• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.350-357
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• 1997

The transient incompressible flow behind the axisymmetric bluff body is numerically simulated using the random vortex method(RVM). Based on the vorticity formulation of the unsteady Navier-Stokes equations, the Lagrangian approach with a stochastic simulation of diffusion using random walk technique is employed to account for the transport processes of the vortex elements. The numerical solutions for 2-dimensional recirculating flow behind a backward-facing step in the laminar range of Reynolds number are compared with experimental data. The present simulation focuses on the transitional flow regime where the recirculation zone behind the bluff body becomes highly unsteady and large-scale vortex eddies are shed from the bluff body wake due to intrinsic shear layer instabilities. The unsteady vertical flow structures and the mixing characteristics behind the bluff body are discussed in detail.

• Journal of Industrial Technology
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• v.15
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• pp.153-168
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• 1995

The purpose of this study is to develop a method for predicting the aerodynamic performance of the subsonic airfoils in the 2-dimensional, steady and viscous flow. For this study, the airfoil geometry is specified by adopting the longest chord line system and by considering local surface curvature. In case of the inviscid-incompressible flow, the analysis is accomplished by the linearly varying strength vortex panel method and the Karman-Tsien correction law is applied for the inviscid-compressible flow analysis. The Goradia's integral method and the Truckenbrodt integral method are adopted for the boundary layer analysis of the laminar flow and the turbulent flow respectively. Viscous and inviscid solutions are converged by the Lockheed iterative calculating method using the equivalent airfoil geometry. And the analysis of the seperated flow is performed using the Dvorak and Maskew's method as the basic method. The wake effect is also considered and its geometry expressed by the formula of Summey & Smith when no seperation occurs. A computational efficiency is verified by the comparison of the computational results with experimental data and by the shorter execution time.

• Journal of the Korean Society of Visualization
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• v.18 no.2
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• pp.39-45
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• 2020

Problems related with flows around structures are typical in various engineering fields. The characteristics of these flow structures depend strongly on the shape of the body. The flow regime around square cylinders which are also employed in various applications has also been investigated. In addition to a single body, flows past closely spaced structures arranged in tandem are observed in numerous practical applications. In this study, the flow characteristics around the circular and the square cylinder were investigated according to S/D. The velocity fields and Reynolds stress of the single cylinders were acquired to explain the flow behaviors between tandem cylinders. The differences observed in the flow behaviors of square and circular cylinders were studied. The flow patterns around two tandem cylinders can be classified into three types of wake interference behaviors according to S/D. This is related with the flows between cylinders.

• Journal of Ship and Ocean Technology
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• v.4 no.3
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• pp.33-45
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• 2000

A computational system for wave and viscous flow analysis (WAVIS) has been developed. The system includes a pre-processor, flow solvers and a post-processor. The pre-processor is composed of full form presentation, surface mesh and field grid generation. The flow solvers are for potential and viscous flow calculation. The post-processor has graphic utility for result analysis. All the programs are integrated in a GUI-launcher package. To validate the developed CFD programs of WAVIS, the calculated results for modern commercial hull forms are compared with measurements. It is found that the results from WAVIS are in good agreement with the experimental data, illustrating the accuracy of the numerical methods employed for WAVIS.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.5
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• pp.1076-1085
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• 2001

Experimental investigations of the longitudinal vortices, which are produced by wing type vortex generators set up behind a circular cylinder in a rectangular channel, are presented. When the circular cylinder is set up in the rectangular channel, a horseshoe vortex is formed just upsteam of the circular cylinder. It generates a turbulent wake region behind the circular cylinder. Therefore, the region of the pressure loss behind the circular cylinder in increased and the size of the wake is small. These problems can be achieved by longitudinal vortices which are generated by wing-type vortex generator. In order to control the strength of longitudinal vortices, the angle of attack of the vortex generators is varied from 20 degree to 45, but the spacing between the vortex generators is fixed 6cm. The 3-dimensional mean velocity measurements are made using a five-hole probe. The vorticity field and streamwise velocity contour are obtained from the velocity field. The following results are obtained. Circulation strength is the maximum value when the angle of attack($\beta$) is $30^{\circ}$, and the vorticity field and streamwise velocity contour in case of $\beta$=$20^{\circ}$ show the trend similar to these in case of $\beta$=$30^{\circ}$, but do not in case of $\beta$=$45^{\circ}$.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.2
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• pp.157-164
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• 2015

