Ratio Of Orifice Research Articles

Enhancing wave energy harvesting: Performance analysis of a dual chamber oscillating water column

This study investigates the hydrodynamic characteristics of a dual chamber oscillating water column (OWC) setup through a series of experiments, aiming to assess its potential for harvesting wave energy. The investigation involves varying frontwall drafts, power take-off (PTO) dampings, and incident wave conditions, while quantitatively evaluating the OWC system's performance using the capture width ratio (CWR) as the key metric. The findings indicate that the dual chamber configuration consistently exhibits enhanced performance for all combinations of orifice ratios, opening heights, and incident wave frequencies studied. As expected, increasing the opening height of the second chamber leads to improved performance of the OWC. Interestingly, the effect of varying applied PTO damping on improvement of CWR values is found to be relatively insensitive. The most significant improvements in CWR are observed for larger incident wave frequency values. For instance, for dimensionless wave frequency (Kh) values of 1.43 and 1.68, the CWR increases from 0.47 and 0.26 to 0.72 and 0.52, respectively, with the orifice ratio combination of τ1, 0.015, and τ2, 0.018. It is worth noting that the single chamber OWC operates most efficiently within the resonant frequency range of 0.94–1.23, while the dual chamber design extends this frequency range, enabling efficient wave energy capture over a wider spectrum of wave conditions. The dual chamber configuration offers considerable advantages for wave energy conversion applications by increasing the effective frequency bandwidth for optimal energy capture. The research findings suggest that this innovative design has the potential to significantly enhance the efficiency and adaptability of wave energy converters, contributing to the advancement of sustainable and renewable energy technologies.

Numerical Investigation of Optimal Hydrodynamic Performance by Changing the Orifice Ratio and Relative Opening of a Land-Fixed Rectangular-based OWC

The energy that can be extracted from the ocean is inexhaustible. An oscillating water column (OWC) is a wave energy converter that extracts this energy. A numerical investigation has been conducted by altering relative opening (α) and orifice ratio (τ) to assess the maximal energy of a land-fixed rectangular-based OWC model in a nonlinear wave field. The power of OWC has also been evaluated by the wave steepness (H/L) alteration. The numeric analysis has been imposed to obtain the optimal power using Fluent software in a three-dimensional tank. Validation of the present numeric model’s result correlates with the printed empirical data. The Finite Volume Method (FVM) solves RANS equations, and the relevant waves are generated at the inlet of the numerical tank by the inlet velocity approach. The efficiency (η) increases with relative openings (α) increase. The efficiency (η) decreases with wave steepness (H/L) increase. The η reaches the optimum shown in the study at H/L = 0.02 and τ = 1.03% for entire values of α. The excellent energy of around 71.3% is attained at α =75% and H/L = 0.02. This study is a highly relevant source of information that finds the optimal efficiency of a land-fixed rectangular base OWC and gives prior knowledge of the performance of OWC before the real-life experiment.

