The water entry of a sphere in a jet

2019 ◽  
Vol 863 ◽  
pp. 956-968 ◽  
Author(s):  
Nathan B. Speirs ◽  
Jesse Belden ◽  
Zhao Pan ◽  
Sean Holekamp ◽  
George Badlissi ◽  
...  
Keyword(s):  
Structural Damage ◽  
High Speed ◽  
Early Time ◽  
Water Entry ◽  
Rigid Sphere ◽  
High Speed Imaging ◽  
Near Surface ◽  
Image Velocimetry ◽  
Surface Particle ◽  
Force Reduction

The forces on an object impacting the water are extreme in the early moments of water entry and can cause structural damage to biological and man-made bodies alike. These early-time forces arise largely from added mass, peaking when the submergence is much less than one body length. We experimentally investigate a means of reducing impact forces on a rigid sphere by placing the sphere inside a jet of water so that the jet strikes the quiescent water surface prior to entry of the sphere into the pool. The water jet accelerates the pool liquid and forms a cavity into which a sphere falls. Through on-board accelerometer measurements and high-speed imaging, we quantify the force reduction compared to the case of a sphere entering a quiescent pool. Finally, we find the emergence of a critical jet volume required to maximize force reduction; the critical volume is rationalized using scaling arguments informed by near-surface particle image velocimetry (PIV) data.

scholarly journals Dual-camera system for high-speed imaging in particle image velocimetry

2012 ◽  
Vol 15 (3) ◽  
pp. 193-195 ◽  
Author(s):  
K. Hashimoto ◽  
A. Hori ◽  
T. Hara ◽  
S. Onogi ◽  
H. Mouri
Keyword(s):  
Particle Image Velocimetry ◽  
High Speed ◽  
Particle Image ◽  
High Speed Imaging ◽  
Camera System ◽  
Image Velocimetry

scholarly journals Controlled impact of a disk on a water surface: cavity dynamics

2009 ◽  
Vol 633 ◽  
pp. 381-409 ◽  
Author(s):  
RAYMOND BERGMANN ◽  
DEVARAJ VAN DER MEER ◽  
STEPHAN GEKLE ◽  
ARJAN VAN DER BOS ◽  
DETLEF LOHSE
Keyword(s):  
Particle Image Velocimetry ◽  
Water Surface ◽  
High Speed ◽  
Particle Image ◽  
Boundary Integral ◽  
Infinite Cylinder ◽  
High Speed Imaging ◽  
Image Velocimetry ◽  
Minimal Radius ◽  
Surface Cavity

In this paper we study the transient surface cavity which is created by the controlled impact of a disk of radius h0 on a water surface at Froude numbers below 200. The dynamics of the transient free surface is recorded by high-speed imaging and compared to boundary integral simulations giving excellent agreement. The flow surrounding the cavity is measured with high-speed particle image velocimetry and is found to also agree perfectly with the flow field obtained from the simulations.We present a simple model for the radial dynamics of the cavity based on the collapse of an infinite cylinder. This model accounts for the observed asymmetry of the radial dynamics between the expansion and the contraction phases of the cavity. It reproduces the scaling of the closure depth and total depth of the cavity which are both found to scale roughly as ∝ Fr1/2 with a weakly Froude-number-dependent prefactor. In addition, the model accurately captures the dynamics of the minimal radius of the cavity and the scaling of the volume Vbubble of air entrained by the process, namely, Vbubble/h03∝(1 + 0.26Fr1/2)Fr1/2.

scholarly journals In situ analysis of flow dynamics and deformation fields in cutting and sliding of metals

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150194 ◽  
Author(s):  
Yang Guo ◽  
W. Dale Compton ◽  
Srinivasan Chandrasekar
Keyword(s):  
Material Removal ◽  
High Speed ◽  
Ductile Failure ◽  
Rake Angle ◽  
Flow Dynamics ◽  
High Speed Imaging ◽  
Image Velocimetry ◽  
Material Forming ◽  
Continuous Chip

