Flow Field Variables Research Articles

The impact of piston and sloshing motions on added resistance from moonpool configurations

Moonpools are vertical watertight openings employed in the decks and lower structures of marine vessels and offshore platforms to allow drilling pipes and risers to be lowered into the sea. In the present work, the resistance performance of a drillship with varied moonpool configurations under calm water and regular wave conditions is investigated using a shear-stress transport (SST) k-ω model based on OpenFOAM. It is confirmed by comparing experimental and numerical results that this method can accurately predict the resistance of a ship with a moonpool. The numerical results suggest that the added resistance caused by a moonpool can be effectively reduced by optimally arranging the notch on the recess. A significant variation in the local flow field of the moonpool accounts for this. The implementation of the notch affects the development of vortices structures, thus transforms the free surface evolutions as well as the fluid resonance. Finally, the variation in pressure distribution contributes to a decline in the added resistance associated with the moonpool.

Numerical investigation on the interactions between rotating detonation wave complex and planar turbine cascade

AbstractDue to pressure gain characteristics, the rotating detonation combustor (RDC) can be integrated into gas turbines by further improving the system's performance. The matching of unsteady flows in the RDC and turbine is a key challenge. Here, interactions in an RDC and planar turbine cascade are investigated using the unsteady Reynolds time‐averaged Navier‐Stokes method. The effects of the blade profiles on interactions between the oblique shock wave (OSW) and turbine cascade are analyzed, and the suppression effect of the turbine cascade on high‐frequency pressure oscillations is evaluated. The results show that the OSW interacts with the leading edge, pressure side, suction side, and trailing edge of the turbine stator and rotor blades, which generates complex wave systems in the cascade passage. The opposite propagation direction causes the OSW to be aligned or misaligned with the stator blade. The position of the OSW that operates on the turbine cascade changes, and two different wave system structures appear. The various pitches of the turbine cascade at different blade heights cause differing intensities and propagation directions in the reflected wave as generated by the action of the OSW and turbine cascade and the variable flow fields at different blade heights. The turbine cascade can significantly suppress the high‐frequency pressure oscillations, while the pressure amplitude attenuation rate can reach over 80% when the OSW propagates through the turbine cascade. These findings expound on the interaction mechanism between the rotating detonation wave complex and the turbine stator and rotor blades.

Three-dimensional hydraulic tomography analyses to investigate commingling issues of reproducibility, data density, and geological prior models

Over the past two decades, geostatistics-based hydraulic tomography (HT) has been proven to be a robust method for subsurface heterogeneity characterization. However, the reproducibility of estimated parameter fields, namely the hydraulic conductivity (K) and specific storage (Ss), obtained over different data collection periods and under different flow scenarios have been rarely studied. In this study, we investigate the reproducibility and predictivity of HT estimates using data collected in 2019 and 2020 at a field site of varying boundary conditions underlain by sedimentary units in Japan, with different data density and prior geological information. Model performance of each case is evaluated qualitatively and quantitatively by examining results from model calibration, self-validation and cross-validation, in terms of parameter fields comparison, drawdown matches and cross-correlation distributions. Results of this study reveal that: 1) overall, the parameter fields for 2019 and 2020 HT estimates are generally reproducible, while fine-scale discrepancy exists; 2) they are also found to be reproducible in terms of consistency of estimated geostatistical parameters; 3) higher levels of reproducibility and predictivity associated with estimated K and Ss fields are obtained when higher data density is included for geostatistical inverse modeling with more accurate prior geological information; and 4) the different spatial distributions of cross-correlation between head and parameter fields induced through the significant variation of the groundwater flow field from 2019 to 2020 strengthen the notion of reproducibility of HT results. These results collectively suggest that HT has the potential for mapping changes to K and Ss heterogeneity over time broadening its future applications to various practical problems.

