LES-Based Study of the Influence of Thermal Boundary Condition and Combustor Confinement on Premix Flame Transfer Functions

2012 ◽  
Author(s):  
Luis Tay-Wo-Chong ◽  
Wolfgang Polifke
Keyword(s):  
Boundary Condition ◽  
Flow Field ◽  
Cross Section ◽  
Transfer Functions ◽  
Thermal Boundary Condition ◽  
Series Data ◽  
Reference Case ◽  
Flame Response ◽  
Flame Shape ◽  
The Impact

The influence of thermal boundary condition at the combustor wall and combustor confinement on the dynamic flame response of a perfectly premixed axial swirl burner is investigated. Large Eddy Simulations are carried out using the Dynamically Thickened Flame combustion model. Then, system identification methods are used to determine the flame transfer function (FTF) from the computed time series data. Two configurations are compared against a reference case with 90 mm × 90 mm combustor cross section and nonadiabatic walls: 1) combustor cross section similar to the reference case with adiabatic combustor walls, and 2) different confinement (160 mm × 160 mm) with nonadiabatic walls. It is found that combustor confinement and thermal boundary conditions have a noticeable influence on the flame response due to differences in flame shape and flow field. In particular the FTF computed with adiabatic wall boundary condition, which produces a flame with significant heat release in both shear layers, differs significantly from the FTF with nonadiabatic walls, where the flame stabilizes only in the inner shear layer. The observed differences in flow field and flame shape are discussed in relation to the unit impulse response of the flame. The impact of the differences in FTF on stability limits is analyzed with a low-order thermoacoustic model.

Large Eddy Simulation-Based Study of the Influence of Thermal Boundary Condition and Combustor Confinement on Premix Flame Transfer Functions

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Luis Tay-Wo-Chong ◽  
Wolfgang Polifke
Keyword(s):  
Boundary Condition ◽  
Flow Field ◽  
Cross Section ◽  
Thermal Boundary Condition ◽  
Series Data ◽  
Reference Case ◽  
Large Eddy ◽  
Flame Response ◽  
Flame Shape ◽  
The Impact

The influence of the thermal boundary condition at the combustor wall and combustor confinement on the dynamic flame response of a perfectly premixed axial swirl burner is investigated. Large eddy simulations are carried out using the dynamically thickened flame combustion model. Then system identification methods are used to determine the flame transfer function (FTF) from the computed time series data. Two configurations are compared against a reference case with a 90 mm × 90 mm combustor cross section and nonadiabatic walls: (1) a combustor cross section similar to the reference case with adiabatic combustor walls, and (2) a different confinement (160 mm × 160 mm) with nonadiabatic walls. It is found that combustor confinement and thermal boundary conditions have a noticeable influence on the flame response due to differences in the flame shape and flow field. In particular, the FTF computed with an adiabatic wall boundary condition which produces a flame with a significant heat release in both shear layers, differs significantly from the FTF with nonadiabatic walls, where the flame stabilizes only in the inner shear layer. The observed differences in the flow field and flame shape are discussed in relation to the unit impulse response of the flame. The impact of the differences in the FTF on stability limits is analyzed with a low-order thermoacoustic model.

Impact of Boundary Conditions on the Reconstructed Flame Transfer Function for Gas Turbine Combustion Systems

2008 ◽  
Author(s):  
Krzysztof Kostrzewa ◽  
Axel Widenhorn ◽  
Berthold Noll ◽  
Manfred Aigner ◽  
Werner Krebs ◽  
...  
Keyword(s):  
Transfer Function ◽  
Boundary Conditions ◽  
Gas Turbine ◽  
Transfer Functions ◽  
Feedback Mechanism ◽  
Pressure Amplitude ◽  
Flame Response ◽  
Gas Turbine Combustion ◽  
Combustion Systems ◽  
The Impact

In order to achieve low levels of pollutants modern gas turbine combustion systems operate in lean and premixed modes. However, under these conditions self-excited combustion oscillations due to a complex feedback mechanism between pressure and heat release fluctuations can be found. These instabilities may lead to uncontrolled high pressure amplitude oscillations which can damage the whole combustor. The flame induced acoustic source terms are still analytically not well described and are a major topic of thermo-acoustic investigations. For the analysis of thermo-acoustic phenomena in gas turbine combustion systems flame transfer functions can be utilized. The purpose of this paper is to introduce and to investigate modeling parameters, which could influence a novel computational approach to reconstruct flame transfer functions known as the CFD/SI method. The flame transfer function estimation is made by application of a system identification method based on Wiener-Hopf formulation. Varying acoustic boundary conditions, combustion models and time resolutions may strongly affect the reconstructed flame response characterizing overall system dynamics. The CFD/SI approach has been applied to a generic gas turbine burner to derive a flame response. 3D unsteady simulations excited with white noise have been performed and the reconstructed flame transfer functions have been validated with experimental data. Moreover, the impact on the reconstructed flame transfer functions because of different boundary condition configurations has been examined.