The flow dynamics, deformation fields and chip-particle formation in cutting and sliding of metals are analysed, in situ , using high-speed imaging and particle image velocimetry. The model system is a brass workpiece loaded against a wedge indenter at low speeds. At large negative rake angles, the flow is steady with a prow of material forming ahead of the indenter. There is no material removal and a uniformly strained layer develops on the workpiece surface—the pure sliding regime. When the rake angle is less negative, the flow becomes unsteady, triggered by formation of a crack on the prow free surface and material removal ensuing—the cutting regime. The strain on the prow surface at crack initiation is found to be constant. Chip morphologies, such as discrete particle, segmented chip and continuous chip with mesoscale roughness, are shown to arise from a universal mechanism involving propagation of the prow crack, but to different distances towards the indenter tip. The simple shear deformation in continuous chip formation shows small-angle oscillations also linked to the prow crack. Implications for material removal processes and ductile failure are discussed.

scholarly journals Unsteady forces on spheres during free-surface water entry

2012 ◽  
Vol 704 ◽  
pp. 173-210 ◽  
Author(s):  
Tadd T. Truscott ◽  
Brenden P. Epps ◽  
Alexandra H. Techet
Keyword(s):  
Free Surface ◽  
Surface Water ◽  
High Speed ◽  
Accurate Determination ◽  
Water Entry ◽  
High Speed Imaging ◽  
Air Cavity ◽  
Unsteady Forces ◽  
Unsteady Force ◽  
Low Mass

AbstractWe present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments.

scholarly journals Dynamics of Bubble Motion and Gas-Liquid Interfacial Phenomena

2003 ◽  
Author(s):  
Katsumi Tsuchiya
Keyword(s):  
Mass Transfer ◽  
Surface Wave ◽  
High Speed ◽  
Bubble Surface ◽  
Liquid Interface ◽  
Oscillatory Motion ◽  
Wave Formation ◽  
High Speed Imaging ◽  
Vertical Projection ◽  
Near Surface

Two aspects of the dynamics associated with oscillating bubbles are discussed in this paper: oscillatory motion of bubble itself and bubble-surface wave. The primary issue here is whether it is the case that the surface wave occurs in sychronization with the bubble’s oscillatory motion. The dynamic process of wave formation and propagation along the surface of an oscillating bubble is studied based on high-speed imaging, through which the wave characteristics such as wavelength and phase/propagation speed are evaluated as mostly the vertical projection of rather regularly generated bubble-surface ripples. The bubble oscillating motion is characterized quantitatively by the bubble-gyration (or edge-rotation) frequency, diameter and velocity. In addition, dynamics of mass transfer across gas–liquid interface in a gas-dispersed (continuous liquid) system are examined via high-sensitivity, high-speed imaging. The dispersive dynamics of the dissolved component from the gas into the liquid phase are visualized using laser-induced fluorescence (LIF) with pH-sensitive pyrene (HPTS) for both a single and multi-bubble systems. The coupling between these dynamics of surface/interfacial flow and mass transfer is attempted towards better understanding of such complex phenomena prevailing in the vicinity of the fluctuating gas–liquid interface. Enhancement of the mass transfer is found to be associated with the (nonlinear) wave formation, influence of which could be included in modeling the mass-transfer coefficient, apart from an physical account of the near-surface concentration gradient. Due to significant bubble–bubble interactions in a multi-bubble system, the dispersive pattern of low-pH region arising from gas dissolution becomes extremely complex; the visual estimate of time variation in fluorescence level is then mainly made over a fixed space in the gas–liquid flow system.

scholarly journals Water entry of deformable spheres

2017 ◽  
Vol 824 ◽  
pp. 912-930 ◽  
Author(s):  
Randy C. Hurd ◽  
Jesse Belden ◽  
Michael A. Jandron ◽  
D. Tate Fanning ◽  
Allan F. Bower ◽  
...  
Keyword(s):  
Material Properties ◽  
High Speed ◽  
Large Scale ◽  
Hydrodynamic Pressure ◽  
Oscillation Period ◽  
Water Entry ◽  
Effective Diameter ◽  
High Speed Imaging ◽  
Rigid Spheres ◽  
Velocity Change

