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Venu Chandra

Bio: Venu Chandra is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Vortex & Settling. The author has an hindex of 7, co-authored 24 publications receiving 112 citations. Previous affiliations of Venu Chandra include Eindhoven University of Technology & Indian Institute of Technology Kanpur.

Papers
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Journal ArticleDOI
04 Feb 2022-Water
TL;DR: In this paper , the effects of the spatial distribution of roughness elements on water surface levels and head loss were analyzed in a 15 m long, 0.9 m wide flume with a slope of 5% under large Froude numbers.
Abstract: Accurate estimation of head loss introduced via randomly placed roughness elements found in natural or constructed streams (e.g., fish passages) is essential in order to estimate flow variables in mountain streams, understand formation of niches for aquatic life, and model flow structure. Owing to the complexity of the involved processes and the often missing detailed data regarding the roughness elements, the head loss in such streams is mostly approximated using empirical models. In our study, we utilize flume experiments to analyze the effects of the spatial distribution of roughness elements on water surface levels and head loss and, moreover, use the produced data to test three empirical models estimating head loss. The experiments were performed in a 15 m long, 0.9 m wide flume with a slope of 5% under large Froude numbers (2.5–2.8). Flow velocities and water levels were measured with different flow rates at 58 points within a 3.96 m test section of the flume. We could show that different randomly arranged patterns of roughness elements significantly affected head loss (differences up to 33.6%), whereas water jumps occurred when flow depths were in the same size range as the roughness elements. The roughness element position and its size influenced water surface profiles. None of the three tested empirical models were able to well reproduce the differences in head loss due to the different patterns of roughness elements, with overestimated head loss from 12 to 94.7%, R2 from 41 to 73%, NSE from −21.1 to 0.09, and RRMSE from 18.4 to 93%. This generally indicates that these empirical models are conditionally suitable to consider head loss effects of random patterns of roughness elements.

1 citations

Journal ArticleDOI
TL;DR: In this paper, a regression equation of the form Power-Allometric1 has been proposed to relate the normalized turbulent kinetic energy with the velocity magnitude, and the range of Reynolds shear stress and energy dissipation factor existent in the step-pool systems.
Abstract: The morphology of step-pools is often implemented for ecological restoration and for the creation of close-to-nature fish passes. Step-pools display spatio-temporal variations in bed and flow characteristics due to meso-scale units such as step, tread, base of step, and pool. Exclusive research on the effects of bed variations in step-pools on the flow dynamics is limited. Here, we conducted laboratory experiments on a physical model downscaled from a field site in the Western Ghats, Kerala, India. The results of Kruskal–Wallis ANOVA show significant differences in the velocity and turbulent intensities for the morphological units. A regression equation of the form Power-Allometric1 has been proposed to relate the normalized turbulent kinetic energy with the velocity magnitude. The present study also estimated the range of Reynolds shear stress and energy dissipation factor existent in the step-pool systems. The normalized values of Reynolds shear stress in the x–z plane ranged from − 19.477 to 13.729, and energy dissipation factors obtained for the three step-pool systems are 321, 207, and 123 W/m3; both the results reveal insufficient pool volume for adequate energy dissipation. The study concludes that while designing close-to-nature step-pool fish passes, pool dimensions should be finalized with respect to the target aquatic species.

1 citations

Journal ArticleDOI
TL;DR: In this article , the authors studied the three-dimensional transition in the wake of two tandem co-rotating cylinders for Reynolds numbers and showed that the 3-D instability shifts from one mode to another as the rotating cylinders transition via Mode-C and Mode-D instabilities.
Abstract: Abstract Three-dimensional (3-D) transition in the wake of two tandem co-rotating cylinders is studied numerically for Reynolds numbers $180\le Re\le 500$. Infinite cylinders of equal diameter ($D$) and span ($8D$) are placed at streamwise gaps $Lx=2.5D$ and $7.5D$, and rotated at rotation rates $\alpha =0$, $0.5$, $1$ and $2$. For $\alpha =0$ and $Lx=7.5D$, 3-D transition in the wake of the upstream cylinder resembles that for an isolated cylinder with the formation of Mode-A and Mode-B instabilities, whereas for the downstream cylinder, only Mode-A instability occurs in both the $Lx=2.5D$ and $7.5D$ cases with $\alpha =0$. When the cylinders rotate at $\alpha =1$ for $Lx=7.5D$, staggered transition takes place with the appearance of only Mode-B and only Mode-A instabilities in the near-wake regions of the upstream and downstream bodies, respectively. In the case $Lx=2.5D$, the wake of the rotating cylinders transitions via Mode-C and Mode-D instabilities for $\alpha =0.5$, Mode-D and Mode-D$^\prime$ for $\alpha =1$, and Mode-C and Mode-A for $\alpha =2$. A sudden decrease in near-wake fluctuations, accompanied by a downward jump in the force coefficients, is observed as the 3-D instability shifts from one mode to another, for $\alpha \ge 1$ and $Lx=2.5D$. This discontinuity is caused by the formation of a pair of opposite-signed recirculation zones that mitigate each other's effects in the near-wake region.
Journal ArticleDOI
TL;DR: In this paper , the authors developed design charts and rating curves based on numerical modeling using the computational fluid dynamics software FLOW-3D® HYDRO for step-pool nature-like fishways.
Abstract: Hydraulic considerations specific for the design of step-pool nature-like fishways (NLFs) are limited to the body dimensions of the target species. Additional hydraulic criteria for flow depth, maximum values for each of pool depth, velocity, and turbulent kinetic energy in terms of the weir opening width and discharge can help design an optimum step-pool NLF. The present study developed design charts and rating curves based on numerical modeling using the computational fluid dynamics software FLOW-3D® HYDRO. Instantaneous velocity measurements on a 1:4 scaled physical model of a step-pool nature-like fishway designed as per the available design guidelines have been used to validate the numerical model. The hydrodynamics of the fishway with respect to the weir opening ratio b r (0.10, 0.25, 0.45, 0.65, and 1.00) and discharge Q (0.1–1.5 m3/s) was analyzed through numerical simulations on a prototype scale. The simulation results showed that the maximum flow velocity and the averaged velocity over the crest at b r = 0.10 and 0.25 are considerably lower than at b r > 0.25. The maximum turbulent kinetic energy and energy dissipation factors for the tested range of discharges were within recommended limits for b r = 0.10 and 0.25. The present study outcome in terms of the design charts and rating curves that illustrate the relationship between different variables can be used for an optimum design and ease in field implementation. In addition, the bed structure of the step-pool NLF presented in this study can be used to recreate full-scale or pilot models.
Proceedings ArticleDOI
01 Jan 2016
TL;DR: In this paper, circular pile models are suggested as scour reducing structures at river confluences and are studied experimentally and shown to be effective for reducing bed scour and possibly bank erosion.
Abstract: River confluence is a region of merging of two flows of different flow characteristics and sediment loads that result in complex hydrodynamics. The momentum transfer from lateral flow and the flow acceleration causes flow constriction resulting in bed and bank erosion. In this study, circular pile models are suggested as scour reducing structures at river confluences and are studied experimentally. From the scour depth contour maps, it was observed that the bed profiles are remarkably modified with installation of the pile models within the confluence. The scour depth was reduced by 28% with installation of pile models of 12mm diameter at a spacing of 2h. When pile models of 8mm diameter are placed at 2h spacing, the scour depth decreases by 26%. Therefore, the present study shows that pile models are effective for reducing bed scour and possibly bank erosion at confluences.

