scholarly journals The water entry of multi-droplet streams and jets

2018 ◽  
Vol 844 ◽  
pp. 1084-1111 ◽  
Author(s):  
Nathan B. Speirs ◽  
Zhao Pan ◽  
Jesse Belden ◽  
Tadd T. Truscott
Keyword(s):  
Low Frequency ◽  
Bond Number ◽  
Water Entry ◽  
Liquid Pool ◽  
Scaling Analysis ◽  
Cavity Depth ◽  
Solid Objects ◽  
Jet Impact ◽  
Energy Scaling ◽  
Quiescent Liquid

Water entry has been studied for over a century, but few studies have focused on multiple droplets impacting on a liquid bath sequentially. We connect multi-droplet streams, jets and solid objects with physical-based scaling arguments that emphasize the intrinsically similar cavities. In particular, the cavities created by the initial impact of both droplet streams and jets on an initially quiescent liquid pool exhibit the same types of cavity seal as hydrophobic spheres at low Bond number, some of which were previously unseen for jets and droplet streams. Low-frequency droplet streams exhibit an additional three new cavity seal types unseen for jets or solid spheres that can be predicted with a new non-dimensional frequency. The cavity depth and cavity velocity for both droplet and jet impact are rationalized by an energy scaling analysis and the Bernoulli equation.

EFFECTS OF BOUNDARY-LAYER THICKNESS ON FLOW OSCILLATIONS INSIDE OPEN CAVITIES AT SUPERSONIC SPEEDS

2010 ◽  
Vol 24 (04n05) ◽  
pp. 487-493
Author(s):  
DANG-GUO YANG ◽  
ZHAO-LIN FAN ◽  
JIANG-QIANG LI ◽  
DAN YAO
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Low Frequency ◽  
Cavity Depth ◽  
Oscillation Modes ◽  
Open Cavities ◽  
Flow Oscillations ◽  
Unsteady Characteristics ◽  
Modified Equation

An experiment was conducted in a wind-tunnel to study the internal acoustic field and flow oscillations inside rectangular-box cavities. The length-to-depth ratio of the cavities was 8. The data presented herein was obtained over a Mach number of 1.5 at a Reynolds number of 2.26×107 per meter with different boundary-layer thicknesses of approximately 24 mm and 5.5 mm. The experimental angle of attack, yawing and rolling angles were 0°. The rules were revealed as governing the effects of boundary-layer thickness on flow oscillations and unsteady characteristics by comparing the experimental results with flow oscillation modes predicated by Rossiter's and Heller's modified equation. The results indicate that a decrease in the ratio of boundary-layer thickness to cavity-depth (δ/D) induces flow oscillations amplification, peak oscillation frequency splitting and shifting phenomena of open cavity tones in the low-frequency region.

scholarly journals Sound absorption properties of multi-layer structural composite materials based on waste corn husk fibers

2020 ◽  
Vol 15 ◽  
pp. 155892502091086
Author(s):  
Lihua Lyu ◽  
Jing Lu ◽  
Jing Guo ◽  
Yongfang Qian ◽  
Hong Li ◽  
...  
Keyword(s):  
Composite Materials ◽  
Absorption Coefficient ◽  
Sound Absorption ◽  
Low Frequency ◽  
Sound Absorption Coefficient ◽  
Absorption Properties ◽  
Cavity Depth ◽  
Air Cavity ◽  
Corn Husk ◽  
Structural Composite

In order to find a reasonable way to use the waste corn husk, waste degummed corn husk fibers were used as reinforcing material in one type of composite material. And polylactic acid particles were used as matrix material. The composite materials were prepared by mixing and hot-pressing process, and they were processed into the micro-slit panel. Then, the multi-layer structural sound absorption composite materials were prepared sequentially by micro-slit panel, air cavity, and flax felt. Finally, the sound absorption properties of the multi-layer structural composite materials were studied by changing flax felt thickness, air cavity depth, slit rate, and thickness of micro-slit panel. As the flax felt thickness varied from 0 to 10 mm in 5 mm increments, the peak of sound absorption coefficient shifted to low frequency. The sound absorption coefficient in the low frequency was improved with the air cavity depth varied from 0 to 10 mm in 5 mm increments. With the slit rate increased from 3% to 7% in 2% increments, the peak of sound absorption coefficient shifted to high frequency. With the thickness of micro-slit panel increased from 2 to 6 mm in 2 mm increments, the sound absorption bandwidth was broaden, and the peak of sound absorption coefficient was increased and shifted to low frequency. Results showed that the highest sound absorption coefficient of the multi-layer structural composite materials was about 1 under the optimal process conditions.