When a rigid body collides with a liquid surface with sufficient velocity, it creates a splash curtain above the surface and entrains air behind the sphere, creating a cavity below the surface. While cavity dynamics has been studied for over a century, this work focuses on the water entry characteristics of deformable elastomeric spheres, which has not been studied. Upon free surface impact, an elastomeric sphere deforms significantly, giving rise to large-scale material oscillations within the sphere resulting in unique nested cavities. We study these phenomena experimentally with high-speed imaging and image processing techniques. The water entry behaviour of deformable spheres differs from rigid spheres because of the pronounced deformation caused at impact as well as the subsequent material vibration. Our results show that this deformation and vibration can be predicted from material properties and impact conditions. Additionally, by accounting for the sphere deformation in an effective diameter term, we recover previously reported characteristics for time to cavity pinch off and hydrodynamic force coefficients for rigid spheres. Our results also show that velocity change over the first oscillation period scales with the dimensionless ratio of material shear modulus to impact hydrodynamic pressure. Therefore, we are able to describe the water entry characteristics of deformable spheres in terms of material properties and impact conditions.

Autoignition Limits of Hydrogen at Relevant Reheat Combustor Operating Conditions

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
J. Fleck ◽  
P. Griebel ◽  
A.M. Steinberg ◽  
M. Stöhr ◽  
M. Aigner ◽  
...  
Keyword(s):  
Flue Gas ◽  
Gas Turbines ◽  
High Speed ◽  
Initial Position ◽  
Operating Conditions ◽  
Dominant Factor ◽  
High Speed Imaging ◽  
Lean Premixed Combustion ◽  
Fuel Jet ◽  
Image Velocimetry

The use of highly reactive fuels in the lean premixed combustion systems employed in stationary gas turbines can lead to many practical problems, such as unwanted autoignition in regions not designed for combustion. In the present study, autoignition characteristics for hydrogen, diluted with up to 30 vol. % nitrogen, were investigated at conditions relevant to reheat combustor operation (p = 15 bar, T >1000 K, hot flue gas, relevant residence times). The experiments were performed in a generic, optically accessible reheat combustor, by applying high-speed imaging and particle image velocimetry. Autoignition limits for different mixing section (temperature, velocity) and fuel jet (N2 dilution) parameters are described. The dominant factor influencing autoignition was the temperature, with an increase of around 2% leading to a reduction of the highest possible H2 concentration without “flame-stabilizing autoignition kernels” of approximately 16 vol. %. Furthermore, the onset and propagation of the ignition kernels were elucidated using the high-speed measurements. It was found that the ability of individual autoignition kernels to develop into stable flames depends on the initial position of the kernel and the corresponding axial velocity at that position. While unwanted autoignition occurred prior to reaching the desired operating point for most investigated conditions, for certain conditions the reheat combustor could be operated stably with up to 80 vol. % H2 in the fuel.

scholarly journals Study of Layer Formation During Droplet-Based Three-Dimensional Printing of Gel Structures

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Kyle Christensen ◽  
Yong Huang
Keyword(s):  
Inkjet Printing ◽  
High Speed ◽  
Three Dimensional ◽  
Layer By Layer ◽  
Layer Formation ◽  
High Speed Imaging ◽  
Three Dimensional Printing ◽  
Drop On Demand ◽  
Image Velocimetry ◽  
Dimensional Printing

Additive manufacturing, also known as three-dimensional (3D) printing, is an approach in which a structure may be fabricated layer by layer. For 3D inkjet printing, droplets are ejected from a nozzle, and each layer is formed droplet by droplet. Inkjet printing has been widely applied for the fabrication of 3D biological gel structures, but the knowledge of the microscale interactions between printed droplets is still largely elusive. This study aims to elucidate the layer formation mechanism in terms of the formation of single lines and layers comprised of adjacent lines during drop-on-demand inkjet printing of alginate using high speed imaging and particle image velocimetry. Inkjet droplets are found to impact, spread, and coalesce within a fluid region at the deposition site, forming coherent printed lines within a layer. The effects of printing conditions on the behavior of droplets during layer formation are discussed and modeled based on gelation dynamics, and recommendations are presented to enable controllable and reliable fabrication of gel structures. The effects of gelation on droplet impact dynamics are found to be negligible during alginate printing, and interfaces are found to form between printed lines within a layer depending on printing conditions, printing path orientation, and gelation dynamics.

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