On pressure invariance, wake width and drag prediction of a bluff body in confined flow

2009 ◽  
Vol 622 ◽  
pp. 321-344 ◽  
Author(s):  
W. W. H. YEUNG
Keyword(s):  
Experimental Data ◽  
Pressure Distribution ◽  
Bluff Body ◽  
Reynolds Numbers ◽  
Momentum Equation ◽  
Base Pressure ◽  
Vertex Angle ◽  
Bluff Bodies ◽  
Arbitrary Vertex ◽  
Confined Flow

In the present investigation, the form drag on a bluff body in confined flow is studied. From the observation of invariance in pressure distribution between a disk and a flat plate normal to free upstream in unconfined flow, a linear relation linking the drag to the base pressure is derived when the potential-flow model by Parkinson & Jandali (J. Fluid Mech., vol. 40, 1970, p. 577) is incorporated. A theoretical wake width deduced from well-documented experimental data for a disk is proposed such that the wake Strouhal number is independent of inclination. This width, when combined with the momentum equation and solved simultaneously with the aforementioned linear equation, leads to realistic predictions of the drag and the base pressure. The method is consistent when applied to a cone of arbitrary vertex angle, a circular cylinder at subcritical Reynolds numbers and a sphere at subcritical as well as supercritical Reynolds numbers. The case of the inclined disk is also discussed. As the pressure distribution is invariant under wall constraint, analytical expressions for the effect of confinement on the loading of bluff bodies are derived and found to provide the correct trend of experimental data.

Base pressure prediction in bluff-body potential-flow models

2000 ◽  
Vol 423 ◽  
pp. 381-394 ◽  
Author(s):  
W. W. H. YEUNG ◽  
G. V. PARKINSON
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Separated Flow ◽  
Momentum Equation ◽  
Base Pressure ◽  
Vertex Angle ◽  
Arbitrary Vertex ◽  
Flow Models ◽  
Pressure Drag ◽  
Body Potential

In a recent study by Yeung & Parkinson (1997), a wake width was proposed which allowed the bluff-body potential-flow model by Parkinson & Jandali (1970) to be extended to include the flow around an oblique flat plate. By incorporating this wake width in the momentum equation originally derived by Eppler (1954) for separated flow, the drag of the plate is related to its inclination and base pressure through a simple analytical condition. It allows the base pressure, which is usually treated as an empirical input, to be determined theoretically and thus the model becomes self-contained. Predictions of the base pressure, drag and width of wake are found to be in reasonable agreement with the experimental data. When applied to the symmetrical flow around a wedge of arbitrary vertex angle, similar agreement with experimental measurements is obtained as well. It is also demonstrated that this condition is compatible with the free-streamline models by Wu (1962) and Wu & Wang (1964) such that the corresponding predictions are in good agreement with experiment.

Vortex shedding from bluff bodies in a shear flow

1973 ◽  
Vol 60 (2) ◽  
pp. 401-409 ◽  
Author(s):  
D. J. Maull ◽  
R. A. Young
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Uniform Flow ◽  
Base Pressure ◽  
Longitudinal Vortex ◽  
Bluff Bodies ◽  
Stream Direction

Experiments are described in which the vortex shedding from a bluff body and the base pressure coefficient have been measured in a shear flow. It is shown that the shedding breaks down into a number of spanwise cells in each of which the frequency is constant. The division between the cells is thought to be marked by a longitudinal vortex in the stream direction and this is supported by evidence from experiments where a longitudinal vortex was generated in an otherwise uniform flow.

Numerical and Experimental Evaluation of Lift Forces in Flows Around Surface-Mounted Bluff Bodies

2002 ◽  
Author(s):  
T. Stengel ◽  
F. Ebert ◽  
M. Fallen
Keyword(s):  
Velocity Field ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Separation Zone ◽  
Laser Doppler Anemometry ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
The Body ◽  
Bluff Bodies ◽  
Large Eddy

The flow around a surface-mounted bluff body with cuboid shape is investigated. Therefore, the velocity field including the distribution of the turbulent kinetic energy is computed and compared with experimental Laser Doppler Anemometry data. Several different turbulence models, namely the standard k-ε model, the Wolfshtein two-layer k-ε model and a Large-Eddy approach are validated. Since the Large-Eddy model remains the only model representing the flow accurate, it is chosen for further investigations. The pressure distribution on the body and on the carrying surface around the body is analysed. The lift coefficients are computed for Reynolds numbers, ranging from 1.1 × 104 up to 4.4 × 104. The lengths of the separation zone above and the recirculation zone downstream the body are evaluated.

