Momentum Flux Development From Three-Dimensional Free Jets

1976 ◽  
Vol 98 (2) ◽  
pp. 256-260 ◽  
Author(s):  
J. P. Narain
Keyword(s):  
Axial Velocity ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Core Region ◽  
Potential Region ◽  
Potential Core ◽  
Free Jets ◽  
Flow Development ◽  
Velocity Decay

The momentum-flux development from three-dimensional free jets has been investigated. The analysis is presented for free jets from circular, triangular, rectangular and elliptical orifices. The bluff jets, with eccentricity near unity, show the usual potential region and the axisymmetric decay region for the maximum axial velocity decay. The slender jets, with smaller than one eccentricity values, show three zones of flow development. The potential core region is followed by a characteristic decay region where velocity decay is dependent on the shape and eccentricity of the orifice. The maximum axial velocity of all slender jets finally decay axisymmetrically with increasing downstream distances.

Heated Three-Dimensional Turbulent Jets

1979 ◽  
Vol 101 (2) ◽  
pp. 353-358 ◽  
Author(s):  
P. M. Sforza ◽  
W. Stasi
Keyword(s):  
Initial Conditions ◽  
Three Dimensional ◽  
Subsequent Development ◽  
Turbulent Jets ◽  
Core Region ◽  
Potential Core ◽  
Free Jets ◽  
Flow Quality ◽  
Profile Characteristics ◽  
Flow Variables

An experimental investigation of heated three-dimensional turbulent free jets is presented. Emphasis is placed on the basic character of such flows and their relation to their unheated counterparts and to heated axisymmetric jets. Temperature and velocity distributions indicate that these flow fields may be characterized by three distinct regions in terms of the axis decays: a potential core region where axis values are close to the exit values, a characteristic decay region wherein the axis decays are dependent upon orifice geometry, and an axisymmetric decay region where the axis decay is axisymmetric in nature and thus independent of orifice geometry. These regions are not exactly the same for temperature as for velocity, the former being shifted somewhat upstream of the latter. Half-width data indicate that heated three-dimensional jets change shape as they proceed downstream, ultimately becoming axisymmetric in nature, regardless of initial orifice shape. Profile characteristics and similarity are discussed as well as cross-plane contours of pertinent flow variables. Some of the effects of initial conditions and exit flow quality on the subsequent development of three-dimensional jets are shown and the sensitivity of such flows to these factors is described.

Dynamic characteristics of supersonic turbulent free jets from four types of circular nozzles

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Mingli He ◽  
Guang Zhang ◽  
Shaohua Hu ◽  
Cheng Wang
Keyword(s):  
Dynamic Characteristics ◽  
Axial Velocity ◽  
Working Pressure ◽  
Perfect Agreement ◽  
Potential Core ◽  
Free Jets ◽  
Eddy Simulation ◽  
Work Pressure ◽  
Velocity Decay ◽  
Spreading Rates

Abstract The effects of nozzle structures and working pressure on the dynamic characteristics of supersonic turbulent free jets have been investigated numerically. Four types of nozzles (namely Laval, pipe, contraction I, and contraction II, respectively) and four pressure conditions (namely K = 0.8, 1, 1.5, and 2, respectively) were considered. A Standard k-ε model was utilized for the calculation of the supersonic turbulent free jets. Validation of the model was performed on the Laval jet by comparing it with the experiment and large-eddy simulation (LES). A perfect agreement was achieved in terms of the centerline and radial axial velocity profiles. The jets issuing from the Laval and the pipe had a longer potential core and a larger centerline axial velocity with the same outlet momentum. The length of the potential core was proportional to the working pressure, but variations of the centerline axial velocity decay rate were inverse for all nozzles. The effects of nozzle structures and work pressure on the spreading rates of the jets were insignificant. No obvious change trend could be observed on the kinematic and geometric virtual origins. The study can provide references for the nozzle and working pressure selection in practical application.

