Flow Characteristics of Round Jet Issuing Into Counter-Flowing Uniform Stream

2003 ◽  
Author(s):  
Masafumi Miyata ◽  
Tatsushi Yagi
Keyword(s):  
Stagnation Point ◽  
Turbulence Intensity ◽  
Velocity Ratio ◽  
Water Channel ◽  
Recirculation Region ◽  
Mean Velocity ◽  
Penetration Length ◽  
Round Jet ◽  
Jet Axis ◽  
Uniform Stream

Two-color four beam LDV measurements were conducted for the round jet issuing into a counter-flowing uniform stream under well controlled boundary conditions. A comprehensive set of the velocity data was documented for velocity ratios from 0.8 to 7. The linear dependence of jet penetration length on velocity ratio was confirmed for all conditions investigated, including those with velocity ratios less than 1. The proportional coefficient estimated is substantially larger than those reported for similar jets in a water channel. The streamwise variations of mean velocity and turbulence intensity on the jet axis also depend only on velocity ratio. It is very interesting to know that the streamwise turbulence intensity on the jet axis, non-dimensionalized by uniform velocity, is at a maximum near at the stagnation point and that the maximum has a constant value near 1 for velocity-ratios greater than 2. The static pressure was found to become near to zero at the stagnation point and is negative in the core of the recirculation region.

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.

scholarly journals Measurements in Film Cooling Flows: Hole L/D and Turbulence Intensity Effects

1998 ◽  
Vol 120 (4) ◽  
pp. 791-798 ◽  
Author(s):  
S. W. Burd ◽  
R. W. Kaszeta ◽  
T. W. Simon
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Stream Flow ◽  
Free Stream ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Mean Velocity ◽  
Free Stream Turbulence ◽  
Cooling Hole ◽  
Film Cooling Holes

Hot-wire anemometry measurements of simulated film cooling are presented to document the influence of the free-stream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and on turbulence intensity. Measurements are taken in the zone where the coolant and free-stream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35 deg and no lateral injection and with a coolant-to-free-stream flow velocity ratio of 1.0 is investigated under free-stream turbulence levels of 0.5 and 12 percent. The coolant-to-free-stream density ratio is unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. The Measurements document that under low free-stream turbulence conditions pronounced differences exist in the flowfield between L/D= 7.0 and 2.3. The difference between L/D cases are less prominent at high free-stream turbulence intensities. Generally, Short-L/D injection results in “jetting” of the coolant farther into the free-stream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in free-stream turbulence intensity to engine-representative conditions are documented.

A round jet in an ambient co-axial stream

1962 ◽  
Vol 13 (4) ◽  
pp. 597-608 ◽  
Author(s):  
J. F. J. Maczyński
Keyword(s):  
Local Equilibrium ◽  
Velocity Profiles ◽  
Mixing Length ◽  
Mean Velocity ◽  
Round Jet ◽  
The Mean ◽  
Rate Of Dissipation ◽  
Jet Axis

Measurements were made of the mean velocity profiles in a jet immersed in a stream whose velocity was in the same direction as that of the jet. They showed a mean velocity on the jet axis falling inversely as the distance downstream of the jet origin, a behaviour demonstrably inconsistent with any theory which assumes that the turbulence at each section of the jet is in local equilibrium. A mixing length, LM, and a length, Ld, characterizing the rate of dissipation are defined and it is shown that LM increases with distance downstream more rapidly than the jet width, and Ld less rapidly.

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.

Time Resolved PIV Measurements of a Slot Lobed Jet Issuing Into a Crossflow

2021 ◽  
Author(s):  
Michael Lewandowski ◽  
Paul Kristo ◽  
Abdullah Weiss ◽  
Mark Kimber
Keyword(s):  
Velocity Ratio ◽  
Leading Edge ◽  
Residual Effects ◽  
Low Velocity ◽  
Mean Velocity ◽  
Time Resolved ◽  
Freestream Velocity ◽  
Round Jet ◽  
Jet In Crossflow ◽  
Turbulent Statistics