CFD Study of the Pressure Distribution on the Back of a 3-D Bluff Body (CUBE) of Air Flow in Different Reynolds Numbers

2009 ◽  
Author(s):  
Mohammad Javad Izadi ◽  
Pegah Asghari ◽  
Malihe Kamkar Delakeh
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Free Stream ◽  
Fluid Flows ◽  
Reynolds Numbers ◽  
The Body ◽  
Stream Velocity ◽  
Bluff Bodies ◽  
Unsteady Forces ◽  
Flow Round

The study of flow around bluff bodies is important, and has many applications in industry. Up to now, a few numerical studies have been done in this field. In this research a turbulent unsteady flow round a cube is simulated numerically. The LES method is used to simulate the turbulent flow around the cube since this method is more accurate to model time-depended flows than other numerical methods. When the air as an ideal fluid flows over the cube, flow separate from the back of the body and unsteady vortices appears, causing a large wake behind the cube. The Near-Wake (wake close to the body) plays an important role in determining the steady and unsteady forces on the body. In this study, to see the effect of the free stream velocity on the surface pressure behind the body, the Reynolds number is varied from one to four million and the pressure on the back of the cube is calculated numerically. From the results of this study, it can be seen that as the velocity or the Reynolds number increased, the pressure on the surface behind the cube decreased, but the rate of this decrease, increased as the free stream flow velocity increased. For high free stream velocities the base pressure did not change as much and therefore the base drag coefficient stayed constant (around 1.0).

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

A note on bluff body vortex formation

1995 ◽  
Vol 284 ◽  
pp. 217-224 ◽  
Author(s):  
Owen M. Griffin
Keyword(s):  
Bluff Body ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Initial Position ◽  
Bluff Bodies ◽  
Near Wake ◽  
Formation Region ◽  
Low Reynolds Numbers ◽  
Region Length ◽  
Low Reynolds

Green & Gerrard (1993) have presented in a recent paper the results of experiments to measure the distribution of vorticity in the near wake of a circular cylinder at low Reynolds numbers (up to Re = 220). They also compared the various definitions of the vortex formation region length which have been proposed by Gerrard (1966), Griffin (1974), and others for both high and low Reynolds numbers. The purpose of this note is to expand the work of Green & Gerrard, and to further their proposition that the end of the vortex formation region at all Reynolds numbers mark both the initial position of the fully shed vortex and the location at which its strength is a maximum. The agreement discussed here between several definitions for the formation region length will allow further understanding to be gained from investigations of the vortex wakes of stationary bluff bodies, and the wakes of oscillating bodies as well.

On the Relationships Among Strouhal Number, Pressure Drag, and Separation Pressure for Blocked Bluff-Body Flow

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
W. W. H. Yeung
Keyword(s):  
Experimental Data ◽  
Strouhal Number ◽  
Bluff Body ◽  
Current Method ◽  
Momentum Equation ◽  
Pressure Drag ◽  
Bluff Body Flow ◽  
Confined Environment ◽  
Axisymmetric Bodies ◽  
Statistical Results

Strouhal number, pressure drag, and separation pressure are some of the intrinsic parameters for investigating the flow around a bluff-body. An attempt is made to formulate a relationship involving these quantities for flow around a two-dimensional bluff section of various shapes in a confined environment such as a wind tunnel. It includes (a) establishing a relation between the Strouhal number and a modified Strouhal number by a theoretical wake width and (b) incorporating this wake width into a momentum equation to determine the pressure drag. Comparisons have been made with the experimental data, a theoretical prediction (for unconfined flow), and an empirical proposal in literature to indicate that the present methodology is appropriate. Together with its extension to axisymmetric bodies, the current method is able to provide proper limits to the experimental data for a rectangular flat-plate of various width-to-span ratios. In addition, if the separation pressure is given, then the Strouhal number is inversely proportional to the drag coefficient, being comparable to a proposal based on statistical results. Finally, through an example, it is also demonstrated how one of these three parameters may be reasonably estimated from the measured values of the other two.

