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Yang, James, adj prof
Publications (10 of 12) Show all publications
Yang, J., Teng, P. & Zhang, H. (2019). Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility. Engineering Applications of Computational Fluid Mechanics, 13(1), 48-66
Open this publication in new window or tab >>Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility
2019 (English)In: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 13, no 1, p. 48-66Article, review/survey (Refereed) Published
Abstract [en]

Mathematical formulations of two-phase flows at an aerator remain a challenging issue for spillway design. Due to their complexities in terms of water-air interactions subjected to high flow velocities, experiments play an essential role in evaluations of numerical models. The paper focuses on the underlying influence of the air-water momentum exchange in the two-phase Two-Fluid Model. It is modified to better represent the drag force acting on a group of air bubbles and the wall lubrication force accounting for near-wall phase interactions. Based on data from a large aerator rig with an approach velocity of 14.3 m/s, the models are evaluated for calculations of entrained air characteristics of a flow mixture. The air bubble diameter used in the modeling ranges from 0.5 to 4 mm as suggested by the experiments. In terms of air cavity configurations and aerator air demand, smaller air bubbles lead to better agreement with the test results. As far as air concentrations are concerned, the modified model gains by comparison. In the air cavity zone, smaller bubble sizes also provide better matches with the experiments. However, the near-base air concentration remains overestimated downstream from the impact area. The fact that the program user must pre-define a single air bubble size in simulations presumably limits the correct reproduction of near-base air concentrations and of their decay.

Place, publisher, year, edition, pages
HONG KONG POLYTECHNIC UNIV, DEPT CIVIL & STRUCTURAL ENG, 2019
Keywords
Aerator, two-phase flow, two-fluid model, drag force, wall lubrication force, air cavity
National Category
Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-239964 (URN)10.1080/19942060.2018.1552201 (DOI)000451548900001 ()
Note

QC 20181211

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2018-12-11Bibliographically approved
Xie, Q., Yang, J. & Lundström, T. S. (2019). Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load. FLUIDS, 4(1), Article ID 15.
Open this publication in new window or tab >>Field Studies and 3D Modelling of Morphodynamics in a Meandering River Reach Dominated by Tides and Suspended Load
2019 (English)In: FLUIDS, ISSN 2311-5521, Vol. 4, no 1, article id 15Article in journal (Refereed) Published
Abstract [en]

Meandering is a common feature in natural alluvial streams. This study deals with alluvial behaviors of a meander reach subjected to both fresh-water flow and strong tides from the coast. Field measurements are carried out to obtain flow and sediment data. Approximately 95% of the sediment in the river is suspended load of silt and clay. The results indicate that, due to the tidal currents, the flow velocity and sediment concentration are always out of phase with each other. The cross-sectional asymmetry and bi-directional flow result in higher sediment concentration along inner banks than along outer banks of the main stream. For a given location, the near-bed concentration is 2-5 times the surface value. Based on Froude number, a sediment carrying capacity formula is derived for the flood and ebb tides. The tidal flow stirs the sediment and modifies its concentration and transport. A 3D hydrodynamic model of flow and suspended sediment transport is established to compute the flow patterns and morphology changes. Cross-sectional currents, bed shear stress and erosion-deposition patterns are discussed. The flow in cross-section exhibits significant stratification and even an opposite flow direction during the tidal rise and fall; the vertical velocity profile deviates from the logarithmic distribution. During the flow reversal between flood and ebb tides, sediment deposits, which is affected by slack-water durations. The bed deformation is dependent on the meander asymmetry and the interaction between the fresh water flow and tides. The flood tides are attributable to the deposition, while the ebb tides, together with run-offs, lead to slight erosion. The flood tides play a key role in the morphodynamic changes of the meander reach.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
tidal meandering river, field measurements, 3D numerical model, flow features, sediment transport, erosion-deposition patterns
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-251366 (URN)10.3390/fluids4010015 (DOI)000464467200002 ()2-s2.0-85063378020 (Scopus ID)
Note

