Search

In order to solve the problems of uneven component diffusion, weak mass transfer capability and flow field flooding in the conventional flow field of proton exchange membrane fuel cell (PEMFC), and to improve the cell output power. In this paper, a novel folded porous cathode flow field is proposed. A numerical model of three-dimensional multiphase flow is established for comparative study, which reveals the relationship between the component flow characteristics and mass transfer performance of PEMFC. The folding rib structure of the novel flow field triggers gas vortices in the channel and generates secondary flow, improves the mass transfer capability of reactants between the channel and the GDL, and alleviates the drainage problem of the porous layer under the rib. The angle, length and number of folding at the rib of the flow field were mainly changed, and the mass fraction difference coefficient (CV Mi) was used to compare the uniformity of the distribution of the components of the flow field, and the optimal flow field structure was obtained as FP6-7, which increased the current density by 44.9% compared with the traditional linear flow field. For the first time, the secondary flow evaluation criterion absolute vortex flux number J ABS n was introduced to evaluate the mass transfer performance. The influence of fluid flow characteristics on the mass transfer performance is revealed. • The folded porous (FP) flow field improves the mass transfer capacity. • The current density of PEMFC based on FP6-7 flow field was increased by 44.9%. • The mass fraction difference coefficient (CV Mi) was used to evaluate the uniformity of water-air distribution in the flow field. • The absolute vortex flux (J ABS n ) is used for the first time to evaluate the mass transfer characteristics. • The relationship between the flow characteristics of components and the mass transfer capacity in the flow field is revealed. [ABSTRACT FROM AUTHOR]

The purpose of this study was to quantify the accuracy of partial volume-corrected three-dimensional volume flow (3DVF) measurements as a function of spatial sampling beam density using carefully-designed parametric analyses in order to inform the target applications of 3DVF. Experimental investigations employed a mechanically-swept curvilinear ultrasound array to acquire 3D color flow (6.3 MHz) images in flow phantoms consisting of four lumen diameters (6.35, 4.88, 3.18 and 1.65 mm) with volume flow rates of 440, 260, 110 and 30 mL/min, respectively. Partial volume-corrected three-dimensional volume flow (3DVF) measurements, based on the Gaussian surface integration principle, were computed at five regions of interest positioned between depths of 2 and 6 cm in 1 cm increments. At each depth, the color flow beam point spread function (PSF) was also determined, using in-phase/quadrature data, such that 3DVF bias could then be related to spatial sampling beam density. Corresponding simulations were performed for a laminar parabolic flow profile that was sampled using the experimentally-measured PSFs. Volume flow was computed for all combinations of lumen diameters and the PSFs at each depth. Accurate 3DVF measurements, i.e., bias less than ±20%, were achieved for spatial sampling beam densities where at least 6 elevational color flow beams could be positioned across the lumen. In these cases, greater than 8 lateral color flow beams were present. PSF measurements showed an average lateral-to-elevational beam width asymmetry of 1:2. Volume flow measurement bias increased as the color flow beam spatial sampling density within the lumen decreased. Applications of 3DVF, particularly those in the clinical domain, should focus on areas where a spatial sampling density of 6 × 6 (lateral x elevational) beams can be realized in order to minimize measurement bias. Matrix-based ultrasound arrays that possess symmetric PSFs may be advantageous to achieve adequate beam densities in smaller vessels. [ABSTRACT FROM AUTHOR]

Shock drag and aeroheating are major problems faced by hypersonic vehicles. This study proposes a novel three-dimensional model combining spike-aerodisk with a bleed air channel featuring multiple lateral nozzles for drag and aeroheating reduction. The high-temperature and high-pressure air at the stagnation point of the aerodisk is introduced into the channel and ejected laterally through multiple nozzles to modify the flow field structure and reduce drag and aeroheating. In contrast to previous research employing a two-dimensional axisymmetric assumption, our innovation considers the structure of the exit nozzles and the spacing between nozzles. Due to multiple lateral nozzles, the connection thickness between nozzles can lead to asymmetric flow phenomena. Three-dimensional flow field simulation has been employed with the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k-ω turbulence model. The effects of the convergence half-angle of the channel inlet, the divergent angle of the nozzle, and the nozzle position on modifying the characteristics of the flow field are studied. Increasing the convergence half-angle of the channel inlet can further push away the reattachment shock, but when it exceeds 60°, the drag reduction performance degrades. Reducing the divergent angle of the nozzle and increasing the number of nozzles can reduce the drag coefficient and the peak value of the Stanton number. However, when the divergent angle is reduced to 10°, the performance of reducing drag and aeroheating is weakened. In the range of research parameters, when the convergence half-angle is 60°, the divergent angle is 15°, and the nozzles are located in the middle of the spike, compared with the plain spike-aerodisk model, the drag coefficient and peak Stanton number of the combined model are further reduced by 17.8 % and 34.8 %, respectively. Our findings confirm that a multi-nozzle can effectively reduce drag and aeroheating while the channel structure is viable in practice. • A new model of lateral jet without gas source is studied by 3-D numerical simulation. • The gas for the lateral jet is coupled with the outside flow. • A distribution form of multiple lateral nozzles is proposed. • A realistic 3-D simulation is conducted, enhancing its practical applicability. [ABSTRACT FROM AUTHOR]

The flow field structure of the bipolar plates is a key factor in determining the heat and mass transfer performance of proton exchange membrane fuel cells (PEMFC). To improve its performance and obtain an optimized design and fabrication method, this paper proposes a novel baffled flow field bipolar plate and successfully realizes its preparation using 3D printing technology. A PEMFC computational fluid dynamics model was established for numerical simulation, and polarization tests were also performed to verify the simulation results. The results show that the incorporation of 30°, 60°, and 90° sub-baffles helped to increase the maximum power density of the PEMFC by 3.5%, 8.4%, and 14.7%, respectively, compared to no sub-baffles. The oxygen mass transfer efficiency of the flow field with a 90° sub-baffle increased by 9.4% and 22.1% compared to the 60° and 30° sub-baffles, respectively. However, the increase in inclination angle also causes more water and heat in the flow channel to enter the membrane electrode, which hinders the further improvement of PEMFC performance. This study will provide new ideas and solutions for the flow field structure design and preparation of bipolar plates. [Display omitted] • A novel flow field structure with main and sub-baffle was designed. • Forming of metal bipolar plates with complex flow field structure by 3D printing. • The mass and heat transfer characteristics in different flow field structures were studied. • Oxygen transfer efficiency increases with increasing inclination of the sub-baffle. [ABSTRACT FROM AUTHOR]

Optimizing the flow field structure is an important means to enhance gas transport and improve the proton exchange membrane fuel cell (PEMFC) performance. Based on the structural features of the spider-web, a three-dimensional multiphase flow model of the PEMFC with a spider-web biomimetic flow field (SWFF) was established firstly, and the influence of inlet and outlet positions on the performance of the PEMFC was investigated, then the cathode side catalytic layer (CL) oxygen utilization as an evaluation index based on the cluster model was proposed, which is used to investigate the effect of inlet and outlet positions on internal mass transfer and performance of PEMFC. Finally, the influence of different structural parameters on the performance of PEMFC with SWFF was investigated based on the orthogonal experimental design method. The results show that a reasonable arrangement of inlet and outlet positions can effectively increase the peak current density by 2.31% and reduce the pressure drop by 96.07% compared to a serpentine flow field. The placement of baffles at the intersection of the main channel and divergent channels can significantly improve the PEMFC performance. The results of the research provide a new evaluation index and a theoretical basis for the optimal design of flow field structures. • A spider-web bionic flow field was innovatively proposed. • Compared the performance of flow field at different inlet and outlet positions. • The oxygen utilization is introduced to verify the superiority of flow fields. • Studied the influence of different geometric parameters on current density. [ABSTRACT FROM AUTHOR]

