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.

Turbulent Vorticity Diffusion in the Stronger Wall Jet Managed by a Flat Plate Wing in the Outer Layer

2015 ◽  
Author(s):  
Takuma Katayama ◽  
Shinsuke Mochizuki
Keyword(s):  
Shear Stress ◽  
Flat Plate ◽  
Outer Layer ◽  
Large Scale ◽  
Reynolds Shear Stress ◽  
Three Dimensional ◽  
Quantitative Relationship ◽  
Wall Jet ◽  
Mean Velocity ◽  
The Mean

The present experiment focuses on the vorticity diffusion in a stronger wall jet managed by a three-dimensional flat plate wing in the outer layer. Measurement of the fluctuating velocities and vorticity correlation has been carried out with 4-wire vorticity probe. The turbulent vorticity diffusion due to the large scale eddies in the outer layer is quantitatively examined by using the 4-wire vorticity probe. Quantitative relationship between vortex structure and Reynolds shear stress is revealed by means of directly measured experimental evidence which explains vorticity diffusion process and influence of the manipulating wing. It is expected that the three-dimensional outer layer manipulator contributes to keep convex profile of the mean velocity, namely, suppression of the turbulent diffusion and entrainment.

On the mean motion induced by internal gravity waves

1969 ◽  
Vol 36 (4) ◽  
pp. 785-803 ◽  
Author(s):  
Francis P. Bretherton
Keyword(s):  
Gravity Waves ◽  
Wave Energy ◽  
Wave Train ◽  
Three Dimensional ◽  
Internal Gravity Waves ◽  
Wave Number ◽  
Mean Flow ◽  
Mean Velocity ◽  
Mean Motion ◽  
The Mean

A train of internal gravity waves in a stratified liquid exerts a stress on the liquid and induces changes in the mean motion of second order in the wave amplitude. In those circumstances in which the concept of a slowly varying quasi-sinusoidal wave train is consistent, the mean velocity is almost horizontal and is determined to a first approximation irrespective of the vertical forces exerted by the waves. The sum of the mean flow kinetic energy and the wave energy is then conserved. The circulation around a horizontal circuit moving with the mean velocity is increased in the presence of waves according to a simple formula. The flow pattern is obtained around two- and three-dimensional wave packets propagating into a liquid at rest and the results are generalized for any basic state of motion in which the internal Froude number is small. Momentum can be associated with a wave packet equal to the horizontal wave-number times the wave energy divided by the intrinsic frequency.

Experimental Study of the Flow in a Simulated Hard Disk Drive

2006 ◽  
Vol 128 (5) ◽  
pp. 1090-1100 ◽  
Author(s):  
Charlotte Barbier ◽  
Joseph A. C. Humphrey ◽  
Eric Maslen
Keyword(s):  
Hard Disk Drive ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Hard Disk ◽  
Disk Drive ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Local Flow ◽  
The Mean ◽  
Fundamental Value

Instantaneous circumferential and radial velocity components of the air flowing past a symmetrical pair of suspension/slider-units (SSUs) attached to an E-Block/arm were measured in a specially designed corotating disk apparatus simulating a hard disk drive (HDD) using the particle image velocimetry technique. The geometrical dimensions of the components in the apparatus test section were scaled up by a factor of two, approximately, relative to those of a nominal 312 inch HDD. Most of the measurements were obtained on the interdisk midplane for two angular orientations of the arm/SSUs: (a) One with the tip of the SSUs near the hub supporting the disks; (b) another with the tip of the SSUs near the rims of the disks. Data obtained for disk rotational speeds ranging from 250 to 3000rpm (corresponding to 1250 to 15,000rpm, approximately, in a 312 inch HDD) were post-processed to yield mean and rms values of the two velocity components and of the associated shear stress, the mean axial vorticity, and the turbulence intensity (based on the two velocity components). At the locations investigated near the arm/SSUs, and for disk rotational speeds larger than 1500rpm, the mean velocity components are found to be asymptotically independent of disk speed of rotation but their rms values appear to still be changing. At two locations 90 and 29deg, respectively, upstream of the arm/SSUs, the flow approaching this obstruction displays features that can be attributed to the three-dimensional wake generated by the obstruction. Also, between these two locations and depending on the angular orientation of the arm/SSUs, the effect of the obstruction is to induce a three-dimensional region of flow reversal adjacent to the hub. Notwithstanding, the characteristics of the flow immediately upstream and downstream of the arm/SSUs appear to be determined by local flow-structure interactions. Aside from their intrinsic fundamental value, the data serve to guide and test the development of turbulence models and numerical calculation procedures for predicting this complex class of confined rotating flows, and to inform the improved design of HDDs.

