bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Numerical Analysis of Control Effect on Cavitation Instabilities in a Cascade With a Random Slit
Authors: Hagiwara Ryosuke , Iga Yuka 
Published: July 2018

In the present study, numerical analysis was carried out around the a cyclic flat-plate cascade with a random slit, so as to examine the suppressing or controlling effect of the slit for cavitation instabilities such as a cavitation surge and rotating cavitation. These instabilities cause various problem for the turbomachinery, for example, rotating cavitation causes an asynchronous axial vibration, and cavitation surge causes a pulsation of working fluid by resonance phenomenon of the system. Especially, in liquid propellant rocket engine, suppression process for these instabilities bring increase in cost of the launch. Therefore, it is thought that to find effective suppression technique is significant for turbomachinery.
In this paper, two types of the flat-plate three blades cascade which has a slit at different position (herein called “random slit”) was analyzed, and the results ware compared with the result of cascade without slit. As a result, the cavitation surge is perfectly suppressed in both of two types cascade with a random slit. Also, in the one case of them, sub-synchronous rotating cavitation and rotating stall cavitation is suppressed. Furthermore, super-synchronous rotating cavitation which is not observed in single-stage cascade, is detected by arranging a random slit. These results indicate the possibility of suppressing cavitation instabilities or controlling the type of the cavitation instabilities by the arrangement of the slit. Moreover, the head performance at the almost same cavitation number is equal or slightly increasing by arranging the random slit.
Experimental and Analytical Study of Coriolis Effects in Bladed Disk
Authors: Ruffini Valentina , Schwingshackl Christoph , Green Jeff 
Published: July 2018

Modern aero-engines have reached a high level of sophistication and only significant changes will lead to the improvements necessary to achieve the economic and environmental targets of the future. Open rotors constitute a major leap in this direction, both in terms of efficiency and of technological innovation. This calls for a revision of the accepted design practices, and a new focus on phenomena that have been little investigated in the past, such as the Coriolis effect, or the gyroscopic coupling of the blades with the shaft. Experimental results from modern fans, with large blades and strong stagger angles, are showing dependence on Coriolis gyroscopic effects already, an effect that is expected to be strongly enhanced with the proposed open rotor designs.
For an accurate prediction of the Coriolis and gyroscopic effects in rotating assemblies a fully experimentally validated approach is needed. Today’s FE models can capture the basic physical phenomena, but experimental confirmation is still needed for the evolution of the mode shapes with angular speed, and the influence of damping and geometric nonlinearities when gyroscopic coupling is considered. To support this validation effort a new rotating test rig will be introduced, initial measurement data will be discussed, and a comparison with a finite element analysis presented.
Different forcing patterns, including forward and backward travelling-wave engine order excitation could be experimentally excited in the new rig, Coriolis-induced frequency splits were found in the dynamic response, showing a significant change in the dynamic behaviour of the investigated dummy disk, and only a minor impact of the mistuning was observed on the frequency splits due to Coriolis effects. The experimental results have been compared to a finite element analysis, and after some updating a good agreement between the predicted and measured Campbell diagrams could be obtained, demonstrating the reliability of the modelling approach.
Vibration-Based SHM of Ordinary Buildings: Detection and Quantification of Structural Damage
Authors: Pierdicca Alessio , Clementi Francesco , Maracci Diletta , Isidori Daniela , Lenci Stefano 
Published: July 2018

One of the most important issues in civil and in mechanical engineering is the detection of structural damages, which are defined as changes of material properties, of boundary conditions and of system connectivity, which adversely affect the system’s performances. The damage identification process generally requires establishing existence, localization, type and intensity of the damage.
During its service life, a structure, besides his natural aging, can be subjected to earthquakes. These events may have a deep impact on building safety and a continuous monitoring of the structure health conditions, through Structural Health Monitoring (SHM) techniques, is necessary in many cases.
Within this a background, the purpose of this work is to propose an integrated novel approach for the diagnosis of structures after a seismic event. The proposed monitoring system is based on recording the accelerations of the real structure during a seismic input, and the reintroduction of them into a numerical model, suitably tuned, in order to outline a possible post-earthquake scenario.
This approach provides an estimation of the health of the building and of its residual life, and to detect and quantify the damage, some of the crucial aspects of SHM. Actually, we also get both online and self-diagnosis of the structural health.
The technique is applied to a real structure, an industrial building liable of some seismic vulnerabilities. It it did not undergo an earthquake, so we have not recordered accelerations, and get them from a different numerical models subjected to the ground acceleration of a realistic earthquake.
Damping in a Composite Beam With a Jointed Interface
Authors: Goyder Hugh , Ind Philip , Brown Daniel 
Published: July 2018