Discussed in this investigation is the three-dimensional gravity-driven flow of a thin fluid layer down an incline and over topography. A new three-dimensional integral-boundary-layer (IBL) model is proposed to describe the flow. Numerical simulations are presented and comparisons with lubrication and two-dimensional IBL models are discussed for both steady and unsteady flows. Subcritical and supercritical cases are considered, along with symmetrical and asymmetrical bottom topographies. Also, good agreement was found with experiments. [ABSTRACT FROM AUTHOR]

Compared with the conventional two-dimensional flow field, the novel three-dimensional flow field can rely on the slope to force the reaction gas into the catalytic layer (CL), which effectively improves the performance of the proton exchange membrane fuel cell (PEMFC). Three novel three-dimensional flow field bipolar plates (3D-Ⅰ, 3D-Ⅱ, 3D-Ⅲ) composed of hollow slope units were designed and prepared by selective laser melting (SLM) technology in this study. The characteristics of gas-liquid mass transfer in different flow fields are compared by experiments and numerical simulations, and the effects of through-holes on the slope on the performance of PEMFC are discussed in depth. The results showed that the maximum power density generated by 3D-III was 451.4 mW/cm2, which is 21.2% and 3% higher than that of 3D-Ⅰ and 3D-Ⅱ, respectively. 3D-III was better than 3D-II in terms of oxygen concentration distribution, water distribution and uniformity of current density distribution. This is due to the through-holes on the main slope of 3D - Ⅲ can not only facilitate the discharge of product water and reduce the water delivered to CL but also makes full use of the hollow part of the slope unit, expanding the space in which the gas can flow. [ABSTRACT FROM AUTHOR]

The goal of this study is to determine the maximum energy and solute particles' transportation growth in a 3D-heated region of Prandtl martial through a dynamic magnetic field. The effects of this field on the properties of solvent molecules and heat conduction are studied. A correctly stated functional method and a finite element approach are comparable to a certain type of differential equations. In order demonstrate the effects of various factors such as mass diffusion, heat generation, and thermal diffusivity on the investigation of the diffusion coefficient and thermal mass in a three-dimensional Newtonian flow, the study of viscous and heat conduction rates is presented. The results show that the comparisons of hybrid nanofluid F e 2 O 3 and A l 2 O 3 with base fluid and w.r.t Local skin friction coefficient, Nusselt number and Sherwood number. [ABSTRACT FROM AUTHOR]

This article introduces a novel method to calculate the structural sensitivity in non-linear flows. The method is completely data-driven and only uses direct solutions, avoiding the need to calculate the adjoint solution. Moreover, the method can be directly applied to calculate the structural sensitivity in three-dimensional flows. Depending on the nature and the complexity of the data analysed, the methodology presented to calculate this so-called non-linear structural sensitivity, uses dynamic mode decomposition (DMD) or higher order DMD to identify the global modes leading the flow dynamics. The performance of this novel technique has been tested in the two-dimensional wake of a circular cylinder at Reynolds number (Re) 50, 60, 85, 100, 130 and 160, the three-dimensional wake of a circular cylinder at Re = 280 and spanwise wavelength L z = 1.67 and 6.99, in a Food and Drug and Administration nozzle at Re = 800 and in two-concentric jets with similar velocity ratio at Re = 1500. The results have been compared with the structural sensitivity predicted by the linear theory, finding some similarities and discrepancies between both methods. Nevertheless, the highest structural sensitivity regions identified by this novel algorithm are in good agreement with the literature, where the flow instabilities have been controlled using different mechanisms of passive flow control located in the regions predicted by the non-linear structural sensitivity calculated in this article. [ABSTRACT FROM AUTHOR]

Engineering wake models that accurately predict wake in a computationally efficient manner are very important for tasks such as layout optimization and control of wind farms. In this paper, we explore an application of deep learning (DL) to learn the wake model from hierarchies of physics-based approaches ranging from analytical models to an approximate form of the Reynolds-averaged Navier–Stokes equations. We first illustrate the application of principal component analysis to obtain a lower-dimensional representation that allows a computationally tractable training and deployment of DL models. Then, the DL model is trained to learn the mapping from input parameter space to the principal components, which are then used to reconstruct the three-dimensional flow field. Additionally, we investigate a composite framework consisting of two neural networks to learn the correlation between low- and high-fidelity data with Gauss and curl models treated as proxies for low- and high-fidelity models, respectively. The prediction from both DL models matches well with the high-fidelity data with a maximum relative percentage error for the kinetic energy flux of <1%. This work opens up possibilities for data-efficient construction of surrogate models for wake prediction that can be used to study the influence of wind speed and yaw angles on wind farm power production. • Deep learning models are proposed for wake modeling of wind turbines. • A composite neural network can be trained by merging information from low-fidelity models with high-fidelity data. • The three-dimensional wake flow for a single wind turbine is accurately predicted using deep learning methods. • Deep learning can achieve the same computational time for execution as the analytical wake models. [ABSTRACT FROM AUTHOR]

Cleaning is an important process step in the food industry, especially to avoid contamination during increasingly frequent product changes. The equipment is cleaned almost daily causing high ecological and economic expenses. Predicting the cleaning time required to remove a thin soil layer for given operating conditions can prevent the use of unneeded resources. The purpose of the present contribution is to apply a recently published model for an adhesively detaching soil at the next level of geometrical complexity. To this end, a square duct with a stepwise expansion of each wall is considered. The Reynolds numbers of the flows investigated are between 13,000 and 39,000, based on the hydraulic diameter of the upstream duet. In a square duct, the flow is three-dimensional due to secondary flows of the second kind, and the existing model for two-dimensional flow needs to be extended in the first step. In course of that, a simple method is presented for the consideration of turbulent fluctuations in the calculation of the hydrodynamic loads. The model is validated using cleaning experiments in a fully developed channel flow without step. After that, it is applied to the channel flow with sudden expansion. Various cleaning parameters, such as the soil mass coverage and the flow velocity, are varied and the quality of the model predictions is investigated. The results are compared with experiments in a channel flow with sudden expansion. Good agreement between experiments and simulation is achieved, proofing that the model can be used to investigate the cleaning in complex, three-dimensional flow scenarios. [ABSTRACT FROM AUTHOR]

A novel closed-loop, multi-level, multi-branch, U-shaped borehole heat exchanger geothermal system is proposed to achieve a more efficient method to exploit deep geothermal resources. Compared with single U-shaped closed-loop geothermal systems, the new system can reduce the drilling cost and increase the heating length. In this study, first, a three-dimensional unsteady-state flow and heat transfer model was established. Then, the temperature distribution of the working fluid in the tube and a hot dry rock reservoir was analyzed. Third, the key factors that influence heat production were analyzed. The results show that increasing the injection rate blindly does not improve the heat production power; the maximum heat production power can only be obtained by controlling the injection rate to a certain extent. The heat production power has a good linear relationship with reservoir temperature and horizontal well length. Under different reservoir temperatures, the unit power generation price of the proposed geothermal system reaches the lowest value when the horizontal well length is 3000 m and the horizontal well branches number is 4. Overall, this novel design can improve the heat exchange efficiency, reduce the power generation cost and can serve as a reference for the study of exploiting deep geothermal resources. [ABSTRACT FROM AUTHOR]

