutive formulation of inelastic strain in terms of mechanism-strain components such as rate-independent plasticity, dislocation glide-plus-climb, and grain boundary sliding, the dominant deformation mechanisms at the critical locations are thus identified quantitatively with the corresponding mechanism-strain component. The material selection scenarios are discussed with regards to damage accumulated during take-off and cruise. The interplay of those deformation mechanisms in the failure process are elucidated such that an “optimum” material selection solution may be achieved.
Investigation on the Performance and Flow Structure of Centrifugal Compressor: Understand the Inlet Bent Duct Configurations
Authors: Yang Ce , Liu Yixiong , Wang Leilei , Lao Dazhong , Yang Changmao
Published: September 2016

In turbocharger systems, the inlets of centrifugal compressor often connect with bent ducts, producing a non-uniform flow field distribution at the compressor impeller inlet, which degrades the compressor performance and deteriorate the flow structure of the compressor significantly.

In present work, a group of typical bent ducts is designed by adjusting the torsion angle of the U-shaped duct to investigate the effects of these bent ducts on the performance and flow field of the compressor. The experimental tests of the compressor with various inlet bent duct configurations were carried out to obtain the aerodynamic performance and pressure distributions. The experimental performance curves showed the bent ducts affect the aerodynamic performance and surge margin of the compressor.

To understand these effects fundamentally, the unsteady flow calculations were conducted to capture the detailed flow in the bent ducts and compressor internal. The flow distortion distributions and swirl patterns in various bent ducts were compared by numerical calculation results and analyzed in theory. The results showed the total pressure distorted region at the duct exit expands along the circumferential direction and distortion degree is weakened with the torsion angle of bent duct increases. Moreover, the swirl distortion patterns vary in different inlet ducts. The further analysis showed that an appropriate bent duct configuration is helpful for improving the surge margin of the compressor effectively. By observing the static pressure in the impeller inlet and shroud region, it found that the bent ducts produce non-uniform static pressure at impeller inlet and reduce the static pressure in shroud wall. It also found that the change of the pressure in compressor internal has some relation with the swirl structure of bent duct exit.
Investigation on the Effect of Cooling Hole Structure on the Steam Cooling Performance of the Intermediate Pressure Turbine Stages
Authors: Li Jun , Huo Wenhao , Feng Zhenping
Published: September 2016

Effect of cooling hole structure on the steam cooling performance of the solid components (including the rotor blades, roots and wheel discs) in intermediate pressure turbine stages for an ultra-supercritical steam turbine was numerically investigated using the hybrid method of flow field calculation and conjugated heat transfer. Numerical solutions were carried out for four cooling hole structures, which includes a designed structure and three modified structures. Numerical results presented and compared the steam flow patterns in the disc cavities and temperature distributions in the rotating components for all cooling hole structures. Reducing through flow area of the cooling hole at the bottom of the blade root results in a significant strengthen in the preventing ability to hot main stream ingress of the cooling steam, as well as an increase in the cooling regions of the blade root and wheel disc. Furthermore, the overall solid temperature and temperature gradient can be efficiently reduced by modifying the cooling hole structure. Numerical results also reveal that it is possible to prevent the hot main steam ingress and increase cooling performance by modifying the steam cooling hole structure, which optimizes the flow pattern and flow rate distribution of the cooling steam.
Multidisciplinary Optimization Design of Long Blade Turbine Stage Based on Parallel Self-Adaptive Multi-Objective Differential Evolution Algorithm
Authors: Li Jun , Li Bin , Song Liming , Feng Zhenping
Published: September 2016

An automated multidisciplinary optimization system for multi-objective design of the long blade turbine stage for steam turbines is developed in this paper. The Self-adaptive Multi-objective Differential Evolution (SMODE) algorithm, cubic non-uniform B-Spline curves based on surface modeling technology for three-dimensional turbine blade parameterization method, aerodynamic and mechanical performance of long blade turbine stage evaluation approach are coupled in the presented multidisciplinary optimization system. The aerodynamic performance of long blade turbine stage design candidates is evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions. The mechanical performance of the designed long rotor blade is analyzed using Finite Element Analysis (FEA) method based on the software ANSYS. Multi-objective design of long blade turbine stage is conducted using the developed multidisciplinary optimization methodology for the maximization of specific power and minimization of maximum Von Mises Stress with constraints on mass flow rate. The design variables are specified by the stator and rotor blade parameterization method. The Pareto solutions of the multidisciplinary optimization design for the long blade turbine stage are obtained. The aerodynamic and strength performance of obtained Pareto solutions improves obviously by comparison of the referenced design. The dynamic frequency with pre-stress of the referenced and optimized long rotor blade is also calculated in order to avoid resonance. The availability of the presented multidisciplinary optimization system for multi-objective design of long blade turbine stage for steam turbines is also demonstrated.
Combined Effects of Freestream Pressure Gradient and Density Ratio on the Film Cooling Effectiveness of Round and Shaped Holes on a Flat Plate
Authors: Vinton Kyle R. , Watson Travis B. , Wright Lesley M. , Crites Daniel C. , Morris Mark C. , Riahi Ardeshir
Published: September 2016

