Analytical expression for velocity profiles and flow resistance in channels with a general class of noncircular cross sections

2015 ◽  
Vol 99 (1) ◽  
pp. 103-118 ◽  
Author(s):  
Shahin Navardi ◽  
Sukalyan Bhattacharya ◽  
Martin Azese
Keyword(s):  
Cross Sections ◽  
General Class ◽  
Flow Resistance ◽  
Velocity Profiles ◽  
Analytical Expression

scholarly journals Underway velocity measurements in the Alderney Race: towards a three-dimensional representation of tidal motions

2020 ◽  
Vol 378 (2178) ◽  
pp. 20190491 ◽  
Author(s):  
Alexei Sentchev ◽  
Thinh Duc Nguyen ◽  
Lucille Furgerot ◽  
Pascal Bailly du Bois
Keyword(s):  
Power Law ◽  
Cross Sections ◽  
Velocity Profiles ◽  
Significant Advance ◽  
Velocity Measurements ◽  
Energy Potential ◽  
Profile Shape ◽  
Power Law Exponent ◽  
The Cross ◽  
Flood Flow

The Alderney Race, located northwest of the Cotentin Peninsula (France), is a site with high tidal-stream energy potential. Circulation through the Alderney Race is complex, with current speed exceeding 3 m s −1 at neap tide. Towed acoustic Doppler current profiler (ADCP) measurements and static point velocity measurements were performed in July 2018 focusing on assessment of circulation and vertical structure of tidal currents. Transect surveys revealed peculiar features of local dynamics such as change in location of the tidal jet on ebb and flood flow. The spatial expanse of the tidal jet was quantified and regions with largely sheared or nearly homogeneous velocity distributions were identified on the cross-sections. Velocity profiles acquired along the cross-sections were accurately characterized using a power law. The spatial variability of the power-law exponent α was found to be large and correlated with the tidal conditions. The largest variation in profile shape was observed in the northern sector and assumed to be generated by the current interaction with a bathymetric constriction. The velocity profiles were found to vary from highly sheared on flood flow to nearly homogeneous on ebb flow, with corresponding range of power-law exponent α variation from 6 to 14. In the southern sector, over a relatively smooth bathymetry, the velocity profile shape was accurately approximated using the 1/7 power law with a range of variation of α from 6.5 to 8, with respect to the tidal conditions. To our knowledge, this is the largest field survey done using towed ADCP and the results could represent a significant advance in tidal site characterization and provide advanced information to turbine developers. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race'.

scholarly journals Velocity and concentration profiles of saline and turbidity currents flowing in a straight channel under quasi-uniform conditions

2014 ◽  
Vol 2 (1) ◽  
pp. 167-180 ◽  
Author(s):  
M. Stagnaro ◽  
M. Bolla Pittaluga
Keyword(s):  
Cross Sections ◽  
Longitudinal Velocity ◽  
Fixed Bed ◽  
Velocity Profiles ◽  
Doppler Velocity ◽  
Turbidity Currents ◽  
Straight Channel ◽  
Densimetric Froude Number ◽  
Vertical Coordinate ◽  
Dimensionless Velocity

Abstract. We present a series of detailed experimental observations of saline and turbidity currents flowing in a straight channel. Experiments are performed by continuously feeding the channel with a dense mixture until a quasi-steady configuration is obtained. The flume, 12 m long, is characterized by a concrete fixed bed with a uniform slope of 0.005. Longitudinal velocity profiles are measured in ten cross sections, 1 m apart, employing an ultrasound Doppler velocity profiler. We also measure the density of the mixture using a rake of siphons sampling at different heights from the bottom in order to obtain the vertical density distributions in a cross section where the flow already attained a quasi-uniform configuration. We performed 27 experiments changing the flow discharge, the fractional excess density, the character of the current (saline or turbidity) and the roughness of the bed in order to observe the consequences of these variations on the vertical velocity profiles and on the overall characteristics of the flow. Dimensionless velocity profiles under quasi-uniform flow conditions were obtained by scaling longitudinal velocity with its depth averaged value and the vertical coordinate with the flow thickness. They turned out to be influenced by the Reynolds number of the flow, by the relative bed roughness, and by the presence of sediment in suspension. Unexpectedly, the densimetric Froude number of the current turned out to have no influence on the dimensionless velocity profiles.

