Wyniki wyszukiwania - BazTech

1

Numerical simulation of channel flow over a skewed equilateral cavity

Kamel Abanoub G., Haraz Eman H., Hanna Sarwat N.

Journal of Applied Mathematics and Computational Mechanics

|

2020

|

Vol. 19, nr 3

29--43

EN

In this paper, an incompressible, two-dimensional (2D), time-dependent, Newtonian, laminar, and internal channel fluid flow over a skewed equilateral cavity is simulated using the finite difference method (FDM) and alternating direction implicit (ADI) technique. Navier-Stokes equations are solved numerically in stream function-vorticity formulation. The goal of tackling this problem depends on its academic significance by studying the difference between lid-driven and shear-driven cavity flows in terms of the formation of Moffatt eddies at the sharp corner, also to obtain the length and intensity ratios of these counter-rotating vortices. The value of velocity components along the centerlines of the skewed cavity was revealed at low and intermediate Reynolds numbers (Re), typically (Re = 200 and 2000) at two different skew angles of mainly 30° and 45°. Likewise, the blocked-off regions’ method is used to deal with the geometry of the skewed cavity especially the sharp corners. Furthermore, as Re increases, the main vortex approaches the skewed cavity center and the counter-rotating vortices get bigger in size and intensity, and their number increases.

2

Homotopy simulation of non-Newtonian Spriggs fluid flow over a flat plate with oscillating motion

Ray A. K., Vasu B., Gorla R. S. R.

International Journal of Applied Mechanics and Engineering

|

2019

|

Vol. 24, no. 2

359--385

EN

An incompressible flow of a non-Newtonian Spriggs fluid over an unsteady oscillating plate is investigated using the Homotopy Analysis Method (HAM). An analytic solution of sine and cosine oscillations of the plate has been obtained. The similarity transformation is introduced to reduce the governing partial differentia equations into a single non-linear dimensionless partial differential equation. The effects of the power index of Spriggs fluid and convergence control parameter of HAM for the flow are studied extensively. The range of the convergence control parameter for convergence of series solution for different values of the power index of Spriggs fluid is obtained. The solution for a Spriggs fluid is noticeably different from the solution obtained for a Newtonian fluid. The influences of the shear thinning and shear thickening fluid on the velocity profile are shown graphically. The transient flow effect is higher for non-Newtonian Spriggs fluid than that of a Newtonian fluid. It is also observed that the interval to reach the steady state for the cosine case is less than the sine case. The applications of Stokes’ second problem have been widely found in the variety of fields of biomedical, medical, chemical, micro and nanotechnology.

3

Investigation of thermal mixing in the control rod top tube using large eddy simulations

Pegonen R., Edh N., Angele K., Anglart H.

Journal of Power Technologies

|

2014

|

Vol. 94, nr 1

67--78

EN

Thermal mixing and thermal fatigue has led to component failures in the nuclear industry. The thermal fatigue phenomenon is intimately linked with the mixing of streams of different temperatures in proximity to a solid wall. Due to conjugate heat transfer, temperature fluctuations are induced in the wall. One of the key issues is to predict the amplitude and the frequency of the fluctuations. This paper presents pre-calculations of the thermal mixing experiments that are under preparation at the KTH Royal Institute of Technology as part of the THEMFE project (Thermal Mixing and Fatigue Experiment). The proposed geometry is a simplification of a reactor control rod and consists of a top-tube and control rod stem, which are modeled as concentric cylinders. In addition there are only two hot inlet jets and two cold inlet jets, whereas in reality there are 8 upper inlets and 4 lower inlets for hot bypass water and the cold flow is annular. Thermal mixing was studied by using a transient Computational Fluid Dynamics (CFD) solver for the incompressible filtered Navier-Stokes equations and employing a Large Eddy Simulation model of turbulence implemented in OpenFOAM. The aim was to verify that the proposed simplified geometry and the flow conditions of the experiment will lead to low frequent temperature fluctuations of the order of 0.1-1 Hz, as seen in previous experiments with the real geometry. Such low frequencies are typical for the thermal fatigue phenomenon. The study was focused on the region near the control rod stem and therefore a refined grid was used in that region. The final mesh consisted of over one million cells. The results did indeed reveal low frequent temperature fluctuations in the lower part of the mixing region near the control rod stem. The results of this paper indicate that the length of the mixing region is 23 cm, which is large enough to be resolved in the experiment. It was also found that the most dangerous region, where the dominant high amplitude temperature fluctuations have a frequency of the order of 0.1 Hz, is 4 cm long. As expected, the instant flow field is asymmetric with large secondary flows. The present results verify that the proposed geometry and flow conditions can be applied in the experiment.

