Observation of cusps during the levelling of free surfaces in viscous flows

1998 ◽  
Vol 377 ◽  
pp. 137-149 ◽  
Author(s):  
S. BETELÚ ◽  
R. GRATTON ◽  
J. DIEZ
Keyword(s):  
Aspect Ratio ◽  
Viscous Flows ◽  
Viscous Fluids ◽  
Industrial Processes ◽  
Lateral Compression ◽  
Critical Aspect ◽  
Free Surfaces ◽  
The Third ◽  
Aspect Ratios ◽  
Sinusoidal Surface

We experimentally study the formation of cusps at the free surfaces of viscous fluids in three simple cases that portray possible natural or industrial processes. Two cases concern levelling driven by gravity: the case (A) of a sinusoidal surface and the case (B) of a single groove. In the third case (C), an initially sinusoidal surface evolves under the action of a fast enough lateral compression that the effects of gravity are negligible. Case (A) shows a critical aspect ratio above which the cusps form. Case (B) allows a more detailed study of the evolution of the cuspidal structure, which does not change in shape but reduces its size according to a simple power law dependence in time. In case (C), cusps form even for small initial aspect ratios.

Comparison of Tooling Materials in Injection Molding of Microscale Features

2009 ◽  
Author(s):  
Sung-Hwan Yoon ◽  
Prabhu Palanisamy ◽  
Purushotham Padmanabha ◽  
Joey L. Mead ◽  
Carol M. F. Barry
Keyword(s):  
Aspect Ratio ◽  
Injection Molding ◽  
Optical Profilometry ◽  
Free Surfaces ◽  
Polymer Hybrid ◽  
Aspect Ratios ◽  
Replication Quality ◽  
Repeated Use ◽  
Metal Polymer ◽  
Scanning Electron

Although high aspect ratio micro and nanoscale polymer features have been replicated in a range of polymers using injection molding, researchers have also used tooling inserts with a range of sizes, aspect ratios, and tooling materials. In this work, microscale features with molded in polymethylmethacrylates using three types of tooling with similar features. The tooling materials included silicon wafers with an antistiction coating, gold-coated nickel inserts, and a metal-polymer hybrid tooling. Tooling was evaluated based on the ease of melt filling and part ejection; the replication quality as characterized using optical profilometry, confocal microscopy, and scanning electron microscopy; and the damage to the tooling after repeated use. With lower aspect ratio features, the tooling type did not significantly affect replication, but for higher aspect ratio features the hybrid tooling provided far better replication than the silicon tooling. This difference was attributed to retardation of heat transfer in the features of the hybrid tooling. All three tooling materials exhibited polymer-free surfaces after injection molding.

scholarly journals A fate-alternating transitional regime in contracting liquid filaments

2018 ◽  
Vol 860 ◽  
pp. 640-653 ◽  
Author(s):  
F. Wang ◽  
F. P. Contò ◽  
N. Naz ◽  
J. R. Castrejón-Pita ◽  
A. A. Castrejón-Pita ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Capillary Waves ◽  
Ohnesorge Number ◽  
Critical Aspect ◽  
Constructive Interference ◽  
Transitional Regime ◽  
Aspect Ratios ◽  
New Phase ◽  
Liquid Filament

The fate of a contracting liquid filament depends on the Ohnesorge number ($Oh$), the initial aspect ratio ($\unicode[STIX]{x1D6E4}$) and surface perturbation. Generally, it is believed that there exists a critical aspect ratio $\unicode[STIX]{x1D6E4}_{c}(Oh)$ such that longer filaments break up and shorter ones recoil into a single drop. Through computational and experimental studies, we report a transitional regime for filaments with a broad range of intermediate aspect ratios, where there exist multiple $\unicode[STIX]{x1D6E4}_{c}$ thresholds at which a novel breakup mode alternates with no-break mode. We develop a simple model considering the superposition of capillary waves, which can predict the complicated new phase diagram. In this model, the breakup results from constructive interference between the capillary waves that originate from the ends of the filament.

