• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1995년도 춘계학술대회논문집; 전남대학교, 19 May 1995
• /
• pp.196-201
• /
• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• 조명전기설비학회논문지
• /
• 제27권10호
• /
• pp.21-29
• /
• 2013

The short circuit and overload is presented by main cause of electrical fire. However, 85% of the fan directly connected the outlet box without switch in total 110 fans as a research in manufacturing industries. In installation direction of vertical type fans which was placed on the horizontal surface, only 39 vertical type fans were placed on vertical surface and 71 fans were placed on the horizontal type. The installation direction of the fans warns of the risk of the fire hazard due to the motor stall to the user manual of the maker. However, it is the representative nonconformity example of construction which the people or builder disregards. In addition, the condition of ground connection with the earth leakage prevention was investigated in grounding of 5 fans, non-grounding of 105 fans. The double insulation structure is generally used for small fan and it can't connect ground wire as electric plug of non-grounding type. However, industrial iron fan needs ground wire for electric leakage and to protect against electric shock.

• 항공우주기술
• /
• 제4권2호
• /
• pp.36-41
• /
• 2005

진동하는 익형(NACA0012)의 공력특성을 KARI 1m 풍동에 설치된 익형진동장치를 사용하여 시험적으로 측정하였다. 사용된 익형의 기준시위는 0.2m 스팬은 0.75m이다. 익형표면에 설치된 스트레인-게이지 형식의 압력센서를 사용하여 측정된 압력을 적분하여 익형의 양력과 피칭모멘트를 계산하였다. 시험조건은 표준진동계수 k<01, Re~820,000, Mach<0.25이며, 시험결과를 타 기관에서 시험한 결과와 비교하였다.

• International Journal of Fluid Machinery and Systems
• /
• 제3권3호
• /
• pp.211-220
• /
• 2010

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.

• 대한기계학회논문집B
• /
• 제23권1호
• /
• pp.82-91
• /
• 1999

A numerical analysis based on the three-dimensional Reynolds-averaged Navier-Stokes equation has been conducted to investigate the flow within a NASA rotor 67 transonic fan. General coordinate transformations are used to represent the complex blade geometry and an H-type grid is used. The governing equations are solved using implicit LU-SGS scheme for the time-marching integration and a standard ${\kappa}-{\varepsilon}$ model is used with wall functions for the turbulence modeling. The computations are compared with the experimental data and a detailed study of the flow structures near peak efficiency and near stall is presented. The calculated overall aerodynamic efficiency and three-dimensional shock system agree well with the laser anemometer data.

• International Journal of Fluid Machinery and Systems
• /
• 제1권1호
• /
• pp.92-100
• /
• 2008

The main objective of this study was to clarify the origin of the unsteady flows arising in a mixed-flow vaneless diffuser system and also the effects of physical components of the system. The testing equipment consists of a straight tube, a swirl generator, and a mixed-flow vaneless diffuser. Pressure fluctuations of the flow through the tube and diffuser were measured by using a semiconductor-type pressure transducer and analyzed by an FFT analyzer. In the experiment, the velocity ratio (axial velocity/peripheral velocity) of the internal flow, and the geometric parameters of the diffuser were varied. Two kinds of unsteady flows were measured according to the combination of the components, and the origin of each unsteady flow was clarified. The fundamental frequencies of unsteady flows arose were examined by two-dimensional small perturbation analysis.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1566-1569
• /
• 2008

The flow visualization is conducted in order to investigate an unsteady flight characteristic of a model dragonfly. The flapping wings are analyzed using smoke-wire and high speed camera. The results of this experiment show that three mechanisms and high incidence angle of the wings are responsible for the lift. The leading edge vortex, which is induced by the rapid acceleration of the wing at the beginning of a stroke, causes the lift enhancement. The delayed stall during the stroke and the fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Asian-Australasian Journal of Animal Sciences
• /
• 제6권3호
• /
• pp.389-394
• /
• 1993

A study on housing and management of dairy cows was conducted in three villages. All activities of husbandry related to the housing and the condition of the cows were observed and farmers were interviewed using a questionnaire. The main type of housing was a tie stall mostly in the back yard area with a gable or shed type roof. Inside the shed the temperature ranged from 17 to $29^{\circ}C$ and the relative humidity ranged from 62 to 73%. Drainage and manure handling was poor which lead to poor cleanliness of the stables and animal skins. The floor space was mostly wide and the roof level was low (less than 2.5 m). The slope of the floor (1-3%) was sufficient, the roughness of the floor was of medium quality. The shape and size of the feed trough was good with a surface of mostly irregular forms. Concentrate was mixed with water and offered in liquid form in pails made from plastic or from parts of rubber car tires. Hoof length was too long which could lead to unstable position and self injury. It is concluded that the housing conditions of dairy cattle need to be improved in order to improve the condition of the animals and the production performance.

• International Journal of Fluid Machinery and Systems
• /
• 제4권2호
• /
• pp.217-222
• /
• 2011

The rotordynamic fluid forces acting on a closed type impeller in whirling motion were measured and the influence of the clearance geometry on the stability of the impeller was examined. At small positive whirling speed, the rotordynamic forces acted as destabilizing forces for all casings. A small clearance between the shroud of the impeller and the casing caused large fluid force, but did not change the destabilizing region. Radial grooves in the clearance were effective for reducing the fluid forces and destabilizing region due to the reduction of the circumferential velocity without the deterioration of the pump performance. A rotating phenomenon like a rotating stall of the impeller occurred at low flow rate and the resonance between it and the whirling motion led to a sudden increase in force at the whirling speed ratio of 0.7.

• 한국전산유체공학회지
• /
• 제21권3호
• /
• pp.48-54
• /
• 2016

In the present work, numerical simulations were conducted on the scaled model of the BWB type UCAV in the subsonic region using ANSYS FLUENT V15. The prediction method was validated through comparison with experimental results and the effect of the twisted wing was investigated. To consider the transitional flow phenomenon, ${\gamma}$ transition model based on SST model was adopted. The coefficients of lift, drag and pitching moment were compared with experimental results and the pressure distribution and streamlines were investigated. The twisted wing decreases the lift force but increases lift-to-drag ratio through delay of stall and leading edge vortex's movement to the front, also the non-linearity of the pitching moment is decreased.