Experimental investigations of dust explosions in standard industrial testing equipment such as the MIKE3 minimum ignition energy (MIE) testing device are promising ways of producing fundamental insights into dust cloud ignitability. However, advanced experimental methods must be developed to characterize the dust cloud ignition and combustion behavior of various types of dust. In this work, high-speed broadband and species-specific chemiluminescence imaging diagnostics are implemented to explore similarities and differences between organic and metal powder ignition kernel development. A selected set of 600-mg niacin (ϕ = 2.9) and aluminum (ϕ = 1.6) powder samples were dispersed in the air and ignited using a high-voltage spark inside a standard MIKE3 device. The resulting broadband flame emission was recorded at 4 kHz using a high-speed camera for the first 10 ms after the spark. For the niacin sample, species-specific chemiluminescence emissions from excited-state hydroxyl (OH*) and methylidyne (CH*) radicals were also recorded at 4 kHz and 1 kHz, respectively. The flame kernel in each image frame was detected using an intensity thresholding algorithm and tracked throughout the video sequence, yielding quantitative size, position, and velocity measurements of the evolving flame kernel during the first 10 ms after the ignition spark. For the niacin sample, a continuous and non-uniform reaction zone composed of burning particle clusters and excited-state radicals was observed. The niacin flame kernels grew from 5 mm to 17 mm with an initial velocity of 5 m/s. Conversely, an intensely bright reaction zone and discrete burning particles near the flame kernel boundary were observed in the aluminum sample. The aluminum flame kernels grew from 7 mm to 10 mm with an initial velocity of 3 m/s. The niacin and aluminum flame kernels traveled 7–11 mm away from the central spark gap and slowed down to 1 m/s by the end of the 10-ms period. This time-resolved imaging study, when coupled with previously reported three-dimensional particle and flow field data prior to the arrival of the ignition spark, sets the foundation for an improved multi-physics understanding of the initiation of dust cloud ignition and explosion processes. [ABSTRACT FROM AUTHOR]

This study proposes a systematic methodology for improving PEMFC's performance combining computational fluid dynamic (CFD), artificial neural network (ANN), and intelligent optimization algorithms. Firstly, a three-dimensional (3-D) multiphase PEMFC CFD model with 3-D fine-mesh flow field is developed. Then the key structural features of the fine-mesh flow field are extracted as optimization decision variables, and the sampling points are selected by using the Latin hypercube sampling (LHS) experimental method. The power density and oxygen uniformity index of sampling points are calculated by CFD modeling to form the database, which is used to train the artificial neural network (ANN) surrogate model. Finally, the single-objective optimization (SOO) and multi-objective optimization (MOO) are implemented by using genetic algorithm (GA) and non-dominated sorting genetic algorithm (NSGA-II), respectively. It was found that using trained ANN surrogate models can get a high prediction precision. The maximum power density of SOO is increased by 7.546% than that of base case and is 0.562% larger than that of MOO case. However, the overall pressure drop in cathode flow field of SOO case is greater than that of MOO case and the base case. Furthermore, the oxygen concentration, the oxygen uniformity index and the water removal capacity of MOO case are better than that of SOO case. It is recommended that the improved flow field structure optimized by MOO is more beneficial to improve the overall performance of PEMFC. [Display omitted] • A novel three-dimensional fine-mesh flow field of PEMFC is designed. • Proposing a co-simulation model for improving the novel PEMFC's performance. • The single-objective and multi-objective optimizations are performed using genetic algorithm. [ABSTRACT FROM AUTHOR]

The rational design of flow fields is of vital importance for the internal distribution uniformity and overall power output of solid oxide fuel cells (SOFCs). This study reports the design of discrete cylindrical landing flow fields for planar SOFCs to tackle the in-plane unevenness problems. The effect of key geometric parameters on the internal mass and current distribution and the overall power output of SOFCs has been investigated using three-dimensional (3D) multi-physics numerical simulations. It is found that the cylindrical landing flow fields significantly reduce the local variation of mass distribution and improve the uniformity of current distribution compared with the parallel landing flow fields. The overall output performance of the cell is improved by the cylindrical landing flow field (D2.0-S1.0) due to the synergetic effect of increased pressure drop, enhanced gas transport and reduced ohmic loss. The results of this study demonstrate the effective of the cylindrical landing flow fields for improving the distribution uniformity of planar SOFCs and provide theoretical insights for further development and optimization of the cylindrical landing flow fields for related applications. • The cylindrical landing flow field is designed and studied by 3D numerical modeling for planar SOFCs. • The effectiveness of this design for improving the distribution uniformity is demonstrated. • Relationships of key structural parameters with in-plane distribution and power output are identified. • Effect of contact resistance on distribution properties is decoupled with structural variation. • Theoretical insights for further development of cylindrical landing flow fields are provided. [ABSTRACT FROM AUTHOR]

• PIV experiment and 3D unsteady simulation study of cross-flow fan. • Three-dimensional characteristics of internal flow in cross-flow fan. • The distortion of the eccentric vortex and the development of the recirculation zone. • Structure optimization improves the aerodynamic performance and the aeroacoustics performance of cross-flow fan. The cross-flow fan is an essential component of an air-conditioner indoor unit, and its aerodynamic performance seriously affects the performance and heat exchange efficiency of air-conditioning. The internal flow of the cross-flow fan is studied by PIV measurements combined with the three-dimensional unsteady simulation. It is observed that the internal flow of the cross-flow fan is unevenly distributed along the axial direction, and it presents prominent three-dimensional characteristics. Due to the influence of the end-wall, the eccentric vortex is strong in the middle and weak at both ends. Therefore, a pressure gradient along the axial direction in the eccentric vortex area, resulting in axial fluid transport inside the eccentric vortex. At the exit of the impeller, there is a small recirculation zone near the end-wall, which grows continually as it moves downstream in the diffuser section, thereby blocking the outlet. This paper further proposes a structure optimization, which effectively enhances the eccentric vortex near the end-wall and reduces the recirculation zone in the diffuser section, resulting in a 2.1% increase in the flow rate of air-conditioner indoor unit and a 0.8dB reduction in noise level. It is indicated that the structure optimization strategy based on the understanding of three-dimensional flow is beneficial to the internal flow and effectively improves the aerodynamic performance and the aeroacoustics performance of the whole air-conditioner indoor unit. [ABSTRACT FROM AUTHOR]

• Flow sensing of primary cilia numerically explored from the viewpoint of FSI. • The simulation is three-dimensional and two-way fluid-cilia interaction is considered. • Ciliary basal rotations are modelled by attaching a rotational spring to the cilium basal end. • The interaction and synchronization between the primary cilia and the flow are analyzed. • The impact of primary cilia on the wall shear stress field is examined. Primary cilia at mammalian cells play a crucial role in mechanosensing of biological flows. Understanding the fluid-cilia interaction not only help to interpret the role of primary cilia as a flow sensor but also could shed light on the design of bio-inspired flow sensors. This study thus investigates the dynamics of primary cilia in an oscillating viscous flow via a three-dimensional simulation. In our simulations, a two-way fluid-structure interaction is considered using the immersed boundary-lattice Boltzmann method. To reproduce the experimentally observed ciliary basal rotations, the primary cilium is modelled as a slender filament whose basal end is connected to a nonlinear rotational spring. For the scenario considered, the primary cilium is observed to do an in-plane flapping motion which is symmetrical in term of the superimposed cilium profiles. For a cilium undergoes such a flapping motion, the flow-induced curvature (or tensile stress) at its lower part is found to synchronize better with the applied pressure gradient signal. Therefore, the lower part of primary cilia may be more responsible for detecting the real-time variations of the flow information. Our simulation results also suggest that the location of the maximal tensile stress is propagatable rather than staying at a fixed site, e.g., the base point, possibly due to the asynchronous deflection occurs at the cilium's different parts. The presence of primary cilia is also found to reduce the spatial-averaged wall shear stress (WSS) level and alter the oscillation characteristic of the WSS field by making the WSS less oscillatory in some regions. [ABSTRACT FROM AUTHOR]