Variable cross-section flow field structure for improved water management in PEMFC

Variable cross-section flow field structure for improved water management in PEMFC

Impact of passive fuel injections techniques in the flow field of the scramjet combustor

• The introduction of passive injection techniques in a parallel cavities scramjet combustor influences the internal flow filed charateristics. • The effect of fuel injection location on the internal flow field charaterictics is also investigated. • Out of all the configuration , the scrmajet combustor showef optimum performance when the fuel is injected through the wall only. The development of scramjet technology has paved the path of possibilities for researchers to develop light-weighted space missions in the years to come. Many countries around the globe have already tested successful scramjet engines. The researchers are making continuous efforts to improve the combustor design by improvising turbulence inserts and flame holders in the combustor. One such improvisation is the introduction of strut into the parallel-cavities combustor. The research paper uses computational fluid dynamics to investigate the effect of internal flow field variables on a strut and cavity-based scramjet combustor. The current work presents a comparative study by analyzing two different scramjet combustor configurations namely case A and Case B to understand the effect of presence of strut in the cavity combustor. The velocity and static pressure profiles are analyzed at different streamwise locations. At x = 70 mm, the velocity values are reduced to lower magnitude for case B as compared to case A and the static pressure values towards downstream detoriates with reduction in intensity of shock waves. It is seen that the magnitude of velocity values and pressure values increases with increase is Mach number. The high-pressure values are observed for M-2.75. A performance assessment of the combustor is carried out for both the configurations, maximum combustion and mixing performance is obtained for M-2.52 for case B as compared to Case A. The paper further analyses three different fuel injection locations namely fuel injection strut only, fuel injection through the wall only and fuel injection through both strut+wall recognized as the case I, II, and III respectively. From various flow-field parameters analysis, it is seen that the production of eddies and vortices in the combustor region indicates proper mixing which is observed for case I. On studying the mass fraction concentration of H 2 0 species for all the cases it is observed that the H 2 0 species is increasing in the lateral direction which indicates that the combustion efficiency is incrementing in the same direction. The maximum combustion and mixing efficiency is observed for case I than the other two cases.

Cooling characteristics of hot rolled seamless steel tube by jet impingement

The flow and temperature field variation of hot rolled seamless steel tube with outer diameter of 140 mm and wall thickness of 10 mm were studied by experiment and numerical simulation. The finite element model of circular jet impinging cooling steel tube was established, and the steel tube was divided into different regions in circumferential direction. It was found that the uniformly arranged multiple jets have non-uniform cooling characteristics under the influence of gravity and hollow characteristic. Under the condition of 12 jets, the average heat transfer coefficient in circumferential direction of −15 ∼ −45° region is 8385 W/(m2K), and the fluctuation of the average heat transfer coefficient in different regions reaches 3222 W/(m2K). According to statistical average cooling rate of the experiment, the average cooling rate increases by 34% when 2 jets are increased to 4 jets. When the number of jets exceeds 8, increasing the number of jets has a limited effect on improving average cooling rate. Through reasonable configuration of jet velocity of different nozzle positions, a way to realize uniform cooling was proposed and preliminarily verified. The improved average heat transfer coefficient fluctuation of circumferential was limited to 1000 W/(m2K), which significantly improved the uniformity of jet cooling.

Numerical investigation of the spark discharge process in a crossflow

The present study numerically investigates the spark discharge process under crossflow conditions using a thermal equilibrium plasma solver that fully couples the electromagnetic physics and fluid dynamics in a computational framework. Numerical results are validated by the comparison with experimental data. The spark discharge experiment is performed in a constant volume vessel using an inductive coil ignition system for automotive applications, and the evolution of the spark channel is measured using high-speed imaging. The crossflow in the gap between the spark-plug electrodes is generated by a rotating fan with two different fan speeds, and the flow velocity across the gap is characterized by particle image velocimetry (PIV) measurement. A computational fluid dynamics (CFD) solver is employed to simulate the crossflow and provide the flow field variables (velocity, pressure, temperature) to the plasma solver. The crossflow velocity predicted in the flow simulation agrees well with the PIV data in that the non-uniform velocity profiles at monitoring points are reproduced by the CFD code. With the crossflow initialization in the plasma solver, the simulated spark discharge process from the breakdown to spark discharge matches the experimental data, including the voltage and circuit waveforms and the high-speed images of the spark channel evolution. The stretch of spark channel captured by plasma simulations agrees with the measured data. The plasma simulation reveals that the mean temperature of the spark channel is maintained at 5000 K during the discharge phase, and the temperature varies along the spark channel so that the highest value is obtained at the spark root on the center electrode. Overall, the results presented in this paper are meant to provide valuable information about the properties of the plasma generated by the spark discharge.

