scholarly journals Motion of Passive Scalar by Elasticity-Induced Instability in Curved Microchannel

2014 ◽  
Vol 6 ◽  
pp. 734175 ◽  
Author(s):  
Xiao-Bin Li ◽  
Hong-Na Zhang ◽  
Yang Cao ◽  
Marie Oshima ◽  
Feng-Chen Li
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Function Analysis ◽  
Passive Scalar ◽  
Main Direction ◽  
Mixing Enhancement ◽  
Chaotic Flow ◽  
Wide Range ◽  
Elastic Instabilities ◽  
Passive Mixing

This paper presented a direct numerical simulation (DNS) study on the elasticity-induced irregular flow, passive mixing, and scalar evolution in the curvilinear microchannel. The mixing enhancement was achieved at vanishingly low-Reynolds-number chaotic flow raised by elastic instabilities. Along with the mixing process, the passive scalar transportation carried by the flow was greatly affected by the flow structure and the underlying interaction between microstructures of viscoelastic fluid and flow structure itself. The simulations are conducted for a wide range of viscoelasticity. As the elastic effect exceeds the critical value, the flow tends to a chaotic state, while the evolution of scalar gets strong and fast, showing excellent agreement with experimental results. For the temporal changing of scalar gradients, they vary rapidly in the form of isosurfaces, with the shape of “rolls” in the bulk and evolving into “threads” near the wall. That indicates that the flow fields should be related to the deformation of viscoelastic micromolecules. The probability distribution function analysis between micromolecular deformation and flow field deformation shows that the main direction of molecular stretching is perpendicular to the main direction of flow field deformation. It implies they are weakly correlated, due to the confinement of channel wall.

Motion of Passive Particles Carried by Viscoelastic Fluid Flow in the Curvilinear Microchannel

2013 ◽  
Author(s):  
Xiao-Bin Li ◽  
Dong-Yang Li ◽  
Hong-Na Zhang ◽  
Feng-Chen Li
Keyword(s):  
Fluid Flow ◽  
Flow Field ◽  
Viscoelastic Fluid ◽  
Passive Scalar ◽  
Weissenberg Number ◽  
Main Direction ◽  
Pdf Analysis ◽  
Passive Mixing ◽  
Micro Deformation ◽  
Molecular Deformation

Chaotic flow can be obtained in the viscoelastic fluid flow in the curved microchannel at very low Reynolds number. Influenced by the microstructures of viscoelastic fluid, the passive particles (scalar) transportation carried by the flow will be greatly enhanced. This paper presents a direct numerical simulation (DNS) for the chaotic viscoelastic flow and passive mixing in the curvilinear microchannel. The flow structures, mixing effect, passive scalar evolution with time are discussed. The simulations are conducted for a large range of viscoelasticity, which is parameterized by Weissenberg number (Wi). As Wi grows, the flow tends to a chaotic state, while the evolution of scalar gets strong and fast, showing excellent agreement with experiments. For the structures of scalar gradients in the flow field, they varies quickly in the form of isosurfaces with time, with “rolls” in the bulk changing into “threads” near the wall. That indicates the flow fields should be related to the micro deformation of viscoelastic molecules. The probability distribution function (pdf) analysis between micro-molecular deformation and flow field deformation shows that the main direction of molecular stretching is perpendicular to the main direction of flow field deformation. It implies they are weakly correlated, due to the confinement of channel wall.

Analysis of Measurements in Vaned Diffusers of Centrifugal Compressors

1988 ◽  
Vol 110 (1) ◽  
pp. 115-121 ◽  
Author(s):  
W. Stein ◽  
M. Rautenberg
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Calculation Method ◽  
Geometric Parameters ◽  
Variable Geometry ◽  
Centrifugal Compressors ◽  
Wide Range ◽  
Performance Curves ◽  
Different Types ◽  
Flow Phenomena

In vaned diffusers of centrifugal compressors many different flow phenomena interfere with one another, and different geometric parameters influence the flow field. Variations of these parameters allow the designer to optimize the diffuser for a certain application or to use a variable geometry for controlling the stage over a wide range. Two vaned diffusers that differ only in their passage widths are investigated using different types of measuring technique, in order to analyze the flow structure and to use it as a verification of a calculation method that allows detailed predictions of flow field parameters inside the diffuser, by taking into account geometric variations. Using this method predictions of the flow field of a variable geometry diffuser are made and are compared with the measured performance curves of the stage.

scholarly journals Impact of Powder Properties on the Rheological Behavior of Excipients