QC 20190513

Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-05-23Bibliographically approved
Yang, J., Andreasson, P., Teng, P. & Xie, Q. (2019). The Past and Present of Discharge Capacity Modeling for Spillways-A Swedish Perspective. Paper presented at H, 1958, Report of Hydraulic Model Tests of Spillway and Log Flume at Holjes Dam,. FLUIDS, 4(1), Article ID 10.
Open this publication in new window or tab >>The Past and Present of Discharge Capacity Modeling for Spillways-A Swedish Perspective
2019 (English)In: FLUIDS, ISSN 2311-5521, Vol. 4, no 1, article id 10Article, review/survey (Refereed) Published
Abstract [en]

Most of the hydropower dams in Sweden were built before 1980. The present dam-safety guidelines have resulted in higher design floods than their spillway discharge capacity and the need for structural upgrades. This has led to renewed laboratory model tests. For some dams, even computational fluid dynamics (CFD) simulations are performed. This provides the possibility to compare the spillway discharge data between the model tests performed a few decades apart. The paper presents the hydropower development, the needs for the ongoing dam rehabilitations and the history of physical hydraulic modeling in Sweden. More than 20 spillways, both surface and bottom types, are analyzed to evaluate their discharge modeling accuracy. The past and present model tests are compared with each other and with the CFD results if available. Discrepancies do exist in the discharges between the model tests made a few decades apart. The differences fall within the range -8.3%-+11.2%. The reasons for the discrepancies are sought from several aspects. The primary source of the errors is seemingly the model construction quality and flow measurement method. The machine milling technique and 3D printing reduce the source of construction errors and improve the model quality. Results of the CFD simulations differ, at the maximum, by 3.8% from the physical tests. They are conducted without knowledge of the physical model results in advance. Following the best practice guidelines, CFD should generate results of decent accuracy for discharge prediction.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
spillway, bottom outlet, design flood, discharge capacity, model tests, computational fluid dynamics (CFD)
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-251367 (URN)10.3390/fluids4010010 (DOI)000464468000001 ()2-s2.0-85063403125 (Scopus ID)
Conference
H, 1958, Report of Hydraulic Model Tests of Spillway and Log Flume at Holjes Dam,
Note

QC 20190513

Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-05-23Bibliographically approved
Yang, J., Lin, C., Kao, M.-J. -., Teng, P. & Raikar, R. V. (2018). Application of SIM, HSPIV, BTM, and BIV techniques for evaluations of a two-phase air-water chute aerator flow. Water, 10(11), Article ID 1590.
Open this publication in new window or tab >>Application of SIM, HSPIV, BTM, and BIV techniques for evaluations of a two-phase air-water chute aerator flow
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2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 11, article id 1590Article in journal (Refereed) Published
Abstract [en]

Four image-based techniques-i.e., shadowgraphic image method (SIM), high-speed particle image velocimetry (HSPIV), bubble tracking method (BTM), and bubble image velocimetry (BIV)-are employed to investigate an aerator flow on a chute with a 17° inclination angle. The study focuses on their applications to the following issues: (1) to explore the characteristic positions of three water-air interfaces; (2) to interpret the evolution process of air bubbles shed from the wedged tip of the air cavity; (3) to identify the probabilistic means for characteristic positions near the fluctuating free surface; (4) to explore the probability distribution of intermittent appearance of air bubbles in the flow; (5) to obtain the mean streamwise and transverse velocity distributions of the water stream; (6) to acquire velocity fields, both instantaneous and mean, of air bubbles; (7) to construct a two-phase mean velocity field of both water flow and air-bubbles; and (8) to correlate the relationship among the probability distribution of air bubbles, the mean streamwise and transverse velocity profiles of air bubbles, and water stream. The combination of these techniques contributes to a better understanding of two-phase flow characteristics of the chute aerator.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
Aerator, Air bubbles, Air cavity, Bubble image velocimetry (BIV), Bubble tracking method (BTM), Flow impingement point, High-speed particle image velocimetry (HSPIV), Shadowgraphic image method (SIM), Two-phase flow, Air, Flow of water, Flow visualization, Phase interfaces, Transpiration, Velocimeters, Velocity, Velocity distribution, Velocity measurement, Water aeration, Bubble tracking method, High-speed particles, Image method, Image velocimetry, Two phase flow, air bubble, cavity, detection method, flow velocity, free surface flow, groundwater flow, instrumentation, numerical method, particle image velocimetry, two-dimensional flow, water flow
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-247072 (URN)10.3390/w10111590 (DOI)000451736300097 ()2-s2.0-85055960679 (Scopus ID)
Note

