Particle Diagnostics and Turbulence Measurements in a Confined Isothermal Liquid Spray

1993 ◽  
Vol 115 (3) ◽  
pp. 499-506 ◽  
Author(s):  
A. Bren˜a de la Rosa ◽  
S. V. Sankar ◽  
G. Wang ◽  
W. D. Bachalo
Keyword(s):  
Flow Field ◽  
Size Distribution ◽  
Swirling Flow ◽  
Laser Sheet ◽  
Recirculation Region ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Velocity Correlation ◽  
Mean Velocity ◽  
Liquid Spray

This work reports an experimental study of the behavior and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane-type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distribution, and size-velocity correlation were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A two-component PDPA system with a frequency-based Doppler signal analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and nonuniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed; however, large variations outside of it are also present. Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.

scholarly journals Particle Diagnostics and Turbulence Measurements in a Confined Isothermal Liquid Spray

1992 ◽  
Author(s):  
A. Breña de la Rosa ◽  
S. V. Sankar ◽  
G. Wang ◽  
W. D. Bachalo
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Laser Sheet ◽  
Recirculation Region ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Recirculation Flow ◽  
Liquid Spray ◽  
Secondary Air

This work reports an experimental study of the behaviour and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distributions, and size-velocity correlations were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A 2-component PDPA system with a frequency based Doppler Signal Analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and non-uniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed, however large variations outside of it are also present. Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.

The Effect of Swirl on the Velocity and Turbulence Fields of a Liquid Spray

1992 ◽  
Vol 114 (1) ◽  
pp. 72-81 ◽  
Author(s):  
A. Bren˜a de la Rosa ◽  
G. Wang ◽  
W. D. Bachalo
Keyword(s):  
Kinetic Energy ◽  
Swirling Flow ◽  
Energy Content ◽  
High Energy ◽  
Recirculation Region ◽  
Shear Stresses ◽  
Swirl Number ◽  
Double Peak ◽  
Mean Velocity ◽  
Liquid Spray

The work reports an experimental study of the effect of swirl on the structure of a liquid spray, i.e., on the behavior of drops and their interaction with the gaseous phase, and on the velocity and turbulence fields of the spray in the swirling flow. Three vane-type swirlers having low, medium, and high swirl numbers were used in the tests. The swirlers were placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Properties of the dispersed phase such as velocity and size distributions, particle number density, and volume flux were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. The results show that flow reversal of the drops is present at the high swirl number within the recirculation region. The spatial distribution of drops reveals a widening of the spray with increasing swirl strength while the concentration of large drops is shown to increase near the core of the swirling field with increasing swirl number. Plots of the turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high energy content, mean velocity gradients, and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence. The significance of the turbulence measurements is that these double-peak profiles indicate a deviation of the swirling spray from isotropy. This information should be relevant to researchers modeling these complex flows.

The Effect of Swirl on the Velocity and Turbulence Fields of a Liquid Spray

1990 ◽  
Author(s):  
A. Breña de la Rosa ◽  
G. Wang ◽  
W. D. Bachalo
Keyword(s):  
Kinetic Energy ◽  
Swirling Flow ◽  
Energy Content ◽  
High Energy ◽  
Recirculation Region ◽  
Shear Stresses ◽  
Swirl Number ◽  
Double Peak ◽  
Mean Velocity ◽  
Liquid Spray

This work reports an experimental study of the effect of swirl on the structure of a liquid spray, i.e., on the behaviour of drops and their interaction with the gaseous phase, and on the velocity and turbulence fields of the spray in the swirling flow. Three vane type swirlers having low, medium, and high swirl numbers were used in the tests. The swirlers were placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Properties of the dispersed phase such as velocity and size distributions, particle number density, and volume flux were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. The results show that flow reversal of the drops is present at the high swirl number within the recirculation region. The spatial distribution of drops reveals a widening of the spray with increasing swirl strength while the concentration of large drops is shown to increase near the core of the swirling field with increasing swirl number. Plots of the turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses show double-peak radial distributions which indicate regions in the flow where high energy content, mean velocity gradients, and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence. The significance of the turbulence measurements is that these double peak profiles indicate a deviation of the swirling spray from isotropy. This information should be relevant to researchers modelling these complex flows.