scholarly journals Biorheological Model on Flow of Herschel-Bulkley Fluid through a Tapered Arterial Stenosis with Dilatation

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
S. Priyadharshini ◽  
R. Ponalagusamy
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Power Law ◽  
Flow Resistance ◽  
Velocity Profiles ◽  
Arterial Stenosis ◽  
Axial Distance ◽  
Tapered Artery ◽  
Wall Shear

An analysis of blood flow through a tapered artery with stenosis and dilatation has been carried out where the blood is treated as incompressible Herschel-Bulkley fluid. A comparison between numerical values and analytical values of pressure gradient at the midpoint of stenotic region shows that the analytical expression for pressure gradient works well for the values of yield stress till 2.4. The wall shear stress and flow resistance increase significantly with axial distance and the increase is more in the case of converging tapered artery. A comparison study of velocity profiles, wall shear stress, and flow resistance for Newtonian, power law, Bingham-plastic, and Herschel-Bulkley fluids shows that the variation is greater for Herschel-Bulkley fluid than the other fluids. The obtained velocity profiles have been compared with the experimental data and it is observed that blood behaves like a Herschel-Bulkley fluid rather than power law, Bingham, and Newtonian fluids. It is observed that, in the case of a tapered stenosed tube, the streamline pattern follows a convex pattern when we move fromr/R=0tor/R=1and it follows a concave pattern when we move fromr/R=0tor/R=-1. Further, it is of opposite behaviour in the case of a tapered dilatation tube which forms new information that is, for the first time, added to the literature.

scholarly journals Downstream relaxation of velocity profiles in pipe-flow with swirl disturbances

2016 ◽  
Vol 83 (12) ◽  
Author(s):  
Simon Graner ◽  
Denis F. Hinz ◽  
Christian Breitsamter
Keyword(s):  
Cross Sections ◽  
Pipe Flow ◽  
Performance Indicators ◽  
Laser Doppler Velocimetry ◽  
Swirling Flow ◽  
Flow Patterns ◽  
Velocity Profiles ◽  
Doppler Velocimetry ◽  
Characteristic Shape ◽  
And Performance

AbstractWe study characteristic flow patterns downstream of a standardized swirl disturbance generator using laser-Doppler velocimetry (LDV). To investigate the spatial development of flow patterns, we conduct LDV measurements in cross-sections located at various distances downstream from the swirl disturbance generator. Focusing on velocity profiles, decay of swirl, and performance indicators used to describe the characteristic shape of the velocity profiles, we systematically compare the experimental results with available references and various theories for decay of swirl disturbances. We find that the standardized swirl disturbance generator provides exponentially decaying swirling flow that is best captured by the theory of Steenbergen and Voskamp

scholarly journals Flow Resistance in Lowland Rivers Impacted with Distributed Aquatic Vegetation

2021 ◽  
Author(s):  
Saeid Okhravi ◽  
Radoslav Schügerl ◽  
Yvetta Velísková
Keyword(s):  
Cross Sections ◽  
Flow Resistance ◽  
Aquatic Vegetation ◽  
Roughness Coefficient ◽  
Sources Of Resistance ◽  
Lowland Rivers ◽  
Lowland Streams ◽  
Resistance Factors ◽  
Seasonal Flow ◽  
Bed Roughness

Abstract The study addresses the research concern that the employment of fixed value for bed roughness coefficient in lowland rivers (mostly ‌sand-bed rivers) is deemed practically questionable in the presence of a mobile bed and time-dependent changes in vegetation patches. To address this issue, we set up 45 cross-sections in four lowland streams to investigate seasonal flow resistance values within a year. The results first revealed that the significant sources of boundary resistance in lowland rivers with lower regime flow are bed forms and aquatic vegetation. Then, the study uses flow discharge as an influential variable reflecting the impacts of the above-mentioned sources of resistance to flow. The studied approach ended up with two new flow resistance predictors which simply connect dimensionless unit discharge with flow resistance factors, Darcy-Weisbach (f) and Manning (n) coefficients. A comparison between the computed and measured flow resistance values indicates that 87-89% of data sets were within the ±20% error bands. The flow resistance predictors are also verified against large independent sets of field and flume data. The obtained predictions using the developed predictors may overestimate flow resistance factors to about 40% for other lowland rivers. From a different view of this research, the findings on seasonal variation of vegetation abundance hint at the augmentation in flow resistance values, both f, and n, in low summer flows when the vegetation covers river bed and side banks. The highest amount of flow resistance was observed during the summer period, July-August.

