Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces

2015 ◽  
Author(s):  
Bulent Guzel ◽  
Fatih C. Korkmaz
Keyword(s):  
Experimental Investigation ◽  
Flow Separation ◽  
High Speed ◽  
Water Entry ◽  
Air Entrapment ◽  
Hydrophobic Surfaces ◽  
Blunt Bodies ◽  
Drop Tests ◽  
Set Up ◽  
The Impact

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces. In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.

scholarly journals Research on Blade-Casing Rub-Impact Mechanism by Experiment and Simulation in Aeroengines

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Jie Hong ◽  
Tianrang Li ◽  
Zhichao Liang ◽  
Dayi Zhang ◽  
Yanhong Ma
Keyword(s):  
High Speed ◽  
High Performance ◽  
Element Model ◽  
Physical Parameters ◽  
Test Rig ◽  
Calculation Results ◽  
Rotor Support ◽  
Blade Tip ◽  
Set Up ◽  
The Impact

Aeroengines pursue high performance, and compressing blade-casing clearance has become one of the main ways to improve turbomachinery efficiency. Rub-impact faults occur frequently with clearance decreasing. A high-speed rotor-support-casing test rig was set up, and the mechanism tests of light and heavy rub-impact were carried out. A finite element model of the test rig was established, and the calculation results were in good agreement with the experimental results under both kinds of rub-impact conditions. Based on the actual blade-casing structure model, the effects of the major physical parameters including imbalance and material characteristics were investigated. During the rub-impact, the highest stress occurs at the blade tip first and then it is transmitted to the blade root. Deformation on the impact blade tip generates easily with decreased yield strength, and stress concentration at the blade tip occurs obviously with weaker stiffness. The agreement of the computation results with the experimental data indicates the method could be used to estimate rub-impact characteristics and is effective in design and analyses process.

scholarly journals Experimental investigation of wing flexibility on force generation of a hovering flapping wing micro air vehicle with double wing clap-and-fling effects

2017 ◽  
Vol 9 (3) ◽  
pp. 187-197 ◽  
Author(s):  
Quoc V Nguyen ◽  
Woei L Chan ◽  
Marco Debiasi
Keyword(s):  
Experimental Investigation ◽  
Power Consumption ◽  
High Speed ◽  
Electrical Power ◽  
Leading Edge ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Custom Made ◽  
Air Vehicle ◽  
Set Up

Experimental investigation of wing flexibility on vertical thrust generation and power consumption in hovering condition for a hovering Flapping-Wing Micro Air Vehicle, namely FlowerFly, weighing 14.5 g with a 3 g onboard battery and having four wings with double wing clap-and-fling effects, was conducted for several wing configurations with the same shape, area, and weight. A data acquisition system was set up to simultaneously record aerodynamic forces, electrical power consumption, and wing motions at various flapping frequencies. The forces and power consumption were measured with a loadcell and a custom-made shunt circuit, respectively, and the wing motion was captured by high-speed cameras. The results show a phase delay of the wing tip displacement observed for wings with high flexible leading edge at high frequency, resulting in less vertical thrust produced when compared with the wings with less leading edge flexibility at the same flapping frequency. Positive wing camber was observed during wing flapping motion by arranging the wing supporting ribs. Comparison of thrust-to-power ratios between the wing configurations was undertaken to figure out a wing configuration for high vertical thrust production but less power consumption.

Experimental Investigation of the Green Water Loads on a Wave-Piercing Tumblehome Ship

2017 ◽  
Author(s):  
Hui Li ◽  
Bao-Li Deng ◽  
Shu-Zheng Sun ◽  
Wen-Lei Du ◽  
Hao-Dong Zhao
Keyword(s):  
Experimental Investigation ◽  
High Speed ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Green Water ◽  
Strong Nonlinearity ◽  
Water Tank ◽  
Water Tank Experiment ◽  
The Impact ◽  
Ship Speed

This paper presents the results of an experimental investigation of green water loads on a wave-piercing tumblehome ship. A water tank experiment was carried out in head regular waves by using a self-propelling segmented ship model. Wave probes and pressure sensors were arranged on the bow deck along the longitudinal and transverse directions. The height of water and the impact pressure on the deck were measured and their distributions in different wave conditions studied. The motion of the water flowing on the deck was recorded by a high-speed video system. Based on the experimental results, it was found that the green water is more serious with the increase of incident wave height and ship speed. The bow shape has little effects on the occurrence of green water, but it influences the green water loads to some extent. The distribution of green water pressure is different from that of green water height due to the strong nonlinearity of green water pressure.

