The Effects of Nozzle Orientation on Mixing Characteristics of Elliptic Twin Free Jets

2019 ◽  
Author(s):  
Ella M. Morris ◽  
Neelakash Biswas ◽  
Seyed S. Aleyasin ◽  
Mark F. Tachie
Keyword(s):  
Symmetry Plane ◽  
Velocity Profiles ◽  
Particle Image Velocimetry System ◽  
Equivalent Diameter ◽  
Linear Contraction ◽  
Turbulent Characteristics ◽  
Major Plane ◽  
Single Jet ◽  
Nozzle Orientation ◽  
Minor Plane

Abstract The effects of nozzle orientation on the mixing and turbulent characteristics of elliptical free twin jets were studied experimentally. The experiments were conducted using modified contoured nozzles with a sharp linear contraction. The centers of the nozzle pair had a separation ratio of 5.5. Four nozzle configurations were tested, one twin jet orientated along the minor plane (Twin_Minor), one twin jet orientated along the major plane (Twin_Major), one single jet orientated along the minor plane (Single_Minor) and one single jet orientated along the major plane (Single_Major). In each case, the Reynolds number based on the maximum jet velocity and the equivalent diameter was 10,000. A planar particle image velocimetry system was used to measure the velocity field in the jet symmetry plane. It was observed that the velocity decay rate is not sensitive to nozzle orientation. However, close to the jet exit the spread rate was highest in the minor plane. In addition, contour plots of Reynolds shear stress and turbulence intensities revealed significant differences between the minor and major plane. Velocity profiles showed little variation close to the jet exit, while further downstream the variations between the velocity profiles were more pronounced between the major and minor planes.

Particle Image Velocimetry Measurements of Turbulent Jets Issuing From Twin Elliptic Nozzles With Various Orientations

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Ella Marie Morris ◽  
Neelakash Biswas ◽  
Seyed Sobhan Aleyasin ◽  
Mark Francis Tachie
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Symmetry Plane ◽  
Velocity Profiles ◽  
Equivalent Diameter ◽  
Linear Contraction ◽  
Turbulent Characteristics ◽  
Image Velocimetry ◽  
Nozzle Orientation ◽  
Minor Plane

Abstract The effects of nozzle orientation on the mixing and turbulent characteristics of elliptical free twin jets were studied experimentally. The experiments were conducted using modified contoured nozzles with a sharp linear contraction. The centers of the nozzle pair had a separation ratio of 5.5. Two nozzle configurations were tested, twin nozzles oriented along the minor plane (Twin_Minor) and twin nozzles oriented along the major plane (Twin_Major) and the results were compared with a single jet. In each case, the Reynolds number based on the maximum jet velocity and the equivalent diameter was 10,000. A planar particle image velocimetry (PIV) system was used to measure the velocity field in the jet symmetry plane. It was observed that the velocity decay rate is not sensitive to nozzle orientation. However, close to the jet exit, the spread rate was highest in the minor plane. In addition, contour plots of swirling strength, Reynolds shear stress and turbulent intensities revealed significant differences between the minor and major planes. Velocity profiles showed little variation close to the jet exit, while further downstream the variations between the velocity profiles were more pronounced between the major and minor planes.

Experimental Investigation of Nozzle Orientation Effects on Mixing Characteristics of Elliptic Triple Free Jets

2019 ◽  
Author(s):  
Ella M. Morris ◽  
Seyed S. Aleyasin ◽  
Neelakash Biswas ◽  
Mark F. Tachie
Keyword(s):  
Experimental Investigation ◽  
Potential Core ◽  
Linear Contraction ◽  
Free Jets ◽  
Orientation Effects ◽  
Core Length ◽  
Turbulent Characteristics ◽  
Major Plane ◽  
Nozzle Orientation ◽  
Minor Plane

Abstract An experimental investigation of nozzle orientation effects on turbulent characteristics of elliptic triple free jets was carried out for three nozzle configurations. The first configuration had all three nozzles oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (2_Minor_1_Major) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (1_Minor_2_Major). The experiments were conducted using modified contoured nozzles with a sharp linear contraction for a nozzle-to-nozzle distance of 4.1, a nozzle equivalent diameter of 9 mm and a Reynolds number of 10,000. The effects of nozzle orientation on the mean velocity, turbulence intensity and Reynolds shear stress were discussed. The velocity decay, jet spread, merging point, combined point and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. The results show that the 3_Minor configuration had shorter potential core length and closer merging point location which are indicative of a faster mixing in the converging region. Two-point correlation, skewness and flatness factors were used to provide insight into the effects of nozzle orientation on turbulence structure and higher order turbulence statistics.

