scholarly journals DRAG COEFFICIENT OF VEGETATION IN FLOW MODELING

2012 ◽  
Vol 1 (33) ◽  
pp. 4
Author(s):  
Zhan Hu ◽  
M. Stive ◽  
T. Zitman ◽  
T. Suzuki
Keyword(s):  
Drag Coefficient ◽  
Numerical Models ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Local Flow ◽  
Rigid Vegetation ◽  
Flow Through ◽  
The Mean ◽  
Empirical Coefficients

Flow through vegetation has a significant impact on sediment transport and ecosystem robustness in the coastal and fluvial environment. Numerical models (Nepf and Vivoni, 2000; Uittenbogaaard, 2003) have been developed to simulate this type of flow. The success of these models depends on proper characterization of the main processes and appropriate setting of pre-defined empirical coefficients. Among others, the drag coefficient CD is one of the most important coefficients, which influences the mean velocity and the turbulence characteristics (Nepf and Ghisalberti, 2008). Tanino and Nepf (2008) and Cheng (2011) have derived empirical relationships of CD for flow through emerged rigid vegetation. Both studies confirm that CD is related to canopy properties (plants density, diameter, etc.) as well as flow conditions. However, in both studies CD is estimated by simply equating the vegetation drag force to the water level gradient. Bed shear stress and Reynolds stress were ignored. More importantly, the CD provided by these expressions is depth averaged, which is not suitable for modelling flow and canopy that both vary in vertical (Nepf and Vivoni, 2000). In this study, the CD relation proposed by Cheng (2011) is modified. This new relation depends on the local flow conditions and canopy properties in the vertical. Further, this relation is implemented in an iterative scheme of a 1DV flow model. The modelling results are compared with experiment data of flow through emerged and submerged rigid vegetation. Our results show that when special defined Reynolds number is small, this relation performs less well compare to that when it is larger.

The Estimation of Discharge in an Experimental Open Channel

2014 ◽  
Vol 905 ◽  
pp. 369-373
Author(s):  
Choo Tai Ho ◽  
Yoon Hyeon Cheol ◽  
Yun Gwan Seon ◽  
Noh Hyun Suk ◽  
Bae Chang Yeon
Keyword(s):  
Unsteady Flow ◽  
River Discharge ◽  
Open Channel ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Velocity Equation ◽  
The Mean ◽  
Loop Form

The estimation of a river discharge by using a mean velocity equation is very convenient and rational. Nevertheless, a research on an equation calculating a mean velocity in a river was not entirely satisfactory after the development of Chezy and Mannings formulas which are uniform equations. In this paper, accordingly, the mean velocity in unsteady flow conditions which are shown loop form properties was estimated by using a new mean velocity formula derived from Chius 2-D velocity formula. The results showed that the proposed method was more accurate in estimating discharge, when compared with the conventional formulas.

Numerical Study on the Effect of Bend Angle on Turbulent Flow through Oscillating Bend

2009 ◽  
Vol 4 (1) ◽  
Author(s):  
Elham Ameri ◽  
M Nasr Esfahany
Keyword(s):  
Numerical Study ◽  
Bend Angle ◽  
Curvature Radius ◽  
Primary Flow ◽  
Mean Velocity ◽  
Contour Map ◽  
Curved Pipes ◽  
Flow Through ◽  
The Mean ◽  
Turbulent Air Flow

The effect of the bend angle on the unsteady developing turbulent air flow through oscillating circular-sectioned curved pipes with the various angles of 180°, 135° and 90° was investigated numerically. The bends had a diameter of 106 mm and a curvature radius ratio of 6.0 with long, straight upstream and downstream sections. Results of the mean velocity and static pressure were obtained at a Reynolds number of 31200 and at various longitudinal stations. The velocity of the primary flow was illustrated in the form of contour map and vector diagram. From the inlet plane of the three oscillating bends to the angle of 45°, the velocity fields in 180°, 90° and 135° bends are similar. The high velocity regions, however, occur near the upper and lower parts in 90° and 180° bends, respectively.

Axisymmetric Flow in a Motored Reciprocating Engine

1978 ◽  
Vol 192 (1) ◽  
pp. 213-223 ◽  
Author(s):  
A. D. Gosman ◽  
A. Melling ◽  
J. H. Whitelaw ◽  
P. Watkins
Keyword(s):  
Laser Doppler Anemometry ◽  
Axisymmetric Flow ◽  
Flow Characteristics ◽  
Small Scale ◽  
Mean Velocity ◽  
Inlet Velocity ◽  
Reciprocating Engine ◽  
Laminar And Turbulent Flow ◽  
Flow Through ◽  
The Mean

