The response of a propeller anemometer to turbulent flow with the mean wind vector perpendicular to the axis of rotation

The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.

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III. Researches in physical astronomy

Philosophical Transactions of the Royal Society of London ◽

10.1098/rstl.1831.0004 ◽

1831 ◽

Vol 121 ◽

pp. 17-66

Keyword(s):

Angular Velocity ◽

Major Axis ◽

The Body ◽

Fixed Plane ◽

Resisting Medium ◽

Axis Of Rotation ◽

Geographical Latitude ◽

The Mean ◽

The Stability ◽

Revolving Body

In last April I had the honour of presenting to the Society a paper containing expressions for the variations of the elliptic constants in the theory of the motions of the planets. The stability of the solar system is established by means of these expressions, if the planets move in a space absolutely devoid of any resistance*, for it results from their form that however far the approximation be carried, the eccentricity, the major axis, and the tangent of the inclination of the orbit to a fixed plane, contain only periodic inequalities, each of the three other constants, namely, the longitude of the node, the longitude of the perihelion, and the longitude of the epoch, contains a term which varies with the time, and hence the line of apsides and the line of nodes revolve continually in space. The stability of the system may therefore be inferred, which would not be the case if the eccentricity, the major axis, or the tangent of the inclination of the orbit to a fixed plane contained a term varying with the time, however slowly. The problem of the precession of the equinoxes admits of a similar solution; of the six constants which determine the position of the revolving body, and the axis of instantaneous rotation at any moment, three have only periodic inequalities, while each of the other three has a term which varies with the time. From the manner in which these constants enter into the results, the equilibrium of the system may be inferred to be stable, as in the former case. Of the constants in the latter problem, the mean angular velocity of rotation may be considered analogous to the mean motion of a planet, or its major axis ; the geographical longitude, and the cosine of the geographical latitude of the pole of the axis of instantaneous rotation, to the longitude of the perihelion and the eccentricity; the longitude of the first point of Aries and the obliquity of the ecliptic, to the longitude of the node and the inclination of the orbit to a fixed plane; and the longitude of a given line in the body revolving, passing through its centre of gravity, to the longitude of the epoch. By the stability of the system I mean that the pole of the axis of rotation has always nearly the same geographical latitude, and that the angular velocity of rotation, and the obliquity of the ecliptic vary within small limits, and periodically. These questions are considered in the paper I now have the honour of submitting to the Society. It remains to investigate the effect which is produced by the action of a resisting medium; in this case the latitude of the pole of the axis of rotation, the obliquity of the ecliptic, and the angular velocity of rotation might vary considerably, although slowly, and the climates undergo a considerable change.

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On Turbulent Flow Between Parallel Plates

Journal of Applied Mechanics ◽

10.1115/1.4010602 ◽

1953 ◽

Vol 20 (1) ◽

pp. 109-114

Author(s):

S. I. Pai

Keyword(s):

Turbulent Flow ◽

Velocity Distribution ◽

Poiseuille Flow ◽

The Other ◽

Turbulent Velocity ◽

Parallel Plates ◽

Mean Velocity ◽

Reynolds Equations ◽

Mean Pressure ◽

The Mean

Abstract The Reynolds equations of motion of turbulent flow of incompressible fluid have been studied for turbulent flow between parallel plates. The number of these equations is finally reduced to two. One of these consists of mean velocity and correlation between transverse and longitudinal turbulent-velocity fluctuations u 1 ′ u 2 ′ ¯ only. The other consists of the mean pressure and transverse turbulent-velocity intensity. Some conclusions about the mean pressure distribution and turbulent fluctuations are drawn. These equations are applied to two special cases: One is Poiseuille flow in which both plates are at rest and the other is Couette flow in which one plate is at rest and the other is moving with constant velocity. The mean velocity distribution and the correlation u 1 ′ u 2 ′ ¯ can be expressed in a form of polynomial of the co-ordinate in the direction perpendicular to the plates, with the ratio of shearing stress on the plate to that of the corresponding laminar flow of the same maximum velocity as a parameter. These expressions hold true all the way across the plates, i.e., both the turbulent region and viscous layer including the laminar sublayer. These expressions for Poiseuille flow have been checked with experimental data of Laufer fairly well. It also shows that the logarithmic mean velocity distribution is not a rigorous solution of Reynolds equations.

