Synchronous Vortex Shedding (Vortex Pumping) Downstream of a Flat Plate Array

Flow visualization and statistics, obtained downstream of an array of flat plates, are presented. Flow visualization shows that the mean separation between streaklines for the flow downstream of adjacent channels is negatively correlated. Consistent with this observation, the zero-time cross correlation of the fluctuating velocity between adjacent plates is negative. Vortices shed at the trailing edges of the bounding surfaces that form a channel in the plate array are in-phase, but they are nearly 180 deg out-of-phase with the vortices shed at the trailing edges of the bounding surfaces of adjacent channels. Relative to the mean velocity, the axial velocity on the midplane of the channel increased in the region between each pair of vortices. At downstream positions not near the vortex pair, the velocity on the midplane is relatively decreased. Hence, vortices shed at the trailing edges of the channel surfaces lead to “vortex pumping,” which is consistent with the negative correlation of the fluctuating velocity on the midplanes between adjacent channels. [S0098-2202(00)01701-6]

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Kinematical studies of the flows around free or surface-mounted obstacles; applying topology to flow visualization

Journal of Fluid Mechanics ◽

10.1017/s0022112078001068 ◽

1978 ◽

Vol 86 (1) ◽

pp. 179-200 ◽

Cited By ~ 490

Author(s):

J. C. R. Hunt ◽

C. J. Abell ◽

J. A. Peterka ◽

H. Woo

Keyword(s):

Shear Stress ◽

Flow Visualization ◽

Saddle Points ◽

Three Dimensional ◽

Topological Classification ◽

List Type ◽

Surface Shear Stress ◽

Mean Velocity ◽

The Mean ◽

Dimensional Surface

In flows around three-dimensional surface obstacles in laminar or turbulent streamsthere are a number of points where the shear stress or where two or more component,s of the mean velocity are zero. In the first part of this paper we summarize and extend the kinematical theory for the flow near these points, particularly by emphasizing the topological classification of these points as nodes or saddles. We show that the zero-shear-stress points on the surface and on the obstacle must be such that the sum of the nodes ΣNand the sum of the saddles Σssatisfy\[ \Sigma_N -\Sigma_S = 0. \]If the obstacle has a hole through it, such as a passageway under a building,\[ \Sigma_N -\Sigma_S =-2. \]If the surface is a junction between two pipes,\[ \Sigma_N -\Sigma_S =-1. \]We also consider, in two-dimensional plane sections of the flow, the points where the components of the mean velocity parallel to the planes are zero, both in the flow and near surfaces cutting the sections. The latter points are half-nodes N′ or half-saddles S′. We find that\[ (\Sigma_N +{\textstyle\frac{1}{2}}\Sigma_{N^{\prime}}-(\Sigma_{S^{\prime}}+{\textstyle\frac{1}{2}}\Sigma_{S^{\prime}}) = 1-n, \]where n is the connectivity of the section of the flow considered.In the second part new flow-visualization studies of laminar and turbulent flows around cuboids and axisymmetric humps (i.e. model hills) are reported. A new method of obtaining a high resolution of the surface shear-stress lines was used. These studies show how enumerating the nodes and saddle points acts as a check on the inferred flow pattern.Two specific conclusions drawn from these studies are that:for all the flows we observed, there are no closed surfaces of mean streamlines around the separated flows behind three-dimensional surface obstacles, which con-tradicts most of the previous suggestions for such flows (e.g. Halitsky 1968);the separation streamline on the centre-line of a three-dimensional bluff obstacle does not, in general, reattach to the surface.

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Organized motions in a jet in crossflow

Journal of Fluid Mechanics ◽

10.1017/s0022112001005407 ◽

2001 ◽

Vol 444 ◽

pp. 117-149 ◽

Cited By ~ 48

Author(s):

A. RIVERO ◽

J. A. FERRÉ ◽

FRANCESC GIRALT

Keyword(s):

Velocity Field ◽

Velocity Ratio ◽

Mean Field ◽

Vortex Pair ◽

Leeward Side ◽

Mean Velocity ◽

Jet In Crossflow ◽

Planar Laser ◽

The Mean ◽

Counter Rotating Vortex Pair

An experimental study to identify the structures present in a jet in crossflow has been carried out at a jet-to-crossflow velocity ratio U/Ucf = 3.8 and Reynolds number Re = UcfD/v = 6600. The hot-wire velocity data measured with a rake of eight X-wires at x/D = 5 and 15 and flow visualizations using planar laser-induced fluorescence (PLIF) confirm that the well-established pair of counter-rotating vortices is a feature of the mean field and that the upright, tornado-like or Fric's vortices that are shed to the leeward side of the jet are connected to the jet flow at the core. The counter-rotating vortex pair is strongly modulated by a coherent velocity field that, in fact, is as important as the mean velocity field. Three different structures – folded vortex rings, horseshoe vortices and handle-type structures – contribute to this coherent field. The new handle-like structures identified in the current study link the boundary layer vorticity with the counter-rotating vortex pair through the upright tornado-like vortices. They are responsible for the modulation and meandering of the counter-rotating vortex pair observed both in video recordings of visualizations and in the instantaneous velocity field. These results corroborate that the genesis of the dominant counter-rotating vortex pair strongly depends on the high pressure gradients that develop in the region near the jet exit, both inside and outside the nozzle.

