A Comparative Analysis of Flow Fields around a Composite Hydrokinetic Device

2020 ◽  
Vol 897 ◽  
pp. 173-178
Author(s):  
Asim Kuila ◽  
Subhasish Das ◽  
Asis Mazumdar
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Velocity Vector ◽  
Vertical Plate ◽  
Horseshoe Vortex ◽  
Horizontal Cylinder ◽  
Cylinder Surface ◽  
Outer Diameter ◽  
Acoustic Doppler Velocimeter ◽  
Flow Feature

. The flow pattern on the combined effect of a horizontal cylinder and a vertical plate is observed and analysed in this experimental study. The experiment was conducted with a 4 cm outer diameter cylinder arranged horizontally across flow above 2 cm from the bed and a vertical plate of 5 cm placed 9 cm downstream from cylinder surface reference as tilting flume bed surface. The water depth was maintained at 17 cm through a constant discharge of 35 lps in a re-circulating flume. Acoustic Doppler Velocimeter (ADV) was used to store the velocity fluctuation of velocity components and further used as a pictorial frame to understand the turbulence and the turbulent kinetic energy around the cylinder, plate and in between the cylinder - vertical plate. From the pictorial contour diagrams drawn, the velocity vector represents the flow feature over the cylinder and it is found that a horseshoe vortex, developed upstream of the plate, does effect on turbulent kinetic energy formed in between cylinder and vertical plate. The observation and obtained results from present study is compared with a 5 cm horizontal cylinder above 2 cm from the bed and a plate situated on 5.5 cm from cylinder curvature towards downstream.

Inner Flow Field PIV Measurement and Study on Turbulence Generator of Medium Consistency Pump

2017 ◽  
Author(s):  
Ye Daoxing ◽  
Lai Xide
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Turbulent Kinetic Energy ◽  
Rotational Speed ◽  
Outer Diameter ◽  
External Diameter ◽  
Plane Flow ◽  
Piv Measurement ◽  
Flow Plane ◽  
Turbulence Generator

In order to study the flow characteristic in turbulence generator of medium consistency pump, a new particle image velocimetry (PIV) test rig was established. 2D-plane flow field was acquired fast and effective by adjusting the angle and position of mirror. For investigate the effect of speed on flow field, velocity and turbulent kinetic energy were measured at speed 80r/min, 130r/min and 200r/min. Dimensionless method was adopted to analyze flow field by quantitative approach. The results showed that on vertical flow plane axial velocities decrease with radius increasing in the region of turbulence generator blade, and axial velocity direction was changed and increase with radius increasing outside the region of turbulence generator blade. Internal flow direction of turbulence generator is at opposite direction with outside flow. Fluid flows from inlet to outlet of turbulence generator blade and then go back to inlet, which forms a circle. On horizontal flow plane, circumferential velocity increase with radius increasing firstly, and then the maximum appears at Outer diameter of turbulence generator, and last it decreases gradually. Turbulent kinetic energy increases with rotational speed increasing at inner of turbulence generator flow field, and high turbulent kinetic energy mainly concentrates near the blade inlet and external diameter of turbulence generator. Therefore, in order to achieve better turbulence effect, high turbulent kinetic energy can be obtained by changing the shape of blade inlet structure, increasing the blade outside diameter and improving rotational speed.

scholarly journals Flow around a scoured bridge pier: a stereoscopic PIV analysis

2020 ◽  
Vol 61 (10) ◽  
Author(s):  
Ulrich Jenssen ◽  
Michael Manhart
Keyword(s):  
Kinetic Energy ◽  
Shear Layer ◽  
Turbulent Kinetic Energy ◽  
Symmetry Plane ◽  
Horseshoe Vortex ◽  
Stereoscopic Particle Image Velocimetry ◽  
Shear Stresses ◽  
Wall Jet ◽  
Velocity Fluctuations ◽  
Scour Hole

Abstract We performed stereoscopic particle image velocimetry of the turbulent flow inside a scour hole around a cylinder in a sandy bed. At two planes, symmetry plane and $$45^\circ$$ 45 ∘ with respect to the approach flow, the flow and its turbulence structure were investigated. We used two Reynolds numbers (20, 000 and 39, 000) based on the cylinder diameter and the depth-averaged velocity in the symmetry plane. The flow is characterized by a strong down-flow in front of the cylinder, a large horseshoe vortex inside the scour, and an upstream directed wall jet underneath. The values of vorticity in the horseshoe vortex and of the velocity in the wall jet are larger than in a comparable configuration on a flat bed. Enhanced levels of turbulent kinetic energy are found around the horseshoe vortex and in the shear layer detaching from the rim. The orientation of the main axis of the velocity fluctuations changes when the flow enters the scour hole: from about wall-parallel in the detaching shear layer to vertical at the horseshoe vortex. The production of turbulent kinetic energy shows a maximum upstream of the horseshoe vortex centre with considerable production in the shear layer and in the wall jet underneath the horseshoe vortex. Furthermore, strong wall-parallel velocity fluctuations are visible in this region, and bimodal velocity distributions are found, but not anywhere else. The time-averaged wall-shear stresses are largest under the horseshoe vortex and most likely larger than in a corresponding flat-bed configuration. Graphic abstract

