Turbulent Flow Around Two Interfering Surface-Mounted Cubic Obstacles in Tandem Arrangement

1999 ◽  
Vol 122 (1) ◽  
pp. 24-31 ◽  
Author(s):  
Robert J. Martinuzzi ◽  
Brian Havel
Keyword(s):  
Pressure Fluctuations ◽  
Horseshoe Vortex ◽  
Surface Flow ◽  
Wake Flow ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Frequency Spectra ◽  
Approach Velocity ◽  
Lock In

The flow around two in-line surface-mounted cubes in a thin laminar boundary layer was experimentally investigated as a function of obstacle spacing for a Reynolds number of 22,000 based on approach velocity and cube height. Mean velocity measurements with Laser Doppler Velocimetry and surface flow patterns, obtained with an oil film technique, show that three distinct mean flow field structures exist based on obstacle spacing. Frequency spectra of velocity and surface pressure fluctuations reveal that these structures are related to three regimes of wake flow periodicity. For small spacings, the shear layer separating from the first cube reattaches on the sides of the second obstacle and wake periodicity can only be detected in the wake of the downstream cube. For a critical spacing range, the fluctuations in the gap and wake lock-in. For larger spacings, a second horseshoe vortex appears at the windward base of the second cube. Observations using dye-injection and smoke-wire techniques are consistent with these results. [S0098-2202(00)02401-9]

scholarly journals A Design for Vortex Suppression Downstream of a Submerged Gate

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 750
Author(s):  
Ender Demirel ◽  
Mustafa M. Aral
Keyword(s):  
Internal Flow ◽  
Vortex Pair ◽  
Horseshoe Vortex ◽  
Vortex Structures ◽  
Downstream Face ◽  
Mean Flow ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Drag Forces ◽  
The Stability

Interaction of recirculating and mean flow downstream of a submerged gate may form significant vortex structures, which may affect the stability of the gate. Although these flow structures that appear in submerged hydraulic jumps received considerable attention in the literature, relatively less work was devoted to the analysis and suppression of the vortex structures downstream of a submerged gate. In this work, internal flow structure and vortex dynamics around a submerged gate were investigated through laboratory tests and large-eddy simulation (LES) using computational fluid dynamics (CFD). It is shown that numerical results obtained for mean velocity field are in good agreement with the experimental measurements. A helical vortex pair connected with a horseshoe vortex system was identified within the roller region using high-resolution numerical simulations. Damping performance of different types of anti-vortex elements placed on the downstream face of the gate are evaluated based on numerical studies. It is shown that the horizontal porous baffle mounted at an elevation below the free surface reduced the vortex magnitudes in the roller region by 26.8%. With the implementation of the proposed vortex breaker, lift forces acting on the gate lip were reduced by 9.4% and drag forces acting on the downstream face of the gate were reduced by 8.6%. Finally, in this study, we assess the performance of the vortex breaker under different flow conditions.

Reynolds-number dependence of wall-pressure fluctuations in a pressure-induced turbulent separation bubble

2017 ◽  
Vol 833 ◽  
pp. 563-598 ◽  
Author(s):  
Hiroyuki Abe
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Large Scale ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Local Maximum ◽  
Wall Pressure ◽  
Mean Flow ◽  
Frequency Spectra ◽  
Wall Pressure Fluctuations

