scholarly journals STUDY ON FLOW CHARACTERISTICS IN AN OPEN-CHANNEL WITH A SUDDEN EXPANSION AND A CONTRACTION

2000 ◽  
Vol 44 ◽  
pp. 509-514
Keyword(s):  
Open Channel ◽  
Flow Characteristics ◽  
Sudden Expansion

scholarly journals Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1718
Author(s):  
Hasan Zobeyer ◽  
Abul B. M. Baki ◽  
Saika Nowshin Nowrin
Keyword(s):  
Turbulent Flow ◽  
Open Channel ◽  
Recirculation Zone ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Recirculation ◽  
Tandem Cylinders ◽  
Flow Development ◽  
The Mean ◽  
Recirculation Length

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.

Transverse Distribution of the Streamwise Velocity for the Open-channel Flow With Floating Vegetated Islands

2021 ◽  
Author(s):  
Xuecheng Fu ◽  
Feifei Wang ◽  
Mengyang Liu ◽  
Wenxin Huai
Keyword(s):  
Channel Flow ◽  
Open Channel ◽  
Flow Characteristics ◽  
Open Channel Flow ◽  
Streamwise Velocity ◽  
Transport Efficiency ◽  
Transverse Distribution ◽  
Floating Vegetation ◽  
Shear Turbulence ◽  
Field Disturbance

Abstract Floating vegetation islands (FVIs) have been widely utilized in various river ecological restoration projects due to their ability to purify pollutants. FVIs float at the surface of shallow pools with their roots unanchored in the sediment. Biofilm formed by roots under islands filters nutrients and particles in the water flowing through it. Flow field disturbance will occur and transverse distribution of flow velocity will change due to the existence of FVIs. Transport efficiency of suspended solids, nutrients, and pollutants will also be altered. A modified analytical model that considers effects of boundary friction, drag force of vegetation, transverse shear turbulence, and secondary flow is established to predict transverse variation of depth-averaged streamwise velocity for the open-channel flow with FVIs using Shiono and Knight method. The simulation results with suitable boundary conditions successfully predicted lateral profile of the depth-averaged streamwise velocity compared with the experimental results of symmetrical and unsymmetrical arrangements of FVIs. Hence, the presented model can provide guidance for investigating flow characteristics of rivers with FVIs.

A New Tailpipe Design for GE Frame-Type Gas Turbines to Substantially Lower Pressure Losses

2003 ◽  
Vol 125 (1) ◽  
pp. 128-132
Author(s):  
Richard Golomb ◽  
Vivek Sahai ◽  
Dah Yu Cheng
Keyword(s):  
Power Systems ◽  
Gas Turbines ◽  
Large Angle ◽  
Flow Characteristics ◽  
Exhaust System ◽  
Sudden Expansion ◽  
Pressure Losses ◽  
Turbine Efficiency ◽  
Fluid Systems ◽  
Large Pressure

Many GE frame gas turbines have a unique 90-deg tailpipe exhaust system that contains struts, diffusers, and turning vanes. As confirmed in a recent report by GE and other authors, it is known in the industry that this tailpipe design has large pressure losses. In this recent report a pressure loss as high as 60 in. of water (0.15 kgs/sqcm) was cited. Due to the flow separations they create, the report indicates that the struts can cause very high-pressure losses in the turbine. The report also states that these pressure losses can vary with different turbine load conditions. Cheng Fluid Systems and Cheng Power Systems have conducted a study aimed at substantially reducing these pressure losses. Flow control technology introduced to the refinery industry, i.e., the Cheng Rotation Vane (CRV) and the Large Angle Diffuser (LAD) can be used to mitigate the flow separation and turbulence that occurs in turns, bends, and large sudden expansions. Specifically the CRV addresses the flow separations in pipe turns, and the LAD addresses the flow problems that occur with large sudden expansion areas. The paper will introduce the past experience of the CRV and LAD, and will then use computer simulations to show the flow characteristics around a new design. First, the study meticulously goes through the entire GE exhaust system, starting with the redesign of the airfoil shape surrounding the struts. This new design has a larger angle of attack and minimizes the flow separations over a much wider operating range. Second, the pros and cons of the concentric turning vanes are studied and it is shown that they are more flow restrictive, rather than flow enhancing. Third, it is shown that the highly turbulent rectangular box-type exhaust ducting design, substantially contributes to high noise levels and pressure losses. In this paper a completed design will be shown that incorporates a new airfoil shape for the struts, and by using CRV flow technology in combination with the LAD flow technology, the pressure recovery can be enhanced. If the pressure losses could be reduced by 40 inches of water (0.10 kgs/sqcm), the turbine efficiency could be increased by 5%, and the power output could be increased by 6%.