Effects of Aspect Ratio on Higher-Order Moments, Conditional Statistics, TKE Budget and Anisotropy in Narrow Open Channel Flow

2020 ◽  
Author(s):  
Minakshee Mahananda ◽  
Prashanth Reddy Hanmaiahgari ◽  
Ram Balachandar ◽  
Vesselina Roussinova
Keyword(s):  
Aspect Ratio ◽  
Open Channel ◽  
Outer Region ◽  
Higher Order ◽  
Third Order ◽  
Velocity Fluctuations ◽  
The Third ◽  
Aspect Ratios ◽  
Ejections And Sweeps ◽  
Conditional Statistics

The paper investigates the influence of aspect ratio on the higher-order statistics of velocity fluctuations in hydraulically rough narrow OCF. In the experiments, the aspect ratios were varied between 2.5 and 4. Velocities were measured with ADV. The third-order moments were found to be sensitive to the aspect ratio in the outer region. The contributions of all quadrant events are approximately equal in lower aspect ratio flows, whereas ejections and sweeps are the dominant as the aspect ratio increases. The upward transfer of TKE flux increases in the outer layer with increase in aspect ratio. The TKE production and dissipation are found to be dependent on the aspect ratio. The analysis of Reynolds stress AIM reveals that for low aspect ratio flows turbulence tends to attain rod like axisymmetric turbulence only in the intermediate layer whereas for higher aspect ratio, turbulence attains rod like axisymmetric turbulence throughout the depth.

Experimental Investigation on the Motion of Particle Cloud in Viscous Fluids

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Amir H. Azimi
Keyword(s):  
Aspect Ratio ◽  
Drag Coefficient ◽  
Viscous Fluids ◽  
Air Bubbles ◽  
Aspect Ratios ◽  
Particle Clouds ◽  
Flow Through ◽  
Using Data ◽  
The Stability ◽  
Individual Particles

Laboratory experiments were conducted to study the dynamics of particle clouds in viscous fluids. Different shapes of frontal head and trailing stems were observed, and particle clouds were classified using data mining methodology. The stability of the frontal head of particle clouds was found to be correlated with the nozzle diameter and mass of sand particles in the form of an initial aspect ratio. The formation of particle clusters into a torus and the split of the frontal head into two or three clusters were investigated in detail. The cluster of particles flow through viscous fluid experienced partial separation due to the release of air bubbles from the rear of frontal head. It was observed that the time and location of major particle separation increase linearly with the aspect ratio. The oscillatory motion of the frontal head, caused by an uneven release of air bubbles from the rear of the frontal head, was found to be correlated with the initial aspect ratio. Both amplitude and wavelength exhibited a linear relationship with nondimensional time. The average drag coefficient of particle clouds Cd in viscous fluids was calculated for different aspect ratios, and the results were compared with the drag coefficient of individual particles. It was found that the averaged drag coefficients of particle clouds were smaller than the drag coefficient of individual particles, and Cd slightly increases with the increasing initial aspect ratio.

scholarly journals Effects of Steel Fiber Percentage and Aspect Ratios on Fresh and Harden Properties of Ultra-High Performance Fiber

2021 ◽  
Vol 2 (3) ◽  
pp. 501-515
Author(s):  
Rajib Kumar Biswas ◽  
Farabi Bin Ahmed ◽  
Md. Ehsanul Haque ◽  
Afra Anam Provasha ◽  
Zahid Hasan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Aspect Ratio ◽  
High Performance ◽  
Steel Fiber ◽  
Setting Time ◽  
Fiber Reinforced Concrete ◽  
Future Research ◽  
Manufacturing Cost ◽  
Aspect Ratios ◽  
High Performance Fiber

Steel fibers and their aspect ratios are important parameters that have significant influence on the mechanical properties of ultrahigh-performance fiber-reinforced concrete (UHPFRC). Steel fiber dosage also significantly contributes to the initial manufacturing cost of UHPFRC. This study presents a comprehensive literature review of the effects of steel fiber percentages and aspect ratios on the setting time, workability, and mechanical properties of UHPFRC. It was evident that (1) an increase in steel fiber dosage and aspect ratio negatively impacted workability, owing to the interlocking between fibers; (2) compressive strength was positively influenced by the steel fiber dosage and aspect ratio; and (3) a faster loading rate significantly improved the mechanical properties. There were also some shortcomings in the measurement method for setting time. Lastly, this research highlights current issues for future research. The findings of the study are useful for practicing engineers to understand the distinctive characteristics of UHPFRC.

