scholarly journals Experimental Investigation of the Reynolds Shear Stress Exceedance Rate for the Injury and Disorientation Biocriteria Boundary in the Pool-Orifice and Vertical Slot Type Fishways

2021 ◽  
Vol 11 (16) ◽  
pp. 7708
Author(s):  
Gordon Gilja ◽  
Eva Ocvirk ◽  
Robert Fliszar
Keyword(s):  
Shear Stress ◽  
Flow Field ◽  
Negative Impact ◽  
Swimming Performance ◽  
Reynolds Shear Stress ◽  
Ecological Status ◽  
Migration Flow ◽  
Vertical Slot ◽  
Flow Field Characteristics ◽  
Orifice Size

Fragmentation of rivers has a negative impact on river’s ecological status which can be improved by the construction of fishways next to obstacles in rivers that prevent a free migration. Flow field characteristics are key factors in the design process of hydraulically efficient fishways—flow and turbulence patterns in a functional fishway allow fish to enter, progress through and exit with minimum time/energy expenditure. The aim of this paper is an experimental study of the flow field characteristics measured in the physical fishway model with the goal of providing information on the Reynold’s shear stress distribution that would facilitate their design in accordance with the environmental requirements. The focus of the research was on the nominally hydraulically efficient con-figuration pool-type fishways—pool-orifice and vertical slot. Fishway geometry was varied for bottom slope (7.5%, 10% and 12.5%), pool length (45 cm, 60 cm and 90 cm) and orifice size (8 × 8 cm, 10 × 10 cm and 12 × 12 cm) in a model scaled 1:3 to the prototype. Since Reynold’s shear stress has been identified as the main turbulent parameter affecting fish swimming performance and behavior, it is used as the basis for the analyses. The velocity data were collected with Vectrino ADV and processed in all three planes—streamwise, horizontal and vertical. Reynold’s shear stress data were analyzed according to the injury (>50 N/m2) and disorientation (>30 N/m2) biocriteria boundaries defined in the literature. The percentage of the flow field exceeding the boundaries were analyzed depending on the fishway geometry. The results obtained in this research suggest that the critical design parameter is the orifice size for the pool-orifice fishways and the pool length for the VS fishway. The Reynold’s shear stress is generally the highest in the bottom layer for pool-orifice fishways and the surface layer for vertical slot fishways.

scholarly journals Reynolds shear-stress and velocity: positive biological response of neotropical fishes to hydraulic parameters in a vertical slot fishway

2012 ◽  
Vol 10 (4) ◽  
pp. 813-819 ◽  
Author(s):  
Bernardo Alan de Freitas Duarte ◽  
Isabella Cristina Resende Ramos ◽  
Hersília de Andrade e Santos
Keyword(s):  
Shear Stress ◽  
Fish Species ◽  
Velocity Fluctuation ◽  
Reynolds Shear Stress ◽  
Neotropical Fishes ◽  
Fish Ladder ◽  
Vertical Slot ◽  
Structure Of Flow ◽  
Vertical Slot Fishway ◽  
Pimelodus Maculatus

The barriers created by dams can cause negative impacts to aquatic communities, and migratory fish species are directly affected. Fishways have been developed to allow the upstream passage of fishes through dams. In Brazil, after the implementation of environmental laws, these structures have been built based on European and American fishway designs. Studies have shown selectivity for different neotropical fishes in some Brazilian fishways, and the main challenge has been to promote upstream passage of a large number of diverse fish species. The patterns of flow circulation within the fish ladder may explain fish selectivity although few studies detail the fish response to hydraulic characteristics of fish ladder flow. This paper presents a laboratory study, where a vertical slot fishway was built in a hydraulic flume and the behavior of two neotropical fish species (Leporinus reinhardti and Pimelodus maculatus) were analyzed. The structure of flow was expressed in terms of mean velocity, Reynolds shear-stress and velocity fluctuation fields. The individuals of Leporinus reinhardti had higher passage success than Pimelodus maculatus in the laboratory flume. Both species preferred areas of low to zero Reynolds shear-stress values. In addition, different preferences were observed for these species concerning the horizontal components of velocity fluctuation.