Development and Scale-up of High Performance Electrodes for Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is a promising technology for energy storage because of its independent energy to power ratio and long cycle life. However, VRFB commercialization is still hindered by some technological issues, among which the limited power density. This results in increased cell area and system costs.In order to tackle this issue is fundamental to boost the sluggish electrode kinetic. In the literature different wet processes, such as acid treatments, have been widely employed to add catalytic functionalities to commercial carbon electrodes [1,2]. Also plasma etching or plasma doping have been adopted for the improvement of electrode performance [3]. Recently, the introduction of heteroatoms is becoming one of the most common method to enhance the catalytic activity of carbon electrodes. Zhao et al. [21] performed thermal treatment of graphite felt combined with electrochemical deposition of Bismuth nanoparticles, obtaining 80% energy efficiency at 600 mA cm-2. Li et al. [22] developed a hierarchical nitrogen doped electrode, reaching 76.8% energy efficiency at 400 mA cm-2.In this work it is proposed a prototypal deposition method, called NanoJeD. It is a high throughput, dry and easily scalable process starting from gas phase. It consists in radiofrequency (RF) plasma operating in dusty mode, through which a non-flammable mixture of Acetylene and Argon is fluxed and the RF plasma ignites the decomposition and clasterization of the Acetylene. The former nanoparticles, following the gas streamline are dragged to a high aspect ratio orifice and ejected in a low-pressure chamber where a substrate is placed. Kinetic energy of the nanoparticles ejected in the chamber defines their impact energy with the substrate and the consequent collection mechanism. Subsequently, a vacuum thermal treatment is performed and this two-steps process allows a fine tuning of the material properties and the formation of a carbon allotropes with catalytic peculiarities known as Carbon Nano Onions (CNOs).Deposited CNOs were firstly characterized with Raman spectroscopy, Scanning Electrode Microscopy (SEM) and Transmission Electrode Microscopy (TEM). Electrochemical characterization was performed in a three-electrode setup with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CNOs exploit their unique properties: high conductivity, high chemical-mechanical stability, and catalytic activity towards redox reactions. The peculiarities of CNO reside in the edge of graphene sheet, which is ascertained to share a higher catalytic activity with respect to the basal plane of the same graphene sheet [6].Afterwards CNOs were deposited on a commercial carbon paper electrode, Sigracet® SGL 39 AA (nominal thickness of ∼290 μm), that was tested in 4 cm2 symmetric cell with Nafion® 211, permitting to evaluate the effect of CNOs on both positive and negative electrode. Subsequently, full cell test at different current densities was performed in cycles with fixed cut-off voltages (1-1.65 V), obtaining an energy efficiency of 81% and 74% at 400 mA cm-2 and 600 mA cm-2, respectively. The corresponding electrolyte utilization was 70% and 59%. Moreover, electrode stability has been evaluated during 1’000 cycles operation.Finally, the process has been scaled-up permitting to obtain a 100 cm2 electrode. The corresponding full cell test with Nafion® 212 resulted in 75% energy efficiency at 0.3 A cm-2.

Cylindrical frontwall entrance geometry optimization of an oscillating water column for utmost hydrodynamic performance

The present research focuses on optimizing the diameter of the cylindrical frontwall entrance shape of an Oscillating Water Column (OWC). In particular, 240 experimental runs are performed for five diameter values, various PTO dampings, dimensionless wave frequencies (Kh) and wave heights. The cylindrical front wall entrance geometry is found to improve the Capture Width Ratio (CWR) of the Oscillating Water Column (OWC) under all conditions. The maximum and average CWR improvement are calculated as 45% and 25%, respectively. The simplicity of the front wall entrance modification makes this achievement even more remarkable. A negative correlation is identified between the diameter size and Kh. In particular, for relatively low, intermediate and large Kh values, optimum diameter sizes are found as 12 cm, 7 cm and 5 cm, respectively. In a specific frequency band, diameter that makes CWR maximum is also found as a function of wave height and orifice ratio. Free decay experimental tests are performed to verify the superiority of the cylindrical geometry. Experimental results indicate that cylindrical frontwall entrance geometry prevents or at least diminishes the flow separation that occurs due to sharp frontwall underlip. Consequently, the reduction in diameter size helps to alleviate the shear stresses on both sides of the front wall, thereby improving the structural integrity of the Oscillating Water Column (OWC) chamber.

