Calibration and use of a sailplane variometer to measure vertical velocity fluctuations

1979 ◽  
Vol 16 (1) ◽  
pp. 99-105 ◽  
Author(s):  
S. Sethuraman ◽  
R. M. Brown ◽  
G. S. Raynor ◽  
W. A. Tuthill
Keyword(s):  
Vertical Velocity ◽  
Velocity Fluctuations

scholarly journals Physical controls on orographic cirrus inhomogeneity

2007 ◽  
Vol 7 (14) ◽  
pp. 3771-3781 ◽  
Author(s):  
J. E. Kay ◽  
M. Baker ◽  
D. Hegg
Keyword(s):  
Vertical Velocity ◽  
Cloud Cover ◽  
Particle Growth ◽  
Physical Processes ◽  
Velocity Fluctuations ◽  
Ice Nuclei ◽  
Weather Model ◽  
Model Cloud ◽  
Homogeneous Freezing ◽  
The Relationship

Abstract. Optical depth distributions (P(σ)) are a useful measure of radiatively important cirrus (Ci) inhomogeneity. Yet, the relationship between P(σ) and underlying cloud physical processes remains unclear. In this study, we investigate the influence of homogeneous and heterogeneous freezing processes, ice particle growth and fallout, and mesoscale vertical velocity fluctuations on P(σ) shape during an orographic Ci event. We evaluate Lagrangian Ci evolution along kinematic trajectories from a mesoscale weather model (MM5) using an adiabatic parcel model with binned ice microphysics. Although the presence of ice nuclei increased model cloud cover, our results highlight the importance of homogeneous freezing and mesoscale vertical velocity variability in controlling Ci P(σ) shape along realistic upper tropospheric trajectories.

Spectral analysis and coherence of aerodynamic lift on rectangular cylinders in turbulent flow

2017 ◽  
Vol 830 ◽  
pp. 408-438 ◽  
Author(s):  
Shaopeng Li ◽  
Mingshui Li
Keyword(s):  
Turbulent Flow ◽  
Closed Form ◽  
Vertical Velocity ◽  
Lift Force ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Dimensional Effects ◽  
Decay Parameters ◽  
Rectangular Cylinders

The goal of the present work is to derive the closed-form expressions of coherence and admittances to describe the spatial distribution of lift on rectangular cylinders in turbulent flow, which can be used to investigate the three-dimensional effects of turbulence. The coherence of the three-dimensional aerodynamic admittance (3D AAF), which takes into full account the spanwise variations in the vertical velocity fluctuations, is introduced to assess the validity of the strip assumption. A theoretical coherence model expressed in a double-exponential form is derived starting from the two-wavenumber spectral tensor of the lift on a thin aerofoil in Fourier space, providing us with explicit insight into the coherence of the lift force. Notably, it is an intrinsic property that the lift force on the structure is more strongly correlated than the oncoming flow and 3D AAF. This coherence model is extended to rectangular cylinders by the introduction of three floating parameters into the decay parameters of the 3D AAF. Based on theoretical and experimental investigations, it is shown that the three-dimensional effects of turbulence grow more prominent as the difference between the decay parameters of the 3D AAF and vertical velocity fluctuations decreases. A generalized approach for rapidly deriving the closed-form expressions of the admittances is proposed to study the unsteady behaviour of the lift force and the distortion of the free stream passing through the rectangular cylinders.

Experimental Investigation of Unstably Stratified Buoyant Wakes

2005 ◽  
Vol 128 (3) ◽  
pp. 488-493 ◽  
Author(s):  
Wayne N. Kraft ◽  
Malcolm J. Andrews
Keyword(s):  
Vertical Velocity ◽  
Cold Water ◽  
Water Channel ◽  
Mixing Layer ◽  
Splitter Plate ◽  
Wake Region ◽  
Return To Equilibrium ◽  
Velocity Fluctuations ◽  
Unstable Stratification ◽  
Plane Wake

A water channel has been used as a statistically steady experiment to investigate the development of a buoyant plane wake. Parallel streams of hot and cold water are initially separated by a splitter plate and are oriented to create an unstable stratification. At the end of the splitter plate, the two streams are allowed to mix and a buoyancy-driven mixing layer develops. The continuous, unstable stratification inside the developing mixing layer provides the necessary environment to study the buoyant wake. Downstream a cylinder was placed at the center of the mixing layer. As a result the dynamic flows of the plane wake and buoyancy-driven mixing layer interact. Particle image velocimetry and a high-resolution thermocouple system have been used to measure the response of the plane wake to buoyancy driven turbulence. Velocity and density measurements are used as a basis from which we describe the transition, and return to equilibrium, of the buoyancy-driven mixing layer. Visual observation of the wake does not show the usual vortex street associated with a cylinder wake, but the effect of the wake is apparent in the measured vertical velocity fluctuations. An expected peak in velocity fluctuations in the wake is found, however the decay of vertical velocity fluctuations occurs at a reduced rate due to vertical momentum transport into the wake region from buoyancy-driven turbulence. Therefore for wakes where buoyancy is driving the motion, a remarkably fast recovery of a buoyancy-driven Rayleigh-Taylor mixing in the wake region is found.

scholarly journals Wind-profiler observations of gravity waves produced by convection at mid-latitudes