scholarly journals Surface Texturing of Si with Periodically Arrayed Oblique Nanopillars to Achieve Antireflection

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 380
Author(s):  
Jun-Hyun Kim ◽  
Sanghyun You ◽  
Chang-Koo Kim
Keyword(s):  
Aspect Ratio ◽  
Plasma Etching ◽  
Surface Texturing ◽  
Light Reflection ◽  
Si Substrate ◽  
Weighted Mean ◽  
Optical Reflectance ◽  
Si Substrates ◽  
Aspect Ratios ◽  
Shadowing Effect

Si surfaces were texturized with periodically arrayed oblique nanopillars using slanted plasma etching, and their optical reflectance was measured. The weighted mean reflectance (Rw) of the nanopillar-arrayed Si substrate decreased monotonically with increasing angles of the nanopillars. This may have resulted from the increase in the aspect ratio of the trenches between the nanopillars at oblique angles due to the shadowing effect. When the aspect ratios of the trenches between the nanopillars at 0° (vertical) and 40° (oblique) were equal, the Rw of the Si substrates arrayed with nanopillars at 40° was lower than that at 0°. This study suggests that surface texturing of Si with oblique nanopillars reduces light reflection compared to using a conventional array of vertical nanopillars.

scholarly journals Strength Analysis of Alternative Airframe Layouts of Regional Aircraft on the Basis of Automated Parametrical Models

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 80
Author(s):  
Dmitry V. Vedernikov ◽  
Alexander N. Shanygin ◽  
Yury S. Mirgorodsky ◽  
Mikhail D. Levchenkov
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
High Performance ◽  
Strength Analysis ◽  
Labor Input ◽  
Aerodynamic Loading ◽  
Aspect Ratios ◽  
Wide Range ◽  
Parametrical Design

This publication presents the results of complex parametrical strength investigations of typical wings for regional aircrafts obtained by means of the new version of the four-level algorithm (FLA) with the modified module responsible for the analysis of aerodynamic loading. This version of FLA, as well as a base one, is focused on significant decreasing time and labor input of a complex strength analysis of airframes by using simultaneously different principles of decomposition. The base version includes four-level decomposition of airframe and decomposition of strength tasks. The new one realizes additional decomposition of alternative variants of load cases during the process of determination of critical load cases. Such an algorithm is very suitable for strength analysis and designing airframes of regional aircrafts having a wide range of aerodynamic concepts. Results of validation of the new version of FLA for a high-aspect-ratio wing obtained in this work confirmed high performance of the algorithm in decreasing time and labor input of strength analysis of airframes at the preliminary stages of designing. During parametrical design investigation, some interesting results for strut-braced wings having high aspect ratios were obtained.

Influence of nozzle exit geometrical parameters on supersonic jet decay

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Prasanta Kumar Mohanta ◽  
B. T. N. Sridhar ◽  
R. K. Mishra
Keyword(s):  
Aspect Ratio ◽  
Nozzle Exit ◽  
Ambient Air ◽  
Schlieren Image ◽  
Geometrical Parameters ◽  
Image Study ◽  
Aspect Ratios ◽  
Core Length ◽  
Supersonic Core Length ◽  
The Impact

Abstract Experiments and simulations were carried on C-D nozzles with four different exit geometry aspect ratios to investigate the impact of supersonic decay characteristics. Rectangular and elliptical exit geometries were considered for the study with various aspect ratios. Numerical simulations and Schlieren image study were studied and found the agreeable logical physics of decay and spread characteristics. The supersonic core decay was found to be of different length for different exit geometry aspect ratio, though the throat to exit area ratio was kept constant to maintain the same exit Mach number. The impact of nozzle exit aspect ratio geometry was responsible to enhance the mixing of primary flow with ambient air, without requiring a secondary method to increase the mixing characteristics. The higher aspect ratio resulted in better mixing when compared to lower aspect ratio exit geometry, which led to reduction in supersonic core length. The behavior of core length reduction gives the identical signature for both under-expanded and over-expanded cases. The results revealed that higher aspect ratio of the exit geometry produced smaller supersonic core length. The aspect ratio of cross section in divergent section of the nozzle was maintained constant from throat to exit to reduce flow losses.

