scholarly journals Effects of a Diverging Cup on Swirl Number, Flow Pattern, and Topology of Premixed Flames

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
A. Degenève ◽  
P. Jourdaine ◽  
C. Mirat ◽  
J. Caudal ◽  
R. Vicquelin ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Premixed Flames ◽  
Leading Edge ◽  
Pressure Effects ◽  
Swirl Number ◽  
Recirculation Bubble ◽  
Cross Section Area ◽  
Axial Pressure Gradient ◽  
Number Flow ◽  
Swirled Flow

Impact of the diverging cup angle of a swirling injector on the flow pattern and stabilization of technically premixed flames is investigated both theoretically and experimentally with the help of OH* chemiluminescence, OH laser-induced fluorescence and particle image velocimetry (PIV) measurements. Recirculation enhancement with a lower position of the internal recirculation zone (IRZ) and a flame leading edge protruding further upstream in the swirled flow are observed as the injector nozzle cup angle is increased. A theoretical analysis is carried out to examine whether this could be explained by changes of the swirl level as the diffuser cup angle is varied. It is shown that pressure effects need in this case to be taken into account in the swirl number definition and expressions for changes of the swirl level through a diffuser are derived. It is demonstrated that changes of the swirl level including or not the pressure contribution to the axial momentum flux are not at the origin of the changes observed of the flow and flame patterns in the experiments. The swirl number without the pressure term, designated as pressure-less swirl, is then determined experimentally with laser Doppler velocimetry (LDV) measurements at the injector outlet for a set of diffusers with increasing quarl angles under nonreacting conditions and the values found corroborate the predictions. It is finally shown that the decline of axial velocity and the rise of adverse axial pressure gradient, both due to the cross section area change through the diffuser cup, are the dominant effects that control the leading edge position of the IRZ of the swirled flow. This is used to develop a model for the displacement of the recirculation bubble as the quarl angle varies that shows very good agreement with experiments.

scholarly journals Effects of a Diverging Cup on Swirl Number, Flow Pattern and Topology of Premixed Flames

2018 ◽  
Author(s):  
A. Degeneve ◽  
P. Jourdaine ◽  
C. Mirat ◽  
J. Caudal ◽  
R. Vicquelin ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Recirculation Zone ◽  
Laser Diagnostics ◽  
Premixed Flames ◽  
Leading Edge ◽  
Pressure Effects ◽  
Swirl Number ◽  
Cross Section Area ◽  
Axial Pressure Gradient ◽  
Swirled Flow

Impact of the diverging cup angle of a swirling injector on the flow pattern and stabilization of technically premixed flames is investigated both theoretically and experimentally with the help of laser diagnostics. Recirculation enhancement with a lower position of the internal recirculation zone and a flame leading edge protruding further upstream in the swirled flow are observed as the injector nozzle cup angle is increased. A theoretical analysis is carried out to examine if this could be explained by changes of the swirl level as the diffuser cup angle is varied. It is shown that pressure effects need in this case to be taken into account in the swirl number definition and expressions for its variation through a diffuser are derived. They indicate that changes of the swirl level including or not the pressure contribution to the axial momentum flux cannot explain the changes observed of the flow and flame patterns in the experiments. The swirl number without the pressure term, designated as pressure-less swirl, is then determined experimentally for a set of diffusers with increasing quarl angles under non-reacting conditions and the values found corroborate the predictions. It is finally shown that the decline of axial velocity and the rise of adverse axial pressure gradient, both due to the cross section area change through the diffuser cup, are the dominant effects that control the leading edge position of the internal recirculation zone of the swirled flow. This in turn is used to develop a model for the change of this position as the quarl angle varies that shows good agreement with experiments.

Topological Flow Structures of Annular Swirling Jets

2001 ◽  
Vol 17 (3) ◽  
pp. 131-138
Author(s):  
Feng Chin Tsai ◽  
Rong Fung Huang
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Single Bubble ◽  
Flow Structures ◽  
Complex Flow ◽  
Swirl Number ◽  
Recirculation Bubble ◽  
Annular Jet ◽  
Ring Mode ◽  
Dual Ring

AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.

