scholarly journals LES for the Evaluation of Acoustic Damping of Effusion Plates

2012 ◽  
Author(s):  
A. Andreini ◽  
C. Bianchini ◽  
B. Facchini ◽  
A. Peschiulli ◽  
I. Vitale
Keyword(s):  
Flow Field ◽  
Computational Models ◽  
Pressure Fluctuations ◽  
General Purpose ◽  
Acoustic Properties ◽  
Acoustic Damping ◽  
Bias Flow ◽  
Staggered Arrangement ◽  
Grazing Flow ◽  
Set Up

Effusion cooled liners, commonly used in gas turbine combustion chambers to reduce wall temperature, may also help reducing the propagation of pressure fluctuations due to thermoacoustic instabilities. Large Eddy Simulations were conducted to accurately model the flow field and the acoustic response of effusion plates subject to a mean bias flow under external sinusoidal forcing. Even though existing lower order computational models showed good predicting capabilities, it is interesting to verify directly the influence of those parameters such as the staggered arrangement, the hole inclination, the presence of a grazing flow and the level of bias flow, which are not fully included in those models. A first bi-periodic single hole configuration with normal acoustic forcing was selected to investigate the acousting behavior with varying inclination angle, bias and grazing flow. 90° and 30° perforations were simulated for bias flow Mach number in the range 0.05–0.1 and grazing flow between 0 and 0.08. Those conditions were chosen to expand the knowledge of acoustic properties towards actual liners working conditions. A second more computationally expensive set-up, including 4 inclined holes at 30°, focused on the damping of parallel to the plate waves. Details of the computational methods implemented in the general purpose open-source unstructured CFD code OpenFOAM® exploited to conduct this analysis are reported together with an analysis of the results obtained from the acoustic computations both regarding the flow field generated and the absorption and energy dissipation coefficient.

Nanoparticle Precipitation in a T-Mixer: Coupling Experimental and Numerical Investigations of the Fluid Dynamics With the Solid Formation Processes

2006 ◽  
Author(s):  
Johannes Gradl ◽  
Florian Schwertfirm ◽  
Hans-Christoph Schwarzer ◽  
Hans-Joachim Schmid ◽  
Michael Manhart ◽  
...  
Keyword(s):  
Flow Field ◽  
Fluid Dynamic ◽  
Concentration Field ◽  
Population Balance ◽  
Mixing Process ◽  
Image Velocimetry ◽  
Modeling Material ◽  
Field Information ◽  
Set Up ◽  
3D Information

Mixing and consequently fluid dynamic is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. Due to fast and intensive mixing a static T-mixer configuration is capable for synthesizing continuously nanoparticles. The flow and concentration field of the applied mixer is investigated experimentally at different flow rates by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). Due to the PIV measurements the flow field in the mixer was characterized qualitatively and the mixing process itself is quantified by the subsequent LIF-measurements. A special feature of the LIF set up is to detect structures in the flow field, which are smaller than the Batchelor length. Thereby a detailed insight into the mixing process in a static T-Mixer is given. In this study a CFD-based approach using Direct Numerical Simulation (DNS) in combination with the solid formation kinetics solving population balance equations (PBE) is applied, using barium sulfate as modeling material. A Lagrangian Particle Tracking strategy is used to couple the flow field information with a micro mixing model and with the classical theory of nucleation. We found that the DNS-PBE approach including macro and micro mixing, combined with the population balance is capable of predicting the full PSD in nanoparticle precipitation for different operating parameters. Additionally to the resulting PSD, this approach delivers a 3D-information about all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which is visualized for different process variables.

