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.

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.

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.

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.

Interaction between a spatially growing turbulent boundary layer and embedded streamwise vortices

1996 ◽  
Vol 326 ◽  
pp. 151-179 ◽  
Author(s):  
Junhui Liu ◽  
Ugo Piomelli ◽  
Philippe R. Spalart
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Vortex Core ◽  
Eddy Viscosity ◽  
Shear Stresses ◽  
Streamwise Vortices ◽  
Mean Velocity ◽  
Production Term

The interaction between a zero-pressure-gradient turbulent boundary layer and a pair of strong, common-flow-down, streamwise vortices with a sizeable velocity deficit is studied by large-eddy simulation. The subgrid-scale stresses are modelled by a localized dynamic eddy-viscosity model. The results agree well with experimental data. The vortices drastically distort the boundary layer, and produce large spanwise variations of the skin friction. The Reynolds stresses are highly three-dimensional. High levels of kinetic energy are found both in the upwash region and in the vortex core. The two secondary shear stresses are significant in the vortex region, with magnitudes comparable to the primary one. Turbulent transport from the immediate upwash region is partly responsible for the high levels of turbulent kinetic energy in the vortex core; its effect on the primary stress 〈u′v′〉 is less significant. The mean velocity gradients play an important role in the generation of 〈u′v′〉 in all regions, while they are negligible in the generation of turbulent kinetic energy in the vortex core. The pressure-strain correlations are generally of opposite sign to the production terms except in the vortex core, where they have the same sign as the production term in the budget of 〈u′v′〉. The results highlight the limitations of the eddy-viscosity assumption (in a Reynolds-averaged context) for flows of this type, as well as the excessive diffusion predicted by typical turbulence models.

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.

Roughness Effect Downstream of Flow Over a Forward Facing Step

2014 ◽  
Author(s):  
Yaw Y. Afriyie ◽  
Ebenezer E. Essel ◽  
Eric W. Thacher ◽  
Mark F. Tachie
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Shear Stress ◽  
Recirculation Region ◽  
Roughness Effects ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Image Velocimetry ◽  
Forward Facing Step

This paper presents results of an experimental research conducted to study roughness effects downstream of a forward facing step (FFS). A rough surface and a hydraulically smooth surface were used as a rough-FFS and a smooth-FFS, respectively. The upstream condition was kept smooth. Particle image velocimetry (PIV) technique was used for the velocity measurements. The Reynolds number based on the step height (h) and freestream velocity of the approach flow was kept constant at 8685. The results show that the mean reattachment length for the smooth-FFS (SM-SM) is 1.9h. Roughness reduced the peak values of the streamwise mean velocity, Reynolds shear stress and turbulent kinetic energy by 3%, 45% and 16.7% respectively in the recirculation region. In the early redevelopment region, roughness also reduced the peak values of turbulent kinetic energy and the Reynolds shear stress by 41% and 22% respectively.

Velocity Characteristics of Confined Coaxial Jets With and Without Swirl

1980 ◽  
Vol 102 (1) ◽  
pp. 47-53 ◽  
Author(s):  
M. A. Habib ◽  
J. H. Whitelaw
Keyword(s):  
Stokes Equations ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Velocity Ratio ◽  
Equation Model ◽  
Navier Stokes ◽  
Recirculation Region ◽  
Jet Flows ◽  
Mean Velocity ◽  
Navier Stokes Equations

Measured values of the velocity characteristics of turbulent, confined, coaxial-jet flows have been obtained, without swirl, for ratios of maximum annulus to pipe velocities of 1.0 and 3.0 and with a swirl number of 0.23 for a velocity ratio of 3.0. They were obtained by a combination of pressure probes, hot-wire and laser-Doppler anemometry. The results are compared with calculations, based on the solution of finite-difference forms of the steady, Navier-Stokes equations, and an effective-viscosity hypothesis. The measurements allow the influence of confinement and swirl to be quantified and show, for example, the increased tendency towards centerline recirculation which results from both. The results with the three types of instrumentation allow a comparison within the corner recirculation region which reveals that serious errors of interpretation of mean-velocity measurements need not arise. The two-equation model, although able to represent the non-swirling flow is less appropriate to the swirling flow and the reasons are indicated.

