scholarly journals Self-similar properties of decelerating turbulent jets

2017 ◽  
Vol 833 ◽  
Author(s):  
Dong-hyuk Shin ◽  
A. J. Aspden ◽  
Edward S. Richardson
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Turbulent Jets ◽  
Entrainment Rate ◽  
Velocity Statistics ◽  
Radial Profiles ◽  
Axial Velocity Profile ◽  
Self Similar ◽  
The Mean ◽  
Analytical Relations

The flow in a decelerating turbulent round jet is investigated using direct numerical simulation. The simulations are initialised with a flow field from a statistically stationary turbulent jet. Upon stopping the inflow, a deceleration wave passes through the jet, behind which the velocity field evolves towards a new statistically unsteady self-similar state. Assumption of unsteady self-similar behaviour leads to analytical relations concerning the evolution of the centreline mean axial velocity and the shapes of the radial profiles of the velocity statistics. Consistency between these predictions and the simulation data supports the use of the assumption of self-similarity. The mean radial velocity is predicted to reverse in direction near to the jet centreline as the deceleration wave passes, contributing to an approximately threefold increase in the normalised mass entrainment rate. The shape of the mean axial velocity profile undergoes a relatively small change across the deceleration transient, and this observation provides direct evidence in support of previous models that have assumed that the mean axial velocity profile, and in some cases also the jet spreading angle, remain approximately constant within unsteady jets.

scholarly journals Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets

2021 ◽  
Author(s):  
Pourya Nejatipour ◽  
Babak Khorsandi
Keyword(s):  
Mass Flow ◽  
Cross Sections ◽  
Turbulent Jets ◽  
Nozzle Geometry ◽  
Entrainment Rate ◽  
Radial Profiles ◽  
Self Similar ◽  
The Mean ◽  
Elliptical Jet ◽  
Velocity Variances

Abstract The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.

Physical characteristics of subsonic jets in a cross-stream

1974 ◽  
Vol 62 (1) ◽  
pp. 41-64 ◽  
Author(s):  
P. Chassaing ◽  
J. George ◽  
A. Claria ◽  
F. Sananes
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Turbulent Jets ◽  
Velocity Profiles ◽  
Local Flow ◽  
Axial Velocity Profile ◽  
Velocity Decay ◽  
The Law

This paper deals with local flow characteristics of subsonic turbulent jets in the presence of a cross-flow. For the various types of jet considered (a cylindrical jet and coaxial jets) the experimental results concern the axes and the velocity profiles in the plane of symmetry of the flow. In the case of the cylindrical jet, the shape of the universal axial velocity profile is defined, as are the law of velocity decay along the axis and the laws of variation of the thicknesses of the jet. Finally, the existence of a link between the axis equation and the law of axial velocity decay in the zone of similarity of the velocity profiles is established.

Turbulent Flow in Axially Rotating Pipes

1980 ◽  
Vol 102 (1) ◽  
pp. 97-103 ◽  
Author(s):  
Mitsukiyo Murakami ◽  
Kouji Kikuyama
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Flow Pattern ◽  
Axial Velocity ◽  
Hydraulic Loss ◽  
Pressure Distributions ◽  
Axial Velocity Profile ◽  
Fully Developed Turbulent Flow ◽  
Smooth Pipe ◽  
Pipe Rotation

Experimental results concerning the flow pattern and hydraulic resistance in a rotating pipe are described. A fully developed turbulent flow was introduced into a long smooth pipe rotating about its axis, and changes of the flow pattern, together with hydraulic loss within the pipe, were examined by measuring the velocity and pressure distributions across sections at various distance from the pipe entrance. Increase of pipe rotation continuously reduces the hydraulic loss and gradually changes the axial velocity profile from a turbulent type to a laminar one. Governing factors for these changes are discussed.

The Elimination of Wall Effects in Axial-Flow Compressor Stages

1953 ◽  
Vol 57 (508) ◽  
pp. 241-243
Author(s):  
J. M. Stephenson
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Radial Profile ◽  
Axial Flow ◽  
Gas Velocity ◽  
Wall Effects ◽  
Axial Velocity Component ◽  
Axial Velocity Profile ◽  
Flow Compressor ◽  
Work Done

Compressor stages are usually designed on the assumption that the gas velocity is nowhere affected by the friction at the walls. The only way in which viscosity is taken into account is in the assumed efficiency, and in a guessed “work-done factor,” which ensures that by aiming high the required work is actually attained.It is known that the radial profile of the axial velocity component becomes more and more peaked through successive stages of a compressor, so that the assumptions just quoted become very inaccurate. It is possible that the efficiency of a stage could be raised considerably if the axial velocity profile were controlled; moreover up to 20 per cent. more work could be done if a “ work-done factor ” did not have to be applied.