• The film cooling performance of tip with inclined cavity bottom is experimental studied. • The blade tip with inclined cavity bottom enhances cooling performance at some blowing ratios. • The blade tip with cavity bottom inclined to suction side can reduce the aerodynamic loss. The gas turbine blade tip poses as one of the most challenging areas for blade cooling, primarily due to its intricate three-dimensional flow characteristics, which make it one of the primary contributors to aerodynamic loss within the turbine stage. In this paper, the adiabatic film cooling effectiveness (η) distributions at five squealer tip structures (Original, PS7.5, PS15, SS7.5, SS15) with varying inclined angles of cavity bottom surface were obtained using pressure sensitive paint technique (PSP) under five coolant blowing ratios (BR = 0.4, 0.8, 1.2, 1.6, 2.0). Combined with the numerical simulations verified by the experimental data, the tip flow field details were described to reveal the cooling characteristics of the tip region. The results indicate that, at low BR s, the film hole downstream exhibits apparent cooling traces, which are most pronounced at the SS15 tip. With the increase of BR , the cooling traces gradually fade, and the area-averaged film cooling effectiveness (η Α-avg) rises. At low BR s (BR = 0.4, 0.8), the η Α-avg of the SS15 tip is 12.8 %, and 8.4 % higher than that of the Original tip, respectively. At BR = 1.6, the η Α-avg of the PS15 tip is the highest, 3.9 % higher than that of the Original tip. The η Α-avg of SS7.5 is the lowest at all BR s. In addition, the pitch-averaged η (η avg) of PS7.5 at some BR s is higher in the front part of the tip, compared to the Original tip. At BR = 1.2, the area-averaged total pressure loss coefficient ( C p t ¯)of the PS7.5 and PS15 is 1.46 % and 1.58 % higher than that of the Original tip, respectively. However, the C p t ¯ of the SS7.5 and SS15 is 1.77 % and 10.28 % lower than that of the Original tip, respectively. [ABSTRACT FROM AUTHOR]

This aerodynamic study is an attempt to build up efficient flow control computations on a detached high Reynolds number flow behind a 25°inclined ramp enabling to reduce the turbulence energy of recirculating zones. Flow control is performed with a synthetic jet row placed at the top edge of this inclined ramp. Baseline simulations are validated with experiments and a key target is to yield numerically a deeper knowledge of flow control impact on flow separation and vortex dynamics. Average results of large eddy simulations, performed with and without flow control, show a vortex size reduction in the recirculation zone associated to a small pressure increase on the ramp with the selected synthetic jet conditions. A dynamic modal decomposition (DMD) involving a singular value decomposition (SVD) is explained and realized in the wake with and without control. Periodic DMD modes, which are below the integral scale of the turbulence are split in three frequency ranges : frequencies of the shear layer close to the frequency of the integral scale, frequency of the recirculation vortex corresponding to the lowest frequency range and an intermediate frequency range, corresponding to vortex structures situated behind the shear layer. Flow control activated in the shear layer at a frequency equal to the integral scale enables to damp energy of the intermediate frequency range situated in the most energetic POD mode. Vortex structures behind the shear layer are then significantly reduced. [Display omitted] • High Reynolds number three-dimensional flow over a ramp is analyzed and studied. • Active flow control with synthetic jets is carried out. • A significant decrease of the recirculation area and wall pressure as well as shear effects' change is observed. • Dynamic Mode Decomposition (DMD) is implemented to deepen understanding of the control spectral behavior. • A crucial shift and reduction of some dominant frequencies is observed. [ABSTRACT FROM AUTHOR]

Accurately measuring the three-dimensional flow field characteristics in complex flow fields, particularly in turbomachines, is of utmost importance and is commonly achieved through experimental methods. Multi-hole pressure probes are a proven measuring technique to provide precise readings of flow characteristics in both two-dimensional (2D) and three-dimensional (3D) flow fields. However, manufacturing imperfections have an impact on their measuring accuracy so each probe has a slightly different measuring behavior. In order to take these specific characteristics into account a thorough calibration process prior to utilization has to be applied. This calibration process involves positioning the probe in various flow conditions in a wind tunnel and collecting all relevant data. A model is then established to correlate the measured pressure distribution across the probe holes with known flow conditions. Unfortunately, this calibration process is time-consuming and requires costly equipment. To address these challenges, this study introduces a novel calibration technique that leverages advanced machine learning methods, specifically artificial neural networks (ANNs), to significantly streamline the process. ANNs are renowned for their ability to model diverse systems and adapt and generalize well, making them a promising solution for simplifying the calibration of multi-hole probes. In this research, an ANN calibration model was developed specifically for a 5-hole probe, and its configuration was optimized through an automated hyperparameter optimization process. The performance of the ANN model was then compared to that of a conventional polynomial model. After confirming its accuracy, the ANN model was successfully re-adapted and applied to new probes, requiring minimal calibration data collection. The results highlight the potential of ANNs in probe calibration, as they enable a simplified process that demands fewer calibration data points. • Manufacturing imperfections impact probe accuracy, emphasizing the need for a calibration process to mitigate these effects. • An ANN calibration model is developed and optimized through automated hyperparameter optimization for a 5-hole probe. • Successful re-adaptation of the ANN model allowed its application to new probes with minimal calibration data collection. • The potential of ANNs in simplifying probe calibration by reducing the number of calibration data points is demonstrated. • Careful selection of specific points is paramount during the re-adaptation process, further enhancing calibration precision. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fabrication method of a three-dimensional spiral microreactor for continuous flow PCR is presented. • The method offers a simple and convenient way to develop three-dimensional microreactors with multiple spiral channels. • Three-dimensional continuous flow PCR is performed by a single temperature driver. • The temperature distribution and amplification performance of the three-dimensional spiral microreactor were investigated. [ABSTRACT FROM AUTHOR]

This study investigates the three-dimensional turbulence flow properties in a meandering channel under subcritical flow conditions, specifically focusing on a few critical parameters such as three-dimensional velocity behaviour, Turbulent kinetic energy, skewness, and kurtosis. A model study has been attempted by considering the same sinuosity, Froude number, and bed material from an Indian peninsular river to understand the basic hydrodynamics of a meandering channel. Understanding these critical parameters is crucial for comprehending the complex flow behaviour and its implications in meandering channels. Experimental measurements were conducted to collect data on Velocity, Turbulent Kinetic energy, skewness, and kurtosis in all three directions. The objective was to analyse their variations and behaviour along the meandering path, providing insights into the flow dynamics and turbulence characteristics. Advanced measurement techniques, such as Acoustic Doppler Velocimeters (ADV), were utilized to obtain accurate and detailed data. The study revealed distinct patterns and trends in the velocity, Turbulent Kinetic energy, skewness, and kurtosis along the flow path of a sand bed meandering channel. These parameters were found to vary significantly in different sections, highlighting the influence of channel geometry and flow conditions. Graphical representations of the flow profiles were employed to visualize the spatial distribution and understand the variations in these turbulence properties. The findings of this study enhance our understanding of the three-dimensional turbulence flow properties in sand bed meandering channels under subcritical flow conditions. The results offer valuable information for designing hydraulic structures, flood control measures, and river restoration projects. • This study aims to understand the behaviour of three-dimensional flow parameters in a meandering channel which are responsible for the morphological variations. • The Froude number data of the Mahanadi River is collected and same Froude number, sinuosity and bed material were maintained in the laboratory setup to perform the experiment. • The graphical variations of the Velocity, TKE, Skewness and Kurtosis in three directions were presented which describes the changes in the morphology and river bank erosion. [ABSTRACT FROM AUTHOR]

