scholarly journals Wrapping up a century of splashes

2016 ◽  
Vol 800 ◽  
pp. 1-4 ◽  
Author(s):  
Devaraj van der Meer
Keyword(s):  
High Speed ◽  
Vacuum Chamber ◽  
State Of The Art ◽  
Classical Problem ◽  
Liquid Pool ◽  
Scientific World ◽  
The Impact ◽  
Shed Light

Few fluid phenomena are as beautiful, fragile and ephemeral as the crown splash that is created by the impact of an object on a liquid. The crown-shaped phenomenon and the physics behind it have mesmerised and intrigued scientists for over a century, and still the scientific world has not yet uncovered all of the secrets of the splash. This is exemplified in a particularly striking manner in Marston et al. (J. Fluid Mech., vol. 794, 2016, pp. 506–529) where a 6 m tall vacuum chamber is employed to study the splash formed upon impact of a sphere onto a deep liquid pool, at both atmospheric and reduced ambient pressures. They shed light into the classical problem of the surface seal and study the buckling of the splash. With an almost magical touch they devise a method to create a splash without the liquid and the sphere ever coming into contact. The images that accompany the paper – taken with state-of-the-art high-speed cameras – are as stunning as the physics that is uncovered in them.

Crown sealing and buckling instability during water entry of spheres

2016 ◽  
Vol 794 ◽  
pp. 506-529 ◽  
Author(s):  
J. O. Marston ◽  
T. T. Truscott ◽  
N. B. Speirs ◽  
M. M. Mansoor ◽  
S. T. Thoroddsen
Keyword(s):  
Contact Line ◽  
High Speed ◽  
Ambient Pressure ◽  
Classical Problem ◽  
Sphere Diameter ◽  
Ambient Conditions ◽  
Buckling Instability ◽  
Fine Spray ◽  
Liquid Pools ◽  
The Impact

We present new observations from an experimental investigation of the classical problem of the crown splash and sealing phenomena observed during the impact of spheres onto quiescent liquid pools. In the experiments, a 6 m tall vacuum chamber was used to provide the required ambient conditions from atmospheric pressure down to $1/16\text{th}$ of an atmosphere, whilst high-speed videography was exploited to focus primarily on the above-surface crown formation and ensuing dynamics, paying particular attention to the moments just prior to the surface seal. In doing so, we have observed a buckling-type azimuthal instability of the crown. This instability is characterised by vertical striations along the crown, between which thin films form that are more susceptible to the air flow and thus are drawn into the closing cavity, where they atomize to form a fine spray within the cavity. To elucidate to the primary mechanisms and forces at play, we varied the sphere diameter, liquid properties and ambient pressure. Furthermore, a comparison between the entry of room-temperature spheres, where the contact line pins around the equator, and Leidenfrost spheres (i.e. an immersed superheated sphere encompassed by a vapour layer), where there is no contact line, indicates that the buckling instability appears in all crown sealing events, but is intensified by the presence of a pinned contact line.

scholarly journals High Speed PIV Measurements in Water Hammer

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Roberto Capanna ◽  
Philippe M. Bardet
Keyword(s):  
Experimental Study ◽  
High Speed ◽  
State Of The Art ◽  
Water Hammer ◽  
Compressed Air ◽  
Piv Measurements ◽  
Laser Measurements ◽  
Relaxation Coefficient ◽  
The Impact ◽  
Metal Wall

An experimental study addressing the challenge to measure relaxation coefficient of very fast phenomena such as water hammers is presented. An acrylic projectile containing water is accelerated and impacts a metal wall creating a water hammer. State of the art laser measurements techniques will be deployed in order to achieve such goal. A compressed air custom built cannon is used to accelerate the projectile and create the impact leading to the water hammer. First experimental results for Shadowgraphy and PIV measurements are presented and discussed with focus on the future development for the presented facility.

Confidence-Based Uncertainty Quantification and Model Validation for Simulations of High-Speed Impact Problems

2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Min-Yeong Moon ◽  
Oishik Sen ◽  
Nirmal Kumar Rai ◽  
Nicholas J. Gaul ◽  
Kyung K. Choi ◽  
...  
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Computational Models ◽  
Classical Problem ◽  
Simulation Models ◽  
Confidence Levels ◽  
Model Confidence ◽  
Wide Range ◽  
Final Length ◽  
The Impact

Abstract Validation exercises for computational models of materials under impact must contend with sparse experimental data as well as with uncertainties due to microstructural stochasticity and variabilities in thermomechanical properties of the material. This paper develops statistical methods for determining confidence levels for verification and validation of computational models subject to aleatoric and epistemic uncertainties and sparse stochastic experimental datasets. To demonstrate the method, the classical problem of Taylor impact of a copper bar is simulated. Ensembles of simulations are performed to cover the range of variabilities in the material properties of copper, specifically the nominal yield strength A, the hardening constant B, and the hardening exponent n in a Johnson–Cook material model. To quantify uncertainties in the simulation models, we construct probability density functions (PDFs) of the ratios of the quantities of interest, viz., the final bar diameter Df to the original diameter D0 and the final length Lf to the original length L0. The uncertainties in the experimental data are quantified by constructing target output distributions for these QoIs (Df/D0 and Lf/L0) from the sparse experimental results reported in literature. The simulation output and the experimental output distributions are compared to compute two metrics, viz., the median of the model prediction error and the model confidence at user-specified error level. It is shown that the median is lower and the model confidence is higher for Lf/L0 compared to Df/D0, implying that the simulation models predict the final length of the bar more accurately than the diameter. The calculated confidence levels are shown to be consistent with expectations from the physics of the impact problem and the assumptions in the computational model. Thus, this paper develops and demonstrates physically meaningful metrics for validating simulation models using limited stochastic experimental datasets. The tools and techniques developed in this work can be used for validating a wide range of computational models operating under input uncertainties and sparse experimental datasets.