2006 ◽  
Vol 6 (10) ◽  
pp. 2825-2836 ◽  
Author(s):  
Y. G. Choi ◽  
S. C. Lee ◽  
A. J. McDonald ◽  
D. A. Hooper
Keyword(s):  
Gravity Waves ◽  
Vertical Velocity ◽  
Small Scale ◽  
Wind Profiler ◽  
Convective Activity ◽  
Velocity Fluctuations ◽  
Short Period ◽  
Horizontal Momentum ◽  
Scale Inhomogeneity

Abstract. This work presents a case study which includes regions of large rapidly varying vertical velocities observed by a VHF wind-profiler at Aberystwyth (52.4° N, 4.1° W). Analysis indicates that this region is associated with gravity waves above the tropopause level and simultaneous regions of convective activity below the tropopause level. This case study also suggests that convective activity can be identified effectively by finding periods of large uncertainties on the derived velocities. These regions are hypothesized to be related to regions of small-scale inhomogeneity in the wind field. Examination suggests that the large vertical velocity fluctuations above these convective regions are short period gravity wave packets as expected from theory. In addition the vertical flux of the horizontal momentum associated with the gravity waves also displays the pattern of reversal observed in previous studies.

scholarly journals Detailed measurements of a statistically steady Rayleigh–Taylor mixing layer from small to high Atwood numbers

2010 ◽  
Vol 659 ◽  
pp. 127-190 ◽  
Author(s):  
ARINDAM BANERJEE ◽  
WAYNE N. KRAFT ◽  
MALCOLM J. ANDREWS
Keyword(s):  
Vertical Velocity ◽  
Mass Flux ◽  
Mixing Layer ◽  
Splitter Plate ◽  
Hot Wire ◽  
Operating Characteristics ◽  
Velocity Fluctuations ◽  
Gas Channel ◽  
Wide Range ◽  
Turbulent Mass Flux

The self-similar evolution to turbulence of a multi-mode miscible Rayleigh–Taylor (RT) mixing layer has been investigated for Atwood numbers 0.03–0.6, using an air–helium gas channel experiment. Two co-flowing gas streams, one containing air (on top) and the other a helium–air mixture (at the bottom), initially flowed parallel to each other at the same velocity separated by a thin splitter plate. The streams met at the end of the splitter plate, with the downstream formation of a buoyancy unstable interface, and thereafter buoyancy-driven mixing. This buoyancy-driven mixing layer experiment permitted long data collection times, short transients and was statistically steady. Several significant designs and operating characteristics of the gas channel experiment are described that enabled the facility to be successfully run for At ~ 0.6. We report, and discuss, statistically converged measurements using digital image analysis and hot-wire anemometry. In particular, two hot-wire techniques were developed for measuring the various turbulence and mixing statistics in this air–helium RT experiment. Data collected and discussed include: mean density profiles, growth rate parameters, various turbulence and mixing statistics, and spectra of velocity, density and mass flux over a wide range of Atwood numbers (0.03 ≤ At ≤ 0.6). In particular, the measured data at the small Atwood number (0.03–0.04) were used to evaluate several turbulence-model constants. Measurements of the root mean square (r.m.s.) velocity and density fluctuations at the mixing layer centreline for the large At case showed a strong similarity to lower At behaviours when properly normalized. A novel conditional averaging technique provided new statistics for RT mixing layers by separating the bubble (light fluid) and spike (heavy fluid) dynamics. The conditional sampling highlighted differences in the vertical turbulent mass flux, and vertical velocity fluctuations, for the bubbles and spikes, which were not otherwise observable. Larger values of the vertical turbulent mass flux and vertical velocity fluctuations were found in the downward-falling spikes, consistent with larger growth rates and momentum of spikes compared with the bubbles.

Decay laws, anisotropy and cyclone–anticyclone asymmetry in decaying rotating turbulence

2010 ◽  
Vol 666 ◽  
pp. 5-35 ◽  
Author(s):  
F. MOISY ◽  
C. MORIZE ◽  
M. RABAUD ◽  
J. SOMMERIA
Keyword(s):  
Vertical Velocity ◽  
Large Scale ◽  
Large Time ◽  
Initial Conditions ◽  
Shear Instability ◽  
Vorticity Field ◽  
Rotating Platform ◽  
Velocity Fluctuations ◽  
Vertical Vorticity ◽  
Rotating Turbulence

The effect of a background rotation on the decay of grid-generated turbulence is investigated from experiments using the large-scale ‘Coriolis’ rotating platform. A first transition occurs at 0.4 tank rotation (instantaneous Rossby number Ro ≃ 0.25), characterized by a t−6/5 → t−3/5 transition of the energy-decay law. After this transition, anisotropy develops in the form of vertical layers, where the initial vertical velocity fluctuations remain trapped. The vertical vorticity field develops a cyclone–anticyclone asymmetry, reproducing the growth law of the vorticity skewness, Sω(t) ≃ (Ωt)0.7, reported by Morize, Moisy & Rabaud (Phys. Fluids, vol. 17 (9), 2005, 095105). A second transition is observed at larger time, characterized by a return to vorticity symmetry. In this regime, the layers of nearly constant vertical velocity become thinner as they are advected and stretched by the large-scale horizontal flow, and eventually become unstable. The present results indicate that the shear instability of the vertical layers contributes significantly to the re-symmetrization of the vertical vorticity at large time, by re-injecting vorticity fluctuations of random sign at small scales. These results emphasize the importance of the nature of the initial conditions in the decay of rotating turbulence.

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