Numerical Investigation of High Speed Combustion and its Impact on Thermal Structure

2014 ◽  
Author(s):  
Litao Zhang ◽  
Lili Zheng ◽  
Lingyun Hou
Keyword(s):  
Heat Flux ◽  
Thermal Stress ◽  
High Speed ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Thermal Structure ◽  
Great Influence ◽  
Leading Edge ◽  
Reacting Flow ◽  
Fuel Flow

This paper presents numerical study of high-speed combustion and its relationship with thermal stress distribution on a cavity combustion chamber. First, a physical model is established to describe high speed compressible turbulent reacting flow as well as thermal transport in combustor structure. It is then applied to a model combustor with two-staged fuel injections to examine the effects of fuel flow rate and inflow conditions on the heat flux intensity and thermal stress distributions across the thickness of the combustor wall. The result shows that the injection method of the first stage has a great influence on the flow field near the second one, and it affects combustion and heat release distribution inside the combustor. The intensity of heat flux passing through the combustor wall changes along the downstream of the flow, and large thermal stresses are generated in the vicinity of the injector, the leading edge and the trailing edge of the cavity.

Numerical Study of Thermal Stresses in a Planar Solid Oxide Fuel Cell Stack

2017 ◽  
Author(s):  
Cun Wang ◽  
Tao Zhang ◽  
Cheng Zhao ◽  
Jian Pu
Keyword(s):  
Thermal Stress ◽  
Fuel Cell ◽  
Solid Oxide Fuel Cell ◽  
Thermal Stresses ◽  
Coefficient Of Thermal Expansion ◽  
Numerical Study ◽  
Solid Oxide ◽  
Oxide Fuel ◽  
Compressive Loads ◽  
Cte Mismatch

A three dimensional numerical model of a practical planar solid oxide fuel cell (SOFC) stack based on the finite element method is constructed to analyze the thermal stress generated at different uniform temperatures. Effects of cell positions, different compressive loads, and coefficient of thermal expansion (CTE) mismatch of different SOFC components on the thermal stress distribution are investigated in this work. Numerical results indicate that the maximum thermal stress appears at the corner of the interface between ceramic sealants and cells. Meanwhile the maximum thermal stress at high temperature is significantly larger than that at room temperature (RT) and presents linear growth with the increase of operating temperature. Since the SOFC stack is under the combined action of mechanical and thermal loads, the distribution of thermal stress in the components such as interconnects and ceramic sealants are greatly controlled by the CTE mismatch and scarcely influenced by the compressive loads.

Development of High Speed and High Temperature Atomic Layer Thermopiles

2019 ◽  
Author(s):  
Lakshya Bhatnagar ◽  
Guillermo Paniagua
Keyword(s):  
Heat Flux ◽  
High Temperature ◽  
High Speed ◽  
Cooling System ◽  
Numerical Study ◽  
Measurement Data ◽  
Atomic Layer ◽  
Heat Fluxes ◽  
Heat Transfer Analysis ◽  
Uncertainty Estimates

Abstract This work aims to provide a technique with which high frequency heat flux measurement data can be acquired in systems with high operational temperatures and high-speed flows with quantifiable and accurate uncertainty estimates. This manuscript presents the detailed calibration and application of an atomic layer thermopile, for heat fluxes with a frequency bandwidth of 0 to 1MHz. Two calibration procedures with a detailed uncertainty analysis. The first procedure consists using a laser to deliver radiation heat flux, while the second consists of a convective heat blowdown experiment. The use of this probe is demonstrated in a high-speed environment at Mach 2. The sensor effectively captures the passage of the normal shock wave and the values are compared with those computed using surface temperature measurement. Finally, a numerical study is carried out to design a cooling system that will allow the sensor to survive in high temperature conditions of 1273K while the sensor film is maintained at 323K. A two-dimensional axisymmetric conjugate heat transfer analysis is carried out to obtain the desired geometry.

