• Title/Summary/Keyword: 2-Frame PTV

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Development of 2-frame PTV system and its application to a channel flow (2-프레임 PTV 시스템의 개발 및 채널유동에의 응용)

  • Baek, Seung-Jo;Lee, Sang-Jun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.6
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    • pp.874-887
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    • 1998
  • A 2-frame PTV (particle tracking velocimetry) system using the concept of match probability between two consequent image frames has been developed to obtain instantaneous velocity fields. The overall 2-frame PTV system including image pre-processing, tracking algorithm and post-processing routine was implemented to apply to real flows. The developed 2-frame PTV system has several advantages such as high recovery ratio of velocity vectors, low error ratio and small computational time compared with the conventional 4-frame PTV and the FFT-based cross-correlation PIV technique. The 2-frame PTV system was applied to a turbulent channel flow over a rectangular block to check its reliability and usefulness. Total 96 sequential image frames have been captured and processed to get both mean and fluctuating velocity vector fields over the recirculating region. The mean velocity and turbulent intensity profiles were well agreed with hte LDV measurements in the separated region behind the block. Time-averaged reattachment length is about 6.3 times of the block height.

Performance Improvement of 2-Frame PTV Method Using an Adaptive Hybrid Scheme (적응형 하이브리드 기법을 이용한 2-Frame PTV 기법의 성능향상 연구)

  • Kim, Hyoung-Bum;Lee, Sang-Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.3
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    • pp.443-449
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    • 2000
  • The performance of 2-frame PTV(particle tracking velocimetry) system was improved using an adaptive hybrid scheme. The original 2-frame PTV method based on the match probability concept employs global match parameters for the entire flow field. Since this does not reflect fully the detailed local velocity change, it sometimes reduces the recovery rate of velocity vectors and increases the number of erroneous vectors in the region where an extraordinary flow structure exists. In this study, the preliminary FFT-based PIV results are used as an input parameter to determine the local match parameters needed for the 2-frame particle tracking algorithm. A computer simulation using synthetic particle images was carried out to study the performance of the adaptive 2-frame PTV technique. The adaptive hybrid method shows the better performance with increasing the velocity vector recovery rate and decreasing the computation time, compared to the original 2-frame PTV method.

Development of a New 2-Frame Particle Tracking Algorithm Using Match Probability (일치확률방식의 2-프레임 PTV 알고리듬 개발)

  • 백승조;이상준
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.7
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    • pp.1741-1748
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    • 1995
  • A new particle tracking algorithm using the concept of match probability between two consequent image frames has been developed to obtain an instantaneous 2-dimensional velocity field. A computer simulation has been carried out to check the performance and usefulness of the developed algorithm by comparing with the conventional 4-frame Particle Tracking Velocimetry(PTV) method. As a result the newly developed algorithm shows very good performance. Although the major part of the developed algorithm is time-consuming iterative updating routine of match probability, computational elapse time to get the resonable results is a very short compared with the 4-frame PTv.Additionally, the present 2-frame PTV algorithm recovers more velocity vectors and has higher dynamic range and lower error ratio compared with the conventional 4-frame PTV.

Velocity Field Measurement of Flow Around an Axial Fan Using a Phase Averaged 2-Frame PTV Technique (위상평균 PTV 기법을 이용한 축류 홴 주위 유동의 속도장 측정 연구)

  • Choi, Jay-Ho;Kim, Hyoung-Bum;Lee, Sang-Joon;Lee, In-Seop
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.1
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    • pp.114-123
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    • 2000
  • The flow structure around a rotating axial-fan was experimentally investigated using a phase averaging velocity field measurement technique. The fan blades were divided into 4 different phases, for which 500 velocity fields were acquired for each phase angle with a 2-frame PTV system. Velocity field measurements were also carried out at two planes parallel to the axis of rotation, with offsets toward the radial direction of the fan. For accurate synchronization of the PTV system with the phase of the axial fan, two synchronization circuits were employed with a photo-detector attached to the rotating shaft. The phase averaged velocity fields show periodic variations with respect to the blade phase. The periodic formation of vortices at the blade tip is also observed in vorticity contour plots. Locations of local maximum turbulence intensities in the axial and radial directions are found to be located in an alternating pattern. These experimental results can be used to validate numerical calculations and to understand the flow characteristics of an axial fan.

Development of Stereoscopic PTV Technique and Performance Tests (Stereoscopic PTV 기법의 개발과 성능비교 연구)

  • Lee Sang-Joon;Yoon Jong-Hwan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.3 s.246
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    • pp.215-221
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    • 2006
  • A stereoscopic particle tracking velocimetry (SPTV) technique based on the 2-frame hybrid particle tracking velocimetry (PTV) method was developed. The expansion of 2D PTV to SPTV is facilitated by the fact that the PTV method tracks individual particle centroids. To evaluate the performance and measurement accuracy of the present SPTV technique, it was applied to flow images of rigid body translation and synthetic standard images of jet shear flow and impinging jet flow. The data processing routine and measurement uncertainty of the SPTV technique are compared with those of conventional stereoscopic particle image velecimet.y (SPBV). In addition, the centroid translation effect of 2D particle image velocimetry (PIV) is defined and its effect on SPIV measurements is discussed. Compared to the SPIV method, the SPTV technique has inherited merits of concise and precise velocity evaluation procedures and provides better spatial resolution and measurement accuracy.