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Optimal energy growth in stably stratified turbulent Couette flow

10.5194/egusphere-egu21-10311 ◽

2021 ◽

Author(s):

Grigory Zasko ◽

Andrey Glazunov ◽

Evgeny Mortikov ◽

Yuri Nechepurenko ◽

Pavel Perezhogin

Keyword(s):

Boundary Layer ◽

Turbulent Flow ◽

Couette Flow ◽

Large Scale ◽

Thin Layers ◽

Plane Couette Flow ◽

Turbulent Layer ◽

Wide Range ◽

The Mean ◽

Optimal Disturbances

In this report, we will try to explain the emergence of large-scale organized structures in stably stratified turbulent flows using optimal disturbances of the mean turbulent flow. These structures have been recently obtained in numerical simulations of turbulent stably stratified flows [1] (Ekman layer, LES) and [2] (plane Couette flow, DNS and LES) and indirectly confirmed by field measurements in the stable boundary layer of the atmosphere [1, 2]. In instantaneous temperature fields they manifest themselves as irregular inclined thin layers with large gradients (fronts), spaced from each other by distances comparable to the height of the entire turbulent layer, and separated by regions with weak stratification.Optimal disturbances of a stably stratified turbulent plane Couette flow are investigated in a wide range of Reynolds and Richardson numbers. These disturbances were computed based on a simplified linearized system of equations in which turbulent Reynolds stresses and heat fluxes were approximated by isotropic viscosity and diffusion with coefficients obtained from DNS results. It was shown [3] that the spatial scales and configurations of the inclined structures extracted from DNS data coincide with the ones obtained from optimal disturbances of the mean turbulent flow.Critical value of the stability parameter is found starting from which the optimal disturbances resemble inclined structures. The physical mechanisms that determine the evolution, energetics and spatial configuration of these optimal disturbances are discussed. The effects due to the presence of stable stratification are highlighted.Numerical experiments with optimal disturbances were supported by the RSF (grant No. 17-71-20149). Direct numerical simulation of stratified turbulent Couette flow was supported by the RFBR (grant No. 20-05-00776).References:[1] P.P. Sullivan, J.C. Weil, E.G. Patton, H.J. Jonker, D.V. Mironov. Turbulent winds and temperature fronts in large-eddy simulations of the stable atmospheric boundary layer // J. Atmos. Sci., 2016, V. 73, P. 1815-1840.[2] A.V. Glazunov, E.V. Mortikov, K.V. Barskov, E.V. Kadantsev, S.S. Zilitinkevich. Layered structure of stably stratified turbulent shear flows // Izv. Atmos. Ocean. Phys., 2019, V. 55, P. 312&#8211;323.[3] G.V. Zasko, A.V. Glazunov, E.V. Mortikov, Yu.M. Nechepurenko. Large-scale structures in stratified turbulent Couette flow and optimal disturbances // Russ. J. Num. Anal. Math. Model., 2010, V. 35, P. 35&#8211;53.

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Bubble behaviour in a horizontal high-speed solid-body rotating flow

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.683 ◽

2021 ◽

Vol 925 ◽

Author(s):

Majid Rodgar ◽

Hélène Scolan ◽

Jean-Louis Marié ◽

Delphine Doppler ◽

Jean-Philippe Matas

Keyword(s):

Aspect Ratio ◽

Solid Body ◽

High Speed ◽

Lift Coefficient ◽

Rotating Flow ◽

Axis Of Rotation ◽

Large Fluctuations ◽

The Mean ◽

Drag And Lift ◽

The Impact

We study experimentally the behaviour of a bubble injected into a horizontal liquid solid-body rotating flow, in a range of rotational velocities where the bubble is close to the axis of rotation. We first study the stretching of the bubble as a function of its size and of the rotation of the cell. We show that the bubble aspect ratio can be predicted as a function of the bubble Weber number by the model of Rosenthal (J. Fluid Mech., vol. 12, 1962, 358–366) provided an appropriate correction due to the impact of buoyancy is included. We next deduce the drag and lift coefficients from the mean bubble position. For large bubbles straddling the axis of rotation, we show that the drag coefficient $C_D$ is solely dependent on the Rossby number $Ro$, with $C_D \approx 1.5/Ro$. In the same limit of large bubbles, we show that the lift coefficient $C_L$ is controlled by the shear Reynolds number $Re_{shear}$ at the scale of the bubble. For $Re_{shear}$ larger than 3000 we observe a sharp transition, wherein large fluctuations in the bubble aspect ratio and mean position occur, and can lead to the break-up of the bubble. We interpret this regime as a resonance between the periodic forcing of the rotating cell and the eigenmodes of the stretched bubble.