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30°) or laidback, fan-shaped holes (θ = 30°, β = γ = 10°) using the pressure sensitive paint (PSP) technique. In a low speed wind tunnel, both non-accelerating and accelerating flows were considered while the density ratio varied from 1–4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.
A Computational and Experimental Compressor Design Project for Japanese and British High-School Students
Authors: Grimshaw S. D. , Sequeira C. L. , Hewkin-Smith M.
Published: September 2016

This paper describes an innovative, three-day, turbomachinery research project for Japanese and British high-school students. The project is structured using modern teaching theories which encourage student curiosity and creativity. The experience develops team-work and communication, and helps to break-down cultural and linguistic barriers between students from different countries and backgrounds. The approach provides a framework for other hands-on research projects which aim to inspire young students to undertake a career in engineering.

The project is part of the Clifton Scientific Trust’s annual UK-Japan Young Scientist Workshop Programme. The work focuses on compressor design for jet engines and gas turbines. It includes lectures introducing students to turbomachinery concepts, a computational design study of a compressor blade section, experimental tests with a low-speed cascade and tutorials in data analysis and aerodynamic theory. The project also makes use of 3D printing technology, so that students go through the full engineering design process, from theory, through design, to practical experimental testing.

Alongside the academic aims, students learn what it is like to study engineering at university, discover how to work effectively in a multinational team, and experience a real engineering problem. Despite a lack of background in fluid dynamics and the limited time available, the lab work and end of project presentation show how far young students can be stretched when they are motivated by an interesting problem.
Mesoscopic Modeling of 3D Four-Directional Braided Composites
Authors: Wang Rongqiao , Zhang Long , Hu Dianyin , Shen Xiuli , Song Jun
Published: September 2016

3D four-directional braided composites are becoming widely used in the aeroengines due to their excellent transverse properties such as stiffness, strength, fracture toughness and damage resistance. In spite of great achievements in composite materials, the model of 3D four-directional braided composites gives rise to considerable challenge in establishing interior fiber bundle structure which is curved and twisted in jamming condition. Original circular cross-section of fiber bundle is squeezed into oval shape ellipse in manufacturing process of the jamming action. Thus, a novel mesoscopic modeling approach for 3D four-directional braided composites was proposed in this study, which considered the fiber bundle cross-section’s deformation. Firstly, an analytic equation to describe the transformation of fiber bundle cross-section was established based on the equal area of the ellipse and circle. Secondly, the parameters of this equation were achieved using the Matlab simulation. It was concluded that the compacted, non-interfered fiber bundle model constructed was in good agreement with actual structure. This paper provides the mathematical relationship between braiding parameters and geometric dimensions of unit cell model. Numerical results showed that the value of braiding pitch length has a relative calculation error less than 4% compared with test data. The modeling technique lays a foundation for further mesomechanics investigation on 3D four-directional braided composites.
Power Setting Sensor Fault Detection and Accommodation for Gas Turbine Engines Using Artificial Neural Networks
Authors: Courdier A. , Li Y. G.
Published: September 2016

Sensors installed on gas turbine gas path are used to obtain gas path measurement parameters for control and condition monitoring purpose. These sensors are prone to degradation or failure due to hostile working environment around them. Most gas path sensor diagnostic research is based on an assumption that the power setting sensor, a sensor used by engine control system to control engine power output, has no fault so engine measurement data can always be obtained at desired operating conditions. However in practice, power setting sensor may also be faulty, which may result in misleading measurement data and diagnostic results.

