Calculation Of Flow Field Research Articles

Isoparametric Finite Element Method to Generate Structured Grid for Numerical Flow Simulation

Eight-nodded quadrilateral finite element is used to generate structured grid for a numerical simulation. The computational domain is sub-divided into number of quadrilateral regions that display the geometry of each sub-domain. The inner and the outer boundaries of the computational domain are described in terms of the surface coordinates. An algebraic homotopy procedure is used to generate grid clustering in order to resolve boundary layer. The structured grid is linked with the flow solver based on finite volume of space discretiztion scheme with multi-stage Runge-Kutta time stepping technique. Examples are illustrated to demonstrate the grid generation procedure and data processing for a forward facing aero-disc spike attached to a hemispherical blunt body at Mach 6 and over a heat shield of a satellite launch vehicle at Mach 0.8 at an angle of attack 5 deg. The present grid generation method is convenient for checking the grid independence test by varying the stretching factor. The quadrilateral grid generated by finite element, vector plot of velocity and contour plots of the computed flow field data are easily drawn with the help of MATLAB.

Study on sediment erosion generated by a deep-sea polymetallic-nodule collector based on double-row jet

The hydraulic double-row jet collector is widely used due to its high collection efficiency. Deep-sea sediments are usually characterized by high water content and semi-fluid dynamics, and there are few studies on the erosion properties of such sediments under jets. Resulting in the failure to accurately assess the efficiency and disturbance of a two-row jet collector. In this paper, the flow field characteristics are simulated for different double-row jet parameters (jet outlet pressure, nozzle-to-seabed height, target distance and number of nozzles). The erosion of a high water content, semi-fluid dynamic sediment layer (similar to the deep sea) under a double-row jet is experimentally investigated. According to the results from study, the jet flow field had a powerful central flow field, and decayed to both sides gradually. The formulas of flow field attenuation distribution in the upper jet zone and the maximum axial pressure are proposed. Moreover, the experiments showed that the erosion holes on the surface layer was mainly a "bowl" shape with a flat bottom and concave side, which had self-similarity. The erosion depth grew with the increase of jet outlet pressure, decreased with the increase of the nozzle height to the seabed. With the increase of target distance, the erosion depth first increased and then decreased. A new model of the erosion depth-time and erosion depth prediction are proposed. These results can provide theoretical reference for flow field calculation in nodule mining operation with double-row jet collector. It may have potential benefits on melioration of the collection efficiency and reduction of the jet disturbance.

Calibration of Turbulent Model Constants Based on Experimental Data Assimilation: Numerical Prediction of Subsonic Jet Flow Characteristics

Experimental measurements and numerical simulations are two primary methods for studying turbulence. However, these methods often struggle to balance the accuracy and breadth of results. In order to accurately predict the flow characteristics of subsonic jet exhaust and provide a research foundation for the runway crossing operation after the takeoff point, this study utilizes the ensemble Kalman filter algorithm to recalibrate the SA turbulence model constants by integrating NASA’s experimental particle image velocimetry (PIV) data with a sample library generated using Latin hypercube sampling to obtain corresponding flow field calculations. The modified model constants effectively improve the prediction of jet flow characteristics, reducing the spatially averaged relative error along the horizontal axis behind the nozzle from 13.04% to 4.6%. This study focuses on enhancing the accuracy of numerical predictions for subsonic jet flows via the adjustment of turbulence model constants. The recalibrated model constants are then validated to improve the prediction of jet flows under various conditions. The findings have important implications for acquiring high-fidelity data on rear engine jet flows after takeoff, enabling precise determination of safety separation distances, and enhancing the operational efficiency of airports.