scholarly journals Water entry of spheres with various contact angles

2019 ◽  
Vol 862 ◽  
Author(s):  
Nathan B. Speirs ◽  
Mohammad M. Mansoor ◽  
Jesse Belden ◽  
Tadd T. Truscott
Keyword(s):  
Contact Angle ◽  
Weber Number ◽  
Bond Number ◽  
Water Entry ◽  
Contact Angles ◽  
Cavity Formation ◽  
Liquid Impact ◽  
Critical Impact Velocity ◽  
Solid Liquid ◽  
Rough Sphere

It is well known that the water entry of a sphere causes cavity formation above a critical impact velocity as a function of the solid–liquid contact angle; Duez et al. (Nat. Phys., vol. 3 (3), 2007, pp. 180–183). Using a rough sphere with a contact angle of $120^{\circ }$ , Aristoff & Bush (J. Fluid Mech., vol. 619, 2009, pp. 45–78) showed that there are four different cavity shapes dependent on the Bond and Weber numbers (i.e., quasistatic, shallow, deep and surface). We experimentally alter the Bond number, Weber number and contact angle of smooth spheres and find two key additions to the literature: (1) cavity shape also depends on the contact angle; (2) the absence of a splash crown at low Weber number results in cavity formation below the predicted critical velocity. In addition, we use alternate scales in defining the Bond, Weber and Froude numbers to predict the cavity shapes and scale pinch-off times for various impacting bodies (e.g., spheres, multidroplet streams and jets) on the same plots, merging the often separated studies of solid–liquid and liquid–liquid impact in the literature.

scholarly journals How lovebirds maneuver through lateral gusts with minimal visual information

2019 ◽  
Vol 116 (30) ◽  
pp. 15033-15041 ◽  
Author(s):  
Daniel Quinn ◽  
Daniel Kress ◽  
Eric Chang ◽  
Andrea Stein ◽  
Michal Wegrzynski ◽  
...  
Keyword(s):  
Visual Information ◽  
Low Frequency ◽  
Control Algorithms ◽  
Scaling Analysis ◽  
Local Wind ◽  
Point Light Source ◽  
Aerial Robots ◽  
Forest Lake ◽  
In Captivity ◽  
Point Light

Flying birds maneuver effectively through lateral gusts, even when gust speeds are as high as flight speeds. What information birds use to sense gusts and how they compensate is largely unknown. We found that lovebirds can maneuver through 45° lateral gusts similarly well in forest-, lake-, and cave-like visual environments. Despite being diurnal and raised in captivity, the birds fly to their goal perch with only a dim point light source as a beacon, showing that they do not need optic flow or a visual horizon to maneuver. To accomplish this feat, lovebirds primarily yaw their bodies into the gust while fixating their head on the goal using neck angles of up to 30°. Our corroborated model for proportional yaw reorientation and speed control shows how lovebirds can compensate for lateral gusts informed by muscle proprioceptive cues from neck twist. The neck muscles not only stabilize the lovebirds’ visual and inertial head orientations by compensating low-frequency body maneuvers, but also attenuate faster 3D wingbeat-induced perturbations. This head stabilization enables the vestibular system to sense the direction of gravity. Apparently, the visual horizon can be replaced by a gravitational horizon to inform the observed horizontal gust compensation maneuvers in the dark. Our scaling analysis shows how this minimal sensorimotor solution scales favorably for bigger birds, offering local wind angle feedback within a wingbeat. The way lovebirds glean wind orientation may thus inform minimal control algorithms that enable aerial robots to maneuver in similar windy and dark environments.

On standing gravity wave-depression cavity collapse and jetting

2019 ◽  
Vol 866 ◽  
pp. 112-131 ◽  
Author(s):  
D. Krishna Raja ◽  
S. P. Das ◽  
E. J. Hopfinger
Keyword(s):  
Wave Amplitude ◽  
Bond Number ◽  
Working Fluid ◽  
Cavity Depth ◽  
Depth Limit ◽  
Cavity Collapse ◽  
Jet Velocity ◽  
Surface Jet ◽  
Singular Wave ◽  
Surface Jets