Rotating Stall Observations in a High Speed Compressor—Part II: Numerical Study

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Dodds ◽  
M. Vahdati
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Numerical Predictions ◽  
Stage 1 ◽  
Variable Stator

In this two-part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (Part I) and numerically (Part II). The experimental observations reported in Part I are now explored through the use of 3D unsteady Reynolds-averaged Navier–Stokes (RANS) simulation. The objective is to both validate the computational model and, where possible, explore some physical aspects of the phenomena. Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part I. The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multicell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multicell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes (VSVs) are mismatched further, pushing each region deeper into stall. The numerical predictions show a credible match with the experimental findings of Part I. This suggests that a RANS modeling approach is sufficient to capture some important aspects of part span rotating stall behavior.

Numerical investigation of the role of hyper-mixers in supersonic mixing

2010 ◽  
Vol 114 (1161) ◽  
pp. 659-672 ◽  
Author(s):  
S. L. N. Desikan ◽  
K. Kumaran ◽  
V. Babu
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Numerical Study ◽  
Mie Scattering ◽  
Stagnation Pressure ◽  
Reacting Flow ◽  
Qualitative Comparison ◽  
Supersonic Mixing ◽  
High Speed Flows

Abstract In this numerical study, the role of hyper-mixers on supersonic mixing is investigated for six different strut configurations. To this end, 3D, compressible, turbulent, non-reacting flow calculations with air as the secondary injectant have been carried out. A qualitative comparison of the predictions with experimental results is made through Schlieren and Mie scattering images. A quantitative evaluation of the predictions is made by comparison with experimentally measured exit stagnation pressure, wall static pressure and the degree of unmixedness. Based on these results, three strut configurations have been selected for carrying out simulations with hydrogen as the injectant. Results from the hydrogen simulations are compared with the predictions using air and also across the strut configurations. The results clearly demonstrate that castellated strut configurations are very effective in enhancing mixing in such high speed flows.

Numerical Study on Aero-Thermal Performance of HP Turbine Endwalls Under Influence of Hot Streak and High Mainstream Turbulence

2016 ◽  
Author(s):  
Zhiduo Wang ◽  
Wenhao Zhang ◽  
Zhaofang Liu ◽  
Chen Zhang ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbulence Intensity ◽  
Wall Temperature ◽  
Numerical Study ◽  
Leading Edge ◽  
Heat Transfer Characteristics ◽  
Adiabatic Wall ◽  
Transfer Characteristics ◽  
Hot Streak

In this paper, unsteady RANS simulations were performed at two hot streak (HS) circumferential positions with inlet turbulence intensity of 5% and 20%. The interacted HS and high mainstream turbulence effects on endwall heat transfer characteristics of a high-pressure (HP) turbine were discussed by analyzing the flow structures and presenting the endwall adiabatic wall temperature, heat transfer coefficient (HTC) and heat flux distributions. The results indicate that both the wall temperature and HTC increase with the turbulence intensity at most stator endwall regions. In addition, the increase of wall temperature plays a greater role than HTC of influencing the wall heat flux. However, higher turbulence intensity decreases the intensity of the stator passage horse-shoe vortex, also the corresponding region HTC and heat flux are reduced. In rotor passage, the variation of HS circumferential position would alter the hub and casing endwall temperature, however, the discrepancy is weakened at higher turbulence. The elevated HS attenuation at higher turbulence results in temperature augmentation at the leading edge of rotor hub and casing endwalls, while temperature decrease after 50% axial chord, thus obtains more uniform temperature distributions on the endwalls. However, the rotor endwall HTC is only augmented significantly at the leading edge on hub endwall, and pressure side and downstream of trailing edge on casing endwall. Variation of HTC and adiabatic wall temperature jointly determines the rotor hub and casing endwall heat flux, and the temperature variation has dominant effects in the most regions. In general, the variation of adiabatic wall temperature and HTC should be considered simultaneously when analyzing the turbine endwall heat transfer characteristics.