The present work performs three-dimensional flow calculations based on Reynolds Averaged Navier-Stokes (RANS) and Delayed Detached Eddy Simulation (DDES) to investigate the flow field of a transonic rotor (NASA Rotor 37) at near-stall condition. It is found that the DES approach is likely to predict well the complex flow characteristics such as secondary vortex or turbulent flow phenomenon than RANS approach, which is useful to describe the flow mechanism of a transonic compressor. Especially, the DES results show improvement of predicting the flow field in the wake region and the model captures reasonably well separated regions compared to the RANS model. Besides, it is discovered that the three-dimensional vortical flows after the vortex breakdown from the rotor tip region are widely distributed and its vortex structures are clearly present. Near the rotor leading edge, a part of the tip leakage flows in DES solution spill over into next passage of the blade owing to the separation vortex flow and the backflow is clearly seen around the trailing edge of rotor tip. Furthermore, the DES solution shows strong turbulent eddies especially in the rotor hub, rotor tip section and the downstream of rotor trailing edge compared to the RANS solution.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.4
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• pp.551-559
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• 2014

The influence of the battle damage hole on the velocity and vorticity flow field have been studied by using particle image velocimetry. Time averaged velocity and vorticity vector fields in the vicinity of jet are presented. The perforated damage hole on a wing created from a hit by anti-air artillery was modeled as a 10% chord size hole which positioned at quarter chord. At low angles of attack, the vorticity in the forward side of the jet is cancelled due to mixing with the wing surface boundary layer. Stretching of vorticity in the backside of the jet generates a semi-cylindrical vortical layer that enclosing a domain with slow moving reverse flow. Conversely, at higher the angles of attack, the jet vorticity advected away from the wing surface and remains mostly confined to the jet. The mean flow behind the jet has a wake-like structure.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.38-45
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• 2000

A breaking-wave caused by a cylinder moving under the free-surface is studied, which is designed to unveil the interaction between breaker and cylinder using PIV at CWC. The detailed structures of the vortical flow is obtained from the velocity field measured by PIV technique. The vorticity distribution behind the breaker and originated from the breaker. It has been obvious that the vortices from breaker greatly affect the whole wake field at S/D=1. Certainly PIV was confirmed to be a very versatile means to investigate the complex flow fields such as breaking wave.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.11-20
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• 2012

In this paper, the authors test various open codes and commercial codes based on CFD technology on the wind field around the complex terrain, which is a very important transport physics in the event of forrest fire. To study the physical mechanism inside the transition from surface fire to crown fire, the wake flow behind a parallel array of trees is studied numerically to show the flow separation in the turbulent boundary layer. Two sites near to Kunsan National University are chosen for the measurement of real wind field, and obtained data are compared with those from various computational codes such as Wind-Ninja, NIST-FDS, ANSYS-CFX, and ANSYS-FlUENT, etc. Through this research, feasibility and accuracy of the present CFD codes are investigated quantitatively, compared with the measured data with AWS.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2617-2629
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• 1995

The flow through a centrifugal compressor rotor was calculated using the quasi-3-dimensional and fully 3-dimensional Navier-Stokes solution methods. The calculated results, obtained during the development of the computer codes for both methods are discussed. In the inviscid quasi 3-dimensional analysis, stream function formulation was used for the blade to blade (B-B) plane calculations, and the streamline curvature method was used for the meridional (H-S) plane calculations. In the viscous 3-dimensional flow analysis, a control volume method based on a general rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. The quasi-3-dimensional analysis reasonably predicts the pressure distributions and requires much less computation time in the region where viscous effects are not strong; however, it fails to predict velocity field and loss mechanism through the impeller passage. The viscous 3-dimensional flow analysis shows reasonable pressure distributions and typical jet-wake flow field through the impeller passage. Secondary flow and total pressure distributions on cross-sectional planes explain the loss mechanisms through the impeller.