Among the various solutions suggested for wave energy harvesting, the ones based on the oscillating water column (OWC) principle are considered as the most promising, due to their constructive simplicity and reliability. These systems convert sea wave energy into pneumatic energy in the form of a bi-directional airflow that can conveniently turned into mechanical energy by a Wells turbine. Since their introduction, Wells turbines have been studied extensively in order to characterize their performance. Most of the experimental studies have focused on global machine performance analyses, while the studies focusing on local performance analyses are limited. This work presents a detailed experimental investigation of a small-scale Wells turbine coupled to an OWC simulator. The turbine aerodynamic characteristic has been identified with global measurements, while a miniaturized aerodynamic probe has been used to evaluate local performance, by reconstructing the three-dimensional flow field upstream and downstream of the turbine during a complete regular wave period. Local analyses aid to explain global turbine performance, highlighting the main differences between inflow and outflow phases. Moreover, they allow to describe the variation in loading along the blade radius, and to evaluate the blade design law, which justifies the limited Wells turbine aerodynamic performance. • A Wells turbine is tested coupled to an OWC simulator. • Experimental investigation of the local 3D flow field in a Wells turbine. • Flow field reconstruction during the inflow and outflow phases. • Different performance for the two phases are due to a swirl flow inside the chamber. • Rotor losses for the two phases are different due to a larger exhaust kinetic energy. • Constant chord blade design results in a reduction of the work in the tip region. [ABSTRACT FROM AUTHOR]

The present article assesses the capability of the partially averaged Navier-Stokes (PANS) method to reproduce accurately the self-sustained shock oscillations, also known as transonic buffet, occurring on airfoils and wings at transonic regime under certain conditions of Mach number and angle of attack. The test case under analysis is an OAT15A unswept wing at Mach number M ∞ = 0.73 and Reynolds number Re c = 3 × 10 6. The three-dimensional flow is studied by accounting for the wind tunnel walls adopted in the experiments of Jacquin et al. [1] in the simulations. The computations on a large-span, confined configuration reveal a strong three-dimensionality of the flow both before and after the buffet onset. Attention is paid to the comparison with unsteady Reynolds-averaged Navier Stokes (URANS) results, to show the benefits of PANS in resolving flow unsteadiness at different flow resolutions, especially on affordable CFD grids, at limited additional cost. In this context, the role of the mesh metrics and the local turbulence level in the formulation of the model is described, as well as the relation of this latter with the spatiotemporal discretization used for the numerical simulations. The aim is to extend the use of PANS and obtain accurate predictions of flow cases involving shock-wave boundary layer interactions without expensive approaches. [ABSTRACT FROM AUTHOR]

The goal of this research is to investigate aerodynamic performance and high-speed impulsive (HSI) noise of various blade tips for the helicopter's main rotor in forward flight. For this purpose, three-dimensional compressible flow field around the rotor blades is numerically simulated by the solution of the unsteady Reynolds averaged Navier-Stokes (URANS) equations with the "SST k-ω" turbulence model. Solution is quantified by the calculation of torque, drag, and thrust coefficients of C Q , C D , C T , and L/D ratio. HSI noise on the rotor plane is assessed by the calculation of sound pressure level at certain points of the flow field using the Ffowcs Williams-Hawking (FW-H) equation. Blade tips are eleven and include anhedral, dihedral, Eagle and combinations of them, and also Blue Edge and rectangular. The combinations are inspired by the tip configurations of the fixed wings. In this regard effects of the tip geometry parameters including curvature and height of its parts have been considered as well. All of the tips are examined for two flight conditions of Caradonna and Tung two-blade rotor with fixed pitch angle and time-varying pitch angles. Based on the present results, it is found that blade tips of dihedral family do not improve the aerodynamic performance of the helicopter blade. Also, addition of anhedral part to the blade tip improves the L/D ratio. According to the present acoustic analysis, it was seen that after the Blue Edge, the Eagle tip stands in order of priority. For the condition of Caradonna and Tung two-blade rotor with tip Mach number of 0.8 and advance ratio of 0.2, HSI noise of the Eagle-tip blade decreases by 2.39 % compared to that of the two-blade rotor with rectangular tip. However, the aerodynamics performance of the Eagle tip is much better than that of the Blue Edge. [ABSTRACT FROM AUTHOR]

This paper investigates the structural implications of constant vorticity for steady three-dimensional internal water waves governed by the equatorial f -plane approximation. Under the assumption that the first components of the non-zero constant vorticity vectors in the upper and lower layers are zeros, it is proved that every three-dimensional traveling internal wave with bounded velocity is either two-dimensional or a trivially three-dimensional shear flow with the pressures in both layers are identically equal. [ABSTRACT FROM AUTHOR]

The three-dimensional flow of a wavy elliptic cylinder and its wake are investigated for wavelength (λ) to hydraulic diameter (D m) ratio λ/D m = 3.43, 4.58, and 6.01. The study aims to gain insights into flow separation, flow dynamics, and three-dimensional flow topologies for the selected wavelengths. Three-dimensional flow structures are visualized through time-averaged streamlines with critical point theory. The results for λ/D m = 3.43 show spiral flow directed from the node to the saddle, counter-rotating vortices, and a wavy vortex structure. On the contrary, the flows for λ/D m = 4.58 and 6.01 respectively undergo bifurcation in stable recirculation and vortex shedding on a half-span of the cylinder wavelength. The bifurcation results in a spiral flow toward the saddle and the other spiral flow toward the node. The bifurcations of recirculation and vortex shedding are revealed for the first time. The findings contribute to an improved understanding of the insight into intricate flow physics around wavy elliptic cylinders. • The three-dimensional flow of a wavy elliptic cylinder for wavelength λ/D m = 3.43, 4.58, and 6.01. • The λ/D m = 3.43 is characterized by spiral flow, counter-rotating vortices, and wavy vortex structure. • The flow for λ/D m = 4.58 undergoes bifurcation in stable recirculation, generating spiral flows toward the saddle and node. • The flow for λ/D m = 6.01 undergoes bifurcation in vortex shedding on a half-span of the cylinder wavelength. [ABSTRACT FROM AUTHOR]

The injection mode of oxidizer gas significantly affects the flow and heat transfer characteristics of rocket motors with separated oxidizer and fuel propellants. In the present study, the effect of the multi-hole injector on flow and heat transfer of a novel combined rocket motor is studied with a three-dimensional numerical model. The results show that as the number of injection holes increases from one to five, muti-jet interference effect could occur. The original single coupled combustion zone is split into multiple coupled combustion zones. Multi-peak distributions of temperature and velocity are thus observed. As the combustion heat release is gradually advanced towards the injector, the multiple injection flows form three high-flow velocity zones. The three-dimensional distribution of heat transfer coefficient is highly consistent with that of flow velocity. The average heat transfer coefficient first increases and then decreases with the increase in the number of injection holes. The 4-hole injector renders the largest average heat transfer coefficient. Due to the multi-peak distribution of flow velocity and heat transfer, a multi-peak distribution of regression rate for solid propellant is thus observed. The average regression rate increases greatly and reaches the maximum value for the 4-hole injector. The results also show that the regression rate is controlled by the combustion reaction kinetics in the proximal injector region but is controlled by heat transfer in the region far away from injector. The present study contributes to a better insight into the flow and heat transfer effects on combustion performance of the combined solid rocket motor with multi-hole injector. • Obtained three-dimensional distribution of heat transfer coefficient of the motor. • Revealed multi-jet interference effect on mixing and heat transfer properties. • Observed multi-peak distributions of temperature and flow velocity. • Identified effects of flow and heat transfer on regression rate distribution. [ABSTRACT FROM AUTHOR]