4

Incompressible SPH Model for Simulating Violent Free-Surface Fluid Flows

Staroszczyk R.

Archives of Hydro-Engineering and Environmental Mechanics

|

2014

|

Vol. 61, nr 1-2

61--83

EN

In this paper the problem of transient gravitational wave propagation in a viscous incompressible fluid is considered, with a focus on flows with fast-moving free surfaces. The governing equations of the problem are solved by the smoothed particle hydrodynamics method (SPH). In order to impose the incompressibility constraint on the fluid motion, the so-called projection method is applied in which the discrete SPH equations are integrated in time by using a fractional-step technique. Numerical performance of the proposed model has been assessed by comparing its results with experimental data and with results obtained by a standard (weakly compressible) version of the SPH approach. For this purpose, a plane dam-break flow problem is simulated, in order to investigate the formation and propagation of a wave generated by a sudden collapse of a water column initially contained in a rectangular tank, as well as the impact of such a wave on a rigid vertical wall. The results of simulations show the evolution of the free surface of water, the variation of velocity and pressure fields in the fluid, and the time history of pressures exerted by an impacting wave on a wall.

5

Towards using adaptive hybrid meshes in FEM simulations of flow in artificial heart chambers

Banaś K., Cybułka P., Macioł P., Michalik K., Płaszewski P.

Computer Methods in Materials Science

|

2011

|

Vol. 11, No. 1

190-195

EN

The paper presents an implementation and the performance of adaptive hybrid meshes in FEM code designed for 3D simulations of flow in artificial heart chambers. Special emphasis is put on taking into account moving parts of artificial heart chambers, like valves.

PL

Artykuł przedstawia zasady wykorzystania adaptacyjnych siatek hybrydowych w programie do trójwymiarowych obliczeń metodą elementów skończonych, zaprojektowanym do symulacji przepływu w sztucznych komorach serca. Szczególny nacisk został położony na uwzględnienie ruchomych części siatki występujących w sztucznym sercu, takich jak np.: zastawki. W celu poprawnego modelowania rozważanych zagadnień zostało opracowane specjalne sformułowanie słabe dla problemów z przemieszczającym się brzegiem, jak również algorytmy do poprawnego zarządzania przemieszczającą się siatką, w tym m.in. do remeshingu.

6

Incompressible flow of electrically conductive medium in timevariable magnetic field solved in monolithic formulation

Doleżel I., Dubcova L.

Przegląd Elektrotechniczny

|

2010

|

R. 86, nr 12

32-35

EN

Incompressible flow of electrically conductive medium driven by time-variable magnetic field in an axisymmetric channel is modeled. Numerical solution of the model is carried out by a higher-order finite element method in the monolithic formulation by our own code Hermes.

PL

W artykule modelowany jest nieściśliwy przepływ cieczy elektrycznie przewodzącej wywołany polem magnetycznym zmiennym w czasie. Rozwiązanie numeryczne wykorzystuje metodę elementów skończonych wyższych rzędów w sformułowaniu monolitycznym przy użyciu własnego kodu Hermes.

7

The quality of numerical modelling of the flow around two buildings with different heights

Błazik-Borowa E.

Computer Assisted Mechanics and Engineering Sciences

|

2009

|

Vol. 16, No. 3/4

309-319

EN

The paper is devoted to the problems with ąuality of numerical modeling for two-dimensional incompressible flow around two models of buildings with different heights. The calculations have been made with use of the turbulence model k - e in the standard version and with the Finite Volume Method. The quality evaluation for the calculation is based on the comparison of the results with measurements in a wind tunnel. Hence, in this paper there have been presented the graphs of averaged velocities which are results of author's own measurements, as well as the graphs presenting the error in the calculated flow velocities. The main conclusion drawn from the research is that the flow around two models is more complicated than the flow around the single one and therefore the calculation results for the set of models are less accurate in comparison with the ones obtained for the single model.