Tailoring Flow Field Channel Aspect Ratio for Efficient Mass Transport and Compression in Fuel Cells

The adverse effects of global warming have made it critical to transition our reliance on fossil fuels to more sustainable energy sources. Polymer electrolyte membrane fuel cells (PEMFCs) can facilitate this transition by providing on-demand power with zero local carbon emissions. However, the high cost and poor durability of fuel cells hinder their widespread adoption. Particularly, PEMFC performance is strongly dependent on the flow fields which should be designed to optimize the transport of reactants and byproducts while maintaining uniform compression with subsequent layers. An important flow field design parameter is the channel aspect ratio which directly influences compression and the transport of reactants and products. Although novel flow field configurations have been studied previously, a comprehensive investigation on the effects of channel aspect ratio on cell performance has yet to be performed. In this study, we compared the electrochemical performance across varying flow field channel aspect ratios (channel width by height) from 0.5-2.0 with a fixed active area. The ohmic and mass transport resistances were quantified using electrochemical impedance spectroscopy. Operando X-ray imaging was performed to spatially resolve water saturation under the land and channel regions of the flow fields. We observed that lower channel aspect ratios (or higher number of channels for the given active area) led to lower ohmic resistance but resulted in higher mass transport losses at higher current densities due to significant water saturation under the hydrophilic ribs of the flow field. Notably, from these results we elucidated that there exists an ideal channel to rib width ratio to facilitate efficient mass transport and effective contact between the porous microstructures.

UNCERTAINTY QUANTIFICATION OF SELF-PROPULSION ANALYSES WITH RANS-CFD AND COMPARISON WITH FULL-SCALE SHIP TRIALS

RANS-CFD is a well-established tool with widespread use in maritime industry and research. Valuable information might be extracted from the results of such simulations in terms of ship resistance and flow field variables. With recent advancements in computational power, it became possible to investigate the performance of ships in self-propulsion conditions with RANS method. This paper presents the results of a study in which self-propulsion analyses of a small size product/oil tanker has been carried out at ship scale. The methodology proposed in this study makes use of open water propeller performance predictions, resistance analyses at model scale and self-propulsion computations at ship scale for a minimum of 2 different propeller loadings to obtain the self-propulsion point and respective performance parameters. In order to speed up the time-consuming self-propulsion computations, these cases have been solved with a single-phase approach. Resistance predictions have been compared with experimental findings. Uncertainty associated with prediction of resistance and thrust has been quantified. Additionally, sea trials have been conducted on the subject vessel and its two sisters and measured delivered power data have been used for evaluating the capability of the numerical method in self-propulsion predictions. Comparison of results indicate that the proposed self-propulsion computation methodology with RANS CFD at ship scale is capable of predicting delivered power with sufficient accuracy at an acceptable computational cost.

Full-Scale Reynolds Number Testing of Rotor Hub Drag and Wake Turbulence

A 1:4.25-scale model of a generic helicopter rotor hub was tested at Reynolds numbers ranging from 1. 75× 106 to 7×106 at advance ratio of 0.2 in The Pennsylvania State University Applied Research Laboratory Garfield Thomas 48-inch diameter water tunnel. Measurements including drag and wake characteristics were performed up to full-scale Reynolds number with respect to an industry-representative helicopter rotor hub. In particular, the variation of drag and flow field with Reynolds number was characterized. Load measurements were conducted using an improved load cell design, with greater accuracy than in previous experiments. Wake velocity was measured using laser Doppler velocimetry at two downstream planes, yielding velocity statistics to the second order. Improved load measurement accuracy and wake velocity spatial resolution, at full-scale Reynolds number, provide a unique dataset for computational fluid dynamics validation as part of the Penn State Rotor Hub Flow Prediction Workshops and physical insight into rotor hub flows.