Stereographic Backlit Imaging and Bubble Identification From a Plunging Jet With Floor Interactions

2021 ◽  
Author(s):  
Roy A. Pillers ◽  
Theodore J. Heindel
Keyword(s):  
High Speed ◽  
Imaging Techniques ◽  
Primary Source ◽  
Breaking Waves ◽  
Bubble Plume ◽  
Shape Estimation ◽  
Fish Farms ◽  
Automated Identification ◽  
Set Up ◽  
The Impact

Abstract Plunging jets have been extensively studied for their relatively simple set-up but complex multiphase interactions. This phenomenon includes gas carry-under and mixing, which occurs when shear effects between the plunging liquid jet and surrounding gas are sufficient to entrain gas at the impact site. Previous investigations typically assume the floor has an infinite depth and neglect compressive effects caused by the jet interacting with the catch tank floor. While this assumption is ideal for breaking waves in the middle of the ocean, many other applications have to contend with floor effects. These include waterfalls, wastewater treatment, dams, fish farms, mineral separation, and molten metal pouring. It is hypothesized that floor interactions will significantly affect the multiphase flow hydrodynamics, especially in places where the uninhibited jet would approach or pass the floor region. Using a large catch tank with an adjustable floor region designed to hold a constant water level, data were collected using high-speed backlit stereographic imaging to capture and compare the effects of three separate tank depths with those found using an infinite pool assumption. To identify bubbles in each stereographic projection, a uniform bubble recognition procedure was developed that was used across all data sets. This allowed for the automated identification of bubble entrainment regions, which could be compared with different flow conditions. Preliminary results are inconclusive as to the effects of the floor region on the bubble plume dynamics; however, the results showed consistent measurements between trials and the two stereographic cameras, implying the time variation of the jet dynamics was the primary source of uncertainty in the results and not the identification procedure. Therefore, the identification methods have provided a method for plume volume and shape estimation, which will be used in future studies using 3D imaging techniques.

Analysis of Dynamic Response of Simply-Supported Girder Bridge in High-Speed Railway Based on the Moving Rows Mass-Spring Model

2012 ◽  
Vol 193-194 ◽  
pp. 919-924
Author(s):  
Jin Feng Wu ◽  
Zhi Jun Zhang ◽  
Xiao Zhen Li
Keyword(s):  
High Speed ◽  
Damping Ratio ◽  
Spring Model ◽  
Simply Supported ◽  
Mass Spring Model ◽  
Girder Bridge ◽  
Set Up ◽  
Mass Spring ◽  
The Impact ◽  
Bridge System

The vibration theory of beam and D’Alembert principle are used to set up vehicle-bridge system for a simply-supported girder bridge under the moving rows mass-spring model. The kinematic equations of vehicle and bridge are derived separately. And with the force balanced relationship and the displacement compatibility conditions between wheels and rail, the equations of vehicle-bridge system are established. A calculating program is complicated with MATLAB language and solved by Newmark-β method. Results show that the effect of the damping ratio on the impact factor is significant and running speed of the vehicle is one of the main actors resulting in vibration of the system.

Optical Observation of the Supercavitation Induced by High-Speed Water Entry

2000 ◽  
Vol 122 (4) ◽  
pp. 806-810 ◽  
Author(s):  
Hong-Hui Shi ◽  
Motoyuki Itoh ◽  
Takuya Takami
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Shock Waves ◽  
High Speed ◽  
Bubbly Flow ◽  
Water Entry ◽  
Gas Pressure ◽  
Optical Observation ◽  
Water Tank ◽  
Experimental Facility

When a high-speed projectile penetrates into water, a cavity is formed behind the projectile. The gas enclosed in the cavity experiences a nonequilibrium process, i.e., the gas pressure decreases as the projectile moves more deeply into water. As a result, the cavity is sealed near the free surface (surface closure) and subsequently the cavity breaks up in water (deep closure). Accompanying the break-up of the cavity, secondary shock waves appear. This is the so-called supercavitation in water entry. This paper describes an experimental investigation into the water entry phenomenon. Projectiles of 342 m/s were generated from a small-bore rifle that was fixed vertically in the experimental facility. The projectiles were fired into a windowed water tank. A shadowgraph optical observation was performed to observe the entry process of the projectile and the formation and collapse of the cavity behind the projectile. A number of interesting observations relating to the motion of the free surface, the splash, the underwater bubbly flow and so on were found. [S0098-2202(00)00204-2]

Air entrapment by a falling water mass

1995 ◽  
Vol 294 ◽  
pp. 181-207 ◽  
Author(s):  
Hasan N. Oguz ◽  
Andrea Prosperetti ◽  
Ali R. Kolaini
Keyword(s):  
High Speed ◽  
Water Mass ◽  
Boundary Integral ◽  
Surface Shape ◽  
Water Tank ◽  
Air Entrapment ◽  
Free Surface Shape ◽  
Large Water ◽  
The Impact ◽  
Good Agreement

The impact of a nearly cylindrical water mass on a water surface is studied both experimentally and theoretically. The experiments consist of the rapid release of water from the bottom of a cylindrical container suspended above a large water tank and of the recording of the free-surface shape of the resulting crater with a high-speed camera. A bubble with a diameter of about twice that of the initial cylinder remains entrapped at the bottom of the crater when the aspect ratio and the energy of the falling water mass are sufficiently large. Many of the salient features of the phenomenon are explained on the basis of simple physical arguments. Boundary-integral potential-flow simulations of the process are also described. These numerical results are in fair to good agreement with the observations.

