Oscillatory Water Flow Research Articles

Design and Fabrication of a Four-Electrodes PVDF Fiber for a Flow Sensor

Inspired by seal vibrissa, an ingenious bionic flow sensor, that had four electrodes and dual-sensing circuits, was designed and fabricated using polyvinylidene fluoride (PVDF) and optical fiber. Based on the piezoelectric equation, the sensing model of this bionic vibrissa sensor (BVS) was deduced. The BVS was thoroughly investigated for airflow and oscillatory water flow monitoring applications. The results indicated that the BVS had a faster response to airflow compared with the anemometer, and it could sense the direction and the magnitude of the airflow simultaneously. The BVS could recognize the frequencies, phases, and waveforms of the oscillatory water flow. The unique dual-sensing circuit and flexible characteristics endowed the BVS with excellent underwater sensing abilities. It exhibited a very low-velocity detection threshold (0.15 mm/s). It could accurately sense the flow speed and direction at the same time by measuring only once. The success of this study paves the way for extending this technology to many applications, such as underwater detection, water leak monitoring, and blood/urine flow monitoring.

Development and Sensitivity Analysis of an Empirical Equation for Calculating the Amplitude of Pressure Head Loss of Oscillating Water Flow in Different Types of Pipe

Low pressure oscillating water flow can reduce the investment and energy consumption of irrigation. It is also effective in reducing the clogging of an emitter and improving the spraying quality of sprinklers. In order to overcome the problem of the complex process in calculating the amplitude of the pressure head loss of oscillating water flow in different types of pipes, in this study, an empirical equation for the amplitude of the pressure head loss of oscillating water flow in different types of pipe has been developed. Further, validation experiments have been conducted to verify the accuracy of the calculated amplitudes of the pressure head loss by the empirical equation. The results show that average relative error between the measured and the calculated amplitudes of the pressure head loss by the empirical equation is 10.77%. Since the relative errors are small, it is an indication that the amplitudes of the pressure head loss calculated by the empirical equation are accurate. For the empirical equation developed in this study, the sensitivity of the model parameters has been analyzed. The results show that the amplitude of velocity, the internal pipe diameter, and the length of pipe are classified as highly sensitive. The average velocity, the period of oscillating water flow, and the modulus of elasticity of the pipe material are classified as sensitive. The thickness of the pipe wall is classified as medium sensitive. Compared with the calculation models of the existing researches, the empirical equation reduces the number of parameters required to be calculated, by which many complicated calculations are avoided, which greatly improves the computing efficiency. This is conducive to the efficient operation and management of oscillating water flow in irrigation pipe networks and also provides help for the optimal design of irrigation pipe networks.

The Wave-to-Wire Energy Conversion Process for a Fixed U-OWC Device

Oscillating water column (OWC) devices, either fixed or floating, are the most common wave energy converter (WEC) devices. In this work, the fluid dynamic interaction between waves and a U-shaped OWC breakwater embedding a Wells turbine has been investigated through unsteady Computational Fluid Dynamic (CFD) simulations. The full-scale plant installed in the harbor of Civitavecchia (Italy) was numerically modeled. A two-dimensional domain was adopted to simulate the unsteady flow, both outside and inside the U-OWC device, including the air chamber and the oscillating flow inside the conduit hosting the Wells turbine. For the numerical simulation of the damping effect induced by the Wells turbine connected to the air chamber, a porous medium was placed in the computational domain, representing the conduit hosting the turbine. Several simulations were carried out considering periodic waves with different periods and amplitudes, getting a deep insight into the energy conversion process from wave to the turbine power output. For this purpose, the three main steps of the overall energy conversion process have been examined. Firstly, from the wave power to the power of the water oscillating flow inside the U-duct. Secondly, from the power of the oscillating water flow to the air pneumatic power. Finally, from the air pneumatic power to the Wells turbine power output. Results show that the U-OWC can capture up to 66% of the incoming wave power, in the case of a wave period close to the eigenperiod of the plant. However, only two-thirds of the captured energy flux is available to the turbine, being partially dissipated due to the losses in the U-duct and the air chamber. Finally, the overall time-average turbine power output is evaluated showing that it is strongly influenced by a suitable choice of the turbine characteristics (mainly geometry and rotational speed).

