scholarly journals Discrete Vortex Prediction of Flows around a Cylinder Near a Wall Using Overlapping Grid System

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 211
Author(s):  
Wisnu Wardhana ◽  
Ede Mehta Wardhana ◽  
Meitha Soetardjo
Keyword(s):  
Grid Point ◽  
The Body ◽  
Cylinder Surface ◽  
Grid System ◽  
Vortex Interaction ◽  
Discrete Vortex ◽  
Cpu Time ◽  
Comparison Of The Results ◽  
Circular Grid ◽  
Interaction Velocity

Modelling of unidirectional and oscillatory flows around a cylinder near a wall using an overlapping grid system is carried out. The circular grid system of the cylinder was overlapped with the rectangular grid system of the wall. The use of such an overlapping grid system is intended to reduce the CPU time compared to the cloud scheme in which vortex-to-vortex interaction is used, i.e., especially in calculating the shedding vortex velocity, since calculating the vortices velocity takes the longest CPU time. This method is not only time efficient, but also gives a better distribution of surface vorticity as the scattered vortices around the body are now concentrated on a grid point. Therefore, grid-to-grid interaction is used instead of vortex-to-vortex interaction. Velocity calculation was also carried out using this overlapping grid in which the new incremental shift position was summed up to obtain the total new vortices position. The engineering applications of this topic are to simulate the loading of submarine pipeline placed close to the seabed or to simulate the flow as a result of the scouring process below the cylinder since there is space for the fluid to flow beneath it. The in-line and transverse force coefficients are found by integrating the pressure around the cylinder surface. The flow patterns are then obtained and presented. The comparison of the results with experimental evidence is presented and the range of good results is discussed.

scholarly journals Vortex Simulation of Two Cylinders in Tandem Using Overlapping Grid System

2020 ◽  
Author(s):  
Wisnu Wardhana ◽  
Ede Wardhana ◽  
Meitha Soetardjo
Keyword(s):  
Grid Point ◽  
The Body ◽  
Structural Elements ◽  
Grid System ◽  
Considerable Time ◽  
Discrete Vortex ◽  
Cpu Time ◽  
Tandem Cylinders ◽  
Flow Phenomena ◽  
Comparison Of The Results

Abstract To give a considerable time reduction in the calculation of the vortex velocity and in the CPU time, discrete vortex modelling of flows using overlapping grid system for two tandem cylinders is carried out. This simple and time efficient method gives a better scatter of surface vorticity as the vortices around the body are now calculated on grid point. This research is to simulate the loading on structural elements of the structures due to their interaction with anodes or with other members. To show the flow phenomena and interactions involved, the in-line and transverse force coefficients are presented. The comparison of the results with experimental and numerical results and the range for good results is presented.

scholarly journals Discrete Vortex Method Of Flow Around A Cylinder In A Channel Using Simple Grid System

2021 ◽  
Vol 12 (4) ◽  
pp. 1121-1134
Author(s):  
Wisnu Wardhana, Et. al.
Keyword(s):  
Grid Point ◽  
Vortex Method ◽  
The Body ◽  
Cylinder Surface ◽  
Cylinder Wall ◽  
Grid System ◽  
Rectangular Grid ◽  
Discrete Vortex ◽  
Cpu Time ◽  
Polar Grid

Modelling of unidirectional and oscillatory flows around a cylinder in a channel using a simple overlapping grid system are carried out. The importance of this cylinder-wall configuration is the effect of blockage which suppress the development of the vortex shedding The polar grid system of the cylinder is then overlapped with the rectangular grid system of the wall. The length of rectangular grid element is about the same as the length of the polar grid system in the cylinder surface. The use of such overlapping grid system is for reducing the CPU time, i.e. in calculating the vortex velocity since the CPU time in calculating the vortices velocity takes the longest time. This method is not only time efficient, but also gives a better distribution of surface vorticity as the scattered vortices around the body are now concentrated on grid point. In this study there is no vortex-to-vortex interaction, but instead it uses node-to-node interactions. Velocity calculation also uses this overlapping grid in which the new incremental shift position then summed up to get the total new vortices position. In this overlapping system the grid can be either off or on depend on process involved to get rid of the nodes not being used. The engineering applications of this topic is to simulate the loading pipeline placed in the channel such as in the heat exchanger or simulation of U-tube experiment or other system. The in-line and transverse force coefficients are found by integrating the pressure around the cylinder surface. The flow patterns are then can be obtained and presented. The comparison of the results with experimental evidence is presented and also the range of good results is discussed.