Experimental study on hydrodynamic behavior and energy conversion of multiple oscillating-water-column chamber in regular waves

An oscillating water column (OWC) device is a promising wave energy converter that uses ocean wave energy resources. The OWC chamber absorbs the energy of ocean waves and significantly affects energy conversion performance. In this study, the hydrodynamic performance of a multiple OWC chamber was investigated experimentally, emphasizing its hydrodynamic behavior and energy conversion characteristics. A series of regular wave tests were conducted for single-, triple-, and asymmetric triple OWC chambers in a two-dimensional wave tank. The same orifice ratio was applied to the single and triple chambers to induce an equivalent turbine-chamber interaction owing to the pressure drop. It was found that the triple OWC chamber contributes to an increase in the converted pneumatic power compared to the single OWC chamber due to reducing the sloshing motion of the internal fluid. Moreover, the temporal fluctuation of the overall output power was reduced because of the water column motion of each triple OWC chamber with a phase difference. The rear chamber of the asymmetric triple chamber traps the wave energy and contributes to not only increasing the output power but also the variability. Therefore, it can be observed that multiple OWC chambers improve energy conversion performance by increasing the mean power output and reducing temporal fluctuation.

Research on the structure of pre-chamber and jet orifice of a turbulent jet ignition rotary engine fueled with methanol/gasoline blends

This study used both methanol fuel and turbulent jet ignition (TJI) mode to improve the combustion and emission performance of a gasoline rotary engine (RE). Further, in order to research the combustion process of the turbulent jet ignition rotary engine (TJI-RE) fueled with methanol/gasoline blended fuel in depth, the experimental bench and numerical simulation model were established respectively. Moreover, the reliability of the numerical simulation model was verified by the experiments. Eventually, based on the numerical simulation model, the effects of the volume ratio of pre-chamber (VR-PC) and the length diameter ratio of jet orifice (LDR-JO) on the in-cylinder flame propagating were studied. The study results showed that for any fixed LDR-JO, increasing VR-PC could provide higher ignition energy for the cylinder.But the timing of the jet flame entering the cylinder, meanwhile, would be delayed. Therefore, considering the “trade-off” relationship between ignition energy and the timing of jet flame entering the cylinder, VR-PC is recommended to be 2.2%. For any fixed VR-PC, increasing LDR-JO could increase the injection speed of jet flame. But the cross-sectional area of the jet flame at the outlet of the jet orifice, meanwhile, would become smaller. Therefore, considering the “trade-off” relationship between the injection speed of jet flame and the cross-sectional area of the jet flame at the outlet of the jet orifice, LDR-JO is recommended to be 2.5. Additionally, for TJI-RE fueled with methanol/gasoline blended fuel, the higher the in-cylinder peak pressure, the more sufficient the combustion, and the lower the CO emission. And the trend of NO emission was opposite to that of CO emission.

Analysis of the flow mixing and energy separation in a Ranque–Hilsch vortex tube based on an area ratio study

Ranque-Hilsch vortex tube is a pressure-driven thermal device that is an essential component of waste pressure utilization, especially in gas industry. However, the lack of an effective optimization design method and relative low efficiency restrict its development. In this study, the flow field and energy separation of five area ratios (AR) from 0.02–0.32 with the same inlet areas were analyzed based on the AR study of a vortex tube through experiments and numerical simulation. To determine the correlation of area ratio and energy separation, the basic flow field distributions are obtained and the flow structure is analyzed. The results show that for the fifth tube, denoted by AR5, the inlet mass flowrate remains largely constant (min = 9.27–9.24 g/s) with extremely small changes in the back pressure at hot exit (Ph = 11.2–18 kPa); in contrast, for AR1, the back pressure at hot exit (Ph = 10–148 kPa) and inlet mass flowrate (min = 6.8–4.26 g/s) vary significantly with increasing cold mass fraction. Moreover, despite using the same moderate cold orifice ratio of 0.48 for all the five tubes, back flow can occur at the cold exit even at an extremely large cold mass fraction of 0.82 for AR5. In addition, various flow structures and mixing and their corresponding causes inside the vortex tube are summarized. The comparison of the flow and thermal behaviors under the five ARs reveals opposite working patterns of reverse flow boundary and off-optimization under the non-flow mixing condition. These conflicting working patterns of reverse flow boundary can be attributed to the multi-parameter interaction of vortex tube. Thus, the criteria for tube optimization may unilaterally fail unless the precession frequency is studied. Finally, a performance evaluation index that quantifies the energy separation performance is proposed. The index serves to improve the tube optimization criteria and further develop the optimization of vortex tubes.

