• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.790-798
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• 2008

Counter-rotating axial flow fan(CRF) consists of two counter-rotating rotors without stator blades. CRF shows the complex flow characteristics of the three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in CRF, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential to improve the aerodynamic characteristics and to reduce the aerodynamic noise level and vibration characteristics of the CRF. In this paper, experimental study on the three-dimensional unsteady flow of the CRF is performed at the design point(operating point). Flow fields in the CRF are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. The phase-locked averaged hot-wire technique utilizes the inclined hot-wire, which rotates successively with 120 degree increments about its own axis. Three-dimensional unsteady flow characteristics such as tip vortex, secondary flow and tip leakage flow in the CRF are shown in the form of the axial, radial and tangential velocity vector plot and velocity contour. The phase-locked averaged velocity profiles of the CRF are analyzed by means of the stationary unsteady measurement technique. At the mean radius of the front rotor inlet and the outlet, the phase-locked averaged velocity profiles show more the periodical flow characteristics than those of the hub region. At the tip region of the CRF, the axial velocity is decreased due to the boundary layer effect of the fan casing and the tip vortex flow. The radial and the tangential velocity profiles show the most unstable and unsteady flow characteristics compared with other position of rotors. But, the phase-locked averaged velocity profiles of the downstream of the rear rotor show the aperiodic flow pattern due to the mixture of the front rotor wake period and the rear rotor rotational period.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.407-408
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• 2006

Passenger safety is one of the most important considerations in the purchase of an automobile. A curtain-type air bag is increasingly adapted in deluxe cars for protecting passengers from the danger of side clash. Inflator housing is a main part of the curtain-type air bag system for supplying high-pressure gases to pump up the air bag-curtain. Although the inflator housing is fundamental in designing a curtain-type air bag system, flow information on the inflator housing is very limited. In this study, we measured instantaneous velocity fields of a high-speed flow ejecting from the inflator housing using a dynamic PIV system. From the velocity field data measured at a high frame-rate, we evaluated the variation of the mass flow rate with time. From the instantaneous velocity fields of flow ejecting from the airbag inflator housing in the initial stage, we can see a flow pattern of broken shock wave front and its downward propagation. The flow ejecting from the inflator housing was found to have large velocity fluctuations and the maximum velocity was about 700m/s. The velocity of high-speed flow was decreased rapidly and the duration of high-speed flow over 400m/s was maintained only to 30ms. After 100ms, there was no perceptible flow.

• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.23-27
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• 2011

This experimental study was performed to find rpms of the impeller and the surface flow accelerator to make a uniform velocity vertical distribution in the circular water channel. PIV technique was employed to measure the water velocity profiles into the water depth from the free surface. The number of instantaneous velocity profiles was decomposed into mean and turbulence velocity components, and the distribution of velocity fluctuation and turbulence intensity were computed for each experimental condition. From these results, the velocity uniformity was quantitatively determined to present the flow quality in the measuring section of the circular water channel. It has been shown that the proper operation of the surface flow accelerator would make the uniform velocity profiles and reduce the velocity fluctuation near the free surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.3
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• pp.209-216
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• 2001

A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.

• Journal of environmental and Sanitary engineering
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• v.13 no.2
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• pp.14-25
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• 1998

To investigate the behavior of reaction products with the reactor heights by the change of upflow velocity, a typical real height USAB reactor was built and experiment was conducted. The flow in the reactor by the upflow velocity was flug flow at low upflow velocity but the flow was completely mixed flow at high upflow velocity. Therefore, the concentration of pH, alkalinity and volatile acid was not so different with reactor heights at high upflow velocity. And comparing with low upflow velocity, the distribution of microorganisms with reactor heights did not show big different at high upflow velocity. The removal efficiency of organic compounds depended on the distribution of microorganisms and it was low at high upflow velocity. It is concluded that the operation of reactor with proper upflow velocity to improve contact with organic compounds and microorganisms is recommended.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.05a
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• pp.140-145
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• 2000

The objective of experimental study is to apply simultaneous measurement by PIV(Particle Image Velocimetry) to high_speed flow characteristics within ginseng cleaner model. Three different kinds of flow rate(15.20 27ℓ/min) are selected as experimental condition. Optimized cross correlation identification to obtain velocity vectors is implemented by direct calculation of correlation coefficients. The instantaneous velocity distribution time0mean velocity distribution and velocity profile are represented quantitatively for the deeper understanding of the flow characteristics in a ginseng cleaner model.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1121-1136
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• 2002

The flow characteristics of film coolant issuing into turbulent boundary layer developing on a convex surface have been investigated by means of flow visualization and three-dimensional velocity measurement. The Schlieren optical system with a spark light source was adopted to visualize the jet trajectory injected at 35° and 90° inclination angles. A five-hole directional pressure probe was used to measure three-dimensional mean velocity components at the injection angle of 35°. Flow visualization shows that at the 90° injection, the jet flow is greatly changed near the jet exit due to strong interaction with the crossflow. On the other hand, the balance between radial pressure gradient and centrifugal force plays an important role to govern the jet flow at the 35° injection. The velocity measurement shows that at a velocity ratio of 0.5, the curvature stabilizes downstream flow, which results in weakening of the bound vortex structure. However, the injectant flow is separated from the convex wall gradually, and the bound vortex maintains its structure far downstream at a velocity ratio of 1.98 with two pairs of counter rotating vortices.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.12
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• pp.153-156
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• 1994

An in vitro steady flow experiment was performed in order to test the accuracy of velocity measurement obtained through a pulsed Doppler echocardiography. A flow phantom was designed for the use in a wide velocity range at a given flow rate. The results showed that the pulsed Doppler velocity measurement obtained in this flow phantom is accurate at low flow rates. However, ultrasound velocity measurement should be performed under a careful considerations of PRF and Doppler gain settings, especially at higher flow rates.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1037-1042
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• 1990

The air-fuel ratio of an internal combustion engine must be controlled with accuracy for the improvements of exhaust emission and fuel consumption. Therefore, it is necessary to measure the exact instantaneous amounts of fuel and suction air, so we carried out the experiments for measuring the air flow velocity in a suction pipe of an internal combustion engine using three types of instantaneous air flowmeter. The results obtained can be summarized as follows: (1) The laminar-flow type flowmeter is able to measure both the average and the instantaneous flow rate, but it is necessary to rectify the pulsating air flow in the suction pipe. (2) The a spark-discharge type flow velocity meter is able to measure the instantaneous air velocity, but it is necessary to choose the suitable electrode form and the spark character. (3) The tandem-type hot-wire flow velocity meter indicates the instantaneous flow velocity and its flow direction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.671-686
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• 2005

The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.