Characterization of drag reduction performance over rotating microgrooves with different cross-sections

2019 ◽  
Vol 234 (6) ◽  
pp. 1746-1758
Author(s):  
Suping Wen ◽  
Wenbo Wang ◽  
Zhixuan Zhang
Keyword(s):  
Drag Reduction ◽  
Cross Sections ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Cross Sectional ◽  
Dimensionless Velocity ◽  
Velocity Shift ◽  
Maximum Drag Reduction ◽  
Sectional Parameters

This paper presents a study of cross-sectional parameters and optimal drag reduction performance specifically for drag reduction in rotating microgroove applications. Rotating triangular microgrooves with nine asymmetrical and symmetrical cross-sections were numerically studied. In addition, a representative symmetrical rotating microgroove was experimentally tested. Positive asymmetrical microgrooves (including symmetrical microgrooves) were found to be sensitive to rotating Reynolds numbers and produced more significant drag reduction. Compared with a dimensioned asymmetry variable and other dimensionless parameters, the dimensionless asymmetry variable i+ could be used to describe drag reduction performance, which captured both the influence of microgroove cross-sectional asymmetry and turbulence intensity. A maximum drag reduction of up to 8.9% was obtained at 9.2 i+. With the exception of the torque, the velocity shift obtained from dimensionless velocity profiles could also be used to predict drag reduction performance, which has the potential for wider and more comprehensive application for any drag reduction technology.

scholarly journals Dynamics of viscoelastic pipe flow at low Reynolds numbers in the maximum drag reduction limit

2019 ◽  
Vol 874 ◽  
pp. 699-719 ◽  
Author(s):  
Jose M. Lopez ◽  
George H. Choueiri ◽  
Björn Hof
Keyword(s):  
Drag Reduction ◽  
Turbulent Flows ◽  
Pipe Flow ◽  
Domain Size ◽  
Reynolds Numbers ◽  
Weissenberg Number ◽  
Pipe Length ◽  
Low Reynolds Numbers ◽  
Maximum Drag Reduction ◽  
Low Reynolds

Polymer additives can substantially reduce the drag of turbulent flows and the upper limit, the so-called state of ‘maximum drag reduction’ (MDR), is to a good approximation independent of the type of polymer and solvent used. Until recently, the consensus was that, in this limit, flows are in a marginal state where only a minimal level of turbulence activity persists. Observations in direct numerical simulations at low Reynolds numbers ($Re$) using minimal sized channels appeared to support this view and reported long ‘hibernation’ periods where turbulence is marginalized. In simulations of pipe flow at $Re$ near transition we find that, indeed, with increasing Weissenberg number ($Wi$), turbulence expresses long periods of hibernation if the domain size is small. However, with increasing pipe length, the temporal hibernation continuously alters to spatio-temporal intermittency and here the flow consists of turbulent puffs surrounded by laminar flow. Moreover, upon an increase in $Wi$, the flow fully relaminarizes, in agreement with recent experiments. At even larger $Wi$, a different instability is encountered causing a drag increase towards MDR. Our findings hence link earlier minimal flow unit simulations with recent experiments and confirm that the addition of polymers initially suppresses Newtonian turbulence and leads to a reverse transition. The MDR state on the other hand results at these low$Re$ from a separate instability and the underlying dynamics corresponds to the recently proposed state of elasto-inertial turbulence.

Characterization of the Centroidal Geometry of Human Ribs

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Matthew W. Kindig ◽  
Richard W. Kent
Keyword(s):  
Cross Sections ◽  
Posterior Extremity ◽  
Radius Of Curvature ◽  
Cross Sectional ◽  
Surface Reconstructions ◽  
C1 Continuity ◽  
Best Fit ◽  
Novel Model ◽  
Geometric Primitives