Numerically Investigated the Performance of Parabolic Bottom Profile Land-Fixed OWC by Changing the Orifice Ratio and Relative Opening

Numerically Investigated the Performance of Parabolic Bottom Profile Land-Fixed OWC by Changing the Orifice Ratio and Relative Opening

Co-design and aerodynamic study on a two-step high pressure reducing system for hydrogen decompression: From hydrogen refueling station to hydrogen fuel cell vehicle

Fuel for hydrogen fuel cell vehicles comes from hydrogen refueling stations. During the hydrogen filling process, a high-pressure gradient from 35 MPa (hydrogen storage pressure) to 0.16 MPa (fuel cell pressure) is generated. Such a large pressure gradient posed a challenge to the design of the pressure reducing system. Traditional system is difficult to reduce hydrogen pressure from 35 MPa to 0.16 MPa without accompanying large noise and energy consumption. This work is exploring a new concept to combine the multi-stage continuous resistance perforated components and the Tesla valve to design a two-step high pressure reducing system for hydrogen decompression. To validate the superiority of the developed system, a detailed aerodynamic study on the new system is performed, since aerodynamic performance directly affects the operating flexibility and stability. Finally, the optimized co-design of the system is achieved. Results show that the new system is well-designed for hydrogen decompression with the function of control noise and energy consumption. Larger orifice radius (r1/r0) and orifice ratio (k) contribute the better aerodynamic performance. Angle α = 45° is considered the best for better aerodynamic performance. The descending order of the effects on better aerodynamic performance is angle (α), row (m), sleeve stage (N), orifice radius (r1/r0) and width (t1/t0). This study provides basic support for experts to achieve throttling design of related pressure control systems in hydrogen industry.

Stability and thermal analysis of a single-phase natural circulation looped parabolic trough receiver

The sustainability and reliability of solar parabolic trough technology can be enhanced by introducing a natural circulation loop. The configuration that suits better is horizontal heater horizontal cooler, which is the most efficient but least stable loop. Hence, as an effort towards the evolution of natural circulation looped collector, 3D computational analysis of a 70 mm uniform diameter square loop (Dowtherm A as the heat transfer fluid) is done with uniform and non-uniform heat flux (SolTrace based) as well as different instability restraining techniques. Prior to the analyses, the stability maps were generated and validated, which predicts high level of instability. Later, the validated computational model is used for parametric analyses, which includes heat flux pattern, loop tilt, use of orifice, and combination of tilt and orifice. Since the loop geometry is highly unstable (ratio of loop length to diameter is 57), the stable operation is observed only with high tilt (θ = 45°), low beta ratio (β = 0.25) and combinations of tilt and orifice (β (0.50) + θ (15°) and β (0.50) + θ (30°)). However, the latter method is suggested for trough application as the former two versions are impractical. Further, the heat load analysis with uniform and non-uniform flux designated insignificant variation in system performance. Since the loop is effective with restraining techniques and its performance is on par with the conventional trough system (predicted by the analytical model), an effort towards implementation of natural circulation loop in parabolic trough technology is prolific.

Three-dimensional MHD flow in moderate change ratio orifice

In fusion reactor blanket design, liquid metals are attractive working fluids since it is possible to combine in a single fluid the functions of coolant, tritium carrier and breeder. These electrically conductive fluids flow in the presence of a strong magnetic field, inducing the appearance of Lorentz forces and magnetohydrodynamic MHD effects. Increased pressure loss, particularly in complex geometry elements, is a critical point for blanket design. The MHD flow through an orifice plate made by electroconductive walls (c = 0.01 ÷ 0.1) has been analysed in this paper using ANSYS CFX in the range Re = 108, and Ha = 0 ÷ 300. A wide recirculation region is detected after the flow exits the orifice, with potentially harmful consequences for efficient tritium removal. Large pressure loss occurs in the orifice due to conductive wall and non-negligible axial length. The 3D pressure drop term is characterized through a local resistance coefficient (k) that is found to be k ≈ 0.205 for well conducting walls (c = 0.1) and k ≈ 0.063 for poorly conducting ones (c = 0.01).

