Centreline velocity decay measurements in low-velocity axisymmetric jets

1997 ◽  
Vol 346 ◽  
pp. 363-377 ◽  
Author(s):  
TOR G. MALMSTRÖM ◽  
ALLAN T. KIRKPATRICK ◽  
BRIAN CHRISTENSEN ◽  
KEVIN D. KNAPPMILLER
Keyword(s):  
Experimental Data ◽  
Streamwise Velocity ◽  
Velocity Profiles ◽  
Low Velocity ◽  
Decay Coefficient ◽  
Axisymmetric Jets ◽  
Previous Experimental Data ◽  
Velocity Decay ◽  
Centreline Velocity ◽  
Different Diameters

The streamwise velocity profiles of low-velocity isothermal axisymmetric jets from nozzles of different diameters were measured and compared with previous experimental data. The objective of the measurements was to examine the dependence of the diffusion of the jet on the outlet conditions. As the outlet velocity was decreased, the centreline velocity decay coefficient began to decrease at an outlet velocity of about 6 m s−1.

scholarly journals Smoothed Particle Hydrodynamics Simulations of Water Flow in a 90° Pipe Bend

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1081
Author(s):  
Leonardo Di G. Sigalotti ◽  
Carlos E. Alvarado-Rodríguez ◽  
Jaime Klapp ◽  
José M. Cela
Keyword(s):  
Experimental Data ◽  
Water Flow ◽  
Smoothed Particle Hydrodynamics ◽  
Streamwise Velocity ◽  
Velocity Profiles ◽  
Pipe Bend ◽  
Cross Sectional ◽  
Wide Range ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

The flow through pipe bends and elbows occurs in a wide range of applications. While many experimental data are available for such flows in the literature, their numerical simulation is less abundant. Here, we present highly-resolved simulations of laminar and turbulent water flow in a 90° pipe bend using Smoothed Particle Hydrodynamics (SPH) methods coupled to a Large-Eddy Simulation (LES) model for turbulence. Direct comparison with available experimental data is provided in terms of streamwise velocity profiles, turbulence intensity profiles and cross-sectional velocity maps at different stations upstream, inside and downstream of the pipe bend. The numerical results are in good agreement with the experimental data. In particular, maximum root-mean-square deviations from the experimental velocity profiles are always less than ∼1.4%. Convergence to the experimental measurements of the turbulent fluctuations is achieved by quadrupling the resolution necessary to guarantee convergence of the velocity profiles. At such resolution, the deviations from the experimental data are ∼0.8%. In addition, the cross-sectional velocity maps inside and downstream of the bend shows that the experimentally observed details of the secondary flow are also very well predicted by the numerical simulations.

Growth of vortical disturbances entrained in the entrance region of a circular pipe

2021 ◽  
Vol 932 ◽  
Author(s):  
Pierre Ricco ◽  
Claudia Alvarenga
Keyword(s):  
Reynolds Number ◽  
Initial Conditions ◽  
Maximum Growth ◽  
Streamwise Velocity ◽  
Velocity Profiles ◽  
Boundary Region ◽  
Base Flow ◽  
Entrance Region ◽  
Circular Pipe ◽  
Large Reynolds Number

The development and growth of unsteady three-dimensional vortical disturbances entrained in the entry region of a circular pipe is investigated by asymptotic and numerical methods for Reynolds numbers between $1000$ and $10\,000$ , based on the pipe radius and the bulk velocity. Near the pipe mouth, composite asymptotic solutions describe the dynamics of the oncoming disturbances, revealing how these disturbances are altered by the viscous layer attached to the pipe wall. The perturbation velocity profiles near the pipe mouth are employed as rigorous initial conditions for the boundary-region equations, which describe the flow in the limit of low frequency and large Reynolds number. The disturbance flow is initially primarily present within the base-flow boundary layer in the form of streamwise-elongated vortical structures, i.e. the streamwise velocity component displays an intense algebraic growth, while the cross-flow velocity components decay. Farther downstream the disturbance flow occupies the whole pipe, although the base flow is mostly inviscid in the core. The transient growth and subsequent viscous decay are confined in the entrance region, i.e. where the base flow has not reached the fully developed Poiseuille profile. Increasing the Reynolds number and decreasing the frequency causes more intense perturbations, whereas small azimuthal wavelengths and radial characteristic length scales intensify the viscous dissipation of the disturbance. The azimuthal wavelength that causes the maximum growth is found. The velocity profiles are compared successfully with available experimental data and the theoretical results are helpful to interpret the only direct numerical dataset of a disturbed pipe-entry flow.