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Self-consistent triple decomposition of the turbulent flow over a backward-facing step under finite amplitude harmonic forcing

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2019.0018 ◽

2019 ◽

Vol 475 (2225) ◽

pp. 20190018

Author(s):

E. Yim ◽

P. Meliga ◽

F. Gallaire

Keyword(s):

Turbulent Flow ◽

Finite Amplitude ◽

Navier Stokes ◽

Reynolds Stresses ◽

Mean Flow ◽

Backward Facing Step ◽

Eddy Viscosity Model ◽

Coherent Interaction ◽

Self Consistent ◽

The Mean

We investigate the saturation of harmonically forced disturbances in the turbulent flow over a backward-facing step subjected to a finite amplitude forcing. The analysis relies on a triple decomposition of the unsteady flow into mean, coherent and incoherent components. The coherent–incoherent interaction is lumped into a Reynolds averaged Navier–Stokes (RANS) eddy viscosity model, and the mean–coherent interaction is analysed via a semi-linear resolvent analysis building on the laminar approach by Mantič-Lugo & Gallaire (2016 J. Fluid Mech. 793 , 777–797. ( doi:10.1017/jfm.2016.109 )). This provides a self-consistent modelling of the interaction between all three components, in the sense that the coherent perturbation structures selected by the resolvent analysis are those whose Reynolds stresses force the mean flow in such a way that the mean flow generates exactly the aforementioned perturbations, while also accounting for the effect of the incoherent scale. The model does not require any input from numerical or experimental data, and accurately predicts the saturation of the forced coherent disturbances, as established from comparison to time-averages of unsteady RANS simulation data.

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Effects of a fully submerged boulder within a boulder array on the mean and turbulent flow fields: Implications to bedload transport

Acta Geophysica ◽

10.2478/s11600-012-0044-6 ◽

2012 ◽

Vol 60 (6) ◽

pp. 1502-1546 ◽

Cited By ~ 44

Author(s):

Athanasios N. Papanicolaou ◽

Casey M. Kramer ◽

Achilleas G. Tsakiris ◽

Thorsten Stoesser ◽

Sandeep Bomminayuni ◽

...

Keyword(s):

Turbulent Flow ◽

Flow Fields ◽

Bedload Transport ◽

The Mean ◽

Boulder Array

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Sedimentation of finite-size spheres in quiescent and turbulent environments

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.698 ◽

2016 ◽

Vol 788 ◽

pp. 640-669 ◽

Cited By ~ 49

Author(s):

Walter Fornari ◽

Francesco Picano ◽

Luca Brandt

Keyword(s):

Turbulent Flow ◽

Settling Velocity ◽

Solid Phase ◽

Density Ratio ◽

Finite Size ◽

Spherical Particles ◽

Volume Fractions ◽

Turbulent Environments ◽

The Mean ◽

Quiescent Fluid

Sedimentation of a dispersed solid phase is widely encountered in applications and environmental flows, yet little is known about the behaviour of finite-size particles in homogeneous isotropic turbulence. To fill this gap, we perform direct numerical simulations of sedimentation in quiescent and turbulent environments using an immersed boundary method to account for the dispersed rigid spherical particles. The solid volume fractions considered are ${\it\phi}=0.5{-}1\,\%$, while the solid to fluid density ratio ${\it\rho}_{p}/{\it\rho}_{f}=1.02$. The particle radius is chosen to be approximately six Kolmogorov length scales. The results show that the mean settling velocity is lower in an already turbulent flow than in a quiescent fluid. The reductions with respect to a single particle in quiescent fluid are approximately 12 % and 14 % for the two volume fractions investigated. The probability density function of the particle velocity is almost Gaussian in a turbulent flow, whereas it displays large positive tails in quiescent fluid. These tails are associated with the intermittent fast sedimentation of particle pairs in drafting–kissing–tumbling motions. The particle lateral dispersion is higher in a turbulent flow, whereas the vertical one is, surprisingly, of comparable magnitude as a consequence of the highly intermittent behaviour observed in the quiescent fluid. Using the concept of mean relative velocity we estimate the mean drag coefficient from empirical formulae and show that non-stationary effects, related to vortex shedding, explain the increased reduction in mean settling velocity in a turbulent environment.