Numerical analysis of micropolar hybrid nanofluid in the presence of non-Fourier flux model and thermal radiation

The influence of various influential factors on the flow field, temperature, and concentration variations are observed throughout the study of thermo-physical properties. The transfer of heat in fluids and thermal instability/stability are fascinating areas of study because of their vast range of applications, and physical significance in many engineering systems. This research aims to investigate and evaluate the flow characteristic, heat and concentration variations of hybrid nanofluids containing MHD natural convection flow of micropolar CuO-Ag/water in porous media across a vertically positioned plate. The flow model is treated with suction/injection at the plate’s surface, thermal radiation, heat generation and absorption, Joule heating, and viscous dissipation. The non-Fourier theory for the heat flux model is used to diminish the thermal instability. Mathematical system for the proposed model having some physical aspects results in a system of PDEs form which is restricted the boundary layer approximation is used. The PDEs model is then converted into an ODEs system using the suitable transformations. Numerical scheme RK-4 in collaboration shooting technique is used to find the best approximate results. For the validation of the employed technique, a comparison is offered from literature to confirm the dependability of the produced solution. Physical characteristics of the given solution have been studied and demonstrated against various associated influential factors. In the case of hybrid nano-structures, thermal growth is accelerated rather than in the event of nanofluid. The momentum layer thickness is more essential in hybrid nanoparticles than in nanoparticles. It’s also being looked at how crucial flow parameters affect heat transmission and skin friction.

Effect of Flow-Field Variation on Hydrogen Adsorption in a Carbon Electrode Integrated into a Modified Reversible Polymer Electrolyte Membrane Fuel Cell

Effect of Flow-Field Variation on Hydrogen Adsorption in a Carbon Electrode Integrated into a Modified Reversible Polymer Electrolyte Membrane Fuel Cell

Thermal onsets of Soret and Dufour aspects for species of microorganisms transport by a movable riga surface

In nature, there are different groups of microorganisms. These groups are: archaea, bacteria, fungi (yeasts and molds), protozoa, algae and viruses. In this research, general species of microorganisms is considered. The intension of recent work is to scrutinize heat transfer analysis for viscous flow of pseudoplastic nanomaterial including motile microorganisms over a Riga plate. Soret and Dufour aspects and convection conditions are accounted. Energy expression is modeled with heat generation and radiation effects. Characteristics of nanofluid is scrutinized through Boungiorno's model. Presence of species of gyrotactic microorganisms is considered. In addition, chemically reactive flow of first order is discussed. Similarity transformation is used to transforms non-linear differential system into non-dimensional ordinary differential system. The resultant coupled systems are solved through ND-solve method. Graphical results of liquid flow, concentration, microorganism concentration and thermal field versus influential variables are presented. Numerical outcomes of velocity gradient, solutal transfer rate, microorganism density and Nusselt number for sundry variables are examined in tubularized form. A decrement in fluid flow is seen for magnetic variable, while reverse characteristics reserved for drag force. Larger approximation of Dufour number lead to enlarge the temperature similar characteristics for thermal field is found through random and thermophoretic variables.

Characterizing Residual Current Circulation and Its Response Mechanism to Wind at a Seasonal Scale Based on High-Frequency Radar Data

Residual current characteristics are indicators for the net transports of sediments, nutrients, and pollutants, and for the dilution and diffusion of soluble substances in coastal areas, yet their driving mechanisms remain poorly understood. Here, we studied the characteristics of surface residual currents along the west coast of the island of Ireland, as well as the response mechanisms to wind at a seasonal scale based on the continuous observation data of high-frequency radar (HFR) for one year. Our analyses indicate that wind has a significant effect on generating surface residual currents, with correlation coefficients of 0.6–0.8 between wind speeds and residual current speeds at both annual and seasonal scales. However, the correlation between the directions of residual currents and the wind was not as significant as speed, likely because the directions of residual currents were not only affected by sea surface wind, but also by land boundary conditions in the research area. Moreover, the residual currents had a significant eastward flow trend identical to the wind direction at the maximum wind speed time, during which the effect of the tide on residual currents was relatively weak. Additionally, when compared with wind fields, HFR surface flow fields and surface residual current fields show that wind is the dominant driver of the variations of surface and residual flow fields. These findings shed light on coastal ecological and environmental management and can assist in the prevention and mitigation of marine disasters, by providing helpful information for improving the ability and accuracy of forecasting coastal currents.