Turbulent Properties of Triple Elliptic Free Jets With Various Nozzle Orientation

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Ella Marie Morris ◽  
Seyed Sobhan Aleyasin ◽  
Neelakash Biswas ◽  
Mark Francis Tachie
Keyword(s):  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Turbulent Intensity ◽  
Potential Core ◽  
Free Jets ◽  
Orientation Effects ◽  
Core Length ◽  
Major Plane ◽  
Nozzle Orientation ◽  
Minor Plane

Abstract An experimental investigation of nozzle orientation effects on turbulent characteristics of elliptic triple free jets was carried out for three nozzle configurations. The first configuration had each nozzle oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (Min_Maj_Min) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (Maj_Min_Maj). The experiments were conducted using modified contoured nozzles with a sharp linear contraction for a nozzle spacing ratio of 4.1d, a nozzle equivalent diameter of 9 mm, and Reynolds number of 10,000. Nozzle orientation effects on the mean velocity, turbulent intensity, and Reynolds shear stress were discussed. The velocity decay, jet spread, merging point (MP), combined point (CP), and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. The 3_Minor configuration had shorter potential core length and closer MP location which are indicative of a faster mixing in the converging region. The early merging of 3_Minor led to higher levels of streamwise turbulent intensity. One-dimensional plots revealed that jets approached self-similarity at a faster rate in the major axis. The orientation of the middle jet was found to be a key factor in determining transverse diffusion of the Reynolds shear stress in the plane of observation. Two-point correlations were used to provide insight into the effects of nozzle orientation on the spatial coherence of the large-scale turbulence structure and integral length scale.

The Lid-Driven Cavity Flow: A Synthesis of Qualitative and Quantitative Observations

1984 ◽  
Vol 106 (4) ◽  
pp. 390-398 ◽  
Author(s):  
J. R. Koseff ◽  
R. L. Street
Keyword(s):  
Heat Flux ◽  
Flow Visualization ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Lower Boundary ◽  
Thymol Blue ◽  
Width Ratio ◽  
Cavity Depth ◽  
Driven Cavity ◽  
Turbulent Characteristics

A synthesis of observations of flow in a three-dimensional lid-driven cavity is presented through the use of flow visualization pictures and velocity and heat flux measurements. The ratio of the cavity depth to width used was 1:1 and the span to width ratio was 3:1. Flow visualization was accomplished using the thymol blue technique and by rheoscopic liquid illuminated by laser-light sheets. Velocity measurements were made using a two-component laser-Doppler-anemometer and the heat flux on the lower boundary of the cavity was measured using flush mounted sensors. The flow is three-dimensional and is weaker at the symmetry plane than that predicted by accurate two-dimensional numerical simulations. Local three-dimensional features, such as corner vortices in the end-wall regions and longitudinal Taylor-Go¨rtler-like vortices, are significant influences on the flow. The flow is unsteady in the region of the downstream secondary eddy at higher Reynolds numbers (Re) and exhibits turbulent characteristics in this region at Re = 10,000.

Experimental and theoretical study of wave–current turbulent boundary layers

2015 ◽  
Vol 765 ◽  
pp. 480-523 ◽  
Author(s):  
Jing Yuan ◽  
Ole S. Madsen
Keyword(s):  
Boundary Layer ◽  
Analytical Model ◽  
Current Velocity ◽  
Nonlinear Waves ◽  
Velocity Profiles ◽  
Particle Image Velocimetry System ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Flow Generation ◽  
Future Work

AbstractAn experimental study of turbulent wave–current boundary layer flows is performed using a state-of-the-art oscillating water tunnel (OWT) for flow generation and a particle image velocimetry system for velocity measurements. The current velocity profiles in the presence of sinusoidal waves indicate a two-log-profile structure suggested by the widely-used Grant–Madsen model. However, for weak currents in the presence of nonlinear waves, the two-log-profile structure is contaminated or even totally obliterated by the boundary layer streaming which is produced by the asymmetry of turbulence in successive half-periods of nonlinear waves. To interpret experimental results, a semi-analytical model which adopts a rigorous way to account for a time-varying turbulent eddy viscosity is developed. The model can accurately predict turbulence asymmetry streaming, which leads to successful predictions of the mean velocity embedded in nonlinear-wave tests and the current velocity profiles in the presence of either sinusoidal or nonlinear waves. Since the Longuet-Higgins-type streaming due to wave propagation is absent in OWT flows and not included in the semi-analytical model, future work is necessary to extend this study for applications in the coastal environment.

Oscillatory Fluid Flow Through a Porous Medium Channel Bounded by Two Impermeable Parallel Plates

1991 ◽  
Vol 113 (3) ◽  
pp. 509-511 ◽  
Author(s):  
J. M. Khodadadi
Keyword(s):  
Porous Medium ◽  
Fluid Flow ◽  
Symmetry Plane ◽  
Velocity Profiles ◽  
Net Energy ◽  
Phase Lag ◽  
High Porosity ◽  
Parallel Plates ◽  
Frictional Drag ◽  
Flow Through

In the absence of the inertia effects, the analytic solution to the fully developed oscillatory fluid flow through a porous medium channel bounded by two impermeable parallel plates is presented. For the limiting case when a highly viscous fluid undergoes slow pulsation in a high porosity medium, the phase lag vanishes and similar velocity profiles are observed. At the other extreme limiting situation, fluid flow near the symmetry plane has a phase lag of 90 deg from the pressure gradient wave. Moreover, the velocity profiles exhibit maxima next to the wall which is similar to the “channeling” phenomenon observed in variable-porosity studies. It is shown that the temporal average of the frictional drag over a period vanishes, indicating no net energy losses due to oscillations.

