Proceedings of the 9th International Conference

on Hydrodynamics (ICHD 2010)

October 11 – 15, 2010,Shanghai, China
Editors: Y. S. Wu, S. Q. Dai, H. Liu, L. D. Zhou, X. C. Yang

Experiments and Measurements in Hydrodynamics (11)

C1-1 An experimental study of compressed air generation using a pendulum wave energy converter

Shuji Ogai, Shinya Umeda, Hajime Ishida.

LWJ Co., Ltd., Nishiyodogawa-ku, Osaka, Japan

Abstract :

This study describes a novel system of compressed air generation using a pendulum wave energy converter installed in a coastal defense structure. The objective of this study is to understand how much energy from the incoming waves can be captured for use by the system. Laboratory experiments were carried out to determine the effects of wave and system load conditions on energy conversion efficiency and wave reflection. The test results show that the system can operate with a high degree of efficiency understanding wave and high-load conditions. A reduction of wave reflection can be achieved by the system under a wide range of wave conditions.

C1-2 Optimization of particle image distortion for PIV measurements.

Wen-chu Weng, Sheng-yuk Jaw, Jiahn-horng Chen, Robert R. Hwang.

Department of Systems Engineering and Naval Architecture, National Taiwan Ocean University, Keelung, China

Abstract :

In this study, a jump matching correlation scheme is proposed. For the multi-grid, iterative particle image distortion analysis, the coarse grid solutions are not obtained from coarse pixel image constructed by binning small pixels to large pixel, but by jumping the interrogation window the number of pixels specified during the particle image matching process. With the jump matching scheme applied and particle image interpolated, the central difference particle image pattern matching and image distortion analysis are easily linked together to resolve flow fields from coarsest grid to super-resolution grid. Optimization of particle image distortion is achieved by averaging a forward and a backward image distortion correlation for every iteration process. The proposed method is first verified by standard particle images of impinging jet flow that has exact solution available, and then applied to analyze uniform flow past two side-by-side circular cylinders. Satisfactory results are obtained from the jump matching scheme proposed.

C1-3 Water tunnel experimental investigation onthe drag reduction characteristics of the traveling wavy wall.

Yan Yao , Jin-ling Luo , Chuan-jing Lu , Hong-yu Mao.

Department of Engineering Mechanics, Shanghai Jiaotong University, Shanghai, China.

Abstract :

Drag reduction experiment of the traveling wavy wall at high Reynolds number is conducted. A suit of traveling wavy wall device is developed. The drag forces of the traveling wavy wall with various wave speeds (c) are measured under different water speeds (U) in the K15 cavitation water tunnel and are compared with that of the flat plate. The results show that the mean drag force of the traveling wavy wall have decreased and then increased with oscillation frequency increasing at the same flow speed. Under different flow speeds, when traveling wave wall reached to the minimum of drag force, the corresponding the ratio of the wall motion phase speed c to flow speed U, c/U is slightly different. Within the parameters of the experiment, when c/U reaches a certain value, the drag force of the traveling wavy wall can be less than that of the flat plate. The drag reduction can be up to 42%. Furthermore, as the value of c/U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field.

C1-4 Laboratory investigation of hydraulic performance of silt screens.

Thu Trang Vu, Soon Keat Tan.

School of Civil and Environmental Engineering, Nanyang Technological University (NTU).

Abstract :

Silt screen is a type of flexible barrier that has been widely deployed for the purpose of sediment containment in an aquatic environment. Yet, its working mechanism is still largely unknown. In this study, the authors presented the findings of an investigation of the hydraulic performance of silt screen using Particles Imaging Velocimetry (PIV) technique. The experiments were conducted in a 30 cm-wide flume, with a silt screen spanned across the whole width, normal to the flow. Three average flow velocities, U0 of 0.5 m/s, 0.1 m/s, and 0.2 m/s and different values of the penetration ratio (the ration between screen’s penetration depth and flow depth) were simulated in the experiments. PIV images of the flow approaching the screen and that at the lee side of the silt screen were captured in the vertical mid-plane of the flume. The images were then processed, and analyzed to determine the velocity distribution, turbulence characteristics and streamlines patterns of the flow in the vicinity of the silt screen. Preliminary results showed that underflow through the gap between silt screen’s lower end and the flume’s bottom could be large. The experimental results also suggested a distinct change of flow patterns with the formation of recirculation areas at both sides of the screen. This paper attempts to elucidate the hydraulic performance of silt-screen in response to the magnitude of the environmental flow and different scenarios of screen configurations.

C1-5 An experimental study of inertia and drag coefficients for a truncated circular cylinder in regular waves.

Zhi-da Yuan, Zhen-hua Huang.

School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Republic of Singapore.

Abstract :

It is of academic and practical importance to predict accurate wave loads on cylindrical members of finite length. In this study, the in-line force on a small segment of a vertical circular cylinder of various truncated lengths was experimentally investigated in regular waves. Based on Morison equation, the inertia and drag coefficients (CD and CM) were evaluated and presented as a function of KC number for various values of relative truncated length in order to understand 3-D end wake effects on the truncated cylinder. The factors that may affect the determination of CD and CM were also discussed. A weighted least square method was employed to improve the predictive accuracy of maximum measured forces.

