Two- and three-dimensional Direct Numerical Simulation of particle-laden gravity currents

Direct numerical simulation of bi-disperse particle-laden gravity currents in the channel configuration

Two-dimensional (2D) and three-dimensional (3D) numerical simulations are carried out for uniform flow past a normal flat plate with two semicircular ends to investigate the three-dimensional effects of the wake flow behind the plate. The Reynolds numbers under investigation based on the inflow velocity and the width of the plate (H) are Re= 125, 200, 250, 500, and 1000. The instantaneous vortical structures show that the three-dimensionality characterized by streamwise vortical ribs becomes obvious at Re=200. Their spatial densities increase with the increasing Re. The time-averaged drag coefficient remains almost the same from Re=500 to 1000. The relative difference of the predicted drag coefficients between 2D and 3D simulations can be up to 77%. The amplitude of the lift force obtained using 2D simulations can be up to 30 times that obtained using 3D simulations. A drag force element decomposition analysis is conducted for the results obtained using 2D and 3D simulations. It is found that although the time-averaged wake flows obtained using the 2D and 3D simulations are different, the relative difference of their contributions to the time-averaged drag coefficient is only 10% while the difference comes mainly from the contribution of the Reynolds shear stress. The three-dimensionality of the wake flow is further investigated using quadrant and the Lumley triangle analysis of the Reynolds stress. The spanwise spatial scales of the streamwise vortices are quantified using Hilbert transform along the spanwise direction. The width of the streamwise vortices is approximately 0.5–1H in the near wake region. The dependence of the spatial scales on Re is discussed.

Influence of two- and three-dimensional simulations on bubble behavior in gas–solid fluidized beds with and without immersed horizontal tubes

In spite of the importance of a detailed description of the filamentary current constriction of the IGBT during the turn-off operation that could lead to the device’s failure, there are to date no quantitative 3D simulation results of the filament growth and dynamic that can be compared with experimental results. In this paper we present 3D numerical simulations on the failure mode in the Unclamped Inductance Switching (UIS) test operation, extended to the full device area, which will be usefully compared with detailed experimental results on a large number of trench IGBT test samples. For the first time extended 3D dynamic electrothermal simulations of the whole die are made, to take into account both the electric and thermal effects of the filamentary conduction in avalanche mode. The onset of a filament growth condition for a current level just above the turnover voltage evaluated by the 3D simulations, and the area of the filament, obtained for the first time, are well in agreement with the quantitative data extracted by the experimental evaluations. Moreover, the thermal heating due to the filament formation is found to be quite independent from the current level, because it depends on the current density in the filament, rather than on the injected current. The delay time between the filament formation and the final failure time seen in the experimental results is verified to be due to the movement of the filament all around the chip surface in search of a cooler spot. The movement of the filament along the whole die area is verified for the first time by full area 3D electrothermal dynamic simulations, with times in agreement with the experimental delay between filament formation and final failure seen in all the failure reports.

There have been remarkable advances in semiconductor industry but the miniaturization of magnetic devices is progressed very slowly. So many studies are carried out overcoming the gap. To develop small size devices, proper design and property simulation of the devices are requested to spare the efforts before fabrication processes. However, there is a few of simulation studies have been reported. In this work, we fabricated thin film toroidal inductors using permalloy as a core material and measured the properties to estimate 2D and 3D simulation in the magnetic devices. The 3D simulation shows more agreeable results than the 2D simulation. On the other hand, when we changed core materials, the inductor using Fe-Hf-C-N nanocrystalline alloys as core material shows the better properties than using permalloy and Fe-Zr-C-N alloys.

The aim of the present studies is construction of reference data for the prediction of the bending of sensor hairs close to the wall in a boundary-layer flow. Three-dimensional direct numerical simulations (DNS) of finite cylinders in single and tandem configuration are carried out. The numerical setup is guided by a towing-tank experiment performed at the Technical University of Freiberg. All numerical configurations are chosen to complement and extend the experimental work. The bending curve of the cylinders is estimated by a static approach according to 1st-order Euler-Bernoulli beam theory. Based on the forces, extrapolated from the DNS of the flow field, the influence of wall- and top-end effects and Reynolds numbers between 5 and 40 is examined more deeply. Also, varying positions of cylindrical tandem configurations in stream- and spanwise directions are investigated. The present work shows good agreement between simulation and experiment.

Three-dimensional particle-resolved direct numerical simulation study of behaviors of a particle settling near a vertical wall

We used ultrasonic shear waves for nondestructive defect detection in a billet using transmitted waves. We utilized the deviation the time-of-flight (TOF) obtained by cross-correlation of transmitted waves of a defect-free reference plane and that of a measurement plane containing a defect. We compared the performance of longitudinal waves and shear waves at different wavelengths in detecting the diameter of a circular defect in two-dimensional (2D) simulation and the TOF for a cylindrical defect while changing the vibration direction of shear waves in three-dimensional (3D) simulation. Shear waves detected defects better than longitudinal waves in the 2D simulation, especially at wavelengths of 1.4–2.4 mm. In the 3D simulation, the maximum TOF was larger when the vibration direction was perpendicular to the defect’s major axis than when it was parallel in the measurement using shear waves. This suggests a defect’s shape can be estimated by measurement using shear waves.