The Effect of Mach Number on the Loss Generation of LP Turbines

2012 ◽  
Author(s):  
Raúl Vázquez ◽  
Diego Torre
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
High Speed ◽  
State Of The Art ◽  
Pressure Coefficient ◽  
Airfoil Surface ◽  
High Lift ◽  
Pressure Losses ◽  
Coefficient Distribution ◽  
The Impact

The effect of Mach number on the loss generation of Low Pressure (LP) Turbines has been investigated experimentally in a pair of turbine high-speed rigs. Both rigs consist of a rotor-stator configuration. All the airfoils are high lift, high aspect ratio and high turning blades that are characteristic of state of the art LP Turbines. Both rigs are identical with exception of the stator. Two sets of stators have been manufactured and tested. The aerodynamic shape of both stators have been designed in order to achieve the same spanwise distribution of Cp (Compressible Pressure coefficient) over the airfoil surface, each one to its corresponding design Mach number (0.61 and 0.88 respectively). The aim of this experiment is to obtain the sensitivity of profile and endwall losses to Mach number by means of a back-to-back comparison between both sets of airfoils. Because the two sets of stators maintain the same pressure coefficient distribution, Reynolds number and velocity triangles, each one to its corresponding design Mach number; one can state that the results are only affected by the compressibility. Experimental results are presented and compared in terms of area average, radial pitchwise average distributions and exit plane contours of total pressure losses. To complete the paper, the impact of the results on the design of LP Turbines is discussed and presented.

Impact of a high-speed train of microdrops on a liquid pool

2016 ◽  
Vol 792 ◽  
pp. 850-868 ◽  
Author(s):  
Wilco Bouwhuis ◽  
Xin Huang ◽  
Chon U Chan ◽  
Philipp E. Frommhold ◽  
Claus-Dieter Ohl ◽  
...  
Keyword(s):  
Surface Tension ◽  
High Speed ◽  
Scaling Laws ◽  
Liquid Pool ◽  
Boundary Integral ◽  
High Speed Train ◽  
Cavity Depth ◽  
Simple Scaling ◽  
The Individual ◽  
The Impact

A train of high-speed microdrops impacting on a liquid pool can create a very deep and narrow cavity, reaching depths more than 1000 times the size of the individual drops. The impact of such a droplet train is studied numerically using boundary integral simulations. In these simulations, we solve the potential flow in the pool and in the impacting drops, taking into account the influence of liquid inertia, gravity and surface tension. We show that for microdrops the cavity shape and maximum depth primarily depend on the balance of inertia and surface tension and discuss how these are influenced by the spacing between the drops in the train. Finally, we derive simple scaling laws for the cavity depth and width.

The impact of a translating plunging jet on a pool of the same liquid

2011 ◽  
Vol 680 ◽  
pp. 5-30 ◽  
Author(s):  
R. GÓMEZ-LEDESMA ◽  
K. T. KIGER ◽  
J. H. DUNCAN
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Liquid Pool ◽  
Translation Speed ◽  
Dramatic Effect ◽  
Image Velocimetry ◽  
Inclination Angles ◽  
Quiescent Liquid ◽  
Short Time ◽  
The Impact

An experimental study on the impact of a translating two-dimensional transient jet on an initially quiescent liquid pool is studied experimentally using high-speed cinematic visualization and particle image velocimetry methods. Six jet conditions (covering a range of jet thicknesses, velocities and inclination angles relative to vertical) are considered, with measurements performed over a range of horizontal translation speeds for each jet condition. For all conditions studied herein, the jet penetrates into the pool and forms two craters – one upstream and one downstream of the jet. Gravity acts to close these craters, which after a short time pinch off at intermediate depths, thereby entrapping cavities of air. The translation speed of the jet is found to have a dramatic effect on the cavity shapes, pinch-off depths and pinch-off times. A simple theory based on a potential flow and a hydrostatically driven collapse is used to model this flow, and the resulting jet tip trajectories and cavity shapes compare favourably with the experimental data.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Case study: Prediction and field tests of railway noise and effects of a low-height noise barrier

2020 ◽  
Vol 68 (4) ◽  
pp. 303-314
Author(s):  
Yuna Park ◽  
Hyo-In Koh ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
...  
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Residential Areas ◽  
Railway Systems ◽  
Railway Noise ◽  
Sound Levels ◽  
Noise Barrier ◽  
The Difference ◽  
Reduction Effect ◽  
The Impact

Railway noise is calculated to predict the impact of new or reconstructed railway tracks on nearby residential areas. The results are used to prepare adequate counter- measures, and the calculation results are directly related to the cost of the action plans. The calculated values were used to produce noise maps for each area of inter- est. The Schall 03 2012 is one of the most frequently used methods for the production of noise maps. The latest version was released in 2012 and uses various input para- meters associated with the latest rail vehicles and track systems in Germany. This version has not been sufficiently used in South Korea, and there is a lack of standard guidelines and a precise manual for Korean railway systems. Thus, it is not clear what input parameters will match specific local cases. This study investigates the modeling procedure for Korean railway systems and the differences between calcu- lated railway sound levels and measured values obtained using the Schall 03 2012 model. Depending on the location of sound receivers, the difference between the cal- culated and measured values was within approximately 4 dB for various train types. In the case of high-speed trains, the value was approximately 7 dB. A noise-reducing measure was also modeled. The noise reduction effect of a low-height noise barrier system was predicted and evaluated for operating railway sites within the frame- work of a national research project in Korea. The comparison of calculated and measured values showed differences within 2.5 dB.

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