• The KSFM Journal of Fluid Machinery
• /
• v.2 no.2 s.3
• /
• pp.57-63
• /
• 1999

The flow through multistage turbomachinery is affected by the interaction between a rotor and a stator. The interaction is due to the inviscid potential effect and viscous effect between closely spaced rotor and stator airfoils. Three-dimensional, unsteady, incompressible Navier-Stokes equations with a standard $k-{\epsilon}$ model are solved using a non-staggered grid system. This method is applied to the flow through a multistage compressor measured by Stauter et al. The results have shown strong interaction between the rotating and stationary flow field. The decay of rotor wake and the pressure profiles agree very well with experimental data. The wake produced by rotor causes unsteady pressure on the surface of a stator. The rotor/stator interaction produces the unsteady pressure force on the rotor and stator blades.

• Journal of Environmental Science International
• /
• v.17 no.11
• /
• pp.1203-1210
• /
• 2008

Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.4
• /
• pp.315-323
• /
• 2002

The commercial viability of heat exchanger is mainly dependent on their long-term fouling characteristics because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the drag force coefficients of particles in the internal flow were higher than those in the external flow, in addition, the solid particle periodically hitting the tube wall broke the thermal boundary layer, and increased the rate of heat transfer. Particularly when the flow velocity was low, the effect was more pronounced.

• Tribology and Lubricants
• /
• v.29 no.1
• /
• pp.27-32
• /
• 2013

This study examined the effects of surface roughness in the mixed lubrication regime of smooth and rough surfaces for roller bearings. The average flow model was adopted for interaction between the flow rheology of the lubricant and the surface roughness. The average Reynolds equation and related flow factor that describes the coupled effects of surface roughness and flow rheology, the viscosity-pressure and density-pressure equations, the elastic deformation equation, and the force balance equation were solved simultaneously. The results showed that the effects of surface roughness on the film thickness and pressure distribution should be considered, especially in elastohydrodynamic lubrication contact problems.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.95-98
• /
• 2006

Many LNG ships will be constructed in Korea and the demand of safety valves is increasing. The most important performance of the developed safety relief valves for LNG ship is flow capacity. Flow capacity tests for 8 sizes of developed safety valves were conducted in the high pressure gas flow standard system in KRISS. The initial spring force adjustment was important for setting pressure of the safety valve. The procedure of data reduction and evaluation of the safety valve performance are suggested. This procedure was approved by French Bureau Veritas and Lloyd's Register.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.1942-1947
• /
• 2003

The valve is the key part which governs the efficiency, noise and reliability of the compressor, so the development of analytical model about valve performance is necessary. As the valve leed is opened and closed by pressure pulsation, the flow characteristic of the refrigerant passing the valve is very important. In the present study, a circular disk with inclination is assumed to be the valve reed of a reciprocating compressor and numerical analysis of three dimensional velocity fields are perfomed for the radial flow through the valve model. The effective flow and force area which are required to predict the efficiency of the valve are measured and compared with the numerical analysis in this research.

• 한국가시화정보학회:학술대회논문집
• /
• 2007.11a
• /
• pp.84-87
• /
• 2007

Recently, many studies concern on the slip flow and slip length, which allow liquid flow to reduce drag force in microchannel. However, until now not enough investigation is performed experimentally to understand the slip flow in the superhydrophobic microchannel exhibiting riblet structures on vertical wall. Here we investigated and compared the slip flows according to the surface characteristics; hydrophilic, hydrophobic, and superhydrophobic wettabilities. Using the micro-PIV, velocity profiles can be obtained in the glass (hydrophilic), PDMS (hydrophobic), and micro-structured PDMS (superhydrophobic) microchannels. For both PDMS and superhydrophobic PDMS microchannels, we observed the slip effects showing the microscale slip lengths. Due to the micro-riblet, there are two distinctive flow characteristics on the riblet surface and the liquid meniscus in the valleys.

• Proceedings of the KSME Conference
• /
• 2002.08a
• /
• pp.459-462
• /
• 2002

Many active and passive flow control methods have been studied since decades, but there are only few works about flow control methods using ion wind. This paper presents an experimental study on the wake control behind a circular cylinder using ion wind, a bulk motion of neutral molecules driven by locally ionized air of corona discharge. Experiments are done f3r different electrohydrodynamic numbers - the ratio of an electrical body farce to a fluid Inertial force - from 0 to 2 and for the Reynolds number ranging from $4{\times}10^3\;to\;8{\times}10^3$. Pressure distributions over a cylinder surface are measured and flow visualizations are carried out by smoke wire method. Flow visualizations confirm that ion wind affects significantly the wake structure behind a circular cylinder and pressure drag could be dramatically reduced by the superimposing ion wind.

• Journal of Mechanical Science and Technology
• /
• v.18 no.2
• /
• pp.262-271
• /
• 2004

Hydropneumatic suspension unit is an important part of tracked vehicles to absorb external impact load exerted from the non-paved road and the cannon discharge. Its absorption performance is strongly influenced by both damping and spring forces of the unit. In this paper, we numerically analyze the damping characteristics of the in-arm-type hydropneumatic suspension unit (ISU) by considering four distinct dynamic modes of the ISU damper: jounce-loading, jounce-unloading, rebound-loading and rebound-unloading. The flow rate coefficients determining the oil flow rate through the damper orifice are decided with the help of independent experiments. The wheel reaction force, the flow rate at cracking and the damping energy are parametrically investigated with respect to the orifice diameter and the wheel motion frequency.

• Textile Coloration and Finishing
• /
• v.10 no.2
• /
• pp.1-7
• /
• 1998

In this study, PET fabric was hydrolyzed with NaOH using the Tank m/c and Liquor-flow m/c to determine the alkali hydrolysis properties of PET fabrics. The results were as follows ： The weft density and tensile strength of PET fabrics hydrolyzed with Liquor-flow m/c were higher than those hydrolyzed with Tank m/c in case of less than 10％ of weight loss. However, above 10％ of weight loss, reverse phenomenon was showed. K/S value of hydrolyzed PET with Liquor-flow m/c was higher than that with Tank m/c above 10％ of weight loss. It was observed that the micropores of PET surface were collapsed due to physical force(abrasion and collision) during hydrolysis. Bending rigidity of hydrolyzed PET fabric was about 32％ and 40％ of bending rigidity of warp and weft direction of untreated fabric at 7％ of weight loss, respectively. Above 7％ of weight loss, decrease rate was decreased.