Graph attention network-based fluid simulation model

Traditional computational fluid dynamics (CFD) techniques deduce the dynamic variations in flow fields by using finite elements or finite differences to solve partial differential equations. CFD usually involves several tens of thousands of grid nodes, which entail long computation times and significant computational resources. Fluid data are usually irregular data, and there will be turbulence in the flow field where the physical quantities between adjacent grid nodes are extremely nonequilibrium. We use a graph attention neural network to build a fluid simulation model (GAFM). GAFM assigns weights to adjacent node-pairs through a graph attention mechanism. In this way, it is not only possible to directly calculate the fluid data but also to adjust for nonequilibrium in vortices, especially turbulent flows. The GAFM deductively predicts the dynamic variations in flow fields by using spatiotemporally continuous sample data. A validation of the proposed GAFM against the two-dimensional (2D) flow around a cylinder confirms its high prediction accuracy. In addition, the GAFM achieves faster computation speeds than traditional CFD solvers by two to three orders of magnitude. The GAFM provides a new idea for the rapid optimization and design of fluid mechanics models and the real-time control of intelligent fluid mechanisms.

Determining the position of a fish passage facility entrance based on endemic fish swimming abilities and flow field.

Hydropower development can significantly mitigate climate change and reduce carbon emissions, but it can also have substantial negative impacts on river environments and fish biodiversity. Fish passage facilities are built to ensure sustainable hydropower development and the biodiversity of fish populations. The locations of the entrances to these facilities play a key role in their efficiency. This study presents a reliable approach that combines the swimming ability of fish and a numerical flow field simulation to determine the optimal location for a fish passage facility entrance. In this study, we used the Gujun Reservoir upstream of the Yangtze River as a case study. A field experiment was conducted, and the swimming abilities of eight endemic fish species in the upstream region of the Yangtze River were measured. Among the tested species, the fastest induced swimming speed (0.14m/s) was achieved by Glyptothorax sinense, while the slowest critical swimming speed (0.30m/s) was observed for Paracobitis potanini. We propose that the velocity near the fish passage facility entrance should be higher than the maximum induced swimming speed and lower than the minimum critical swimming speed, making the suitable range between 0.14 and 0.30m/s. On this basis, velocity fields 500m downstream of the dam of the Gujun Reservoir under 4 operating conditions with discharge flows of 5.7 m3/s, 23.3 m3/s, 32.5 m3/s, and 41.1 m3/s were calculated. The results showed that the flow field variation downstream of the dam was between 0.1 and 0.9m/s. After comparing the suitable areas for the target species, the left bank at location 2 was recommended as the optimal location for the fish passage facility entrance in the Gujun Reservoir.

Radiative and Hydromagnetic Heat Transfer Analysis of a Reiner–Philippoff Fluid

The aim of this work is to characterize the buoyancy-driven flow of a Reiner–Philippoff fluid over a vertical plate under the combined influences of a sinusoidal hydromagnetic effect and thermal radiation. This study focuses on the prediction of the conveyance of heat in the gravity-induced regime both qualitatively and quantitatively. Pertaining to this investigation, the governing transport equations, which are coupled, nonlinear, and time dependent, are solved numerically using a well-organized Crank–Nicolson scheme, consistent with the finite difference method. By demonstrating the graphical representations of flow velocity, temperature, drag coefficient, and heat transfer rate, obtained for a set of physical parameters, namely, magnetic parameter (, 1.0, 1.5, and 2.0), rheological parameter (, 1.0, 1.5, and 2.52), and radiation parameter (, 1.5, 2.5, and 3.5) relevant to this analysis, this paper establishes their influence on the underlying thermohydrodynamics. The results of this analysis show that the impact of periodic magnetic field remarkably enhances the flowfield variables, while the evolution of flow contours deviates periodically with a higher amplitude when the magnitude of the periodic magnetic and thermal radiation parameters is increased. The results of this analysis seem to provide a basis for the design of a modern electromagnetic pump, largely used in applications of traditional energy resources.