The counterbalance of endothelial glycocalyx and high wall shear stress to low-density lipoprotein concentration polarization in mouse ear skin arterioles

Background and aimsAtherosclerosis preferentially occurs at regions in arterial branching, curvature, and stenosis, which may be explained by the geometric predilection of low-density lipoprotein (LDL) concentration polarization that has been investigated in major arteries in previous studies. Whether this also happens in arterioles remains unknown. MethodsHerein, a radially non-uniform distribution of LDL particles and a heterogeneous endothelial glycocalyx layer in the mouse ear arterioles, as shown by fluorescein isothiocyanate labeled wheat germ agglutinin (WGA-FITC), were successfully observed by a non-invasive two-photon laser-scanning microscopy (TPLSM) technique. The stagnant film theory was applied as the fitting function to evaluate LDL concentration polarization in arterioles. ResultsThe concentration polarization rate (CPR, the ratio of the number of polarized cases to that of total cases) in the inner walls of curved and branched arterioles was 22% and 31% higher than the outer counterparts, respectively. Results from the binary logistic regression and multiple linear regression analysis showed that endothelial glycocalyx thickness increases CPR and the thickness of the concentration polarization layer (CPL). Flow field computation indicates no obvious disturbances or vortex in modeled arterioles with different geometries and the mean wall shear stress is about 7.7–9.0 Pa. ConclusionsThese findings suggest a geometric predilection of LDL concentration polarization in arterioles for the first time, and the existence of an endothelial glycocalyx, acting together with a relatively high wall shear stress in arterioles, may explain to some extent why atherosclerosis rarely occurs in these regions.

Structural and flow field analysis of an airfoil subjected to blast-impacted

The shock wave from the explosion of the munition can cause severe damage to the aircraft structure, thereby affecting the aerodynamic performance of the aircraft. This paper aims to propose a Computational Fluid Dynamics (CFD) analysis for the aerodynamic behaviour of the wing after the damage and deformation caused by the impact load. To obtain the damaged deformed wing model for CFD analysis, the explosion damage process was calculated using LS-DYNA software, and the obtained structural deformed wing model was imported into the CFD solver for flow field calculation to obtain lift, drag, and moment coefficients and lift-to-drag ratio. The lift of the damage-deformed wing model decreases due to the destruction of the pressure distribution of the damage-deformed wing model. The lift-to-drag ratio is also affected by shock loading, with smaller values at all considered angles of attack. Similarly, the damage deformed wing model has larger moment coefficients at angles of attack less than 19.5°.

Modeling Sediment Resuspension and Transport Processes Induced by Propeller Wash from Ship Traffic

Resuspension and redistribution of sediments induced by propeller wash may significantly influence aquatic ecosystems at contaminated sediment sites. This study describes a numerical modeling method developed to predict the sediment resuspension and subsequent transport processes resulting from ship traffic, with a fully coupled simulation of hydrodynamics, sediment transport, and propeller wash. By including propeller momentum effects in the flow field computation, the advection and dispersion of resuspended sediments are better represented than in previously available methods. To achieve this improvement, a computational algorithm was first developed to calculate the propeller wash effects from one or more ships (e.g., erosion rate and momentum flux); these results were then dynamically linked to a hydrodynamic and sediment transport computation using Environmental Fluid Dynamics Code Plus (EFDC+). This modeling framework was evaluated using a field experiment conducted by the US Navy. The model was calibrated with flow velocities and sediment erosion depths, and then validated with resuspended sediment concentrations in the water column. The model results reproduced the horizontal and vertical distributions of resuspended sediments better when the propeller-induced momentum was incorporated into the flow field computation. The sensitivity test indicated that the increased flow energy from propeller momentum resulted in significant dispersion of resuspended sediments in both longitudinal and lateral directions. The maximum scour was dependent on the propeller revolution speed, the ship engine power, and the distance between the propellers and the sediment bed.

Numerical and Experimental Analysis of the Cold Flow Physics of a Nonpremixed Industrial Gas Burner