Abstract The near field mixing phenomenon created by a round jet with three slot lobes exhausting into a crossflow are investigated at a velocity ratio of 0.5. Time-resolved particle image velocimetry measurements provide instantaneous velocity fields of the slotted jet in crossflow, allowing for evaluation of the first and second order turbulent statistics in two perpendicular planes of interest. The independently controlled jet exit and crossflow inlet are first characterized extensively to confirm the velocity ratio and anticipated momentum exchanges. Spanwise and transverse mean velocity profiles reveal that the interaction of the three slot lobes and the center round jet primarily occur in the immediate jet exit region, though residual effects are also found in the wake. Evaluation of the Reynold stresses aims to quantify the near region mixing between the jets collated geometric features and their interaction with the crossflow. Frequency analysis reveals that low-frequency harmonics in the wake region provide greater energy contributions than that of the higher-frequency harmonics found along the leading edge shear layer. This behavior is attributed to the low velocity ratio, where the freestream velocity is twice as large as the jet exit velocity. The experimental data and observations herein serve analogous computational modeling efforts for the slotted jet in crossflow at low velocity ratios, with ample information to inform necessary boundary conditions, fluid properties, and flow fields for validation.

The Turbulent Incompressible Jet in a Curved Coflow

1996 ◽  
Vol 118 (2) ◽  
pp. 300-306 ◽  
Author(s):  
M. V. O¨tu¨gen ◽  
F. Girlea ◽  
P. M. Sforza
Keyword(s):  
Turbulence Intensity ◽  
Velocity Ratio ◽  
Axial Flow ◽  
Streamwise Velocity ◽  
Half Width ◽  
Outer Side ◽  
Mean Velocity ◽  
Streamline Curvature ◽  
The Mean ◽  
Pronounced Peak

The effects of small streamline curvature on the growth and axial flow development of a turbulent incompressible jet in a curved coflow was investigated experimentally. The jet streamline curvature was achieved by introducing the initially round jet tangentially into a stream flowing through a curved channel of square cross-section. The jet issued from a straight pipe and had a fully developed velocity profile at the exit plane. The jet Reynolds number and the coflow-to-jet-velocity ratio were 4300 and 0.11, respectively. A single component laser Doppler anemometer was used to measure the streamwise velocity. Axial mean velocity and turbulence intensity profiles were measured at various streamwise locations in both the plane of curvature and the surface perpendicular to the plane of curvature. The results indicate that the jet growth and turbulence intensity are influenced by the small streamline curvature. The growth rate of the curved jet in the plane of curvature is slightly increased compared to that of a straight jet. However, the growth of the same curved jet is suppressed in the plane perpendicular to the plane of curvature. In the plane of curvature, the inner jet half-width is larger than the outer jet half-width. The mean velocity profiles in this plane are nearly Gaussian when the lateral distance is normalized by the respective inner and outer side jet half-widths. The axial turbulence intensity profiles show asymmetry in the plane of curvature with a pronounced peak on the outer side of the jet.

scholarly journals Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different atmospheric inflow conditions

2016 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Blind Test ◽  
The Mean ◽  
Inlet Conditions ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth Blind test workshop which was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at NTNU's wind tunnel. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within Computational Fluid Dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development up until 9 rotor diameters downstream at three different atmospheric inflow conditions. Besides a spatially uniform inflow field of very low turbulence intensity (TI = 0.23 %) as well as high turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated atmospheric shear flow (TI = 10.1 %). Five different research groups contributed with their predictions using a variety of simulation models, ranging from fully resolved Reynolds Averaged Navier Stokes (RANS) models to Large Eddy Simulations (LES). For the three inlet conditions the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. The prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (Improved Delayed Detached Eddy Simulation) model, however, are consistently managing to provide fairly accurate predictions of the wake turbulence.

Similarity Solutions of the MHD Stagnation-Point Flow over a Power-Law Stretching Sheet

2011 ◽  
Vol 52-54 ◽  
pp. 1895-1900
Author(s):  
Jing Zhu ◽  
Lian Cun Zheng ◽  
Xue Hui Chen
Keyword(s):  
Stagnation Point ◽  
Power Law ◽  
Stretching Sheet ◽  
Velocity Ratio ◽  
Similarity Solutions ◽  
Stagnation Point Flow ◽  
Electrically Conducting ◽  
Power Law Exponent ◽  
Permeability Parameter ◽  
Scaling Group Of Transformations

A similarity analysis is performed for a steady laminar boundary layer stagnation-point flow of an electrically conducting fluid in a porous medium subject to a transverse non-uniform magnetic field past a non-linear stretching sheet. A scaling group of transformations is applied to get the invariants. Using the invariants, a third order ordinary differential equation corresponding to the momentum is obtained. We show the existence and uniqueness of convex and concave solutions for the power law exponent, according to the values of magnetic parameter, permeability parameter and velocity ratio parameter.

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