A model for the approximation of cavitation-induced air release in three-dimensional flow simulations is proposed. A cavitating orifice flow is investigated. It is assumed that vapor vanishes in the proximity of the orifice, and bubbles further downstream consist essentially of air. The model is based on a homogeneous mixture assumption and comprises one main parameter, which needs to be adjusted to the experimentally measured degassing fraction. Experimental validation is based on transmission light images downstream of the orifice. In the proximity of the orifice, the inclusion of air release in the CFD simulation yields a better agreement to experimentally measured cavitation intensity than the consideration of pure vapor only. It is concluded that a considerably larger amount of air is released than is dissolved in the evaporated amount of liquid. The simulation results suggest that the released air mass corresponds to about 1% of the evaporated liquid mass. These observations may be a good basis for purposeful future experiments, which are indispensable for the development of a more predictive approach of cavitation-induced air release in 3D CFD methods. [Display omitted] • A compressible solver for cavitating flow is extended by air release. • Air release is modeled by a homogeneous mixture approach. • Inclusion of released air improves the match to shadowgraphy data. • Mass of released air equals about 1% of evaporated liquid mass. [ABSTRACT FROM AUTHOR]

• A single-well enhanced geothermal combined organic Rankine cycle system is proposed. • Detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. • The effect of various parameters on the ORC system performance is probed. • The optimal operation parameters of SEGS ORC are obtained. This study proposes a single-well enhanced geothermal system (SEGS) to mitigate the high-risk of traditional Enhanced Geothermal Systems (ESGs) with two or more wells and enhance the general applicability. A detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. For the reservoir, a three-dimensional flow and heat transfer model featuring a discrete fracture network is employed. The effects of injection flow rate, injection temperature, branch well length, and branch well spacing on net output work, pump power consumption, thermal efficiency, and exergy efficiency have been investigated. The results indicate that an increase in the injection flow rate improves the shaft power of the expander and the power consumption of the injection pump. An optimal flow rate of 30 kg/s is identified, which maximizes the annual net power output to 1221.2 kW. Additionally, an increase in the injection temperature is found to enhance the buoyancy effect, thereby improving both thermal and exergy efficiency, and reducing the power consumption of the injection pump. The maximum net output power is achieved at an injection temperature of 60 °C. The study also notes that the branch well length has a negligible effect on thermal and exergy efficiency and expander shaft work. However, a longer branch well length contributes to a decrease in the power consumption of the injection pump and an increase in the net power output. Finally, it is observed that increasing the lateral well spacing slows the rate decay of the production temperature. A spacing of 360 m is found to yield a maximum annual net output power of 1259.4 kW. In conclusion, this study offers significant insights and practical guidance for the development and utilization of SEGS, demonstrating its potential as an effective alternative to conventional EGS methodologies. [ABSTRACT FROM AUTHOR]

• Distributed ECVT was proposed to enlarge the imaging spatial scale. • A 64-electrode ECVT sensor with a HDR of 12 was built to investigate the axial flow. • Axial dynamic flow of slugging flow in a CFB riser was investigated experimentally. • Axial dispersion of solid fraction, slug velocity, and slug length are extracted. Understanding particle flow characteristics within circulating fluidized bed (CFB) reactors is crucial for enhancing reaction efficiency. To study the flow characteristics of Geldart D particles with a mean diameter of 3.0 mm and a bulk density of 1640 kg/m3 in a CFB riser with a height of 1090 mm, a 64-electrode electrical capacitance volume tomography (ECVT) sensor with a height-to-diameter ratio (HDR) of 12 is arranged on the CFB riser with an inner diameter of 59 mm. A distributed ECVT architecture under the control of a timing controller is formed to synchronously acquire capacitance data of two 32-electrode ECVT data acquisition systems. So, the three-dimensional axial flow imaging of a CFB riser with a branch pipe is realized with a 14-plane ECVT sensor. The flow rules of slugging flow in the CFB riser under gas velocities of 3.5 m/s, 2.86 m/s, and 2.5 m/s are analyzed from the continuous ECVT images, especially the process of rupture, decomposition, and collapse of particle slugs. The flow parameter characteristics, such as the solid fraction in the riser, the slug rising tail velocity, the slug length, and the spectral characteristics, are investigated. The experimental results demonstrate that the proposed distributed ECVT can effectively realize the collaborative operation of multiple ECVT data acquisition systems and then splice sub-ECT images to achieve complex space imaging. [ABSTRACT FROM AUTHOR]

Developing state-of-the-art bipolar plate structures, to optimize fluid distribution, is essential to achieve better cell performance. In this paper, a three-dimensional model of PEMFC is developed and two cathode-side flow field structures are designed: two-dimensional and three-dimensional types. The two-dimensional type is the traditional "bipolar plate + gas diffusion layer" flow field structure, easily resulting in uneven distribution of reactant gas and other problems. This study describes three novel three-dimensional type flow fields (metal foam, fine-mesh, and wire-mesh). Through comprehensive performance analysis using numerical simulations, it is found that the three-dimensional type flow fields significantly improve mass transfer and output performance compared to two-dimensional type flow fields. The proposed three-dimensional type flow fields create forced convective fluid flow. It further enhances the diffusion dispersion of reactant gas, thus making fuller use of the active region. Among them, the wire-mesh flow field shows the best performance in terms of oxygen distribution, water distribution and electrical properties. The net output power density produced is 0.75068 W cm−2, higher than parallel flow field by 32.78%. • The PEMFC model with different cathode-side flow fields is developed using CFD simulation. • The three-dimensional type of flow field structure enhances mass transport. • The optimal current density distribution uniformity index is 0.1199. • The net output power density of the developed wire-mesh flow field is 0.75068 W cm−2. [ABSTRACT FROM AUTHOR]

Porous metal foam holds substantial promise as a material for bipolar plates in high-performance proton exchange membrane fuel cells (PEMFC) due to its exceptional properties in reactant redistribution. However, the intricate structure of metal foam flow field (MFF) presents challenges for mass transfer and water management. In this study, a three-dimensional two-phase flow model for metal foam is developed to analyze and capture flow patterns. MFFs are reconstructed based on detailed structural analysis and various pore sizes are discussed. Employing the Volume of Fluid (VOF) method, we delve into multiphase flow dynamics, specifically focusing on the removal of liquid droplets within the MFF. It reveals the MFF with moderate pore sizes exhibit a trade-off performance, striking a balance between optimal mass transfer and minimal parasitic loss. The porous structure's pivotal role is highlighted, contributing significantly to both through-plane and in-plane mass transfer and convection. Furthermore, we classify three flow patterns of liquid droplet, with the "split-up" pattern emerging as the most effective for water management and mass transfer. This study illuminates water behavior in porous metal foam bipolar plates, introduces a systematic methodology for assessing mass transfer and water management capabilities in MFFs for PEMFC. [ABSTRACT FROM AUTHOR]