Three-Dimensional Free Jets

1967 ◽  
Vol 71 (684) ◽  
pp. 858-859
Author(s):  
N. Rajaratnam ◽  
K. Subramanya
Keyword(s):  
Three Dimensional ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Axisymmetric Jet ◽  
Plane Jets ◽  
Velocity Decay ◽  
Different Shapes ◽  
Semi Empirical

Fairly elegant semi-empirical theories are available for predicting the turbulent diffusion of axisymmetric and plane jets. However, there are relatively few investigations on the non-axisymmetric jets, herein denoted as three-dimensional jets. The extensive investigations conducted at the Polytechnic Institute of Brooklyn on three-dimensional jets have shown that the flow field is characterised by three distinct regions; the potential core, the characteristic decay (CD) region and the axisymmetric decay (AD) region. In the CD region the velocity profiles in the direction of the minor axis are similar but the maximum velocity decay curves are different for different shapes. In the AD region the flow characteristics are similar to that of an axisymmetric jet. Yevdjevich has recently conducted another investigation on rectangular jets.

Enhanced Mixing of 2D Lobed Nozzles

1995 ◽  
Author(s):  
Huo-Xing Liu ◽  
Shou-Sheng Wu
Keyword(s):  
Axial Velocity ◽  
Small Scale ◽  
Test Results ◽  
Low Velocity ◽  
Rapid Decay ◽  
Potential Core ◽  
Aspect Ratios ◽  
Viscous Shear ◽  
Velocity Decay ◽  
Scale Turbulence

The jet axial velocity decay and velocity distributions of two 2D Lobed Nozzles (2DLN), and three baseline nozzles, one circular and two rectangular with different aspect ratios (AR), were measured and compared at low velocity (M0 <0.35) and ambient temperature conditions. The five nozzles have the same exit area. Test results show: 1) The jet axial velocity decay of the 2DLN may be characterized by three distinct regions; i.e., “potential core region”, where the jet axial velocity almost remains constant; “rapid decay region”, where streamwise and normal vortices play major roles for enhanced mixing; and, “smooth-down decay region”, where the mixing process is dominated by viscous shear layer spreading and small-scale turbulence. 2) The jet potential core length of the two 2DLN tested is only half to one-third that of the baseline rectangular nozzle (AR=4.37), and about one-fourth to one-sixth compared with the baseline circular nozzle. The length, in which the jet mixed with surrounding air is nearly uniform, is one to two times that of the 2DLN equivalent exit diameter, and depends on lobe design.

scholarly journals Experimental Investigation on Mean Flow Development of a Three-Dimensional Wall Jet Confined by a Vertical Baffle

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 237
Author(s):  
Ming Chen ◽  
Haijin Huang ◽  
Xingxing Zhang ◽  
Senpeng Lv ◽  
Rengmin Li
Keyword(s):  
Three Dimensional ◽  
Wall Jet ◽  
Lateral Growth ◽  
Mean Flow ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Flow Development ◽  
Velocity Decay ◽  
The Mean ◽  
Vertical Baffle

Three-dimensional (3D) confined wall jets have various engineering applications related to efficient energy dissipation. This paper presents experimental measurements of mean flow development for a 3D rectangular wall jet confined by a vertical baffle with a fixed distance (400 mm) from its surface to the nozzle. Experiments were performed at three different Reynolds numbers of 8333, 10,000 and 11,666 based on jet exit velocity and square root of jet exit area (named as B), with water depth of 100 mm. Detailed measurements of current jet were taken using a particle image velocimetry technique. The results indicate that the confined jet seems to behave like an undisturbed jet until 16B downstream. Beyond this position, however, the mean flow development starts to be gradually affected by the baffle confinement. The baffle increases the decay and spreading of the mean flow from 16B to 23B. The decay rate of 1.11 as well as vertical and lateral growth rates of 0.04 and 0.19, respectively, were obtained for the present study, and also fell well within the range of values which correspond to the results in the radial decay region for the unconfined case. In addition, the measurements of the velocity profiles, spreading rates and velocity decay were also found to be independent of Reynolds number. Therefore, the flow field in this region appears to have fully developed at least 4B earlier than the unconfined case. Further downstream (after 23B), the confinement becomes more pronounced. The vertical spreading of current jet shows a distinct increase, while the lateral growth was found to be decreased significantly. It can be also observed that the maximum mean velocity decreases sharply close to the baffle.