Pharmaceutics ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1198
Author(s):  
Pauline H. M. Janssen ◽  
Sébastien Depaifve ◽  
Aurélien Neveu ◽  
Filip Francqui ◽  
Bastiaan H. J. Dickhoff
Keyword(s):  
Flow Field ◽  
Rheological Behavior ◽  
Quality By Design ◽  
Filling Process ◽  
Dynamic Flow ◽  
Die Filling ◽  
Flow Characterization ◽  
Wide Range ◽  
Powder Properties ◽  
The Impact

With the emergence of quality by design in the pharmaceutical industry, it becomes imperative to gain a deeper mechanistic understanding of factors impacting the flow of a formulation into tableting dies. Many flow characterization techniques are present, but so far only a few have shown to mimic the die filling process successfully. One of the challenges in mimicking the die filling process is the impact of rheological powder behavior as a result of differences in flow field in the feeding frame. In the current study, the rheological behavior was investigated for a wide range of excipients with a wide range of material properties. A new parameter for rheological behavior was introduced, which is a measure for the change in dynamic cohesive index upon changes in flow field. Particle size distribution was identified as a main contributing factor to the rheological behavior of powders. The presence of fines between larger particles turned out to reduce the rheological index, which the authors explain by improved particle separation at more dynamic flow fields. This study also revealed that obtained insights on rheological behavior can be used to optimize agitator settings in a tableting machine.

scholarly journals Quantification of Measurement and Model Effects in Monopile Foundation Scour Protection Experiments

2021 ◽  
Vol 9 (6) ◽  
pp. 585
Author(s):  
Minghao Wu ◽  
Leen De Vos ◽  
Carlos Emilio Arboleda Chavez ◽  
Vasiliki Stratigaki ◽  
Maximilian Streicher ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Flow Field ◽  
Three Dimensional ◽  
Small Scale ◽  
Maximum Wave Height ◽  
Chaotic Flow ◽  
The Mean ◽  
Scour Protection ◽  
Damage Number ◽  
Measurement Effects

The present work introduces an analysis of the measurement and model effects that exist in monopile scour protection experiments with repeated small scale tests. The damage erosion is calculated using the three dimensional global damage number S3D and subarea damage number S3D,i. Results show that the standard deviation of the global damage number σ(S3D)=0.257 and is approximately 20% of the mean S3D, and the standard deviation of the subarea damage number σ(S3D,i)=0.42 which can be up to 33% of the mean S3D. The irreproducible maximum wave height, chaotic flow field and non-repeatable armour layer construction are regarded as the main reasons for the occurrence of strong model effects. The measurement effects are limited to σ(S3D)=0.039 and σ(S3D,i)=0.083, which are minor compared to the model effects.

Radial Flow Velocity Field for Predicting Upper-Bound Solutions for Plane Strain Extrusion

1968 ◽  
Vol 90 (1) ◽  
pp. 45-50
Author(s):  
R. G. Fenton
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Flow Velocity ◽  
Plane Strain ◽  
Upper Bound ◽  
Radial Flow ◽  
Flow Velocity Field ◽  
Wide Range ◽  
Ram Pressure ◽  
Considerable Range

The upper bound of the average ram pressure, based on an assumed radial flow velocity field, is derived for plane strain extrusion. Ram pressures are calculated for a complete range of reduction ratios and die angles, considering a wide range of frictional conditions. Results are compared with upper-bound ram pressures obtained by considering velocity fields other than the radial flow field, and it is shown that for a considerable range of reduction ratios and die angles, the radial flow field yields better upper bounds for the average ram pressure.

Flow Visualization by Means of Contactless Inductive Flow Tomography in the Presence of a Magnetic Brake

2015 ◽  
Vol 15 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Matthias Ratajczak ◽  
Thomas Wondrak ◽  
Klaus Timmel ◽  
Frank Stefani ◽  
Sven Eckert
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Flow Field ◽  
Continuous Casting ◽  
Flow Structure ◽  
Cross Section ◽  
Two Dimensional ◽  
Slab Casting ◽  
Two Dimensional Flow

AbstractIn continuous casting DC magnetic fields perpendicular to the wide faces of the mold are used to control the flow in the mold. Especially in this case, even a rough knowledge of the flow structure in the mold would be highly desirable. The contactless inductive flow tomography (CIFT) allows to reconstruct the dominating two-dimensional flow structure in a slab casting mold by applying one external magnetic field and by measuring the flow-induced magnetic fields outside the mold. For a physical model of a mold with a cross section of 140 mm×35 mm we present preliminary measurements of the flow field in the mold in the presence of a magnetic brake. In addition, we show first reconstructions of the flow field in a mold with the cross section of 400 mm×100 mm demonstrating the upward scalability of CIFT.