In this paper, an artificial neural network based gas path diagnostic approach for engine power setting sensor fault detection and quantification has been introduced. Nested artificial neural networks (ANN) are used to detect power setting sensor fault and ensure prediction accuracy. Measurement noise is also considered in the training and testing samples to ensure the robustness of the diagnostic system.

The developed power setting sensor diagnostic approach has been applied to a model 2-shafts industrial gas turbine engine similar to a GE LM2500+G4 engine to test the effectiveness of the approach. The selected power setting parameter is the shaft power output measured by a power setting sensor. An engine performance model is produced using Cranfield University’s gas turbine performance and diagnostics software, Pythia. Training samples with the consideration of sensor faults were simulated with the engine model assuming one of the sensors, either the power setting sensor or other gas path sensors may be faulty. In the nested neural network for sensor fault diagnostics, the system separately performs sensor fault detection, sensor fault identification and sensor fault quantification.

Results show that the developed nested neural network diagnostic system is able to identify the power setting sensor fault and correctly predict the magnitude of the fault. This would allow the engine control system correct its control schedule and accommodate the power setting sensor fault.
Rotating Heat Transfer Measurements on a Multi-Pass Internal Cooling Channel: I — Rig Development
Authors: Pagnacco Fabio , Furlani Luca , Armellini Alessandro , Casarsa Luca , Davis Anthony
Published: September 2016

The present contribution describes the design and realization of a rotating test rig for heat transfer measurements on internal cooling passages of gas turbine blades. The aim is to study the effects of Coriolis and buoyancy forces on the heat transfer distribution inside realistic cooling schemes.

Spatially resolved heat transfer data are obtained by means of transient thermochromic liquid crystals (TLC) technique. In order to replicate the same buoyancy effects induced by the Coriolis forces during rotation, the transient measurements are performed with a cold temperature step on the coolant flow. New solutions are adopted to generate the cold temperature step, acquire the experimental data on board of the rotating test model and to control the experimental parameters during tests execution. The main components of the rig will be described in the paper, together with an overview of the data processing methodology that has been developed.
Investigation on Flow Induced Vibrations of a Steam Turbine Inlet Valve Considering Fluid Structure Interaction Effects
Authors: Domnick Clemens Bernhard , Benra Friedrich-Karl , Brillert Dieter , Dohmen Hans Josef , Musch Christian
Published: September 2016

The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate a huge amount of energy in throttled operation. The dissipation process generates strong pressure fluctuations resulting in high dynamic forces causing valve vibrations. A brief survey of the literature dealing with valve vibrations reveals that vibrational problems and damages mostly occur in throttled operation when high speed jets, shocks, and shear layers are present. As previous investigations reveal that a feedback mechanism between the dynamic flow field and the vibrating valve plug exists, the vibrations are investigated with two-way coupled simulations. The fluid dynamics are solved with a scale-adaptive approach to resolve the pressure fluctuations generated by the turbulent flow. The finite element model solving the structural dynamics considers both frictional effects at the valve packing and contact effects caused by the plug impacting on the valve bushing. As different flow topologies causing diverse dynamic loads exist, the fluid flow and the structural dynamics are simulated at different operating points. The simulations show that differences to the one-way coupled approach exist leading to a change of the vibrational behavior. The physics behind the feedback mechanisms causing this change are analyzed and conclusions regarding the accuracy of the one-way coupled approach are drawn.
Auxiliary Bearing System Optimization for AMB Supported Rotors Based on Rotor Drop Analysis: Part I — Rotor Drop Analysis Method
Authors: Cao Jianming , Allaire Paul , Dimond Timothy , Dousti Saeid
Published: September 2016

For rotors supported with active magnetic bearings (AMBs), the auxiliary bearing system or backup bearing system is needed to avoid serious potential internal damaging in the event of AMB loss of power or overload. The evolution of auxiliary systems has been made a priority by the American Petroleum Institute using analytical or experimental methods. In part I of this paper, a detailed rotor drop nonlinear transient analysis method including flexible shaft, rolling element bearing components including inner/outer races and balls, as well as flexible/damped supporting structures is given. A finite element based 6-DOF flexible rotor model is used to indicate shaft motion before the drop (operating conditions) and during the rotor drop event. Un-lubricated Hertzian contact models are used between the shaft and inner/outer races, between balls and races. To avoid heavy calculating time, two different methods to calculate ball bearing contact loads are discussed and the simulation results are compared. These models are applied to predict shaft-race-ball displacements and angular speeds, contact loads and ball bearing stresses during the drop for angular contact auxiliary bearings. This method also can be used to design and optimize the auxiliary bearing system as presented in the 2nd part of this paper.
Kalman Filter Development for Real Time Proper Orthogonal Decomposition Disc Temperature Model
Authors: van Paridon Andrew , Bacic Marko , Ireland Peter T.
Published: September 2016