WWW.TELD.NET: Online Courseware Engine for Teaching by Examples and Learning by Doing

2001 ◽  
Vol 29 (3) ◽  
pp. 219-235 ◽  
Author(s):  
G. Q. Huang ◽  
B. Shen ◽  
K. L. Mak
Keyword(s):  
Teaching And Learning ◽  
Virtual Classroom ◽  
Learning By Doing ◽  
General Purpose ◽  
Project Based Learning ◽  
Course Materials ◽  
Summative Assessments ◽  
On Line ◽  
Set Up ◽  
Electronic Delivery

TELD stands for “Teaching by Examples and Learning by Doing.” It is an on-line courseware engine over the World Wide Web. There are four folds of meanings in TELD. First, TELD represents a teaching and learning method that unifies a number of contemporary methods such as Problem-Based Learning (PBL) in medical education, Project-Based Learning (PBL) in engineering education, and Case Method (CM) in business education. Second, TELD serves as a Web server for hosting teaching and learning materials especially based on the TELD method. A variety of on-line facilities are provided for editing and uploading course materials such as syllabus, schedule, curriculum, examples of case study, exercises of mini-project, formative and summative assessments, etc. Third, TELD is a courseware search engine where educators are able to register their course materials and search for materials suitable for a particular course. In contrast with general-purpose search engines, TELD is set up for the special purpose of education. Therefore, the time and efforts spent on surfing are expected to be reduced dramatically. Finally, TELD is an on-line virtual classroom for electronic delivery of electronic curriculum materials. In addition to providing the lecture notes, TELD not only provides discussion questions for conducting in-class discussions and homework as formative assessment but also provides facilities for students to plan and submit their group work. This article presents an overview of the TELD courseware engine together with its background and underlying philosophy.

Pump Performance Improvement by Restraining Back Flow in Screw-Type Centrifugal Pump

2005 ◽  
Vol 127 (4) ◽  
pp. 755-762 ◽  
Author(s):  
Yasushi Tatebayashi ◽  
Kazuhiro Tanaka ◽  
Toshio Kobayashi
Keyword(s):  
Pressure Fluctuations ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Simple Method ◽  
Back Flow ◽  
Pump Performance ◽  
Impeller Outlet ◽  
Pump Head ◽  
The Difference ◽  
Set Up

The authors have been investigating the various characteristics of screw-type centrifugal pumps, such as pressure fluctuations in impellers, flow patterns in volute casings, and pump performance in air-water two-phase flow conditions. During these investigations, numerical results of our investigations made it clear that three back flow regions existed in this type of pump. Among these, the back flow from the volute casing toward the impeller outlet was the most influential on the pump performance. Thus the most important factor to achieve higher pump performance was to reduce the influence of this back flow. One simple method was proposed to obtain the restraint of back flow and so as to improve the pump performance. This method was to set up a ringlike wall at the suction cover casing between the impeller outlet and the volute casing. Its effects on the flow pattern and the pump performance have been discussed and clarified to compare the calculated results with experimental results done under two conditions, namely, one with and one without this ring-type wall. The influence of wall’s height on the pump head was investigated by numerical simulations. In addition, the difference due to the wall’s effect was clarified to compare its effects on two kinds of volute casing. From the results obtained it can be said that restraining the back flow of such pumps was very important to achieve higher pump performance. Furthermore, another method was suggested to restrain back flow effectively. This method was to attach a wall at the trailing edge of impeller. This method was very useful for avoiding the congestion of solids because this wall was smaller than that used in the first method. The influence of these factors on the pump performance was also discussed by comparing simulated calculations with actual experiments.

Predicting the Influence of Damping Devices on the Stability Margin of an Annular Combustor

2017 ◽  
Author(s):  
Max Zahn ◽  
Michael Betz ◽  
Moritz Schulze ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Resonance Frequency ◽  
Stability Margin ◽  
Numerical Approach ◽  
Acoustic Mode ◽  
Acoustic Properties ◽  
Azimuthal Mode ◽  
Acoustic Damping ◽  
Linearized Euler Equations ◽  
Annular Combustor ◽  
The Impact

A numerical modeling approach based on linearized Euler equations is applied to predict the linear stability of an annular combustor with and without dampers. The acoustic properties of all relevant combustor components such as damping devices, swirl burner characteristics, swirl flame dynamics, and combustor exit are individually evaluated via experimental and numerical approaches. All of the components are incorporated subsequently into the combustor model using impedances and acoustic transfer matrices to obtain an efficient procedure. This study focuses on using this approach to predict an annular combustor’s stability margin and to assess how dampers influence the modal dynamics of the first azimuthal mode. Stability predictions are successfully validated with experimental data. Different combustor components’ contributions to the acoustic damping of the entire system is also determined based on that numerical approach. Damper application in combustors can engender uncertainties in resonance frequency in the case of hot-gas ingestion. The impact of “detuned” resonators on the predicted damping rates with respect to a deviation in the resonance frequency and the eigenfrequency of the attenuated acoustic mode is therefore evaluated. The influence of dampers on the annular combustor’s stability margin is also determined.