8

Central limit theorem for a Gaussian incompressible flow with additional Brownian noise

Miernowski T.

Probability and Mathematical Statistics

|

2003

|

Vol. 23, Fasc. 2

413--434

EN

We generalize the result of Komorowski and Papanicolaou published in [7]. We consider the solution of stochastic differential equation dX (t) = V (t, X(t)) dt + √2κdB(t), where B(t) is a standard d-dimensional Brownian motion and V (t, x), (t, x) ∈ R × Rd, is a d-dimensional, incompressible, stationary, random Gaussian field decorrelating in finite time. We prove that the weak limit as ε ↓ 0 of the family of rescaled processes Xε(t) = εX(t/ε2) exists and may be identified as a certain Brownian motion.

9

Steady 3D incompressible flow analysis for the simplified train-tunnel interaction

Kim S, Soni B. K.

Computer Assisted Mechanics and Engineering Sciences

|

2000

|

Vol. 7, No. 1

23-37

EN

This paper describes the phenomena that occur when a simplified model of train interacts with the tunnel at three locations - before, entering and leaving the tunnel. The Navier-Stokes equation is solved by introducing the artificial compressibility to change the governing equation type from the elliptic to hyperbolic. The Baldwin-Lomax turbulence modeling is employed to simulate the flow field with a Reynolds number of 10^6, and the computation domain is divided into three blocks considering the train and tunnel geometries. The grid is algebraically adapted determining the maximum solution change plane and solution weighting factors. The pressure in the adapted solution is not changed much, however, the skin friction is severely varied comparing with those of the non-adapted solutions. When the train enters into the tunnel, there are large increase in the surface pressure and skin friction distribution on the train surface.

10

Multiblock parallel computation of an incompressible 3-D flow in turbomachines

Papierski A., Rabiega M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

1999

|

Vol. 3, No 1

39-52

EN

A finite volume numerical method for the prediction of a fluid flow in complex geometries such as turbomachinery channels has been parallelized using a domain decomposition approach. A mathematical formulation of a 3-D incompressible steady flow has been presented on the basis of the N-S equations in a grid-oriented co-ordinate system with contravariant velocity components. A parallelized pressure-based implicit algorithm with discretization on a staggered grid has been developed. A message exchange system with a boundary exchange, developed by the authors, has been described. Exemplary calculations have been carried out for a laminar flow through a curved duct and for an inviscid flow through a stage of the centrifugal pump. A good agreement has been obtained in both the cases. Despite considerable simplification that has been introduced in the flow through the pump stage, the computations have shown nearly the same pressure rise in the stage as the measurements. Further directions of numerical investigations of a flow through turbomachines, including in particular those devoted to pressure losses related to the rotor-stator interaction, have been mentioned.

11

Numerical solution for laminar unsteady flow about fixed and oscillating cylinders

Baranyi L., Shirakashi M.

Computer Assisted Mechanics and Engineering Sciences

|

1999

|

Vol. 6, No. 3-4

263-277

EN

This paper presents a finite-difference solution of two-dimensional, time dependent incompressible Navier-Stokes equations for laminar flow about fixed and oscillating cylinders placed in an otherwise uniform flow. Using boundary fitted coordinates, the equations are transformed to a non-inertial reference frame fixed to the cylinder. The primitive variable formulation is used for the solution of the problem. A special transformation provides a fine grid scale near the cylinder walls and a coarse grid in the far field. Forward difference is used in time, fourth order central difference in space exept for convective terms for which a modified third-order upwind scheme is used. Velocity values are obtained explicitly , and the successive vortex shedding values were compared with experimental results for rigid cylinders and a very good agreement has been obtained. Amplitude bounds of locked-in vortex shedding due to forced crossflow oscilation of a circular cylinder are also determined for Re = 180.