Solution of Levi Civita’s Problem by Infinite Matrix Inversion

1973 ◽  
Vol 40 (1) ◽  
pp. 31-36 ◽  
Author(s):  
M. Bentwich
Keyword(s):  
Flow Pattern ◽  
Flow Direction ◽  
Leading Edge ◽  
Arbitrary Cross Section ◽  
Matrix Inversion ◽  
Infinite Matrix ◽  
Algebraic Equations ◽  
Flow Past ◽  
Linear Algebraic Equations ◽  
Wet Surface

The author proposes a new method by which one can solve for the two-dimensional irrotational fully cavitating flow past a cylinder of arbitrary cross section. Unlike the available solutions, it is in the form of two expansions each valid in part of the complex potential plane w = Φ + iΨ. The a priori unknown coefficients in the two expansions are linked by infinitely many linear algebraic equations. By inverting the associated matrix and utilizing the boundary condition, that represent the geometry of the wet surface, the coefficients in the expansions are evaluated and the solution is completed. Cases in which the wet surface is circular, the pressure along the free streamlines is constant, and the entire flow pattern is symmetric with respect to flow direction at infinity are considered in detail. Also, the well-known solution for the flow past a flat plate is compared to that obtained by the method of matrix inversion. Judging from these results, the convergence of the series appears to be very rapid. The author finally discusses the applicability of the method to cases in which the obstacle has a sharp leading edge, the pressure in the cavity is not uniform, or the flow pattern is not symmetric.

Intermittent Phenomena in the Flow Over a Rib Roughened Surface

1991 ◽  
Vol 113 (2) ◽  
pp. 206-209 ◽  
Author(s):  
T. Mullin ◽  
S. R. Martin
Keyword(s):  
Strouhal Number ◽  
Nuclear Reactor ◽  
Laser Doppler Anemometry ◽  
Leading Edge ◽  
Main Stream ◽  
Recirculation Bubble ◽  
Nuclear Reactor Fuel ◽  
Roughened Surface ◽  
Turbulent Water ◽  
Rib Roughened

Laser Doppler anemometry has been used to make measurements of a small recirculation bubble in a turbulent water flow over a rib roughened surface. The bubble occurs near the leading edge of a transverse rib which is a model of the ribbed surface used to enhance cooling on nuclear reactor fuel pins. The bubble is transient, and spectral and correlation measurements were made to investigate any periodicity. It was found that the bubble itself did not show any periodicity but there was evidence for fluctuations in the main stream with a Strouhal number of 0.1.

Slot suction from inviscid channel flow

1989 ◽  
Vol 200 ◽  
pp. 265-282 ◽  
Author(s):  
J. N. Dewynne ◽  
S. D. Howison ◽  
J. R. Ockendon ◽  
L. C. Morland ◽  
E. J. Watson
Keyword(s):  
Flow Pattern ◽  
Stagnation Point ◽  
Turbine Blade ◽  
Channel Flow ◽  
Mass Flux ◽  
Channel Wall ◽  
Leading Edge ◽  
Turbine Blade Cooling ◽  
Blade Cooling ◽  
Slot Suction

Motivated by a problem in turbine blade cooling, we consider suction from an inviscid channel flow into a slot in the channel wall. The flow is assumed to separate smoothly from the leading edge of the slot and the pressure in the stagnant separated region controls the suction. The mass flux into the slot is found in terms of the pressure; for small values of this flux the predicted flow pattern is found to be quite different from that which would result if there were no separated region. In particular, the stagnation point never penetrates more than approximately 0.05 slot widths into the slot.

The effect of the aerofoil thickness on the performance of the MAV scale cycloidal rotor

2015 ◽  
Vol 119 (1213) ◽  
pp. 343-364 ◽  
Author(s):  
Y. Hu ◽  
H.L. Zhang ◽  
C. Tan
Keyword(s):  
Flow Pattern ◽  
Cfd Simulation ◽  
Leading Edge ◽  
Dynamic Stall ◽  
Test Cases ◽  
Sliding Mesh ◽  
Large Fluctuations ◽  
Edge Vortex ◽  
Rotor Cage ◽  
Different Thickness

AbstractThe numerical simulations for cycloidal propellers based on five aerofoils with different thickness are presented in this paper. The CFD simulation is based on sliding mesh and URANS. The results of CFD simulation indicates that all test cases share similar flow pattern. There are leading edge vortex and trailing-edge vortex due to blade dynamic stall. Interaction between the vortices shed from upstream blade and the downstream blade can be observed. There is variation of blade relative inflow velocity due to downwash in the cycloidal rotor cage. These factors result in large fluctuations of the aerodynamics forces on the blade. The comparison of the forces and flow pattern indicates that the thickness and leading edge radius of the aerofoil can significantly influent the flow pattern and hence the performance of the cycloidal propeller.