Abstract The flow field of a nonpremixed industrial gas burner is analyzed with Reynolds-averaged Navier–Stokes computational fluid dynamics validated against velocity and pressure measurements. Combustion is not modeled because the aim is optimizing the predictive capabilities of the cold flow before including chemistry. The system's complex flow physics, affected by a 90 deg turn, backward and forward facing steps, and transversal jets in the mainstream is investigated at full and partial load. The sensitivity of the computed flow field to inflow boundary condition setup, approach for resolving/modeling wall-bounded flows, and turbulence closure is assessed. In the first sensitivity analysis, the inflow boundary condition is prescribed using measured total pressure or measured velocity field. In the second, boundary layers are resolved down to the wall or modeled with wall functions. In the third sensitivity analysis, the turbulence closure uses the k−ω shear stress transport eddy viscosity model or two variants of the Reynolds stress model. The agreement between the predictions of most simulation setups among themselves and with the measurements is good. For a given type of inflow condition and wall flow treatment, the ω-based Reynolds stress model gives the best agreement with measurements among the considered turbulence models at full load. At partial load, the comparison with measured data highlights some scatter in the predictions of different patterns of the flow measurements. Overall, the findings of this study provide insight into the fluid dynamics of industrial gas burners and guidelines for their simulation-based analysis.

The Ocean Surface Current in the East China Sea Computed by the Geostationary Ocean Color Imager Satellite

High-frequency observations of surface current field data over large areas and long time series are imperative for comprehending sea-air interaction and ocean dynamics. Nonetheless, neither in situ observations nor polar-orbiting satellites can fulfill the requirements necessary for such observations. In recent years, geostationary satellite data with ultra-high temporal resolution have been increasingly utilized for the computation of surface flow fields. In this paper, the surface flow field in the East China Sea is estimated using maximum cross-correlation, which is the most widely used flow field computation algorithm, based on the total suspended solids (TSS) data acquired from the Geostationary Ocean Color Imager satellite. The inversion results were compared with the modeled tidal current data and the measured tidal elevation data for verification. The results of the verification demonstrated that the mean deviation of the long semiaxis of the tidal ellipse of the inverted M2 tide is 0.0335 m/s, the mean deviation of the short semiaxis is 0.0276 m/s, and the mean deviation of the tilt angle is 6.89°. Moreover, the spatially averaged flow velocity corresponds with the observed pattern of tidal elevation changes, thus showcasing the field’s significant reliability. Afterward, we calculated the sea surface current fields in the East China Sea for the years 2013 to 2019 and created distribution maps for both climatology and seasonality. The resulting current charts provide an intuitive display of the spatial structure and seasonal variations in the East China Sea circulation. Lastly, we performed a diagnostic analysis on the surface TSS variation mechanism in the frontal zone along the Zhejiang coast, utilizing inverted flow data collected on 3 August 2013, which had a high spatial coverage and complete time series. Our analysis revealed that the intraday variation in TSS in the local surface layer was primarily influenced by tide-induced vertical mixing. The research findings of this article not only provide valuable data support for the study of local ocean dynamics but also verify the reliability of short-period surface flow inversion of high-turbidity waters near the coast using geostationary satellites.

Numerical Simulation of Ice Crystal Supercooled Droplet Mixed Phase Icing Based on the Improved Messinger Model

The ice crystal supercooled droplet mixed phase icing problem is an important research direction in aircraft icing and has received more attention in recent years. The thermodynamic process of the water film after the ice crystals impact on the surface determines the final ice shape, which is an important part of the accurate prediction of aircraft icing. In this paper, a thermodynamic model of ice crystal supercooled droplet mixed phase icing is proposed based on the extended Messinger model, according to the results of flow field and particle trajectory calculations. In this model, the mass and energy conservation equations of ice crystals, supercooled droplets, and liquid water are considered. The equations take the process of ice crystal adhesion and erosion into account, and the solution method of the equations is given. Ice shapes are calculated under various ice crystal supercooled droplet mixed phase conditions and compared with experimental results to demonstrate the validity of the numerical method. The effects of ice crystal erosion rate, melting ratio, and adhesion coefficient on the calculation results are analyzed by a numerical method. The results show that the ice crystal erosion rate has little effect on the ice shape, while a larger melting ratio and adhesion coefficient lead to more ice accretion.