The Effect of Cross-sectional Geometry on ZT Enhancement in Rough Silicon Nanostructures

2010 ◽  
Vol 1267 ◽  
Author(s):  
Jyothi Swaroop Sadhu ◽  
Marc G Ghossoub ◽  
Sanjiv Sinha
Keyword(s):  
Thermal Conductivity ◽  
Boundary Condition ◽  
Cross Section ◽  
Silicon Nanowires ◽  
Silicon Nanostructures ◽  
Dramatic Reduction ◽  
Cross Sectional ◽  
The Wire ◽  
Phonon Localization ◽  
The Impact

AbstractThe dramatic reduction in the thermal conductivity of rough silicon nanowires is due to phonon localization in the wire resulting from multiple scattering of phonons from the rough walls. We report the dependence of thermal conductivity of the nanowires as a function of the surface roughness and the diameter of the wire by modeling the nanowire as a waveguide. In addition, we estimate the impact of boundary condition, dimensionality and cross section of rough wire on the thermal conductivity. This theoretical model gives insights for tailoring thermal conductivity and enhancing the ZT of silicon to 1 for its use in thermoelectrics

Analysis of Lumped Deterministic Source Terms and Their Sub-Components in a Stage 1 High Pressure Turbine Rotor

2008 ◽  
Author(s):  
Jon Ratzlaff ◽  
Paul D. Orkwis ◽  
Christopher Noll ◽  
Gary Steuber
Keyword(s):  
Flow Field ◽  
Time Series Data ◽  
Turbine Rotor ◽  
Series Data ◽  
Numerical Dissipation ◽  
Source Terms ◽  
Governing Equations ◽  
High Pressure Turbine ◽  
Stage 1 ◽  
The Impact

A GE proprietary code has been used to extract the Lumped Deterministic Source Terms (LDSTs) for the five governing equations: continuity, r, θ, z-momentum, and energy; as well as the two turbulence equations, from a converged unsteady time-averaged flow field. LDSTs are the opposite of the fluxes contained in the solution residuals for a time averaged flow field. They describe the cumulative effects of unsteadiness contained in the time-averaged solution. It has been shown that the addition of these terms to the steady residual operator in this code will drive the solution to the time averaged unsteady solution. The contributions of the LDST components, i.e. the residuals from the Euler, viscous and numerical dissipation, were studied to assess how they build the total LDST. Another approach to computing the inviscid source terms directly from time series data was also compared to the respective total and shows that the LDSTs are composed primarily of the inviscid component terms. In addition, attaining a time-averaged solution with a steady solver has been found to be sensitive to the boundary conditions. Results from one boundary condition set are presented in an error form to gauge the impact on the solution.

Heat Transfer Analysis of Turbulent Flow in Rectangular-Sectioned U-Bends

2004 ◽  
Author(s):  
Sassan Etemad ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Cross Section ◽  
Heat Transfer Analysis ◽  
Reference Case ◽  
Aspect Ratios ◽  
The Impact

The turbulent flow in rectangular-sectioned U-bend ducts with bend mid-line radius 3.35 and with aspect-ratios AR=0.5, 1, 2, and 4 were explored using linear and non-linear high- and low-Re k-ε turbulence models at a Reynolds number of 56000. The impact of the cross-section aspect ratio on the flow field and the associated thermal field was studied. Experimental data were found [1–3] for the square-sectioned cross section (AR=1) and this case was chosen as the reference case for comparison and validation with experimental data. The other cases were evaluated in relation to the square-sectioned case. The predicted data for AR=1 agreed well with the experimental data. The velocity profile upstream the bend has fundamental influence on the strength of the secondary flow and heat transfer. Complex secondary motion was detected for all cases but in particular for AR=1. The mixing process due to the secondary flow decreased in general with increasing aspect ratio.

scholarly journals DAMPAK TRANSFER FISKAL (CONDITIONAL GRANT) TERHADAP PEMBANGUNAN PERTANIAN, KEMISKINAN DAN KETIMPANGAN DI INDONESIA: ANALISIS DATA PANEL

Agriekonomika ◽  
2017 ◽  
Vol 6 (2) ◽  
pp. 164 ◽  
Author(s):  
Nor Qomariyah ◽  
Suharno Suharno ◽  
D. S. Priyarsono
Keyword(s):  
Time Series ◽  
Income Inequality ◽  
Cross Section ◽  
Urban Areas ◽  
Agricultural Development ◽  
Central Government ◽  
Labour Force ◽  
Series Data ◽  
Fiscal Transfer ◽  
The Impact