• A novel technique is developed for measuring the free surface and surface velocity. • Measurement accuracy is verified by wave probes, planes and fringe projection method. • The measurement technique is applied to the flood propagation in a compound channel. River flooding can pose a significant threat to people's lives and properties on the floodplain. Due to the difficulty and potential danger of monitoring field river floods, laboratory experiments have become the main and key method for exploring flood propagation and evaluating potential flood risks. However, the complex three-dimensional flow state of floods in the compound channel makes current measurement techniques inadequate for meeting monitoring requirements. To this end, a new technique is developed in this study that can simultaneously monitor the flood free surface and the surface velocity in the laboratory compound channel. The developed measurement technique combines stereoscopy and the particle tracking velocimetry (PTV) method through the pixel coordinate fitting method, so that the coordinates of the tracer particles can be reconstructed in the three-dimensional state. This method can not only increase the basic data in the free surface construction but can also capture the complex three-dimensional flood flow behavior. The proposed technology was applied to measure the free surface of flood propagation in a laboratory compound channel. Water level, flow velocity, wave velocity, and wave height were simultaneously measured. The measurement accuracy was verified using wave probes, spatial planes, and fringe projection techniques. The results indicate that the water level measurement error is approximately 1.6 mm, and the flow velocity measurement error is around 3 %. The developed measurement system is simpler than previous methods based on light reflection or absorption. Most importantly, it can simultaneously measure both the flood free surface and surface velocity by only sowing tracer particles on the water surface. The current measurement technology offers a new tool for studying flood propagation in a laboratory compound channel. [ABSTRACT FROM AUTHOR]

High-performance compressor cascades are crucial components of aero-engine compressor stages and require wide operational ranges for optimal efficiency. This study examines the aerodynamic effects of implementing 0.5 mm high backward-facing steps (BFS) on the suction side of transonic compressor cascades. Numerical analyses were conducted to assess the influence of step position under specific operating conditions. It was concluded that placing the step in the middle of the cascade is most conducive to improving performance. Subsequent evaluation delineates the flow patterns and modifications to shock wave structures, especially when the step is implanted within the post-leading-edge acceleration zone. Additionally, further comparisons were made on cascade characteristics, channel separation flow dynamics, and blade load distribution at varying incidence angles when incorporating a central step. The adjusted cascade expanded the functional incidence angle from 2.6° to 3.8°, a substantial rise of 46 %. The step primarily affects the flow within a 60 % to 80 % axial chord length sector. Despite engendering a localized recirculation zone, the step notably aids in relocating the end-wall boundary layer, prompting the low-momentum fluid from the root to move spanwise, thereby reducing the channel separation vortex intensity. This leads to a noticeable decrease in blockage factor near the end-wall at the outlet across divergent incidence angles, with reductions of 5 % and 3.4 %, respectively. Overall, these findings propose that situating the BFS proximate to the mid-cascade separation zone enhances the operational capacity of the compressor cascade. The research underscores BFS as a potential asset in broadening the working range for compressor cascades within aeronautical applications. [ABSTRACT FROM AUTHOR]

At present, research on integrating deep learning with fluid dynamics has mostly focused on two-dimensional (2D) flow fields. Shifting from the study of 2D flow fields to the study of three-dimensional (3D) flow fields is crucial for accelerating the practical applications of deep learning in the real world. In this paper, we possess a high-quality direct numerical simulation dataset: 3D inclined circular disk flow fields with Reynolds numbers between 150 and 250, and a 3D convolutional autoencoder based on this dataset has been established to explore the specific performance of deep learning techniques in the reconstruction of 3D flow fields. The proposed model achieved significantly higher accuracy than proper orthogonal decomposition in terms of feature extraction in 3D inputs. When adding mask and noise to the inputs, the model exhibited impressive robustness: It had strong denoising capability under the Gaussian noise of k = 10 , and it can also reconstruct the flow fields well with inputs covered by one-eighth of the area. Additional slicing processing was applied to the model's output results during the research to highlight the differences between 3D flow field reconstruction tasks and the 2D scenario, allowing for detailed comparative analysis. • Proposed a practical deep learning model that can directly process three-dimensional flow field data. • Established a neural network structure that is highly robust to three-dimensional flow field noise and mask. • Discovered that the most difficult regions for the model to learn emerge in the rear half of the flow field. [ABSTRACT FROM AUTHOR]

This paper aims to improve existing models for drag, lift, and pitching torque coefficients of cylindrical disc particles with a wider range of aspect ratios and particle Reynolds numbers. The full body-fitted direct numerical simulations (DNS) are carried out for three-dimensional flow past cylindrical discs in order to quantify the coefficients at aspect ratios from 0.2 to 0.6, incidence angles from 0°to 90°, and Reynolds numbers from 0.1 to 300. The CFD results are validated against the aerodynamic coefficients of both spherical and non-spherical particles presented in the literature. A full set of new correlations for the coefficients, dependent on aspect ratio, incidence angle, and Reynolds number, is further derived according to the CFD predicted data. The results show that the new correlations have a promising performance for the disc particles considered in this study. [Display omitted] • CFD simulations are performed for drag, lift, and pitching torque coefficients. • A complete set of correlations for C D , C L , and C T is proposed. • Proposed correlations work well outside the Stokes regime. • The correlation predictions agree with the CFD simulations. [ABSTRACT FROM AUTHOR]

This paper introduces an adaptive sampling strategy for a multi-vehicle sensor network to explore an underwater biological system known as the pelagic scattering layer, which is a region in the water column with a high density of marine organisms that reflect sound. Ever-changing ocean flow presents a challenge to multi-vehicle coordination in this process. The presence of an ocean flow field may disrupt inter-vehicle spacing so that the group loses communication, strays from a desired formation, or ends up with reduced area of coverage, especially for robotic drifting vehicles whose motion is largely influenced by the ambient flow field. However, those vehicles may also take advantage of the vertical variation of the flow to form a desired cohesive configuration since they can tune their vertical position via depth control. A motion-control algorithm, therefore, is a key element of the adaptive sampling strategy. The paper derives a decentralized coordination algorithm to stabilize a cohesive formation in a two-dimensional flow field with an initial unknown vertical distribution. The algorithm works with a distributed extended Kalman filter that generates a local estimate of the flow from pairwise range measurements between vehicles. Another component of the sampling strategy is the modeling of organism density dynamics using estimation of the density with local optical measurements, such as from onboard cameras. The density evolution is estimated using an ensemble Kalman filter and the results are fed into the motion-coordination algorithm. Numerical simulations illustrate the efficacy of this strategy and motivate ongoing and future efforts to extend the result to a three-dimensional geophysical flow. • A decentralized depth control algorithm guides multiple drifting vehicles to varying depths, ensuring cohesive, collision-free formation in shear flow. • Buoyancy control extends to unknown shear flow using extended Kalman filter for parameter estimation, enabling formation. • Ensemble Kalman filter estimates scattering layer density from depth predictions using operator and local measurements. [ABSTRACT FROM AUTHOR]

As the core component of the ORC, the optimal design of the radial inflow turbine (RIT) is crucial for enhancing system performance. An improved 1-D mean-line optimization design model based on real gas physical properties of the RIT is proposed. Compared to conventional 1-D mean-line models, the proposed model integrates numerous critical aerodynamic and structural constraint conditions, reducing the uncertainty dimension of critical design parameters, and narrowing the range of values for the reaction degree and the velocity ratio. The three-dimensional flow characteristics and aerodynamic performance of the RIT are investigated through a three-dimensional computational fluid dynamics (CFD) analysis. The flow characteristics and loss mechanisms of tip leakage flow under various blade tip clearances are further investigated. The results indicate that the leakage flow through the tip clearance has a tremendous impact on the internal flow characteristics of the RIT and is a key factor leading to a substantial increase in flow losses. With an increase in relative blade tip clearance from 0 to 15.63%, the isentropic efficiency of the RIT gradually decreases from 88.57% to 80.32%. It is equivalent to an approximate 0.53% reduction in isentropic efficiency for every 1% increase in the relative tip clearance. • Improved 1-D mean-line optimization design model based on real gas physical properties of RIT used in ORVC is proposed. • The flow characteristics and loss mechanisms of tip leakage flow under various blade tip clearances are analyzed. • The effect of leakage flow on turbine performance is presented in theory and compared with the result of the CFD method. [ABSTRACT FROM AUTHOR]

