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Yang, James, adj prof
Publications (10 of 18) Show all publications
Yang, J., Teng, P. & Lin, C. (2019). Air-vent layouts and water-air flow behaviors of a wide spillway aerator. Theoretical and Applied Mechanics Letters, 9(2), 130-143
Open this publication in new window or tab >>Air-vent layouts and water-air flow behaviors of a wide spillway aerator
2019 (English)In: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 9, no 2, p. 130-143Article in journal (Refereed) Published
Abstract [en]

A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics (CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group (RNG) k - epsilon turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Spillway, Wide aerator, Air entrainment, Air-vent layout, Jet trajectory, CFD
National Category
Water Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-258934 (URN)10.1016/j.taml.2019.02.009 (DOI)000470901800010 ()2-s2.0-85066931897 (Scopus ID)
Note

QC 20190917

Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-09-19Bibliographically approved
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 ()2-s2.0-85063395379 (Scopus ID)
Note

QC 20181211. QC 20191107

Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2019-11-07Bibliographically 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
Lin, C., Wong, W.-Y., Kao, M.-J., Yang, J., Raikar, R. V. & Yuan, J.-M. (2019). Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach. Water, 11(8), Article ID 1556.
Open this publication in new window or tab >>Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach
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2019 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, no 8, article id 1556Article in journal (Refereed) Published
Abstract [en]

The hydrodynamic characteristics, including local and convective accelerations as well as pressure gradient in the horizontal direction, of the external stream of an undular bore propagating on a 1:20 sloping beach are experimentally studied. A bore with the water depth ratio of 1.70 was generated downstream of a suddenly lifted gate. A high-speed particle image velocimetry was employed to measure the velocity fields during the run-up and run-down motions. The time series of free surface elevation and velocity field/profile of the generated bore, comprising a pure bore accompanied by a series of dispersive leading waves, are first demonstrated. Based on the fast Fourier transform (FFT) and inverse FFT (IFFT) techniques, the free surface elevation of leading waves and the counterpart of pure bore are acquired separately at a specified measuring section (SMS), together with the uniform horizontal velocity of the pure bore. The effect of leading-wave-induced velocity shift on the velocity profiles of the generated bore are then evaluated at the SMS. To understand the calculation procedure of accelerations and pressure gradient, three tabulated forms are provided as illustrative examples. Accordingly, the relationships among the partially depth-averaged values of the non-dimensional local acceleration, convective acceleration, total acceleration and pressure gradient of the generated/pure bore acquired at the SMS versus the non-dimensional time are elucidated. The trends in the non-dimensional accelerations and pressure gradient of the external stream of generated bore are compared with those of the pure bore. During the run-up motion from the instant of arrival of the bore front to the moment of the peak level at the SMS, continuous decrease in the onshore uniform horizontal velocity, and successive deceleration of the pure bore in the onshore direction are evidenced, exhibiting the pure bore under the adverse pressure gradient with decreasing magnitude. However, the pure bore once ridden by the leading waves is decelerated/accelerated spatially and accelerated/decelerated temporally in the onshore direction during the rising/descending free surface of each leading wave. This fact highlights the effect of pre-passing/post-passing of the leading wave crest on the velocity distribution of generated bore. It is also found that, although the leading waves have minor contribution on the power spectrum of the free surface elevation as compared with that of the pure bore, the leading waves do play an important role on the magnitudes of both accelerations and pressure gradient. The largest magnitude of the acceleration contributed by the leading waves is around 26 times the counterpart contributed by the pure bore. Further, during the run-down motion right after the moment for the peak level of the bore, a linear increase in the magnitude of the offshore uniform horizontal velocity and a constant local acceleration with increasing time are both identified. The partially depth-averaged value of the non-dimensional pressure gradient is equal to a small negative constant (-0.0115) in the offshore direction, indicating that the bore is subject to a constant favorable pressure gradient.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
undular bore, leading waves, high-speed particle image velocimetry (HSPIV), run-up, run-down, velocity shift, local acceleration, convective acceleration, pressure gradient
National Category
Construction Management
Identifiers
urn:nbn:se:kth:diva-261339 (URN)10.3390/w11081556 (DOI)000484561500030 ()2-s2.0-85070266031 (Scopus ID)
Note

QC 20191007

Available from: 2019-10-07 Created: 2019-10-07 Last updated: 2019-10-07Bibliographically 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: 2019-09-19Bibliographically 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: 2019-09-19Bibliographically approved
Teng, P. & Yang, J. (2018). Modeling and Prototype Testing of Flowsover Flip-Bucket Aerators. Journal of Hydraulic Engineering, 144(12)
Open this publication in new window or tab >>Modeling and Prototype Testing of Flowsover Flip-Bucket Aerators
2018 (English)In: Journal of Hydraulic Engineering, ISSN 0733-9429, E-ISSN 1943-7900, Vol. 144, no 12Article 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 andavoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead tocontradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aerationneed. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations andCFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancyis due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakupdoes not exist. To correctly reproduce similar water–air flow phenomena, the model should be large enough to meet the air-entrainmentcriterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model resultsand make corrections, if needed.

Keywords
Spillway; Aerator; Jet oscillation; Model tests; Prototype tests; Computation fluid dynamics (CFD)
National Category
Water Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-258940 (URN)10.1061/(ASCE)HY.1943-7900.0001531 (DOI)
Note

QC 20190917

Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-09-17Bibliographically approved
Yang, J., Teng, P. & Xie, Q. (2018). MODELLING OF AIR DEMAND OF A SPILLWAY AERATOR WITH TWO-PHASE FLOW MODELS. In: E-proceedings of the 2nd International Symposium onHydraulic Modelling and Measuring Technology Congress: . Paper presented at 2nd International Symposium on Hydraulic Modelling and Measuring Technology Congress, 2018.
Open this publication in new window or tab >>MODELLING OF AIR DEMAND OF A SPILLWAY AERATOR WITH TWO-PHASE FLOW MODELS
2018 (English)In: E-proceedings of the 2nd International Symposium onHydraulic Modelling and Measuring Technology Congress, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Air demand is an issue of concern for a spillway aerator. To numerically map its air-water flow behavior has a bearing on its design. The recently completed spillway at Bergeforsen features a 35-m wide chute aerator with 13 air vents. With this in background, CFD modelling is performed with three commonly used two-phase flow models, i.e. the Volume-of-Fluid (VOF) Model, Two-Fluid Model and Mixture Model. The purpose is to evaluate these models in terms of water-air flow properties. The simulations have shown that the VOF Model generates the lowest air demand, while the Two-Fluid Model points to a 34% higher value, which is attributable to the differences in the two-phase flow formulations. The resulting air pressure in the air cavity including the air groove leads also to considerable discrepancy in the vent air-flow distribution across the chute and spatial air concentration. Evaluations of two-phase models are necessary, so that a reliable model is adopted for engineering design.

Keywords
spillway, aerator, air demand, two-phase model
National Category
Water Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-258939 (URN)
Conference
2nd International Symposium on Hydraulic Modelling and Measuring Technology Congress, 2018
Note

QC 20190930

Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-09-30Bibliographically 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
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