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The influence of a mesh-type bubble breaker in a two-phase vertical co-flow is experimentally investigated using high-speed imaging. A range of liquid and gas flow rates were considered that correspond to the gas-to-liquid flow rates ratios (GLRs) from 0.05 to 39.6 covering bubbly, slug and churn flow regimes. The mesh-type bubble breaker was found to be effective in reducing the size of nozzle-generated bubbles in two-phase co-current vertical flow. The bubble size reduction by 50%-70% is observed in the presence of the mesh-type bubble breaker compared to that without a bubble breaker. The results also show that at a given GLR, the mesh-type bubble breaker delayed the flow regime transition compared to that without a bubble breaker. A Froude number correlation was proposed to predict the mean bubble size downstream of the bubble breaker for the bubbly flow regime, which accurately predicted the bubble size over a range of bubble breaker parameters. It is observed that the geometry of the bubble breaker influence the two-phase flow regime transition. At low liquid flow rates, small pore size of the breaker was found to be effective. This effect diminishes at higher liquid flow rate due to the elongation of the bubbles by the liquid inertia. The results also show that a longer bubble breaker located closer to the bubble generating nozzle is the most effective in producing bubbly flow over a longer range of gas-liquid flowrates ratios. [ABSTRACT FROM AUTHOR]

The rotating waves within a hollow vortex core (polygonal patterns) are generated under shallow water conditions inside a cylindrical tank by a revolving disk at its bottom. We previously reported some basic features of these polygonal patterns during transition and at the equilibrium states. The present paper includes a more comprehensive investigation into the transition process of these polygonal patterns and expands the recent partial results that have been previously reported. We show that the parent wave (or the N- gon pattern) to disk frequencies ratio is around one-third (1/3) regardless of the flow conditions . A detailed insight into the transition process from the parent wave N- gon to daughter wave ( N + 1)- gon is provided, which consists of two regimes, quasi-periodic and synchronized. Based on these observations, we explained the shrinking of the disk speed subintervals over which the N- gon patterns occur, when N increases. [ABSTRACT FROM AUTHOR]

Results from an experimental study, investigating the similarities and dissimilarities of the airflow structure over water and solid surfaces for smooth and wavy conditions, are reported. The experiments were conducted at the same location, under identical flow conditions. The two-dimensional velocity fields were measured using particle image velocimetry technique over a wind speed range from 1.5 to 4.4 m s-1. The mean velocity profiles for all surface configurations showed the logarithmic behavior. The profiles of different turbulent properties followed similar trend over water and solid surfaces, however, their magnitudes varied over different surface types. The results show that the level of enhancement of normalized Reynolds stress, rates of energy production, and dissipation from the free-stream region toward the surface is higher over the water surface especially in the presence of waves as compared to that over the solid surface. It is also observed that the normalized magnitudes of turbulent properties are largest above the water surface and smallest above the wavy solid wall. It is concluded that, at a given free stream condition, the flow behavior over the solid surface is not necessarily similar to that over the water surface. [ABSTRACT FROM AUTHOR]

This article reports on an experimental study conducted to investigate slosh forces and moments caused by fluid slosh within a partly-filled tank subjected to lateral and longitudinal excitations applied independently. The experiments were performed on a scale model cleanbore and a baffled tank with laterally placed single- and multiple-orifice baffles. The experiments were conducted for three different fill volumes and different types of excitations: continuous harmonic and single-cycle sinusoidal excitations of different amplitudes and discrete frequencies. The dynamic forces and moments' caused by fluid slosh with the baffled and cleanbore tank configurations were measured for different fill volumes and excitations using three-axis dynamometers. it is shown that the resulting forces and moments comprise many spectral components that can be associated with the excitation, resonance, and vibration and beat frequencies. Modulation of excitation frequency with the resonant frequency was also evident for all fill conditions and tank configurations when the two were in close proximity. The results also showed that the peak amplifications of forces and moments occur in the vicinity of the resonant frequency. At higher frequencies, the peak magnitudes of the forces, however reduced significantly to values lower than the inertial forces developed by an equivalent rigid mass. At a given excitation condition, the slosh force amplitude increased with a decrease in the fill volume. it was `also observed that the presence of baffles has negligible effect on the lateral slosh force and the corresponding resonant frequency However it caused a significant increase in the longitudinal mode resonant frequency. The baffles greatly reduced the amplifications in longitudinal force and pitch moment under longitudinal acceleration excitations. [ABSTRACT FROM AUTHOR]

The flow structure inside the valveless standing wave pump is investigated experimentally. The two-dimensional velocity fields inside the chamber of this novel pump at different phases of the excitation signal are measured using the synchronized particle image velocimetry technique. The variations in the pump flow rate, pressure loss coefficients, and rectification capability of the diffuser-nozzle element are analyzed. According to the results obtained in this paper, the net flow rate of the pump increases with an increase in the pressure (or Reynolds number). The interactions of three different flow fields inside the pump chamber (pumping flow, acoustic, and streaming velocities) are studied. It is found that, while the pumping flow has an effect on the acoustic velocity patterns only around the inlet and outlet orifices, the streaming velocity structures are drastically affected by the pumping flow. [ABSTRACT FROM AUTHOR]

We report on an experimental study conducted to investigate the airside flow structure above an evaporative water surface during natural convection. Two-dimensional airside velocity fields were measured using particle image velocimetry for three different surface heat flux conditions. Detailed analysis of the turbulent velocity fields shows a complex flow structure due the local interactions of fluid motions in vertical, horizontal, and normal directions. The trends of turbulent intensity profiles on airside and waterside are found to be similar. However, the airside turbulent intensities are approximately 20 times stronger than that on the waterside. The spectral analysis of the turbulent velocities showed the existence of two distinct power law regimes. In low wavenumber range, the buoyancy subrange is observed with a slope of -3 whereas, in high wavenumber range, the inertial subrange with the classical slope of -5/3 is observed. The results also indicate that the airside turbulent velocity fields control the local evaporation rate, which in turn influences the water surface temperature field and the waterside velocity field. [ABSTRACT FROM AUTHOR]

Abstract: Influence of differentially heated horizontal walls on shape and amplitude of acoustic streaming velocity field inside a gas-filled rectangular enclosure subject to acoustic standing wave are experimentally investigated. The synchronized particle image velocimetry (PIV) technique has been used to measure the streaming velocity fields. The results show that the temperature difference between the top and the bottom walls deforms the symmetric streaming vortices to the asymmetric ones. As the temperature difference increases, the amplitude of streaming velocity increases. [Copyright &y& Elsevier]

Abstract: An experimental study was conducted to investigate the impact of a rectangular baffle inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for two Reynolds numbers in the fully turbulent regime. The changes to the flow structure due to the insertion of a baffle were quantified by a direct comparison with the flow structure in the absence of a baffle, under similar conditions. Results show that the turbulent velocities are enhanced by a factor of two to three and the rates of energy production and dissipation are enhanced by more than an order of magnitude when a baffle is inserted in the channel. Significant enhancement of turbulence was observed in a region up to two times the baffle height immediately downstream of the baffle and the thickness of this layer increased to three times the baffle height further downstream of the baffle. [Copyright &y& Elsevier]