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The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.
Hasan Zobeyer; Abul Baki; Saika Nowrin. Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics. Water 2021, 13, 1718 .
AMA StyleHasan Zobeyer, Abul Baki, Saika Nowrin. Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics. Water. 2021; 13 (13):1718.
Chicago/Turabian StyleHasan Zobeyer; Abul Baki; Saika Nowrin. 2021. "Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics." Water 13, no. 13: 1718.
Three-dimensional numerical simulations were performed for different flow rates and various geometrical parameters of step-pools in steep open channels to gain insight into the occurrence of energy loss and its dependence on the flow structure. For a given channel with step-pools, energy loss varied only marginally with increasing flow rate in the nappe and transition flow regimes, while it increased in the skimming regime. Energy loss is positively correlated with the size of the recirculation zone, velocity in the recirculation zone and the vorticity. For the same flow rate, energy loss increased by 31.6% when the horizontal face inclination increased from 2° to 10°, while it decreased by 58.6% when the vertical face inclination increased from 40° to 70°. In a channel with several step-pools, cumulative energy loss is linearly related to the number of step-pools, for nappe and transition flows. However, it is a nonlinear function for skimming flows.
Suresh Kumar Thappeta; S. Murty Bhallamudi; Venu Chandra; Peter Fiener; Abul Basar M. Baki. Energy Loss in Steep Open Channels with Step-Pools. Water 2020, 13, 72 .
AMA StyleSuresh Kumar Thappeta, S. Murty Bhallamudi, Venu Chandra, Peter Fiener, Abul Basar M. Baki. Energy Loss in Steep Open Channels with Step-Pools. Water. 2020; 13 (1):72.
Chicago/Turabian StyleSuresh Kumar Thappeta; S. Murty Bhallamudi; Venu Chandra; Peter Fiener; Abul Basar M. Baki. 2020. "Energy Loss in Steep Open Channels with Step-Pools." Water 13, no. 1: 72.
This experimental study investigated the higher-order velocity moments, turbulence time and length scales, and energy dissipation rates around an intermediately submerged boulder within a wake-interference flow regime in a rock-ramp fish passage. The results show a noticeable variation in the studied parameters in the wake of the boulder, as well as near the bed and boulder crest. The higher-order velocity moments show the presence of infrequent strong ejections downstream of the boulder, which may lead to higher sediment deposition and vertical mixing. The eddy length scales and the volumetric energy dissipation in this experimental model were discussed in relation to fish behavior for both the experimental model and a prototype. Relationships were proposed to roughly estimate integral length scales and energy dissipation rates around the boulder over the flow depth. The findings of this study may improve the design of rock-ramp fish passages considering the effects of turbulence on fish swimming performance and sediment transport.
Amir Golpira; Abul Baki; David Zhu. Higher-order Velocity Moments, Turbulence Scales and Energy Dissipation Rate around a Boulder in a Rock-ramp Fish Passage. Sustainability 2020, 12, 5385 .
AMA StyleAmir Golpira, Abul Baki, David Zhu. Higher-order Velocity Moments, Turbulence Scales and Energy Dissipation Rate around a Boulder in a Rock-ramp Fish Passage. Sustainability. 2020; 12 (13):5385.
Chicago/Turabian StyleAmir Golpira; Abul Baki; David Zhu. 2020. "Higher-order Velocity Moments, Turbulence Scales and Energy Dissipation Rate around a Boulder in a Rock-ramp Fish Passage." Sustainability 12, no. 13: 5385.
This study experimentally investigated the effect of boulder spacing and boulder submergence ratio on the near-bed shear stress in a single array of boulders in a gravel bed open channel flume. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. Four methods of estimating near-bed shear stress were compared. The results suggested a significant effect of boulder spacing and boulder submergence ratio on the near-bed shear stress estimations and their spatial distributions. It was found that at unsubmerged condition, the turbulent kinetic energy (TKE) and modified TKE methods can be used interchangeably to estimate the near-bed shear stress. At both submerged and unsubmerged conditions, the Reynolds method performed differently from the other point-methods. Moreover, a quadrant analysis was performed to examine the turbulent events and their contribution to the near-bed Reynolds shear stress with the effect of boulder spacing. Generally, the burst events (ejections and sweeps) were reduced in the presence of boulders. This study may improve the understanding of the effect of the boulder spacing and boulder submergence ratio on the near-bed shear stress estimations of stream restoration practices.
Amir Golpira; Fengbin Huang; Abul B.M. Baki. The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel. Water 2020, 12, 1423 .
AMA StyleAmir Golpira, Fengbin Huang, Abul B.M. Baki. The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel. Water. 2020; 12 (5):1423.
Chicago/Turabian StyleAmir Golpira; Fengbin Huang; Abul B.M. Baki. 2020. "The Effect of Habitat Structure Boulder Spacing on Near-Bed Shear Stress and Turbulent Events in a Gravel Bed Channel." Water 12, no. 5: 1423.