C2-1 Numerical and experimental investigations of the unsteady cavitating flow in a vortex pump.

Alexander Steinmann, Hendrik Wurm, Alfred Otto.

Group Research and Technology Center – Fluid Mechanics, WILO SE Nortkirchenstr. Germany.

Abstract :

In order to develop an understanding of the flow conditions in Vortex Pumps, numerical investigations (commercial URANSE-CFD-Solver ANSYS CFX, Volume-of Fluid Rayleigh-Plesset cavitation model, eight impeller revolutions) and experimental  investigations (High-Speed Exposures of the cavitation clouds through acrylic glass window) have been carried out. A further objective was to investigate the URANSE-CFD method using the mentioned cavitation model regarding numerical stability and accuracy.

C2-2 Development of an acoustic instrument for bubble size distribution measurement.

Xiong-jun Wu, Georges L. Chahine.

DYNAFLOW, INC. ,Jessup, Maryland, U.S.A..

Abstract :

Measurement of bubble size distribution and void fraction is of vital importance in many multiphase flow applications. This paper describes an acoustics based device, the ABS Acoustic Bubble Spectrometer®, which can conduct measurements accurately in near real-time in a cost-effective fashion. By propagating short bursts of sound at different frequencies through bubbly medium, it measures frequency dependent attenuations and phase velocities of the acoustic waves and uses them to obtain the bubble size distribution (number of bubbles per size) by solving an inverse problem. Recent developments, both in hardware and software, as well as their validations are presented, these new advancements enable the ABS to measure void fractions up to 3x10-3with bubble sizes ranging from 10 μm to 3mm.

C2-3 Experimental investigation of drag reduction in micro-channels with surfaces adsorbed hydrophobic nanoparticles.

Qin-feng Di, Chun-yuan Gu, Xin-liang Wang, etc..

Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University

Abstract :

Reconstructing the capillaries and complicated core micro-channels by using the adsorption method with Hydrophobic Nanoparticles(HNPs) can change the properties of walls of micro-tubes and hence decrease the water resistance. It is shown that under the conditions of pressure this can increase obviously the water flux in micro-tubes or microchannels. It is further found that the adsorption method with HNPs can increase dramatically the water phase permeability of core and decrease the water resistance. This is because the HNPs of SiO2 can enhance the hydrophobility of micro-tube walls, which would generate the water-flow-slip effects. This method is of great significance to reduce the resistance in core’s micro-channels with complicated structures, and is expected to be a new technology to decrease the water injection pressure of reservoir.

C2-4 Experimental study on braking force characteristics of tugboat.

Lin-jia Yang, Bi-guang Hong, K. Inoue , H. Sadakane

Navigation College, Dalian Maritime University, Dalian, China.

Abstract :

The braking force produced by tugboat has been scarcely examined and little data on the proper characteristics of the braking force can be obtained. Therefore, it is necessary to investigate the braking performance of tugboat. In this paper, the braking force characteristics of tugboat-self in braking condition are obtained and the related unstable phenomena is pointed out and analyzed according to the results of model experiments. Furthermore some new understanding on the braking co-operation by using tugboat is suggested.

C2-5 PIV studies on turbulence structure in air/water interface with wind-induced water waves.

Michio Sanjou , Iehisa Nezu, Akihiro Toda.

Department of Civil Engineering, Kyoto University, Katsura Campus, Kyoto.

Abstract :

When wind appears over the free surface, water waves and turbulence are generated by an interfacial shear stress. In particular, turbulent diffusion promotes significantly mass and momentum transport beneath the interface between the water and air significantly in ocean and lakes, and thus it is very important for global environment problems to reveal such turbulence property and coherent structure. Simultaneous measurements of velocities and free-surface elevation allow us to conduct reasonably the phase analysis of the coherent structure in interfacial shear layer. Furthermore, multi-point measurements such as PIV are very powerful to detect the space-time structure of coherent motions. Therefore, in the present study, we developed a specially designed PIV system which can measure the velocity components and surface elevation fluctuation simultaneously by using two sets of high speed cameras to reveal the coherent structure in the interfacial shear layer.

C2-6 Experimental study on a dynamic contaminant release into overlying water-body across sediment-water interface.

Jing-yu Fan, Dao-zeng Wang, Kun Zhang.

Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China.

Abstract :

The dynamic release process from the contaminated sediments into the overlying water-body was experimentally investigated in an open channel flume under different hydrodynamic conditions. The time-dependent concentration variation and relative significance of the static release due to diffusive transport and the dynamic release due to resuspension/settling of the sediments were determined based on the obtained data. The experimental results indicate that before reaching an equilibrium stage, the dynamic release caused by the resuspension/settling of the sediments is much more effective than the static release by the molecular diffusion in an initial release stage. The impacts of the static and dynamic release on the overlying water column are further analyzed under different flow velocity and water depth conditions.