The evolution of local instability regions in turbulent non-premixed flames

2016 ◽  
Vol 803 ◽  
pp. 18-50 ◽  
Author(s):  
Y. Dagan ◽  
E. Arad ◽  
Y. Tambour
Keyword(s):  
Experimental Study ◽  
Large Scale ◽  
Turbulent Flame ◽  
Three Dimensional ◽  
Decomposition Analysis ◽  
Premixed Turbulent Combustion ◽  
Flame Instability ◽  
Recirculating Flow ◽  
Analytical Stability ◽  
Pulsating Flames

Unsteady turbulent flame evolution in non-premixed combustion has been computationally investigated using large eddy simulations. A simple coaxial combustion chamber, subjected to highly unsteady, turbulent recirculating flow is considered, following the experimental study of Owen et al. (Proc. Combust. Inst., vol. 16, 1976, pp. 105–117). Large-scale flame fluctuations, reported in the above experimental study, such as pulsating flames in swirling and non-swirling conditions, were identified here in our computation. New criteria for flame three-dimensional inhomogeneity are suggested and implemented in the present study, providing the ability to quantify the flame unsteadiness. Using this technique, it is shown that local, large quenched regions develop in the flame’s mixing area and rotate continuously, even when swirl is not imposed on the inlet. However, this rotation appears to be disordered, abruptly changing its direction. On the other hand, our study shows that when swirl is imposed on the inlet, a larger quenched region is identified, rotating in steady ordered rotation in the direction of the imposed swirl. In addition, large-scale radial flame fluctuations are increased downstream with the increase of swirl number. Consequently, significant correlations between radial and circumferential flame fluctuation frequencies were retrieved. Proper orthogonal decomposition analysis reveals coherent flame structures of five dominant modes that contain most of the energy in the fluctuating flame. A simplified analytical stability model is derived and implemented here to assess the hydrodynamic contribution to the flame instability; it is shown that radial fluctuations are excited by circumferential perturbations in the mixing region, providing new insight into the mechanism responsible for the onset of radial fluctuations. The computed radial flame fluctuation spectrum is predicted well using the linear stability analysis. Thus, our findings may therefore be applicable to a large class of non-premixed turbulent combustion problems.

The Effect of Aspect-Ratio on the Development of the Large-Scale Structures in the Three-Dimensional Wall Jet

2005 ◽  
Author(s):  
Joseph W. Hall ◽  
Daniel Ewing
Keyword(s):  
Aspect Ratio ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Decomposition Analysis ◽  
Wall Pressure ◽  
Symmetric Mode ◽  
Large Scale Structures ◽  
Aspect Ratios ◽  
Scale Structures

The development of the large-scale structures in three-dimensional wall jets exiting rectangular nozzles with aspect-ratios of 1 and 4 was investigated using simultaneous measurements of the fluctuating wall pressure across the jet. The pressure fluctuations in the jets were asymmetric and caused the fluctuating wall pressure to be poorly correlated across the jet centerline. A Proper Orthogonal Decomposition analysis indicated that both the first and second modes make similar contributions to the variance of the fluctuating pressure, and were symmetric and antisymmetric, respectively, and the interplay between these modes caused the asymmetry in the instantaneous pressure fluctuations across the jet centreline. A wavelet analysis of the instantaneously reconstructed pressure fields indicated that the fluctuations were predominantly in two frequency bands near the jet centerline, but were only contained in one band on the outer lateral edges of the jet, indicating there were two different large-scale motions present. The development of large-scale structures in the two jets initially differed in the intermediate field with the antisymmetric mode being more prominent in the square jet and the symmetric mode being more prominent in the larger aspect-ratio jet. Further downstream, the symmetric mode was more prominent in both jets.

Experimental study of three-dimensional separation on a large-scale model

AIAA Journal ◽  
1995 ◽  
Vol 33 (11) ◽  
pp. 2107-2113 ◽  
Author(s):  
D. Barberis ◽  
P. Molton
Keyword(s):  
Experimental Study ◽  
Large Scale ◽  
Three Dimensional ◽  
Scale Model ◽  
Large Scale Model

Experimental Study on Seismic Responses of Piping Systems With Friction—Part 1: Large-Scale Shaking Table Vibration Test

