• 대한기계학회논문집B
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• 제26권2호
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• pp.201-210
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• 2002

Experiments were done for performance and flow characteristics of a counter-rotating axial flow fan. Performance curves of a counter-rotating axial flow fan were obtained and compared by varying the blade pitch angles. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fan flow characteristics were measured using a five-hole probe and a slanted hot-wire. The velocity profiles between the hub and tip of the fans were measured and analyzed at the peak efficiency point. The peak efficiency of the counter-rotating axial flow fan was improved about 15% respectively, compared with the single rotating axial fan. The single rotating axial flow fan showed relatively law efficiency due to the swirl velocities behind rotor exit which produced pressure losses. The counter-rotating axial flow fan showed that the swirl velocity generated by the front rotor was eliminated by the rear rotor and the associated dynamic pressure is recovered in the from of the static pressure rise.

• 설비공학논문집
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• 제19권2호
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• pp.191-201
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• 2007

It was noted by the several researchers that the voltage outputs in response to a single yawed hot-wire sensor in a flow perpendicular to the axis deviate from the theoretical voltage output by King's law and Jorgensen's relation. This study noticed that the calibration coefficients of original Grande's method are not constant and fairly sensitive to the radial angle (${\alpha}_{R}$). For more accuracy, this study interpolated the parameters of the Grande relation as a function of radial angle and compared velocity components with ones by Jorgensen and original Grande relation in the calibration jet flow. Finally, as a test case, 3-dimensional turbulent flows of the inlet plane of 180 degree bend are measured and compared the velocity components by above three methods and showed the characteristics of the flows.

• 대한기계학회논문집B
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• 제25권4호
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• pp.514-522
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• 2001

In order to investigate the relation between wall vorticity and streamwise velocity fluctuations in a turbulent boundary layer, a wall vorticity probe has been developed, which consists of two hot-wires on the wall aligned in V configuration. Although the measured intensity of spanwise wall vorticity fluctuations is somewhat lower than previous results, the intensity of streamwise wall vorticity fluctuations is in good agreement with them. It has been shown that the measured intensity of spanwise wall vorticity fluctuations is affected by transverse length of the wall vorticity probe. Instantaneous streamwise and spanwise wall vorticity fluctuations are compared with the results of DNS. Probability density function of spanwise wall vorticity fluctuations shows good agreement with previous results and is different from that of streamwise wall vorticity fluctuations. Energy spectrum of streamwisw wall vorticity fluctuations is lower than that of spanwise wall vorticity fluctuations in low frequency region.

• 설비공학논문집
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• 제15권1호
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• pp.9-18
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• 2003

An experimental study was performed to investigate the turbulence intermittency measuring methods across the boundary layer in the transition region. A single type hot-wire probe was used to measure instantaneous streamwise velocities in laminar, transitional and turbulent boundary layer To estimate wall shear stresses on the flat plate, near wall mean velocities are applied to the principle of CPM. Distribution of intermittency factor is obtained by dual-slope method and compared to the results of four methods,$\'{u},\;\{U}$, TERA and M-TERA method. In these methods, M-TERA shows a good agreement in the near wall region. However, the result of M-TERA method shows that intermittency factor is underestimated in the outer part and outside of the boundary layer and the dimensional constant of M-TERA method should be changed appropriately depending on measuring point.

• 대한기계학회논문집B
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• 제21권1호
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• pp.140-152
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• 1997

A simultaneous measurement of the wall skin friction and near-wall streamwise velocity fluctuations is performed using hot film and hot wire anemometers to investigate the relation between them. Near-wall turbulence statistics measured with a hot-wire probe are in good agreement with previous results. Turbulence properties of the wall skin friction fluctuations measured with a hot film also show fairly good agreements with those measured by others except that rms level is lower in the present study. Long-time averaged space- time correlations show that the wall skin friction is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction. Tilting angles are obtained from the phase shifts between the wall skin-friction and streamwise velocity fluctuations. The convection velocity of the near-wall streamwise velocity obtained from the space-time correlation is in good agreement with that from the direct numerical simulation database.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1255-1263
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• 2000