scholarly journals NUMERICAL SIMULATION OF THE FLOW AROUND A SQUARE CYLINDER USING THE VORTEX METHOD

2004 ◽  
Vol 3 (2) ◽  
pp. 161
Author(s):  
V. G . Guedes ◽  
G . C. R. Bodstein ◽  
M. H. Hirata
Keyword(s):  
Reynolds Number ◽  
Incompressible Flows ◽  
Pressure Coefficient ◽  
Vortex Method ◽  
Panel Method ◽  
The Body ◽  
Cylinder Surface ◽  
Square Cylinder ◽  
Aerodynamic Forces ◽  
Discrete Vortex

The study of external incompressible flows around bluff bodies finds extensive applicability to real-life problems. Such flows are characterized by unsteady flow separation for high values of the Reynolds number, where a Von Karman-type periodic wake is formed. The prediction of these flows is very difficult, and one has usually to rely on specific experimental data to calculate the aerodynamic forces on the body. In order to numerically simulate this flow, this paper uses a new mesh-free two-dimensional Discrete Vortex Method associated with a Panel Method to calculate the lift and drag coefficients, as well as the pressure coefficient on a square cylinder, for a high Reynolds number flow. Lamb vortices are generated along the cylinder surface, whose strengths are determined to ensure that the no-slip condition is satisfied and that circulation is conserved. The impermeability condition is imposed through a source panel method, so that mass conservation is explicitly enforced. The dynamics of the body wake is computed using the convection-diffusion splitting algorithm, where the diffusion process is simulated using the random walk method, and the convection process is carried out with a lagrangian second-order time-marching scheme. Results for the aerodynamic forces and pressure distribution are presented.

scholarly journals NUMERICAL SIMULATION OF THE FLOW AROUND A SQUARE CYLINDER USING THE VORTEX METHOD

2004 ◽  
Vol 3 (2) ◽  
Author(s):  
V. G . Guedes ◽  
G . C. R. Bodstein ◽  
M. H. Hirata
Keyword(s):  
Reynolds Number ◽  
Incompressible Flows ◽  
Pressure Coefficient ◽  
Vortex Method ◽  
Panel Method ◽  
The Body ◽  
Cylinder Surface ◽  
Square Cylinder ◽  
Aerodynamic Forces ◽  
Discrete Vortex

The study of external incompressible flows around bluff bodies finds extensive applicability to real-life problems. Such flows are characterized by unsteady flow separation for high values of the Reynolds number, where a Von Karman-type periodic wake is formed. The prediction of these flows is very difficult, and one has usually to rely on specific experimental data to calculate the aerodynamic forces on the body. In order to numerically simulate this flow, this paper uses a new mesh-free two-dimensional Discrete Vortex Method associated with a Panel Method to calculate the lift and drag coefficients, as well as the pressure coefficient on a square cylinder, for a high Reynolds number flow. Lamb vortices are generated along the cylinder surface, whose strengths are determined to ensure that the no-slip condition is satisfied and that circulation is conserved. The impermeability condition is imposed through a source panel method, so that mass conservation is explicitly enforced. The dynamics of the body wake is computed using the convection-diffusion splitting algorithm, where the diffusion process is simulated using the random walk method, and the convection process is carried out with a lagrangian second-order time-marching scheme. Results for the aerodynamic forces and pressure distribution are presented.

A numerical study of vortex interaction

1984 ◽  
Vol 146 ◽  
pp. 331-345 ◽  
Author(s):  
I. G. Bromilow ◽  
R. R. Clements
Keyword(s):  
Flow Visualization ◽  
Numerical Study ◽  
Experimental Studies ◽  
Shear Layers ◽  
Controlled Study ◽  
Vortex Interaction ◽  
Flow Conditions ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Discrete Vortex Model

Flow visualization has shown that the interaction of line vortices is a combination of tearing, elongation and rotation, the extent of each depending upon the flow conditions. A discrete-vortex model is used to study the interaction of two and three growing line vortices of different strengths and to assess the suitability of the method for such simulation.Many of the features observed in experimental studies of shear layers are reproduced. The controlled study shows the importance and rapidity of the tearing process under certain conditions.