1995 ◽  
Vol 117 (3) ◽  
pp. 245-249 ◽  
Author(s):  
K. Suzuki ◽  
T. Watanabe ◽  
T. Mitsumori ◽  
N. Shimizu ◽  
H. Kobayashi ◽  
...  
Keyword(s):  
Experimental Study ◽  
Large Scale ◽  
Earth Science ◽  
Three Dimensional ◽  
Power Spectra ◽  
Reduction Factor ◽  
Oil Refinery ◽  
Shaking Table ◽  
Piping Systems ◽  
Frictional Vibration

This report deals with the experimental study of seismic response behavior of piping systems in industrial facilities such as petrochemical, oil refinery, and nuclear plants. Special attention is focused on the nonlinear dynamic response of piping systems due to frictional vibration appearing in piping and supporting devices. A three-dimensional mock-up piping and supporting structure model wherein piping is of 30-m length and 200-mm diameter is excited by a large-scale (15 m × 15 m) shaking table belonging to the National Research Institute for Earth Science and Disaster Prevention in Tsukuba, Ibaraki. Power spectra of the response vibration and the loading-response relationship in the form of a hysteresis loop under several loading conditions are obtained. The response reduction effect caused by frictional vibration is evaluated and demonstrated in terms of “response reduction factor.”

Experimental study of deformation processes in large-scale concrete structures under quasistatic loading

2020 ◽  
Vol 15 (5) ◽  
pp. 619-633
Author(s):  
Igor Shardakov ◽  
Irina Glot ◽  
Aleksey Shestakov ◽  
Roman Tsvetkov ◽  
Valeriy Yepin ◽  
...  
Keyword(s):  
Experimental Study ◽  
Large Scale ◽  
Concrete Structures ◽  
Deformation Processes ◽  
Quasistatic Loading

scholarly journals A Review on Additive Manufacturing Possibilities for Electrical Machines

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1940
Author(s):  
Muhammad Usman Naseer ◽  
Ants Kallaste ◽  
Bilal Asad ◽  
Toomas Vaimann ◽  
Anton Rassõlkin
Keyword(s):  
Additive Manufacturing ◽  
Large Scale ◽  
Three Dimensional ◽  
Electrical Machines ◽  
Electromagnetic Properties ◽  
Scale Production ◽  
Performance Parameters ◽  
Large Scale Production ◽  
One Step ◽  
Manufacturing Techniques

This paper presents current research trends and prospects of utilizing additive manufacturing (AM) techniques to manufacture electrical machines. Modern-day machine applications require extraordinary performance parameters such as high power-density, integrated functionalities, improved thermal, mechanical & electromagnetic properties. AM offers a higher degree of design flexibility to achieve these performance parameters, which is impossible to realize through conventional manufacturing techniques. AM has a lot to offer in every aspect of machine fabrication, such that from size/weight reduction to the realization of complex geometric designs. However, some practical limitations of existing AM techniques restrict their utilization in large scale production industry. The introduction of three-dimensional asymmetry in machine design is an aspect that can be exploited most with the prevalent level of research in AM. In order to take one step further towards the enablement of large-scale production of AM-built electrical machines, this paper also discusses some machine types which can best utilize existing developments in the field of AM.

scholarly journals Vibration characteristics of triple-gear-rotor system in compressed air energy storage under variable torque load

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042098705
Author(s):  
Xinran Wang ◽  
Yangli Zhu ◽  
Wen Li ◽  
Dongxu Hu ◽  
Xuehui Zhang ◽  
...  
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Element Model ◽  
Rotor System ◽  
Dynamic Responses ◽  
System Response ◽  
Rotating Speed ◽  
Torque Load ◽  
Set Up ◽  
Two Stages

This paper focuses on the effects of the off-design operation of CAES on the dynamic characteristics of the triple-gear-rotor system. A finite element model of the system is set up with unbalanced excitations, torque load excitations, and backlash which lead to variations of tooth contact status. An experiment is carried out to verify the accuracy of the mathematical model. The results show that when the system is subjected to large-scale torque load lifting at a high rotating speed, it has two stages of relatively strong periodicity when the torque load is light, and of chaotic when the torque load is heavy, with the transition between the two states being relatively quick and violent. The analysis of the three-dimensional acceleration spectrum and the meshing force shows that the variation in the meshing state and the fluctuation of the meshing force is the basic reasons for the variation in the system response with the torque load. In addition, the three rotors in the triple-gear-rotor system studied show a strong similarity in the meshing states and meshing force fluctuations, which result in the similarity in the dynamic responses of the three rotors.

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