Large Scale Motions and Shear Stress Fluctuations in Turbulent Shear Flow

2015 ◽  
Author(s):  
Hinori Ito ◽  
Tatsuya Tsuneyoshi ◽  
Shan Feng ◽  
Takahiro Ito ◽  
Yoshiyuki Tsuji ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shear Flow ◽  
Large Scale ◽  
Time Lag ◽  
Recirculation Region ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Stress Fluctuation ◽  
Wall Shear

We simultaneously measured the flow field and wall shear stress in a straight pipe and behind an orifice by means of particle image velocimetry (PIV) and the limiting diffusion current technique (LDCT), respectively[1]. The spatio-temporal correlation coefficients of the local vertical velocity and the shear stress fluctuations are presented, and the canonical correlations between the proper orthogonal decomposition (POD) spatial eigenmodes in the recirculation region and the wall shear stress are also discussed[2]. A response time lag occurs between the wall shear stress and the velocity field. The large canonical correlation between the POD eigenmodes and wall shear stress suggests that large-scale flow structures are important for the shear stress fluctuation. These analyses are applied to the shear flow in channel and large scale motions are studied in relation with the shear stress fluctuations.

215 Development of micro-fabricated hot-film sensor by MEMS and study on its validation of the wall shear stress fluctuation measurement

2014 ◽  
Vol 2014.63 (0) ◽  
pp. _215-1_-_215-2_
Author(s):  
Takuya SAWADA ◽  
Osamu TERASHIMA ◽  
Yasuhiko SAKAI ◽  
Kouji Nagata ◽  
Mitsuhiro SHIKIDA ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Film Sensor ◽  
Stress Fluctuation ◽  
Wall Shear ◽  
Hot Film ◽  
Fluctuation Measurement ◽  
Hot Film Sensor

Time-dependent rheological behavior of blood at low shear in narrow vertical tubes

1993 ◽  
Vol 265 (2) ◽  
pp. H553-H561 ◽  
Author(s):  
C. Alonso ◽  
A. R. Pries ◽  
P. Gaehtgens
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shear Flow ◽  
Apparent Viscosity ◽  
Flow Behavior ◽  
Time Dependent ◽  
Flow Conditions ◽  
Wall Shear ◽  
Vertical Tubes ◽  
Low Shear

The time-dependent flow behavior of normal human blood after a sudden reduction of wall shear stress from 5,000 mPa to a low level (2-100 mPa) was studied during perfusion of vertical tubes (internal diam 28-101 microns) at constant driving pressures. Immediately after the implementation of low-shear flow conditions the concentration of red blood cells (RBCs) near the tube wall started to decrease, and marginal plasma spaces developed as a result of the assembly of RBC aggregates. This was associated with a time-dependent increase of flow velocity by up to 200% within 300 s, reflecting a reduction of apparent viscosity. These time-dependent changes of flow behavior increased strongly with decreasing wall shear stress and with increasing tube diameter. A correlation between the width of the marginal plasma layer and relative apparent viscosity was obtained for every condition of tube diameter, wall shear stress, and time. Time-dependent changes of blood rheological properties could be relevant in the circulation, where the blood is exposed to rapid and repeated transitions from high-shear flow conditions in the arterial and capillary system to low-shear conditions in the venous system.

A Technique for the Measurement of Wall Shear Stress Based on Micro Fabricated Hot-Film Sensor

2013 ◽  
Author(s):  
Takuya Sawada ◽  
Osamu Terashima ◽  
Yasuhiko Sakai ◽  
Kouji Nagata ◽  
Mitsuhiro Shikida ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flows ◽  
Temporal Resolution ◽  
Large Scale ◽  
High Temporal Resolution ◽  
Film Sensor ◽  
Wall Shear ◽  
Hot Film ◽  
Hot Film Sensor

The objective of this study is to establish a technique for accurately measuring the wall shear stress in turbulent flows using a micro-fabricated hot-film sensor. Previously, we developed a hot-film sensor with a flexible polyimide-film substrate. This sensor can be attached to curved walls and be used in various situations. Furthermore, the sensor has a 20-μm-wide, heated thin metal film. However, the temporal resolution of this hot-film sensor is not very high owing to its substrate’s high heat capacity. Consequently, its performance is inadequate for measuring the wall shear stress “fluctuations” in turbulent flows. Therefore, we have developed another type of hot-film sensor in which the substrate is replaced with silicon, and a cavity has been introduced under the hot-film for reducing heat loss from the sensor and achieving high temporal resolution. Furthermore, for improving the sensor’s spatial resolution, the width of the hot-film is decreased to 10 μm. The structure of the hot-film’s pattern and the flow-detection mechanism are similar to those of the previous sensor. Experimental results show that new hot-film sensor works as expected and has better temporal resolution than the previous hot-film sensor. As future work, we will measure the wall shear stress for a turbulent wall-jet and discuss the relationship between a large-scale coherent vortex structure and wall shear stress based on data obtained using the new hot-film sensor.