Swimming in unsteady water flows: is turning in a changing flow an energetically expensive endeavor for fish?

Unsteady, dynamic flow regimes commonly found in shallow marine ecosystems such as coral reefs pose an energetic challenge for mobile organisms that typically depend on station holding for fitness-related activities. The majority of experimental studies, however, have measured energetic costs of locomotion at steady speeds, with only a few studies measuring the effects of oscillatory flows. In this study, we used a bidirectional swimming respirometer to create six oscillatory water flow regimes consisting of three frequency and amplitude combinations for both unidirectional and bidirectional oscillatory flows. Using the goldring surgeonfish, Ctenochaetus strigosus, a pectoral-fin (labriform) swimmer, we quantified the net cost of swimming (swimming metabolic rate minus standard metabolic rate) associated with station-holding under these various conditions. We determined that the swimming costs of station-holding in the bidirectional flow regime increased by 2-fold compared with costs based on swimming over the same range velocities at steady speeds. Furthermore, as we found minimal differences in energetic costs associated with station-holding in the unidirectional, oscillating-flow compared with that predicted from steady swimming costs, we conclude that the added acceleration costs are minimal, while the act of turning is an energetically expensive endeavor for this reef fish species.

The Development of a Calculation Model for the Instantaneous Pressure Head of Oscillating Water Flow in a Pipeline

Sinusoidal oscillating water flow at low pressure can improve the anti-clogging ability of an emitter in drip irrigation or the water distribution of a nozzle in sprinkler irrigation and reduce the cost and energy consumption of the irrigation system. In this study, the characteristics of instantaneous pressure head attenuation of oscillating water flow along a pipeline have been investigated. By using a complex function to solve the continuity equation and the momentum equation of a pipeline with water hammer motion and using the Darcy–Weisbach formula to estimate the head loss, a calculation model for the instantaneous pressure head of oscillating water flow along a pipeline was developed. The measured value of the amplitude of the pressure head and the average instantaneous pressure head in the experiments have been used to verify the corresponding pressure head calculated by the model. The results show that the amplitude of the pressure head and the average instantaneous pressure head decrease linearly along the pipeline. The calculated value of the amplitude of the pressure head and the average instantaneous pressure head are basically close to the corresponding measured pressure head. From the results of all the tests, the maximum relative error of the calculated and measured value of the amplitude of the pressure head along the pipeline was 9.44%. The maximum relative error of the calculated and measured value of the average instantaneous pressure head along the pipeline was 8.37%. Hence, the model can accurately predict the instantaneous pressure head of oscillating water flow along a pipe and provide a theoretical basis for the application of oscillating water flow in irrigation systems and the design of irrigation pipe networks.

The Influence of Sinusoidal Oscillating Water Flow on Sprinkler and Impact Kinetic Energy Intensities of Laterally-Moving Sprinkler Irrigation Systems

