scholarly journals Numerical Investigation on the Effects of Vortex Shedding on Boundary Layer Unsteadiness

1970 ◽  
Vol 37 ◽  
pp. 33-39
Author(s):  
ABM Toufique Hasan ◽  
Dipak Kanti Das
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Finite Element ◽  
Flow Field ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Number Range ◽  
Rotating Speed ◽  
Rotating Circular Cylinder

The interaction between an initially laminar boundary layer developed spatially on a flat plate under the influence of vortex shedding induced from a rotating circular cylinder has been simulated numerically. The rotational speed of the cylinder is varied to generate the vortex shedding of different intensities. Also the flat plate is kept at different positions from the cylinder. Due to asymmetry in the flow field, the present problem is governed by unsteady Navier-Stokes equations which are simulated numerically by finite element method. Computations are carried out for low Reynolds number range up to 1000. Instantaneous development of the flow field, unsteady boundary layer integral parameters, and wall skin friction are presented on different streamwise locations over the plate. From the computation, it is observed that the vortex shedding substantially affects the boundary layer development. The disturbed displacement and momentum thicknesses of the plate increase up to 1.6 times and 2.6 times of the undisturbed flow, respectively. Also the plate shape factor approaches a value of 1.5 which is typical for turbulent flow. This interaction strongly depends on the rotating speed of the cylinder, the relative positions of the cylinder and the plate and also on Reynolds number of the flow. Keywords: Vortex shedding, finite element, boundary layer, wall skin friction.doi:10.3329/jme.v37i0.817Journal of Mechanical Engineering Vol.37 June 2007, pp.33-39

Heat transfer from a hypersonic turbulent boundary layer on a flat plate

1973 ◽  
Vol 60 (2) ◽  
pp. 257-271 ◽  
Author(s):  
G. T. Coleman ◽  
C. Osborne ◽  
J. L. Stollery
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Mach Number ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Reasonable Agreement ◽  
Skin Friction Coefficient ◽  
Number Range

A hypersonic gun tunnel has been used to measure the heat transfer to a sharpedged flat plate inclined at various incidences to generate local Mach numbers from 3 to 9. The measurements have been compared with a number of theoretical estimates by plotting the Stanton number against the energy-thickness Reynolds number. The prediction giving the most reasonable agreement throughout the above Mach number range is that due to Fernholz (1971).The values of the skin-friction coefficient derived from velocity profiles and Preston tube data are also given.

Hydrodynamic Force Measurements on a Circular Cylinder Fitted With Peripheral Control Cylinders: Preliminary Results on the Development of VIV Suppressors

2015 ◽  
Author(s):  
Mariana Silva-Ortega ◽  
Gustavo R. S. Assi ◽  
Murilo M. Cicolin
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Vortex Shedding ◽  
Hydrodynamic Force ◽  
Force Measurements ◽  
Number Range ◽  
Preliminary Results ◽  
Reynolds Number Range

Recent achievements in controlling the boundary layer by moving surfaces have been encouraging the development and investigation of passive suppressors of vortex-induced vibration. Within this context, the main purpose of the present work is to evaluate the suppression of vortex shedding of a plain cylinder surrounded by two, four and eight smaller control cylinders. Experiments have been carried out on a fixed circular cylinder to investigate the effect of the control cylinders over drag reduction. Control cylinders with diameter of d/D = 0.06 were tested, where D is the diameter of the main cylinder. The gap between the main cylinder and the control cylinders varied between G/D = 0.05 and 0.15. Experiments with a plain cylinder in the Reynolds number range from 5,000 to 50,000 have been performed to serve as reference. It was found that a cylinder fitted with four control cylinders presented less drag and fluctuating lift than cylinders fitted with two or eight small cylinders.

Effect of Surfactant Additives on a Boundary Layer on a Flat Plate

2005 ◽  
Author(s):  
Satoshi Ogata ◽  
Takeshi Fujita
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Velocity Profile ◽  
Flat Plate ◽  
Newtonian Fluid ◽  
Surfactant Concentration ◽  
Shape Parameter ◽  
Tap Water ◽  
Number Range ◽  
Surfactant Solutions

The effect of surfactant solutions on the boundary layer over a flat plate has been investigated in the Reynolds number range of approximately Re < 153,000. Experiments were carried out by measuring the velocity profile using a PIV system. Surfactant solutions tested were aqueous solutions of oleyl-bihydroxyethyl methyl ammonium chloride (Ethoquad O/12) in the concentration range of 50 to 500 ppm, to which sodium salicylate was added as a counterion. It was clarified that the boundary layer thickness of surfactant solutions increases significantly near the leading edge comparing with that of tap water, and parallelly develops in that obtained by the Blasius equation. For lower surfactant concentration (50 and 200 ppm) the velocity profile near the wall is distributed between that of laminar flow and turbulent flow for Newtonian fluid. When the Reynolds number increases, the velocity profile gradually increases from the outer edge of the boundary, and approaches the turbulent velocity profile of Newtonian fluid. For higher surfactant concentration (500 ppm), the velocity profile shows large S-shape. The velocity profile does not change very much, even if the Reynolds increases. The shape parameter with surfactant solutions decreases slightly comparing that of tap water at Re < 92,000, The value of shape parameter H with surfactant solution shows 1.66 < H < 2.32.