Properties of Wall Shear Stress Fluctuations in a Turbulent Duct Flow

1977 ◽  
Vol 44 (3) ◽  
pp. 389-395 ◽  
Author(s):  
K. R. Sreenivasan ◽  
R. A. Antonia
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Probability Density ◽  
Duct Flow ◽  
Zero Crossing ◽  
Number Range ◽  
Stress Fluctuation ◽  
Moderate Reynolds Number ◽  
Wall Shear ◽  
Turbulent Duct Flow

Measurements of wall shear stress fluctuations have been made in a fully developed turbulent duct flow, using a surface heat transfer gauge. Measurements, made over a moderate Reynolds number range, include RMS values, probability density functions, spectra, and zero-crossing frequencies of the wall shear stress fluctuation. The ratio of RMS of the fluctuation to the mean value of the wall shear stress is found to be about 0.25. The zero-crossing frequency computed from the measured spectra using the relation derived by Rice for a Gaussian process is found to be a good approximation to the measured value, although the measured probability density function is not Gaussian. The zero crossing frequency and spectra of wall shear stress fluctuations appear to scale with outer variables for asymptotically large Reynolds numbers.

Tracings of Interaction Between Myoblasts Under Shear Flow in Vitro

2021 ◽  
Author(s):  
Shigehiro Hashimoto ◽  
Takashi Yokomizo
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shear Flow ◽  
Flow Direction ◽  
Time Lapse ◽  
Adjacent Cell ◽  
Contact Ratio ◽  
Rotating Disc ◽  
Wall Shear

Abstract How does the group of cells make orientation perpendicular to the flow direction? How does contact with an adjacent cell affect the orientation of the cell? The orientation of a cell according to the neighbor cell under shear flow fields has been traced in vitro. A Couette type flow device with parallel discs was manufactured for the cell culture under the controlled constant wall shear stress. Cells (C2C12: mouse myoblast cell line) were cultured on the lower disc while applying the shear flow in the medium by the upper rotating disc. After culture for 24 hours without flow for adhesion of cells, 2 Pa of the constant wall shear stress was continuously applied in the incubator for 7 days. The behavior of each cell was traced by time-lapse images observed by an inverted phase contrast microscope placed in an incubator. The experiment shows the following results quantitatively by parameters: the contact ratio, and the angle between major axes of cells approximated to ellipsoids. As the ratio of the contact length with the adjacent cell to the pericellular length increases in the two-dimensional projection images, the adjacent cells tend to be oriented in parallel with each other.

Wall shear stress and velocity in a turbulent axisymmetric boundary layer

1994 ◽  
Vol 259 ◽  
pp. 191-218 ◽  
Author(s):  
Anthony Wietrzak ◽  
Richard M. Lueptow
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Scale ◽  
Low Frequency ◽  
Streamwise Velocity ◽  
Outer Flow ◽  
Planar Wall ◽  
Wall Bounded Flows ◽  
Wall Shear

Instantaneous streamwise fluctuations of the wall shear stress have been measured using a hot-element probe in a thick axisymmetric turbulent boundary layer on a cylinder aligned parallel to the flow. The measurements were made at a momentum-thickness Reynolds number Rθ = 3050 and a ratio of boundary-layer thickness to cylinder radius of δ/a = 5.7. The ratio of the r.m.s. of the fluctuation to the mean value of the wall shear stress, $\tau_{rms}/\bar{\tau}$, is about 0.32, a value slightly lower than that for recent measurements for flow over a flat plate. The probability density function of the wall shear stress is similar to that for planar wall-bounded flows within experimental error. The power spectral density of the wall shear stress shows that a cylindrical boundary layer contains less energy at lower frequencies and more energy at higher frequencies than other wall-bounded flows. Analysis of simultaneous measurement of the streamwise wall shear stress and the streamwise velocity using VITA and peak detection suggests that transverse curvature has little effect on the near-wall burst–sweep cycle compared to planar wall-bounded flows. The angle of inclination of the structures is similar to that measured for large-scale structures in planar wall-bounded flows. However, measurements of the cross-correlation between the shear stress and the velocity suggest the existence of smaller structures yawed to the axis of the cylinder. The coherence between shear stress and velocity shows a low frequency associated with the inclined structures and a higher frequency associated with the yawed structures. The yawed structures could have an arrowhead or half-arrowhead shape and may be associated with fluid from the outer flow washing over the cylinder.

Very Large-Scale Structures and Their Effects on the Wall Shear-Stress Fluctuations in a Turbulent Channel Flow up to Reτ=640

2004 ◽  
Vol 126 (5) ◽  
pp. 835-843 ◽  
Author(s):  
Hiroyuki Abe ◽  
Hiroshi Kawamura ◽  
Haecheon Choi
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
High Reynolds Number ◽  
Large Scale ◽  
Turbulent Channel Flow ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Wall Shear ◽  
High Reynolds

Direct numerical simulation of a fully developed turbulent channel flow has been carried out at three Reynolds numbers, 180, 395, and 640, based on the friction velocity and the channel half width, in order to investigate very large-scale structures and their effects on the wall shear-stress fluctuations. It is shown that very large-scale structures exist in the outer layer and that they certainly contribute to inner layer structures at high Reynolds number. Moreover, it is revealed that very large-scale structures exist even in the wall shear-stress fluctuations at high Reynolds number, which are essentially associated with the very large-scale structures in the outer layer.

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