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Experimental and Numerical Investigations of the 3-D Turbulent Flow Characteristics Around Submerged Permeable Breakwaters

Volume 7: Fluids Engineering ◽

10.1115/imece2017-72570 ◽

2017 ◽

Author(s):

Caleb Stanley ◽

Georgios Etsias ◽

Steven Dabelow ◽

Dimitrios Dermisis ◽

Ning Zhang

Keyword(s):

Turbulent Flow ◽

Laboratory Experiments ◽

Flow Characteristics ◽

Mean Flow ◽

Turbulent Structures ◽

3 Dimensional ◽

The Mean ◽

Design Simplicity ◽

Study Laboratory ◽

Geometric Designs

Submerged breakwaters are favored for their design simplicity in projects intended to dissipate wave energy and reduce erosion on coastlines. Despite their popularity, the effects that submerged breakwaters exhibit on the surrounding hydrodynamics are not clearly understood, mainly due to the flow complexity generated from 3-dimensional turbulent structures in the vicinity of the breakwaters that affect the mean flow characteristics and the transport of sediment. The objective of this study was to evaluate the effects that various geometric designs of submerged permeable breakwaters have on the turbulent flow characteristics. To meet the objective of this study, laboratory experiments were performed in a water-recirculating flume, in which the 3-dimensional velocity field was recorded in the vicinity of scaled breakwater models. Breakwaters that were tested include non-permeable, three-hole, and ten-hole models. The experimental data obtained was compared to results obtained from numerical simulations. Results demonstrated that permeable breakwaters exhibit more vertical turbulent strength than their non-permeable counterparts. It was also discovered that three-hole breakwater models produce higher turbulent fluctuations than that of the ten-hole breakwaters. The results from this study will be used eventually to enhance the performance of restoration projects in coastal areas in Louisiana.

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Study on the Characteristics of Turbulent Flow of Viscoelastic Fluid Through a Planar Sudden Expansion by PIV System

Volume 1: Symposia ◽

10.1115/ajkfluids2015-25079 ◽

2015 ◽

Author(s):

Lu Wang ◽

Jia-Qi Bao ◽

Tong-Zhou Wei ◽

Wei-Hua Cai ◽

Feng-Chen Li

Keyword(s):

Turbulent Flow ◽

Particle Image ◽

Reynolds Shear Stress ◽

Streamwise Velocity ◽

Velocity Fields ◽

Sudden Expansion ◽

Image Velocimetry ◽

The Mean ◽

Cetyltrimethyl Ammonium ◽

Component Particle

The influences of drag-reducing surfactant additives on the characteristics of a turbulent flow over a planar sudden expansion with expansion ration R = D/d = 3 and aspect ratio A = w/h = 30 were experimentally investigated by a 2D-2C (two dimensional-two component) particle image velocimetry (PIV) system. The 2D-2C velocity fields in the streamwise-wall-normal planes (x-y planes) at three spanwise locations are measured for the flows of water and 50ppm aqueous solution of CTAC/NaSal (CTAC: cetyltrimethyl ammonium chloride; NaSal: sodium salicylate) under the Reynolds number of 1.85 × 104. From the streamline in the x-y plane, it is observed that the reattachment lengths of the vortices in CTAC/NaSal solution are longer. Then the mean streamwise velocity fields and the apparent flow rate at three spanwise locations show that the flow fields in the other two x-y planes are practically symmetrical about the x-y centreplane in CTAC/NaSal solution, as compared with that in water flow. Finally, it is perceived that the Reynolds shear stress for three spanwise locations in CTAC/NaSal solution are obviously decreased.

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