A study was made of axisymmetric, laminar and turbulent flow in a motored reciprocating engine with flow through a cylinder head port. Measurements were obtained by laser-Doppler anemometry and predictions for the laminar case were generated by finite-difference means. Agreement between calculated and measured results is good for the main features of the flow field, but significant small scale differences exist, due partly to uncertainties in the inlet velocity distribution. The measurements show, for example, that the mean velocity field is influenced more strongly by the engine geometry than by the speed. In general, the results confirm that the calculation method can be used to represent the flow characteristics of motored reciprocating engines without compression and suggest that extensions to include compression and combustion are within reach.

scholarly journals HYSTERESIS AND VORTICES DYNAMICS IN A TURBULENT FLOW

2009 ◽  
Vol 19 (08) ◽  
pp. 2695-2703 ◽  
Author(s):  
JAVIER BURGUETE ◽  
ALBERTO DE LA TORRE
Keyword(s):  
Turbulent Flow ◽  
Additive Noise ◽  
Potential Model ◽  
Time Dependent ◽  
Small Range ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Bistable Regime ◽  
The Mean

Recent results about the slow dynamics present in a fully developed turbulent flow are reported. In a previous paper [de la Torre & Burguete, 2007] we showed that the mean velocity field in a turbulent flow bifurcates subcritically breaking some symmetries of the problem and becomes time-dependent because of equatorial vortices moving with a precession movement. This subcriticality produces a bistable regime, whose main characteristics were successfully reproduced using a three-well potential model with additive noise. In this paper we present the characterization of the hysteresis region, not previously observed, in this bifurcation. This hysteresis appears only for an extremely small range of parameters.

scholarly journals Characterisation of vortex shedding on a hydrofoil using PIV measurements

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Hervé Bonnard ◽  
Ludovic Chatellier ◽  
Laurent David
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Statistical Data ◽  
Two Dimensional ◽  
Mean Velocity ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
The Mean ◽  
Flow Configurations

An experimental study of vortex shedding on a hydrofoil Eppler 817 was conducted using two-dimensional two components Particle Image Velocimetry. This foil section’s characteristics are adapted for naval applications but sparsely documented. The characterization of the flow modes was realized based on statistical data such as the mean velocity field and the standard deviation of the vertical velocities. The data were acquired at very low Reynolds number which are not often covered for such hydrofoil and at four angles of attack ranging from 2◦ to 30◦. A map of different characteristic flow modes was made for this space of parameters and was used to identify flow configurations exhibiting particular dynamics.

scholarly journals Turbulent Flow through Random Vegetation on a Rough Bed

Water ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 2564
Author(s):  
Francesco Coscarella ◽  
Nadia Penna ◽  
Aldo Pedro Ferrante ◽  
Paola Gualtieri ◽  
Roberto Gaudio
Keyword(s):  
Flow Field ◽  
Flow Conditions ◽  
Bed Sediments ◽  
Turbulence Characteristics ◽  
Rigid Vegetation ◽  
Laboratory Flume ◽  
Rough Bed ◽  
Flow Through ◽  
Bed Roughness

River vegetation radically modifies the flow field and turbulence characteristics. To analyze the vegetation effects on the flow, most scientific studies are based on laboratory tests or numerical simulations with vegetation stems on smooth beds. Nevertheless, in this manner, the effects of bed sediments are neglected. The aim of this paper is to experimentally investigate the effects of bed sediments in a vegetated channel and, in consideration of that, comparative experiments of velocity measures, performed with an Acoustic Doppler Velocimeter (ADV) profiler, were carried out in a laboratory flume with different uniform bed sediment sizes and the same pattern of randomly arranged emergent rigid vegetation. To better comprehend the time-averaged flow conditions, the time-averaged velocity was explored. Subsequently, the analysis was focused on the energetic characteristics of the flow field with the determination of the Turbulent Kinetic Energy (TKE) and its components, as well as of the energy spectra of the velocity components immediately downstream of a vegetation element. The results show that both the vegetation and bed roughness surface deeply affect the turbulence characteristics. Furthermore, it was revealed that the roughness influence becomes predominant as the grain size becomes larger.

Experimental and Numerical Investigation of Two-Dimensional Parallel Jets

2001 ◽  
Vol 123 (2) ◽  
pp. 401-406 ◽  
Author(s):  
Elgin A. Anderson ◽  
Robert E. Spall
Keyword(s):  
Good Accuracy ◽  
Stokes Equations ◽  
Numerical Models ◽  
Symmetry Plane ◽  
Turbulence Models ◽  
Turbulent Jets ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Navier Stokes Equations ◽  
The Mean

The flowfield of dual, parallel planar turbulent jets is investigated experimentally using an x-type hot-wire probe and numerically by solving the Reynolds-averaged Navier-Stokes equations. The performance of both differential Reynolds stress (RSM) and standard k-ε turbulence models is evaluated. Results show that the numerical models predict the merge and combined point characteristics to good accuracy. However, both turbulence models show a narrower width of the jet envelope than measured by experiment. The predicted profiles of the mean velocity along the symmetry plane agree well with the experimental results.