Laterally-moving sprinkler irrigation systems under low pressure experience problems including small spraying range, low uniformity, surface runoff, and low water utilization rate. To solve these problems, experiments were carried out on a laterally-moving sprinkler irrigation system using a Nelson D3000 sprinkler (Nelson Irrigation Co., Walla Walla, WA, USA) under low pressure, sinusoidal oscillating water flow. The sprinkler intensity and impact kinetic energy intensity distribution were investigated for sprinklers both static and in motion. The test data were used to calculate combined sprinkler intensity and impact kinetic energy intensity uniformity for different nozzle spacings, and were compared with constant water pressure test results. It was found that sinusoidal oscillating water flow can effectively increase spraying range, as well as reducing the peak value of the sprinkler intensity and impact kinetic energy intensity. Within an optimal range of amplitude and nozzle spacing, sinusoidal oscillating water flow significantly improves the combined sprinkler intensity, impact kinetic energy intensity uniformity, and the spraying quality of laterally-moving sprinkler irrigation systems under low pressure conditions. When the average water pressure is 100 kPa, the optimal range of amplitude of sinusoidal oscillating flow applied to the laterally-moving sprinkler irrigation system is 50–60 kPa. When the amplitude is 50 kPa, the optimal nozzle spacing is 3.5–4 m; when the amplitude is 60 kPa, the optimal nozzle spacing is 3.5–4.5 m. The related parameters can provide a reference for the application of sinusoidal oscillating water flow in laterally-moving sprinkler irrigation systems.

The role of pore size in heat transfer of oscillating liquid flow in metal foam

The huge accessible surface area, high conductivity make metal foam attractive for energy technologies, e.g., reactors, regenerators and Stirling engines. An experiment establishing the impact of pore density of metal foam on heat transfer caused by oscillating water flow through foam is described. Various pertinent parameters for two foams having 10 and 40 pores per inch (ppi), of commercial high-porosity metal foams were obtained in this experiments; and are compared to those of a 20-ppi results from the literature. Experimental runs were conducted at kinetic Reynolds numbers between 1875 and 9366. The wall temperature uniformity and cycle-averaged Nusselt number for the three pore densities were compared to their counterpart for steady-state heat transfer. The pressure drop in the three pore densities was measured and discussed along with the heat transfer results. The effect of pore density was evident in the cycle-average wall temperature and Nusselt number, with the 10-ppi foam outperforming the 20- and 40-ppi foams. The benefit of oscillating flow was seen in producing more uniform wall temperature. It seemed possible for steady-state flow to produce higher heat transfer rates compared to steady-state flow, if the flow displacements were not sufficiently long compared to the length of metal foam.

Relative impacts of the invasive Pacific oyster, Crassostrea gigas, over the native blue mussel, Mytilus edulis, are mediated by flow velocity and food concentration

The ecological impacts of invasive species can be severe, but are generally viewed as highly unpredictable. Recent methods combiningper capitafeeding rates, population abundances and environmental contexts have shown great utility in predicting invader impacts. Here, clearance rates of the invasive Pacific oyster,Crassostreagigas, and native mussel,Mytilusedulis, were investigated in a laboratory experiment where oscillatory water flow and algal food concentrations were manipulated. Invasive oysters had lower clearance rates than native mussels in all experimental groups and did not differ among flow velocities or food concentrations. Native mussel clearance rates were higher at 5 cm s-1compared to 0 and 15 cm s-1flow velocities and increased with increasing food concentration. The Relative Impact Potential (RIP) metric was used to assess (i) the influence of flow velocity and food concentration on potential impacts ofC.gigason plankton resources and, (ii) the impacts of coexisting reefs, containing both species, on resources compared to monospecific native mussel beds. Greatest Relative Impact Potential of invasive oysters was seen at the lowest flow velocity, but became reduced with increasing flow velocity and food concentration. Relative Impact Potentials of coexisting reefs were generally greater than monospecific native mussel beds, with greatest impacts predicted at lowest flow velocity. We suggest that the greatest ecological impacts and competition potential ofC.gigaswill occur in areas with low flow velocity, but that increased flow will mediate co-existence between the two species.