scholarly journals Study on the Spatial Pattern of Migration Population in Egypt and Its Flow Field Characteristics from the Perspective of “Source-Flow-Sink”

2021 ◽  
Vol 13 (1) ◽  
pp. 350
Author(s):  
Zhishan Ma ◽  
Susu Zhang ◽  
Sidong Zhao
Keyword(s):  
Flow Field ◽  
Spatial Pattern ◽  
Local Development ◽  
Mediterranean Coast ◽  
Population Migration ◽  
Channel Network ◽  
Central System ◽  
Migration Flow ◽  
Flow Field Characteristics ◽  
Source Flow

Based on the provinces as the spatial nodes of population migration, a “Source-Flow-Sink” analysis framework of population migration flow in Egypt was established by “Source-Sink” Theory and Flow Field Theory to study the migration population in Egypt. It reveals the spatial pattern of the migration population in Egypt and its flow field characteristics and provides theoretical basis for the formulation of population development policies and regional spatial governance planning. The results show that: (1) there are significant spatial differences in the size and rate of migration in Egypt. In 2017, the migration population in Egypt exceeded 2.2 million in total, with a migration rate of 2.33%, and the extreme multiple reached 80 and 12. (2) According to the spatial pattern of geographical distribution, the Source System is divided into five types: axis type, layer type, fan type, oblique symmetry type, and scattered jump type. There are only three types in Sink System, namely wide area coverage type, local development type, and scattered jump type. Source Places lie in the middle, Sink Places are symmetrical from east to west, and Exchange Places are concentrated along the Mediterranean coast in the north of Cairo on the whole, with the initial formation of a “core-periphery” spatial pattern. (3) The interprovincial population migration flow in Egypt is dominated by neighborhood penetration and polarization of high-rank nodes (capitals or regional economic centers), giving rise to 7 modes of central system spatial structures and 3 modes of pole-core interaction. The central system of flow fields with clear priorities and the streamline channel network with layered trunks and branches basically take shape, overall characterized by stepped runoff from east to west, and local convection from south to north.

Structure of Turbulence Within a Sheared Wake of a Rotor Blade

2006 ◽  
Author(s):  
Francesco Soranna ◽  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Production Rate ◽  
Rotor Blade ◽  
Energy Production ◽  
Reynolds Shear Stress ◽  
Suction Side ◽  
Velocity Fluctuations

Stereoscopic PIV measurements examine the flow structure and turbulence within a rotor near wake located within a non-uniform field generated by a row of Inlet Guide Vanes (IGVs). The experiments are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. The data are acquired at 10 closely spaced radial planes located near mid-span, enabling measurements of all the components of the phase averaged velocity and strain rate, as well as the Reynolds stress and the triple correlation tensors. The rotor wake is sheared and bent towards the pressure (inner) side by a non-uniform flow field generated by IGV wake segments that propagate along the suction and pressure sides of the rotor passage with different speeds. The axial velocity fluctuations increase along the suction/outer side of the wake, while the other components decay. On the pressure/inner part of the bent wake the circumferential velocity fluctuations are higher. The Reynolds shear stress has a complex distribution, but is higher on the suction side. The turbulent kinetic energy is also consistently higher on the outer (suction) side of the wake. This trend is fundamentally different from those observed in prior studies of curved wakes where turbulence is enhanced on the inner side of the wake due to the destabilizing effect of curvature. To explain the difference, we examine the contributors to turbulent kinetic energy production rate in a curvilinear coordinate system aligned with the wake-centerline. The contribution of streamwise curvature to the production rate of turbulent kinetic energy, although consistent with expected trends, is overwhelmed by effects of wake shearing. The primary contributor to turbulent kinetic energy production rate is the product of Reynolds shear stress with cross-stream gradients of streamwise (in a frame of reference relative to the rotor blade) velocity in the wake. The location of peak in turbulent kinetic energy is almost aligned with that of production rate. The turbulence diffusion term opposes the production rate peaks, but also has high values along the edge of the wake.