Three-Dimensional Curved Wall Jets

1972 ◽  
Vol 94 (2) ◽  
pp. 339-344 ◽  
Author(s):  
U. M. Patankar ◽  
K. Sridhar
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Ambient Air ◽  
Jet Flow ◽  
Jet Flows ◽  
Wall Jet ◽  
Wall Jets ◽  
Potential Core ◽  
Velocity Decay

This paper presents an experimental investigation of mean velocities of turbulent, three-dimensional incompressible air jets from various rectangular orifices issuing tangentially to and flowing along the surface of a curved wall into quiescent ambient air. An experimental study of the jet separation is also presented. The three-dimensional curved wall jet is found to be drastically different in its mean property behavior from its so-called two-dimensional counterpart. Velocity contour plots show the resultant effect on the jet flow of two diverging tendencies—the free jet flow and the Coanda flow. This effect is found to occur earlier with smaller aspect-ratio orifices. Within the range of variables studied, three-dimensional curved wall jets may be characterized by three regions of maximum velocity decay. The rate of maximum velocity decay is dependent on orifice aspect ratio, except in the potential core region. Further, the curved wall jet differs from other three-dimensional jet flows in its growth behavior.

Experimental Study of a Rectangular Jet Impinging on a Circular Cylinder

2003 ◽  
Author(s):  
Michiharu Ishii ◽  
Xiao Feng Yang ◽  
Masaharu Matsubara ◽  
Yoshiaki Tsuchiya ◽  
Takashi Yoshida
Keyword(s):  
Circular Cylinder ◽  
Pressure Distribution ◽  
Three Dimensional ◽  
Separated Flow ◽  
Industrial Applications ◽  
Core Region ◽  
Potential Core ◽  
Rectangular Jet ◽  
Sudden Decrease ◽  
Saddle Shape

It was known that development of a jet from a rectangular orifice could be divided into three regions, which are 1) potential core region 2) characteristic decay region and 3) axisymmetric decay region. When a circular cylinder is placed in the rectangular jet, characteristic separation occurs around the cylinder and shapes of non-separation area on the cylinder are distinguished with the streamwise position of the cylinder. This flow geometry can be frequently seen in the industrial applications and drag and heat transfer of the cylinder would be important for the designs. In this study the rectangular jet impinging on a circular cylinder has been experimentally investigated. The relation between the jet development before impinging and separation area on the cylinder is especially focused. In the case that the cylinder is in the potential core region, the non-separation area distributes as saddle shape and the spanwise pressure distribution at the impinging line on the cylinder is almost constant around jet center and in the edge of jet impinging region it decreases with the distance. Then the pressure reaches at the minimum in the outside of the edge and recovers to the pressure of the circumference far from the edge. This pressure distribution suggests that flow just above the impinging line of cylinder blows toward the center and that the impinging flow is incredibly three-dimensional. When the cylinder is in the characteristic decay region, the non-separation area distributes as saddle shape as well as in the case of the potential core region. The spanwise impinging pressure distribution on the cylinder has maximums at the spanwise edges of impinging jet and sudden decrease out side of the jet. In this case the minima in the fringes of the jet were not observed. In the case of the axisymmetric region, the area of non-separation is elliptic and at the spanwise center the non-separated flow reaches backside of the cylinder.

scholarly journals Characteristic study of non-circular incompressible free jet

2013 ◽  
Vol 17 (3) ◽  
pp. 787-800 ◽  
Author(s):  
Ponnambalam Manivannan ◽  
Banbla Sridhar
Keyword(s):  
Three Dimensional ◽  
Growth Potential ◽  
Mean Flow ◽  
Potential Core ◽  
Free Jet ◽  
Air Jets ◽  
Circular Jets ◽  
Velocity Decay ◽  
Rates Of Decay ◽  
Axis Switching

This paper reports an experimental investigation of bulk properties of turbulent, which is three dimensional, incompressible, air jets issuing into still air surrounding from the nozzles. The jet orifices utilized included circular, hexagonal and cruciform geometries. Experimental results of pertinent mean flow properties such as axis velocity decay, half width growth, potential core and turbulence intensities are reported. Single Hotwire anemometer was used for measurements of the velocity field. The experiment for the three jets was conducted under the same nominal conditions with the exit Reynolds number of 15,400. Consistent with previous investigations of other non circular jets, the cruciform jet is found to have an overall superior mixing capability over the circular counter part. Immediately downstream of the nozzle exit, it entrains, and then mixes with, the surroundings at a higher rate. This jet has a shorter potential core with higher rates of decay and spread than the circular jet. This phenomenon of axis switching is also found to occur in this jet.

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