• 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.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.113-119
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• 1998

An experimental study was carried out in a three-dimensional cubic cavity driven by 2-dimensional plane Poiseuille flow for three kinds of Reynolds number, $10^4$, 3 $\times$ $10^4$ and 5 $\times$ $10^4$ based on the cavity width and cavity inlet mean flow velcoity. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system. Laser based illumination and two-frame grey-level cross correlation algorithm are adopted. Severe unsteady flow fluctuation within the cavity are remarkable at above Re = 3 $\times$ $10^4$ Reynolds numbers and sheared mixing layer phenomena are also found at the region where inlet driving Poiseuille flow is collided with the clock-wise rotating main primary vortex at upper center area. Instant velocity profiles reveal that deformed forced vortex formation is observed throughout the separate two areas.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.361-371
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• 1983

The turbulent structures of the free plane jet and two dimensional impinging jet are investigated experimentally. In order to get the two dimensional jet, the contour of the cubic equation suggested by Morel is used for a contracting nozzle. A linearized constant-temperature hot-wire anemometer is used for measurement. Mean velocities and turbulent intensities are measured along the centerline of the jet. Jet halp width spatial double velocity correlation coefficients and integral length scales are obtained. It is established that the free plane jet is truly self-preserving about 40 slot widths downstream of the nozzle. The experiments for the impinging jet are carried out at four different impingement wall locations within the self-preserving region of the free plane jet, and comparing the results with that of free plane jet, the mean velocity is changed in the region of 0.25H and turbulent intensities are affected in the region of 0.2H from the wall, respectively, where H means the distance between the nozzle exit and the wall.

• Solar Energy
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• v.9 no.2
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• pp.51-57
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• 1989

A two-dimensional velocity map of natural convection in a rectangular cavity is determined using laser speckle photography. Isovelocity contour drawn by spatial filtering and local velocity by pointwise method are obtained. These results are compared with those of numerical analysis.

• Journal of Power System Engineering
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• v.10 no.3
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• pp.23-31
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• 2006

Mean velocities and turbulent characteristics in the three-dimensional flow fields of a gun-type gas burner were measured by using triple hot-wire probe (T-probe) in order to compare them with the results already presented by X-type hot-wire probe (X-probe). Vectors obtained by the measurement of two kinds of probes in the horizontal plane and in the cross section respectively show more or less difference in magnitude each other, but comparatively similar shape in overall distribution. Axial mean velocity component along the centerline shows that the value by T-probe is about ten times smaller than that by X-probe above the range of X/R=3. Also, the axial component of turbulent intensity along the centerline appears the biggest difference between the two probes. Moreover, axial mean velocity component, axial turbulent intensity component and rotational along the Y-directional distance show a big difference between slits and swirl vanes. On the whole, the values by T-probe appear smaller than those by X-probe.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.117-124
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• 2004

The mixing enhancement is one of the most important problems for the development of scramjet engines. The influence of the streamwise vortices produced by a ramp in a unheated supersonic flow on the mixing of twin jets injected from its base was experimentally investigated. Nominal Mach number of the main airstream and of the twin jets at the nozzle exits were 2.35 and 2.0, respectively. Three dimensional velocity distributions near the ramp with and without injection were measured by Particle Image Velocimetry (PIV). A pair of counter rotating streamwise vortices could be seen behind the injector without injection. On the other hand, two pairs of streamwise vortices could be seen with injection. The outer one had the same direction as the vortex pair produced by the ramp, but they were stronger than those produced by the ramp. The inner ones had the opposite directions to the outer ones. It is considered that these vortices enhance the mixing near the injector.

• Journal of the Korean Society of Visualization
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• v.9 no.4
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• pp.63-68
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• 2011

The flow-field of a liquid-metal system is very important for the safety analysis and the design of the steam generator of liquid-metal fast breeder reactor. Dynamic neutron radiography (DNR) is suitable for a visualization and measurement of a liquid metal flow and a two-phase flow in a metallic duct. However, the three dimensional DNR techniques is not enough to obtain the velocity information in the wide channel up to now. In this research, a high speed DNR technique was applied to visualize the heavy liquid-metal flow field in the narrow channel with the HANARO-beam facility. The images were taken with a high frame-rate neutron radiography at 250 fps and analyzed with a Particle Image Velocimetry(PIV) method. The images were compared with the results of the commercial CFX code to study the feasibility of DNR technique for the measuring the heavy liquid-metal flow field. The PIV images could discern the turbulent vortex flow in the two-dimensional narrow channel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.904-911
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• 2007

A measurement technique fur void fraction has been proposed using a time-resolved two-phase PIV system and the bubble dynamics has been investigated in gas-liquid two-phase flows. For the three-dimensional evaluation of the bubble information, both the images from the front and side views are simultaneously recorded into a high speed CCD camera by reflecting the side view image on a $45^{\circ}$ oriented mirror to be juxtaposed with the front view image. Then, a stereo-matching technique is applied to calculate the void fraction, bubble size and shape. To obtain the rising bubble velocities, the 2-frame PTV method was adopted. The present technique is applied to freely rising bubby flows in stagnant liquid. The results show that the increase of bubble flow rate gives rise to the increase of bubble size and rising velocity at first. If it goes over a certain level, the rising velocity becomes constant and the horizontal velocity grows bigger instead due to the obstruction of other bubbles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.362-373
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• 2002

A stereoscopic PIV (SPIV) measurement system based on the translation configuration was developed and applied to the flow behind a forward-swept axial-fan. Measurement of three orthogonal velocity components is essential for flow analysis of three-dimensional flows such as flow around a fan or propeller. In this study, the translation configuration was adopted to calculate the out-of-plane velocity component from 2-D PIV data obtained from two CCD cameras. The error caused by the out-of-plane motion was estimated by direct comparison of the 2-D PIV and 3-D SPIV results that measured from the particle images captured simultaneously. The comparison shows that the error ratio is relatively high in the region of higher out-of-plane motion near the axial fan blade. The turbulence intensity measured by the 2-D PIV method is bigger by about 5.8% in maximum compared with that of the 3-D SPIV method. The phase-averaged velocity field results show that the wake behind an axial fan has a periodic flow structure with respect to the blade phase and the characteristic flow structure is shifted downstream in the next phase.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.930-937
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• 2011

The characteristics of mean velocity and turbulence have been analyzed in the circular open channel flow using PIV measurement data for a wide range of water depth. The measured data are fitted to a velocity distribution function over the whole depth of the open channel. Reynolds shear stress and mean velocity in wall unit are compared with the analytic models for fully-developed turbulent boundary layer. Both the mean velocity and Reynolds shear stress have different distributions from the two-dimensional boundary layer flow when the water depth increases over 50% since the influence of the side wall penetrates more deeply into the free surface. The cross-stream Reynolds normal stress also has considerably different distribution in view of its peak value and decreasing rate in the outer region whether the water depth is higher than 50% or not.