Experimental and Numerical Investigation of a Cold Turbulent Jet Impinging on a Hot Plate

2012 ◽  
Author(s):  
D. I. Maldonado ◽  
J. K. Abrantes ◽  
L. F. A. Azevedo ◽  
A. O. Nieckele
Keyword(s):  
Flow Field ◽  
Laser Doppler Anemometry ◽  
Turbulence Models ◽  
Impinging Jets ◽  
Reynolds Stresses ◽  
Hot Plate ◽  
Mean Velocity ◽  
Velocity Statistics ◽  
Reliable Assessment ◽  
Anisotropic Structures

Impinging jets are an efficient mechanism to enhance wall heat transfer, and are widely used in engineering applications. The flow field of an impinging jet is quite complex and it is a challenging case for turbulence models validation as well as measurements techniques. In the present work, a detailed investigation of a cold jet impinging on a hot plate operating in the turbulent flow regime was conducted. The flow field was characterized by both Laser Doppler Anemometry and Particle Image Velocimetry (PIV) techniques in order to collect 1st and 2nd order velocity statistics to allow a reliable assessment of the numerical simulations. Comparison was performed with two turbulence methodologies: RANS (κ–ω SST model) and LES (Dynamic Smagorinsky model). The comparison was performed to assess LES feasibility and accuracy in capturing the anisotropic structures that several tested RANS models missed. The mean velocity, instantaneous velocity, Reynolds stresses and Nusselt profiles obtained numerically are compared with experimental data. A physical insight about the general flow dynamics was obtained with the extensive amount of information available from the LES.

scholarly journals Flow field of a diffusion flame attached to a thick-walled injector between two coflowing reactant streams

1996 ◽  
Vol 329 ◽  
pp. 389-411 ◽  
Author(s):  
F. J. Higuera ◽  
A. Liñán
Keyword(s):  
Thermal Expansion ◽  
Flow Field ◽  
Pressure Gradient ◽  
Heat Release ◽  
Diffusion Flame ◽  
Adverse Pressure Gradient ◽  
Recirculation Region ◽  
Shear Stresses ◽  
Stoichiometric Ratio ◽  
Exothermic Reactions

The flow field of a diffusion flame attached to a thick-rim injector between two coflowing streams of fuel and oxidiser is analysed in the Burke–Schumann limit of infinitely fast reaction rate. The length of the recirculation region immediately behind the injector and the velocity of the recirculating fluid are proportional to the shear stresses of the reactant streams on the wall of the injector for a range of rim thicknesses, and the structure of the flow in the wake depends then on three main non-dimensional parameters, measuring the gas thermal expansion due to the chemical heat release, the air-to-fuel stoichiometric ratio of the reaction, and the air-to-fuel ratio of wall shear stresses. The recirculation region shortens with increasing heat release, and the position of the flame in this region depends on the other two parameters. An asymptotic analysis is carried out for very exothermic reactions, showing that the region of high temperature around the flame is confined by neatly defined boundaries and the hot fluid moves like a high-velocity jet under a favourable self-induced pressure gradient. The immediate wake is surrounded by a triple-deck region where the interacting flow leads to an adverse pressure gradient and a reduced shear stress upstream of the injector rim for sufficiently exothermic reactions. Separation of the boundary layers on the wall of the injector, however, seems to be postponed to very large values of the gas thermal expansion.

The turbulence structure of the annular non-swirling flow past an axisymmetric poppet valve

1998 ◽  
Vol 212 (6) ◽  
pp. 455-471 ◽  
Author(s):  
S Nadarajah ◽  
S Balabani ◽  
M J Tindal ◽  
M Yianneskis
Keyword(s):  
Kinetic Energy ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Turbulence Kinetic Energy ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Length Scales ◽  
Gaussian Form ◽  
Poppet Valve

This paper describes an experimental investigation of the non-swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions using laser Doppler anemometry. The three velocity components and the associated Reynolds stresses were measured by ensemble-averaged techniques and the turbulence kinetic energy and its production rate were determined. Time-resolved measurements were also taken in order to determine turbulence time and length scales and the dissipation rate of the turbulence kinetic energy. The Reynolds number, based on the minimum cross-sectional area of the port, was 25000. The flow is characterized by an annular jet which forms two vortices, one on either side of the jet. A jet flapping instability is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. This instability causes an intermittent mixing between eddies in the jet region and the vortices which introduces a non-turbulent contribution to the measured quantities. The production rates of the turbulence kinetic energy were found to be negative in some regions of the flow, indicating counter-gradient transport of momentum by turbulence; according to the coherent structures approach, the distribution of the Reynolds shear stresses and the length scales in these regions imply possible changes in the orientation of eddies.