Parametrically forced gravity waves can give rise to high-velocity surface jets via the wave-depression cavity implosion. The present results have been obtained in circular cylindrical containers of 10 and 15 cm in diameter (Bond number of order $10^{3}$) in the large fluid depth limit. First, the phase diagrams of instability threshold and wave breaking conditions are determined for the working fluid used, here water with 1 % detergent added. The collapse of the wave-depression cavity is found to be self-similar. The exponent $\unicode[STIX]{x1D6FC}$ of the variation of the cavity radius $r_{m}$ with time $\unicode[STIX]{x1D70F}$, in the form $r_{m}/R\propto \unicode[STIX]{x1D70F}^{\unicode[STIX]{x1D6FC}}$, is close to 0.5, indicative of inertial collapse, followed by a viscous cut-off of $\unicode[STIX]{x1D6FC}\approx 1$. This supports a Froude number scaling of the surface jet velocity caused by cavity collapse. The dimensionless jet velocity scales with the cavity depth that is shown to be proportional to the last stable wave amplitude. It can be expressed by a power law or in terms of finite time singularity related to a singular wave amplitude that sets the transition from a non-pinching to pinch-off cavity collapse scenario. In terms of forcing amplitude, cavity collapse and jetting are found to occur in bands of events of non-pinching and pinching of a bubble at the cavity base. At large forcing amplitudes, incomplete cavity collapse and splashing can occur and, at even larger forcing amplitudes, wave growth is again stable up to the singular wave amplitude. When the cavity is formed, an impulse model shows the importance of the singular cavity diameter that determines the strength of the impulse.

Prediction of Scattered Noise for Two Dimensional Non-Compact Cylinders with Compressible Calculations

2013 ◽  
Vol 378 ◽  
pp. 19-25
Author(s):  
Fang Wang ◽  
Qiu Hong Liu ◽  
Jin Sheng Cai
Keyword(s):  
Acoustic Noise ◽  
Low Frequency ◽  
Computational Method ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Solid Objects ◽  
Total Noise ◽  
Scattering Effects ◽  
Prime Objective ◽  
Flow Variables

A computational method is presented to evaluate non-compact noise produced by compressible flow interacting with arbitrarily shaped solid objects. In conjunction with compressible calculation, hybrid computational aeroacoustics method is used to develop noise calculation. Scattering effect induced by non-compact surfaces is the prime objective to study in the present research, the fluctuations of flow variables are decomposed into hydrodynamic component mainly produced by fluid flow and acoustic component mainly produced by noise propagation. Non-compact integral surface is divided into enough fine elements, and scattered pressure on body surface is firstly captured by acoustic calculation. The acoustic noise of two dimensional stationary circular cylinders at low Mach number is considered with diameter D=0.019m (Re=90000) and D=1m (Re=100). Numerical results indicate that the noise predicated by the present method is as accurate as noise directly computed by Curles equations at low frequency, the total noise of cylinder model has a dipole-like directivity, but a petal-like pattern at high frequency when scattering effects gradually strengthen. This method exactly captures scattered noise produced by noncompact bodies, and the influence of scattered noise with increased frequency is evaluated simultaneously in this paper.

Transient Marangoni convection induced by an isothermal sidewall of a rectangular liquid pool

2021 ◽  
Vol 928 ◽  
Author(s):  
Enhui Chen ◽  
Feng Xu
Keyword(s):  
Marangoni Number ◽  
Scaling Laws ◽  
Marangoni Convection ◽  
Liquid Pool ◽  
Surface Flow ◽  
Scaling Analysis ◽  
Zero Gravity ◽  
Vertical Flow ◽  
Gravity Condition ◽  
Good Agreement

Transient Marangoni convection induced by an isothermal sidewall of a rectangular pool under a zero-gravity condition is studied using scaling analysis. Scaling analysis shows that there exist a number of flow regimes in each evolution scenario, depending on the Marangoni number, the Prandtl number and the aspect ratio. In a typical evolution scenario, a horizontal surface flow and a vertical flow adjacent to the sidewall may appear. Additionally, a number of scaling laws of the velocity and thickness of transient Marangoni convection are obtained. Further, numerical simulation is performed for validation of the selected scaling laws. There exits good agreement between the numerical results and the scaling predictions.

Axisymmetric bubble collapse in a quiescent liquid pool. II. Experimental study

2008 ◽  
Vol 20 (11) ◽  
pp. 112104 ◽  
Author(s):  
R. Bolaños-Jiménez ◽  
A. Sevilla ◽  
C. Martínez-Bazán ◽  
J. M. Gordillo
Keyword(s):  
Experimental Study ◽  
Liquid Pool ◽  
Bubble Collapse ◽  
Quiescent Liquid
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