• 대한조선학회논문집
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• 제43권2호
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• pp.186-196
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• 2006

The turbulent wake flow of an axisymmetric body at incidence of $10.1^{\circ}$ is investigated by commericial CFD code, Fluent 6.2. Reynolds stress turbulence model with wall function is applied for the turbulent flow computation. For the grid generation, the Gridgen V15 is used. Numerical predictions are compared with experimental data for the validation. The computed results show goof agreements with the experimental measurements, implying that the CFD analysis is a useful and efficient tool for predicting turbulent flow characteristics of wake field of an axisymmetric body at incidence.

• 대한기계학회논문집B
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• 제24권7호
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• pp.945-956
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• 2000

The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.295-302
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• 2009

The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the following fundamental question: is it possible to compute the circumferentially averaged flow field induced by the precessing vortex rope by using an axisymmetric turbulent swirling flow model? In other words, instead of averaging the measured or computed 3D velocity and pressure fields we would like to solve directly the circumferentially averaged governing equations. As a result, one could use a 2D axi-symmetric model instead of the full 3D flow simulation, with huge savings in both computing time and resources. In order to answer this question we first compute the axisymmetric turbulent swirling flow using available solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Numerical results obtained with both models are compared against measured axial and circumferential velocity profiles, as well as for the vortex rope location. Although the circumferentially averaged flow field cannot capture the unsteadiness of the 3D flow, it can be reliably used for further stability analysis, as well as for assessing and optimizing various techniques to stabilize the swirling flow. In particular, the methodology presented and validated in this paper is particularly useful in optimizing the blade design in order to reduce the stagnant region extent, thus mitigating the vortex rope and expending the operating range for Francis turbines.

• Journal of Mechanical Science and Technology
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• 제15권11호
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• pp.1599-1604
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• 2001

Axisymmetric compressible flow field induced by shock diffraction from a finite cone is investigated with experimental and computational methods. Double-exposure holographic interferograms show ima ges of the density field integrated along the light path. Using the sight-integrated density based on the Able transformation, the axisymmetric computational results are compared qualitatively with the experiment. In the present paper, we observed some distinguishing flow physics: the fault structure of vortex ring, the shock-vortex interaction, and the morphological transformation of shock waves.

• 소음진동
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• 제10권4호
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• pp.602-609
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• 2000

When an axisymmetric body moves through air the boundary layer near the stagnation region remains laminar and subsequently it goes through transition to turbulent. The experimental investigation described in this paper concerns the characteristics of wall pressure fluctuations at the initial stage of boundary layer flow including transition. Flush-mounted microphones are used to measure the wall pressure fluctuations at the transition and turbulent boundary layer region of a blunt axisymmetric body in the low noise wind tunnel. It if found from this study that the wall pressure fluctuations in the transition region is higher than that in the turbulent region.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.628-633
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• 2003

An analysis on the steady-state has been made of flow of a compressible fluid rapidly-rotating in a pipe. The flow is induced by an small arbitrary azimuthally-varying thermal forcing added on the basic state of rigid body isothermal rotation. The system Ekman number is assumed to be very small value. Analytic solutions have been obtained for axisymmetric and non-axisymmetric types, in which the axisymmetric solution comes from the azimuthally-averaged wall boundary condition and the non-axisymmetric solution from fluctuating wall boundary condition.

• Structural Engineering and Mechanics
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• 제58권4호
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• pp.719-729
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• 2016

The main objective of the present paper is to study the effect of the yield criterion on the magnitude of the strain rate and plastic work rate intensity factors in axisymmetric flow of isotropic incompressible rigid perfectly plastic material by means of a problem permitting a closed-form solution. The boundary value problem consisting of the axisymmetric deformation of a plastic tube is solved. The outer surface of the tube contracts. The radius of the inner surface does not change. The material of the tube obeys quite a general yield criterion and its associated flow rule. The maximum friction law is assumed at the inner surface of the tube. Therefore, the velocity field is singular near this surface. In particular, the strain rate and plastic work rate intensity factors are derived from the solution. It is shown that the strain rate intensity factor does not depend on the yield criterion but the plastic work rate intensity factor does.

• 대한기계학회논문집B
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• 제33권2호
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• pp.69-78
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• 2009

Cavitating flow simulation is of practical importance for many hydraulic engineering systems, such as pump, turbine, nozzle, injector, etc. In the present work, a solver for cavitating flow has been developed and applied to simulate the flows past axisymmetric cylinders. Governing equations are the two-phase Navier-Stokes equations, comprised of continuity equation of liquid and vapor phase. The momentum equation is in the mixture phase. The solver employed an implicit, dual time, preconditioned algorithm in curvilinear coordinates. Computations were carried out for three axisymmetric cylinders: hemispherical, ogive, and caliber-0 forebody shape. Then, the present calculations were compared with experiments and other numerical results to validate the present solver. Also, the code has shown its capability to accurately simulate the re-entrant jet phenomena and ventilated cavitation. Hence, it has been found that the present numerical code has successfully accounted for cavitating flows past axisymmetric cylinders.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1271-1278
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• 2004

In order to measure non-intrusively velocity profile in liquid metal flow, a modified electromagnetic flowmeter was designed, which was based on electromagnetic tomography technique. Under the assumption that flow is fully-developed, axisymmetric and rectilinear, the velocity profile was reconstructed after the flowmeter equation, the first kind of Fredholm integration equation, was linearized. In reconstruction process Tikhonov regularization method with regularization parameter was used. The reconstructed velocity profile had the nearly same as turbulent flow profile which was approximately represented as log law. In addition, flowmeter output fur a fixed magnet rotation angle was linearly proportional to flow rate. When magnet rotation angle was 54$^{\circ}$, axisymmetric weight function was nearly uniform so that the flowmeter gives a constant signal for any fully-developed, axisymmetric and rectilinear profile with a constant flow rate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1749-1754
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• 2004

In order to measure non-intrusively velocity profile in liquid metal flow, a modified electromagnetic flowmeter was designed, which was based on electromagnetic tomography technique. Under the assumption that flow is fully-developed, axisymmetric and rectilinear, the velocity profile was reconstructed after the flowmeter equation, the first kind of Fredholm integration equation, was linearized. In reconstruction process Tikhonov regularization method with regularization parameter was used. The reconstructed velocity profile had the nearly same as turbulent flow profile which was approximately represented as log law. In addition, flowmeter output for a fixed magnet rotation angle was linearly proportional to flow rate. When magnet rotation angle was $54^{\circ}$, axisymmetric weight function was nearly uniform so that the flowmeter gives a constant signal for any fully-developed, axisymmetric and rectilinear profile with a constant flow rate.