Modeling and prediction for the oxidation efficiency of magnesium sulfite in aeration tank of magnesium-based seawater exhaust gas clean system

2017 ◽  
Vol 233 (1) ◽  
pp. 164-173
Author(s):  
Quan Liu ◽  
Yimin Zhu ◽  
Tie Li ◽  
Xiaojia Tang ◽  
Weifeng Liu ◽  
...  
Keyword(s):  
Flow Field ◽  
Initial Conditions ◽  
Negative Impact ◽  
Fluid Model ◽  
Aeration Tank ◽  
Exhaust Gas ◽  
Clean System ◽  
Physics Modeling ◽  
Set Up ◽  
Oxidation Efficiency

In magnesium-based seawater exhaust gas clean system, the desulfurization by-product, magnesium sulfite (MgSO3), has a negative impact on the ecological environment, which needs to be treated to make harmless. Due to the limited space on board, the aeration oxidation method is used to convert it to magnesium sulfate. Because of the variable size, shape and flow field of aeration tank, it is difficult and expensive to design and verify the oxidation efficiency of the aeration tank by experimental method. In this work, in order to predict the oxidation efficiency accurately, RFlow, a computational fluid dynamics software, was used to analyze the flow field and MgSO3 oxidation reaction in aeration tank. The subdomain technology was adopted for physics modeling and mesh generation of the aeration tank, and the total number of meshes was 285,000. The multi-phase flow field model was set up using the multi-fluid model and dispersive k-ε turbulence model. Under the given initial conditions, the predicted oxidation efficiency was 94.2%. Compared with the results of the actual ship test, the prediction model for MgSO3 oxidation efficiency of the aeration tank is reliable.

Design of Acoustic Liner in Small Gas Turbine Combustor Using One-Dimensional Impedance Models

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Daesik Kim ◽  
Seungchai Jung ◽  
Heeho Park
Keyword(s):  
Gas Turbine ◽  
Side Wall ◽  
Acoustic Energy ◽  
Gas Turbine Combustor ◽  
Design Guideline ◽  
Acoustic Damping ◽  
Thermoacoustic Instabilities ◽  
Acoustic Dissipation ◽  
Acoustic Liner ◽  
Bias Flow

The side-wall cooling liner in a gas turbine combustor serves main purposes—heat transfer and emission control. Additionally, it functions as a passive damper to attenuate thermoacoustic instabilities. The perforations in the liner mainly convert acoustic energy into kinetic energy through vortex shedding at the orifice rims. In the previous decades, several analytical and semi-empirical models have been proposed to predict the acoustic damping of the perforated liner. In the current study, a few of the models are considered to embody the transfer matrix method (TMM) for analyzing the acoustic dissipation in a concentric tube resonator with a perforated element and validated against experimental data in the literature. All models are shown to quantitatively appropriately predict the acoustic behavior under high bias flow velocity conditions. Then, the models are applied to maximize the damping performance in a realistic gas turbine combustor, which is under development. It is found that the ratio of the bias flow Mach number to the porosity can be used as a design guideline in choosing the optimal combination of the number and diameter of perforations in terms of acoustic damping.