An experimental investigation has been made of two identical beams of length 750mm bolted together (a composite beam) which have contact over the whole of the neutral plane. The objective is to determine how friction between the two beams influences the damping. In one set of experiments the beams were held apart using washers while in the second set the beams could contact each other over their whole length. The number of bolts used to hold the beams together was varied between three and 17. The damping of the first two or more modes of the beams was measured. The material damping of the beams when not bolted together was also measured. It was found that the material damping and the damping of the fully bolted composite beam were very similar (damping ratio 0.0005). However, when the beams were in contact and had few bolts (just 3) and the amplitude of vibration was large the damping ratio changed to a much larger value of 0.01.
The experiments suggest that the damping due to the bolts is similar to that of material damping. It is only when other friction sites, not involving bolts, are slipping that damping becomes large.
The consequences for the designer of a built-up structure who wishes to increase damping is thus to use the smallest number of bolts and to arrange for other surfaces to be in sliding contact.
An Attempt to Improve Stance Mechanics of Trans-Tibial Amputee Gait by the Design of a Modular Ankle Joint Prosthetic
Authors: During Alastair B. , Sivarasu Sudesh , Vicatos George 
Published: July 2018

A-priori research show that trans-tibial (TT) amputees display poor gait parameters when walking with passive mechanical ankle-foot prosthetics (AFP’s). This has large implications for the amputee populations in the developing world, who have limited access to advanced prosthetic technologies and instead rely on baseline AFP’s. Analysis of such baseline AFP’s in literature indicates that the predominant issue with these devices are their inability to adequately replicate the mechanics of a normal ankle during the stance phase of a walking gait cycle. This has shown to be a contributory cause of increased energy expenditure, as well as secondary complications such as osteoarthritis and joint deterioration.
This paper presents the design and analysis of a modular low-cost ankle-joint prosthetic (AJP) that serves as an attachment to existing prosthetic feet, with the intention to improve the ankle mechanics thereof. The AJP is modelled to reproduce ankle joint mechanisms, specifically controlled relative angular flexion in the sagittal plane, using only simple mechanical elements (i.e. compression springs instead of electronics). Initial results were positive, indicating that the AJP improves the stance phase mechanics of the baseline AFP in a simulated TT amputee gait cycle. During forefoot dorsiflexion rollover, an 80%–132% (p < 0.001) increase in joint angle and a 42–56% decrease in ankle stiffness (p < 0.001 for all but one participant) is observed. Following heelstrike a 22%–77% (p < 0.001) increase in joint angle is observed. However equipment and methodology errors left the moment response of this phase unverifiable. The overall conclusion of this paper is that the introduction of the AJP to baseline AFP’s supplies evidence of improved rollover shapes, easier phase transitions, and the facilitation of footflat during mid-stance.
Troubleshooting of Vibration Problems in Gas Turbines With Proximity and Seismic Probes
Authors: Gopalakrishnan Padmanabhan , Sharma Pankajkumar 
Published: July 2018

Gas Turbines generally have heavy rotors and light casings, and some of them exhibit significant motion between bearing housing and free space. Hence, rotor forces would have higher transmissibility when measured on the bearing housing. This makes casing absolute measurement as bare sufficient for vibration monitoring and protection in Gas Turbines. Most of the Industrial Gas Turbines in field have their acceptable vibration limits defined in velocity units. Typically 1/2 inch per sec 0-pk is referred to as alert set point where as 1 inch per sec 0-pk as danger set point as per ISO-10816-1.
However, such casing based measurements many a times doesn’t yield necessary information on what might be going on in the journal bearings, which are having larger clearances with rotor. This also happens when the Gas Turbine does not exhibit significant motion between bearing housing and free space as said by Maalouf [1]. Some typical situations arise in Gas Turbines which might also need shaft relative vibration measurements using proximity probes. This paper discusses some of the experiences of the author in the field of Gas Turbine vibration diagnosis using shaft relative and casing absolute methodology. It explains how shaft relative measurement adds more value to find out the actual malfunction diagnosis when casing measurement data becomes insufficient in such cases.
CFD Modeling to Study the Effect of Spacer Design on Centrifugal Compressor Exit Scroll Performance
Authors: Patri Vrushabhendra V. , Meduri Uday K. , Iurisci Giuseppe , Giachi Marco 
Published: July 2018