Steady-State Characteristics of Spiral Groove Floating Ring Gas-film Seal Considering Temperature-Viscosity Effect

During the operation of the floating ring gas film seal, a certain amount of heat is generated inside the seal gap, giving rise to thermal deformation of the seal rings, and further leading to operation unstable and increased leakage rate. Based on the gas lubrication theory, the control equations of gas pressure and gas film thickness of the floating ring gas film seal are obtained. And the energy and temperature-viscosity equation are also introduced. The above equations were solved by the finite difference method and their correctness was verified by experiments. The variation of opening force, leakage rate, friction force, and gas film temperature rise with rotating speed, inlet pressure, and eccentricity were analyzed. The results reveal that, for leakage rate, the difference between the modeled and tested values is only 2.94% at high speeds, taking into account the influence of the temperature-viscosity effect. The experiment substantiates that the temperature-viscosity effect model is scientifically valid. Operation parameters also have different effects on sealing performance. Compared with isothermal flow, the pressure distribution in the gas film flow field will change significantly with increasing gas temperature, which means that the temperature-viscosity effect cannot be neglected in the flow field calculation. These results provide grounds for further study of the thermoelastic effect of air film seal of floating ring and have important engineering significance.

New Parent Flowfield for Streamline-Traced Intakes

The prespecified flowfield is essential in the inverse design method for generating inward-turning streamline-traced intakes, i.e., the parent flowfield. The internal conical flow C (ICFC) flowfield shows superiority over other parent flowfields in terms of performance and length. A drawback to the ICFC flowfield is the existence of the expansion zone, which creates a second reflected shock and decreases the flow uniformity. Hence, this paper proposes a new basic flowfield called the internal conical flow M (ICFM) to overcome the shortcoming of the ICFC flowfield. For the proposed basic flowfield, a new methodology has been devised for connecting the M-flow and truncated Busemann flowfields. This methodology merges the singular line of the M-flow with the truncated ray of Busemann flowfield in order to reduce the flow inclination angle difference effectively. The concept of the basic flowfield is reviewed, and the new ICFM basic flowfield is calculated using the Taylor–Maccoll equations. Complete details of the new merging procedure and calculation of the ICFM flowfield are presented. The characteristics of the new basic flowfield with design conditions of Mach 4.0, 5.0, 6.0, and 7.0 are examined at different outflow conditions. A comparison with the ICFC flowfield indicates that the new ICFM basic flowfield demonstrates better inviscid performance and a shorter length. Besides, the expansion region is significantly reduced, and the second reflected shock wave is eradicated.

Simulating airflows with a deep attention network for physical interpretability

Machine learning model offers interpretability, accuracy, and computational efficiency for flow field calculations

Multifidelity Prediction Framework with Convolutional Neural Networks Using High-Dimensional Data

This paper proposes two novel multifidelity neural network architectures developed for high-dimensional inputs such as computational flowfields. We employed a two-dimensional flow-varying transonic supercritical airfoil problem while exploring and comparing our methods with the former “multifidelity deep neural networks” from the literature. We call these novel methods “modified multifidelity deep neural networks” and “multifidelity convolutional neural networks.” The main objective of this study is to establish an advanced multifidelity prediction framework that can be applied to any computational data; however, here, we applied our methods to the prediction of aerodynamic coefficients using pressure coefficient fields around the airfoil. To generate the dataset, first, a coarse grid is employed using the SU2 Euler solver for low-fidelity data; then, a relatively finer grid is used to obtain the viscous solutions by using the Spalart–Allmaras turbulence model for the high-fidelity data. The performance metrics to compare the methods are determined as the test accuracy, the physical training time, and the size of the high-fidelity samples. The results demonstrate that the proposed multifidelity neural network architectures outperform the multifidelity deep neural networks in predictive modeling using high-dimensional inputs by improving the multifidelity prediction accuracy significantly.

Effect of Y-groove morphology on welding performance of SiCp/Al composites in powder filled laser welding

Since there is an uneven distribution of reinforcement particles in the welding process of silicon carbide particles/aluminum (SiCp/Al) composites, a detailed study on the influence of Y-groove morphology on welding performance of SiCp/Al composites in powder filled laser welding is essentially required. By optimizing the root face height and V-groove angle, modifying the filling area of the molten pool in the process of powder filled laser welding, and combining with the numerical calculation of the cross-scale molten pool flow field, the inherent law of the molten pool flow field on the influence of the welding quality is revealed in this paper. The macroscopic morphology of the weld is analyzed by a metallographic microscope, and the tensile strength of the joint is measured by a universal tensile testing machine. It is observed that under the action of Marangoni force and virtual mass force, the flow at the bottom of the molten pool is directed from the center of the weld to the periphery. Different Y-groove morphologies change the application point of virtual mass force, and then affect the flow of molten pool. At the same time, the distribution of reinforcement particles is relatively uniform and the weldment is well formed at an optimized root face height of 0.2 mm and V-groove angle as 40°. The mechanical properties of the welded joint are the optimum, reaching 70% of the base material, and the maximum strength value is 266 MPa.

