scholarly journals PTV Measurement of Periodic Flow Fields with Wide Range of Velocity

1997 ◽  
Vol 17 (Supplement2) ◽  
pp. 129-132
Author(s):  
Fujio AKAGI ◽  
Sumio YAMAGUCHI ◽  
Youichi ANDO ◽  
Yosinori KADOTA
Keyword(s):  
Flow Fields ◽  
Periodic Flow ◽  
Wide Range ◽  
Ptv Measurement

Observations of Complex Oscillations in a Closed Thermosyphon

1985 ◽  
Vol 107 (4) ◽  
pp. 833-839 ◽  
Author(s):  
J. E. Hart
Keyword(s):  
Isothermal Section ◽  
Temperature Difference ◽  
Periodic Flow ◽  
Wide Range ◽  
Tube Assembly ◽  
Thermal Oscillations ◽  
Steady Convection

Observations have been made of thermal oscillations in a slightly inclined closed thermosyphon. The thermosyphon is made up of two isothermal tubes, capped at the outer ends, and joined along their axes by an insulating section. The tube assembly is filled with liquid and inclined slightly with respect to the vertical. The lower isothermal section is hotter than the upper one and convection is driven across the insulating region. Between the applied temperature difference at which simple steady convection occurs, and that required for persistent turbulent motions, there is a wide range over which thermal oscillations are observed. These oscillations reflect quasi-periodic flow as well as a type of periodic chaos.

scholarly journals Deformation-induced actuation of cells in asymmetric periodic flow fields

2021 ◽  
Author(s):  
Sebastian W. Krauss ◽  
Pierre-Yves Gires ◽  
Matthias Weiss
Keyword(s):  
Soft Matter ◽  
Microfluidic Channel ◽  
Flow Fields ◽  
Rapid Screening ◽  
General Question ◽  
Microfluidic Channels ◽  
Periodic Flow ◽  
Topical Problem ◽  
Net Migration ◽  
Unsupervised Approach

Analyzing and sorting particles and/or biological cells in microfluidic devices is a topical problem in soft-matter and biomedical physics. An easy and rapid screening of the deformation of individual cells in constricted microfluidic channels allows, for example, the identification of sick or aberrant cells with altered mechanical properties, even in vast cell ensembles. The subsequently desired softness-specific segregation of cells is, however, still a major challenge. Moreover, aiming at an intrinsic and unsupervised approach raises a very general question: How can one achieve a softness-dependent net migration of particles in a microfluidic channel? Here we show that this is possible by exploiting a deformation-induced actuation of soft cells in asymmetric periodic flow fields in which rigid beads show a vanishing net drift.

Flow Modifiers for Preventing Sedimentation in Heat Exchangers

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Timo Kulju ◽  
Markus Riihimäki ◽  
Tiina M. Pääkkönen ◽  
Ossi Vilhunen ◽  
Kyösti Lipiäinen ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Flow Fields ◽  
Particulate Material ◽  
Cfd Modeling ◽  
Shear Stresses ◽  
Tube Heat Exchanger ◽  
Critical Areas ◽  
Wide Range ◽  
Wall Shear

Heat exchangers are commonly used in process industries; however, fouling, such as sedimentation of particulate material is a significant challenge hindering the efficient use of heat exchangers in a wide range of industrial processes. This research studied the prevention of sedimentation in tube heat exchanger header sections, which typically are the critical areas for sediment accumulation. Numerous flow modifiers were explored, of which the most advantageous ones are presented in this paper. The study included construction and analysis of a miniature, validation of the used CFD model, and finally simulating an industrial scale heat exchanger. This research considered both flow fields and wall shear stresses for reducing sedimentation. The study showed that CFD models are capable of describing flow fields and their spatial variations in heat exchangers especially in their header sections. The selected flow modifier setups increased wall shear stresses in critical areas and hence reduced sedimentation. The presented solution consisted of utilizing different flow modifiers, filling elements, and their combinations. Industry should consider utilizing flow modifiers in heat exchangers as a potential solution to prevent sedimentation. Industrial cases are worth analyzing by using miniatures and CFD modeling. Analyses should pay special attention to flow fields and wall shear stresses. Heat exchangers include also other fouling mechanisms beside sedimentation; however, further study is required to clarify how flow modifiers influence these mechanisms.