Extending disc life through online health monitoring has been a proven method of minimising engine downtime and maintenance costs. To properly monitor the disc requires a robust model of the disc’s non-linear thermal dynamics. A model can be improved by filtering the output using a measurement of the disc in real time. The damage models can then be computed with higher statistical confidence leading to increased safe life prediction. Recently, a model of disc temperature has been developed based on the proper orthogonal decomposition of simulated data. The model produced detailed thermal gradients for use in damage calculation and life assessment. This paper presents the development and implementation of a Kalman filter to augment that model. The location of the measurement has been assessed in order to select the most appropriate target for instrumentation. Points all around the front and back of the disc have been assessed, and the best practice result is found to be near the centre of the disc neck. Matching temperatures at this point represents a compromise between the fast dynamic response of the rim, with the slower response of the cob. The new model has been validated against an independent flight simulation that had previously been excluded from any training process. The addition of the Kalman filter allows the model to match aircraft dynamics outside the regular training trajectories. The accuracy is approximately ±30K, and there is a root-mean-square error of only 2K over the whole model at any one point in time.
A Simple Model for Identifying the ‘Flutter Bite’ of Fan Blades
Authors: Zhao Fanzhou , Smith Nigel , Vahdati Mehdi
Published: September 2016

This paper presents a simple model for the prediction of the ‘flutter bite’ of fan blades due to acoustic reflections from the intake. In a previous work by the authors, it was shown that the acoustic effects of the intake is very important and needs to be considered during the design of a fan blade. It was also shown that the damping due to blade motion and intake acoustics are independent and can be analysed separately. The acoustic reflections from the intake changes the damping of the blade by modifying the phase and amplitude of the unsteady pressure at the leading edge of the fan. It will be shown in the paper that, for a given intake, the phase and amplitude of the reflected acoustic waves can be evaluated analytically based on established theories independent of the fan design. The proposed model requires only the design intent of the fan blade and the geometry of the intake, which are available in the early design stages of a new engine, and can predict the operating conditions at which fan flutter is likely to occur. The proposed simple model can be used in two ways:

(i) For a particular intake design, the flutter bite speed can be determined based on the fan operating line. This type of analysis can be very useful before the experimental testing stages of an engine, where possible ‘flutter bite’ regions must be identified prior to the experiments so as to avoid potential damages to the engine. Moreover, whole annulus unsteady CFD flutter computations are usually performed for a ‘fan plus intake’ design prior to manufacture. However due to the high demands on both computational time and resources, these computations cannot be carried out over the entire fan speed range in the early design stages. The proposed model can predict the fan speeds at which fan flutter is likely to occur, so that CFD investigations can be carried out accordingly.

(ii) For a particular fan design, the effects of different intakes on the fan flutter stability can be determined so as to devise an optimal intake design which minimises the chance of potential flutter bite.
Operability Limits of Tubular Injectors With Vortex Generators for a Hydrogen Fuelled Recuperated 100kW Class Gas Turbine
Authors: Bauer Stefan , Hampel Balbina , Sattelmayer Thomas
Published: September 2016

Vortex generators are known to be effective in augmenting the mixing of fuel jets with air. The configuration investgated in this study is a tubular air passage with fuel injection from one single orifice placed in the side wall. In the range of typical gas turbine combustor inlet temperatures, the performance vortex generator premixers (VGPs) have already been investigated for natural gas as well as for blends of natural gas and hydrogen. However, for highly reactive fuels, the application of VGPs in recuperated gas turbines is particularly challenging because the high combustor inlet temperature leads to potential risk with regard to premature self-ignition and flame flashback. As the current knowledge does not cover the temperature range far above the self-ignition temperature, an experimental investigation of the operational limits of VGPs is currently being conducted at the Thermodynamics Institute of the Technical University of Munich, which is particularly focused on reactive fuels and the thermodynamic conditions present in recuperated gas turbines with pressure ratios of 4–5. For the study presented in the paper, an atmospheric combustion VGP test rig has been designed, which facilitates investigations in a wide range of operating conditions in order to comply with the situation in recuperated micro gas turbines, namely global equivalence ratios between 0.2 and 0.7, air preheating temperatures between 288K and 1100K, and air bulk flow rates between 6–16 g/s. Both the entire mixing zone in the VGP and the primary combustion zone of the test rig are optically accessible. High speed OH* chemiluminescence imaging is used for the detection of the flashback and blow-off limits of the investigated VGPs. Flashback and blow-off limits of hydrogen in a wide temperature range covering the auto-ignition regime are presented, addressing the influences of equivalence ratio, air preheating temperature and momentum ratio between air and hydrogen on the operational limits in terms of bulk flow velocity. It is shown that flashback and blow-off limits are increasingly influenced by auto-ignition in the ultra-high temperature regime.
Random Vibration Analysis for Centrifugal Compressor Impellers With Unsteady Aerodynamic Excitations
Authors: Wang Yuefang , Liu Yan , Wang Xuejun , Li Hongkun , Jiang Daren
Published: September 2016