Hydrodynamics and Heat Convection From a Disk Facing a Uniform Flow

Volume 1 ◽  
2004 ◽  
Author(s):  
Abdullah Abbas Kendoush
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Pressure Distribution ◽  
Dynamical Behavior ◽  
Circular Disk ◽  
Reynolds Numbers ◽  
Inviscid Flows ◽  
High Reynolds Numbers ◽  
Axis Of Symmetry ◽  
High Reynolds

Exact solutions of the equations of momentum and energy of a circular disk in a uniform incompressible flow directed along its axis of symmetry are obtained. Laminar, irrotational and inviscid flows were assumed. The solutions for the pressure distribution, drag coefficient and convective heat transfer of the disk are presented in explicit forms. Some peculiar fluid-dynamical behavior of the pressure distribution at low and high Reynolds numbers are revealed. The derived equations were agreeable with other numerical and analytical solutions and experimental data.

A universal Strouhal number for the ‘locking-on’ of vortex shedding to the vibrations of bluff cylinders

1978 ◽  
Vol 85 (3) ◽  
pp. 591-606 ◽  
Author(s):  
Owen M. Griffin
Keyword(s):  
Strouhal Number ◽  
Reynolds Numbers ◽  
Base Pressure ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Pressure Drag ◽  
Wide Range ◽  
Pressure Parameter ◽  
The Individual ◽  
Good Agreement

It is well known that the vortices shed from a circular cylinder lock on in frequency to the vibrations when the cylinder is forced to vibrate or is naturally excited to sufficient amplitudes by flow-induced forces. This paper presents a model for a universal wake Strouhal number, valid in the subcritical range of Reynolds numbers, for both forced and vortex-excited oscillations in the locking-on regime. The Strouhal numbers thus obtained are constant atSt*= 0·178 over the range of wake Reynolds numbersRe*= 700-5 × 104. This value is in good agreement with the results obtained by Roshko (1954a) and Bearman (1967) for stationary circular cylinders and other bluff bodies in the same range of Reynolds numbers. A correspondence between the amplification of the cylinder base pressure, drag and vortex circulation is demonstrated over a wide range of frequencies and for vibration amplitudes up to a full cylinder diameter (peak to peak). The fraction ε of the shed vorticity in the individual vortices is found to be dependent upon the base-pressure parameter K = (1 −Cpb)½. Consequently, ε is also a function of the amplitude and frequency of the vibrations in the locking-on regime.

Flow Profile Around Bluff Body

1986 ◽  
pp. 38-42
Author(s):  
Abdul Aziz Ibrahim
Keyword(s):  
Experimental Data ◽  
Analytical Study ◽  
Bluff Body ◽  
Vertical Component ◽  
Bluff Bodies ◽  
Flow Profile ◽  
Roughness Effects ◽  
Turbulence Effect ◽  
First Time ◽  
Logarithmic Velocity Profile

This paper presents the results of an analytical study on local scour around bluff bodies. An equation has been developed which allowed the velocity distribution of the vertical component of velocity induced by the presence of a body to be predicted. The equation, equation (16) was obtained by re-organising known facts and incorporating them in a new fashion e.g. the logarithmic velocity profile was modified to include turbulence effect. Much of this has been done before but it is believed that this is the first time that the particular combination of turbalence effects, roughness effects, etc has been presented. Equation ( 16) is a modification of equation (16) in reference (7).The predicted vertical velocity distributions have been compared with analytically obtained data from previous investigations. The results of the comparison are encouraging but unfortunately not conclusive due to the lack of sufficient reliable experimental data.

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