Plate-injection into a separated supersonic boundary layer. Part 2. The transition regions

1974 ◽  
Vol 62 (2) ◽  
pp. 289-304 ◽  
Author(s):  
K. Stewartson
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
Asymptotic Expansions ◽  
Stokes Equations ◽  
Supersonic Boundary Layer ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Consistent Solution ◽  
Strong Injection

The model proposed by Smith & Stewartson (1973), to describe the separated boundary layer induced by strong injection over a finite length of a flat plate in a supersonic mainstream, is shown to provide the basis for a fully consistent solution of the Navier–Stokes equations for this problem, valid in the limit of infinite Reynolds number. The solution takes the form of asymptotic expansions in each of a large number of overlapping regions of the flow field, which are consistently matched across areas of common validity.

Wake-Boundary Layer Interactions Behind a Square Cylinder for a Reynolds Number in Periodic Vortex Shedding Regime

2015 ◽  
Author(s):  
Arti Pal ◽  
Sudipto Sarkar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Navier Stokes Equation ◽  
Ansys Fluent ◽  
Boundary Layer Interaction

Flow over a square cylinder in proximity to a wall for different gap-to-diameter ratios (G/D = 0 to 2, where G is the gap between the cylinder and flat plate and D is the side of the square cylinder) has been studied extensively for a Reynolds Number (Re = U∞D/v, where v is the kinematic viscosity of the fluid and U∞ is the free stream velocity) in the periodic vortex shedding regime. Ansys Fluent is used to solve two-dimensional (2-D), time dependent, incompressible Navier-Stokes equation by SIMPLE [1] algorithm implemented in finite volume method. Interesting flow features and changes in vortex dynamics can be seen by the present simulation, when the cylinder approaches very close to the plate. The boundary layer formed over the flat plate changes its characteristics for these low gap-ratios. Also the modification of the aerodynamic forces and the vortex shedding frequency are thoroughly described to understand the physics behind wake-boundary layer interaction at low Reynolds Number.

Direct numerical simulation of turbulence in a nominally zero-pressure-gradient flat-plate boundary layer

2009 ◽  
Vol 630 ◽  
pp. 5-41 ◽  
Author(s):  
XIAOHUA WU ◽  
PARVIZ MOIN
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Plate Boundary ◽  
Transitional Region ◽  
Bypass Transition ◽  
Number Range ◽  
Flat Plate Boundary Layer

A nominally-zero-pressure-gradient incompressible boundary layer over a smooth flat plate was simulated for a continuous momentum thickness Reynolds number range of 80 ≤ Reθ ≤ 940. Transition which is completed at approximately Reθ = 750 was triggered by intermittent localized disturbances arising from patches of isotropic turbulence introduced periodically from the free stream at Reθ = 80. Streamwise pressure gradient is quantified with several measures and is demonstrated to be weak. Blasius boundary layer is maintained in the early transitional region of 80 < Reθ < 180 within which the maximum deviation of skin friction from the theoretical solution is less than 1%. Mean and second-order turbulence statistics are compared with classic experimental data, and they constitute a rare DNS dataset for the spatially developing zero-pressure-gradient turbulent flat-plate boundary layer. Our calculations indicate that in the present spatially developing low-Reynolds-number turbulent flat-plate boundary layer, total shear stress mildly overshoots the wall shear stress in the near-wall region of 2–20 wall units with vanishing normal gradient at the wall. Overshoots as high as 10% across a wider percentage of the boundary layer thickness exist in the late transitional region. The former is a residual effect of the latter. The instantaneous flow fields are vividly populated by hairpin vortices. This is the first time that direct evidence (in the form of a solution of the Navier–Stokes equations, obeying the statistical measurements, as opposed to synthetic superposition of the structures) shows such dominance of these structures. Hairpin packets arising from upstream fragmented Λ structures are found to be instrumental in the breakdown of the present boundary layer bypass transition.

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

Aero-optics of subsonic turbulent boundary layers

2012 ◽  
Vol 696 ◽  
pp. 122-151 ◽  
Author(s):  
Kan Wang ◽  
Meng Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Dominant Role ◽  
Elevation Angle ◽  
Turbulent Boundary Layers ◽  
Density Field ◽  
Small Scale ◽  
Number Range ◽  
Scale Turbulence

AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

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