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Wind tunnel experiments on wind turbine wakes in yaw: effects of inflow turbulence and shear

Wind Energy Science ◽

10.5194/wes-3-329-2018 ◽

2018 ◽

Vol 3 (1) ◽

pp. 329-343 ◽

Cited By ~ 18

Author(s):

Jan Bartl ◽

Franz Mühle ◽

Jannik Schottler ◽

Lars Sætran ◽

Joachim Peinke ◽

...

Keyword(s):

Wind Turbine ◽

Laser Doppler Anemometry ◽

Vortex Pair ◽

Wake Flow ◽

Turbulent Shear ◽

Mean Velocity ◽

Inflow Turbulence ◽

The Mean ◽

Inflow Conditions ◽

Wake Characteristics

Abstract. The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler anemometry is used to measure the wake flow in two planes at x∕D = 3 and x∕D = 6, while the turbine yaw angle is varied from γ=-30∘ to 0∘ to +30∘. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components. The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter-rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform highly turbulent shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.

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Wind tunnel experiments on wind turbine wakes in yaw: Effects of inflow turbulence and shear

10.5194/wes-2017-59 ◽

2018 ◽

Cited By ~ 1

Author(s):

Jan Bartl ◽

Franz Mühle ◽

Jannik Schottler ◽

Lars Sætran ◽

Joachim Peinke ◽

...

Keyword(s):

Wind Turbine ◽

Laser Doppler Anemometry ◽

Vortex Pair ◽

Wake Flow ◽

Mean Velocity ◽

Inflow Turbulence ◽

The Mean ◽

Center Deflection ◽

Inflow Conditions ◽

Wake Characteristics

Abstract. The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler Anemometry is used to measure the wake flow in two planes at x/D = 3 and x/D = 6 while the turbine yaw angle is varied from −30° and 0° to +30°. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components. The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter-rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.

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On the Effects of Incidence Angle on the Mean Wake of a Surface-Mounted Finite-Height Square Prism

Volume 1: Symposia ◽

10.1115/ajkfluids2015-15011 ◽

2015 ◽

Cited By ~ 1

Author(s):

Ayodele Ogunremi ◽

David Sumner

Keyword(s):

Incidence Angle ◽

Flow Direction ◽

Ground Plane ◽

Vortex Pair ◽

Tip Vortex ◽

Pressure Probe ◽

Mean Velocity ◽

Square Prism ◽

Finite Height ◽

The Mean

The wake of a surface-mounted finite-height square prism of sub-critical aspect ratio AR = 3 was studied experimentally in a low-speed wind tunnel at a Reynolds number of Re = 3.7×104. The ratio of the boundary layer thickness on the ground plane, to the width of the prism, was δ/D = 1.5. The incidence angle of the prism was varied from α = 0° to 45°. Wake mean velocity measurements were made in vertical planes normal to and parallel to the main flow direction using a seven-hole pressure probe. As the prism is rotated from α = 0° to 45°, the mean wake progressively widens and the maximum streamwise extent of the mean recirculation zone increases. The mean streamwise tip vortex pair is symmetric at 0° and 45°, but becomes strongly asymmetric at intermediate α, where the tip vortex is found higher above the ground plane on the wider side of the wake. The wake and tip vortex asymmetry is most pronounced near the critical incidence angle.