Three-dimensional structure and momentum transfer in a turbulent cylinder wake

1999 ◽  
Vol 394 ◽  
pp. 303-337 ◽  
Author(s):  
A. VERNET ◽  
G. A. KOPP ◽  
J. A. FERRÉ ◽  
FRANCESC GIRALT
Keyword(s):  
Velocity Field ◽  
Saddle Point ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Half Width ◽  
Small Scale ◽  
Spanwise Direction ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Simultaneous velocity and temperature measurements were made with rakes of sensors that sliced a slightly heated turbulent wake in the spanwise direction, at different lateral positions 150 diameters downstream of the cylinder. A pattern recognition analysis of hotter-to-colder transitions was performed on temperature data measured at the mean velocity half-width. The velocity data from the different ‘slices’ was then conditionally averaged based on the identified temperature events. This procedure yielded the topology of the average three-dimensional large-scale structure which was visualized with iso-surfaces of negative values of the second eigenvector of [S2+Ω2]. The results indicate that the average structure of the velocity fluctuations (using a triple decomposition of the velocity field) is found to be a shear-aligned ring-shaped vortex. This vortex ring has strong outward lateral velocities in its symmetry plane which are like Grant's mixing jets. The mixing jet region extends outside the ring-like vortex and is bounded by two foci separated in the spanwise direction and an upstream saddle point. The two foci correspond to what has been previously identified in the literature as the double rollers.The ring vortex extracts energy from the mean flow by stretching in the mixing jet region just upstream of the ring boundary. The production of the small-scale (incoherent) turbulence by the coherent field and one-component energy dissipation rate occur just downstream of the saddle point within the mixing jet region. Incoherent turbulence energy is extracted from the mean flow just outside the mixing jet region, but within the core of the structure. These processes are highly three-dimensional with a spanwise extent equal to the mean velocity half-width.When a double decomposition is used, the coherent structure is found to be a tube-shaped vortex with a spanwise extent of about 2.5l0. The double roller motions are integral to this vortex in spite of its shape. Spatial averages of the coherent velocity field indicate that the mixing jet region causes a deficit of mean streamwise momentum, while the region outside the foci of the double rollers has a relatively small excess of streamwise momentum.

Measurement of the Reynolds stresses and the mean-flow field in a three-dimensional pressure-driven boundary layer

1982 ◽  
Vol 119 ◽  
pp. 121-153 ◽  
Author(s):  
Udo R. Müller
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Field ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Acceleration ◽  
The Mean

An experimental study of a steady, incompressible, three-dimensional turbulent boundary layer approaching separation is reported. The flow field external to the boundary layer was deflected laterally by turning vanes so that streamwise flow deceleration occurred simultaneous with cross-flow acceleration. At 21 stations profiles of the mean-velocity components and of the six Reynolds stresses were measured with single- and X-hot-wire probes, which were rotatable around their longitudinal axes. The calibration of the hot wires with respect to magnitude and direction of the velocity vector as well as the method of evaluating the Reynolds stresses from the measured data are described in a separate paper (Müller 1982, hereinafter referred to as II). At each measuring station the wall shear stress was inferred from a Preston-tube measurement as well as from a Clauser chart. With the measured profiles of the mean velocities and of the Reynolds stresses several assumptions used for turbulence modelling were checked for their validity in this flow. For example, eddy viscosities for both tangential directions and the corresponding mixing lengths as well as the ratio of resultant turbulent shear stress to turbulent kinetic energy were derived from the data.

Turbulent flow between a rotating and a stationary disk

2001 ◽  
Vol 426 ◽  
pp. 297-326 ◽  
Author(s):  
MAGNE LYGREN ◽  
HELGE I. ANDERSSON
Keyword(s):  
Shear Stress ◽  
Boundary Layers ◽  
Coherent Structures ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Mean Flow ◽  
Mean Velocity ◽  
Stationary Disk ◽  
Dimensional Boundary ◽  
The Mean