Numerical Simulation of Rivulet Dynamics Associated With Rain-Wind Induced Vibration

2010 ◽  
Author(s):  
Ian J. Taylor ◽  
Andrew C. Robertson
Keyword(s):  
Flow Field ◽  
Thin Liquid Film ◽  
Vortex Method ◽  
The Body ◽  
Wind Loading ◽  
External Loading ◽  
Discrete Vortex ◽  
Unsteady Aerodynamic ◽  
Karman Vortex ◽  
Wind Induced Vibration

On wet and windy days, the inclined cables of cable-stayed bridges can experience large amplitude, potentially damaging oscillations known as Rain-Wind Induced Vibration (RWIV). The phenomenon is believed to be the result of a complicated nonlinear interaction between rivulets of rain water that run down the cables and the wind loading on the cables due to the unsteady aerodynamic flow field. A numerical method has been developed at the University of Strathclyde, to simulate aspects of RWIV, the results of which can be used to assess the importance of the water rivulets on the instability. This combines a Discrete Vortex Method solver to determine the external flow field and unsteady aerodynamic loading and a pseudo-spectral solver based on lubrication theory to model the water on the surface of the body and which is used to determine the evolution and growth of the water rivulets under external loading. These two models are coupled to simulate the interaction between the aerodynamic field and the thin liquid film on a horizontal circular cylinder. The results illustrate the effects of various loading combinations, and importantly demonstrate rivulet formation in the range of angles previous research has indicated that these may suppress the Karman vortex and lead to a galloping instability. These rivulets are found to be of self limiting thickness in all cases.

Evaluation of Radiation Doses from Computed Tomography Conducted in Al Jouf Region (Saudi Arabia)

2021 ◽  
Vol 11 (8) ◽  
pp. 2130-2136
Author(s):  
Ziyad Awadh Alrowaili ◽  
M. Ashari
Keyword(s):  
Computed Tomography ◽  
Saudi Arabia ◽  
Effective Dose ◽  
Computer Software ◽  
Northern Region ◽  
The Body ◽  
Adult Patients ◽  
Dose Length Product ◽  
Comparison Of The Results ◽  
Dose Index

A safe radiation dose from computed tomography (CT) is normally specified through the Computed Tomography Dose Index (CTDI) as an “effective dose.” Radiation exposure from CT is relatively high in comparison with other radiological tests. In this paper, we evaluate doses used on adult patients during typical CT scans, in Al Jouf, the northern region of Saudi Arabia. Scanning processes were taken place in different parts of the body; including the pelvis, head, abdomen, and chest. The dose indices were calculated using the CT-expo v2.5 computer software. A comparison of the results with similar investigations, regionally and globally, was made. Other comparisons between displayed and calculated dose indices were also performed. The main values of CT volume are the dose index (CTDIvol) and dose-length product (DLP). The effectiveness results for head CTs were 45.0 mGy, 488 mGy.cm, and 5.2 mSv; while for pelvic CTs they were 16.4 mGy, 391 mGy.cm, and 4.0 mSv; whereas for abdominal CTs they were 22.2 mGy, 613 mGy.cm, and 6.5 mSv; finally they were 17.5 mGy, 380 mGy.cm, and 3.9 mSv for chest CTs. It is confirmed that the values obtained are within the internationally accepted values, except for the values of the head examination, in which the effective dose value of 5.2 mSv was higher than the recommended value. This work gives an overview of the doses received by adult patients during regular CT examination. It is the first regional CT dose survey and provides a baseline for improvement and quality control in the region of Al Jouf.

Effect of vortex shedding on the coupled roll response of bodies in waves

1988 ◽  
Vol 189 ◽  
pp. 243-261 ◽  
Author(s):  
M. J. Downie ◽  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Vortex Shedding ◽  
Degrees Of Freedom ◽  
Rectangular Cross Section ◽  
Vortex Method ◽  
The Body ◽  
Wave Radiation ◽  
Viscous Damping ◽  
Discrete Vortex ◽  
Hydrodynamic Damping ◽  
Main Component

Hydrodynamic damping of floating bodies is due mainly to wave radiation and viscous damping. The latter is particularly important in controlling those responses of the body for which the wave damping is small. The roll response of ship hulls near resonance in beam seas is an example of this. The present paper applies a discrete vortex method as a local solution to model vortex shedding from the bilges of a barge hull of rectangular cross-section and hence provides an analytic method for predicting its coupled motions in three degrees of freedom, including the effects of the main component of viscous damping. The method provides a frequency-domain solution satisfying the full linearized boundary conditions on the free surface.

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