While a number of studies have quantified overall ribcage morphology (breadth, depth, kyphosis/lordosis) and rib cross-sectional geometry in humans, few studies have characterized the centroidal geometry of individual ribs. In this study, a novel model is introduced to describe the centroidal path of a rib (i.e., the sequence of centroids connecting adjacent cross-sections) in terms of several physically-meaningful and intuitive geometric parameters. Surface reconstructions of rib levels 2–10 from 16 adult male cadavers (aged 31–75 years) were first extracted from CT scans, and the centroidal path was calculated in 3D for each rib using a custom numerical method. The projection of the centroidal path onto the plane of best fit (i.e., the “in-plane” centroidal path) was then modeled using two geometric primitives (a circle and a semiellipse) connected to give C1 continuity. Two additional parameters were used to describe the deviation of the centroidal path from this plane; further, the radius of curvature was calculated at various points along the rib length. This model was fit to each of the 144 extracted ribs, and average trends in rib size and shape with rib level were reported. In general, upper ribs (levels 2–5) had centroidal paths which were closer to circular, while lower ribs (levels 6–10) tended to be more elliptical; further the centroidal curvature at the posterior extremity was less pronounced for lower ribs. Lower ribs also tended to exhibit larger deviations from the best-fit plane. The rib dimensions and trends with subject stature were found to be consistent with findings previously reported in the literature. This model addresses a critical need in the biomechanics literature for the accurate characterization of rib geometry, and can be extended to a larger population as a simple and accurate way to represent the centroidal shape of human ribs.

Drag Reduction by Culture Solutions of Dry Malted Rice

2009 ◽  
Author(s):  
Keizo Watanabe ◽  
Satoshi Ogata
Keyword(s):  
Drag Reduction ◽  
Pipe Flow ◽  
Reynolds Numbers ◽  
Type B ◽  
Turbulent Drag Reduction ◽  
Turbulent Drag ◽  
Diameter Pipe ◽  
Maximum Drag Reduction ◽  
Inner Diameter ◽  
Biopolymer Solutions

Turbulent drag reduction by culture solutions of dry malted rice was investigated in a 2.00mm-inner-diameter pipe flow of length 50 diameters at Reynolds numbers from 500 to 8000. The drag reducing abilities of the solutions were tested by comparing drag reduction effectiveness at different concentrations and culture times in water. Comparisons between polysaccharide biopolymer solutions and culture solutions of dry malted rice revealed that the test solutions exhibited Type B drag reduction, which were roughly parallel to, but displaced upwards from, the Newtonian Prandtl-Ka´rma´n law. The maximum drag reduction ration was about 30% at a Reynolds number of 8,000. It is shown also that the onset point of drag reduction phenomena was Ref = 200.

scholarly journals Study the Characterization of Adding Polymer-Surfactant Agent on the Drag Reduction Phenomena in Pipeline Flow System

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Sahar A. Dawood
Keyword(s):  
Aqueous Solution ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Friction Factor ◽  
Methyl Cellulose ◽  
Fluid Properties ◽  
Maximum Drag Reduction ◽  
Polymer Surfactant ◽  
Good Agreement

  Abstract     In this study, the effect of carboxylic methyl cellulose (CMC), and sodium dodcyl benzene sulfonate (SDBS) as an aqueous solution on the drag reduction was investigated. Different concentrations of (CMC) and (SDBS) such as (50, 100, 150, 200, 250, 300, 350, 400, 450, and 500 ppm) were used to analyze the aqueous solution properties, including surface tension, conductivity, and shear viscosity. The optimum four concentrations (i.e., 50, 100, 200, and 300 ppm) of fluid properties were utilized to find their effect on the drag reduction. Two different PVC pipe diameters (i.e., 1" and 3/4") were used in this work. The  results showed that blending CMC with SDBS gives a good drag reduction percent about (58%) more than using them individually, friction factor decreasing with increasing Reynolds number and gives good agreement with von Karamn equation and maximum drag reduction (MDR) asymptote. Reynolds number, pipe diameter, and polymer-surfactant concentrations were considered as influencing factors. In addition, critical micelle concentration, the onset of drag reduction, and the interactions between the mixed additives were discussed.  Keyword: CMC, SDBS, drag reduction, friction factor, blending of additives.

