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Study on probabilistic mean features of lower and upper free-surface profiles and velocity fields of a highly fluctuating free jet over a chute
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Resurser, energi och infrastruktur.
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2018 (Engelska)Ingår i: Journal of Marine Science and Technology (Taiwan), ISSN 1023-2796, Vol. 26, nr 3, s. 309-326Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

An optic-based method that utilizes the particle-laden images captured during high-speed particle image velocimetry (HSPIV) measurements is presented, aiming to explore the probabilistic mean characteristics of the free surface profiles and velocity fields of a free jet with high-frequency random fluctuations over a chute. The technique based on the gray-level gradients in the smoothed gray level distribution of the contrast-enhanced images is used to determine the probabilistic mean features of the free jet, right beneath and above which the water-air interfaces have I%/(100 I)% intermittent appearance of air/water phase and (100 I)% /I% fitful show-up of water/air phase. Further, the cross-correlation calculation for HSPIV measurements is employed to obtain the instantaneous and probabilistic mean velocity fields of the free jet. A target experiment of the free jet having a mean water-depth of 2.76 cm and a Froude number of 3.92 over a 17 chute model is performed in a re-circulating water channel to demonstrate the application of this method. The entire process for obtaining the probabilistic mean positions of the free surface profiles is elucidated step-by step. The lower/upper part of the free surface changing from the height at which the possibility of intermittent appearance of water phase is 3%/97%, via the counterpart for 50%/50%, to that for 97%/ 3% is identified precisely. In addition, the probabilistic mean velocity field is further categorized into the conditionally and overall time-averaged ones. Each streamwise velocity profile in the conditionally time-averaged velocity field is fairly uniform. However, the counterpart in the overall time-averaged velocity field evidently shows the non-uniform feature with prominent velocity gradient in the lower/upper part between the height at which the possibility of intermittent appearance of water phase is 3%/97% and the counterpart is 97%/3%.

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National Taiwan Ocean University , 2018. Vol. 26, nr 3, s. 309-326
Nyckelord [en]
Air-water interface, Contrast-enhancement techniques, Free jet, Gray-level gradient, High-speed particle image velocimetry (HSPIV), Probabilistic mean, Air, Flow velocity, Flow visualization, Image enhancement, Phase interfaces, Probability distributions, Transpiration, Velocimeters, Velocity measurement, Air water interfaces, Contrast Enhancement, Free jets, High-speed particles, Velocity
Nationell ämneskategori
Meteorologi och atmosfärforskning
Identifikatorer
URN: urn:nbn:se:kth:diva-236424DOI: 10.6119/JMST.2018.06_(3).0003ISI: 000443784400003Scopus ID: 2-s2.0-85054182429OAI: oai:DiVA.org:kth-236424DiVA, id: diva2:1258890
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QC 20181026

Tillgänglig från: 2018-10-26 Skapad: 2018-10-26 Senast uppdaterad: 2018-10-26Bibliografiskt granskad

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Yang, James

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