Numerical Simulation Of Oscillatory Flow Research Articles

Numerical simulation of oscillatory flow and heat transfer in pulsating heat pipes with multi-turns using OpenFOAM

The oscillatory flow and the heat transfer in two-dimensional pulsating heat pipes (PHPs) with multi-turns were simulated using OpenFOAM. The volume of fluid method was used for the phase change, and the behavior of the working fluid was achieved by considering the mass transfer balance between the evaporation and the condensation. Ethanol was used as the working fluid, and the liquid phase and the vapor phase were assumed to be incompressible. The result revealed that the temperature variation curves did not converge to one pattern according to the number of grids in the symmetric shape of the PHP because the starting time of the working fluid circulation was different. In the PHP with the asymmetric shape, the circulation started earlier than in the PHP with symmetric shape. When the bond number was 0, which means being in zero gravity, the working fluid dried out in the evaporator section of the PHPs with 5 and 10 turns. However, the working fluid still remained in the PHPs with 15 and 20 turns. The numerical analysis performed in this article is expected to help to simulate the flow phenomenon in PHP.

Direct Numerical Simulation of Oscillatory Flow Over a Wavy, Rough, and Permeable Bottom

AbstractThe results of a direct numerical simulation of oscillatory flow over a wavy bottom composed of different layers of spherical particles are described. The amplitude of wavy bottom is much smaller in scale than typical bed forms such as sand ripples. The spherical particles are packed in such a way to reproduce a bottom profile observed during an experiment conducted in a laboratory flow tunnel with well‐sorted coarse sand. The amplitude and period of the external forcing flow as well as the size of the particles are set equal to the experimental values and the computed velocity field is compared with the measured velocity profiles. The direct numerical simulation allows for the evaluation of quantities, which are difficult to measure in a laboratory experiment (e.g., vorticity, seepage flow velocity, and hydrodynamic force acting on sediment particles). In particular, attention is focused on the coherent vortex structures generated by the vorticity shed by both the spherical particles and the bottom waviness. Results show that the wavy bottom triggers transition to turbulence. Moreover, the forces acting on the spherical particles are computed to investigate the mechanisms through which they are possibly mobilized by the oscillatory flow. It was found that forces capable of mobilizing surface particles are strongly correlated with the particle position above the mean bed elevation and the passage of coherent vortices above them.

Numerical simulation of oscillatory flow around submarine pipelines

Kazeminezhad, M.H., 2013. Numerical simulation of oscillatory flow around submarine pipelinesSubmarine pipelines, which often installed over seabed without any protection, are widely used to transport products from one location to another. In shallow water regions, the pipelines are affected severely by the wave-induced oscillatory motion. In this study a numerical model is presented to simulate the flow pattern around pipeline exposed to the oscillatory flow. The flow hydrodynamics is described via the solution of the Reynolds-Averaged-Navier-Stokes equations with a k-ϵ turbulence closure model. The numerical model is employed to describe the flow pattern, vortex shedding, gap flow prevailed below the pipe and hydrodynamic forces in oscillatory flow condition. Then, the flow velocity in the gap beneath pipe is discussed for different gap to diameter ratios in both unidirectional and oscillatory flow conditions. Results indicated that the k-ϵ turbulence closure model is capable of simulating the vortex shedding behind the pipe in oscillatory flow condition. It is also indicated that for the oscillatory flow case (KC=7, Re=9500), the maximum velocity of the gap flow increases with decreasing the gap between pipe and bed surfaces. By contrast, in the steady current case (Re=9500), the maximum velocity of the gap flow slightly decreases with decreasing the gap. In oscillatory flow conditions, a phase-lag between the gap flow and free-stream flow was found, especially for the small gap ratios. The relative maximum flow velocity between pipe and bed surfaces (umax gap/um) decreases as the Keulegan-Carpenter number increases. According to the obtained results, the maximum velocity of the gap flow in oscillatory flow conditions is higher than that of the steady currents.

Three-dimensional numerical simulation of oscillatory flow around a circular cylinder at right and oblique attacks