Flow Characteristic of a Cavitating Jet Issuing from a Small Rectangular Orifice

This study focused on the nature of a cavitating jet issuing from a small rectangular orifice the same size as a control port in a water hydraulic spool valve. The aspect ratio of the jet exit was varied to investigate the cavitation jet behavior. The flow characteristics for each aspect ratio were measured, and the jet behavior was observed with a high-speed camera. The flow characteristics of cavitating jets are changed with the aspect ratio and cavitation number. The larger aspect ratio orifice shows a higher flow rate and larger cavitation number of inception. Visualization of a cavitating jet shows that the behavior of cavitation bubbles depends on the aspect ratio. The cavitating jet region is maintained to the same dimensionless position for all aspect ratios. In addition, the distribution and time history of luminance of the visualized images for each aspect ratio shows that the cavitation generates stably in the jet shear layer.

An in depth experimental investigation into effects of incident wave characteristics front wall opening and PTO damping on the water column displacement and air differential pressure in an OWC chamber

Efficiency of an OWC depends solely on the water column heave motion and air pressure differential in the chamber. In this study, an extensive experimental campaign is conducted to investigate the displacement of water column surface (WCS) and chamber air pressure under different incident waves, chamber underwater opening heights and applied PTO dampings. It is found that, transmitted wave height (μ) and transmitted wave pressure (Pw) exponentially decay with the dimensionless wave frequency (Kh) irrespective of the relative opening (α) and orifice ratio (τ) (PTO damping), however, the decay rate slows down as the orifice ratio decreases. Effects of orifice ratio on μ and Pw heavily depend on the value of the Kh such that as Kh increases transmitted wave height, μ and pressure, Pw become less sensitive to variations in the orifice ratio, τ. Pw increase with the relative opening in a linear fashion but the upward trend declines for larger dimensionless wave frequencies. An almost perfect linear association is detected between transmitted wave height and pressure, and, captured wave length (δ) (incident wave length divided by chamber length). In the design stage, in order to prevent sloshing in the chamber δ smaller than approximately 4 should not be selected. Negative pressure peaks are always found to be larger than positive pressure peaks in magnitude. Further, a novel dimensionless pressure number NPR is proposed, which is found to be proportional to μ. Proportionality constant is also presented. Accordingly, prediction of μ or Pw yields the value of the other in an accurate manner. Despite the complex wave-energy conversion processes the most important aspects and the related parameters can be described using very accurate simple analytical models.

An optimization method on managing Ranque–Hilsch vortex tube with the synergy between flow structure and performance

In this paper, the relationship between the flow structures in the vortex tube and its coordinated variation of the performance is numerically investigated. It is shown that the poor performance of vortex tubes is possibly due to the morbid flow structure controlling in it. A new method of managing the flow structures inside the vortex tube to achieve best suitable to the operation condition with a variable cold orifice ratio is proposed. Different cold orifice ratios, ranging from 0.3<D c /D<0.8, were adopted to study how the cold orifice ratio affects the performance, especially the cooling performance. An interesting and important characteristic of the operating performance of a vortex tube can be realized by continuously changing the cold orifice ratios, that is, when the cold mass fraction increasing from 0.1 to 0.9, the total temperature difference can be “monotonically decreasing” (for D c /D ≤ 0.36), “firstly increasing then decreasing” (for 0.36<D c / D <0.72) or “monotonically increasing” (for D c / D = 0.72), which provides a useful method to control the temperature of cold/hot stream and also boosts the cooling capacity. This feature results from the better synergy between the flow structure and the operation conditions, which is also simple and easy to be realized. Besides, a fast and preliminary diagnosis method on the flow field of the main tube with the distribution of the reverse flow boundary is presented, and it is helpful to the optimization design of vortex tube.