scholarly journals Experimental investigation of size effects in colliding droplet

2017 ◽  
Author(s):  
Lars Pasternak ◽  
Martin Sommerfeld
Keyword(s):  
Experimental Investigation ◽  
Size Effects ◽  
Relative Velocity ◽  
High Speed ◽  
Droplet Generator ◽  
Collision Process ◽  
Droplet Collisions ◽  
Process And Outcome ◽  
Binary Collisions ◽  
The Impact

The present work focuses on the size effect of binary collisions of PVP droplets (viscosity 5.5 mPas). The aim was the identification of the boundaries between bouncing, coalescence, stretching and reflexive separation.These boundaries are necessary for numerical simulations of droplet collisions in spray drying processes. Therefore, droplet chains were generated by droplet generators with oscillating membrane and directed towards each other at different angles for producing binary collisions. In the experiments two droplet properties (i.e. droplet size and size ratio) were varied. Two synchronised high-speed cameras were used to observe the collision process and outcome perpendicularly and parallelly to the collision plane. The variation of the impact parameter B was performed by a frequency offset for one droplet generator. The relative velocity (i. e. 0.5 to 4.7 m/s) was set by changing the collision angle.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4781

scholarly journals Liquid Propane Injection in Flash-Boiling Conditions

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6257
Author(s):  
Łukasz Jan Kapusta ◽  
Jakub Bachanek ◽  
Changzhao Jiang ◽  
Jakub Piaszyk ◽  
Hongming Xu ◽  
...  
Keyword(s):  
High Speed ◽  
Saturation Pressure ◽  
Injection Pressure ◽  
Spray Angle ◽  
Liquid Propane ◽  
Spray Tip Penetration ◽  
Commercial Gasoline ◽  
Flash Boiling ◽  
Set Up ◽  
The Impact

This study aimed to investigate the influence of flash-boiling conditions on liquid propane sprays formed by a multi-hole injector at various injection pressures. The focus was on spray structures, which were analysed qualitatively and quantitatively by means of spray-tip penetration and global spray angle. The effect of flash boiling was evaluated in terms of trends observed for subcooled conditions. Propane was injected by a commercial gasoline direct injector into a constant volume vessel filled with nitrogen at pressures from 0.1 MPa up to 6 MPa. The temperature of the injected liquid was kept constant. The evolution of the spray penetration was observed by a high-speed camera with a Schlieren set-up. The obtained results provided information on the spray evolution in both regimes, above and below the saturation pressure of the propane. Based on the experimental results, an attempt to calibrate a simulation model has been made. The main advantage of the study is that the effects of injection pressure on the formation of propane sprays were investigated for both subcooled and flash-boiling conditions. Moreover, the impact of the changing viscosity and surface tension was limited, as the temperature of the injected liquid was kept at the same level. The results showed that despite very different spray behaviours in the subcooled and flash-boiling regimes, leading to different spray structures and a spray collapse for strong flash boiling, the influence of injection pressure on propane sprays in terms of spray-tip penetration and spray angle is very similar for both conditions, subcooled and flash boiling. As for the numerical model, there were no single model settings to simulate the flashing sprays properly. Moreover, the spray collapse was not represented very well, making the simulation set-up more suitable for less superheated sprays.

Numerical Study on High-Speed Impact Between a Water Droplet and a Deformable Solid Surface

2012 ◽  
Author(s):  
Yongqiang Han ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Solid Surface ◽  
Water Droplet ◽  
High Speed ◽  
Numerical Study ◽  
Contact Radius ◽  
Deformable Solid ◽  
Theoretical Predictions ◽  
Steam Turbine Blade ◽  
Set Up ◽  
The Impact

In this study an axisymmetric model is set up to study the impact of a spherical water droplet with a planar deformable solid surface using the Lagrange-Euler coupling method which is based on a penalty formulation. The diameter and velocity of the droplet are 0.4 mm and 500 m/s respectively, while the solid is a kind of steam turbine blade material. The generated pressure distribution in the droplet and its variation with time, the formation of lateral jet, the deformation and stress distribution in the solid are obtained and investigated. It is shown that the compressibility of the droplet and the solid plays a significant role during the impact. The water-hammer pressure and the maximum contact edge pressure are calculated and in good agreement with the existing theoretical predictions. The calculated contact radius for shock departure is larger than that of the conventional theoretical prediction, which is analyzed and attributable to the radial motion of the liquid in the compressed region. The formation of the high-speed lateral jet is calculated and the time for the observable jetting is much later than that of the shock departure. This delay is discussed and the reason needs more research. The pressure of the contact edge region remains highest even after a considerable time of shock departure and lateral jetting. In the mean time, a saucer-shaped depression is generated in the center of the impact. The stress waves in solid move faster even before shock departure in the liquid. This causes disturbance of the solid surface before the high-speed lateral jetting and provides site for the scouring action of it, and subsequently may cause material damage and erosion.

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