Numerical Study of External Flow over Ducts with Various Cross-Sections

2016 ◽  
Vol 366 ◽  
pp. 10-16 ◽  
Author(s):  
Erfan Maleki ◽  
Hani Sadrhosseini
Keyword(s):  
Cross Sections ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
External Flow ◽  
Two Dimensions ◽  
Wake Region ◽  
Reattachment Point ◽  
Cross Sectional ◽  
Low Reynolds Numbers ◽  
Stagnation Points

In this article a comprehensive numerical study is performed to compare the effect of fluid flow across a duct with various cross sectional shapes and with different velocities of the flow. Circular, elliptical and rectangular cross sections have been chosen for the ducts and air flows across them with four values of low Reynolds numbers in the range of Re = 1 to Re = 1000. Continuity and momentum equations with proper boundary conditions are solved in two dimensions. Streamlines, pressure distribution and Velocity profiles are obtained and creation of vortices, boundary layers, separation region, wake region, reattachment point and stagnation points are studied in detail and the results are compared for various cases. The value of the Reynolds number which the flow transits from steady to unsteady has been compared for the different cross sectional shapes.

Cocoa Husk Waste Mucilage as New Flow Improver in Pipelines

2011 ◽  
Vol 312-315 ◽  
pp. 1063-1067 ◽  
Author(s):  
Hayder A. Abdulbari ◽  
K.H. Hamad ◽  
Rosli Bin Mohd Yunus
Keyword(s):  
Drag Reduction ◽  
Power Dissipation ◽  
Aqueous Media ◽  
Environmentally Friendly ◽  
Reynolds Numbers ◽  
Internal Diameter ◽  
Fluid Velocities ◽  
Maximum Drag Reduction ◽  
Flow Improver ◽  
Reduction Percentage

Liquid transportation through pipelines for very long distances is one of the most power consuming sectors in the industry. Synthetic polymers were used as flow improvers for many years to solve the power dissipation problem. These polymers are toxic and expensive. An environmentally friendly and more natural product that can replace the usage of polymers as flow improvers is needed. The present study focused on a new, cheap, natural and environmentally friendly flow improver that was extracted from the cocoa husk wastes. Mucilage was prepared from the cocoa husk waste and tested in aqueous media at concentrations between 100 ppm and 400 ppm using pipes with an internal diameter of 0.0125, 0.0254 and 0.0381 m and five different fluid velocities represented by the corresponding Reynolds Numbers (Re). It was found that the cocoa husk mucilage was an effective drag reducing agent. A maximum drag reduction percentage of 44% could be achieved by adding as little as 400 ppm of mucilage. Drag reduction was found to increase by increasing Reynolds Numbers, additive concentrations and pipe lengths. It also increased with decreasing pipe diameters.

Application of V Shape Riblets to Pipe Flows

1991 ◽  
Vol 113 (4) ◽  
pp. 587-590 ◽  
Author(s):  
Shin-ichi Nakao
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Flat Plate ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Reynolds Numbers ◽  
Pipe Flows ◽  
Maximum Drag Reduction

Pipes with V shape riblets were tested at Reynolds numbers between 5×103 and 4×104. All riblet pipes indicated some drag reduction. The model with h = 0.55 mm and h/S = 0.483 showed the maximum drag reduction of 8 percent and the widest range of Reynolds number over which the riblet reduces drag. The riblet shape desirable for drag reduction in pipe flows was almost the same as that in flat plate boundary layers, but the value of S+ which provided the maximum drag reduction was quite different; S+ = 23 for pipe flows and S+ = 12 for flat plate boundary layers.