In this study, the modification of turbulent boundary layer flow by local wall vibration is investigated. The wall is locally vibrated using a wall deformation actuator, which moves up and down at the frequencies of 100Hz and 50Hz. Simultaneous measurements of the streamwise velocities in the spanwise direction are performed at several wall-normal and streamwise locations using an in-house multi-channel hot wire anemometer and a spanwise hot-wire-probe rake. The mean velocity is reduced in most places due to the wall vibration and its reduced amount becomes small as flow goes downstream. Interestingly, the mean velocity is found to increase very near the wall and near the actuator. This is due to the motion induced by the streamwise vortices which are generated by the downward motion of the actuator. In case of the streamwise velocity fluctuations, their magnitude increases as compared to the unperturbed turbulent boundary layer, and the increased amount becomes small as the flow moves downstream. The modified flow field at the forcing frequency of 50Hz is not much different from that of 100Hz, except the reduced amount of modification.

• 한국분무공학회지
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• 제1권2호
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• pp.16-23
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• 1996

In case of a high-speed D.I. diesel engine. the injected fuel spray is unavoidable that the impinging on the wall of piston cavity and in this case the geometry of piston cavity has a great influence on the atomization structure and air flow fields. In the field of combustion and in many other spray applications, there are clear evidence of correlation between spray structure and emission of pollutants. Ordinary, the combustion chamber of driving engine have unsteady turbulent flow be attendant on such as the change of temperature, velocity and pressure. So the analysis of spray behavior is difficult. In this study, a single spray was impinged on each cavity wall at indicated angle in a quiescent atmosphere at room temperature and pressure, as being the simplest case, and 3 types of piston cavity such as Dish, Toroidal and Re-entrant type was tested for analyzing the influence of cavity geometry. And hot wire probe was used for analyze non-steady flow characteristics of impinging spray, and to investigate the behavior of spray, the aspects of concentration c(t), standard deviation $\sigma(t)$ and variation factor (v.f.) was measured with the lapse of time.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1383-1388
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• 2004

The flow characteristics in the blade passage of a low speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. The tip leakage vortex interfaces with blade pressure surface, and results in high velocity fluctuation near the pressure surface. From the relative velocity distributions near the rotor tip, large axial velocity decay is observed at near stall condition, which results in large blockage compared to that at the design condition. Througout the flow measurements using a quasi-orthogonal measuring points to the tip leakage vortex, it is noted that the radial position of the tip leakage vortex is distributed between 94 and 96 percent span for all flow conditions. High spectrum density due to the large fluctuation of the tip leakage vortex is observed near the blade suction surface below the frequency of 1000 Hz at near stall condition.

• 한국항공우주학회지
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• 제31권4호
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• pp.92-98
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• 2003

한양대학교 중형 아음속 풍동의 설계요구사항에 따라 균일도 증가 및 난류도 감소를 위한 최적설계를 수행하였다. 신뢰성 있는 풍동실험을 위해 먼저 풍동 시험부의 균일도와 난류강도 특성이 먼저 파악되어야 한다. 한양대학교 중형 아음속 풍동의 비균일도와 난류강도는 세 부분의 속도영역에서 피토관과 X형 열선프로브로 각각 측정되었다. 풍동 시험부의 유속이 증가함에 따라 비균일도가 작아졌으나 시험부의 측정단면이 확산부에 가까워질수록 비균일도가 크게 나타났다. 난류강도는 시험부 중앙에서 설계 요구조건에 비해 약간 높게 측정되었다.

• 한국자동차공학회논문집
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• 제4권3호
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• pp.211-219
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• 1996

In a small high-speed D. I. diesel engine, the injected fuel spray into the atmosphere of the high temperature is burnt by go through the process of break up, atomization, evaporation and process of ignition. These process are important to decide the emission control and the rate of fuel consumption and out put of power. Especially, in the case of injected fuel spray impinging on the wall of piston cavity, the geometry of piston cavity gives great influence the ignitability of injected fuel and the flame structure. Ordinary, the combustion chamber of driving engine have unsteady turbulent flow be attendant on such as the change of temperature, velocity and pressure. So the analysis of spray behavior is difficult. In this study, the spray was impinged on the wall of 3 types of piston cavity such as Dish, Toroidal, Re-entrant type, in order to analyze the combustion process of impinging spray precisely and systematically. And hot wire probe was used for analyze non-steady flow characteristics of impinging spray, and to investigate the behavior of spray, the aspects of concentration c(t), standard deviation σ(t) and variation factor(vf) was measured with the lapse of time.