New semi-analytical solutions to the radial advection-dispersion equation for solute transport in a transient divergent radial flow

Solute transport through radial advection–dispersion is a common phenomenon in many applications, such as aquifer decontamination, heat exchange for geothermal exploration, and tracer testing. Numerous analytical solutions to the problem of tracer testing in a radially divergent flow field are available for fitting breakthrough curves. However, all of these analytical solutions assume non-uniform flow velocity based on Thiem's solution, which varies only spatially, not temporally. Although an injection well with a constant injection rate in a tracer test causes both spatial and temporal variability of the radial flow field, previous analytical studies have employed a steady-state groundwater flow solution, i.e. Thiem's solution, to derive analytical solutions for breakthrough curves or spatial concentration distribution curves. To the best of our knowledge, no analytical solution to the radial advection–dispersion equation under spatially and temporally variable flow conditions driven by injection at a constant rate is currently available.Here, we propose a novel semi-analytical solution for describing solute transport in spatially and temporally variable flow induced by an injection well with a constant injection rate. We find that, above certain threshold values of dimensionless parameters related to aquifer flow properties, solute transport parameters, and the injection rate, the differences between previous analytical strategies our proposed semi-analytical solution are negligible. These threshold values tend to increase more sharply with an instantaneous injection source than a continuous injection source. In other words, it is more difficult for an instantaneous injection source to reach the condition where the difference between our approach and previous ones is negligible than for a continuous injection source type. Our findings clarify when existing analytical solutions can be reasonably used for parameter estimation through fitting of the breakthrough curve to field data and when the proposed semi-analytical solution is a better alternative.

Formation and evolution characteristics of hydrothermal flames inside a transpiring wall reactor: A transient numerical investigation

Transpiring-wall reactors with hydrothermal flames are effective in preventing corrosion and salt deposition in supercritical water oxidation systems. To uncover the not-well-understood evolution characteristics of the hydrothermal flame surrounded by a transpiring water film, a 2-D unsteady simulation is firstly conducted in this study. The transient results show that the variations of flow fields and flame shapes are attributed to the competition between inertial forces and buoyant forces. And the quasi-steady results present that high feed concentration may damage transpiring wall and delay the evolution of hydrothermal flames. In addition, a low feed temperature or a big flow area of jet can lead to open hydrothermal flames, which adversely affect the reactor. Furthermore, Froude Number, Fr, shows effectiveness in predicting quasi-steady flame shapes. For large-Fr conditions, the inertial force outweighs the buoyant force and hence closed flames are developed; while for low-Fr cases, open flames are developed.

Analysis of Movements and Behavior of Bighead Carps (Hypophthalmichthys nobilis) Considering Fish Passage Energetics in an Experimental Vertical Slot Fishway.

Simple SummaryHydraulic structures have modified the natural waterways, and they have inevitably blocked fish migration routes and reduced fish habitat. To mitigate the impact on fish, fish passages have been developed as an effective way to restore riverine connectivity. The design of fish passage facilities refers to both hydrodynamics and fish behavior, and the information on the energetic expenditure of fish can be used to identify movement zones that are suitable for fish migration. Thus, this paper intended to identify fish movement behavior in response to water flow field information by means of estimating the energetic expenditure using an IBM approach. The results demonstrated that the fish required more energy in high TKE zones, and they were therefore likely to utilize the low TKE zones. This study provides a reference for optimizing the design of fish passages, and the method can be applied to assess the efficiency of fish passages and other fish bypass structures.An understanding of fish movement behavior in response to flow field variables is important for exploring the hydrodynamic strategies of fish in fish passages. In this paper, bighead carps were taken as an example. The fish movement behavior response to water flow field information by means of estimating the energetic expenditure using an IBM approach in an experimental fishway was investigated. Fish swimming velocity, drag force, and energy expenditure were analyzed in varied flow conditions related to hydraulic variables, including velocity (V), turbulent kinetic energy (TKE), and strain rate (SR). The result indicated that the fish will require more energy in high TKE zones. This study provides a reference for optimizing the design of fish passages and fisheries management. This method can be applied to assess the efficiency of fish bypass structures and conduct fish survival studies.