A Theoretical Analysis of the Influence of Rotation on Flow in a Tube Rotating about a Parallel Axis with Uniform Angular Velocity

1965 ◽  
Vol 69 (651) ◽  
pp. 201-202 ◽  
Author(s):  
W. D. Morris
Keyword(s):  
Angular Velocity ◽  
Velocity Profile ◽  
Axial Velocity ◽  
Cylindrical Tube ◽  
Fluid Flows ◽  
Leading Edge ◽  
Pressure Fields ◽  
Axial Velocity Profile ◽  
Parallel Axis ◽  
Arbitrary Axis

When fluid flows in a tube which rotates about an arbitrary axis, the presence of centripetal and Coriolis acceleration components modify the velocity and pressure fields which exist in the absence of rotation. Barua considered the case of an incompressible fluid flowing in laminar motion through a cylindrical tube which was rotating about an axis perpendicular to itself with uniform angular velocity. For distances well away from the tube entrance Barua illustrated that secondary flow in the r-θ plane occurred and that the axial velocity profile was distorted towards the leading edge of the tube. Since the pressure gradient along the tube is proportional to the gradient of the axial velocity profile at the tube wall the rotation thus has a consequential influence on the resistance to flow offered by the tube.

Gas Dispersion in a Model Pulmonary Bifurcation During Oscillatory Flow

1997 ◽  
Vol 119 (3) ◽  
pp. 309-316 ◽  
Author(s):  
M. Nishida ◽  
Y. Inaba ◽  
K. Tanishita
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Oscillatory Flow ◽  
Gas Transport ◽  
Main Bronchus ◽  
High Frequency Oscillation ◽  
Laser Doppler Velocimeter ◽  
Straight Tube ◽  
Gas Dispersion ◽  
Axial Velocity Profile

In order to clarify the gas transport process in high-frequency oscillation, we measured the axial velocity profile and the axial effective diffusivity in a single asymmetric bifurcating tube, based on the Horsfield airway model, with sinusoidally oscillatory flow. The axial velocity profiles were measured using a laser-Doppler velocimeter, and the effective diffusivities were evaluated using a simple bolus injection method. The axial velocity profile was found to be nonuniform, promoting axial gas dispersion by the spread of the concentration profile and lateral mixing. The geometric asymmetry of the bifurcation was responsible for the difference in gas transport between the main bronchi. The axial gas transport in the left main bronchus was 2.3 times as large as that of the straight tube, whereas the gas transport in the right main bronchus was slightly larger than that of the straight tube. Thus localized variation in gas transport characterized the heterogeneous respiratory function of the lung.

Compressor Design

1953 ◽  
Vol 57 (511) ◽  
pp. 463-463
Author(s):  
R. G. Taylor
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Axial Flow ◽  
Technical Note ◽  
Basic Design ◽  
Wall Effects ◽  
Axial Flow Compressor ◽  
Axial Velocity Profile ◽  
Compressor Design ◽  
Flow Compressor

In Mr. J. M. Stephenson's Technical Note, “ The Elimination of Wall Effects in Axial-Flow Compressor Stages,” in the April 1953 issue of the Journal, the author suggests that the blade rows of an axial flow compressor are so closely spaced as to ensure that the axial velocity profile is unchanged across the rows. Whether this statement is correct or not such an assumption regarding the axial velocity profile is a basic design condition and when made it will not leave any flexibility in the choice of the function f(r).

scholarly journals A Study of Oscillatory Flow in Curved Pipes : 2nd Report, Axial Velocity Profile

1985 ◽  
Vol 28 (245) ◽  
pp. 2644-2651
Author(s):  
Kouzou SUDOU ◽  
Masaru SUMIDA ◽  
Toshihiro TAKAMI ◽  
Ryuichiro YAMANE
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Oscillatory Flow ◽  
Curved Pipes ◽  
Axial Velocity Profile
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