Cited by
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01 Jan 1993
TL;DR: In this article, an in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter in very clear ocean water.
Abstract: Abstract An in situ suspension camera in combination with an image-analysis system was developed at NIOZ to measure the in situ particle size of suspended matter. It differs from other methods in that in sit particle size is measured from ∼ 4 μm upwards in a relatively simple and direct way. It can be used in any waters down to ∼ 4000 m depth (with some adjustments to 7000 m) and in water with a suspended matter concentration up to 200 mg·dm −3 . In very clear ocean water the system becomes inconvenient because of the large number of photographs that have to be taken to obtain a reliable size distribution. This paper describes the camera and the image-analysis system and gives some results of measurements in the Scheldt river and estuary in April 1989. These measurements show a continuous size distribution by volume between 3.6 μm and 644 μm and a good agreement of the data obtained with the 1:1 and 1:10 cameras.

105 citations

Journal ArticleDOI
TL;DR: In this paper, the benefits achieved due to implementation of IWRM in parts of Khulna and Jessore districts, and investigate some technical aspects evolving TRM have been investigated.
Abstract: The south west coastal zone of Bangladesh have been affected by rampant water logging due to vulnerable climate, silted rivers and stumpy terrain; and introduction of IWRM and TRM at some places of the zone has substantially safeguarded the circumstance. This study aims to assess the benefits achieved due to implementation of IWRM in parts of Khulna and Jessore districts, and investigate some technical aspects evolving TRM. Analyses have been carried out using satellite images, RS and GIS technology, Digital Elevation Model (DEM) and field investigations. A mathematical formulation has been made to assess rate of tidal sedimentation due to TRM and selection strategies of tidal basins. The study comes up with evidences of considerable advancements in regional livelihood i.e. flood resistance, cultivated lands, cultivable area, cropping intensities and food security due to IWRM. Moreover, the technical facts established on TRM would help planners to have vivid perception regarding the process.

42 citations

Journal ArticleDOI
01 Nov 2018-Energies
TL;DR: In this article, the amplitude and frequency ratio curves of three cylinders with roughness were numerically studied by 2D-URANS simulations in Reynolds number range of 30,000 < Re < 105,000.
Abstract: The flow-induced vibration (FIV) of multiple cylinders is a common phenomenon in industry and nature. The FIV and energy harvesting of three circular cylinders in tandem are numerically studied by 2D-URANS simulations in Reynolds number range of 30,000 < Re < 105,000. Simulation results match well with experiments in the tested cases. Four branches of FIV are clearly captured in the amplitude and frequency ratio curves of the three cylinders with roughness, including initial branch of vortex-induced vibration (VIV), VIV upper branch, transition from VIV to galloping, and galloping. It is shown that the vortices from downstream cylinder are strongly disrupted and modified by vortices of upstream cylinder. The third cylinder is almost suppressed in VIV initial branch. The 2P vortex pattern is observed for the first cylinder in the VIV upper branch. For Re = 90,000 in the transition regime, the vortex patterns of the first and second cylinders are 2P + 4S and 2P + 2S, respectively. In the galloping branch, the shear layer motion is in synchronization with the motion of the cylinder, and the maximum amplitude of 2.8D is reached by the first cylinder. The total converted power of the three cylinders increases with U*water both in the simulation and experiment. For the three cylinders, the maximum power reaches up to 85.26 W with the increase of Reynolds number. The energy conversion efficiency is stable and higher than 35% in the starting region of VIV upper branch, and the maximum value of 40.41% is obtained when Re = 40,000.

37 citations

Journal ArticleDOI
TL;DR: A systematic analysis of the published literature on flow regime mapping and effects of external disturbances for flow past a single stationary sphere is presented in this paper, where a coherent presentation has been made on the transitional journey of flow past an isolated stationary single sphere from creeping flow to highly turbulent regimes.

34 citations