Area-varying waves on curved vortex tubes with application to vortex breakdown

1989 ◽  
Vol 200 ◽  
pp. 283-307 ◽  
Author(s):  
T. S. Lundgren ◽  
W. T. Ashurst
Keyword(s):  
Shallow Water ◽  
Axial Velocity ◽  
Vortex Tube ◽  
Vortex Breakdown ◽  
Axial Pressure ◽  
Cross Section Area ◽  
Section Area ◽  
Axial Pressure Gradient ◽  
Vortex Tubes ◽  
Axial Waves

Equations which modify those derived by Widnall & Bliss (1971) and Moore & Saffman (1972) are presented in which jet-like flow along the axis of a vortex tube interacts with the motion of the tube. The equations describe two major effects. The first is the propagation of axial waves along the vortex tube which is similar to the flow of shallow water. A local decrease in cross-section area of the vortex tube produces higher swirling velocity and lower pressure. The resulting axial pressure gradient causes a propagating wave of area and axial velocity in order to move fluid into the region of smaller area. The second effect is instability to helical disturbances when the jet-like axial velocity is high enough to overcome the stabilizing effect of the swirling motion. An elementary nonlinear theory of vortex breakdown is presented which has an analogy with the formation of bores in shallow-water theory. A numerical example shows the growth of a helical disturbance behind a vortex breakdown front.

Pressure Effects on Low-Liquid-Loading Oil/Gas Flow in Slightly Upward Inclined Pipes: Flow Pattern, Pressure Gradient, and Liquid Holdup

SPE Journal ◽  
2019 ◽  
Vol 24 (05) ◽  
pp. 2221-2238 ◽  
Author(s):  
Hendy T. Rodrigues ◽  
Eduardo Pereyra ◽  
Cem Sarica
Keyword(s):  
Pressure Gradient ◽  
Flow Pattern ◽  
Slug Flow ◽  
Annular Flow ◽  
Flow Patterns ◽  
Pressure Effects ◽  
Liquid Holdup ◽  
Liquid Loading ◽  
Interfacial Roughness ◽  
Oil Gas

Summary This paper studied the effects of system pressure on oil/gas low–liquid–loading flow in a slightly upward inclined pipe configuration using new experimental data acquired in a high–pressure flow loop. Flow rates are representative of the flow in wet–gas transport pipelines. Results for flow pattern observations, pressure gradient, liquid holdup, and interfacial–roughness measurements were calculated and compared to available predictive models. The experiments were carried out at three system pressures (1.48, 2.17, and 2.86 MPa) in a 0.155–m–inside diameter (ID) pipe inclined at 2° from the horizontal. Isopar™ L oil and nitrogen gas were the working fluids. Liquid superficial velocities ranged from 0.01 to 0.05 m/s, while gas superficial velocities ranged from 1.5 to 16 m/s. Measurements included pressure gradient and liquid holdup. Flow visualization and wire–mesh–sensor (WMS) data were used to identify the flow patterns. Interfacial roughness was obtained from the WMS data. Three flow patterns were observed: pseudo-slug, stratified, and annular. Pseudo-slug is characterized as an intermittent flow where the liquid does not occupy the whole pipe cross section as does a traditional slug flow. In the annular flow pattern, the bulk of the liquid was observed to flow at the pipe bottom in a stratified configuration; however, a thin liquid film covered the whole pipe circumference. In both stratified and annular flow patterns, the interface between the gas core and the bottom liquid film presented a flat shape. The superficial gas Froude number, FrSg, was found to be an important dimensionless parameter to scale the pressure effects on the measured parameters. In the pseudo-slug flow pattern, the flow is gravity–dominated. Pressure gradient is a function of FrSg and liquid superficial velocity, vSL. Liquid holdup is independent of vSL and a function of FrSg. In the stratified and annular flow patterns, the flow is friction–dominated. Both pressure gradient and liquid holdup are functions of FrSg and vSL. Interfacial–roughness measurements showed a small variation in the stratified and annular flow patterns. Model comparison produced mixed results, depending on the specific flow conditions. A relation between the measured interfacial roughness and the interfacial friction factor was proposed, and the results agreed with the existing measurements.

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