Rounded Fin Edge and Step Position Effects on Discharge Coefficient in Rotating Labyrinth Seals

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Andrea Rapisarda ◽  
Alessio Desando ◽  
Elena Campagnoli ◽  
Roberto Taurino
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Leading Edge ◽  
Experimental Tests ◽  
Velocity Profiles ◽  
Pollutant Emission ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Position Effects ◽  
Impact Reduction

The design of modern aircrafts propulsion systems is strongly influenced by the important objective of environmental impact reduction. Through a great number of researches carried out in the last decades, significant improvements have been obtained in terms of lower fuel consumption and pollutant emission. Experimental tests are a necessary step to achieve new solutions that are more efficient than the current designs, even if during the preliminary design phase, a valid alternative to expensive experimental tests is the implementation of numerical models. The processing power of modern computers allows indeed the simulation of more complex and detailed phenomena than the past years. The present work focuses on the implementation of a numerical model for rotating stepped labyrinth seals installed in low-pressure turbines. These components are widely employed in sealing turbomachinery to reduce the leakage flow between rotating components. The numerical simulations were performed by using computational fluid dynamics (CFD) methodology, focusing on the leakage performances at different rotating speeds and inlet preswirl ratios. Investigations on velocity profiles into seal cavities were also carried out. To begin with, a smooth labyrinth seal model was validated by using the experimental data found in the literature. The numerical simulations were extended to the honeycomb labyrinth seals, with the validation performed on the velocity profiles. Then, the effects of two geometrical parameters, the rounded fin tip leading edge, and the step position were numerically investigated for both smooth and honeycomb labyrinth seals. The obtained results are generally in good agreement with the experimental data. The main effect found when the fin tip leading edge was rounded was a large increase in leakage flow, while the step position contribution to the flow path behavior is nonmonotone.

Velocity Profiles of Turbulent Boundary Layers

1969 ◽  
Vol 73 (698) ◽  
pp. 143-147 ◽  
Author(s):  
M. K. Bull
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Boundary Layers ◽  
Experimental Work ◽  
Constant Pressure ◽  
Velocity Profiles ◽  
Turbulent Boundary Layers ◽  
Boundary Layer Equations

Although a numerical solution of the turbulent boundary-layer equations has been achieved by Mellor and Gibson for equilibrium layers, there are many occasions on which it is desirable to have closed-form expressions representing the velocity profile. Probably the best known and most widely used representation of both equilibrium and non-equilibrium layers is that of Coles. However, when velocity profiles are examined in detail it becomes apparent that considerable care is necessary in applying Coles's formulation, and it seems to be worthwhile to draw attention to some of the errors and inconsistencies which may arise if care is not exercised. This will be done mainly by the consideration of experimental data. In the work on constant pressure layers, emphasis tends to fall heavily on the author's own data previously reported in ref. 1, because the details of the measurements are readily available; other experimental work is introduced where the required values can be obtained easily from the published papers.

Turbulent Mixing Process of a Round Jet With Slot Lobes

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Paul J. Kristo ◽  
Coleman D. Hoff ◽  
Ian G. R. Craig ◽  
Mark L. Kimber
Keyword(s):  
Turbulent Mixing ◽  
Near Field ◽  
Streamwise Velocity ◽  
Velocity Profiles ◽  
Separate Flow ◽  
Geometric Feature ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Round Jet ◽  
Turbulent Statistics

Abstract Turbulent mixing in the near region of a round jet with three slot lobes is examined via mean velocity and turbulent statistics and structures at a Reynolds number of 15,000. The design utilizes separate flow motivations upstream of each geometric feature, deviating from conventional nozzles or orifice plates. Immediate outlet velocity profiles are heavily influenced by opposing pressure gradients between the neighboring round and slot streams. Spanwise mean velocity profiles reveal the majority of the convective exchange between a given slot and the round center occurs in the immediate near field, but has lasting effects on the axial centerline profiles downstream. This is also reflected by the velocity half-widths, exhibiting asymmetry across the entirety of available measurements. Centerline turbulence intensities exhibit strong and short-lived isotropy. The increasingly anisotropic intensities found downstream are lower than similar geometries from the literature, implying that mixing development is inhibited. Reynolds stresses at the round-slot interface are significantly smaller than the round-stagnant exchange, but achieve a symmetric condition at x/D ≅ 4. Two-point spatial correlations of the fluctuating streamwise velocity exhibit stronger dependence toward the axial centerline at the round-slot interface in comparison to the nominal round radius. In contrast, spanwise velocity fluctuations exhibit nearly identical, localized behaviors on each side of the jet. Corresponding differences in streamwise integral length scale peak in the range 1.0 ≤ x/D ≤ 1.5, and so too do the turbulent structures in this area, as a result of the collated jet geometry.

