Axial evolution of forced helical flame and flow disturbances

2018 ◽  
Vol 844 ◽  
pp. 323-356 ◽  
Author(s):  
Travis E. Smith ◽  
Christopher M. Douglas ◽  
Benjamin L. Emerson ◽  
Timothy C. Lieuwen
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Unstable Flow ◽  
Natural Oscillations ◽  
Planar Velocity ◽  
Fluorescence Measurements ◽  
Flow Disturbances ◽  
Planar Laser ◽  
Acoustic Forcing

This paper presents 5 kHz stereo particle image velocimetry and OH planar laser induced fluorescence measurements of transversely forced swirl flames. The presence of transverse forcing on this naturally unstable flow both influences the natural instabilities, as well as amplifies disturbances that may not necessarily manifest themselves during natural oscillations. By manipulating the structure of the acoustic forcing field, both axisymmetric and helical modes are preferentially excited away from the frequency of natural instability. The paper presents a method for spatially interpolating the phase locked $r{-}z$ and $r{-}\unicode[STIX]{x1D703}$ planar velocity and flame position data, extracting the full three-dimensional structure of the helical disturbances. These helical disturbances are also decomposed into symmetric and anti-symmetric disturbances about the jet core, showing the subsequent axial evolution (in magnitude and phase) of each of these underlying disturbances. It is shown that out-of-phase acoustic forcing excites $m=\pm 1$ modes, but the flow field preferentially amplifies the counter-winding, co-rotating helical disturbance over the co-winding, counter-rotating helical disturbance. This causes the flow and flame to transition from a transverse flapping near the jet exit to a precessing motion further downstream. In contrast, in-phase forcing promotes axisymmetric $m=0$ disturbances which dominate the flow field over the entire axial domain. In both cases, the amplitudes of the anti-symmetric disturbances about the jet core grow with downstream distance before saturating and decaying, while the symmetric disturbances appear nearly negligible. It is suggested that this saturation and decay is due to linear effects (e.g. a negative spatial growth rate), rather than nonlinear interactions.

Three-dimensional flow within shallow, narrow cavities

2013 ◽  
Vol 735 ◽  
pp. 587-612 ◽  
Author(s):  
Sarah D. Crook ◽  
Timothy C. W. Lau ◽  
Richard M. Kelso
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Particle Image Velocimetry Data ◽  
Cavity Flow ◽  
Dimensional Structure ◽  
Back Surface ◽  
Flow Topology ◽  
Open Type ◽  
Flow Features ◽  
Cavity Opening

AbstractThe three-dimensional structure of incompressible flow in a narrow, open rectangular cavity in a flat plate was investigated with a focus on the flow topology of the time-averaged flow. The ratio of cavity length (in the direction of the flow) to width to depth was $l{: }w{: }d= 6{: }2{: }1$. Experimental surface pressure data (in air) and particle image velocimetry data (in water) were obtained at low speed with free-stream Reynolds numbers of ${\mathit{Re}}_{l} = 3. 4\times 1{0}^{5} $ in air and ${\mathit{Re}}_{l} = 4. 3\times 1{0}^{4} $ in water. The experimental results show that the three-dimensional cavity flow is of the ‘open’ type, with an overall flow structure that bears some similarity to the structure observed in nominally two-dimensional cavities, but with a high degree of three-dimensionality both in the flow near the walls and in the unsteady behaviour. The defining features of an open-type cavity flow include a shear layer that traverses the entire cavity opening ultimately impinging on the back surface of the cavity, and a large recirculation zone within the cavity itself. Other flow features that have been identified in the current study include two vortices at the back of the cavity, of which one is barely visible, a weak vortex at the front of the cavity, and a pair of counter-rotating streamwise vortices along the sides of the cavity near the cavity opening. These vortices are generally symmetric about the cavity centre-plane. However, the discovery of a single tornado vortex, located near the cavity centreline at the front of the cavity, indicated that the flow within the cavity is asymmetric. It is postulated that the observed asymmetry in the time-averaged flow field is due to the asymmetry in the instantaneous flow field, which switches between two extremes at large time scales.

scholarly journals The Flow Field Analysis and Flow Calculation of Ultrasonic Flowmeter Based on the Fluent Software

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Ling Guo ◽  
Yue Sun ◽  
Ling Liu ◽  
Zhixi Shen ◽  
Ruizhen Gao ◽  
...  
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Simulation Method ◽  
Ultrasonic Flowmeter ◽  
Field Analysis ◽  
Dimensional Structure ◽  
Power Correction ◽  
Ideal Condition ◽  
Proposed Model ◽  
Fluent Software

We can build the three-dimensional structure model based on the Gambit software and achieve the distribution of flow field in the pipe and reflux flow condition at the position of transducer in regard to the real position of transducer according to the Fluent software. Under the framework, define the reflux length based on the distance of reflux along the channel and evaluate the effect of reflux on flow field. Then we can correct the power factor with the transmission speed difference method in the ideal condition and obtain the matching expression of power correction factor according to the practice model. In the end, analyze the simulation experience and produce the sample table based on the proposed model. The comparative analysis of test results and simulation results demonstrates the validity and feasibility of the proposed simulation method. The research in this paper will lay a foundation for further study on the optimization of ultrasonic flowmeter, enhance the measurement precision, and extend the application of engineering.