Microstructural characterization of CoPtCr/Cr thin film disks by cross-section TEM and elongated probe micro-diffraction

1991 ◽  
Vol 49 ◽  
pp. 762-763
Author(s):  
M.A. Parker ◽  
K.E. Johnson ◽  
C. Hwang ◽  
A. Bermea
Keyword(s):  
Magnetic Recording ◽  
Electron Probe ◽  
Microstructural Characterization ◽  
Crystallographic Structure ◽  
Recording Media ◽  
Layer By Layer ◽  
Cross Sectional ◽  
New Techniques ◽  
Polished Side

We have reported the dependence of the magnetic and recording properties of CoPtCr recording media on the thickness of the Cr underlayer. It was inferred from XRD data that grain-to-grain epitaxy of the Cr with the CoPtCr was responsible for the interaction observed between these layers. However, no cross-sectional TEM (XTEM) work was performed to confirm this inference. In this paper, we report the application of new techniques for preparing XTEM specimens from actual magnetic recording disks, and for layer-by-layer micro-diffraction with an electron probe elongated parallel to the surface of the deposited structure which elucidate the effect of the crystallographic structure of the Cr on that of the CoPtCr.XTEM specimens were prepared from magnetic recording disks by modifying a technique used to prepare semiconductor specimens. After 3mm disks were prepared per the standard XTEM procedure, these disks were then lapped using a tripod polishing device. A grid with a single 1mmx2mm hole was then glued with M-bond 610 to the polished side of the disk.

TEM characterization of silicon epitaxial layer grown on Si-TaS2, eutectic composites

1991 ◽  
Vol 49 ◽  
pp. 802-803
Author(s):  
C.M. Sung ◽  
M. Levinson ◽  
M. Tabasky ◽  
K. Ostreicher ◽  
B.M. Ditchek
Keyword(s):  
Substrate Surface ◽  
Bulk Sample ◽  
Surface Cleaning ◽  
Native Oxide ◽  
Czochralski Growth ◽  
Ion Milling ◽  
Cross Sectional ◽  
Cleaning Methods ◽  
Field Emission Cathodes

Directionally solidified Si/TaSi2 eutectic composites for the development of electronic devices (e.g. photodiodes and field-emission cathodes) were made using a Czochralski growth technique. High quality epitaxial growth of silicon on the eutectic composite substrates requires a clean silicon substrate surface prior to the growth process. Hence a preepitaxial surface cleaning step is highly desirable. The purpose of this paper is to investigate the effect of surface cleaning methods on the epilayer/substrate interface and the characterization of silicon epilayers grown on Si/TaSi2 substrates by TEM.Wafers were cut normal to the <111> growth axis of the silicon matrix from an approximately 1 cm diameter Si/TaSi2 composite boule. Four pre-treatments were employed to remove native oxide and other contaminants: 1) No treatment, 2) HF only; 3) HC1 only; and 4) both HF and HCl. The cross-sectional specimens for TEM study were prepared by cutting the bulk sample into sheets perpendicular to the TaSi2 fiber axes. The material was then prepared in the usual manner to produce samples having a thickness of 10μm. The final step was ion milling in Ar+ until breakthrough occurred. The TEM samples were then analyzed at 120 keV using the Philips EM400T.

Characterization of Rh/Si multilayer structure by HREM and HAADF

1992 ◽  
Vol 50 (1) ◽  
pp. 122-123
Author(s):  
Y. Cheng ◽  
J. Liu ◽  
M.B. Stearns ◽  
D.G. Steams
Keyword(s):  
Normal Incidence ◽  
High Resolution Electron Microscopy ◽  
X Rays ◽  
Beam Direction ◽  
Cross Sectional ◽  
Optical Elements ◽  
Resolution Electron ◽  
Point To Point ◽  
Better Than

The Rh/Si multilayer (ML) thin films are promising optical elements for soft x-rays since they have a calculated normal incidence reflectivity of ∼60% at a x-ray wavelength of ∼13 nm. However, a reflectivity of only 28% has been attained to date for ML fabricated by dc magnetron sputtering. In order to determine the cause of this degraded reflectivity the microstructure of this ML was examined on cross-sectional specimens with two high-resolution electron microscopy (HREM and HAADF) techniques.Cross-sectional specimens were made from an as-prepared ML sample and from the same ML annealed at 298 °C for 1 and 100 hours. The specimens were imaged using a JEM-4000EX TEM operating at 400 kV with a point-to-point resolution of better than 0.17 nm. The specimens were viewed along Si [110] projection of the substrate, with the (001) Si surface plane parallel to the beam direction.

Sign in / Sign up

Export Citation Format

Share Document