Dynamic response of impeller of centrifugal compressor is studied considering pulsating pressure field on blades due to unsteady flow conditions. The aerodynamic forces on the blades are modeled as random load whose spectral characteristics are determined through computational fluid dynamic simulations in the time domain. The dynamical response in the unsteady case is solved as a random vibration problem in the frequency domain which provides useful power spectral density displacement and stress for early stage of impeller design. A semi-open impeller mounted with 19 blades is modeled using three dimensional solid finite elements. The random vibration problem of the impeller is solved through the Pseudo-Excitation Method considering spatial variance of the pressure field. A user-defined module is developed based on harmonic analysis to generate the auto power spectral density and variance of displacement and stress at 200 nodes. It is demonstrated that solving a random vibration problem through the Pseudo-Excitation Method is faster than the commonly adopted multiple-step transient analysis. It is concluded that evaluating the structural integrity of impeller solids in the regime of random vibration is a feasible and efficient approach at the early design stage of compressors.
Numerical Method for Simulating Flows of Supercritical CO2 Compressor With Nonequilibrium Condensation
Authors: Furusawa Takashi , Miyazawa Hironori , Yamamoto Satoru
Published: September 2016

We recently proposed a numerical method for simulating flows of supercritical CO2 based on a preconditioning method and the thermophysical models programed in a program package for thermophysical properties of fluids (PROPATH). In this study, this method is applied to the investigation of cascade channel. Numerical results obtained by assuming supercritical pressure conditions indicate that the normal shock generated in the cascade channel deeply depends on the pressure condition. In particular, the speed of sound varying with the pressure variation at the supercritical state is a key thermophysical property which changes the flow field in the cascade channel. In addition, we also simulate those flows with nonequilibrium condensation in which the inlet pressure and temperature approaching to those of the critical point are specified. Then a nonequilibrium condensation model developed by our group is further applied to the numerical method. CO2 condensation observed in a case indicates that condensation occurs at a local region near the leading edge due to the flow expansion; the droplets soon grow at the local region and streams downward with keeping almost the same mass fraction.
Rotor-Dynamics of Different Shaft Configurations for a 6 kW Micro Gas Turbine for Concentrated Solar Power
Authors: Arroyo A. , McLorn M. , Fabian M. , White M. , Sayma A. I.
Published: September 2016

Rotor-dynamics of Micro Gas Turbines (MGTs) under 30 kW have been a critical issue for the successful development of reliable engines during the last decades. Especially, no consensus has been reached on a reliable MGT arrangement under 10 kW with rotational speeds above 100,000 rpm, making the understanding of the rotor-dynamics of these high speed systems an important research area. This paper presents a linear rotor-dynamic analysis and comparison of three mechanical arrangements of a 6 kW MGT intended for utilising Concentrated Solar Power (CSP) using a parabolic dish concentrator. This application differs from the usual fuel burning MGT in that it is required to operate at a wider operating speed range. The objective is to find an arrangement that allows reliable mechanical operation through better understanding of the rotor dynamics for a number of alternative shaft-bearings arrangements. Finite Element Analysis (FEA) was used to produce Campbell diagrams and to determine the critical speeds and mode shapes. Experimental hammer tests using a new approach based on optical sensing technology were used to validate the rotor-dynamic models. The FEA simulation results for the natural frequencies of a shaft arrangement were within 5% of the measurements, while the deviation for the shaft-bearings arrangement increased up to 16%.