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Comparison of the Numerical and Experimental Flowfield Downstream of a Plate Array

Journal of Fluids Engineering ◽

10.1115/1.1436094 ◽

2001 ◽

Vol 124 (1) ◽

pp. 284-286 ◽

Cited By ~ 3

Author(s):

D. W. Guillaume ◽

J. C. LaRue

Keyword(s):

Numerical Simulation ◽

Axial Velocity ◽

Thickness Ratio ◽

Velocity Increase ◽

Trailing Edges ◽

Recirculation Zones ◽

Plate Array ◽

Adjacent Channels ◽

Previous Experimental Study ◽

Velocity Decrease

The findings of a numerical solution of the flowfield downstream of a six-plate array are compared to a previous experimental study. In both studies, the chord-to-thickness ratio, c/t, is 6.67, the Reynolds number, Re, is 500, and the spacing-to-thickness ratio, H/t, is 3.67. Consistent with experimental results, the numerical simulation shows that the recirculation zones formed at the trailing edges of the surfaces that form channels in the plate array are in-phase. Also consistent, they are nearly 180 deg out-of-phase with the recirculation zones formed at the trailing edges of the surfaces of adjacent channels. Comparison of the locations of recirculation zones and peaks in the downstream variation in axial velocity confirms that “vortex pumping” is described by 1) the axial velocity increase on the midplane of the channel in the region where the separation between pairs of recirculation zones is a minimum and 2) the axial velocity decrease in the region where the separation between pairs of recirculation zones is a maximum.

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Experimental Study on Compound Swirl Jet

Volume 1: Fora, Parts A, B, C, and D ◽

10.1115/fedsm2003-45225 ◽

2003 ◽

Author(s):

Tsutomu Nozaki ◽

Takashi Ochiai ◽

Tomonari Kai

Keyword(s):

Experimental Study ◽

Flow Visualization ◽

Flow Rate ◽

Rate Ratio ◽

Flow Rate Ratio ◽

Mean Velocity ◽

Fundamental Study ◽

Free Jet ◽

The Mean ◽

Two Jets

This paper concerns the fundamental study on the push-pull type ventilator, especially applied to the smoking table. In order to achieve more effective cleaning of the dirty air, a compound swirl jet, which consists of a round free jet having thick rim and a coaxial annular swirl jet was proposed by the authors. It was found that the compound flow is very useful for the push flow of the push-pull type ventilator selecting the suitable flow rate ratio of the annular swirl jet to the free jet. As a fundamental study on the compound swirl jet, the flow visualization was also carried out using the smoke method. At the same time, the mean velocity components were measured using the cobra Pitot tube. It was found from the results of these experiments that the unique flow structure by the interaction of two jets is created in the compound swirl jet choosing the adequate flow rate ratio, which is suitable for the push flow of the push-pull type ventilator.

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EARLY VARIATIONS OF PLASMA CORTISOL AFTER PULSE INTRAVENOUS INJECTION OF DIBUTYRYL CYCLIC ADENOSINE 3′,5′-MONOPHOSPHATE IN NORMAL SUBJECTS

Acta Endocrinologica ◽

10.1530/acta.0.0720753 ◽

1973 ◽

Vol 72 (4) ◽

pp. 753-761 ◽

Cited By ~ 3

Author(s):

Alberto Angeli ◽

Giuseppe Boccuzzi ◽

Roberto Frajria ◽

Daniela Bisbocci ◽

Franco Ceresa

Keyword(s):

Intravenous Injection ◽

Plasma Cortisol ◽

Time Course ◽

Healthy Adult ◽

Normal Subjects ◽

Adult Women ◽

Healthy Women ◽

Adrenal Steroidogenesis ◽

The Mean ◽

Zero Time

ABSTRACT 10 mg/kg of dibutyryl cyclic adenosine 3′,5′-monophosphate (Db-cAMP) was iv pulse injected into twelve healthy adult women. The plasma cortisol levels were determined as 11-OHCS at zero time and then at 2.5, 5, 7.5, 10, 15, 30, 60 and 180 min after the injection. The data were compared with those obtained at the corresponding times in two groups of eleven and seventeen healthy women after the injection of 250 ng and 250 μg of synthetic β-1-24 corticotrophin performed in the same manner as the injection of the nucleotide. The mean increments in plasma cortisol were significantly lower after Db-cAMP than after ACTH. Differences were noted by analyzing the time course of the responses. In the case of stimulation with Db-cAMP the 11-OHCS levels rose progressively to a maximum at 15–30 min. By contrast, a peak of plasma cortisol was evident in most cases within a few min after the injection of ACTH; after a fall, a later rise was then observed starting from 15 min. The differences in the plasma 11-OHCS responses after the two stimuli may also be of interest clinically for the investigation of some aspects of adrenal steroidogenesis.

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The flow of liquid in a stream from the standard turbine impeller

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19790700 ◽

1979 ◽

Vol 44 (3) ◽

pp. 700-710 ◽

Cited By ~ 10

Author(s):

Ivan Fořt ◽

Hans-Otto Möckel ◽

Jan Drbohlav ◽

Miroslav Hrach

Keyword(s):

Reynolds Number ◽

Kinematic Viscosity ◽

Momentum Flux ◽

Relative Size ◽

Mean Velocity ◽

Axial Profile ◽

The Mean ◽

Hot Film ◽

Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

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