A Numerical Study of Concurrent Flame Propagation Over Methanol Pool Surface

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Seik Mansoor Ali ◽  
Vasudevan Raghavan ◽  
K. Velusamy ◽  
Shaligram Tiwari
Keyword(s):  
Flame Spread ◽  
Numerical Study ◽  
Leading Edge ◽  
Reacting Flow ◽  
Atmospheric Conditions ◽  
Air Velocity ◽  
Two Phase ◽  
Spread Velocity ◽  
Pool Surface ◽  
Initial Flame

Concurrent flame spread over methanol pool surface under atmospheric conditions and normal gravity has been numerically investigated using a transient, two-phase, reacting flow model. The average flame spread velocities for different concurrent air velocities predicted using the model are quite close to the experimental data available in the literature. As the air velocity is increased, the fuel consumption rate increases and aids in faster flame spread process. The flame initially anchors around the leading edge of the pool and the flame tip spreads over the pool surface. The rate of propagation of flame tip along the surface is seen to be steady without fluctuations. The flame spread velocity is found to be nonuniform as the flame spreads along the pool surface. The flame spread velocity is seen to be higher initially. It then decreases up to a point when the flame has propagated to around 40% to 50% of the pool length. At this position, a secondary flame anchoring point is observed, which propagates toward the trailing edge of the pool. As a result, there is an increasing trend observed in the flame spread velocity. As the air velocity is increased, the initial flame anchoring point moves downstream of the leading edge of the fuel pool. The variations of interface quantities depend on the initial flame anchoring location and the attainment of thermodynamic equilibrium between the liquid- and gas-phases.

Blade Tip Carving Effects on the Aero-Thermal Performance of a Transonic Turbine

2013 ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
High Speed ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Geometrical Parameters ◽  
Complex Flow ◽  
Turbine Rotor Blade ◽  
Blade Tip ◽  
Transonic Turbine

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters on the overtip flow require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping. The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern transonic turbine rotor blade (Reynolds number is 5.5 × 105, relative exit Mach number is 0.9) by means of three-dimensional Reynolds-Averaged Navier-Stokes calculations. The novel contoured tip geometry was designed based on a 2D tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.

scholarly journals Numerical Study of Thermal Stresses for the Semiconductor CdZnTe in Vertical Bridgman

2015 ◽  
Vol 55 ◽  
pp. 66-78
Author(s):  
Hanen Jamai ◽  
M. El Ganaoui ◽  
Habib Sammouda ◽  
Bernard Pateyron
Keyword(s):  
Numerical Simulation ◽  
Thermal Stress ◽  
Stress Distribution ◽  
Directional Solidification ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Cooling Temperature ◽  
Stress Components ◽  
Vertical Bridgman

The aim of this work is to present a numerical simulation of thermal stress in directional solidification of CdZnTe in vertical Bridgman apparatus. Especial attention will be attributed to show the importance of cooling temperature and time’s growth affecting the thermal stress. Furthermore, we will focus on investigating the thermal stress’ components and their distribution in crystal, which gives a detailed about the stress distribution and consequently on the distribution of defects during solidification of CdZnTe.

Analysis of High Concrete Arch Dam Thermal-Creep-Stress

2011 ◽  
Vol 243-249 ◽  
pp. 4496-4500 ◽  
Author(s):  
Ke Hong Zheng ◽  
Bing Yin Zheng
Keyword(s):  
Thermal Stress ◽  
Thermal Stresses ◽  
Simulation Analysis ◽  
Great Influence ◽  
Arch Dam ◽  
Thermal Creep ◽  
High Arch Dam ◽  
Finite Element Program ◽  
Concrete Arch Dam ◽  
Creep Stress

The calculation of thermal stress is important to high concrete arch dam. In the progress of construction simulation analysis, the distribution of thermal stresses should be paid attention for it has great influence to arch design and rapid construction. The impacts on thermal stress are water temperature and air temperature and so on. In this paper, the author also thought about of the influence of creep, and applied the formulations of predecessors to finite element program. A engineering example about some high arch dam proves correctness and feasibility of considering thermal-creep –stress.

Blade Tip Carving Effects on the Aerothermal Performance of a Transonic Turbine

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
High Speed ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Geometrical Parameters ◽  
Complex Flow ◽  
Leakage Flows ◽  
Blade Tip ◽  
Exit Mach Number

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping. The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern rotor blade (Reynolds number of 5.5 × 105 and a relative exit Mach number of 0.9) by means of three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) calculations. Two novel contoured tip geometries were designed based on a two-dimensional (2D) tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.

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