Luminal diameter ratio of Vieussens' arterial ring is valuable in determining appropriate clinical management for patients with pathologic Vieussens' arterial ring

BackgroundAlthough the adverse events of pathologic Vieussens' arterial ring (VAR) have been reported, it is difficult to determine optimal clinical management. Thus, we hypothesized that the luminal diameter ratio of VAR obtained from coronary computed tomography angiography (CCTA) could be used as a clinical tool to inform appropriate patient management. MethodA total of 29 patients with pathologic VAR were retrospectively recruited for this study. The VAR luminal diameter ratio was defined as a quotient of VAR fistula divided by the orifice of RCA or LAD, based on which, patients were divided into small fistula group and large fistula group. The AUC, sensitivity, specificity, positive and negative predictive values were obtained from ROC curve. The cutoff value of the VAR luminal diameter ratio was calculated and assessed during the follow-up. ResultsThe VAR luminal diameter ratio of fistula/RCA orifice was 0.505 ± 0.098 in small fistula group and 1.020 ± 0.150 in large fistula group. The VAR luminal diameter ratio of fistula/LAD orifice was 0.507 ± 0.123 in small fistula group and 1.039 ± 0.151 in large group. The value was correlated with the choice of the treatment (r = 0.643 p < 0.01, r = 0.627 p < 0.01). The AUC, sensitivity, specificity, positive and negative predictive values were 0.803, 54.5%, 100%, 100% and 78.3% of the fistula/RCA orifice ratio and 0.833, 63.64%, 94.44%, 87.5% and 81.0% of the fistula/LAD orifice ratio, respectively. The cutoff values of both fistula/RCA orifice and fistula/LAD orifice ratios were 0.676. ConclusionsThe VAR luminal diameter ratio may be a valuable index to determine appropriate treatment for patients with pathologic VAR.

Flow Downstream Sluice Gate with Orifice

Gates and orifices were significant common structures used in controlling and adjusting the flow in water system channels. Installing of an orifice with sluice gates, increase the flow discharge with minimizing the horizontal jets under gate that was attributed with higher bed flow velocity and larger scour geometry downstream these gates. An experimental study was conducted to examine the flow pattern and the bed configurations downstream sluice gates with an orifice. In this research, a circular orifice employed with sluice gates as a means of energy dissipation downstream the gates, was explored. Forty-five runs were completed under 3 discharges, 3 upstream water heads, and 7 tail gate water depths. Five models for sluice gate with orifice were utilized. A series of regime plots were created to help designing the sluice gate with orifice as heading up and flow distributions structures. The outcomes illustrated that combining of an orifice with sluice gates productively scattered the jump energy and diminished the downstream local scour compared to the conventional sluice gate. Additionally, existed equations used to predict the jump length downstream sluice gate were applicable in case of sluice gate with orifice provided similar flow conditions were achieved. The optimum ratio of orifice and under gate areas was also introduced.

Acoustic impedance of perforated plates in the presence of fully developed grazing flow

