scholarly journals WAVE INDUCED VELOCITIES CLOSE TO A RIPPLED BED

1982 ◽  
Vol 1 (18) ◽  
pp. 21
Author(s):  
C.G. Du Toit
Keyword(s):  
Flow Field ◽  
Oscillatory Flow ◽  
Flow Fields ◽  
Flow Reversal ◽  
Velocity Measurements ◽  
Rippled Beds ◽  
Wave Induced ◽  
Rippled Bed

The results are reported of velocity measurements in oscillatory flow over rippled beds. Velocities were measured with a laserdoppler anemometer in both an oscillating tray rig and an oscillatory flow U-tube. Both self-formed and artificial ripples were examined. The results obtained in the two test rigs were compared and it was concluded that the flow fields obtained in the two cases were dynamically similar. Measurements of the flow field clearly showed the formation, growth and ejection of vortices, as well as a strong surge of fluid over the ripples during and after flow reversal.

A numerical study of the wave-induced solute transport above a rippled bed

1995 ◽  
Vol 299 ◽  
pp. 267-288 ◽  
Author(s):  
K. T. Shum
Keyword(s):  
Flow Field ◽  
Solute Transport ◽  
Concentration Profile ◽  
Vortical Flow ◽  
Sediment Surface ◽  
Normal Velocity ◽  
Advective Transport ◽  
Fluid Particles ◽  
Wave Induced ◽  
Rippled Bed

The role of wave-induced separated flow in solute transport above a rippled bed is studied from numerical solutions to the two-dimensional Navier–Strokes equations and the advection-diffusion equation. A horizontal ambient flow that varies sinusoidally in time is imposed far above the bed, and a constant concentration difference between the upper and lower boundaries of computation is assumed. The computed flow field is the sum of an oscillatory rectilinear flow and a vortical flow which is periodic both in time and in the horizontal. Poincaré sections of this flow suggest chaotic mixing. Vertical lines of fluid particles above the crest and above the trough deform into whorls and tendrils, respectively, in just one wave period. Horizontal lines near the bottom deform into Smale horseshoe patterns. The combination of high shear and vortex-induced normal velocity close to the sediment surface results in large net displacements of fluid particles in a period. The resulting advective transport normal to the bed can be higher than molecular diffusion from well within the viscous boundary layer up to a few ripple heights above the bed. When this flow field is applied to the transport equation of a passive scalar, two distinct features – regular temporal oscillations in concentration and a linear time-averaged vertical concentration profile – are found immediately above the bed. These features have also been observed previously in field measurements on oxygen concentration. Advective transport is shown to be dominant even in the region where the time-averaged concentration profile is linear, a region where vertical solute transport has often been estimated using diffusion-type models in many field studies.

scholarly journals Wave-Induced Oscillatory Flow Over a Sloping Rippled Bed

Water ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1618 ◽  
Author(s):  
Carla Faraci ◽  
Pietro Scandura ◽  
Carmelo Petrotta ◽  
Enrico Foti
Keyword(s):  
Oscillatory Flow ◽  
Thin Layers ◽  
Steady Streaming ◽  
Wave Flume ◽  
Flow Asymmetry ◽  
Horizontal Part ◽  
Cohesive Bed ◽  
Sloping Beach ◽  
Wave Induced ◽  
Rippled Bed

In this paper, the findings of an experimental analysis aimed at investigating the flow generated by waves propagating over a fixed rippled bed within a wave flume are reported. The bottom of the wave flume was constituted by horizontal part followed by a 1:10 sloping beach. Bedforms were generated in a previous campaign performed with loose sand, and then hardened by means of thin layers of concrete. The flow was acquired through a Vectrino Profiler along two different ripples, one located in the horizontal part of the bed and the second over the sloping beach. It was observed that, on the horizontal bed, near the bottom, ripple lee side triggered the appearance of an onshore directed steady streaming, whereas ripple stoss side gave rise to an offshore directed steady streaming. On the sloping bed, a strong return current appears at all positions, interacting with the rippled bottom. The turbulence is non-negligible within the investigated water depth, particularly when velocities were onshore directed, due to flow asymmetry. Turbulence caused a considerable flow stirring which, above a non-cohesive bed, could lift the sediment up in the water column and give rise to a strong sediment transport.