An axial turbine in an innovative oscillating water column (OWC) device for sea-wave energy conversion

Wells turbines, self-rectifying air-driven axial turbines, are typically used to convert pneumatic power available in the periodic reversed airflow in Oscillating Water Column (OWC) device into mechanical energy. However, such turbines suffer from low aerodynamic efficiency; low powers produced, and narrow operating range. The current work proposes the operating principle of using water as the working fluid rather than air by submerging the Wells turbine in the sea water to enhance its performance. This gives an advantage for the turbine operation with a fluid having specific weight higher fluid than air. The analysis is carried out for an innovative device proposed by Boccotti in which a vertical axis hydraulic Wells turbine installed inside a vertical duct and contained in a caisson below the sea water surface. The CFD simulations are performed depend on the steady 3D incompressible Reynolds Averaged Navier-Stokes (RANS) calculations on this type of axial turbine rotor with realizable k−ε turbulence model. A comparative analysis between the computational results and experimental results is carried out and a good agreement is found between both results. This paper proved that, the hydraulic (immersed) Wells turbine performance is better than that of the air (conventional) Wells turbine. A substantial improvement in the torque coefficient is achieved with the hydraulic turbine of about 1.4 times the torque of the conventional air turbine. Using water as a working fluid which is the proposed concept leads to a wider operating range unlike using air. In addition, the effects of blade profile and rotor solidity on the turbine performance were clarified computationally. In this work, two kinds of symmetric blade profiles have been used (NACA 0015 and S1046). The present computational investigation was carried out for three rotor solidities (0.64, 0.48 and 0.24) through changing the number of turbine blades (8, 6 and 3 blades). It is found that for a hydraulic Wells turbine operating under oscillating water flow, the rotor geometry preferred is the blade profile of S1046 for the investigated three values of rotor solidities.

Impact of pore density on oscillating liquid flow in metal foam

Oscillating water flow in commercial, highly-porous, open-cell aluminium foam with two common pore densities of 10 and 40 pore per inch (ppi) was investigated experimentally. Flow displacements of 74.35, 97.20 and 111.53 mm were produced in each foam; a sizable range of flow frequency from 0.116 to 0.696 Hz was imposed. The effect of pore density was investigated by comparing the two pore densities of the current study with a third from the literature having 20 ppi. The comparison was at the same porosity of approximately 88%. Results have shown that the pore density has a considerable effect on important oscillating water flow parameters including inlet pressure, pressure drop and friction factor. For high frequencies, the 20-ppi foam produced the highest inlet pressure followed by the 40-ppi and then the 10-ppi foam. For low frequencies, the 10-ppi foam produced the highest inlet pressure followed by the 40-ppi foam and then the 20-ppi foam. These trends were explained by considering viscous and form drag pressure losses according to permeabilities and Forchheimer drag coefficients of the three foams. For low frequencies, the pressure drop was periodic for the three pore densities, while for high frequencies, the periodic behavior of the pressure drop was not clearly discernable, indicating the presence of nonlinear processes and multiple transitions among flow regimes. The friction factor for the oscillating flow was seen to lie above that for steady flow for 10- and 20-ppi foam for all frequencies, as expected. However, there was no difference between the steady-state and oscillating flow friction factors for the 40-ppi foam at low frequencies. The behaviour of friction factors indicated that there was two different regimes based on frequency with the boundary between them occurring at Reynolds number around 4000 for 10- and 20-ppi foams, and at Reynolds number 5500 for the 40-ppi foam. The friction factor correlated with the Reynolds number, with the correlation being generally better for low frequencies. Friction factors for oscillating water flow in metal foam were compared to those obtained for oscillating flow of air and water in some other porous media from the literature. Various effects at play, as well as the interactions among them, were highlighted and discussed. Major conclusions and practical implications were summarized.

Investigation of low-frequency-oscillating water flow in metal foam with 10 pores per inch

In this study, oscillating water flow in metal foam with open cells is investigated experimentally. The metal foam sample has a porosity of 88% and 10 pores. The water was oscillated in the test section with three frequencies between 0.116 Hz and 0.348 Hz, which are considered low for water oscillation, and three flow displacements ranging between 74.35 mm and 111.53 mm. The combinations of frequencies of displacements were studied for their impacts of dimensional and non-dimensional pressure loss quantities. To this purpose, friction factor was correlated as a function of kinetic Reynolds number. The same metal foam sample was studied by exposing it to steady-state water flow to investigate its permeability and drag coefficient in low-velocity flow regimes. The friction factor distribution for oscillating flow was found to be over that found for steady state. The outcomes of the study are important for studying heat transfer under the same flow conditions.