<p><em>Kemiskinan menjadi permasalahan utama bangsa Indonesia, jumlah penduduk miskin sebesar 28.55 juta orang (11. 47%), sementara ketimpangan pendapatan meningkat hingga mencapai 0.41 (BPS, 2013). Penelitian ini bertujuan untuk mengevaluasi dampak Dana Alokasi Khusus (DAK) yang berupa conditional grant terhadap pembangunan pertanian, kemiskinan, dan ketimpangan pendapatan. Penelitian ini menggunakan model persamaan simultan dengan data time series tahun 2009-2013 dan data cross section pada 11 provinsi di Indonesia. Metode untuk estimasi parameter menggunakan 2SLS. Hasil simulasi menunjukkan bahwa peningkatan alokasi DAK jalan dan irigasi dapat meningkatkan kinerja fiskal, sektor PDRB pertanian, total PDRB, dan total penyerapan tenaga kerja, tetapi penyerapan tenaga kerja sektor pertanian menurun disebabkan adanya kenaikan upah, menurunkan ketimpangan pendapatan dan mengurangi kemiskinan baik di daerah pedesaan maupun perkotaan. Penelitian ini merekomendasikan bahwa pemerintah pusat hendaknya meningkatkan injeksi dana langsung ke daerah lewat dana alokasi khusus (DAK) bidang infrastruktur karena dampaknya efektif menurunkan kemiskinan.</em></p><p>THE IMPACT OF FISCAL TRANSFER (CONDITIONAL GRANT) ON AGRICULTURAL DEVELOPMENT, POVERTY AND INEQUALITY : PANEL ANALYSIS DATA</p><p>ABSTRACT</p><p><em>Poverty is the main problem in Indonesia, the number of the poor is 28.55 million people (11.47%), while income inequality increased until 0.41 (BPS, 2013). The main objective of this study was to evaluate the impact of Special Allocation Fund on agricultural development, poverty, and income inequality. This study uses simultaneous equation models with time series data of 2009-2013 and cross section data of 11 provinces in Indonesia. Method for parameter estimation is 2SLS. The simulation results show that the increased allocation of DAK road and irrigation can increase fiscal performance, the agricultural sector GRDP, total GRDP, but the labour force absorbtion of agricultural decreases because of the increasing of wages, the decreasing of income inequality and the reducing of poverty either in rural or urban areas. This study recomends that the central government should improve the injection of funds directly to the regions through a special allocation fund for rural infrastructure and agriculture because it gives an effective impact on poverty alleviation</em><strong><em>.</em></strong></p><p><em>Keywords : Special allocation fund, poverty, income inequality, fiscal transfer.</em></p>

scholarly journals Effect of Congestion on Flow Field of Vented Natural Gas Explosion in a Kitchen

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Lei Pang ◽  
Qianran Hu ◽  
Mengjie Jin ◽  
Kai Yang
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Cross Section ◽  
Large Scale ◽  
Flame Structure ◽  
Small Scale ◽  
Gas Explosion ◽  
Cross Sectional ◽  
Surrounding Areas ◽  
The Impact

The process of gas explosion venting in a typical Chinese civil kitchen was investigated using computational fluid dynamics technology, focusing on the impact of the scale and cross-sectional characteristics of congestion, such as common furniture and electrical appliances, on the explosion flow-field parameters. An asymmetrical distribution of congestion will cause the uneven combustion of explosion flames in the kitchen. The flame will initially spread on one side of the room and then accelerate toward the surrounding areas, thereby increasing the risk of indoor gas explosion. The typical indoor overpressure change process can be divided into five stages, among which Stage V is found to be related to pseudoclosed combustion. Large-scale congestion has an obstructive effect on the explosion flow field, but it changes under certain conditions, while small-scale congestion only acts as a promoter. The flat congestion cross section helps maintain the stability of the flame structure, whereas the continuous and abrupt change of the congestion cross section can induce strong turbulent combustion. The research results provide a theoretical basis for the prevention and control of natural gas explosion hazards in civil kitchens from the perspective of congestion scale and cross-sectional mutation.