Experimental Study of the Flow in a Simulated Hard Disk Drive

2006 ◽  
Vol 128 (5) ◽  
pp. 1090-1100 ◽  
Author(s):  
Charlotte Barbier ◽  
Joseph A. C. Humphrey ◽  
Eric Maslen
Keyword(s):  
Hard Disk Drive ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Hard Disk ◽  
Disk Drive ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Local Flow ◽  
The Mean ◽  
Fundamental Value

Instantaneous circumferential and radial velocity components of the air flowing past a symmetrical pair of suspension/slider-units (SSUs) attached to an E-Block/arm were measured in a specially designed corotating disk apparatus simulating a hard disk drive (HDD) using the particle image velocimetry technique. The geometrical dimensions of the components in the apparatus test section were scaled up by a factor of two, approximately, relative to those of a nominal 312 inch HDD. Most of the measurements were obtained on the interdisk midplane for two angular orientations of the arm/SSUs: (a) One with the tip of the SSUs near the hub supporting the disks; (b) another with the tip of the SSUs near the rims of the disks. Data obtained for disk rotational speeds ranging from 250 to 3000rpm (corresponding to 1250 to 15,000rpm, approximately, in a 312 inch HDD) were post-processed to yield mean and rms values of the two velocity components and of the associated shear stress, the mean axial vorticity, and the turbulence intensity (based on the two velocity components). At the locations investigated near the arm/SSUs, and for disk rotational speeds larger than 1500rpm, the mean velocity components are found to be asymptotically independent of disk speed of rotation but their rms values appear to still be changing. At two locations 90 and 29deg, respectively, upstream of the arm/SSUs, the flow approaching this obstruction displays features that can be attributed to the three-dimensional wake generated by the obstruction. Also, between these two locations and depending on the angular orientation of the arm/SSUs, the effect of the obstruction is to induce a three-dimensional region of flow reversal adjacent to the hub. Notwithstanding, the characteristics of the flow immediately upstream and downstream of the arm/SSUs appear to be determined by local flow-structure interactions. Aside from their intrinsic fundamental value, the data serve to guide and test the development of turbulence models and numerical calculation procedures for predicting this complex class of confined rotating flows, and to inform the improved design of HDDs.

Flow in a Channel With Longitudinal Ribs

1994 ◽  
Vol 116 (2) ◽  
pp. 233-237 ◽  
Author(s):  
C. Y. Wang
Keyword(s):  
Reynolds Number ◽  
Eigenfunction Expansion ◽  
Complex Geometry ◽  
Parallel Plates ◽  
Match Method ◽  
Mean Velocity ◽  
Longitudinal Ribs ◽  
Flow Through ◽  
The Mean ◽  
Wetted Perimeter

The laminar, viscous flow between parallel plates with evenly spaced longitudinal ribs is solved by an eigenfunction expansion and point-match method. The ribs on both plates may be symmetrically placed or staggered. For a given pressure gradient, the mean velocity is plotted as a function of the geometric parameters. We find the wetted perimeter and the friction factor—Reynolds number product are unsuitable parameters for the flow through ducts of complex geometry.

Tidal residuals in the English Channel

1977 ◽  
Vol 57 (2) ◽  
pp. 339-354 ◽  
Author(s):  
R. D. Pingree ◽  
Linda Maddock
Keyword(s):  
Numerical Models ◽  
Residual Flow ◽  
English Channel ◽  
Accurate Representation ◽  
Tidal Circulation ◽  
Circulation Patterns ◽  
Flow Through ◽  
The Mean ◽  
Rotating Table ◽  
Tidal Characteristics

The amplitude and phase of tidal characteristics in the English Channel have been described both using numerical models (Grijalva, 1962; Hyacinthe & Kravtchenko, 1967) and a hydraulic model on a rotating table (Chabert d'Hières & le Provost, 1970). The aim behind the development of the numerical model described here is first to derive an accurate representation of the principal lunar semi-diurnal (M2) tide in the English Channel and then to use the currents generated by the tidal input to determine the tidal circulation patterns and residual flow through the English Channel. A test of the model must be its ability to reproduce the known clockwise eddy in Lyme Bay and the south-ward flow either side of Portland Bill. If these known tidal residuals can be reproduced then the model may help to elucidate residuals in other regions where the flow is unknown. In addition to deriving the mean tidal velocities, horizontal distributions for the mean squared and cubed values are calculated and the importance of these distributions in determining the nature of the bottom and the degree of stratification of the water column in summer is demonstrated.

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