Computation Of Three-dimensional Flows Research Articles

Computation of three-dimensional incompressible flows using high-order weighted essentially non-oscillatory finite-difference lattice Boltzmann method

In the present work, an accurate and robust solution methodology based on the high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (LBM) in the three-dimensional generalized curvilinear coordinates is presented and applied for simulating the three-dimensional incompressible flows over complicated configurations with curved boundaries. Here, the incompressible form of the lattice Boltzmann equation in three dimensions is considered and the discretization of the spatial derivative terms is performed with the fifth-order WENO finite-difference method and the temporal derivative term is discretized with the fourth-order Runge–Kutta scheme to ensure the accuracy and stability of the solution method for both the steady and unsteady problems. The three-dimensional lattice Boltzmann equation applied here is based on a nineteen discrete velocity model for transforming the microscopic properties to the macroscopic ones. To assess the accuracy and robustness of the present three-dimensional high-order finite-difference LBM solver, different incompressible flow benchmarks and practical test cases are studied that are the cavity flow, the Beltrami flow, the flow in the curved ducts of rectangular cross sections, and the flow over a sphere for different flow conditions. The decay of the homogeneous isotropic turbulence is also computed to examine the suitability of the present solution method to be applied as the direct numerical simulation of turbulent flows. It is demonstrated that the solution methodology presented based on the high-order WENO finite-difference LBM in the three-dimensional generalized curvilinear coordinate can be used for accurately and effectively computing the three-dimensional practical incompressible flow problems.

PHYSICAL AND MATHEMATICAL MODELING OF UNSTEADY COUPLED HEAT AND MASS TRANSFER IN CVD-DIAMOND WINDOWS OF THE SIBERIAN CIRCULAR PHOTON SOURCE

The results of physical and mathematical modelling in the ANSYS software package of three-dimensional unsteady coupled heat and mass transfer in the previously developed diamond vacuum window (DVW) of the workstation of the Siberian Circular Photon Source under construction are presented. Previous simulations have convincingly shown: the possibility of using a mini-channel cooling system to implement reliable and proper temperature management of this optical device, the advantage of a mini-channel cooling system over a one channel system in terms of fulfilling the optical requirements for DVW and its design. Here are detailed calculations of unsteady three-dimensional flow in the mini-channels of the cooling system, which will prevent possible dramatic destruction of the workstation due to local overheating of the CVD-diamond foil and its recrystallization.

PHYSICAL AND MATHEMATICAL MODELING OF UNSTEADY COUPLED HEAT AND MASS TRANSFER IN CVD-DIAMOND WINDOWS OF THE SIBERIAN CIRCULAR PHOTON SOURCE

The results of physical and mathematical modelling in the ANSYS software package of three-dimensional unsteady coupled heat and mass transfer in the previously developed diamond vacuum window (DVW) of the workstation of the Siberian Circular Photon Source under construction are presented. Previous simulations have convincingly shown: the possibility of using a mini-channel cooling system to implement reliable and proper temperature management of this optical device, the advantage of a mini-channel cooling system over a one channel system in terms of fulfilling the optical requirements for DVW and its design. Here are detailed calculations of unsteady three-dimensional flow in the mini-channels of the cooling system, which will prevent possible dramatic destruction of the workstation due to local overheating of the CVD-diamond foil and its recrystallization.

The Impact of Installation Angle on the Wind Load of Solar Photovoltaic Panels

In order to explore the wind load characteristics acting on solar photovoltaic panels under extreme severe weather conditions, based on the Shear Stress Transport (SST) κ-ω turbulence model, numerical calculations of three-dimensional incompressible viscous steady flow were performed for four installation angles and two extreme wind directions of the solar photovoltaic panels. The wind load characteristics on both sides of the photovoltaic panels were obtained, and the vortex structure characteristics were analyzed using the Q criterion. The results indicate that, under different installation angles, the windward side pressure of the solar photovoltaic panel is generally higher than the leeward side. The leeward side is prone to forming larger vortices, increasing the fatigue and damage risk of the material, which significantly impacts the solar photovoltaic panel. As the installation angle increases, the windward side pressure of the solar photovoltaic panel also gradually increases. Therefore, optimal installation methods include installing the panel facing the wind at angles of 30° and 45°, or installing it facing away from the wind at a 60° angle, to minimize the impact of wind load on the solar photovoltaic panel.