Spray Characterization and Turbulence Properties in an Isothermal Spray With Swirl

1990 ◽  
Vol 112 (1) ◽  
pp. 60-66 ◽  
Author(s):  
A. Bren˜a de la Rosa ◽  
W. D. Bachalo ◽  
R. C. Rudoff
Keyword(s):  
Dynamic Behavior ◽  
Radial Distribution ◽  
Particle Number ◽  
Swirling Flow ◽  
Particle Number Density ◽  
Recirculation Region ◽  
Liquid Volume ◽  
Volume Flux ◽  
Number Density ◽  
Mean Velocity

The present work reports an experimental study of the effect of swirl on the dynamic behavior of drops and on the velocity and turbulence fields of an isothermal spray using a two-component Phase Doppler Particle Analyzer (PDPA). It represents the first phase of an effort to investigate the effect of swirl on the structure of liquid spray flames, the stability of the flame, and its effect on the emission of pollutants. A vane-type swirler was placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Mean velocity and turbulence properties were obtained for the gas phase. In addition, drop velocity and drop size distributions, particle number densities, and volume flux were measured at different locations within the swirling flow. Large differences in the spatial distribution of the drops over its size, velocity, and number density are observed when the spray in coflowing air with the same axial velocity is compared with the atomizer spraying into the swirling flow field. Large drops seem to be recirculated into the core of the swirling flow, while rather small drops surround this central region. The radial distribution of particle number density and the liquid volume flux are also different when the atomizer spraying into the coflowing air and into the swirling field are compared. Particle number densities for the latter exhibit higher peak values close to the nozzle; but show almost the same peak values as in the coflowing case but at a different radial location further downstream. The velocity of specific drop sizes was also obtained. Drops as large as 5μm are seen to follow closely the mean velocity of the gas. The turbulence properties of the swirling flow show significant influence on the dynamic behavior of the drops. Radial distributions of turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses exhibit double peak values, which delineate the boundaries of the central recirculation region and the external free stream. Within these boundaries the radial distribution of both particle number density and volume flux are seen to attain their maximum values.

Experimental Study of Reynolds Number Effects on Three-Dimensional Offset Jets

2014 ◽  
Author(s):  
Zacharie M. J. Durand ◽  
Shawn P. Clark ◽  
Mark F. Tachie ◽  
Jarrod Malenchak ◽  
Getnet Muluye
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Reynolds Number Effects

The effect of Reynolds number on three-dimensional offset jets was investigated in this study. An acoustic Doppler velocimeter simultaneously measured all three components of velocity, U, V and W, and turbulence intensity, urms, vrms, and wrms, and all three Reynolds shear stresses, uv, uw, and vw. Turbulent kinetic energy, k, was calculated with all three values of turbulence intensities. Flow measurements were performed at Reynolds numbers of 34,000, 53,000 and 86,000. Results of this experimental study indicate the wall-normal location of maximum mean velocity and jet spread to be independent of Reynolds number. The effects on maximum mean velocity decay are reduced with increasing Reynolds number. Profiles of mean velocities, U, V and W, turbulence intensities, urms, vrms, and wrms, and turbulent kinetic energy, k, show independence of Reynolds number. Reynolds shear stress uv was independent of Reynolds number while the magnitude of uw was reduced at higher Reynolds number.

Experimental Study on the Production of CO-NO-HC Emissions in the Radial Swirling Flow Combustion System

2014 ◽  
Vol 69 (2) ◽  
Author(s):  
Mohamad Shaiful Ashrul Ishak ◽  
Mohammad Nazri Mohd Jaafar
Keyword(s):  
Swirling Flow ◽  
Recirculation Region ◽  
Mixing Enhancement ◽  
Swirl Number ◽  
Swirl Angle ◽  
Low Emission ◽  
Air Mixing ◽  
Hc Emissions ◽  
Vane Angle ◽  
Fuel Burner

The main purpose of this paper is to evaluate the production of CO-NO-HC emissions while varying the swirl angle of curve vane radial swirler. Air swirler adds sufficient swirling to the inlet flow to generate central recirculation region (CRZ) which is necessary for flame stability and fuel air mixing enhancement. Therefore designing an appropriate air swirler is a challenge to produce stable, efficient and low emission combustion inside a burner system. Four radial curve vane swirlers with 30o, 40o, 50o and 60o vane angle corresponding to swirl number of 0.366, 0.630, 0.978 and 1.427 respectively were used in this analysis to show the effect of vane angle on emission production at end of combustion chamber. Pollutant NO reduction of more than 10 percent was obtained for the swirl number of 1.427 compared to 0.366. CO emissions were reduced by 20 percent, 25 percent and 38 percent reduction in carbon monoxide (CO) emission for swirl number of 0.630, 0.978 and 1.427 compared to swirl number of 0.366 respectively. Meanwhile, there was a small decrease in unburned HC emissions when increasing the swirl number for the whole range of equivalence ratios.  Results show that the swirling action is augmented with the increase in the vane angle, which leads to better performance of CO-NO-HC emission production inside liquid fuel burner system.

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