On a class of unsteady, non-parallel, three-dimensional disturbances to boundary-layer flows

2001 ◽  
Vol 441 ◽  
pp. 31-65 ◽  
Author(s):  
PETER W. DUCK ◽  
SONIA L. DRY
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Natural Extension ◽  
Three Dimensional ◽  
Bypass Transition ◽  
Boundary Layer Flows ◽  
Unstable Flow ◽  
Similarity Type ◽  
Hypersonic Boundary Layers ◽  
Flow Disturbances

Steady, spatial, algebraically growing eigenfunctions are now known to occur in several important classes of boundary-layer flow, including two-dimensional hypersonic boundary layers and more recently in Blasius boundary layers subject to three-dimensional linearized disturbances, and in more general three-dimensional boundary layers. These spatial eigensolutions are particularly important and intriguing, given that they exist within the broad limits of the classical steady boundary-layer approximation, and as such are independent of Reynolds number.In this paper we make the natural extension to these previous (stability) analyses by incorporating the effects of unsteadiness into the model for treating disturbances to a quite general class of similarity-type boundary-layer flows. The flow disturbances are inherently non-parallel, but this effect is properly incorporated into the analysis.A further motivation for this paper is that Duck et al. (1999, 2000) have shown that by permitting a spanwise component of flow within a boundary layer of the appropriate form (in particular, growing linearly with the spanwise coordinate), it is found that new families of solutions exist – even the Blasius boundary layer has a three-dimensional ‘cousin’. Therefore a further aim of this paper is to assess the stability of the different solution branches, using the ideas introduced in this paper, to give some clues as to which of the solutions may be encountered experimentally.Several numerical methods are presented for tackling various aspects of the problem. It is shown that when algebraically growing, steady eigensolutions exist, their effect remains important in the unsteady context. We show how even infinitesimal, unsteady flow perturbations can provoke extremely large-amplitude flow responses, including in some cases truly unstable flow disturbances which grow algebraically downstream without bound in the linear context. There are some interesting parallels suggested therefore regarding mechanisms perhaps linked to bypass transition in an important class of boundary-layer flows.

Three-Dimensional Structure of Separated and Vortical Flow in a Half-Ducted Propeller Fan

2007 ◽  
Author(s):  
J. H. Jeong ◽  
K. Takahashi ◽  
K. Iwakiri ◽  
M. Furukawa
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Vortical Flow ◽  
Dimensional Structure ◽  
Structure Identification ◽  
Tip Leakage Vortex ◽  
Three Dimensional Structure ◽  
Tip Leakage ◽  
Ducted Propeller

Three-dimensional structure of separated and vortical flow field has been investigated by numerical analysis on a half-ducted propeller fan. Complicated flow phenomena in the fan were captured by the Reynolds-averaged Navier-Stokes flow simulation (RANS) and a vortex structure identification technique based on the critical point theory. The flow field around the fan rotor is dominated by the tip leakage vortex. The tip leakage vortex starts to be formed near the blade mid-chord and grows nearly in the tangential direction without vortex breakdown. In the rotor passage, the high vorticity flow around the tip leakage vortex core is impinging on the pressure surface of the adjacent blade. It is expected that the behavior of the tip leakage vortex plays a major role in characteristics of the fan noise.

scholarly journals Numerical and Experimental Comparative Study on the Flow-Induced Vibration of a Plane Gate

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1551
Author(s):  
Chunying Shen ◽  
Wei Wang ◽  
Shihua He ◽  
Yimin Xu
Keyword(s):  
Flow Field ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Surface Profile ◽  
Computational Method ◽  
Unstable Flow ◽  
Flow Induced Vibration ◽  
Fluid Structure ◽  
Vof Model ◽  
Vibration Parameters

A numerical method is applied here to simulate the unstable flow and the vibration of a plane gate. A combination of the large eddy simulation (LES) method and the volume of fluid (VOF) model is used to predict the three-dimensional flow field in the vicinity of a plane gate with submerged discharge. The water surface profile, the streamline diagrams, the distribution of turbulent kinetic energy, the power spectrum density curve of the fluctuating pressure coefficient at typical points underneath the gate, and the complete vortex distribution around the gate are obtained by LES-VOF numerical calculation. The vibration parameters of the gate are calculated by the fluid-structure coupling interface transferring the hydrodynamic load. A simultaneous sampling experiment is performed to verify the validity of the algorithm. The calculated results are then compared with experimental data. The difference between the two is acceptable and the conclusions are consistent. In addition, the influence of the vortex in the slot on the flow field and the vibration of the gate are investigated. It is feasible to replace the experiment with the fluid-structure coupling computational method, which is useful for studying the flow-induced vibration mechanism of plane gates.

