scholarly journals Axis Ratios of Water Drops Levitated in a Vertical Wind Tunnel

2009 ◽  
Vol 26 (11) ◽  
pp. 2413-2419 ◽  
Author(s):  
B. K. Jones ◽  
J. R. Saylor
Keyword(s):  
Steady State ◽  
Wind Tunnel ◽  
Oscillation Mode ◽  
Vertical Wind ◽  
Drop Diameter ◽  
Dual Polarization ◽  
Axis Ratio ◽  
Oscillation Modes ◽  
Water Drops

Abstract The shapes of falling raindrops are often significantly altered by drop oscillations, complicating dual-polarization radar methods that rely on a predictable, monotonic variation of drop axis ratio α with equivolume drop diameter d. This oscillation behavior varies with d so that time-averaged shapes, which are determined by oscillation mode, sometimes deviate from the d-dependent quiescent shape. The literature identifies a predominance of particular oscillation modes at discrete d, as well as the onset of oscillations at d ≈ 1 mm; however, the specific mechanisms of this phenomenon are unknown. In the present work, measurements of drop axis ratio α were obtained from observations of drops levitated in a vertical wind tunnel. Discordance of the present data with the literature suggests a correlation between oscillation mode and fall trajectory, as well as a steady-state mechanism for the excitation of specific modes for d = 1.3–3-mm drops.

scholarly journals A Wind Tunnel Study on the Shape, Oscillation, and Internal Circulation of Large Raindrops with Sizes between 2.5 and 7.5 mm

2009 ◽  
Vol 66 (3) ◽  
pp. 755-765 ◽  
Author(s):  
Miklós Szakáll ◽  
Karoline Diehl ◽  
Subir K. Mitra ◽  
Stephan Borrmann
Keyword(s):  
Wind Tunnel ◽  
Oscillation Frequency ◽  
Force Balance ◽  
Equivalent Diameter ◽  
Drop Diameter ◽  
Detailed Knowledge ◽  
Shape Parameters ◽  
Internal Circulation ◽  
Frequency Method ◽  
Axis Ratio

Abstract Precipitation prediction using weather radars requires detailed knowledge of the shape parameters of raindrops falling at their terminal velocities in air. Because the raindrops undergo oscillation, the most important shape parameters from the radar prediction point of view are the equilibrium drop shape, the time-averaged axis ratio, and the oscillation frequency. These parameters for individual water drops with equivalent diameter from 2.5 to 7.5 mm were investigated in a vertical wind tunnel using high-speed video imaging. A very good agreement was found between the measured and the theoretically determined raindrop shape calculated by a force balance model. A new method was developed to determine the equivalent drop diameter with the help of the oscillation frequency. The drop size determination by means of the frequency method was found to be three times more precise than by volumetric methods. The time-averaged axis ratio was found to be equal to the equilibrium axis ratio in the investigated raindrop size range. The analysis of the oscillation frequency of the raindrops revealed that the drops undergo multimode oscillations and are oscillating in a transverse mode in addition to an axisymmetric oblate–prolate mode. Experiments are included in which the internal circulation associated with drop oscillation was investigated and compared to theory.

scholarly journals Drop Shapes and Axis Ratio Distributions: Comparison between 2D Video Disdrometer and Wind-Tunnel Measurements

2009 ◽  
Vol 26 (7) ◽  
pp. 1427-1432 ◽  
Author(s):  
M. Thurai ◽  
V. N. Bringi ◽  
M. Szakáll ◽  
S. K. Mitra ◽  
K. V. Beard ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Close Agreement ◽  
Drop Diameter ◽  
Wind Tunnel Experiments ◽  
Axis Ratio ◽  
Wind Tunnel Measurements ◽  
Mean Shape ◽  
The Mean ◽  
Ratio Versus ◽  
Made In

Abstract Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of data implies a certain “robustness” in the mean shape of oscillating drops that may be extended to natural raindrop oscillations, at least in steady rainfall and above the surface layer.