Unsteady Effects due to Rotor Purge Flow Variations in a Dual-Spool Turbine Setup

2020 ◽  
Author(s):  
F. Merli ◽  
P. Z. Sterzinger ◽  
M. Dellacasagrande ◽  
L. Wiesinger ◽  
A. Peters ◽  
...  
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
Pressure Probe ◽  
Wall Region ◽  
Two Stage ◽  
Reference Case ◽  
Time Resolved ◽  
Aerodynamic Pressure ◽  
Purge Flow ◽  
The Impact

Abstract The paper discusses the impact of rotor purge flows on the unsteady flow field downstream of a two-stage, two-spool test turbine. The analyzed setup is representative of the second high-pressure turbine (HPT) and the first low-pressure turbine (LPT) stage in a modern turbofan aero-engine, with a turbine center frame (TCF) with non-turning struts in-between the two turbines. All measurements were carried out for an engine-representative test vehicle setup at the Transonic Test Turbine Facility at Graz University of Technology. The test rig features a secondary air system delivering five purge flows with independent temperature and mass flow control to the HPT and LPT cavities. This work extends the results shown in two recent publications analyzing the time-resolved flow through the same two-stage setup at fixed purge flow rates. The paper aims to provide additional input about the driving sources of unsteadiness in gas turbines for aeronautic applications, by isolating the HPT and LPT purge air contributions. The time-resolved flow field at the LPT exit was acquired with a Fast Response Aerodynamic Pressure Probe (FRAPP) for three different purge conditions (reference case, no HPT purge case, no LPT purge case), to separate and quantify the impact of HPT and LPT purge contributions on the main flow field. The so-called Rotor Synchronic Averaging (RSA) technique was used as phase-averaging approach, to account for the unsteadiness due to both rotors. Proper Orthogonal Decomposition (POD) was then applied to isolate the most important structures and identify their origins. The comparison of the three data-sets shows a significant influence of the HPT purge on the entire flow field at the LPT exit, even though the HPT is located far upstream, while the LPT purge impact appears to mostly affect the end-wall region.

Impact of exchange rate and oil price on the yield of sovereign bond and sukuk: Evidence from Malaysian capital market

2017 ◽  
Vol 5 (4) ◽  
pp. 27
Author(s):  
Huda Arshad ◽  
Ruhaini Muda ◽  
Ismah Osman
Keyword(s):  
Exchange Rate ◽  
Capital Market ◽  
Time Series Data ◽  
Oil Prices ◽  
Oil Price ◽  
Series Data ◽  
Sovereign Bond ◽  
Long Run ◽  
Short Run ◽  
The Impact

This study analyses the impact of exchange rate and oil prices on the yield of sovereign bond and sukuk for Malaysian capital market. This study aims to ascertain the effect of weakening Malaysian Ringgit and declining of crude oil price on the fixed income investors in the emerging capital market. This study utilises daily time series data of Malaysian exchange rate, oil price and the yield of Malaysian sovereign bond and sukuk from year 2006 until 2015. The findings show that the weakening of exchange rate and oil prices contribute different impacts in the short and long run. In the short run, the exchange rate and oil prices does not have a direct relation with the yield of sovereign bond and sukuk. However, in the long run, the result reveals that there is a significant relationship between exchange rate and oil prices on the yield of sovereign bond and sukuk. It is evident that only a unidirectional causality relation is present between exchange rate and oil price towards selected yield of Malaysian sovereign bond and sukuk. This study provides numerical and empirical insights on issues relating to capital market that supports public authorities and private institutions on their decision and policymaking process.

Transport infrastructure of the Rostov Oblast: Problems and prospects for development in the context of national projects implementation

2020 ◽  
Vol 19 (6) ◽  
pp. 1015-1034
Author(s):  
O.Yu. Patrakeeva
Keyword(s):  
Time Series Data ◽  
Mutual Influence ◽  
Rostov Oblast ◽  
Transport Infrastructure ◽  
Series Data ◽  
Cointegration Tests ◽  
Level Of Economic Development ◽  
Short Run ◽  
The Government ◽  
The Impact

Subject. The paper considers national projects in the field of transport infrastructure, i.e. Safe and High-quality Roads and Comprehensive Plan for Modernization and Expansion of Trunk Infrastructure, and the specifics of their implementation in the Rostov Oblast. Objectives. The aim is to conduct a statistical assessment of the impact of transport infrastructure on the region’s economic performance and define prospects for and risks of the implementation of national infrastructure projects in conditions of a shrinking economy. Methods. I use available statistics and apply methods and approaches with time-series data, namely stationarity and cointegration tests, vector autoregression models. Results. The level of economic development has an impact on transport infrastructure in the short run. However, the mutual influence has not been statistically confirmed. The paper revealed that investments in the sphere of transport reduce risk of accidents on the roads of the Rostov Oblast. Improving the quality of roads with high traffic flow by reducing investments in the maintenance of subsidiary roads enables to decrease accident rate on the whole. Conclusions. In conditions of economy shrinking caused by the complex epidemiological situation and measures aimed at minimizing the spread of coronavirus, it is crucial to create a solid foundation for further economic recovery. At the government level, it is decided to continue implementing national projects as significant tools for recovery growth.

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