APU-Noise Reduction by Novel Muffler Concepts

2018 ◽  
Author(s):  
Karsten Knobloch ◽  
Lars Enghardt ◽  
Friedrich Bake
Keyword(s):  
Noise Reduction ◽  
Operating Conditions ◽  
Acoustic Damping ◽  
Broadband Absorption ◽  
Auxiliary Power Unit ◽  
Auxiliary Power ◽  
Absorber Material ◽  
Bias Flow ◽  
Downstream Section ◽  
Broadband Sound

For a GTCP36-28 auxiliary power unit (APU), a set of mufflers has been designed and tested for some representative operating conditions. The first muffler design uses cavities of different sizes in conjunction with a bias flow for efficient broadband sound absorption. The second design — also expected to perform well over a large frequency range — makes use of a variable perforation and some porous absorber material. The acoustic damping performance of the mufflers was assessed using a downstream section of dedicated microphone probes. Individual spectra and circumferential averages have been computed and are used for a comparison to a hard-walled duct section of the same length. Results show a reasonable broadband absorption for most configurations. For one operating point, significant differences were found while comparing the performance of the cavity muffler with and without bias flow. The results suggest, that a small amount of air — less than initially expected — is sufficient to obtain the desired noise reduction.

scholarly journals A Methodology for Recognition of Emotions Based on Speech Analysis, for Applications to Human-Robot Interaction. An Exploratory Study

2014 ◽  
Vol 5 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Mohammad Rabiei ◽  
Alessandro Gasparetto
Keyword(s):  
Exploratory Study ◽  
Speech Rate ◽  
Human Robot Interaction ◽  
Acoustic Properties ◽  
Speech Analysis ◽  
Robot Interaction ◽  
Basic Emotions ◽  
Signal Processing Algorithms ◽  
Recognition Of Emotions ◽  
Set Up

AbstractA system for recognition of emotions based on speech analysis can have interesting applications in human-robot interaction. In this paper, we carry out an exploratory study on the possibility to use a proposed methodology to recognize basic emotions (sadness, surprise, happiness, anger, fear and disgust) based on phonetic and acoustic properties of emotive speech with the minimal use of signal processing algorithms. We set up an experimental test, consisting of choosing three types of speakers, namely: (i) five adult European speakers, (ii) five Asian (Middle East) adult speakers and (iii) five adult American speakers. The speakers had to repeat 6 sentences in English (with durations typically between 1 s and 3 s) in order to emphasize rising-falling intonation and pitch movement. Intensity, peak and range of pitch and speech rate have been evaluated. The proposed methodology consists of generating and analyzing a graph of formant, pitch and intensity, using the open-source PRAAT program. From the experimental results, it was possible to recognize the basic emotions in most of the cases

Pump Performance Improvement by Restraining Back Flow in Screw-Type Centrifugal Pump

2005 ◽  
Author(s):  
Yasushi Tatebayashi ◽  
Kazuhiro Tanaka ◽  
Toshio Kobayashi
Keyword(s):  
Pressure Fluctuations ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Simple Method ◽  
Back Flow ◽  
Pump Performance ◽  
Impeller Outlet ◽  
Pump Head ◽  
The Difference ◽  
Set Up

The authors have been investigating the various characteristics of screw-type centrifugal pumps, such as pressure fluctuations in impellers, flow patterns in volute casings, and pump performance in air-water two-phase flow conditions. During these investigations, numerical results of our investigations made it clear that three back flow regions existed in this type of pump. Among these, the back flow from the volute casing toward the impeller outlet was the most influential on the pump performance. Thus the most important factor to achieve higher pump performance was to reduce the influence of this back flow. One simple method was proposed to obtain the restraint of back flow and so as to improve the pump performance. This method was to set up a Ring-like wall at the suction cover casing between the impeller outlet and the volute casing. Its effects on the flow pattern and the pump performance have been discussed and clarified to compare the calculated results with experimental results done under two conditions — namely, one with and one without this Ring-type wall. The influence of wall’s height on the pump head was investigated by numerical simulations. In addition, the difference due to the wall’s effect was clarified to compare its effects on two kinds of volute casing. From the results obtained it can be said that restraining the back flow of such pumps was very important to achieve higher pump performance. Furthermore, another method was suggested to restrain back-flow effectively. This method was to attach a wall at the trailing edge of impeller. This method was very useful for avoiding the congestion of solids because this wall was smaller than that used in the first method. The influence of these factors on the pump performance was also discussed by comparing simulated calculations with actual experiments.

Sign in / Sign up

Export Citation Format

Share Document