Optimization design of a hybrid thermal runaway propagation mitigation system for power battery module using high-dimensional surrogate models

The demand for high energy density in lithium-ion battery packs for electric vehicles poses a challenge to maintaining its optimum operating temperature while reducing the risk of thermal runaway (TR) propagation. This study proposes a novel hybrid TR propagation mitigation system that balances heat transfer and thermal insulation requirements using low and high thermal conductivity phase change materials (PCM), heat pipes (HP), and air-cooling. The design and optimization of such a mitigation system are complex due to the many design parameters involved. The Adaptive-Kriging-High dimensional model representation (Adaptive-Kriging-HDMR) is used to establish a surrogate model of the system, and the sensitivity of the system's design parameters is evaluated with the maximum battery temperature and the system weight as the targets, thereby improving the efficiency of model calculation and reducing the dimension of optimization parameters. Then, the design of the sensitive parameters is optimized using an extended elitist non‐dominated sorting genetic algorithm (E-NSGA-II) multi-objective optimization algorithm. The results show that the modeling difficulty and optimization calculation time are significantly reduced by using a surrogate model. The calculation time for a single surrogate model only takes a few seconds instead of several hours for the original three-dimensional heat transfer and flow calculation. The thermal conductivity of high thermal conductivity-PCM, the distance between battery and low thermal conductivity-PCM, the battery spacing, and the HP length significantly affect the system. The optimized system substantially reduces the overall weight of the battery system while ensuring its good heat dissipation capability. In the case of TR in a single battery, the system succeeds in limiting the TR propagation to the same row, with the maximum battery temperature in the second row being only 64.3 °C, well below the battery TR trigger point. Under more severe conditions, such as TR occurring in two batteries simultaneously, the maximum battery temperature in the second row is 155.5 °C, and no TR spreads to the adjacent row. This study provides a rapid and effective method for designing a TR propagation mitigation system. It can serve as a reference for the engineering design and optimization of battery thermal management systems.

NUMERICAL SIMULATION OF GAS FLOW PATTERNS AND CHARACTERISTICS OF A CENTRIFUGAL COMPRESSOR

The design of compressors based on one- and two-dimensional flow calculations has reached the limit of development by achieving the maximum efficiency of devices. Further development is possible by conducting expensive experiments or by analyzing the results of the modern mathematical models of three-dimensional flow calculations based on the Reynolds-averaged Navier-Stokes equations. To improve the characteristics of the centrifugal compressor and improve the flow part with the subsequent change in the shape and location of the compressor impeller blades, threedimensional flow calculations were performed. Calculations were made using the Ansys CFX software with a student license. The effect of mesh on the integral flow characteristics is analyzed. There is a qualitative coincidence of the compressor performances, as well as gas flow patterns, and separation zones with experimental data. The research uses a sectoral approach to modeling. Calculations based on different turbulence models were compared and it was found that the models based on the "k – ε" model give practically identical results. Compared with the experimental data of the compressor, the Eddy Viscosity Transport Equation turbulence model showed a significant error in determining the total-to-total polytropic efficiency, this value is underestimated by more than 7 %. Due to an increase in the mass flow rate in the compressor, the velocity in the blade diffuser increases significantly and the flow separates from the blades. Based on the comparison of Mach number contours, in addition to flow separation from the diffuser blades, flow separation from the splitter walls and impeller blades are also observed, even at low mass flow rates. The influence of the sector approach on the calculation results and the mutual location of the impeller sector and the blade diffuser sector require further research, which will be the subject of further research.

Numerical Investigation of Air Flow in Goaf While Mapping Its Flow Parameters

Recent work has presented a numerical model of a longwall ventilated by a U-system, considering the real shape of an adjacent goaf in addition to parameters characterizing the distribution of porosity and permeability. Analogous distributions are used in the two-dimensional model implemented in VentZroby software. A comparison of the results of the three-dimensional flow calculations with the two-dimensional calculations can be used to verify the simpler description and evaluate the impact of simplifications on the simulation results. Air flow calculations were carried out using the selected turbulence model. The obtained results present the possibility of conducting extensive numerical calculations for flow problems in underground mines, considering more precise descriptions and the interpretation of the calculation results carried out using a simpler description.

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.