Influence of Primary and Secondary Flow Interaction on the Near Flow Field Mixing in an Enclosed Space

2006 ◽  
Author(s):  
Ijaz M. Khan ◽  
Tony Gilbert ◽  
Mostafa Barigou
Keyword(s):  
Temperature Distribution ◽  
Flow Field ◽  
Air Entrainment ◽  
Streamwise Velocity ◽  
Nozzle Geometry ◽  
Turbulence Characteristics ◽  
Mass Entrainment ◽  
Diffusion Characteristics ◽  
Velocity Decay ◽  
Enclosed Space

This paper presents the influence of an induction diffuser ports on a turbulent jet and its effect on the axial mean streamwise velocity decay, mass entrainment, turbulence characteristics and the temperature distribution in the near flow field of an enclosed numerical space. Convergence of the steady state simulations is achieved by RNG kappa-epsilon turbulence model. Comparisons of the axial mean streamwise velocity decay, turbulence characteristics and the temperature distribution in an enclosed space are reported for JETs (Jet Environmental Techniques) nozzle, and another similar simulation was conducted for an induction diffuser box with open ports at specific positions to evaluate its performance. The numerical analysis was validated by prototype experiments using the JETs nozzle geometry in a test room 11 m in length, 5.5 m wide and 2.5 m high. The measurement of the streamwise velocity and temperature distribution was measured inside the room on a grid with the help of a hotwire anemometer and digital thermometer, respectively. From the analysis of the data, it was found that the near flow field air entrainment and diffusion characteristics of the jet were significantly influenced by the air induction diffuser.

Three-Dimensional Modeling of Density Current in Confined and Unconfined Channels

2006 ◽  
Author(s):  
Ehsan Aram ◽  
Bahar Firoozabadi
Keyword(s):  
Experimental Data ◽  
Fine Particles ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Velocity Profiles ◽  
Density Current ◽  
Three Dimensional Modeling ◽  
Small Width ◽  
Dimensional Modeling ◽  
Large Width

Dense underflows are continuous currents which move down-slope due to the fact that their density is heavier than that ambient water. In this work, 2-D and 3-D density current in a channel were investigated by a set of experimental studies and the data were used to simulate the density current. The velocity components were measured using Acoustic Doppler Velocimetry (ADV). The height of density current (current's depth) was also measured. In this study, the density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. A low-Reynolds number turbulent model (Launder and Sharma, 1974) has been applied to simulate the structure of 3-D density current in the confined (small width three dimensional density current) and unconfined (large width three dimensional density current) channels. The computed velocity profiles in unconfined channel were compared with the 3-D experimental data for verification. The height and velocity profiles of the confined current were also compared with 2-D experimental data. It was shown that by decreasing in width of the channel, the height of the current and the magnitude of maximum and average velocity increase and the confined current behaves as 2-D current after a distance. These factors prepare the conditions for minimizing sediment deposition and sedimentation rates can be greatly reduced. Although the k - ε Launder and Sharma model is applied here to a conservative density current, it seems that the analysis can be valid in general for turbidity current laden with fine particles.

Mathematical Modeling of Capillary Pumping Within Micron Sized Channels

2013 ◽  
Author(s):  
Yuelei Yang ◽  
Dan Zhang
Keyword(s):  
Mathematical Modeling ◽  
Experimental Data ◽  
Mathematical Model ◽  
Capillary Pressure ◽  
Heat Engine ◽  
Velocity Profiles ◽  
Vof Method ◽  
Numerical Results ◽  
Micro Heat Engine ◽  
Volume Of Fluids

This paper introduces a mathematical model which can be used to simulate the capillary pumping process of a micro heat engine. The micro heat engine has micron sized channels where the capillary pumping occurs. The classic Volume of Fluids (VOF) method is applied to obtain the velocity profiles of the fluids and to track the motions of the liquid-gas interfaces. The numerical results based this model have been compared with the experimental data and the initial retard of the pumping has been found and this phenomenon can be explained by the initial capillary pressure build-ups across the liquid-gas interfaces.

Velocity and Temperature Profiles in Turbulent Boundary Layer Flows Experiencing Streamwise Pressure Gradients

1997 ◽  
Vol 119 (3) ◽  
pp. 433-439 ◽  
Author(s):  
R. J. Volino ◽  
T. W. Simon
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Velocity Profiles ◽  
Temperature Profiles ◽  
Pressure Gradients ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Prandtl Numbers ◽  
Energy Equations ◽  
Near Wall

The standard turbulent law of the wall, devised for zero pressure gradient flows, has been previously shown to be inadequate for accelerating and decelerating turbulent boundary layers. In this paper, formulations for mean velocity profiles from the literature are applied and formulations for the temperature profiles are developed using a mixing length model. These formulations capture the effects of pressure gradients by including the convective and pressure gradient terms in the momentum and energy equations. The profiles which include these terms deviate considerably from the standard law of the wall; the temperature profiles more so than the velocity profiles. The new profiles agree well with experimental data. By looking at the various terms separately, it is shown why the velocity law of the wall is more robust to streamwise pressure gradients than is the thermal law of the wall. The modification to the velocity profile is useful for evaluation of more accurate skin friction coefficients from experimental data by the near-wall fitting technique. The temperature profile modification improves the accuracy with which one may extract turbulent Prandtl numbers from near-wall mean temperature data when they cannot be determined directly.

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