A Correction Formula for Wall Effects on Unsteady Forces of Two-Dimensional Bluff Bodies

1994 ◽  
Vol 116 (3) ◽  
pp. 414-418 ◽  
Author(s):  
Terukazu Ota ◽  
Yasunori Okamoto ◽  
Hiroyuki Yoshikawa
Keyword(s):  
Flow Characteristics ◽  
Separated Flow ◽  
Elliptic Cylinder ◽  
Vortex Method ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Wall Effects ◽  
Discrete Vortex ◽  
Correction Formula ◽  
Wide Range

In wind tunnel studies on the flow around bluff bodies accompanying a large separated wake, the walls of the test section severely effect the flow characteristics around them. Proposed in this paper is a correction formula for the wall effects upon two-dimensional (2-D) unsteady separated flow of incompressible fluid around bluff bodies. The proposed formula is derived from numerical results with the discrete vortex method on 2-D separated flows around an inclined flat plate, a square cylinder, and also an elliptic cylinder located between two parallel walls. It is found that the present correction formula estimates reasonably well the wall effects upon the mean and fluctuating force coefficients over a wide range of blockage ratio and angle of attack through comparing the present calculated results with numerous experimental ones by several authors.

Discrete Vortex Simulation of Pulsating Flow Behind a Normal Plate

1994 ◽  
Vol 116 (4) ◽  
pp. 862-869 ◽  
Author(s):  
Hyung Jin Sung ◽  
Young Nam Kim ◽  
Jae Min Hyun
Keyword(s):  
Numerical Study ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Vortex Method ◽  
Threshold Value ◽  
Numerical Results ◽  
Pulsation Frequency ◽  
Discrete Vortex ◽  
Freestream Velocity ◽  
Variable Position

A numerical study is made of the separated flow behind a flat plate. The plate is placed normal to the direction of the approach flow. The oncoming freestream velocity contains a pulsating part, U∞ = U0(1 + A0cosfpt). The temporal behavior of vortex shedding patterns is scrutinized over broad ranges of the two externally specified parameters, i.e., the pulsation amplitude (A0≤ 0.6), and the dimensionless pulsation frequency, (fp≤0.32). A version of the discrete vortex method is utilized. The variable-position nascent vortex technique is applied, and it proves to be adequate for pulsating approach flows. The numerical results clearly capture the existence of lock-on when fp exceeds a threshold value. The modulation of vorticity shedding is also detected when fp is reasonably low. The influence of A0 on the flow characteristics is examined in detail. As A0 increases to a moderate value (e.g., A0≤0.6), an appreciable broadening is seen of the range of fp for which lock-on occurs. Based on the numerical results, three characteristic flow modes in the wakes are identified. These findings are qualitatively consistent with the existing flow-visualization studies for a cylinder.

Theoretical Study on the Flow About Savonius Rotor

1984 ◽  
Vol 106 (1) ◽  
pp. 85-91 ◽  
Author(s):  
Takenori Ogawa
Keyword(s):  
Dimensional Analysis ◽  
Theoretical Study ◽  
Separated Flow ◽  
Vortex Method ◽  
Experimental Results ◽  
Two Dimensional ◽  
Discrete Vortex ◽  
Discrete Vortex Method ◽  
Savonius Rotor ◽  
Singularity Method

A method for the two-dimensional analysis of the separated flow about Savonius rotors is presented. Calculations are performed by combining the singularity method and the discrete vortex method. The method is applied to the simulation of flows about a stationary rotor and a rotating rotor. Moreover, torque and power coefficients are computed and compared with the experimental results presented by Sheldahl et al. Theoretical and experimental results agree well qualitatively.

scholarly journals Bilge-Keel Influence on Free Decay of Roll Motion of a Realistic Hull1

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Yichen Jiang ◽  
Ronald W. Yeung
Keyword(s):  
Free Surface ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Vortex Method ◽  
Roll Motion ◽  
Two Dimensional ◽  
Desktop Computer ◽  
Roll Damping ◽  
Discrete Vortex ◽  
Bilge Keel