Numerical simulation and experimental validation of an ultra-low head hydro turbine

The huge energy potential is available at ultra-low heads with high-flow rates.The cost-effective prototype hydro turbine was designed for the application at an ultra-low head site, ranging between 1 and 1.30 m. The leading and trailing edges of guide vanes are shaped to give a better aerodynamic performance in a turbulent flow. The cambered airfoil section (NACA 66 mod.) with a uniformly varying cross-section from hub to tip was selected for rotor blades. The cascade effect on the turbine's performance was studied for two different rotors having three and four identical blades. The computation of three-dimensional flow through the turbine was done using ANSYS Fluent code. The calibrated five-hole probes were used to measure absolute velocity along a radial direction at upstream and downstream of the rotor. The results of experimental tests, design and numerical simulations were plotted and compared. The cascade combination of a three-blade rotor and nine guide vanes gave optimum results. This combination at the design flow rate reduced the axial thrust on the shaft. Experimental results of three rotor blade and nine guide blade combination showed good agreement with numerical results.

Large eddy simulation on the vortex evolution in a squirrel-cage fan based on a slice computational model

To investigate the hard-to-measure complex flow in a squirrel-cage fan, a slice model was established in the present study to perform a partial large eddy simulation calculations on an r-θ sectional flow field instead of the large-scale and time-consuming full three-dimensional flow calculations. The method used to build the slice model was first introduced, and then the model was verified by the results obtained by other models and flow measurements. It is shown that to calculated the correct flow field and detailed vortex evolution, the Courant number of the slice model should be below 1, and the model thickness should be at least 2.4% of the impeller outer diameter. Through this simplified model, vortex evolutions rarely observed in other studies were successfully captured, such as vortex shedding caused by leading-edge separation, periodic backflow in the blade cascade, and vortex cluster traveling across the impeller. The flow separations were also illustrated on the inner surface of the volute tongue, accompanied by tiny and high-frequency eddies. The evolution process and frequency characteristics of these flow patterns were analyzed in detail, providing references for the design and noise reduction of this type of fan.

Flow modulation and heat transport of radiatively heated particles settling in Rayleigh–Bénard convection

We investigate the effect of radiatively heated solid particles settling in Rayleigh–Bénard turbulent flow. Three-dimensional fluid flow computations were performed using direct numerical simulation, while the evolution of particle temperature, velocities, and positions are obtained by Lagrangian particle tracking. We consider particles whose diameters vary form 20 µm to 80 µm subject to thermal radiation and settle in Rayleigh–Bénard cell at Rayleigh number Ra=2×106. The results show that the sedimentation behaviors of the particles with different particle sizes are significantly different, and the trajectories of small particles are very chaotic compared to those of large particles. Consequently, small particles can absorb solar energy efficiently and result in gas temperature increase. As the particle size decreases, the thickness of the upper boundary layer becomes thinner, while the thickness of the lower boundary layer becomes thicker. The Nusselt number varies monotonically with a logarithmic function with the diameter of the particle on both the upper and lower walls.

Nonlinear simulation of mucociliary clearance: A three- dimensional study

In this study three-dimensional (3D) numerical simulation of mucociliary clearance from the lung has been studied. The major thrust of this investigation is 3D simulation of mucociliary clearance accounting for non-linear viscoelastic characteristics of the mucus layer which is one of the most complex fluids in our body. Using a numerical code, three-dimensional unsteady flow computations have been carried out to study ciliary motion in a two-layer fluid model of the (bronchial) airway surface liquid (ASL) consisting of a Newtonian lower periciliary layer (PCL) and a nonlinear viscoelastic upper mucus layer. The projection finite difference method is used to solve the governing and constitutive equations on a staggered Eulerian grid. The immersed boundary method (IBM) is also employed to study the effect of cilia propulsive force on the fluid flow. The 5-mode nonlinear Giesekus model has been used as the constitutive equation of mucus which is characterized by nonlinear (non-Newtonian viscosity) properties. Numerical results have been devoted to study the effect of various parameters such as cilia beat frequency, cilia length as well as PCL and mucus depth on mucociliary clearance. The present 3D model shows very good agreement with previous experimental studies, while ca. 2.5-fold larger clearance rates were found for 2D models. 3D results show that cilia beating frequency and cilia length are the most critical factors affecting mucociliary clearance, while PCL depth and mucus depth have little and intermediate effect on mucus flow and hence clearance rate respectively.