Direct numerical simulations are used to examine the behaviour of wall-pressure fluctuations $p_{w}$ in a flat-plate turbulent boundary layer with large adverse and favourable pressure gradients, involving separation and reattachment. The Reynolds number $Re_{\unicode[STIX]{x1D703}}$ based on momentum thickness is equal to 300, 600 and 900. Particular attention is given to effects of Reynolds number on root-mean-square (r.m.s.) values, frequency/power spectra and instantaneous fields. The possible scaling laws are also examined as compared with the existing direct numerical simulation and experimental data. The r.m.s. value of $p_{w}$ normalized by the local maximum Reynolds shear stress $-\unicode[STIX]{x1D70C}\overline{uv}_{max}$ (Simpson et al. J. Fluid Mech. vol. 177, 1987, pp. 167–186; Na & Moin J. Fluid Mech. vol. 377, 1998b, pp. 347–373) leads to near plateau (i.e. $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{uv}_{max}=2.5\sim 3$) in the adverse pressure gradient and separated regions in which the frequency spectra exhibit good collapse at low frequencies. The magnitude of $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{uv}_{max}$ is however reduced down to 1.8 near reattachment where good collapse is also obtained with normalization by the local maximum wall-normal Reynolds stress $\unicode[STIX]{x1D70C}\overline{vv}_{max}$. Near reattachment, $p_{w\,rms}/-\unicode[STIX]{x1D70C}\overline{vv}_{max}=1.2$ is attained unambiguously independently of the Reynolds number and pressure gradient. The present magnitude (1.2) is smaller than (1.35) obtained for step-induced separation by Ji & Wang (J. Fluid Mech. vol. 712, 2012, pp. 471–504). The reason for this difference is intrinsically associated with convective nature of a pressure-induced separation bubble near reattachment where the magnitude of $p_{w\,rms}$ depends essentially on the favourable pressure gradient. The resulting mean flow acceleration leads to delay of the r.m.s. peak after reattachment. Attention is also given to structures of $p_{w}$. It is shown that large-scale spanwise rollers of low pressure fluctuations are formed above the bubble, whilst changing to large-scale streamwise elongated structures after reattachment. These large-scale structures become more prominent with increasing $Re_{\unicode[STIX]{x1D703}}$ and affect $p_{w}$ significantly.

The evolution of strained turbulent plane wakes

2002 ◽  
Vol 463 ◽  
pp. 53-120 ◽  
Author(s):  
MICHAEL M. ROGERS
Keyword(s):  
Wake Flow ◽  
Strain Rates ◽  
Mean Flow ◽  
Mean Velocity ◽  
Velocity Deficit ◽  
Self Similar Solution ◽  
Flow Evolution ◽  
Self Similar ◽  
The Mean ◽  
Pseudo Spectral

Direct numerical simulations of ten turbulent time-evolving strained wakes have been generated using a pseudo-spectral numerical method. In all the simulations, the strain was applied to the same (previously generated) initial developed self-similar wake flow field. The cases include flows in which the wake is subjected to various orientations of the applied mean strain, including both plane and axisymmetric strain configurations. In addition, for one particular strain geometry, cases with differing strain rates were considered. Although classical self-similar analysis does yield a self-similar solution for strained wakes, this solution does not describe the observed flow evolution. Instead, the wake mean velocity profiles evolve according to a different ‘equilibrium similarity solution’, with the strained wake width being determined by the straining in the inhomogeneous cross-stream direction. Wakes that are compressed in this direction eventually exhibit constant widths, whereas wakes in cases with expansive cross-stream strain ultimately spread at the same rate as the distortion caused by the applied strain. The shape of the wake mean velocity deficit profile is nearly universal. Although the effect of the strain on the mean flow is pronounced and rapid, the response of the turbulence to the strain occurs more slowly. Changes in the turbulence intensity cannot keep pace with changes in the mean wake velocity deficit, even for relatively low strain rates.

The Development of a Turbulent Junction Vortex System (Data Bank Contribution)

1992 ◽  
Vol 114 (4) ◽  
pp. 559-565 ◽  
Author(s):  
F. J. Pierce ◽  
J. Shin
Keyword(s):  
Growth And Development ◽  
Flat Surface ◽  
Leading Edge ◽  
Data Bank ◽  
Surface Flow ◽  
The Body ◽  
Wake Flow ◽  
Mean Flow ◽  
Vortex System ◽  
Flow Measurements

The growth and development of a horseshoe vortex system in an incompressible, three-dimensional turbulent junction flow were investigated experimentally. A streamlined cylinder mounted with its axis normal to a flat surface was used to generate the junction vortex flow. The flow environment was characterized by a body Reynolds number of 183,000, based on the leading edge diameter of the streamlined cylinder. The study included surface flow visualizations, surface pressure measurements, and mean flow measurements of total pressure, static pressure, and velocity distributions in three planes around the base of the streamlined cylinder, and in two planes in the wake flow. Some characterizations of vortex properties based on the measured mean cross-flow velocity components are presented. The results show the presence of a single large, dominant vortex, with strong evidence of a very small corner vortex in the junction between the cylinder and the flat surface. The center of the dominant vortex drifts away from both the body and the flat surface as the flow develops along and downstream of the body. The growth and development of the core of the large, dominant vortex are documented.