Turbulent flow between a rotating and a stationary disk is studied. Besides its fundamental importance as a three-dimensional prototype flow, such flow fields are frequently encountered in rotor–stator configurations in turbomachinery applications. A direct numerical simulation is therefore performed by integrating the time-dependent Navier–Stokes equations until a statistically steady state is reached and with the aim of providing both long-time statistics and an exposition of coherent structures obtained by conditional sampling. The simulated flow has local Reynolds number r2ω/v = 4 × 105 and local gap ratio s/r = 0.02, where ω is the angular velocity of the rotating disk, r the radial distance from the axis of rotation, v the kinematic viscosity of the fluid, and s the gap width.The three components of the mean velocity vector and the six independent Reynolds stresses are compared with experimental measurements in a rotor–stator flow configuration. In the numerically generated flow field, the structural parameter a1 (i.e. the ratio of the magnitude of the shear stress vector to twice the mean turbulent kinetic energy) is lower near the two disks than in two-dimensional boundary layers. This characteristic feature is typical for three-dimensional boundary layers, and so are the misalignment between the shear stress vector and the mean velocity gradient vector, although the degree of misalignment turns out to be smaller in the present flow than in unsteady three-dimensional boundary layer flow. It is also observed that the wall friction at the rotating disk is substantially higher than at the stationary disk.Coherent structures near the disks are identified by means of the λ2 vortex criterion in order to provide sufficient information to resolve a controversy regarding the roles played by sweeps and ejections in shear stress production. An ensemble average of the detected structures reveals that the coherent structures in the rotor–stator flow are similar to the ones found in two-dimensional flows. It is shown, however, that the three-dimensionality of the mean flow reduces the inter-vortical alignment and the tendency of structures of opposite sense of rotation to overlap. The coherent structures near the disks generate weaker sweeps (i.e. quadrant 4 events) than structures in conventional two-dimensional boundary layers. This reduction in the quadrant 4 contribution from the coherent structures is believed to explain the reduced efficiency of the mean flow in producing Reynolds shear stress.

Characteristics of Turbulent Three-Dimensional Offset Jets

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
M. Agelin-Chaab ◽  
M. F. Tachie
Keyword(s):  
Three Dimensional ◽  
Symmetry Plane ◽  
Outer Region ◽  
Decay Rates ◽  
Wall Region ◽  
Mean Flow ◽  
Particle Image Velocimetry Technique ◽  
Similar Region ◽  
The Mean ◽  
Turbulence Transport

Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. Three jet exit Reynolds numbers, Rej = 5000, 10,000, and 20,000, and four offset heights, h/d = 0.5, 1.0, 2.0, and 4.0, were studied. The mean flow and turbulence statistics were studied over larger downstream distances than in previous studies. The decay and spread rates were found to be nearly independent of Reynolds number and offset height at certain exit diameters (x = 73d) downstream and h/d ≤ 2. The decay rates of 1.18 ± 0.03 and spread rates of 0.055 ± 0.001 and 0.250 ± 0.005 in the wall-normal and lateral directions were obtained, respectively. The reattachment lengths are also independent of Rej but increase with offset height. The locations of the maximum mean velocities increased linearly with streamwise distance in the self-similar region. It was observed that profiles of the mean velocities, turbulence intensities, and Reynolds shears stresses are nearly independent of Rej and h/d far downstream. The triple products in the symmetry plane indicated turbulence transport from the outer region of the jet towards the wall region.

On Coupling of RANS and LES for Integrated Computations of Jet Engines

2007 ◽  
Author(s):  
Gorazd Medic ◽  
Donghyun You ◽  
Georgi Kalitzin
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Operating Conditions ◽  
Jet Engines ◽  
Mean Flow ◽  
Mean Velocity ◽  
Novel Approach ◽  
The Mean ◽  
Flow Variables

Large scale integrated computations of jet engines can be performed by using the unsteady RANS framework to compute the flow in turbomachinery components while using the LES framework to compute the flow in the combustor. This requires a proper coupling of the flow variables at the interfaces between the RANS and LES solvers. In this paper, a novel approach to turbulence coupling is proposed. It is based on the observation that in full operating conditions the mean flow at the interfaces is highly non-uniform and local turbulence production dominates convection effects in regions of large velocity gradients. This observation has lead to the concept of using auxilliary ducts to compute turbulence based on the mean velocity at the interface. In the case of the RANS/LES interface, turbulent fluctuations are reconstructed from an LES computation in an auxiliary three-dimensional duct using a recycling technique. For the LES/RANS interface, the turbulence variables for the RANS model are computed from an auxilliary solution of the RANS turbulence model in a quasi-2D duct. We have demonstrated the feasibility of this approach for the integrated flow simulation of a 20° sector of an entire jet engine.

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