Towed Underwater SPIV Measurement of Flow Fields Around a Surface-Piercing Cylinder With Free Surface Effects

2015 ◽  
Author(s):  
Jeonghwa Seo ◽  
Bumwoo Han ◽  
Shin Hyung Rhee
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Surface Wave ◽  
Flow Field ◽  
Cross Section ◽  
Surface Effects ◽  
Flow Fields ◽  
Two Dimensional ◽  
Two Dimensional Flow ◽  
Wave Induced

Effects of free surface on development of turbulent boundary layer and wake fields were investigated. By measuring flow field around a surface piercing cylinder in various advance speed conditions in a towing tank, free surface effects were identified. A towed underwater Stereoscopic Particle Image Velocimetry (SPIV) system was used to measure the flow field under free surface. The cross section of the test model was water plane shape of the Wigley hull, of which longitudinal length and width were 1.0 m and 100 mm, respectively. With sharp bow shape and slender cross section, flow separation was not expected in two-dimensional flow. Flow fields near the free-surface and in deep location that two-dimensional flow field was expected were measured and compared to identify free-surface effects. Some planes perpendicular to longitudinal direction near the model surface and behind the model were selected to track development of turbulent boundary layer. Froude numbers of the test conditions were from 0.126 to 0.40 and corresponding Reynolds numbers were from 395,000 to 1,250,000. In the lowest Froude number condition, free-surface wave was hardly observed and only free surface effects without surface wave could be identified while violent free-surface behavior due to wave-induced separation dominated the flow fields in the highest Froude number condition. From the instantaneous velocity fields, Time-mean velocity, turbulence kinetic energy, and flow structure derived by proper orthogonal decomposition (POD) were analyzed. As the free-surface effect, development of retarded wake, free-surface waves, and wave-induced separation were mainly observed.

Applicability of Femtosecond Laser Electronic Excitation Tagging in Combustion Flow Field Velocity Measurements

2018 ◽  
Vol 72 (12) ◽  
pp. 1807-1813 ◽  
Author(s):  
Dayuan Zhang ◽  
Bo Li ◽  
Qiang Gao ◽  
Zhongshan Li
Keyword(s):  
Flow Field ◽  
Femtosecond Laser ◽  
Electronic Excitation ◽  
Flow Fields ◽  
Velocity Measurements ◽  
Molecular Tagging Velocimetry ◽  
Molecular Tagging ◽  
Field Velocity ◽  
Combustion Flow ◽  
Better Than

Femtosecond laser electronic excitation tagging (FLEET) is a molecular tagging velocimetry technique that can be applied in combustion flow fields, although detailed studies of its application in combustion are still needed. We report the applicability of FLEET in premixed CH4–air flames. We found that FLEET can be applied in all of the combustion areas (e.g., the unburned region, the burned region and the reaction zone). The FLEET signal in the unburned region is significantly higher than that in the burned region. This technique is suitable for both lean and rich CH4–air combustion flow fields and its performance in lean flames is better than that in rich flames.

Numerical Analysis of Flow Fields and Temperature Fields in a Regenerative Heating Furnace for Steel Pipes

2018 ◽  
Vol 10 (3) ◽  
Author(s):  
Yi Han ◽  
Feng Liu ◽  
Xin Ran
Keyword(s):  
Temperature Field ◽  
Flow Field ◽  
Flow Velocity ◽  
Gas Flow ◽  
Flow Fields ◽  
Heating Furnace ◽  
Temperature Fields ◽  
Turbulent Layer ◽  
Steel Pipes ◽  
Pipe Blanks