Collision, coalescence, and breakup of large water drops in a vertical wind tunnel

1967 ◽  
Vol 72 (16) ◽  
pp. 4041-4049 ◽  
Author(s):  
William R. Cotton ◽  
Narayan R. Gokhale
Keyword(s):  
Wind Tunnel ◽  
Vertical Wind ◽  
Water Drops ◽  
Large Water

scholarly journals Freezing of Water Drops

1972 ◽  
Vol 11 (63) ◽  
pp. 415-429 ◽  
Author(s):  
W. A. Murray ◽  
R. List
Keyword(s):  
Wind Tunnel ◽  
Air Temperature ◽  
Bubble Size ◽  
Vertical Wind ◽  
Size Distributions ◽  
Air Bubble ◽  
Hexagonal Axis ◽  
Water Drops ◽  
Heat Exchanges ◽  
Tangential Orientation

AbstractInvestigations were made of the ice structures, air-bubble size distributions, and heat exchanges of water drops frozen freely-floating in the purified air of a vertical wind tunnel. Drop diameters varied from 1 to 8 mm, air temperature from −1 to −18.5°C; the ice phase was initiated artificially. It was found that the mass of ice in a freezing drop increases linearly with time. Both mean air bubble and crystal sizes decrease in a regular fashion as the air temperature decreases, whereas the bubble concentration increases. Histograms show a preferred tangential orientation of the projections into the plane of observation of the crystallographic hexagonal axis (c′-axes), a preference which weakens as the temperature decreases.

Vertical wind tunnel experiments and a theoretical study on the microphysics of melting low-density graupel

2021 ◽  
Author(s):  
Karoline Diehl ◽  
Florian Zanger ◽  
Miklós Szakáll ◽  
Andrew Heymsfield ◽  
Stephan Borrmann
Keyword(s):  
Wind Tunnel ◽  
Relative Humidity ◽  
Vertical Wind ◽  
Experimental Results ◽  
Lapse Rate ◽  
Low Density ◽  
Wind Tunnel Experiments ◽  
Maximum Dimension ◽  
Axis Ratio ◽  
Equivalent Radius

Abstract Vertical wind tunnel experiments were carried out to investigate the melting of low-density lump graupel while floating at their terminal velocities. The graupel characteristics such as maximum dimension, density, and axis ratio, were 0.39 ± 0.06 cm, 0.41 ± 0.07 g cm−3, and 0.89 ± 0.06. The air stream of the wind tunnel was gradually heated simulating lapse rates between 4.5 K km−1 and 3.21 K km−1. Each experimental run was performed at a constant relative humidity that was varied between 12 % and 92 % from one experiment to the other. From the image processing of video recordings, variations in minimum and maximum dimension, volume, aspect ratio, density, volume equivalent radius, and ice core radius were obtained. New parameterizations of the terminal velocity prior to melting and during melting were developed. It was found that mass and heat transfer in the dry stage is two times higher compared to that of liquid drops at the same Reynolds number. Based on the experimental results a model was developed from which the external and internal convective enhancement factors during melting due to surface irregularities and internal motions inside the melt water were derived using a Monte Carlo approach. The modelled total melting times and distances deviated by 10 % from the experimental results. Sensitivity tests with the developed model revealed strong dependencies of the melting process on relative humidity, lapse rate, initial graupel density, and graupel size. In dependence on these parameters, the total melting distance varied between 600 m and 1200 m for typical conditions of a falling graupel.

scholarly journals Freezing of Water Drops

1972 ◽  
Vol 11 (63) ◽  
pp. 415-429 ◽  
Author(s):  
W. A. Murray ◽  
R. List
Keyword(s):  
Wind Tunnel ◽  
Air Temperature ◽  
Bubble Size ◽  
Vertical Wind ◽  
Size Distributions ◽  
Air Bubble ◽  
Hexagonal Axis ◽  
Water Drops ◽  
Heat Exchanges ◽  
Tangential Orientation

AbstractInvestigations were made of the ice structures, air-bubble size distributions, and heat exchanges of water drops frozen freely-floating in the purified air of a vertical wind tunnel. Drop diameters varied from 1 to 8 mm, air temperature from −1 to −18.5°C; the ice phase was initiated artificially. It was found that the mass of ice in a freezing drop increases linearly with time. Both mean air bubble and crystal sizes decrease in a regular fashion as the air temperature decreases, whereas the bubble concentration increases. Histograms show a preferred tangential orientation of the projections into the plane of observation of the crystallographic hexagonal axis (c′-axes), a preference which weakens as the temperature decreases.

Minimal modelling approach to describe turbulent rocket roll dynamics in a vertical wind tunnel

2011 ◽  
Vol 226 (9) ◽  
pp. 1042-1060 ◽  
Author(s):  
C E Hann ◽  
M Snowdon ◽  
A Rao ◽  
O Winn ◽  
N Wongvanich ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Vertical Wind ◽  
Modelling Approach
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