scholarly journals Horseshoe Vortex Formation Around a Cylinder

1986 ◽  
Author(s):  
W. A. Eckerle ◽  
L. S. Langston
Keyword(s):  
Saddle Point ◽  
Large Diameter ◽  
Vortex Formation ◽  
Horseshoe Vortex ◽  
Angular Distance ◽  
Surface Flow ◽  
Computational Fluid Mechanics ◽  
Pressure Measurements ◽  
Vortex System ◽  
Mean Velocity

An experimental investigation was conducted to characterize a symmetrical horseshoe vortex system in front of and around a single large-diameter right cylinder centered between the sidewalls of a wind tunnel. Surface flow visualization and surface static pressure measurements as well as extensive mean velocity and pressure measurements in and around the vortex system were acquired. The results lend new insight into the formation and development of the vortex system. Contrary to what has been assumed previously, a strong vortex was not identified in the streamwise plane of symmetry, but started a significant angular distance away from it. Rather than the multiple vortex sytems reported by others, only a single primary vortex and saddle point were found. The scale of the separation process at the saddle point was much smaller than the scale of the approaching boundary layer thickness. Results of the present study not only shed light on such phenomena as the nonsymmetrical endwall flow in axial turbomachinery but can also be used as a test case for three-dimensional computational fluid mechanics computer codes.

scholarly journals On the reduction of aerofoil–turbulence interaction noise associated with wavy leading edges

2016 ◽  
Vol 792 ◽  
pp. 526-552 ◽  
Author(s):  
Jae Wook Kim ◽  
Sina Haeri ◽  
Phillip F. Joseph
Keyword(s):  
Noise Reduction ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Leading Edge ◽  
Mean Flow ◽  
Frequency Spectra ◽  
Phase Interference ◽  
Edge Profile ◽  
Leading Edges ◽  
The Hill

An aerofoil leading-edge profile based on wavy (sinusoidal) protuberances/tubercles is investigated to understand the mechanisms by which they are able to reduce the noise produced through the interaction with turbulent mean flow. Numerical simulations are performed for non-lifting flat-plate aerofoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) subjected to impinging turbulence that is synthetically generated in the upstream zone (free-stream Mach number of 0.24). Full three-dimensional Euler (inviscid) solutions are computed for this study thereby eliminating self-noise components. A high-order accurate finite-difference method and artefact-free boundary conditions are used in the current simulations. Various statistical analysis methods, including frequency spectra, are implemented to aid the understanding of the noise-reduction mechanisms. It is found with WLEs, unlike the SLE, that the surface pressure fluctuations along the leading edge exhibit a significant source-cutoff effect due to geometric obliqueness which leads to reduced levels of radiated sound pressure. It is also found that there exists a phase interference effect particularly prevalent between the peak and the hill centre of the WLE geometry, which contributes to the noise reduction in the mid- to high-frequency range.

The Mean Flow Structure Around and Within a Turbulent Junction or Horseshoe Vortex—Part I: The Upstream and Surrounding Three-Dimensional Boundary Layer

1988 ◽  
Vol 110 (4) ◽  
pp. 406-414 ◽  
Author(s):  
J. D. Menna ◽  
F. J. Pierce
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Vortex Flow ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Mean Flow ◽  
Complex Flow ◽  
Mean Velocity ◽  
Standard Case ◽  
The Mean

The mean flow structure upstream, around, and in a turbulent junction or horseshoe vortex is reported for an incompressible, subsonic flow. This fully documented, unified, comprehensive, and self-consistent data base is offered as a benchmark or standard case for assessing the predictive capabilities of computational codes developed to predict this kind of complex flow. Part I of these papers defines the total flow being documented. The upstream and surrounding three-dimensional turbulent boundary layer-like flow away from separation has been documented with mean velocity field and turbulent kinetic energy field measurements made with hot film anemometry, and local wall shear stress measurements. Data are provided for an initial condition plane well upstream of the junction vortex flow to initiate a boundary layer calculation, and freestream or edge velocity, as well as floor static pressure, are reported to proceed with the solution. Part II of these papers covers the flow through separation and within the junction vortex flow.