scholarly journals Aspect Ratio Driven Relationship between Nozzle Internal Flow and Supersonic Jet Mixing

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 78
Author(s):  
Kalyani Bhide ◽  
Kiran Siddappaji ◽  
Shaaban Abdallah
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Internal Flow ◽  
Shear Stresses ◽  
Loss Mechanism ◽  
Potential Core ◽  
Jet Mixing ◽  
Aspect Ratios

This work attempts to connect internal flow to the exit flow and supersonic jet mixing in rectangular nozzles with low to high aspect ratios (AR). A series of low and high aspect ratio rectangular nozzles (design Mach number = 1.5) with sharp throats are numerically investigated using steady state Reynolds-averaged Navier−Stokes (RANS) computational fluid dynamics (CFD) with k-omega shear stress transport (SST) turbulence model. The numerical shadowgraph reveals stronger shocks at low ARs which become weaker with increasing AR due to less flow turning at the throat. Stronger shocks cause more aggressive gradients in the boundary layer resulting in higher wall shear stresses at the throat for low ARs. The boundary layer becomes thick at low ARs creating more aerodynamic blockage. The boundary layer exiting the nozzle transforms into a shear layer and grows thicker in the high AR nozzle with a smaller potential core length. The variation in the boundary layer growth on the minor and major axis is explained and its growth downstream the throat has a significant role in nozzle exit flow characteristics. The loss mechanism throughout the flow is shown as the entropy generated due to viscous dissipation and accounts for supersonic jet mixing. Axis switching phenomenon is also addressed by analyzing the streamwise vorticity fields at various locations downstream from the nozzle exit.

scholarly journals Atmospheric Ice Particle Shape Estimates from Polarimetric Radar Measurements and In Situ Observations

2017 ◽  
Vol 34 (12) ◽  
pp. 2569-2587 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Carl G. Schmitt ◽  
Maximilian Maahn ◽  
Gijs de Boer
Keyword(s):  
Aspect Ratio ◽  
Particle Shape ◽  
Characteristic Size ◽  
In Situ Measurements ◽  
Department Of Energy ◽  
Depolarization Ratio ◽  
Suggested Approach ◽  
Aspect Ratios ◽  
Radar Measurements

AbstractA remote sensing approach to retrieve the degree of nonsphericity of ice hydrometeors using scanning polarimetric Ka-band radar measurements from a U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program cloud radar operated in an alternate transmission–simultaneous reception mode is introduced. Nonsphericity is characterized by aspect ratios representing the ratios of particle minor-to-major dimensions. The approach is based on the use of a circular depolarization ratio (CDR) proxy reconstructed from differential reflectivity ZDR and copolar correlation coefficient ρhυ linear polarization measurements. Essentially combining information contained in ZDR and ρhυ, CDR-based retrievals of aspect ratios are fairly insensitive to hydrometeor orientation if measurements are performed at elevation angles of around 40°–50°. The suggested approach is applied to data collected using the third ARM Mobile Facility (AMF3), deployed to Oliktok Point, Alaska. Aspect ratio retrievals were also performed using ZDR measurements that are more strongly (compared to CDR) influenced by hydrometeor orientation. The results of radar-based retrievals are compared with in situ measurements from the tethered balloon system (TBS)-based video ice particle sampler and the ground-based multiangle snowflake camera. The observed ice hydrometeors were predominantly irregular-shaped ice crystals and aggregates, with aspect ratios varying between approximately 0.3 and 0.8. The retrievals assume that particle bulk density influencing (besides the particle shape) observed polarimetric variables can be deduced from the estimates of particle characteristic size. Uncertainties of CDR-based aspect ratio retrievals are estimated at about 0.1–0.15. Given these uncertainties, radar-based retrievals generally agreed with in situ measurements. The advantages of using the CDR proxy compared to the linear depolarization ratio are discussed.

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