Present day Centrifugal Compressor (CC) technology trend is moving towards innovative designs for improved performance. Computational Fluid Dynamics (CFD) plays an important role in the assessment and improvement of CC component design. Statoric parts like inlet plenum, diffuser, return channel, and exit scroll play a vital role in determining the overall performance of any compressor.
Exit scrolls (volute) are an integral part of any CC. A volute is essentially a flow collecting duct with its cross-section area increasing around the circumference as more volume of fluid is added. There are different types of volutes used for CC based on the type of application, casing size and the site conditions. The performance of a volute is very important in terms of magnitude of losses, static pressure recovery as well as impact on the upstream impeller. It is essential that the volute is well matched with the impeller and diffuser at the best stage efficiency point.
In addition to that, some obstructions needed for mechanical purposes (spacers, bolts, grooves) result in more losses, decreasing overall compressor efficiency affecting severely the upstream impeller. The purpose of this paper is to describe an extensive CFD analysis that was performed to understand and quantify the negative impact arising due to the presence of spacers, their shapes and circumferential location on the performance of the whole compressor.
The paper is divided into two sections. First section describes the CFD studies to understand performance of a typical scroll with spacers (boat tail spacers) as obstacles and effect of tangential location of spacers. The second section describes the CFD studies to understand the impact of the shape of spacers in a comparative manner.
NO Prediction in Turbulent Diffusion Flame Using Multiple Unsteady Laminar Flamelet Modeling
Authors: Yadav Rakesh , Rajeshirke Pravin , Nakod Pravin 
Published: July 2018

The steady laminar flamelet model (SLFM) [1, 2] has been shown to be reasonably good for the predictions of mean temperature and the major species in turbulent flames [3, 4]. However, the SLFM approach has limitations in the prediction of the slow chemistry phenomena like NO formation [5, 6]. In case of SLFM, the turbulence and chemistry are coupled through a single variable, called scalar dissipation, which is representative of the strain inside the flow. The SLFM model is not able to respond to the steep changes in the scalar dissipation values and generally tend to approach to the equilibrium solution as the strain relaxes [7]. The pollutant like NO is formed in the post flame zones and with a high residence time, where the scalar dissipation diminishes and hence the NO is over predicted using SLFM approach. In order to improve the prediction of slow forming species, a transient history of the scalar dissipation evolution is required. In this work, a multiple unsteady laminar flamelet approach is implemented and used to model the NO formation in two turbulent diffusion flames using detailed chemistry. In this approach, multiple unsteady flamelet equations are solved, where each flamelet is associated with its own scalar dissipation history. The time averaged mean variables are calculated from weighted average contributions from different flamelets.
The unsteady laminar flamelet solution starts with a converged solution obtained from steady laminar flamelet modeling approach. The unsteady flamelet equations are therefore solved as a post processing step with the frozen flow field. The domain averaged scalar dissipation for a flamelet at each time step is obtained by solving a scalar transport equation, which represents the probability of occurrence of the considered flamelet. The present work involves the study of the effect of number of flamelets and also the different methods of probability initialization on the accuracy of NO prediction. The current model predictions are compared with the experimental data. It is seen that the NO predictions improves significantly even with a single unsteady flamelet and further improves marginally with an increase in number of unsteady flamelets.
A Comparative CFD Study on Flamelet Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames
Authors: Nakod Pravin , Yadav Rakesh , Rajeshirke Pravin , Orsino Stefano 
Published: July 2018

Laminar Flamelet Model (LFM) [1–2] represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical non-equilibrium effects considered in this model are due to local turbulent straining only. In contrast, Flamelet Generated Manifold (FGM) [3] model considers that the scalar evolution, the realized trajectories on the thermo-chemical manifold in a turbulent flame is approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry and quenching effects far away from the equilibrium. In FGM, 1D premixed flamelets are solved in reaction-progress space rather than physical space. This helps better solution convergence for the flamelets over the entire mixture fraction range, especially with large kinetic mechanisms at the flammability limits [4].
In the present work, a systematic comparative study of FGM model with LFM for four different turbulent diffusion/premixed flames is presented. First flame considered in this work is methane-air flame with dilution air at the downstream. Second and third flame considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H2 and CH4 flames [5–6] where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer and molecular transport as recirculation burners without the complex recirculating fluid mechanic. The fourth flame considered is Sandia flame D [7], a piloted methane-air jet flame. It is observed that the simulation results predicted by FGM model are more physical and accurate compared to LFM in all the flames presented in this work.
Heat Transfer Analysis of a Gas Turbine and Improving Predictability Using Prototype Test Data
Authors: Reddy T. Vishnu Vardhan , De Prosperis Roberto 
Published: July 2018

