Measurement of Fluid Velocity Gradients Using Laser‐Doppler Techniques

1971 ◽  
Vol 42 (9) ◽  
pp. 1317-1320 ◽  
Author(s):  
R. J. Goldstein ◽  
R. J. Adrian
Keyword(s):  
Fluid Velocity ◽  
Laser Doppler ◽  
Velocity Gradients ◽  
Doppler Techniques

Reflex control of the cutaneous circulation during passive body core heating in humans

2000 ◽  
Vol 88 (5) ◽  
pp. 1756-1764 ◽  
Author(s):  
Jochen K. Peters ◽  
Takeshi Nishiyasu ◽  
Gary W. Mack
Keyword(s):  
Blood Pressure ◽  
Heat Stress ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Laser Doppler ◽  
Vascular Conductance ◽  
Arterial Blood ◽  
Body Core ◽  
Doppler Techniques ◽  
The Impact

The impact of body core heating on the interaction between the cutaneous and central circulation during blood pressure challenges was examined in eight adults. Subjects were exposed to −10 to −90 mmHg lower body negative pressure (LBNP) in thermoneutral conditions and −10 to −60 mmHg LBNP during heat stress. We measured forearm vascular conductance (FVC; ml ⋅ min−1 ⋅ 100 ml−1 ⋅ mmHg−1) by plethysmography; cutaneous vascular conductance (CVC) by laser-Doppler techniques; and central venous pressure, arterial blood pressure, and cardiac output by impedance cardiography. Heat stress increased FVC from 5.7 ± 0.9 to 18.8 ± 1.3 conductance units (CU) and CVC from 0.21 ± 0.07 to 1.02 ± 0.20 CU. The FVC-CVP relationship was linear over the entire range of LBNP and was shifted upward during heat stress with a slope increase from 0.46 ± 0.10 to 1.57 ± 0.3 CU/mmHg CVP ( P < 0.05). Resting CVP was lower during heat stress (6.3 ± 0.6 vs. 7.7 ± 0.6 mmHg; P < 0.05) but fell to similar levels during LBNP as in normothermic conditions. Data analysis indicates an increased capacity, but not sensitivity, of peripheral baroreflex responses during heat stress. Laser-Doppler techniques detected thermoregulatory responses in the skin, but no significant change in CVC occurred during mild-to-moderate LBNP. Interestingly, very high levels of LBNP produced cutaneous vasodilation in some subjects.

SCANNING LASER DOPPLER TECHNIQUES FOR VIBRATION TESTING

2008 ◽  
Vol 16 (6) ◽  
pp. 21-26 ◽  
Author(s):  
P. Sriram ◽  
J. I. Craig ◽  
S. Hanagud
Keyword(s):  
Laser Doppler ◽  
Scanning Laser ◽  
Vibration Testing ◽  
Doppler Techniques

scholarly journals Multiscale preferential sweeping of particles settling in turbulence

2019 ◽  
Vol 871 ◽  
pp. 244-270 ◽  
Author(s):  
Josin Tom ◽  
Andrew D. Bragg
Keyword(s):  
Fluid Velocity ◽  
Coarse Graining ◽  
Coarse Grained ◽  
Gradient Field ◽  
Inertial Particles ◽  
Particle Settling ◽  
Preferential Sampling ◽  
Velocity Gradients ◽  
Settling Speed

In a seminal article, Maxey (J. Fluid Mech., vol. 174, 1987, pp. 441–465) presented a theoretical analysis showing that enhanced particle settling speeds in turbulence occur through the preferential sweeping mechanism, which depends on the preferential sampling of the fluid velocity gradient field by the inertial particles. However, recent direct numerical simulation (DNS) results in Ireland et al. (J. Fluid Mech., vol. 796, 2016b, pp. 659–711) show that even in a portion of the parameter space where this preferential sampling is absent, the particles nevertheless exhibit enhanced settling velocities. Further, there are several outstanding questions concerning the role of different turbulent flow scales on the enhanced settling, and the role of the Taylor Reynolds number $R_{\unicode[STIX]{x1D706}}$. The analysis of Maxey does not explain these issues, partly since it was restricted to particle Stokes numbers $St\ll 1$. To address these issues, we have developed a new theoretical result, valid for arbitrary $St$, that reveals the multiscale nature of the mechanism generating the enhanced settling speeds. In particular, it shows how the range of scales at which the preferential sweeping mechanism operates depends on $St$. This analysis is complemented by results from DNS where we examine the role of different flow scales on the particle settling speeds by coarse graining the underlying flow. The results show how the flow scales that contribute to the enhanced settling depend on $St$, and that contrary to previous claims, there can be no single turbulent velocity scale that characterizes the enhanced settling speed. The results explain the dependence of the particle settling speeds on $R_{\unicode[STIX]{x1D706}}$, and show how the saturation of this dependence at sufficiently large $R_{\unicode[STIX]{x1D706}}$ depends upon $St$. The results also show that as the Stokes settling velocity of the particles is increased, the flow scales of the turbulence responsible for enhancing the particle settling speed become larger. Finally, we explored the multiscale nature of the preferential sweeping mechanism by considering how particles preferentially sample the fluid velocity gradients coarse grained at various scales. The results show that while rapidly settling particles do not preferentially sample the fluid velocity gradients, they do preferentially sample the fluid velocity gradients coarse grained at scales outside of the dissipation range. This explains the findings of Ireland et al., and further illustrates the truly multiscale nature of the mechanism generating enhanced particle settling speeds in turbulence.

Laser Doppler Measurements of Localized Pulsatile Fluid Velocity

1971 ◽  
Vol BME-18 (6) ◽  
pp. 416-420 ◽  
Author(s):  
Satsuki Morikawa ◽  
Otto Lanz ◽  
Curtis C. Johnson
Keyword(s):  
Fluid Velocity ◽  
Laser Doppler

Microvascular Blood Flow, Volume, and Velocity Measured by Laser Doppler Techniques in IDDM

Diabetes ◽  
1989 ◽  
Vol 38 (7) ◽  
pp. 819-824 ◽  
Author(s):  
M. Rendell ◽  
T. Bergman ◽  
G. O'Donnell ◽  
E. Drobny ◽  
J. Borgos ◽  
...  
Keyword(s):  
Blood Flow ◽  
Laser Doppler ◽  
Microvascular Blood Flow ◽  
Flow Volume ◽  
Blood Flow Volume ◽  
Doppler Techniques
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