Due to the deviation of pore water seepage in marine soft soils from Darcy flow under low hydraulic gradients, existing methods face challenges in accurately calculating the time-dependent bearing capacity of piles in such areas. This paper adopts the secondary development of Python to ABAQUS and employs a continuous coupling analysis method to establish a numerical model capable of simultaneously solving the large deformation of pile driving and non-Darcy flow. The model addresses issues such as mesh distortion during pile driving and the numerical implementation of three-dimensional non-Darcy flow. The accuracy of the model was verified through comparison with two experimental cases. Subsequently, the study analyzed how non-Darcy flow affects soil consolidation around the pile and the time-dependent bearing capacity of pile. Results indicate that when the permeability coefficient of the soil around the pile is less than 1 × 10−7 m/s, non-Darcy flow significantly delays the consolidation of soil within three times the pile diameter around the pile, thereby reducing the time-dependent bearing capacity of pile, with a greater impact observed for lower permeability coefficients of the soil. Once the soil around the pile reaches 90% consolidation, subsequent construction can proceed to shorten the project duration while maintaining safety. • Secondary development based on Python-ABAQUS. • A new numerical solution to the large deformation problem of pile driving. • Numerical implementation of three-dimensional non-Darcy flow. • Comparison with centrifuge test and axisymmetric consolidation test. • Analysis of time-varying bearing capacity of pile in coastal soft soil area. [ABSTRACT FROM AUTHOR]

In icy regions, the vibration induced by broken ice poses a hazard to risers, in addition to vortex-induced vibration (VIV). A numerical investigation has been conducted to explore the dynamic response of risers in seas with fragmented ice floes. Assuming the broken ice as a single rigid floating body bonded by particles, the flow with water and ice is considered a two-phase flow, which is established using the Smooth Particle Hydrodynamics (SPH) method based on the quasi-fluid model. Verification of the model was achieved by simulating the three-dimensional flow around a surface-piercing cylinder and VIV. Accurate predictions were made regarding hydrodynamic forces, uplift values of the free liquid surface at the front stagnation point of the cylinder, and riser motion. Furthermore, the SPH model was expanded to encompass the realm of ice-water structural interaction (IWSI) combined with the basic principle of bidirectional fluid-structure coupling, facilitating the simulation of riser vibration within ice-water flows. The results indicate that the ice load remained the principal contributor to the force on the vibrating riser, while the riser exhibited irregular motion, demonstrating a strong coupling between forces and riser movement. • The study is the preliminary implementation of the SPH solution of ice-water two phase flow. • Two-phase control equations of ice-water flow are established based on the quasi-fluid model. • A description of the broken ice SPH method based on the adhesive model is established. • The proposed SPH model is extended to the IWSI field to investigate the IIV of the riser. [ABSTRACT FROM AUTHOR]

The purpose of this study, is to investigate the aeroelastic stability and effect of vortices resulting from passing air over cylindrical shells in three-dimensional condition. Here, the Naiver-Stokes equations in the integral form are considered studying the air flow based on the finite-volume method. The ANSYS Fluent software is used to study the fluid-solid interaction effect. The shear stress transport (SST) turbulence model is utilized to simulate the turbulent viscosity. Effect of different parameters such as two cylindrical shells alignment or two cylinders diameter ratio are considered. The results indicate that the vortices can play a significant role on the aeroelastic stability of the cylindrical shell. • The aeroelastic stability of two cylindrical shells under vortex induced vibration is studied. • A three-dimensional turbulent flow is simulated by a higher order discretization method. • A strongly coupled solver between fluid and solid is used as an FSI algorithm. • Effect of shells alignment in two circular and elliptical configurations are studied. [ABSTRACT FROM AUTHOR]

The high fidelity Navier Stokes equations based CFD codes precisely take care of the turbulent and viscous effects of complex flows passing through the hydraulic turbines. However, for preliminary design synthesis and analysis purposes, this full 3D flow can be assumed as a combination of two 2D flows (meridional axi-symmetric flow and blade-to-blade or cascade flow) which is the basis of low fidelity potential flow theory for hydraulic turbines. This paper presents the utilities of high as well as low fidelity CFD analyses for obtaining a runner blade design which yields an optimum hydrodynamic performance of a prototype Francis Turbine. The complete flow domain of the Francis turbine has been considered for the high-fidelity analysis which is carried out by using ANSYS CFX 16.0 for different operating conditions. Whereas, for the low fidelity investigations, full three-dimensional flow domains of different blade rows (i.e., stay vanes, guide vanes and runner) of the Francis turbine is divided into two 2D flow domains (i.e., an axisymmetric annulus of the turbine space for meridional flow analysis and cascades at different sections from hub to shroud for blade-to-blade analysis). By using the low fidelity analysis, runner blade design parameters have been adequately varied in order to obtain a population of different promising runner blade designs. Performances of these promising designs are evaluated, and the obtained results are thoroughly analysed through the response surface analysis. An optimized hydrodynamic performance design of the runner is obtained for the target values of responses (here, swirl velocity at trailing edge of the runner (C u2) and stagnation pressure at trailing edge of the runner (P 02 /ρ)) at different sections from hub to shroud by determining the design parameters of blade profiles at different sections. The adopted multi-fidelity CFD approach is found very effective and has the potential to yield reasonably accurate hydraulic designs of the Francis turbine in considerably lesser time and cost. • Comprehensive low and high-fidelity analyses of a Francis turbine runner have been carried out. • Using low-fidelity CFD codes for new designs is reliable due to their strong control over local flow and design parameters. • Converged solutions with low-fidelity codes require a uniform distribution of local flow parameters from hub to casing. • Low fidelity codes offer faster convergence rates. • Blade-to-blade space has more influence on the turbine's hydrodynamic performance than that of the meridional space. [ABSTRACT FROM AUTHOR]

The study of the exchange of momentum and energy between wave components of the turbulent velocity field, the so-called triad interactions, offers a unique way of visualizing and describing turbulence. Most often, this study has been carried out by direct numerical simulations or by power spectral measurements. Due to the complexity of the problem and the great range of velocity scales in high Reynolds number developed turbulence, direct measurements of the interaction between the individual wave components have been rare. In the present work, we present measurements and related computations of triad interactions between controlled wave components injected into an approximately laminar and uniform flow from an open wind tunnel by vortex shedding from two rods suspended into the flow. This results in two-dimensional interactions of three-dimensional turbulence, which makes the analysis of the triadic interactions considerably less complex to analyze than in a fully developed three-dimensional flow. With the information obtained from the computations, we are able to isolate the individual triad interactions contributing to the generated frequency components as the flow develops downstream as well as understanding, mapping out and predicting the strengths of these interactions. The analysis also provides the time constants governing the development of higher order frequency components. We are thus able to see the pattern of frequency combinations, the strengths of the individual mode combinations and the time sequence in which they occur. Any of the higher order combinations is not just the result of a single term in the Navier–Stokes Equation, but a combination of various previous combinations occurring with different strengths and in a varied pattern of generation. The combination of these experiments and computations thus provide unique insight into the inner workings of turbulence and shows how the nonlinear term in the Navier–Stokes equation on average forces the energy towards higher frequencies, which is the reason for the so-called energy cascade. • Downstream spectral development of two fundamental spatial Fourier modes is measured. • Experiments confirm the expected behavior of the non-linear interactions. • Downstream development results from repeated action of the Navier–Stokes equation. • Excellent agreement with numerical simulations. • Simulations reveals the details of the nonlinear triadic energy exchanges. [ABSTRACT FROM AUTHOR]