An Improved Calculation Method Based on Newton–Raphson Method for Ion Flow Field of UHVDC Transmission Lines at High Altitude

The fast and accurate solution of the total electric field and ion current density is crucial for the electromagnetic environment of ultra high voltage direct current (UHVDC) transmission lines. In this article, an improved method based on Newton–Raphson method (NRM) and upstream finite element method (UFEM) is proposed to calculate the ion flow field under complex conditions. According to the gas motion theory, the corona-onset electric field, ion mobility, and recombination coefficient are obtained at high altitude and put into the ion flow field model in this article. Subsequently, the charge density is used to solve Poisson’s equation, and the current continuity equations are calculated by UFEM. After that, the charge density of the conductor surface is updated based on NRM. These three parts are iterated repeatedly until the convergence conditions are met. According to the test results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 800-kV UHVDC transmission line at high altitude, the validity and rationality of the proposed method are verified. The result demonstrates that due to the reduction of atmospheric pressure at the high altitude, the corona-onset electric field decreases, and the ion mobility and recombination coefficient increase, which makes the total electric field and ion current density at ground level increase. Compared with the traditional methods, the improved method is insensitive to the initial value of the surface charge density. Moreover, this proposed method can effectively improve the convergence ability and achieve the stable and fast calculation of the ion flow field at high altitude.

Finite-element method based solver for an evaporating sessile droplet on a heated surface

We report the development of a finite-element-based solver to compute transport of mass, momentum and energy during evaporation of a sessile droplet on a heated surface. The evaporation is assumed to be quasi-steady and diffusion-limited. The heat transfer between the droplet and substrate and mass transfer of liquid-vapor are solved using a two-way coupling. In particular, here, we develop and implement the formulation of fluid flow inside the droplet in the model. The continuity and Navier–Stokes equations are solved in axisymmetric, cylindrical coordinates. Jump velocity boundary condition is applied on the liquid–gas interface using the evaporation mass flux. The governing equations are discretized in the framework of the Galerkin weight residual approach. A mesh of finite triangular elements with six nodes is utilized, and quadratic shape functions are used to obtain the second-order accurate numerical solution. Two formulations, namely, penalty function and velocity pressure, are employed to obtain discretized equations. The numerical results are the same using both methods, and the latter is around 30–50% faster than the former for the cases of refined grid. Computed flow fields are in excellent agreement with published results. The solver’s capability is demonstrated by solving the internal flow field for a case of a heated substrate.

Applicability of WorldCover in Wind Power Engineering: Application Research of Coupled Wake Model Based on Practical Project

This paper discusses how the incorporation of high-resolution ground coverage dataset ESA WorldCover into a wind flow field and wake simulation calculation, as well as the use of the coupled wake model for wind farm output simulation, can improve the accuracy of wind resource assessment using engineering examples. In the actual case of grid-connected wind farms in central China, SCADA wind speed data is reconstructed to the free flow wind speed in front of the wind turbine impeller using the transfer function of the nacelle, and the wind farm is modeled using OpenWind software, simulating the wind speed at the height of each wind turbine hub and each wind turbine output. The results show that when other initial data are consistent, using ESA’s high-precision land cover dataset WorldCover 10 m to make roughness lengths which improves the wind farm output simulation accuracy by 8.91%, showing that it is worth trying to apply WorldCover 10 m to the wind farm simulation design. At the same time, this case is used to compare and analyze the application of the Eddy-Viscosity wake model and the two coupled wake models based on the Eddy-Viscosity wake model. The results show that the coupled wake model will have higher accuracy than the Deep Array Eddy Viscosity wake model and it is 1.24% more accurate than the Eddy Viscosity wake model, and the ASM Eddy Viscosity wake model is 5.21% more accurate than the Eddy Viscosity wake model.

