• 대한기계학회논문집B
• /
• 제25권5호
• /
• pp.731-740
• /
• 2001

A numerical study on the quantitative analogy between the fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and that in a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of the two flows, dimensionless parameters K(sub)TR=Re(sup)1/4/√Ro and Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to K(sub)TC=Re(sup)1/4/√λ and curvature ratio, λ, in a stationary curved duct flow so that they have the same dynamical meaning as those of the fully developed laminar flows. For the large values of Ro or λ, it is shown that the flow field satisfies the asymptotic invariance property, that is, there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of K(sub)TR and K(sub)TC.

• 설비공학논문집
• /
• 제9권1호
• /
• pp.55-63
• /
• 1997

A numerical investigation has been made for flows in an axisymmetric circular cylinder with an impulsively rotating cone located at the bottom of the container. The axisymmetric container is completely filled with a viscous fluid. Major parameter for the present research is only the vertex angle of the cone, otherwise Reynolds number and aspect ratio of the vessel are fixed. Main interest concerns on the vortex breakdown of meridional circulation by impulsive rotation of the cone with respect to the longitudinal axis of the cylinder. Numerical method has been used to integrate momentum and continuity equations on a generalized body-fitted grid system. The pattern of vortex breakdown is quite different from that in a right circular cylinder with flat endwall disks. The flow visualization photograph of the preceeding work by Escudier is compared with the present numerical results and the two results are in good agreements. Also flow data are plotted to gain a deep understanding for the present phenomena of the vortex breakdown. The conclusions of this work are clearly explained by the classical theory of the vortex flows in a finite geometry.

• 대한조선학회논문집
• /
• 제48권6호
• /
• pp.501-508
• /
• 2011

In order to control the tip vortex cavitation occurring around the tip of a rotating propeller blade, researches on the propeller cavitation and blade tip vortex flows have been increased. In this paper, the propeller tip vortex flow for a blunt and sharp tips was studied using an unsteady Reynolds-averaged Navier-Stokes equations solver based on a cell-centered finite volume method. In numerical open water test, torques, thrusts, pressure distributions and vortex flows were compared for various rotating speeds. To consider a hull wake, the nominal wake was specified in inlet boundary condition. Pressure distributions and vortex flows with the hull wake were investigated for various propeller rotating angles. From the results, it was confirmed that the blunt tip propeller delayed the tip vortex flow.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집E
• /
• pp.27-32
• /
• 2001

A study has been made of the condition to maintaining Taylor-Proudman column flows in a compressible rotating fluid, which is driven by small mechanical and/or thermal perturbations imposing on the container wall in the basic state of isothermal rigid body rotation. The Rossby and system Ekman numbers are assumed to be very small. The Taylor-Proudman column flow can be produced when energy parameter, e, becomes constant on the whole flow region. Energy balance concept, related to energy parameter, and its physical interpretation are given with comprehensive discussions.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2004년도 춘계 학술대회논문집
• /
• pp.35-41
• /
• 2004

A numerical investigation has been made for flows in an axisymmetric circular cylinder with a rotating cone located at the bottom of the container. The axisymmetric container is completely filled with a viscous fluid. Major parameter for the present research is the vertex angle of the cone, otherwise Reynolds number of fluid and aspect ratio of the vessel is fixed. Main interest is in vortex breakdown of meridional circulation by rotation of the cone with respect to the longitudinal axis of the cylinder. The method to this problem is numerically to integrate momentum and continuity equations on a generalized body fitted grid system. The pattern of vortex breakdown is quite different from that in a right circular cylinder with flat end wall disks. Flow visualization photographs of a preceeding work are compared with the present numerical results.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.627-632
• /
• 2000

Developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. The six orientation hot-wire technique was applied to measured the distributions of 3 mean velocities and 6 Reynolds stress components. Effects of Coriolis and centrifugal forces caused by the curvature and rotation of bend on the mean motion and turbulence structures were experimentally investigated Productive addition of Coriolis and centrifugal forces to the outward radial direction in the entrance region of bend increases the secondary flow intensity according to the rotational speeds. However, after 45 degree of bend, centrifugal force due to the rotation of bend may promote the break down of counter rotating vortex pair into multi-cellular pattern, thereby decreasing the production rate of turbulence energy and Reynolds stresses.