Sinusoidal oscillatory flow around a circular cylinder at right and oblique attacks is investigated by three-dimensional numerical simulation. Calculations are carried out for oblique angles of α=0°, 15°, 30°, 45° and 60°, Reynolds number of 2000 and KC numbers ranging from 6.75 to 30. The oblique angle of α=0° corresponds to the right attack case. The predicted vortex shedding regimes for α=0° agree well with those found in physical experiments. It is found from the numerical simulations that when KC number is in the middle range of a vortex shedding regime (i.e. KC=10, 13, 17.5 and 26.2), the flow is in single mode. In each single mode, the number of vortices shed in each flow period is constant and the sectional hydrodynamic force in the cross-flow direction fluctuates at a unique frequency. As the KC number is close to the boundary between two vortex shedding regimes ( KC=6.75, 15, 20 and 30), the number of vortices shed from the cylinder varies from period to period and the time series of the transverse force contains more than one predominant frequencies, implying the flow switching from one mode to another. This flow mode is referred to as multi-modes. The spanwise correlation factor obtained according to the sectional transverse force is close to 1 for single-mode flows. The correlation length of multi-mode flows depends on the KC number and is generally smaller than that of single-mode flows. Comparison between the numerical results of α=0° and those of α>0° shows that the independent principle is applicable for the calculated KC number range and the oblique angle ( α≤45°). For α=60°, the maximum lift coefficient C L , max and mode-averaged lift force have distinct difference from their counterparts for α=0°.

Simulation of oscillatory flow in an aortic bifurcation using FVM and FEM: A comparative study of implementation strategies

AbstractCardiovascular diseases are one of the major causes of long‐term morbidity and mortality in human beings. The nearly epidemic increase in prevalence of such diseases poses a serious threat to public health and calls for efficient methods of diagnosis and treatment. Non‐invasive diagnostic procedures such as MRI are often used in this context; however, these are limited in terms of spatial and temporal resolution and do not provide information on time‐dependent pressures and wall shear stresses—key quantities considered to be partially responsible for the formation and development of related pathologies.The present study is concerned with the numerical simulation of oscillatory flow through the abdominal aortic bifurcation. Computational fluid dynamics simulation of oscillatory flow in a branched geometry at high Reynolds numbers poses considerable challenges. The present study reports a detailed comparison of simulations performed with a finite volume and a finite element method, two approaches with significant differences in their discretization strategy, treatment of boundary conditions and other numerical aspects. Both solvers were parallelized, using loop parallelization of the BiCGStab linear solver for the finite volume and domain decomposition based on the Schur complement method for the finite element technique. The experience gained with these two approaches for the solution of flow in a bifurcation forms the focus of this study. Although similar results were obtained for both methods, the computation time required for convergence was found to be significantly smaller for the finite element approach. Copyright © 2010 John Wiley & Sons, Ltd.

Direct numerical simulation of oscillatory flow around a circular cylinder at low Keulegan–Carpenter number

The Honji instability is studied using direct numerical simulations of sinusoidal oscillatory flow around a circular cylinder. The three-dimensional Navier–Stokes equations are solved by a finite element method at a relatively small value of the Keulegan–Carpenter numberKC. The generation and subsequent development of Honji vortices are discussed over a range of frequency parameters by means of flow visualization. It is found that the spacing between Honji vortices is only weakly dependent on the frequency of oscillation, but is strongly correlated toKCbecause it is the terms within the governing equation containingKCthat dominate the three-dimensional features of the flow. An empirical relationship betweenKCand the spacing between neighbouring vortices is proposed. The three-dimensional steady streaming structure within the vortices is identified and it is found that at high frequencies the steady streaming is two-dimensional although the instantaneous flow structure is itself fully three-dimensional.

422 拡張・収縮変形を伴う細気道網モデル内振動流の数値シミュレーション(OS3-2:肺・気道のメカニクス,オーガナイズドセッション3:肺・気道のメカニクス)

422 拡張・収縮変形を伴う細気道網モデル内振動流の数値シミュレーション(OS3-2:肺・気道のメカニクス,オーガナイズドセッション3:肺・気道のメカニクス)

519 渦法を用いた円柱まわりの振動流解析(OS.2-4)(オーガナイズドセッション : 振動現象と振動・音響制御をみる)

519 渦法を用いた円柱まわりの振動流解析(OS.2-4)(オーガナイズドセッション : 振動現象と振動・音響制御をみる)

Numerical simulation of oscillatory flow in melt during InSb single crystal growth by RF heating Czochralski method

Oscillatory flow present in the melt during InSb single crystal growth using an RF-heating Czochralski method has been numerically investigated by means of the finite difference method using the HSMAC algorithm. The thermal boundary conditions required for the numerical simulation model were obtained experimentally by measuring the temperature profile along the crucible of a Czochralski system by means of thermocouples mounted in the crucible. Results of numerical simulations showed that the use of a third-order upwind discretization scheme was necessary to catch the oscillatory behaviour of the fluid flow in the melt. It was shown that this oscillatory behaviour strongly depends on the crystal rotation rate. Indeed, the oscillation period increases when the crystal rotation rate is above a critical rotation rate. In order to avoid such oscillations, crystal rotation rates lower than this critical value of crystal rotation rate must be selected for the growth of high quality crystals free of striations. © 1998 John Wiley & Sons, Ltd.