Modelling circulation, impulse and kinetic energy of starting jets with non-zero radial velocity

2013 ◽  
Vol 719 ◽  
pp. 488-526 ◽  
Author(s):  
Michael Krieg ◽  
Kamran Mohseni
Keyword(s):  
Kinetic Energy ◽  
Radial Velocity ◽  
Jet Flows ◽  
Axisymmetric Jet ◽  
Image Velocimetry ◽  
Energy Modelling ◽  
Powerful Analytical Tool ◽  
Drastic Effect ◽  
Specific Configuration ◽  
Starting Jet

AbstractThe evolution of starting jet circulation, impulse and kinetic energy are derived in terms of kinematics at the entrance boundary of a semi-infinite axisymmetric domain. This analysis is not limited to the case of parallel jet flows; and the effect of non-zero radial velocity is specifically identified. The pressure distribution along the entrance boundary is also derived as it is required for kinetic energy modelling. This is done without reliance on an approximated potential function (i.e. translating flat plate), making it a powerful analytical tool for any axisymmetric jet flow. The pressure model indicates that a non-zero radial velocity is required for any ‘over-pressure’ at the nozzle exit. Jet flows are created from multiple nozzle configurations to validate this model. The jet is illuminated in cross-section, and velocity and vorticity fields are determined using digital particle image velocimetry (DPIV) techniques and circulation, impulse and kinetic energy of the jet are calculated from the DPIV data. A non-zero radial velocity at the entrance boundary has a drastic effect on the final jet. Experimental data showed that a specific configuration resulting in a jet with a converging radial velocity, with a magnitude close to 40 % of the axial velocity at its maximum, attains a final circulation which is 90–100 % larger than a parallel starting jet with identical volume flux and nozzle diameter, depending on the stroke ratio. The converging jet also attains a final impulse which is 70–75 % larger than the equivalent parallel jet and a final kinetic energy 105–135 % larger.

scholarly journals The Effects of Curved Blade Turbine on the Hydrodynamic Structure of a Stirred Tank

2020 ◽  
Author(s):  
Bilel Ben Amira ◽  
Mariem Ammar ◽  
Ahmad Kaffel ◽  
Zied Driss ◽  
Mohamed Salah Abid
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mean Square ◽  
Velocity Fluctuations ◽  
Stirred Vessel ◽  
Image Velocimetry ◽  
Trailing Vortices ◽  
Curved Blade ◽  
Blade Tip ◽  
Hydrodynamic Structure

This work is aimed at studying the hydrodynamic structure in a cylindrical stirred vessel equipped with an eight-curved blade turbine. Flow fields were measured by two-dimensional particle image velocimetry (PIV) to evaluate the effect of the curved blade turbine. Velocity field, axial and radial velocity distribution, root mean square (rms) of the velocity fluctuations, vorticity, and turbulent kinetic energy were presented. Therefore, two recirculation loops were formed close to the free surface and in the bottom of the tank. Moreover, the highest value area of the vorticity is localized in the upper region of the tank which follows the same direction of the first circulation loop. The turbulent kinetic energy is maximum at the blade tip following the trailing vortices.

The velocity field under breaking waves: coherent structures and turbulence

2002 ◽  
Vol 454 ◽  
pp. 203-233 ◽  
Author(s):  
W. KENDALL MELVILLE ◽  
FABRICE VERON ◽  
CHRISTOPHER J. WHITE
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Reynolds Stress ◽  
Particle Image ◽  
Early Stage ◽  
Breaking Waves ◽  
Video Frame ◽  
Turbulent Kinetic Energy Budget ◽  
Image Velocimetry ◽  
Coherent Vortex

Digital particle image velocimetry (DPIV) measurements of the velocity field under breaking waves in the laboratory are presented. The region of turbulent fluid directly generated by breaking is too large to be imaged in one video frame and so an ensemble-averaged representation of the flow is built up from a mosaic of image frames. It is found that breaking generates at least one coherent vortex that slowly propagates downstream at a speed consistent with the velocity induced by its image in the free surface. Both the kinetic energy of the flow and the vorticity decay approximately as t−1. The Reynolds stress of the turbulence also decays as t−1 and is, within the accuracy of the measurements, everywhere negative, consistent with downward transport of streamwise momentum. Estimates of the mometum flux from waves to currents based on the measurements of the Reynolds stress are consistent with earlier estimates. The implications of the measurements for breaking in the field are discussed. Based on geometrical optics and wave action conservation, we suggest that the presence of the breaking-induced vortex provides an explanation for the suppression of short waves by breaking. Finally, in Appendices, estimates of the majority of the terms in the turbulent kinetic energy budget are presented at an early stage in the evolution of the turbulence, and comparisons with independent acoustical measurements of breaking are presented.