A Three Dimensional Simulation Model for Liquid Phase Electroepitaxy Under Magnetic Field

2002 ◽  
Author(s):  
Yoncai Liu ◽  
Hamdi Sheibani ◽  
Susumu Sakai ◽  
Yasunori Okano ◽  
Sadik Dost
Keyword(s):  
Magnetic Field ◽  
Liquid Phase ◽  
Flow Field ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Stable Region ◽  
Transitional Region ◽  
Unstable Flow ◽  
Growth Interface ◽  
Flow Intensity

A three-dimensional numerical simulation for the Liquid Phase Electroepitaxial (LPEE) growth of GaAs under a vertical stationary magnetic field was carried out. The effect of magnetic field intensity on the flow field in the liquid solution was investigated. Numerical results show that the flow patterns exhibit three distinct stability characteristics: a stable flow field up to a magnetic field level of Ha = 150, a transitional flow between Ha = 150 and Ha = 220, and an unstable flow above Ha = 220. In the stable region, the applied magnetic field suppresses the flow field, and the flow intensity decreases with increasing magnetic field. In the transitional region, the flow intensity increases dramatically with increase in the magnetic field strength. The flow patterns are significantly different from those in the stable region. The flow field is no longer axisymmetric but still stable. In the unstable region, the flow structure and intensity change with time. Under a strong magnetic field, the flow cells are confined to the vicinity of the vertical wall and exhibit significant non-uniformity near the growth interface. Such strong flow fluctuations and non-uniformities near the growth interface may have an adverse effect on the growth process and lead to an unsatisfactory growth.

scholarly journals On the Nonlinear, Three-Dimensional Structure of Equatorial Oceanic Flows

2019 ◽  
Vol 49 (8) ◽  
pp. 2029-2042 ◽  
Author(s):  
A. Constantin ◽  
R. S. Johnson
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Flow Region ◽  
Azimuthal Velocity ◽  
Surface Flow ◽  
Dimensional Structure ◽  
Rossby Number ◽  
Azimuthal Direction ◽  
Physical Size ◽  
The Pacific

AbstractA systematic development, based on the construction of an asymptotic solution of the Euler equation, written in rotating, spherical coordinates , is used to investigate the flows of the type seen in the neighborhood of the Pacific equator. First, it is shown that the observed poleward surface-flow structure away from the line of the equator is possible only if the flow evolves (changes) in the azimuthal direction. Then, allowing for variations in the azimuthal direction, the shallow-water, small-Rossby-number version of the problem, approximated close to the equator, leads to an asymptotic formulation that admits any prescribed azimuthal velocity profile at some fixed longitude φ. The maximum extent of the flow region inside which we can describe in detail the velocity field is restricted by the size of the Rossby number. The analysis demonstrates that the meridional υ and vertical w velocity components are nonlinearly connected to u, and that all three velocity components appear at the same order in the leading (scaled) equations, even though the physical size of w is very much smaller than that of the other two components. An appropriate choice is made for u, at a given φ, and the corresponding complete three-dimensional flow field, which emerges from the interlinkage of the velocity components, is described; the thermocline is also added to the flow configuration. We compare these results with the available field data, demonstrating that this formulation captures all the main structures of the flow field, but also allows for many choices to be made that can be used to adjust the details of the flow and to model other, similar flows.

Analysis on the Flow Passed a Pervious Cubic-Blunt Body Based on Large Eddy Simulation

2013 ◽  
Vol 353-356 ◽  
pp. 2477-2481
Author(s):  
En Li Ye ◽  
Yi Hong Zhou ◽  
Lei Ren
Keyword(s):  
Comparative Analysis ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Vortex Shedding ◽  
Blunt Body ◽  
Static Pressure ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Eddy Simulation ◽  
Large Eddy

To overcome the deficiency that model experiments are unable to take accurate measurements without damaging the structure of the fine flow fields, a large eddy simulation is employed to simulate the three dimensional structure of the flow passed a pervious cubic-blunt body at Re=2.2×104. A comparative analysis have been taken qualitatively and quantitatively between the flow passed a pervious cubic-blunt body and the flow passed a non-pervious cubic-blunt body from the aspects of the flow structure (mainly including separation and reattachment), unsteady vortex shedding, distribution of static pressure and drag coefficient, etc. Therefore, characteristics of this kind of flow field are concluded and along with a better understanding of concrete effects they bring, which can give guidance to engineering.

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