scholarly journals A numerical investigation into electroosmotic flow in microchannels with complex wavy surfaces

2011 ◽  
Vol 15 (suppl. 1) ◽  
pp. 87-94 ◽  
Author(s):  
Her-Terng Yau ◽  
Cheng-Chi Wang ◽  
Ching-Chang Cho ◽  
Cha’o-Kuang Chen
Keyword(s):  
Cross Sections ◽  
Electroosmotic Flow ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Governing Equations ◽  
Electrical Field ◽  
Flow Recirculation ◽  
Wavy Surfaces ◽  
Pressure Driven Flow ◽  
General Method

This study investigates the flow characteristics of electroosmotic flow in a microchannel with complex wavy surfaces. A general method of coordinate transformation is used to solve the governing equations describing the electroosmotic flow in the microchannel. Numerical simulations are performed to analyze the effects of wave amplitude on the electrical field, flow streamlines, and flow fields in the microchannel. The simulation results show that, compared to a traditional pressure-driven flow, flow recirculation is not developed in the electroosmotic flow in a microchannel with complex wavy surfaces. The simulations also show that the electrical field and velocity profiles change along the channel in the region of wavy surfaces. Non-flat velocity profiles are observed in different cross-sections of the channel in the region of wavy surfaces.

On the effect of surface roughness on velocity profiles and runout lengths of dry granular flows

2020 ◽  
Author(s):  
Lukas Reider ◽  
Roland Kaitna
Keyword(s):  
Surface Roughness ◽  
Cross Sections ◽  
High Speed ◽  
Maximum Flow ◽  
Velocity Profiles ◽  
Small Scale ◽  
Relative Roughness ◽  
Laser Sensors ◽  
Mass Flows ◽  
Set Up

<p>Gravitational mass flows like debris flows are often physically modelled as an assembly of particles flowing in simplified flume configurations. There is indication that natural flows exhibit a combined movement of sliding and internal deformation, which is not well understood and underrepresented in scaled laboratory experiments. In this study we investigate the effect of the surface roughness on the velocity profile and the runout of small-scale, dry granular avalanches. The experimental set-up is a 0.17 m wide flume with an inclination of 34° for the first 1.5 m, following an 0.8 m curved transition zone with a radius of 1.7 m, and ending in a runout zone with an angle of 4°. The tested material consisted of non-perfect spherical ceramic beads with a diameter of 2.8 to 4.3 mm. We tested four different types of surface roughness ranging from 0 to 6 mm height and additionally one macro roughness, which was higher than the maximum flow height. To also get information about the influence of the relative roughness experiments with three different starting volumes were undertaken. All fourteen experimental variations were repeated three times. Flow heights were measured with laser sensors at four different positions along the channel. Three of them were used to calculate the mean front velocity of the flowing mass in two cross sections. Furthermore, the experiments were recorded with a high-speed camera through one sidewall out of acrylic glass. The recordings were analysed using a PIV (Particle Image Velocimetry) software to derive velocity profiles in 1/1500 second time steps. Results show that the velocity profiles changed from the head to the tail of the flow and that the profiles of the two roughest surfaces are more alike than the smooth roughness configurations. The fraction of sliding on the total movement varied between 0 and close to unity. The runout length decreased the higher the roughness was and increased with higher starting volume. The shape of the velocity profiles at the deepest sections of the flows changed with surface roughness and with starting volumes. Only the velocity profiles for the two roughest surfaces show an inflection point. Our experiments highlight the importance of surface roughness as well as relative roughness for granular mass flows and provide data for model testing.</p>

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