Surface-pressure fluctuations induced by boundary-layer flow at finite Mach number

1965 ◽  
Vol 22 (3) ◽  
pp. 507-519 ◽  
Author(s):  
John E. Ffowcs Williams
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Surface Pressure ◽  
Pressure Fluctuations ◽  
Wave Number ◽  
Mean Flow ◽  
Frequency Spectra ◽  
Dissipative Term ◽  
Main Effect ◽  
Layer Flow

A theory describing boundary-layer surface-pressure fluctuations on a rigid surface is presented in a form that illustrates the main effect of compressibility. The most significant effect is that the correlation area is proportional to the square of mean-flow Mach number so it does not vanish in flow of finite compressibility. Modifications of the wave-number and frequency spectra by this effect are described, and the results applied to the computation of large plate response. That computation incorporates the effect of fluid loading, which enters the response equations as a dissipative term for components at supersonic phase velocity but merely as an added loading for subsonic components.

Velocity profiles assessment in natural channels during high floods

2011 ◽  
Vol 42 (2-3) ◽  
pp. 162-170 ◽  
Author(s):  
Tommaso Moramarco ◽  
Carla Saltalippi ◽  
Vijay P. Singh
Keyword(s):  
Flow Velocity ◽  
Maximum Flow ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Flow Area ◽  
The Mean ◽  
Logarithmic Law ◽  
Maximum Flow Velocity

The accuracy of three different approaches for velocity profiles assessment during high floods, when the velocity points sampling is carried out only in the upper portion of the flow area, has been investigated. The first two methods assume the classical logarithmic law with additional terms, to take account of the dip-phenomenon in the velocity profile. The third one is based on the entropy theory and uses the maximum flow velocity occurring in the flow area. A sample of velocity measurements carried out at Pontelagoscuro gauged section (Po River, Italy), has been considered for the analysis. Six flood events have been selected and the accuracy of the investigated methods has been evaluated in terms of mean error in estimating both the mean velocity along each sampled vertical and the mean flow velocity. For high floods, the logarithmic law and the entropic approach were found quite accurate; however, the ability of the latter in reproducing the velocity profiles only by sampling the maximum flow velocity has been shown. Therefore, a procedure for velocity measurements based on the entropic approach has been proposed. The procedure allows one to both to shorten remarkably the time of the velocity sampling and to quickly estimate the discharge.

The Mean Flow Structure on the Symmetry Plane of a Turbulent Junction Vortex

1990 ◽  
Vol 112 (1) ◽  
pp. 16-22 ◽  
Author(s):  
F. J. Pierce ◽  
I. K. Tree
Keyword(s):  
Velocity Field ◽  
Vortex Structure ◽  
Symmetry Plane ◽  
Leading Edge ◽  
Surface Flow ◽  
The Body ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Vortex System ◽  
The Mean

The mean flow structure on the symmetry plane of a turbulent junction vortex is documented. A two-channel, two-color LDV system allowed nonintrusive measurements of the two velocity components on the symmetry plane. Extensive measurements were made in and around the separation point and within the junction vortex system, both very close to the floor and to the leading edge of the body generating the vortex system. Real-time smoke visualizations confirmed a region of strongly time-variant flow with large changes in the scale and position of the principal vortex structure. The extensive velocity field data are correlated with high quality surface visualizations and surface pressure measurements. The mean velocity measurements show one large well-defined vortex structure and one singular saddle point of separation on the symmetry plane. The transverse vorticity field computed from the extensive velocity field suggests a very strong but small second, counter rotating vortex located in the extreme corner formed by the floor and leading edge of the body. The surface flow visualization suggests only one clear separation line. The single pair of counter rotating vortices revealed by these detailed LDV velocity measurements is in agreement with two independent studies which used multiple orifice pressure probes. This measured two vortex model is not in agreement with the frequently pictured four vortex flow model, inferred from surface flow visualizations, showing two pairs of counter rotating vortices.

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