Investigations of Particle Velocities in a Slurry Pump Using PIV: Part 1, The Tongue and Adjacent Channel Flow

2004 ◽  
Vol 126 (4) ◽  
pp. 271-278 ◽  
Author(s):  
Jaikrishnan R. Kadambi ◽  
Pathom Charoenngam ◽  
Amirthaganesh Subramanian ◽  
Mark P. Wernet ◽  
John M. Sankovic ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Particle Image ◽  
Pressure Side ◽  
Pipeline Transport ◽  
Particle Image Velocimetry Technique ◽  
Pump Speed ◽  
Image Velocimetry ◽  
Adjacent Channel ◽  
Particle Velocities ◽  
Solid Liquid

Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric concentrations of 2.5% and 5% and at pump speeds of 725 rpm and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller, tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.

Experimental Investigation of Unsteady Flow Field Within a Two Stage Axial Turbomachine Using Particle Image Velocimetry

2002 ◽  
Author(s):  
Oguz Uzol ◽  
Yi-Chih Chow ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Particle Image Velocimetry ◽  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Particle Image ◽  
Energy Levels ◽  
Shear Stresses ◽  
Image Velocimetry ◽  
Entire Flow ◽  
The Difference

Detailed measurements of the flow field within the entire 2nd stage of a two stage axial turbomachine are performed using Particle Image Velocimetry. The experiments are performed in a facility that allows unobstructed view on the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. The entire flow field is composed of a “lattice of wakes”, and the resulting wake-wake and wake-blade interactions cause major flow and turbulence non-uniformities. The paper presents data on the phase averaged velocity and turbulent kinetic energy distributions, as well as the average-passage velocity and deterministic stresses. The phase-dependent turbulence parameters are determined from the difference between instantaneous and the phase-averaged data. The distributions of average-passage flow field over the entire stage in both the stator and rotor frames of reference are calculated by averaging the phase-averaged data. The deterministic stresses are calculated from the difference between the phase-averaged and average-passage velocity distributions. Clearly, wake-wake and wake-blade interactions are the dominant contributors to generation of high deterministic stresses and tangential non-uniformities, in the rotor-stator gap, near the blades and in the wakes behind them. The turbulent kinetic energy levels are generally higher than the deterministic kinetic energy levels, whereas the shear stress levels are comparable, both in the rotor and stator frames of references. At certain locations the deterministic shear stresses are substantially higher than the turbulent shear stresses, such as close to the stator blade in the rotor frame of reference. The non-uniformities in the lateral velocity component due to the interaction of the rotor blade with the 1st stage rotor-stator wakes, result in 13% variations in the specific work input of the rotor. Thus, in spite of the relatively large blade row spacings in the present turbomachine, the non-uniformities in flow structure have significant effects on the overall performance of the system.

Stabilization mechanisms of lifted laminar flames in axisymmetric jet flows

2000 ◽  
Vol 123 (1-2) ◽  
pp. 23-45 ◽  
Author(s):  
Yung-Cheng Chen ◽  
Robert W. Bilger
Keyword(s):  
Laminar Flames ◽  
Jet Flows ◽  
Axisymmetric Jet

Influence of inlet boundary conditions in computations of turbulent jet flames

2018 ◽  
Vol 28 (6) ◽  
pp. 1433-1456 ◽  
Author(s):  
Michał T. Lewandowski ◽  
Paweł Płuszka ◽  
Jacek Pozorski
Keyword(s):  
Kinetic Energy ◽  
Boundary Conditions ◽  
Dissipation Rate ◽  
Turbulence Kinetic Energy ◽  
Turbulent Jet ◽  
Jet Flows ◽  
Jet Flames ◽  
Mean Velocity ◽  
Content Type ◽  
Inlet Conditions