The structure and budget of turbulent kinetic energy in front of a wall-mounted cylinder

2017 ◽  
Vol 827 ◽  
pp. 285-321 ◽  
Author(s):  
Wolfgang Schanderl ◽  
Ulrich Jenssen ◽  
Claudia Strobl ◽  
Michael Manhart
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Open Channel ◽  
Symmetry Plane ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Bottom Plate ◽  
Minor Role ◽  
Turbulence Structure ◽  
Pressure Transport

We investigate the flow and turbulence structure in front of a cylinder mounted on a flat plate by a combined study using highly resolved large-eddy simulation and particle image velocimetry. The Reynolds number based on the bulk velocity and cylinder diameter is $Re_{D}=39\,000$. As the cylinder is placed in an open channel, we take special care to simulate open-channel flow as the inflow condition, including secondary flows that match the inflow in the experiment. Due to the high numerical resolution, subgrid contributions to the Reynolds stresses are negligible and the modelled dissipation plays a minor role in major parts of the flow field. The accordance of the experimental and numerical results is good. The shear in the approach flow creates a vertical pressure gradient, inducing a downflow in the cylinder front. This downflow, when deflected in the upstream direction at the bottom plate, gives rise to a so-called horseshoe vortex system. The most upstream point of flow reversal at the wall is found to be a stagnation point which appears as a sink instead of a separation point in the symmetry plane in front of the cylinder. The wall shear stress is largest between the main (horseshoe) vortex and the cylinder, and seems to be mainly governed by the strong downflow in front of the cylinder as turbulent stresses are small in this region. Due to a strong acceleration along the streamlines, a region of relatively small turbulent kinetic energy is found between the horseshoe vortex and the cylinder. When passing under the horseshoe vortex, the upstream-directed jet formed by the deflected downflow undergoes a deceleration which gives rise to a strong production of turbulent kinetic energy. We find that pressure transport of turbulent kinetic energy is important for the initiation of the large production rates by increasing the turbulence level in the upstream jet near the wall. The distribution of the dissipation of turbulent kinetic energy is similar to that of the turbulent kinetic energy. Large values of dissipation occur around the centre of the horseshoe vortex and near the wall in the region where the jet decelerates. While the small scales are nearly isotropic in the horseshoe vortex centre, they are anistotropic near the wall. This can be explained by a vertical flapping of the upstream-directed jet. The distribution and level of dissipation, turbulent and pressure transport of turbulent kinetic energy are of crucial interest to turbulence modelling in the Reynolds-averaged context. To the best of our knowledge, this is the first time that these terms have been documented in this kind of flow.

scholarly journals Hydraulic Features of Flow Through Local Non- Submerged Rigid Vegetation in the Y-shaped Confluence Channel

Water ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 146 ◽  
Author(s):  
Xuneng Tong ◽  
Xiaodong Liu ◽  
Ting Yang ◽  
Zulin Hua ◽  
Zian Wang ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Flow Structure ◽  
High Velocity ◽  
Internal Flow ◽  
Acoustic Doppler Velocimeter ◽  
Flow Phenomenon ◽  
Rigid Vegetation ◽  
Flow Through

A laboratory measurement with acoustic Doppler velocimeter (ADV) was used to investigate the flow through a Y-shaped confluence channel partially covered with rigid vegetation on its inner bank. In this study, the flow velocities in cases with and without vegetation were measured by the ADV in a Y-shaped confluence channel. The results clearly showed that the existence of non-submerged rigid plants has changed the internal flow structure. The velocity in the non-vegetated area is greater than in the vegetated area. There is a large exchange of mass and momentum between the vegetated and non-vegetated areas. In addition, due to the presence of vegetation, the high-velocity area moved rapidly to the middle of the non-vegetated area in the vicinity of tributaries, and the secondary flow phenomenon disappeared. The presence of vegetation made the flow in non-vegetated areas more intense. The turbulent kinetic energy of the non-vegetated area was smaller than that of the vegetated area.

Probability law of turbulent kinetic energy in the atmospheric surface layer

2021 ◽  
Vol 6 (7) ◽  
Author(s):  
Mohammad Allouche ◽  
Gabriel G. Katul ◽  
Jose D. Fuentes ◽  
Elie Bou-Zeid
Keyword(s):  
Surface Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Atmospheric Surface Layer

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.

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