Capsule equilibrium positions near channel center in Poiseuille flow

Previous studies on low Reynolds number quasi-2D flow around airfoils were mostly two-dimensional, with issues for stalling behavior at higher angles of attack (AOAs). In the present work, a computational study was conducted to investigate the unsteady quasi2D flow around a streamlined NASA low-speed GA(W)-1 airfoil and a corrugated dragonfly airfoil at the Reynolds numbers of 68,000 and 55,000 with both 2D and 3D simulations. These simulations were carried out by solving the unsteady 2D and 3D Navier-Stokes equations to predict the behavior of the unsteady flow structures around the airfoils at different AOAs. Extensive comparisons were made between the numerical results and wind-tunnel experimental results for the same configurations. It was found that the 2D and 3D simulations differ significantly at relatively high AOAs, and that the 3D computational results agree much better with the experimental data. It is believed that unsteady vortex-dominated flow at high angle of attack is strongly three-dimensional. As a result, the 2D simulations are not adequate in resolving the fundamental flow physics, and 3D simulations are necessary to correctly predict the flow behavior at such conditions.

Direct numerical simulation of confined weak round fountains in homogeneous ambient

Macroscopic characteristics of heavy particle resuspension obtained from direct numerical simulations of pressure driven channel flow

In this study, E-Scaffolding Enhance Learning (ESEL) using Web-based simulation has been designed and implemented. The scaffolding approach in this research is a conceptual scaffolding of the moment of inertia. Web-based simulation consists of 2D and 3D simulation. The 3D simulation was developed using unity software and 2D simulation was developed using scratch and articulate storyline software. All simulation was published as an Html file, and finally inserted into the website. The validation of the product was carried out by experts such as a physics lecturer and a physics teacher. The implementation phase was carried out through collaborative distance learning between one Senior High School in Bandung and one school in West Nusa Tenggara. The validation results show that ESEL using Web-based simulation on moment of inertia is deserved with an average score of 92% in the very good category. Nevertheless, there are several improvements still need to be made in terms of the appearance of the Web-based 3D simulation especially when it is accessed by phone cell. The appearance of the Web-based 3D simulation is still not responsive for smartphones. But based on the questionnaire result of students, ESEL using Web-based simulation on moment of inertia has a value 71% which means that ESEL has a good category of validation and is interesting for the students. ESEL using Web-based simulation also improves students’ activities in the distance learning of physics classroom.

Eddy currents in permanent magnets of synchronous machines may cause their demagnetization due to overheating. Thus eddy current analysis has been discussed widely. 3D transient analyses of eddy current losses yield most accurate results but are also performed at very high computational cost. A previously introduced more efficient 2D approach for accurate eddy current calculation is adapted in this publication for the use with interior permanent magnet machines. Instead of only considering axial eddy currents inside the magnets, radial eddy current displacement is considered by analyzing the magnets in multiple sectional planes. The computed results comply with the theoretical expectations and the results from a 3D simulation. This confirms the method's applicability as a quick and accurate alternative to costly 3D eddy current simulations.

Three-dimensional compressible simplified chemistry-based direct numerical simulations (DNS) of statistically planar turbulent stratified flames at global equivalence ratios ⟨φ⟩ = 0.7 and ⟨φ⟩ = 1.0 have been carried out to analyze the statistical behavior of the transport of the variance of the Favre fuel mass fraction fluctuations (where , and are Reynolds average, Favre mean, and Favre fluctuation of a general quantity q where ρ is the gas density) in the context of Reynolds-averaged Navier-Stokes (RANS) simulations. It has been found that algebraic expressions are inadequate for predicting in low Damköhler number combustion, and a transport equation for may need to be solved. The statistical behaviors of and the unclosed terms of the transport equation (i.e., the terms originating from turbulent transport T 1 , reaction rate T 3 , and molecular dissipation D 2) have been analyzed in detail. It has been found, that T 3 and D 2 remain leading order contributors to the transport in all cases, whereas, the contribution of T 1 remains small in ⟨φ⟩ = 1.0 cases, but plays a more important role in ⟨φ⟩ = 0.7 cases. Through an a-priori DNS analysis, the modeling of T 1, T 3, and D 2 has been addressed in detail. A model has been identified for T 1, which provides satisfactory agreement with the DNS data. The models for T 3 and D 2, which were originally proposed for high Damköhler number flames, have been modified for low Damköhler combustion in the context of RANS simulations, and the predictions of the modified models are found to be in good agreement with the corresponding quantities extracted from the DNS data.