scholarly journals Quantitative flow analysis around aquatic animals using laser sheet particle image velocimetry

1995 ◽  
Vol 198 (2) ◽  
pp. 283-294 ◽  
Author(s):  
E Stamhuis ◽  
J Videler
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Field ◽  
Particle Image ◽  
Light Sheet ◽  
Flow Fields ◽  
Image Correlation ◽  
Dissipated Energy ◽  
Two Dimensional ◽  
Image Velocimetry ◽  
Wide Range

Two alternative particle image velocimetry (PIV) methods have been developed, applying laser light sheet illumination of particle-seeded flows around marine organisms. Successive video images, recorded perpendicular to a light sheet parallel to the main stream, were digitized and processed to map the flow velocity in two-dimensional planes. In particle tracking velocimetry (PTV), displacements of single particles in two subsequent images were determined semi-automatically, resulting in flow diagrams consisting of non-uniformly distributed velocity vectors. Application of grid-cell averaging resulted in flow field diagrams with uniform vector distribution. In sub-image correlation PIV (SCPIV), repetitive convolution filtering of small sub-areas of two subsequent images resulted in automatic determination of cross-correlation peaks, yielding flow field diagrams with regularly spaced velocity vectors. In both PTV and SCPIV, missing values, caused by incomplete particle displacement information in some areas of the images or due to rejection of some erroneous vectors by the vector validation procedure, were interpolated using a two-dimensional spline interpolation technique. The resultant vector flow fields were used to study the spatial distribution of velocity, spatial acceleration, vorticity, strain and shear. These flow fields could also be used to test for flow in the third dimension by studying the divergence, and to detect the presence and location of vortices. The results offer detailed quantitative descriptions of the flow morphology and can be used to assess dissipated energy. The versatile character of the technique makes it applicable to a wide range of fluid mechanical subjects within biological research. So far it has been successfully applied to map the flow around swimming copepods, fish larvae and juvenile fish and the ventilation current of a tube-living shrimp.

scholarly journals Learning Multi-human Optical Flow

2020 ◽  
Vol 128 (4) ◽  
pp. 873-890 ◽  
Author(s):  
Anurag Ranjan ◽  
David T. Hoffmann ◽  
Dimitrios Tzionas ◽  
Siyu Tang ◽  
Javier Romero ◽  
...  
Keyword(s):  
Optical Flow ◽  
3D Model ◽  
Flow Fields ◽  
Human Action ◽  
Human Motion ◽  
Image Sequences ◽  
Training Data ◽  
Flow Networks ◽  
Wide Range ◽  
Human Flow

AbstractThe optical flow of humans is well known to be useful for the analysis of human action. Recent optical flow methods focus on training deep networks to approach the problem. However, the training data used by them does not cover the domain of human motion. Therefore, we develop a dataset of multi-human optical flow and train optical flow networks on this dataset. We use a 3D model of the human body and motion capture data to synthesize realistic flow fields in both single- and multi-person images. We then train optical flow networks to estimate human flow fields from pairs of images. We demonstrate that our trained networks are more accurate than a wide range of top methods on held-out test data and that they can generalize well to real image sequences. The code, trained models and the dataset are available for research.

The effect of wavy surface on boundary layer instabilities of an airfoil

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Zbigniew Rarata
Keyword(s):  
Stability Analysis ◽  
Feedback Loop ◽  
Flow Fields ◽  
Wavy Surface ◽  
Content Type ◽  
Spatial Stability ◽  
Stability Analyses ◽  
Acoustic Feedback ◽  
Wide Range ◽  
Naca 0012

Purpose The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses. Design/methodology/approach Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration. Findings The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism. Practical implications The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics. Originality/value The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

BOUNDARY CONDITIONS FOR PERIODIC FLOW FIELDS

1983 ◽  
Vol 22 (1-2) ◽  
pp. 53-62 ◽  
Author(s):  
J.S. VRENTAS ◽  
C.M. VRENTAS
Keyword(s):  
Boundary Conditions ◽  
Flow Fields ◽  
Periodic Flow
Sign in / Sign up

Export Citation Format

Share Document