QC 20190625

Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-06-25Bibliographically approved
Teng, P. & Yang, J. (2018). Modeling and Prototype Testing of Flows over Flip-Bucket Aerators. Journal of Hydraulic Engineering, 144(12), Article ID 04018069.
Open this publication in new window or tab >>Modeling and Prototype Testing of Flows over Flip-Bucket Aerators
2018 (English)In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 144, no 12, article id 04018069Article in journal (Refereed) Published
Abstract [en]

The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water-air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.

Place, publisher, year, edition, pages
ASCE-AMER SOC CIVIL ENGINEERS, 2018
Keywords
Spillway, Aerator, Jet oscillation, Model tests, Prototype tests, Computation fluid dynamics (CFD)
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-238106 (URN)10.1061/(ASCE)HY.1943-7900.0001531 (DOI)000447254300004 ()2-s2.0-85053633622 (Scopus ID)
Note

QC 20190111

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Lin, C., Kao, M.-J. -., Yang, J., Teng, P.-H. -. & Raikar, R. V. (2018). Study on probabilistic mean features of lower and upper free-surface profiles and velocity fields of a highly fluctuating free jet over a chute. Journal of Marine Science and Technology (Taiwan), 26(3), 309-326
Open this publication in new window or tab >>Study on probabilistic mean features of lower and upper free-surface profiles and velocity fields of a highly fluctuating free jet over a chute
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2018 (English)In: Journal of Marine Science and Technology (Taiwan), ISSN 1023-2796, Vol. 26, no 3, p. 309-326Article in journal (Refereed) 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%.

Place, publisher, year, edition, pages
National Taiwan Ocean University, 2018
Keywords
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
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:kth:diva-236424 (URN)10.6119/JMST.2018.06_(3).0003 (DOI)000443784400003 ()2-s2.0-85054182429 (Scopus ID)
Note

QC 20181026

Available from: 2018-10-26 Created: 2018-10-26 Last updated: 2018-10-26Bibliographically approved
Yang, J., Andreasson, P., Högström, C.-M. & Teng, P. (2018). The Tale of an Intake Vortex and Its Mitigation Countermeasure: A Case Study from Akkats Hydropower Station. Water, 10(7), Article ID 881.
Open this publication in new window or tab >>The Tale of an Intake Vortex and Its Mitigation Countermeasure: A Case Study from Akkats Hydropower Station
2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 7, article id 881Article in journal (Refereed) Published
Abstract [en]

The upgrade of Akkats power station in Sweden included a new, separate waterway for the addition of a 75 MW generating unit. The vertical intake of its headrace was formed by means of lake tapping. A physical model was used to help understand the blasting process involving fragmented rock, water, air, and gas. Upon commissioning of the unit, swirling flows occurred unexpectedly at the intake, which gave rise to negative consequences including limitations in power output. Echo-sounding showed that the blasted piercing resulted in an irregular intake. A hydraulic model, as part of the design process, was built to examine potential countermeasures for vortex suppression. The final solution was a segmented barrier between the intake and the dam. It effectively suppressed the intake flow circulations; only minor intermittent vortices were left. The fabricated steel segments were anchored into the bedrock, stretching to 1.0 m below the lowest legal reservoir level. The local intake headloss was also reduced. The implemented solution was tested under full turbine loading and the result was satisfactory. Even during winter seasons with ice cover above the wall, the power station ran normally. The case study is expected to provide guidance for solving similar problems with vortex formation.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
Akkats, intake, lake tapping, swirling flow, vortex suppression, model tests
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:kth:diva-235146 (URN)10.3390/w10070881 (DOI)000442579700064 ()2-s2.0-85049645374 (Scopus ID)
Note