Double-Ducted Fan as an Effective Lip Separation Control Concept for Vertical-Takeoff-and-Landing Vehicles

This paper describes a novel inlet flow conditioning concept that significantly improves ducted fans’ performance and controllability. High angle-of-attack operation of ducted fans is very common in vertical-takeoff-and-landing systems. The new concept named double-ducted fan (DDF) uses a secondary shroud to control inlet lip-separation-related momentum deficit at the inlet of the fan rotor during edgewise flight. The DDF is helpful in a wide edgewise flight velocity range, and its corrective aerodynamic effect becomes more pronounced with increasing flight velocity. A conventional baseline duct operating at 90 deg angle of attack is compared to other novel double-ducted fan designs via three-dimensional, viscous, and turbulent flow computations. A custom actuator-disk model replaces the zonal computation of the complex and three-dimensional rotor flowfield in the rotating frame of reference. Both hover and edgewise flight conditions are considered around the ducted fan unit and inside the ducts. Significant improvements from several novel ducted fan designs are in the areas of vertical thrust enhancement, nose-up pitching moment reduction, and recovery of fan through-flow mass flow rate in a wide horizontal flight range. A variable DDF design, a partial DDF design, and a fan-in-wing implementation of the DDF are introduced.

Compact High-Order Gas-Kinetic Scheme for Three-Dimensional Flow Simulations

A third-order compact gas-kinetic scheme is proposed for three-dimensional compressible flow computations. The new scheme is based on three key ingredients: the time-accurate gas evolution model for interface flux, the Hermite weighted essentially nonoscillatory reconstruction, and the two-stage temporal discretization. In contrast to the Riemann-solver-based methods, due to the use of time-accurate flux function the proposed scheme can achieve a third-order temporal accuracy with two stages instead of three stages in the standard Runge–Kutta method. As an extension of the existing high-order reconstructions, a Hermite weighted essentially nonoscillatory reconstruction is specifically designed for the current scheme with the implementation of the constrained least-square technique, which subsequently improves the accuracy and robustness of the compact scheme. There is no trouble cell identification in the current scheme. A third-order accuracy can be achieved even with curved boundary. Numerical examples for both smooth and discontinuous flows show the robustness and high accuracy of the compact third-order scheme, which has a comparable performance as the fifth-order noncompact gas-kinetic scheme. A large Courant–Friedrichs–Lewy number around 0.5 can be used in the computations.

3D numerical investigations of the swirling flow in a straight diffuser for the variable speed values of the rotor obtained with a magneto-rheological brake

The self-induced instabilities developed in decelerated swirling flows lead to pressure fluctuations. The swirling flows generated under variable speeds of the rotor of a swirl generator using a magneto-rheological brake are numerically and experimentally investigated. Three-dimensional turbulent flow computation is performed for several rotor speeds. Two mean velocity components numerically computed are validated against LDV data on a survey axis located downstream to the rotor for two speed values. The torque on the rotor blade is examined for several speeds. The numerical results are checked against the design values to identify the benefits and limitations of the concepts applied to the design stage. The flux of moment of momentum is modified when the rotor speed is slow down. The circulation, the total pressure and the swirl free velocity are examined on a cross section located downstream to the rotor for all investigated speeds. As a result, the changes of the hydrodynamic flow field are quantified. The unsteady pressure measured on the cone wall at four levels is acquired. The Fourier spectra associated with different self-induced instabilities developed in the cone are examined revealing the distribution of both plunging and rotating components. A low frequency plunging component in a straight diffuser is determined on a speed range of the rotor.

Research on 3D Hydrodynamic Model Based on Adaptive Mesh

In this paper, a three-dimensional hydrodynamic model based on adaptive mesh was established. The cubic mesh based on octree structure was adopted to solve the three-dimensional Navier-Stokes equation by the step-by-step pressure decomposition method, which realized the automatically encryption and coarsening of the grid. The calculation of three-dimensional square cavity flow showed that the calculation results of this model are in perfect agreement with those of Chen, and the calculation accuracy is high. Through the calculation of three-dimensional flow around a cylinder, the model can automatically encrypt the grid near the complex boundary, and can refine and coarsen the grid reasonably through the vorticity field. Meanwhile, it can also reduce the calculation amount and improve the calculation speed while maintaining the calculation accuracy.

