• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.137-142
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• 2002

The fluid mechanics and operating conditions of gas-lubricated proceeding bearings in micro rotating machinery such as micro polarization modulator and micro gas turbine are different from their larger size ones. Due to non-continuum effects, there is a slip of gas at the walls. Thus in this paper, the slip flow effect is considered to estimate the pressure distribution and load-carrying capacity of micro gas-lubricated proceeding bearings as the local Knudsen number at the minimum film thickness is greater than 0.01. Based on the compressible Reynolds equation with slip flow, the static characteristics of micro gas-lubricated proceeding bearings are obtained. Numerical predictions compare the pressure distribution and load capacity considering slip flow with the performance of micro proceeding bearings without slip f]ow for a range of bearing numbers and eccentricities. The results clearly show that the slip flow effect on the static characteristics is considerable and becomes more significant as temperature increases.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.32-37
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• 2015

The present study is to investigates the convective heat transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The divergent rectangular channel is fabricated with V-shaped ribs on one wall only and the inlet hydraulic diameter to outlet hydraulic diameter ratio($D_{ho}/D_{hi}$) of 1.49 is used. The current investigation has covered a Reynolds number (Re) range of 22,000~75,000, relative roughness height ($e/D_h$) of 0.1~0.2, and rib angle of attack (a) of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ for a fixed relative pitch of 10. Results show that the Nusselt numbers are the greatest in the $60^{\circ}$-angled ribs; however, the total friction factors are the highest in the $30^{\circ}$-angled ribs.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.8-15
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• 2005

Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.83-89
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• 2011

Laminar flow over a cube near a plane wall is numerically investigated in order to understand the effects of the cube-wall gap on the flow characteristics as well as the drag and lift coefficients. The main focus is placed on the three-dimensional vortical structures and its relation to the lift force applied on the cube. Numerical simulations are performed for the Reynolds numbers between 100 and 300, covering several different flow regimes. Without a wall nearby, the flow at Re=100 is planar symmetric with no vortical structure in the wake. However, when the wall is located close to the cube, a pair of streamwise vortices is induced behind the cube. At Re=250, the wall strengthens the existing streamwise vortices and elongates them in the streamwise direction. As a result, the lift coefficients at Re=100 and 250 increase as the cube-wall gap decreases. On the other hand, without a wall, vortex shedding takes place at Re=300 in the form of a hairpin vortex whose strength changes in time. The head of hairpin vortex or loop vortex, which is closely related to the lift force, seems to disappear due to the nearby wall. Therefore, unlike at Re=100 and 250, the lift coefficient tends to decrease more or less as the cube approaches the wall.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.862-869
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• 2005

A study on convective cooling characteristics has been done in the channels with heat pipes and associated Plane fins Analysis with FLUENT V5.0 lies its Purpose on the possible enhancement of heat transfer capability between an existing three in-line arrayed heatpipes and an extending four in-line arrayed heatpipes with increasing channel width. Numerical analysis is limited to the laminar flow in an isolated flow channel by employing cyclic boundary conditions for calculation purposes. Friction factors for three and four in-line arrayed heatpipes are compared with experimental results. In addition, temperature behavior at the plate fin for the three in-line arrayed heatpipes is compared with experiment. Friction factors and overall channel heat transfer coefficients (and/or Nusselt numbers) are presented as a function of Reynolds number. An increase of number of heatpipes and channel width reults in a decrease of the friction factor and doesn't not result in an increase of heat transfer performance. However. considering the 25$\%$ increase of heat load accompanies with maximum 8$^{\circ}C$ rise of average temperature of heat pipes, the four in-line array with the increase of channel width of heat pipe heat sink can be considered appropriate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2283-2296
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• 1995

Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

• Transactions of the Korean Society of Mechanical Engineers
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• v.3 no.4
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• pp.151-157
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• 1979

An experomental study on drg reduction in the rough tubes is presunted using the drrective drag reducing proymer solutions. The friction factors of the rough tubes follow the maximum drag reduction asymptote for the lower Reynolds numbers in the turbulent flow. However, as the Reynols number is increased the rougher tube results deviate from the maximum drag rduction asymptote sooner than the less rough tube results. There appears a systematic deviation from the maximum drag reduction asymptote depending on the relative roughness just as friction factors for the Newtonian hluid inthe rough tubes exhibit in the turbulent region. The minor loss results inthe various fittings such as elbows, tees, and gate valves are presunted The fittings show higher values of the loss coefficient in the drag reducing polymer solutions than in the Newtonian fluid, which is quite contrary to the drag reduction phenomenon in the straight tubes. The eqivalent length of the fittings for the drag reducing polymer solutions is many times longer than that for Newtonian fluids due to the increase of the loss coefficient and the decrease of the friction factor. It is speculated that the solid-like behavior of the polymer solutions in the abruptly changing folw passage plays a significant role in increasing the loss coefficient.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.10
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• pp.757-766
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• 2009

In the present study, the effect of delta-wing vortex generators(DWVG) on the local heat transfer of the plate fin-oval tube was experimentally analyzed for Reynolds numbers for 2000, 2500 and 3200. The local heat transfer coefficient of the fin surface for four type DWVGs was measured by the naphthalene sublimation technique. As the results, the distribution of the heat transfer coefficient at rear of DWVGs showed longitudinal contours for common flow down DWVGs and wavy contours for common flow up DWVGs. The distribution showed many cell type contours at near wall and downstream for all DWVGs. Compared to case without DWVGs in present experimental tests, all DWVGs showed the best enhancement of heat transfer at Re=2000. Of 4 cases of DWVGs, D type showed the best enhancement of heat transfer.

• Journal of the Korean Society of Marine Environment & Safety
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• v.7 no.1
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• pp.15-23
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• 2001

In regulation of IGC code 12.1 mechanical ventilation should be arranged to ensure sufficient air movement through the space to avoid the accumulation of flammable or toxic vapours and ensure a safe working environment, but in no case should the ventilation system have a capacity of less than 30 changes of air per hour baed upon the total volume of the space. In this study, a scaled mode chamber was constructed to investigate the ventilation characteristics and stagnation area in the hood room of LNG carrier and pump room in tanker. An experimental study was performed on the model by using visualization equipment with a laser apparatus and an image intensifier CCD camera. Twelve different kinds of measuring areas were selected as the experimental condition. Instant simultaneous velocity vectors in the whole fields were measured by a 2-D PIV system A three-dimensional numerical simulation was also carried out for three different Reynolds numbers. Then the CFD predictions were discussed with the experimental results. The results show the spiral L-shape flow that moves from the opening on the left wall diagonally to the upper right part dominates the ventilation structure. The stationary area of hood room in the velcoity distributions was located in the upper left stern part.

• Wind and Structures
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• v.13 no.2
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• pp.127-144
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• 2010

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.