Gas turbines are extremely complex & expensive machines that are subjected to various operating and environmental conditions. Increased customer attention towards higher efficiency is driving the industry to move to higher firing temperatures, which imparts higher thermal & mechanical loads on engine components. This in turn demands higher reliability levels for the engine components to ensure availability and safety of the machine. An effective modeling approach, which can accurately predict the thermal behavior of various components of a gas turbine, can be used to understand the critical regions, locate probable areas of failure, and to improve the overall design.
This paper presents a methodology to perform steady state thermal analysis of gas turbine flange to flange components (excluding the main flow path,) using a 2D FE model. A brief overview of the in-house tools and the modeling approach adopted to capture the complex physics using these tools are discussed. The results from this FE analysis are rigorously validated with data collected from various test campaigns of GE industrial Frame5 gas turbines. Several sensitivity studies were performed to study the impact of the uncertainties and to improve the thermal predictions compared to measurements. Studies using CFD tools and hand calculations were also performed to validate assumptions. This approach gives a thorough understanding of how a vast thermal model of gas turbine is developed and validated using test data, resulting in the improvement of thermal predictions of critical components.
Gas Turbine Blade Damper: A Design Optimization Study to Mitigate High Resonance Blade Vibration
Authors: Kumar Dilip , Barad Sanjay , Suresh T. N. 
Published: July 2018

This paper describes the design optimization study of an under platform damper to mitigate high vibration problem of a gas turbine rotor blade under resonance condition. An existing theoretical model explicitly, Casba friction damper model was used to evaluate the dynamic characteristics of the turbine blade with under platform damper. Turbine blade is approximated as two degrees of spring-damper-mass system, which is dynamically equivalent to real turbine blades for its first two eigen values. Blade tip response predictions were carried out for different damper mass, stiffness and coefficient of friction under simulated rotational speed of the rotor, to arrive at an optimum mass to control the blade tip response.
As a practical application, along with damper mass optimization, shape and mass distribution of the damper is obtained by design trials to ensure good contact between the blade root and damper upper surface. Contact analysis was carried using the ANSYS software. The asymmetric skewed damper geometry posed complications with respect to modelling and optimisation.
In realistic application, with the kind of uncertainties in contact pattern, variation in friction coefficient, geometric tolerances, validation/verification plays a major role in assessing the design. As part of verification of this damper design, a full scale gas turbine engine test program was envisaged and completed. Modified optimum damper was implanted as a design change, engine was instrumented for blade vibration measurement. Non-Intrusive Stress Measurement system was used for measuring blade tip amplitudes from all the blades in the rotor. Test blade tip vibration was analysed and compared against the predications.
This optimised damper configuration has showed significant reduction in blade amplitudes during full-scale gas turbine testing, in comparison to original design proving the efficacy of new modified damper.
Numerical Simulation of 2D Electrothermal Flow Using Boundary Element Method
Authors: Ren Qinlong , Chan Cho Lik , Arvayo Alberto L. 
Published: July 2018

Microfluidics and its applications to Lab-on-a-Chip have attracted a lot of attention. Because of the small length scale, the flow is characterized by a low Re number. The governing equations become linear. Boundary element method (BEM) is a very good option for simulating the fluid flow with high accuracy. In this paper, we present a 2D numerical modeling of the electrothermal flow using BEM.
In electrothermal flow the volumetric force is caused by electric field and temperature gradient. The physics is mathematically modeled by (i) Laplace equation for the electrical potential, (ii) Poisson equation for the heat conduction caused by Joule heating, (iii) continuity and Stokes equation for the low Reynolds number flow. We begin by solving the electrical potential and electric field. The heat conduction is caused by the Joule heating as the heat generation term. Superposition principle is used to solve for the temperature field. The Coulomb and dielectric forces are generated by the electrical field and temperature gradient of the system. We analyze the Stokes flow problem by superposition of fundamental solution for free-space velocity caused by body force and BEM for the corresponding homogeneous Stokes equation. It is well known that a singularity integral arises when the source point approaches the field point. To overcome this problem, we solve the free-space velocity analytically. For the BEM part, we also calculate all the integral terms analytically. With this effort, our solution is more accurate. In addition, we improve the robustness of the matrix system by combining the velocity integral equation with the traction integral equation.
Our purpose is to design a pump for the microfluidics system. Since the system is a long channel, the flow is fully developed in the area far away from the electrodes. With this assumption, the velocity profile is parabolic at the inlet and outlet of the channel. So we can get appropriate boundary conditions for the BEM part of Stokes equation. Consequently, we can simulate the electrothermal flow in an open channel.
In this paper, we will present the formulation and implementation of BEM to model electrothermal flow. Results of electrical potential, temperature field, Joule heating, electrothermal force, and velocity field will be presented.