New Blood Vessel Robot Design and Outside Flow Field Characteristic

2010 ◽  
Vol 29-32 ◽  
pp. 2490-2495 ◽  
Author(s):  
Fan Jiang ◽  
Juan Yu ◽  
Zhong Wei Liang
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Field ◽  
Blood Vessel ◽  
Unsteady Flow ◽  
Thrust Force ◽  
Robot Design ◽  
Flow Parameters ◽  
Flow Field Characteristics ◽  
Cfd Method

A new blood vessel robot is designed, which has two fragellas and cylinder, its thrust force and torque equations are given. Through CFD method simulated the outside flow field characteristics of robot, lots of flow parameters could be obtained, these data help us to optimize the outline of robot. From the computation results, the wall shear stress (WSS) should be influent by flow status (steady flow or unsteady flow) and robot outline, along with velocity decreases, the WSS declines, and the WSS, pressure, velocity would vary obviously as the robot outline changes.

scholarly journals A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4136
Author(s):  
Clemens Gößnitzer ◽  
Shawn Givler
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Negative Impact ◽  
Operating Conditions ◽  
Engine Operation ◽  
Gas Engine ◽  
Cycle Simulation ◽  
Simulation Results ◽  
The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

scholarly journals Coupled Fluid–Solid Numerical Simulation for Flow Field Characteristics and Supporting Performance of Flexible Support Cylindrical Gas Film Seal

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 97
Author(s):  
Junfeng Sun ◽  
Meihong Liu ◽  
Zhen Xu ◽  
Taohong Liao ◽  
Xiangping Hu ◽  
...  
Keyword(s):  
Flow Field ◽  
Film Thickness ◽  
Fluid Dynamic ◽  
Structural Characteristics ◽  
Structural Parameters ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
High Rotational Speed ◽  
Flexible Support ◽  
Flow Field Characteristics

A new type of cylindrical gas film seal (CGFS) with a flexible support is proposed according to the working characteristics of the fluid dynamic seal in high-rotational-speed fluid machinery, such as aero-engines and centrifuges. Compared with the CGFS without a flexible support, the CGFS with flexible support presents stronger radial floating characteristics since it absorbs vibration and reduces thermal deformation of the rotor system. Combined with the structural characteristics of a film seal, an analytical model of CGFS with a flexible wave foil is established. Based on the fluid-structure coupling analysis method, the three-dimensional flow field of a straight-groove CGFS model is simulated to study the effects of operating and structural parameters on the steady-state characteristics and the effects of gas film thickness, eccentricity, and the number of wave foils on the equivalent stress of the flexible support. Simulation results show that the film stiffness increases significantly when the depth of groove increases. When the gas film thickness increases, the average equivalent stress of the flexible support first decreases and then stabilizes. Furthermore, the number of wave foils affects the average foils thickness. Therefore, when selecting the number of wave foils, the support stiffness and buffer capacity should be considered simultaneously.

scholarly journals Influence of Vortex Finder Structure on Separation Performance of Double-Overflow Three-Product Hydrocyclones

Separations ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 79
Author(s):  
Yuekan Zhang ◽  
Jiangbo Ge ◽  
Lanyue Jiang ◽  
Hui Wang ◽  
Junru Yang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Experimental Research ◽  
Separation Efficiency ◽  
Structural Parameters ◽  
Separation Performance ◽  
Insertion Depth ◽  
Flow Field Characteristics ◽  
Vortex Finder ◽  
Fine Classification

In view of the difficulty of traditional hydrocyclones to meet the requirements of fine classification, a double-overflow three-product (internal overflow, external overflow and underflow) hydrocyclone was designed in this study. Numerical simulation and experimental research methods were used to investigate the effects of double-overflow flow field characteristics and structural parameters (i.e., internal vortex finder diameter and insertion depth) on separation performance. The research results showed that the larger the diameter of the internal vortex finder, the greater the overflow yield and the larger the cut size. The finest internal overflow product can be obtained when the internal vortex finder is 30 mm longer than the external vortex finder. The separation efficiency is highest when the internal vortex finder is 30 mm shorter than the external vortex finder.

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