The perforated components are widely used in the intake and exhaust mufflers. The coupling between instable shear layer and acoustic fluctuation has a significant influence on the acoustic impedance of perforated components. To obtain practical and precise acoustic impedance of perforated plates in the presence of grazing flow, the three-dimensional (3D) time-domain computational fluid dynamics (CFD) approach was employed in the present study, and the extraction method of acoustic impedance was presented. The predicted non-dimensional acoustic impedance of the rectangular slot is consistent with the previous published measurement, which validates the accuracy of the present approach. Characterization of the turbulent boundary layer of flat-plate flow was studied and the relation between the convection velocity of vorticity and mean grazing flow velocity was provided. Numerical evaluations were carried out for different mean grazing flow Mach number Mmean (0.05–0.20), thickness to diameter ratio of orifice t/dh (0.2–0.5), porosity ϕ (4.51%–24.93%), and Reynolds number Re resulted from the orifice diameter dh (2 mm–6 mm), and their effects on the non-dimensional acoustic impedance of circular orifice were investigated in detail. The acoustic impedance formulae are obtained using the piecewise numerical fitting method based on the parameter analyses. As an application of engineering computation, the transmission loss of straight-perforated tube mufflers was predicted by using the present acoustic impedance model and the empirical impedance model of Lee and Ih via finite element computations. Comparison of the predicted and measured transmission loss (TL) results demonstrates that the present model yields highly accurate prediction.

Determination of hydrodynamic parameters of a fixed OWC by performing experimental and numerical free decay tests

Physical experimental and 3D numerical free decay tests are performed for a stationary oscillating water column (OWC) device with various underwater opening heights and power take-off (PTO) mechanisms. Numerical model results are verified with experimental data. Equivalent linear damping of the system is found by using logarithmic decrement method. Natural and resonant frequencies and added mass are calculated. For the OWC with the orifice, it is found that damping ratio decreases quadratically with increasing orifice ratio and linearly with increasing relative opening. Resonant frequency is found to be a linear function of both opening size and PTO damping. Calculated natural frequency values are compared with extensively used formulas, which are found to overestimate the OWC natural frequency. For the first time, an empirical formula for the natural frequency of a fixed OWC is proposed. Added mass is found to be independent of orifice size and underwater opening height. For the OWC with the porous layer, no noteworthy change is observed for the natural frequency and added mass compared to those of OWC with orifice. However, damping of the system is quite altered, while its change due to the variations in the permeability and under water opening height has similar characteristics.

Numerical Investigation of Vertical Crossflow Jets with Various Orifice Shapes Discharged in Rectangular Open Channel

Vertical jet in flowing water is a common phenomenon in daily life. To study the flow and turbulent characteristics of different jet orifice shapes and under different velocity ratios, the realizable k-ε turbulent model was adopted to analyze the three-dimensional (3D) flow, turbulence, and vortex characteristics using circular, square, and rectangular jet orifices and velocity ratios of 2, 5, 10, and 15. The following conclusions were drawn: The flow trajectory of the vertical jet in the channel exhibits remarkable 3D characteristics, and the jet orifice and velocity ratio have a significant influence on the flow characteristics of the channel. The heights at which the spiral deflection and maximum turbulent kinetic energy (TKE) occur for the circular jet are the smallest, while those for square jets are the largest. As the shape of the jet orifice changes from a circle to a square and then to a rectangle, the shape formed by the plane of the kidney vortices and the region above it gradually changes from a circle to a pentagon. With the increase in the velocity ratio, the 3D characteristics, maximum TKE, and kidney vortex coverage of the flow all gradually increase.

Experimental investigations on the performance of a fixed-oscillating water column type wave energy converter

Oscillating water column (OWC) type wave energy converters are the most promising candidates to harvest untapped ocean wave energy. OWC front wall opening and power take-off (PTO) damping optimization are very significant for feasible energy extraction. A comprehensive experimental investigation was performed for a bottom-fixed oscillating water column to determine the influence of the underwater opening height of the chamber, power take-off damping and wave steepness on the energy converter efficiency. A broad range of opening heights and power take-off dampings was utilized in physical experiments under various wave steepness values. Water column displacements, velocities and motion behaviors were also examined. Optimal orifice ratios were determined to obtain maximum efficiency under different wave steepness values. Based on the results, the key finding of this study is, for a certain range of wave steepness, optimal damping that should be applied on the system does not only depend on the wave characteristics, but also opening height of the chamber. The motion of water column surface behavior also affects the performance of the converter considerably.