Analytical study on a submerged tubular wave energy converter

Abstract A submerged tubular wave energy converter, whose main structure is an upright concentric circular cylinder, is proposed. The turbine is installed near the bottom of the internal tunnel for the survivability consideration. The analytical solution for the wave diffraction problem of the structure is derived based on the linear potential flow theory. The oscillatory mass flow rate in the tunnel is particularly investigated for it can be used to assess the feasibility of the converter that utilises the vertically oscillatory water flow. The effect of the submerged tubular structure in a wave field is to guide the vertically oscillatory motion, the magnitude of which, otherwise, diminishes exponentially with depth, down to the deeper water. That greatly increases the available kinetic energy for the turbine installed in the deep water. Effects of the parameters of the tubular structure on the efficiency of the device are also discussed.

Experimental results for oscillatory water flow in 10-ppi metal foam at low-frequencies

This experimental study presents results and interpretation of oscillatory water flow in open-cell metal foam. The tested foam had 10 pores per inch and a porosity of 88%. At relatively low frequencies, three flow displacements were employed in the experiment. The influence of frequency and displacement on pressure loss and friction factor is discussed. A correlation of friction factor as a function of the kinetic Reynolds number was determined. Porous media parameters, permeability and drag coefficient, were also found for the same foam via steady-state flow experiments in the Darcy and Forchheimer regimes. The friction factor of oscillating flow was found to be higher than that of steady state. The findings of this study are considered important for oscillating heat transfer in metal foam.

LDV を用いた進行波型相変化エンジンの流速振幅測定

The traveling wave thermoacoustic engine amplifies the acoustic power when a traveling wave passes the bundle of narrow channels with an axial temperature gradient. It has been experimentally determined that the maximum gain reaches ratio of absolute temperatures when using an ideal gas. In this study, we set up the traveling wave thermoacoustic engine combined with oscillatory water flow, and for this device with liquidvapor phase change, the acoustic power is measured by both Laser Doppler Velocimeter(LDV) and pressure trasducers. The result indicates that liquid-vapor phase change achieves the acoustic power amplification beyond the theoretical limit of ideal gas.

Experimental heat transfer due to oscillating water flow in open-cell metal foam

While studies concerning heat transfer due to oscillating air (and few other gases) flow in metal foam are available, heat transfer due to oscillating water flow in metal foam has not been offered in the literature. This paper presents characteristics of heat transfer of oscillating water flow in commercial open-cell metal-foam pipe that were obtained experimentally, most likely for the first time. One main difference between gas and liquid flows in porous media is that dispersion is far more significant in the latter. Another difference is the length of the entrance region, which depends strongly on the Prandtl number. The trends in the cycle-averaged wall temperature, length-averaged wall temperature and cycle-averaged Nusselt number were similar to those for oscillating water flow in packed spheres and for oscillating air flow in aluminum, copper and graphite foams in a rectangular channel. For the higher flow frequency of the current study, the cycle-averaged Nusselt number was higher for higher flow displacement amplitude.