Purpose This paper aims to assess the sensitivity of numerical simulation results of turbulent reactive flow to the formulation of inlet boundary conditions. The analysis concerns the profiles of the mean velocity the turbulence kinetic energy k and its dissipation rate ϵ. It is intended to provide guidance to the determination of inlet conditions when only global flow data are available. This situation can be met both in simple laboratory experiments and in industrial full-scale applications, when measurements are either incomplete or infeasible, resulting in lack of detailed inlet data. Design/methodology/approach Two turbulence–chemistry interaction models were studied: eddy dissipation concept and partially stirred reactor. Three different velocity profiles and related turbulence statistics were applied to present feasible scenarios and their consequences. Simulations with the most appropriate inlet data were accompanied with profiles of turbulent quantities obtained with a proposed method. This method was contrasted to other approaches popular in the literature: the pre-inlet pipe and the separate cold flow simulations of a burner. The methodology was validated on two laboratory-scale jet flames: Delft Jet-in-Hot-Coflow and Sandia CHN B. The simulations were carried out with open source code OpenFOAM. Findings The proposed relations for turbulence kinetic energy and its dissipation rate at the inlet are found to provide results comparable to those obtained with the use of experimental data as inlet boundary conditions. Moreover, from a certain location downstream the jet, weakly dependent on the Reynolds number, the influence of inlet conditions on flow statistics was found to be negligible. Originality/value This work reveals the consequences of the use of rather crude assumptions made for inlet boundary conditions. Proposed formulas for the profiles for k and epsilon are attractive alternatives to other approaches aiming to determine the inlet boundary conditions for turbulent jet flows.

scholarly journals Turbulent jet through porous obstructions under Coriolis effect: an experimental investigation

2021 ◽  
Vol 62 (10) ◽  
Author(s):  
Francesca De Serio ◽  
Roni H. Goldshmid ◽  
Dan Liberzon ◽  
Michele Mossa ◽  
M. Eletta Negretti ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Rotation Rate ◽  
Mean Flow ◽  
Rotation Rates ◽  
Jet Trajectory ◽  
Image Velocimetry ◽  
Jet Behavior ◽  
Flow Configurations ◽  
Turbulent Momentum

AbstractThe present study has the main purpose to experimentally investigate a turbulent momentum jet issued in a basin affected by rotation and in presence of porous obstructions. The experiments were carried out at the Coriolis Platform at LEGI Grenoble (FR). A large and unique set of velocity data was obtained by means of a Particle Image Velocimetry measurement technique while varying the rotation rate of the tank and the density of the canopy. The main differences in jet behavior in various flow configurations were assessed in terms of mean flow, turbulent kinetic energy and jet spreading. The jet trajectory was also detected. The results prove that obstructions with increasing density and increased rotation rates induce a more rapid abatement of both jet velocity and turbulent kinetic energy. The jet trajectories can be scaled by a characteristic length, which is found to be a function of the jet initial momentum, the rotation rate, and the drag exerted by the obstacles. An empirical expression for the latter is also proposed and validated. Graphic abstract

Unstable Waves of Jet Flows With Density Inhomogeneity

1989 ◽  
Vol 111 (3) ◽  
pp. 238-242
Author(s):  
Y. T. Fung
Keyword(s):  
Velocity Profile ◽  
Density Gradient ◽  
Necessary Condition ◽  
Jet Flows ◽  
Density Gradients ◽  
Density Inhomogeneity ◽  
Axisymmetric Jet ◽  
Large Density ◽  
Dependent Density

Instability of axisymmetric jet flows of a fluid having a radius-dependent density is investigated. The necessary condition for the existence of unstable waves depends not only on the velocity profile but also on the density gradient as well. Large density gradients, positive or negative, have stabilizing effects. The semicircle theorem for amplified waves is valid in this case. It is shown by considering the top-hat type velocity profile that the velocity-dependent semicircle bound is the best possible.

Experimental Study of Three-Dimensional Laminar Wall Jets of Non-Newtonian Fluid

2009 ◽  
Author(s):  
Kofi K. Adane ◽  
Mark F. Tachie
Keyword(s):  
Newtonian Fluid ◽  
Open Channel ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Jet Flows ◽  
Wall Jet ◽  
Particle Image Velocimetry Technique ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Shear Thinning Fluid

A particle image velocimetry technique was employed to study three-dimensional laminar wall jet flows of a non-Newtonian shear-thinning fluid. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 250 to 800. The PIV measurements were performed in various streamwise-transverse and streamwise-spanwise planes. From these measurements, the velocity profiles, jet growth rate and spread rates were obtained to study the characteristics of three-dimensional wall jet flows of a non-Newtonian fluid.

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