Implications of hydrodynamics on the design of pulsed sieve-plate extraction columns: A one-fluid multiphase CFD model using the volume of fluid method

Presented is a detailed assessment of dispersive mixing and turbulence characterisation of an industrially representative pulsed sieve-plate extraction column (PSEC) obtained using multiphase CFD modelling. The system consists of a 150 mm diameter column with two perforated plates dispersing a 30 vol% dodecane/tributyl phosphate mixture in 3 M nitric acid. Operational conditions were chosen to examine pseudo steady-state dispersion regime operation. Three-dimensional transient flow calculations were performed using large eddy simulation (LES), coupled with the volume of fluid method. This study finds that LES is effective at capturing the different scales of turbulence present within PSECs, and their operational influence. Explicit analysis of the hydrodynamics established that the sieve-plates drive dispersive mixing through their influence on the resulting turbulent flow and flow structures. Furthermore, the standard round-hole sieve-plate design is found to perform poorly at producing and distributing the types of flow and turbulence beneficial to droplet size reduction.

Physics driven real-time blood flow simulations

Predictive modeling of blood flow and pressure have numerous applications ranging from non-invasive assessment of functional significance of disease to planning invasive procedures. While several such predictive modeling techniques have been proposed, their use in the clinic has been limited due in part to the significant time required to perform virtual interventions and compute the resultant changes in hemodynamic conditions. We propose a fast hemodynamic assessment method to aid in interventional planning based on first constructing an exploration space of geometries, tailored to each patient, and subsequently building a physics driven reduced order model in this space. We demonstrate that this method can predict fractional flow reserve derived from coronary computed tomography angiography in response to changes to a patient-specific lumen geometry in real time while achieving high accuracy when compared to computational fluid dynamics simulations. We validated this method on over 1300 patients that received a coronary CT scan and demonstrated a correlation coefficient of 0.98 with an error of 0.005±0.015 (95% CI: (-0.020, 0.031)) as compared to three-dimensional blood flow calculations. This technology is implemented in a product that has received clearance by the U.S. Food and Drug Administration and is being used clinically to enable physicians to predict changes in blood flow resulting from removal of coronary stenoses as might occur with percutaneous coronary interventions. This technology is also cleared for use in Japan and pending regulatory approval in Europe.

Heating modes and design optimization of cogeneration steam turbines of powerful units of combined heat and power plant

An important scientific and technical problem of increasing the efficiency of CHP steam turbine units through the optimization of their operation modes and the creation of new highly efficient flow parts of cogenerating turbines is solved. Solutions to the problem of rational distribution of heat loads between the network heaters of cogeneration turbines during the heating period are presented. The calculations were performed using the software package SCAT which was developed in IPMach NAS of Ukraine. The carrying out of calculations of three-dimensional turbulent flows in flow parts of turbines using modern software systems is an effective direction of increased efficiency of power equipment. For the numerical research of three-dimensional currents, steam in the flow part of the steam turbine software package IPMFlow which is developed in IPMach NAS of Ukraine is used. With the use of software package IPMFlow, the researches of three-dimensional currents steam in the flow part of the medium pressure cylinder of the steam turbine of series T-100-130 are carried, which showed the feasibility of optimizing the geometry of the flow part in order to improve gas-dynamic characteristics of blades apparatuses.

Features of numerical simulation of the unsteady vortex flow around aircraft considering airbrake

The paper presented the specifics of calculating the characteristics of vortex propagation and decay processes which cause aerodynamic tail fin-buffet loads in an aircraft at incompressible subsonic flow. Analysis of numerical diffusion and stability of differencing schemes implemented in OpenFOAM software package has been carried out. Based on the obtained results, differencing schemes are selected and their modification has been done. An algorithm has been presented for combining various approaches for modelling turbulent flows (RANS-LES) by means of zonal isolation and its implementation in OpenFOAM package is carried out. A series of calculations of three-dimensional flow around an aircraft at angles of attack of 0 to 30 degree considering airbrake deflections on 60 degree are conducted. Flow separation at the airbrake side edges and upper edge result in a highly turbulent wake. The corresponding region of vortex flow affects the fin and causes buffet loads.