QC 20180920

Available from: 2018-09-20 Created: 2018-09-20 Last updated: 2018-09-20Bibliographically approved
Yang, J., Liu, T., Dai, W. & Teng, P. (2018). Transient Air-Water Flow and Air Demand following an Opening Outlet Gate. Modelling and Simulation in Engineering, Article ID 3194935.
Open this publication in new window or tab >>Transient Air-Water Flow and Air Demand following an Opening Outlet Gate
2018 (English)In: Modelling and Simulation in Engineering, ISSN 1687-5591, E-ISSN 1687-5605, article id 3194935Article in journal (Refereed) Published
Abstract [en]

In Sweden, the dam-safety guidelines call for an overhaul of many existing bottom outlets. During the opening of an outlet gate, understanding the transient air-water flowis essential for its safe operation, especially under submerged tailwater conditions. Three-dimensional CFD simulations are undertaken to examine air-water flow behaviors at both free and submerged outflows. The gate, hoisted by wire ropes and powered by AC, opens at a constant speed. A mesh is adapted to follow the gate movement. At the free outflow, the CFD simulations and model tests agree well in terms of outlet discharge capacity. Larger air vents lead to more air supply; the increment becomes, however, limited if the vent area is larger than 10 m(2). At the submerged outflow, a hydraulic jump builds up in the conduit when the gate reaches approximately 45% of its full opening. The discharge is affected by the tailwater and slightly by the flow with the hydraulic jump. The flow features strong turbulent mixing of air and water, with build-up and break-up of air pockets and collisions of defragmented water bodies. The air demand rate is several times as much as required by steady-state hydraulic jump with free surface.

Place, publisher, year, edition, pages
HINDAWI LTD, 2018
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-225225 (URN)10.1155/2018/3194935 (DOI)000427596900001 ()2-s2.0-85044092191 (Scopus ID)
Funder
Vattenfall AB
Note

QC 20180404

Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-05-15Bibliographically approved
Xie, Q., Yang, J., Lundström, S. & Dai, W. (2018). Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling. Water, 10(10), Article ID 1424.
Open this publication in new window or tab >>Understanding morphodynamic changes of a tidal river confluence through field measurements and numerical modeling
2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 10, article id 1424Article in journal (Refereed) Published
Abstract [en]

A confluence is a natural component in river and channel networks. This study deals, through field and numerical studies, with alluvial behaviors of a confluence affected by both river run-offand strong tides. Field measurements were conducted along the rivers including the confluence. Field data show that the changes in flow velocity and sediment concentration are not always in phase with each other. The concentration shows a general trend of decrease from the river mouth to the confluence. For a given location, the tides affect both the sediment concentration and transport. A two-dimensional hydrodynamic model of suspended load was set up to illustrate the combined effects of run-offand tidal flows. Modeled cases included the flood and ebb tides in a wet season. Typical features examined included tidal flow fields, bed shear stress, and scour evolution in the confluence. The confluence migration pattern of scour is dependent on the interaction between the river currents and tidal flows. The flood tides are attributable to the suspended load deposition in the confluence, while the ebb tides in combination with run-offs lead to erosion. The flood tides play a dominant role in the morphodynamic changes of the confluence.

Place, publisher, year, edition, pages
MDPI AG, 2018
Keywords
Field measurements, Flow features, Morphological changes, Numerical simulations, Tidal river confluence, Computer simulation, Floods, Flow velocity, Numerical models, Sedimentation, Shear flow, Shear stress, Tides, Field measurement, Natural components, Sediment concentration, Suspended load deposition, Tidal river, Two-dimensional hydrodynamic modeling, Rivers
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-247139 (URN)10.3390/w10101424 (DOI)000451208400139 ()2-s2.0-85054725343 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-03Bibliographically approved
Yang, J. & Andreasson, P. (2016). Bending the spillway flow for safety upgrades. International Water Power and Dam Construction, 68(11), 36-43
Open this publication in new window or tab >>Bending the spillway flow for safety upgrades
2016 (English)In: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 68, no 11, p. 36-43Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Progressive Media Group, 2016
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-218141 (URN)2-s2.0-85033576873 (Scopus ID)
Note

QC 20171123

Available from: 2017-11-23 Created: 2017-11-23 Last updated: 2017-11-23Bibliographically approved
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