In the production process of large-diameter seamless steel pipes, the blank heating quality before roll piercing has an important effect on whether subsequently conforming piping is produced. Obtaining accurate pipe blank heating temperature fields is the basis for establishing and optimizing a seamless pipe heating schedule. In this paper, the thermal process in a regenerative heating furnace was studied using fluent software, and the distribution laws of the flow field in the furnace and of the temperature field around the pipe blanks were obtained and verified experimentally. The heating furnace for pipe blanks was analyzed from multiple perspectives, including overall flow field, flow fields at different cross sections, and overall temperature field. It was found that the changeover process of the regenerative heating furnace caused the temperature in the upper part of the furnace to fluctuate. Under the pipe blanks, the gas flow was relatively thin, and the flow velocity was relatively low, facilitating the formation of a viscous turbulent layer and thereby inhibiting heat exchange around the pipe blanks. The mutual interference between the gas flow from burners and the return gas from the furnace tail flue led to different flow velocity directions at different positions, and such interference was relatively evident in the middle part of the furnace. A temperature “layering” phenomenon occurred between the upper and lower parts of the pipe blanks. The study in this paper has some significant usefulness for in-depth exploration of the characteristics of regenerative heating furnaces for steel pipes.

Numerical Simulation of Muzzle Flow Field of Gun Based on CFD

2013 ◽  
Vol 291-294 ◽  
pp. 1981-1984
Author(s):  
Zhang Xia Guo ◽  
Yu Tian Pan ◽  
Yong Cun Wang ◽  
Hai Yan Zhang
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Stokes Equation ◽  
Wave Structure ◽  
Flow Fields ◽  
Single Equation ◽  
Navier Stokes ◽  
Turbulent Model ◽  
Navier Stokes Equation ◽  
Numerical Simulation Result

Gunpowder was released in an instant when the pill fly out of the shell during the firing, and then formed a complicated flow fields about the muzzle when the gas expanded sharply. Using the 2 d axisymmetric Navier-Stokes equation combined with single equation turbulent model to conduct the numerical simulation of the process of gunpowder gass evacuating out of the shell without muzzle regardless of the pill’s movement. The numerical simulation result was identical with the experimental. Then simulated the evacuating process of gunpowder gass of an artillery with muzzle brake. The result showed complicated wave structure of the flow fields with the muzzle brake and analysed the influence of muzzle brake to the gass flow field distribution.

A Laser-Doppler Investigation of the Flow inside a Backswept, Closed, Centrifugal Impeller

1979 ◽  
Vol 21 (1) ◽  
pp. 1-6 ◽  
Author(s):  
D. Adler ◽  
Y. Levy
Keyword(s):  
Flow Field ◽  
Flow Fields ◽  
Fundamental Difference ◽  
Laser Doppler ◽  
Centrifugal Impeller ◽  
Doppler Technique

A laser-Doppler technique is successfully applied to measure the flow field inside a closed, backswept impeller, through a rotating window. Results show that, in contrast to the flow in many radial-exit impellers, the flow in the backswept impeller is stable and attached. Further, comparison with an open impeller demonstrates the fundamental difference in the flow fields near the shroud.

Innovative Flow-Field Combination Design on Direct Methanol Fuel Cell Performance

2006 ◽  
Vol 4 (3) ◽  
pp. 365-368 ◽  
Author(s):  
Guo-Bin Jung ◽  
Ay Su ◽  
Cheng-Hsin Tu ◽  
Fang-Bor Weng ◽  
Shih-Hung Chan
Keyword(s):  
Fuel Cells ◽  
Flow Field ◽  
Direct Methanol Fuel Cells ◽  
Flow Fields ◽  
Cell Performance ◽  
Fuel Cell Performance ◽  
Serpentine Flow Field ◽  
Structure Of Flow ◽  
Direct Methanol ◽  
Stable Performance

The flow-field design of direct methanol fuel cells (DMFCs) is an important subject about DMFC performance. Flow fields play an important role in the ability to transport fuel and drive out the products (H2O,CO2). In general, most fuel cells utilize the same structure of flow field for both anode and cathode. The popular flow fields used for DMFCs are parallel and grid designs. Nevertheless, the characteristics of reactants and products are entirely different in anode and cathode of DMFCs. Therefore, the influences of flow fields design on cell performance were investigated based on the same logic with respect to the catalyst used for cathode and anode nonsymmetrically. To get a better and more stable performance of DMFCs, three flow fields (parallel, grid, and serpentine) utilized with different combinations were studied in this research. As a consequence, by using parallel flow field in the anode side and serpentine flow-field in the cathode, the highest power output was obtained.

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