Hot-Wire Measurements Inside a Centrifugal Fan Impeller

1989 ◽  
Vol 111 (4) ◽  
pp. 363-368 ◽  
Author(s):  
A. Kjo¨rk ◽  
L. Lo¨fdahl
Keyword(s):  
Suction Side ◽  
Design Flow ◽  
Shear Stresses ◽  
Centrifugal Fan ◽  
Reynolds Stresses ◽  
Low Velocity ◽  
Mean Velocity ◽  
Attached Flow ◽  
The Mean ◽  
Velocity Region

Measurements of the three mean velocity components and five of the Reynolds stresses have been carried out in the blade passage of a centrifugal fan impeller. The impeller was of ordinary design, with nine backward curved blades, and all measurements were carried out at the design flow rate. The mean velocity measurements show that the flow can be characterized as an attached flow with almost linearly distributed velocity profiles. However, in a region near the suction side close to the shroud a low velocity region is created. From the turbulence measurements it can be concluded that relatively low values of the turbulent stresses are predominating in the center region of the channel. Closer to the walls higher values of the normal as well as shear stresses are noted.

Added stresses because of the presence of FENE-P bead–spring chains in a random velocity field

1997 ◽  
Vol 337 ◽  
pp. 67-101 ◽  
Author(s):  
HESHMAT MASSAH ◽  
THOMAS J. HANRATTY
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Velocity Gradient ◽  
Gradient Field ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Random Velocity

FENE-P bead–spring chains unravel in the presence of large enough velocity gradients. In a turbulent flow, this can result in intermittent added stresses and exchanges of energy between the chains and the fluid, whose magnitudes depend on the degree of unravelling and on the orientations of the bead–spring chains. These effects are studied by calculating the average behaviour at different times of an ensemble of chains, contained in a fluid particle that is moving around in a random velocity field obtained from direct numerical simulation of turbulent flow of a Newtonian fluid in a channel. The results are used to evaluate theoretical explanations of drag reduction observed in very dilute solutions of polymers.In regions of the flow in which the energy exchange with the fluid is positive, the possibility arises that turbulence can be produced by mechanisms other than the interaction of Reynolds stresses and the mean velocity gradient field. Of particular interest, from the viewpoint of understanding polymer drag reduction, is the finding that the exchange is negative in velocity fields representative of the wall vortices that are large producers of turbulence. One can, therefore, postulate that polymers cause drag reduction by selectively changing the structures of eddies that produce Reynolds stresses. The intermittent appearance of large added shear stresses is consistent with the experimental finding of a stress deficit, whereby the total local shear stress is greater than the sum of the Reynolds stress and the time-averaged shear stress calculated from the time-averaged velocity gradient and the viscosity of the solvent.

Separated and Reattached Flow Over Square, Rectangular and Semi-Circular Blocks

2007 ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Boundary Layer ◽  
Cross Sections ◽  
Recirculation Region ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Block Height ◽  
Turbulent Statistics ◽  
Image Velocimetry ◽  
The Mean ◽  
Separated And Reattached Flow

A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. The variation of the Reynolds stresses along the separating streamlines is discussed within the context of vortex stretching, longitudinal strain rate and wall damping. It appears wall damping is a more dominant mechanism in the vicinity of reattachment. The levels of turbulence diffusion and production by the normal stresses are significantly higher than in classical turbulent boundary layers. The bulk of turbulence production occurs in mid-layer and transported into the inner and outer layers. The results also reveal that the curvature of separating streamline, separating bubble beneath it as well as the mean velocity and turbulent quantities depend strongly on block geometry.

The effect of swirl on the annular flow past an axisymmetric poppet valve

1998 ◽  
Vol 212 (6) ◽  
pp. 473-484 ◽  
Author(s):  
S Nadarajah ◽  
S Balabani ◽  
M J Tindal ◽  
M Yianneskis
Keyword(s):  
Flow Visualization ◽  
Flow Structure ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Laser Sheet ◽  
Preceding Paper ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Poppet Valve ◽  
Valve Assembly

This paper describes an experimental investigation of the swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions. This work is an extension of the preceding paper, which is a study of the non-swirling flow in the same flow configuration [1]. Three different swirl rates were investigated with the aim to study the effects of swirl on the mean flow and turbulence characteristics of the flow field. The flow structure was studied by means of laser sheet flow visualization and the three velocity components and the associated Reynolds stresses were measured by ensemble-averaged laser Doppler anemometry techniques. The results are compared with those obtained with the non-swirling flow. The addition of the swirl was found to alter the flow structure, particularly below the valve where a new counter-rotating vortex is formed. A toroidal recirculation zone is also formed in the valve passage. The growth and entrainment of the jet emanating from the valve gap increase and its trajectory angle changes. The flow visualization studies showed evidence of precession of the swirl centre and jet flapping. Swirl increases the Reynolds stresses and the turbulence production rate in most regions of the flow.

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