scholarly journals Turbulent Viscosity Concept Downstream an Open-Channel Sudden Expansion

2016 ◽  
Vol 9 (7) ◽  
pp. 2311-2319
Author(s):  
Lei Han ◽  
E. Mignot ◽  
Nicolas Riviere ◽  
◽  
◽  
...  
Keyword(s):  
Open Channel ◽  
Turbulent Viscosity ◽  
Sudden Expansion

scholarly journals Impact of Different Vegetation Zones on the Velocity and Discharge of Open-Channel Flow

2021 ◽  
Author(s):  
Xiaonan Tang ◽  
Yutong Guan ◽  
Yuxiang Hu
Keyword(s):  
Shear Layer ◽  
Management Practices ◽  
Open Channel ◽  
Flow Characteristics ◽  
Flow Region ◽  
Free Flow ◽  
Flow Process ◽  
Riparian Management ◽  
Free Zone ◽  
Rigid Vegetation

Different types of vegetation widely exist in rivers and wetlands. The vegetation will affect the ecological environment and flow process, thus becoming increasingly significant in river engineering and aquatic environmental management. Previous research on vegetated flow is mainly to understand the flow structure of open channels with fully covered one-layer vegetation. However, vegetation often grows along a river bank and co-exists in different heights. The present paper presents experimental results about the flow characteristics of an open-channel with two sides covered by differently layered vegetation, focusing on the effect of vegetation on the velocity distribution and discharge. Two heights of dowels in 10 cm and 20 cm were used to simulate rigid vegetation and arranged in a linear form on both sides of a channel bed under emergent and fully submerged flow conditions. The velocity at different positions was obtained using ADV (Acoustic Doppler Velocimetry). Measured results demonstrate that there exists a shear layer between free-flow and vegetated zones, indicating that the flow transition occurs between fast-moving flow in the free zone and slowly obstructed flow in the vegetated zone and induces a high shear layer and transverse coherent vortices near the interface. Furthermore, compared with the emergent condition, the discharge through the free-flow region slightly decreases under full submerged conditions while the discharge in the vegetated region increases, indicating that the vegetation does not significantly change the discharge percentage in the free region. These findings on differently-layered vegetation would help riparian management practices to maintain healthy ecological and habitat zones.

scholarly journals Two-Phase Flow Characteristics on The Extensive Expansion Channel

2017 ◽  
Vol 16 (2) ◽  
Author(s):  
Latif Ngudi Wibawanto ◽  
Budi Santoso ◽  
Wibawa Endra Juwana
Keyword(s):  
Flow Pattern ◽  
Homogeneous Model ◽  
Flow Characteristics ◽  
Flow Equation ◽  
Pressure Recovery ◽  
Sudden Expansion ◽  
Air Velocity ◽  
Two Phase ◽  
Model Flow ◽  
Two Phases

This research was conducted to find out the flow characteristic of two phases through channel with sudden expansion in the form of change of flow pattern and pressure recovery. The test was conducted with variation of superficial velocity of water 0.2-1.3 m / s and superficial air velocity of 0.2-1.9 m / s resulting in pattern of three flow patterns ie bubble, plug, and slug. The expansion channel resulted in some changes to the flow pattern that originally plugs in the upstream channel into bubble in the downstream channel and the slug becomes plug. Pressure recovery experimental results were compared with the homogeneous model flow equation and Wadle correlation, the two correlations had predictions with standard deviation values of 0.32 and 0.43.

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