A New Multi-Level Grid Multiple-Relaxation-Time Lattice Boltzmann Method with Spatial Interpolation

The traditional multi-level grid multiple-relaxation-time lattice Boltzmann method (MRT-LBM) requires interpolation calculations in time and space. It is a complex and computationally intensive process. By using the buffer technique, this paper proposes a new multi-level grid MRT-LBM which requires only spatial interpolation calculations. The proposed method uses a center point format to store multi-level grid information. The grid type determination in the flow field calculation domain is done using the axis aligned bounding box (AABB) triangle overlap test. According to the calculation characteristics of MRT-LBM, the buffer grid is proposed for the first time at the interface of different levels of grids, which is used to remove the temporal interpolation calculation and simplify the spatial interpolation calculation. The corresponding multi-level grid MRT-LBM algorithm is also presented for two-dimensional and three-dimensional flow field calculation problems. For the two-dimensional problem of flow around a circular cylinder, the simulation results show that a four-level grid MRT-LBM proposed in this paper can accurately obtain the aerodynamic coefficients and Strouhal number at different Reynolds numbers, and it has about 1/9 of the total number of grids as a single-level grid MRT-LBM and is 6.76 times faster. For the three-dimensional flow calculation problem, the numerical experiments of flow past a sphere are simulated to verify the numerical precision of the presented method at Reynolds numbers = 100, 200, 250, 300, and 1000. With the streamlines and velocity contours, it is demonstrated that the multi-level grid MRT-LBM can be calculated accurately even at the interface of different size grids.

Acoustic Model for Leak Detection of Water Supply Pipeline

The leak detection of water supply pipelines is significant for the protection of water resources. Acoustic detection is a common method used to investigate water supply pipeline leaks. Although some acoustic methods for the leak detection of the water supply pipeline have been developed experimentally, the theoretical investigation of said acoustic methods is still limited. Compared with aeroacoustics, the development of quantitative jet acoustic theory towards flow field calculations of liquid pipeline leak has not been reported, and the characteristics of the liquid flow field cannot be quantitatively transformed into the acoustic model. In this paper, the liquid pipeline leak is combined with piston acoustics, and the acoustic model for the leak detection of the water supply pipeline is quantitatively studied for the first time. The acoustic pressure value can be directly calculated using pipe and liquid parameters, and the validity of the model can be verified experimentally. Based on theoretical and experimental investigations, it is found that the leak sound pressure increases significantly with increasing pipeline pressure and decreases with increasing detection distance. The material composition of the pipes has little influence on the leak sound pressure. The theoretical values based on the proposed acoustic model and the experimental values agree well, where the maximum difference between them is 8.5% and the average difference is 2.6%. This study presents a foundation for the development of acoustic leak detection technology of the liquid pipeline.

Improving Indoor Air Ventilation by a Ceiling Fan to Mitigate Aerosols Transmission.

Improving air flow and ventilation in an indoor environment is central to mitigating the airborne transmission of aerosols. Examples include, COVID-19 or similar diseases that transmit by airborne aerosols or respiratory droplets. While there are standard guidelines for enhancing the ventilation of space, the effect of a ceiling fan on the ventilation has not been explored. Such an intervention could be critical, especially in a resource-limited setting. In the present work, we numerically study the effect of a rotating ceiling fan on indoor air ventilation using computational fluid dynamics (CFD) simulations. In particular, we employ RANS turbulence model and compare the computed flow fields for a stationary and rotating fan in an office room with a door and window. While a re-circulation zone spans the whole space for the stationary fan, stronger re-circulation zones and small stagnation zones appear in the flow-field inside the room for the case of a rotating fan. The re-circulation zones help bring in fresh air through the window and remove stale air through the door, thereby improving the ventilation rate by one order of magnitude. We briefly discuss the chances of infection by aerosols via flow-fields corresponding to stationary and rotating fans.