Effect of frequency on heat transfer due to oscillating water flow in open-cell metal foam: An experimental study

Heat transfer due to oscillating water flow in open-cell aluminum-foam pipe subjected to constant wall heat flux was investigated experimentally. The foam had 20 pores per inch and a porosity of 87.6%. Three flow displacements 1.5, 1.9 and 2.2 pipe diameters, at kinetic Reynolds numbers in the range 1873–9366 were applied. Higher flow displacement and higher frequency generally produced higher heat transfer rates and led to lower and more uniform wall temperature. The flow displacement had the most profound influence on heat transfer. A correlation was obtained for the time- and length-average Nusselt number as a function of non-dimensional flow displacement and kinetic Reynolds number. The dependence on kinetic Reynolds number might be universal for oscillating heat transfer in porous media. Steady-state heat transfer experiments were also conducted in the same porous medium and test facility. Oscillating flow was seen to produce lower rates of heat transfer compared to steady flow. This unexpected finding was explained. The current results were compared to other studies from the literature employing oscillating air and water flows in various kinds of porous media. Some agreements and disagreements were stated and discussed.

Characteristics of oscillating liquid flow in foam-like highly-porous media: An experimental study

Characteristics of oscillating water flow in open-cell metal foam were obtained experimentally. The foam had 20pores per inch and a porosity of 87.6%. Three flow displacements 74.35, 97.2 and 111.53mm were applied in the flow frequency range 0.116–0.696Hz. Steady-state experiment was also conducted and the permeability and form/inertial drag coefficient were obtained. The range of flow velocity covered Darcy and Forchheimer flow regimes. The effect of flow displacement and frequency on important variables is presented and discussed. The appropriately defined friction factor correlated well with the Reynolds number for steady-state and oscillating flows, with the friction factor for oscillating flow being higher. The current results were compared to other studies from the literature employing oscillating air and water in various kinds of porous media. Some agreements and disagreements are stated and discussed.

Enhancement of heat transportation by oscillatory flow in a curved tube

The present paper deals with the longitudinal heat transportation by an oscillatory flow in a curved tube heat transportation pipe. The velocity and temperature fields during oscillatory water flow in a curved tube with inner diameter of 10mm were numerically simulated using the commercial software FLUENT. To clarify the effect of the curvature on heat transportation, the ratio of the tube radius to the curvature radius was varied from 0.0125 to 0.075, and oscillatory flow frequency was varied from 0.1 to 2.0Hz. The effective thermal diffusivity exhibited a peak at a curvature ratio around 0.05–0.07 and reached a value 12 times higher than that of a straight tube. It was also found that the dispersion of fluid particles due to secondary flow caused the enhancement of heat transportation.

Heat transfer in porous media of steel balls under oscillating flow

In this paper, heat transfer in porous media under oscillating water flow has been studied experimentally. A total of 54 sets of heat transfer experiments, each representing a different frequency, flow displacement length and heat input, have been conducted for two different porous media of steel balls. Cycle averaged local Nusselt numbers are obtained by measuring the bulk temperatures at the inlet cross sections and the center of the porous medium. It is observed that the local Nusselt number based on time averaged wall and bulk temperatures increases by frequency and maximum fluid displacement, and depends on the axial direction with increasing frequency. The variation of spaced-cycle averaged Nusselt numbers based on the averaged surface and bulk temperatures are introduced for different frequencies and flow displacements. The space-cycle averaged Nusselt number increases by kinetic Reynolds number and non-dimensional fluid displacement. The averaged Nusselt number for a certain porous medium can be correlated with kinetic Reynolds number and non-dimensional fluid displacement. Then, a more general Nusselt number correlation independent from the porous medium type and fluid properties is proposed. It is also shown that the Nusselt correlation which is a function of Ao and ReωDa is in good agreement with experimental data.

Heat transportation by oscillatory flow in a new type of heat transportation pipe

The present paper deals with experimental and numerical study on the longitudinal heat transportation by an oscillatory water flow in a double tube type heat transportation pipe. Experiments were performed to measure the heat transportation rate in the ranges of 2.3 ⩽ Wo ⩽ 7.2 and 400 ⩽ Re max ⩽ 6600. The heat transportation rate was approximately 10–490 times the heat transportation rate of a straight round pipe, and it was around 1–40 times the heat conduction rate through a copper rod. Analytical heat transportation rates agreed well with the experimental ones.