scholarly journals Turbulent Wake-Flow Characteristics in the Near Wake of Freely Flying Raptors: A Comparative Analysis Between an Owl and a Hawk

2020 ◽  
Vol 60 (5) ◽  
pp. 1109-1122 ◽  
Author(s):  
Krishnamoorthy Krishnan ◽  
Hadar Ben-Gida ◽  
Gareth Morgan ◽  
Gregory A Kopp ◽  
Christopher G Guglielmo ◽  
...  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Flight Behavior ◽  
Aerodynamic Noise ◽  
Particle Image Velocimetry System ◽  
Near Wake ◽  
Time Resolved ◽  
Turbulent Characteristics

Synopsis Owl flight has been studied over multiple decades associated with bio-inspiration for silent flight. However, their aerodynamics has been less researched. The aerodynamic noise generated during flight depends on the turbulent state of the flow. In order to document the turbulent characteristics of the owl during flapping flight, we measured the wake flow behind a freely flying great horned owl (Bubo virginianus). For comparison purposes, we chose to fly a similar-sized raptor a Harris’s hawk (Parabuteo unicinctus): one is nocturnal and the other is a diurnal bird of prey. Here, we focus on the wake turbulent aspects and their impact on the birds’ flight performances. The birds were trained to fly inside a large-scale wind tunnel in a perch-to-perch flight mode. The near wake of the freely flying birds was characterized using a long duration time-resolved particle image velocimetry system. The velocity fields in the near wake were acquired simultaneously with the birds’ motion during flight which was sampled using multiple high-speed cameras. The turbulent momentum fluxes, turbulent kinetic energy production, and dissipation profiles are examined in the wake and compared. The near wake of the owl exhibited significantly higher turbulent activity than the hawk in all cases, though both birds are similar in size and followed similar flight behavior. It is suggested that owls modulate the turbulence activity of the near wake in the vicinity of the wing, resulting in rapid decay before radiating into the far-field; thus, suppressing the aerodynamic noise at the far wake.

Computations of Particle-Laden Turbulent Jet Flows Based on Eulerian Model

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Pandaba Patro ◽  
Sukanta K. Dash
Keyword(s):  
Gas Flow ◽  
Fine Particles ◽  
Solid Phase ◽  
Fluid Model ◽  
Particle Diameter ◽  
Velocity Profiles ◽  
Solid Particles ◽  
Jet Flows ◽  
Particle Sizes ◽  
Turbulent Characteristics

Numerical simulations using an Eulerian two-fluid model were performed for spatially developing, two-dimensional, axisymmetric jets issued from a 30-mm-diameter circular nozzle. The nozzle was simulated separately for various flow conditions to get fully developed velocity profiles at its exit. The effect of interparticle collisions in the nozzle gives rise to solids pressure and viscosity, which are modeled using kinetic theory of granular flows (KTGF). The particle sizes are in the range of 30 μm to 2 mm, and the particle loading is varied from 1 to 5. The fully developed velocity profiles are expressed by power law, U=Uc(1-(r/R))N. The exponent, N, is found to be 0.14 for gas phase, irrespective of particle sizes and particulate loadings. However, the solid-phase velocity varies significantly with the particle diameter. For particle sizes up to 200 μm, the exponent is 0.12. The center line velocity (Uc) of the solid phase decreases and, hence, the slip velocity increases as the particle size increases. For 1 mm and 2 mm size particles, the exponent is found to be 0.08 and 0.05, respectively. The developed velocity profiles of both the phases are used as the inlet velocities for the jet simulation. The modulations on the flow structures and turbulent characteristics of gas flow due to the solid particles with different particle sizes and loadings are investigated. The jet spreading and the decay of the centerline mean velocity are computed for all particle sizes and loadings considered under the present study. Additions of solid particles to the gas flow significantly modulate the gas turbulence in the nozzle as well as the jet flows. Fine particles suppress the turbulence, whereas coarse particles enhance it.

Initial Region of Subsonic Coaxial Jets of High Mean-Velocity Ratio

1981 ◽  
Vol 103 (2) ◽  
pp. 335-338 ◽  
Author(s):  
N. W. M. Ko ◽  
H. Au
Keyword(s):  
Experimental Investigation ◽  
Turbulence Intensity ◽  
Velocity Ratio ◽  
Velocity Profiles ◽  
Initial Region ◽  
Mean Velocity ◽  
Coaxial Jets ◽  
Single Jet ◽  
The Mean

This paper describes an experimental investigation of the initial region of subsonic coaxial jets of three different mean-velocity ratios λ higher than unity. Detailed measurements have found similarity of the mean velocity and turbulence intensity profiles within the three zones: initial merging, intermediate, and fully merged zone. Similarity with single jet results has been found. In the inner mixing region, however, only the similarity of the mean velocity profiles has been found.

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