# 3D flow on a 2-D cartesian grid

 Register Blogs Members List Search Today's Posts Mark Forums Read

 February 10, 2008, 11:36 3D flow on a 2-D cartesian grid #1 jinwon park Guest   Posts: n/a Currently, I need to solve a real 3-D compressible flow induced by explosions. Since 3-D simulations are costly, I hope that a reduced 2-D one(or somewhat else) can solve such complex real flows. Could anyone give insights to enhance computing cost? In the literature, people used 2-D axisymmetric model but I thought this is not applicable to mine where a spherical gas bubble is initially embedded on a grid. I could not believe they obtained physically acceptable results. Can anyone explain the way to solve 3-D real flows on a 2D grid? Thanks in advance.

 February 10, 2008, 15:56 Re: 3D flow on a 2-D cartesian grid #2 otd Guest   Posts: n/a Whether 2D axisymmetric is reasonable or not depends the problem - at least that's my first thought. If the charge is small relative to the problem size/time of interest, you might treat it as a point source of mass and momentum at ignition. If you have a 'torpedo' (cylinder) of explosive, such as might be used in an underground well bore hole to fracture the stratum and release oil or natural gas, treat it as a line source on the axis of the bore hore. An above-ground (point charge) explosion might be axisymmetric if the ground is flat. Shocks would (be assumed to) reflect from the ground in axisymmetric fashion about a vertical axis passing through the initial location of the charge. After these more-or-less obvious cases, 3D perhaps becomes more necessary. What configuration are you considering?

 February 10, 2008, 17:51 Re: 3D flow on a 2-D cartesian grid #3 jinwon park Guest   Posts: n/a I am considering the case where a charge is placed above the plate. The charge is usually a spherical-shape charge. If we consider axisymmetric configurations, it might not be right.

 February 10, 2008, 19:54 Re: 3D flow on a 2-D cartesian grid #4 Ananda Himansu Guest   Posts: n/a Every spherically symmetric 3-D solution is also axisymmetric. It is axisymmetric about every axis passing through the center of spherical symmetry. The introduction of an infinite plate will eliminate the spherical symmetry, but the solution should still be axisymmetric about an axis passing through the center of the spherical charge and perpendicular to the plate.

 February 10, 2008, 20:10 Re: 3D flow on a 2-D cartesian grid #5 jinwon park Guest   Posts: n/a Based on my experience, it is not since axisymmetric flows are symmetry only against one axis. So, if one sets a circle which is identical to a spherical charge in 2-D, it represents a tube in real 3-dimensions. Could you make sure me what you mentioned before? Thanks in advance!

 February 11, 2008, 01:27 Re: 3D flow on a 2-D cartesian grid #6 Hafidz Guest   Posts: n/a unless the symmetrical axis runs right through the sphere... Hafidz

 February 11, 2008, 05:28 Re: 3D flow on a 2-D cartesian grid #8 Ananda Himansu Guest   Posts: n/a I forgot to mention, in case (5) if the infinite cylinder is actually parallel to the infinite plane, the solution though non-axisymmetric, is two-dimensional at every instant: it is the same in every spatial slice perpendicular to the axis of the cylinder (and the impenetrable plane).

 February 11, 2008, 07:02 Re: 3D flow on a 2-D cartesian grid #9 Rami Guest   Posts: n/a Just a comment to be precise. Even if the charge is spherical and the ground is flat, it is possible to have non-axisymmetric solution if the charge is initiated asymmetrically relative to the normal to the plane passing through the sphere center (asymmetric boundary condition). If this is not the case, and all boundary conditions are axisymmetric - an axisymmetric solution is reasonable.

 February 11, 2008, 08:02 Re: 3D flow on a 2-D cartesian grid #10 jinwon park Guest   Posts: n/a To Rami, what is axisymmetric boundary condition?

 February 11, 2008, 11:42 Re: 3D flow on a 2-D cartesian grid #11 Ananda Himansu Guest   Posts: n/a This is certainly true. I was assuming that all initial and boundary conditions are symmetric about the appropriate axis, and precluding any symmetry-breaking via instabilities such as is likely to occur on a small scale in the real world.

 February 12, 2008, 02:51 Re: 3D flow on a 2-D cartesian grid #12 Rami Guest   Posts: n/a Axisymmetric = independent of the azimuthal angle (i.e., depends at most on the axial and radial coordinates). Axisymmetric BC = the boundary conditions are independent of the azimuthal angle.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Yanma OpenFOAM Native Meshers: blockMesh 0 July 7, 2010 08:02 saii CFX 2 September 18, 2009 08:07 Prashanth FLUENT 2 November 17, 2008 02:15 Hans Klaufus CFX 1 June 28, 2000 16:43 Tylor Xie Main CFD Forum 0 June 9, 1999 07:33

All times are GMT -4. The time now is 00:40.