Analysis of in-cylinder steady flow for dual-intake-valve gasoline engine using single-frame particle tracking velocimetry (단일 프레임 입자 추적법을 이용한 흡입 2밸브 가솔린 기관의 실린더 내 정상 유동 해석)

  • Lee, Chang-Sik;Lee, Gi-Hyeong;Im, Gyeong-Su;Jeon, Mun-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.5
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    • pp.650-658
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    • 1997
  • Analysis and control of intake charge motion such as swirl and tumble are very important factors in improving the gasoline engine performance. In this paper, single-frame PTV (particle tracking velocimetry) is used to investigate intake tumble patterns in a steady flow test rig of gasoline engine with dual-intake-valve and pent-roof combustion chamber. Intake tumble pattern is quantified in accordance with blockage ratio of TIV (tumble intensifying valve) with single- frame PTv.The view of the instantaneous 2-D velocity field gives a realistic understanding of in-cylinder flow field. Thus it is confirmed that PTV is a effective tool in engine design. In conventional port, two tumble structures appear clearly, and the larger one is observed under the exhaust valve side and the smaller is right below the intake valve side. The larger vorticity is observed in TIV port, thus it is concluded that TIV have an effect on intensified tumble motion in cylinder flow.

Velocity Field Measurement of Flow Around a Surface-Mounted Vertical Fence Using the Two-Frame PTV System (2-프레임 PTV를 이용한 수직벽 주위 유동장 해석)

  • Baek, Seung-Jo;Lee, Sang-Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.10
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    • pp.1340-1346
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    • 1999
  • The turbulent shear flow around a surface-mounted vertical fence was investigated using the two-frame PTV system. The Reynolds number based on the fence height(H) was 2950. From this study, it is revealed that at least 400 instantaneous velocity field data are required for ensemble average to get reliable turbulence statistics, but only 100 field data are sufficient for the time-averaged mean velocity information. Various turbulence statistics such as turbulent intensities, turbulence kinetic energy and Reynolds shear stress were calculated from 700 instantaneous velocity vector fields. The fence flow has an unsteady recirculation region behind the fence, followed by a slow relaxation to the flat-plate boundary layer flow. The time-averaged reattachment length estimated from the streamline distribution is about 11.2H. There exists a region of negative Reynolds shear stress near the fence top due to the highly convex (stabilizing) streamline-curvature of the upstream flow. The large eddy structure in the separated shear layer seems to have significant influence on the development of the separated shear layer and the reattachment process.

Precise Estimations on Vorticities using a Hybrid PTV-PIV Algorithm (하이브리드 PTV-PIV알고리듬에 의한 고정밀 와도 추정)

  • Doh, Deog-Hee;Cho, Gyong-Rae;Lee, Jae-Min
    • Journal of the Korean Society of Visualization
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    • v.8 no.4
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    • pp.26-30
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    • 2010
  • A PTV algorithm was constructed using a linear transformation, in which the merits of the conventional PIV and PTV were adopted. In PIV calculations, the obtained velocity vectors are affected by the filtering effects by its calculation principle. PTV techniques are widely used for their excellences of measuring small scaled flows, such as nano and bio flows. However, PTVs produce vector errors due to interpolation process. To overcome these problems, a hybrid PTV algorithm was constructed by combining PTVs' and PIVs' benefits using a linear transformation. The Taylor-Green vortex flows were generated for the tests of vorticity calculations. The conventional gray-level cross-correlation PIV technique and 2-Frame PTV technique were tested for the same flows for comparisons with those obtained by the constructed hybrid algorithm. The excellence of the constructed hybrid algorithm was validated through an actual experiment on the cylinder wake.

Velocity Field Measurements of Propeller Wake Using a Phase-averaged PTV Technique (위상평균 PTV 기법을 이용한 프로펠러 후류의 속도장 측정)

  • Bu-Geun Paik;Sang-Joon Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.39 no.3
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    • pp.41-47
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    • 2002
  • Turbulent wake behind a ship propeller has been investigated using the adaptive hybrid 2-frame PTV(Particle Tracking Velocimetry). 400 instantaneous velocity fields were measured according to 4 different blade phases and ensemble-averaged to investigate the spatial evolution of the vortical structure of near wake within one propeller diameter downstream. The phase averaged mean velocity fields show the potential wake and the viscous wake formed by the boundary layers developed on the blade surfaces. As the tip vortex evolves downstream, the slipstream is contracted and the turbulent intensity is decreased with viscous dissipation and turbulent diffusion.

A Study on Development of Velocity Measuring Method by PTV-AOM (PTV-AOM을 이용한 속도계측 기법의 개발에 관한 연구)

  • 조대환;김진구;이영호
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.5
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    • pp.591-597
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    • 1997
  • Instantaneous velocity distribution within coaxial circular pipe for measurement velocity of high speed is acquired simultaneously by applying the 2-dimensional PTV system consisting of a pulse generator(AOM:Acousto-Optical Modulator), a continuous-output laser and a PC image grabber together with experimental apparatus. The basic mechanism of AOM and vector identification method and performance-related image processing techniques are discussed. Representative measuring regions $90{\times}90$mm are selected and instantaneous vectors are represented and fully developed turbulent flow of maximum velocity up to about 1.0 m/sec is obtained.

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