Investigation of Coriolis Forces Effect of Flow Structure and Heat Transfer Distribution in a Rotating Dimpled Channel

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Recirculation Zone ◽  
Channel Height ◽  
Coriolis Forces ◽  
Flow Recirculation ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
Large Eddy ◽  
Dimple Surface

Large-eddy simulations are used to investigate Coriolis forces effect on flow structure and heat transfer in a rotating dimpled channel. Two geometries with two dimple depths are considered, δ=0.2 and 0.3 of channel height, for a wide range of rotation number, Rob=0.0–0.70, based on mean bulk velocity and channel height. It is found that the turbulent flow is destabilized near the trailing side and stabilized near the leading side, with secondary flow structures generated in the channel under the effect of Coriolis forces. Higher heat transfer levels are obtained at the trailing surface of the channel, especially in regions of flow reattachment and boundary layer regeneration at the dimple surface. Coriolis forces showed a stronger effect on the flow structure for the shallow dimple geometry (δ=0.2) compared with the deeper dimple where the growth and shrinkage of the flow recirculation zone in the dimple cavity with rotation were more pronounced than the deep dimple geometry (δ=0.3). Under the action of rotation, heat transfer augmentation increased by 57% for δ=0.2 and by 70% for δ=0.3 on the trailing side and dropped by 50% for δ=0.2 and by 45% for δ=0.3 on the leading side from that of the stationary case.

Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds

2016 ◽  
Author(s):  
Johan Dahlqvist ◽  
Jens Fridh
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
High Speed ◽  
Control Volume ◽  
Spatial Average ◽  
Turbine Stage ◽  
Wide Range ◽  
Annulus Flow ◽  
Purge Flow ◽  
Secondary Air

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.

Investigation of Coriolis Forces Effect of Flow Structure and Heat Transfer Distribution in a Rotating Dimpled Channel

2010 ◽  
Author(s):  
Mohammad A. Elyyan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Recirculation Zone ◽  
Channel Height ◽  
Coriolis Forces ◽  
Flow Recirculation ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
Large Eddy ◽  
Dimple Surface

Large-eddy simulations are used to investigate Coriolis forces effect on flow structure and heat transfer in a rotating dimpled channel. Two geometries with two dimple depths are considered, δ = 0.2 and 0.3 of channel height, for a wide range of rotation number, Rob = 0.0–0.70, based on mean bulk velocity and channel height. It is found that the turbulent flow is destabilized near the trailing side and stabilized near the leading side, with secondary flow structures generated in the channel under the effect of Coriolis forces. Higher heat transfer levels are obtained at the trailing surface of the channel, especially in regions of flow reattachment and boundary layer regeneration at the dimple surface. Coriolis forces showed a stronger effect on the flow structure for the shallow dimple geometry (δ = 0.2) compared to the deeper dimple where the growth and shrinkage of the flow recirculation zone in the dimple cavity with rotation were more pronounced than the deep dimple geometry (δ = 0.3). Under the action of rotation, heat transfer augmentation increased by 57% for δ = 0.2 and by 70% for δ = 0.3 on the trailing side and dropped by 50% for δ = 0.2 and by 45% for δ = 0.3 on the leading side from that of the stationary case.

scholarly journals A reduced-complexity model for river delta formation – Part 1: Modeling deltas with channel dynamics

2015 ◽  
Vol 3 (1) ◽  
pp. 67-86 ◽  
Author(s):  
M. Liang ◽  
V. R. Voller ◽  
C. Paola
Keyword(s):  
Sediment Transport ◽  
Flow Field ◽  
Water Surface ◽  
Surface Profile ◽  
River Delta ◽  
Suspended Sediment Transport ◽  
Channel Dynamics ◽  
Wide Range ◽  
Delta Formation ◽  
Reduced Complexity

Abstract. In this work we develop a reduced-complexity model (RCM) for river delta formation (referred to as DeltaRCM in the following). It is a rule-based cellular morphodynamic model, in contrast to reductionist models based on detailed computational fluid dynamics. The basic framework of this model (DeltaRCM) consists of stochastic parcel-based cellular routing schemes for water and sediment and a set of phenomenological rules for sediment deposition and erosion. The outputs of the model include a depth-averaged flow field, water surface elevation and bed topography that evolve in time. Results show that DeltaRCM is able (1) to resolve a wide range of channel dynamics – including elongation, bifurcation, avulsion and migration – and (2) to produce a variety of deltas such as alluvial fan deltas and deltas with multiple orders of bifurcations. We also demonstrate a simple stratigraphy recording component which tracks the distribution of coarse and fine materials and the age of the deposits. Essential processes that must be included in reduced-complexity delta models include a depth-averaged flow field that guides sediment transport a nontrivial water surface profile that accounts for backwater effects at least in the main channels, both bedload and suspended sediment transport, and topographic steering of sediment transport.

Sign in / Sign up

Export Citation Format

Share Document