The prediction of roll motion of a ship with bilge keels is particularly difficult because of the nonlinear characteristics of the viscous roll damping. Flow separation and vortex shedding caused by bilge keels significantly affect the roll damping and hence the magnitude of the roll response. To predict the ship motion, the Slender-Ship Free-Surface Random-Vortex Method (SSFSRVM) was employed. It is a fast discrete-vortex free-surface viscous-flow solver developed to run on a standard desktop computer. It features a quasi-three-dimensional formulation that allows the decomposition of the three-dimensional ship-hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier–Stokes solver Free-Surface Random-Vortex Method (FSRVM) can be applied. In this paper, the effectiveness of SSFSRVM modeling is examined by comparing the time histories of free roll-decay motion resulting from simulations and from experimental measurements. Furthermore, the detailed two-dimensional vorticity distribution near a bilge keel obtained from the numerical model will also be compared with the existing experimental Digital Particle Image Velocimetry (DPIV) images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll-decay coefficients and the flow field are altered by the span of the bilge keels. Plots of vorticity contour and vorticity isosurface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the keels.

Indicial Function Predictions of Two Dimensional Unsteady Viscous Flows Around Bluff Bodies Based on Discrete Vortex Simulations

2012 ◽  
Author(s):  
H. Yadollahi Farsani ◽  
L. Ebrahimnejad ◽  
P. Marzocca ◽  
K. D. Janoyan ◽  
D. T. Valentine
Keyword(s):  
Lift Coefficient ◽  
Least Square Method ◽  
Least Square ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Discrete Vortex ◽  
Flow Solver ◽  
Aeroelastic Analysis ◽  
Unsteady Viscous Flow ◽  
Aerodynamic Moment

This paper provides aerodynamic indicial functions obtained through a discrete vortex computational fluid dynamics method for two-dimensional geometries, including two canonical sections, rectangular and elliptical shapes, and the Great Belt Bridge cross section. This methodology enables one to determine the unsteady lift and aerodynamic moment necessary in aeroelastic analysis of flexible bodies including flutter and vortex induced vibration. The predictions were obtained using an unsteady viscous flow solver, DVMFLOW, developed by COWI. The indicial functions developed have two exponential groups which parameters have been obtained using a nonlinear least square method. The numerical investigations show significant flow separation for the presented sections and an enhanced dynamic stall region at the initiation of a transient leading to higher values in the lift coefficient response. Vortex shedding frequency was also determined and the results are compared with other studies in the literature.

scholarly journals Two dimensional simulation of laminar flow by three- jet in a semi-confined space

2020 ◽  
Vol 9 (1) ◽  
pp. 111-117
Author(s):  
Mohammad Mosaddeghi
Keyword(s):  
Laminar Flow ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Confined Space ◽  
Wide Range ◽  
Critical Reynolds Numbers ◽  
Dimensional Simulation ◽  
Geometric Changes

AbstractEquipment performance improvement in a wide range of working conditions is one of the major goals of aerodynamics. This goal can be achieved by the deformation of the object being examined or by using flow control techniques in active or inactive modes. In different researches, how to change the development ratio on the semi-confined space with input jet system is surveyed. In this study, two-dimensional simulation of the flow has been investigated in three-jet laminar flow in a semi-confined space. To determine the effective and optimal mixing in a laminar flow, critical Reynolds numbers were determined to distinguish when the flow in the channel from a steady-state symmetric flowformed downstream recirculation and ultimately transient flow. To better understand the flow characteristics, the simulations were changed at a fixed jet spacing (input jets distance to height of space ratio). Also, in this paper, for comparison, four jets were considered. Based on the results, it was observed that in all cases, mixing occurred in the space between three jets. Placing the jet along the walls of the semi-confined space allows the best combination, and increase in the distance between the first and third jets and reduction of the particle coefficient caused to reach the critical Reynolds number faster and, as a result, mixing in a laminar flow with geometric changes of the semi-confined space.

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