• 한국전산유체공학회지
• /
• 제3권2호
• /
• pp.27-38
• /
• 1998

Rotating flow of a stratified fluid contained in a circular cylinder with unstable temperature gradient imposed on the side wall of it has been numerically studied. The temperatures at the endwall disks are constant. The top disk of the container is coider than that of the bottob disk, as much as the temperature difference n${\Delta}$T, (0${\leq}$n${\leq}$3). Flows in the vessel are driven by an impulsive rotation of the hot bottom disk with respect to the central axis of the cylinder. Flow details have been acquired. For this flow, the principal balance in the interior core is characterized by a relationship between the radial temperature gradient and the vertical shear in the azimuthal velocity. As the buoyancy effect becomes appreciable, larger portions of the meridional fluid transport are long-circuit from the bottom disk to the interior region via the side wall.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.683-686
• /
• 2002

The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for three cases flows using linear stability theory (i.e. Rossby number, Ro = -1, 0, and 1). Detailed numerical values of the disturbance wave number, wave frequency, azimuth angle, radius (Reynolds number, Re) and other characteristics have been calculated for $K{\acute{a}}rm{\acute{a}}n$, Ekman and $B{\"{o}}ewadt$ boundary-layer flows. Neutral curves for these flows are presented. Presented are the neutral stability results concerning the two instability modes (Type I and Type II) by using a two-point boundary value problem code COLUEW that was based upon the adaptive orthogonal collocation method using B-spline. The prediction from the present results on both instability modes among the three cases agrees with the previously known numerical and experimental data well.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.325-328
• /
• 2002

We present numerical and experimental result of the rotating flows inside a rectangular container under a background rotation. In numerical computation, a parallel-computation technique with MPI is implemented. Flow visualization and PIV measurement are also performed to obtain velocity fields at the free surface. Through a series of numerical and experimental works, we aim to clarify, if any, the fundamental reasons of discrepancy between the two-dimensional computation and the experimental measurement, which was detected in the previous study for the same flow model. Specifically, we check if the various assumptions prerequisite for the validity of the classical Ekman pumping law are satisfied for periodic flows under a background rotation.

• Korea-Australia Rheology Journal
• /
• 제21권1호
• /
• pp.27-37
• /
• 2009

In this work, we numerically investigate the effect of viscoelasticity on 2D laminar vortex dynamics in flows past a single rotating cylinder for rotational rates $0{\leq}{\alpha}{\leq}5$ (the rotational rate ex is defined by the ratio of the circumferential rotating velocity to free stream velocity) at Re=100, in which the vortex shedding has been predicted to occur in literature for Newtonian fluids. The objective of the present research is to develop a promising technique to fully suppress the vortex shedding past a bluff body by rotating a cylinder and controlling fluid elasticity. The predicted vortex dynamics with the present method is consistent with the previous works for Newtonian flows past a rotating cylinder. We also verified our method by comparing our data with the literature in the case of viscoelastic flow past a non-rotating cylinder. For $0{\leq}{\alpha}{\leq}1.8$, the frequency of vortex shedding slightly decreases but the fluctuation of drag and lift coefficient significantly decreases with increasing fluid elasticity. We observe that the vortex shedding of viscoelastic flow disappears at lower ${\alpha}$ than the Newtonian case. At ${\alpha}$=5, the relationship between the frequency of vortex shedding and Weissenberg number (Wi) is predicted to be non-monotonic and have a minimum around Wi=0.25. The vortex shedding finally disappears over critical Wi number. The present results suggest that the vortex shedding in the flow around a rotating cylinder can be more effectively suppressed for viscoelastic fluids than Newtonian fluids.