• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2012.05a
• /
• pp.274-277
• /
• 2012

Large eddy simulation is applied to the turbulent flow and heat transfer in straight cooling passages with varying aspect ratio. The turbulent statistics of the flow and thermal quantities are calculated and the characteristics of Nusselt number are investigated. To scrutinize near-wall streamwise vortices, a conditional sampling technique is adopted. Clockwise and counter-clockwise rotating streamwise vortices are sampled and the probability density function of the vortex circulation Reynolds number and wall Nusselt number are calculated.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.631-636
• /
• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• Journal of Mechanical Science and Technology
• /
• v.19 no.7
• /
• pp.1503-1516
• /
• 2005

Mean flow and turbulence properties of developing turbulent flows in a 90 degree square bend with span-wise rotation are measured by a hot-wire anemometer. A slanted wire is rotated into 6 orientations and the voltage outputs from them are combined to obtain the mean velocity and the Reynolds stress components. Combined effects of the centrifugal and Coriolis forces due to the curvature and the rotation of the bend on the mean motion and turbulence structures are investigated experimentally. Results show that the two body forces can either enhance or counteract each other depending on the flow direction in the bend.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.2
• /
• pp.260-269
• /
• 2000

Oil-film flow visualizations and three-dimensional flow measurements have been conducted in the downstream region of a butterfly-type valve used in air-conditioning systems, with the variation of a disk open angle. The flow visualizations in the flow symmetry plane show that there are a pair of counter-rotating separation/recirculation zones as wall as two jet-like near-wall flows. These flow disturbances are strongly depends on the disk open angle. Based on the flow visualization, a qualitative flow model is suggested in the near-field and downstream region of the valve disk. For a small disk open angle, the mean velocities and turbulent intensities have relatively small values in the near-field of the valve disk, but they do not show uniform distributions even in some downstream region. With an increment of the disk open angle, mean velocity variations and turbulent intensities are greatly increased in the immediate downstream region, but uniform distributions are quickly resumed as departing from the valve disk. The mass flow rate remains nearly constant for the disk open angles less than 30 degrees, meanwhile it strongly depends on the disk open angles between 45 and 75 degrees. The pressure loss is found to be about zero for the disk open angles less than 45 degrees, but is substantially increased for those larger than 75 degrees.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.45-50
• /
• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of a 0.2 % aqueous solution of sodium carbomethyl cellulose (CMC) at a inner cylinder rotational speed of $0{\sim}600$ rpm. The transitional flow has been examined by the measurement of pressure losses, to reveal the relation of the Reynolds numbers with the skin-friction coefficients, in the laminar and transitional flow regimes. The occurrence of transition has been checked by the gradient change of pressure losses and skin-friction coefficient with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.15 no.1
• /
• pp.1-9
• /
• 2007

This study concerns the characteristics of helical flow in a concentric and eccentric annulus with a diameter ratio of 0.52 and 0.9, whose outer cylinders are stationary and inner ones are rotating. Pressure losses and skin friction coefficients have been measured for fully developed flows of water and 0.2% aqueous of sodium carboxymethyl cellulose (CMC), respectively, when the inner cylinder rotates at the speed of 0-500 rpm. The effect of rotation on the skin friction is significantly dependent on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change of skin friction coefficient corresponding to the variation of rotating speed is large for the laminar flow regime, whereas it becomes smaller as Re increases for the transitional flow regime and, then, it gradually approach to zero for the turbulent flow regime.

• Journal of computational fluids engineering
• /
• v.11 no.3 s.34
• /
• pp.52-58
• /
• 2006

A numerical investigation is made of air flow in a spinner equipment used for cleanning and drying flat display panels. A unique feature of the spinner under question is the placement of a torus plate cover over the rotating plate. The turbulent flow is driven by rotation of a large disk and suction by the exhaust system connected to vacuum chamber. The flow is modelled as an axisymmetric two-dimensional flow and computation is conducted by using the FLUENT package with a version of k-$\varepsilon$ turbulence model. The required capacity of the exhaust system is assessed numerically. The usefulness of the cover in controlling air flow circulation is examined. A computational trouble shooting is attempted to resolve the problem of panel rising which occurred in real experiment.

• Proceedings of the KSME Conference
• /
• 2000.11b
• /
• pp.573-578
• /
• 2000

Flow through turbine flow meter is simulated by solving the incompressible Navier-Stockes equations. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved steadily in rotating reference frames and the centrifugal force and tile Coriolis force are added to the equation of motion. The standard $k-{\varepsilon}$ model is employed to evaluate turbulent viscosity. At first the stability and accuracy of the program is verified with the flow through a square duct with a $90^{\circ}$ bend and on the flat plate.

• Journal of ILASS-Korea
• /
• v.11 no.1
• /
• pp.39-47
• /
• 2006

In-cylinder flows in a motored 3.5L four-valve SI engine were investigated quantitatively using three-component LDV system, to determine how engine configuration affects the flow field. The purpose of this work was to develop quantitative methods which correlate in-cylinder flows to engine performance. For this study, two distinct intake/piston arrangements were used to examine the flow characteristics. Quantification of the flow field was done by calculating two major parameters which are believed to characterize adequately in-cylinder motion. These quantities were turbulent kinetic energy(TKE) and tumble ratio in each plane at each crank angle. The results showed that in-cylinder flow pattern is dominated by the intake effects and two counter rotating vortices, developed during the intake stroke, produced relatively low tumble ratio. Therefore, the applicability of these quantities should be carefully considered when evaluating characteristics resulting from the complex in-cylinder flow motions.

• Journal of the korean Society of Automotive Engineers
• /
• v.15 no.3
• /
• pp.81-88
• /
• 1993

This report describes the experimental research on the flow phenomena of the aq uaous polymer solution within the Cuette flow of the concentric, cylinders type with a wide circular gap. We have investigated the phenomena of the fluid flow through torque measuring in the system that the inner cylinder is stationary and the outer one is rotating. Geometrical parameters of the system are the gap ratio of t/R$_{0}$=0.2 and Aspect ratio of l/t=100. The torque increases considerably in about 420-480RPM, So, it is considered a turbulent transition boundary, the higher plymer concentration is, the lower torque value is and the higher transition Reynolds number is. In each of the polymer concentration, the unstable boundary of torque, that is, idiosyncrasies of torque is observed around 220-280RPM. and the boundary is looked upon as a resonant vibration which is caused by the inner cylinder and tortional vibration of torque sensor.r.