I am very new to all this, so please forgive me if I ask stupid questions.

First, thanks for the software!  Couldn't find anything else like it that ran easily on Windows.  gmsh is good software too.

The structure in the geo file to follow is a cooling chamber.  The inlet to the chamber is at the bottom and the outlet is the face nearest you when gmsh loads the file.  I am trying to model gas (nitrogen) flow patterns inside chamber.  It is empty at the moment.  I wanted to get an empty chamber working for simplicity and to learn how to actually model and flow something.

My problem is, no matter the mesh settings that I come up with, openflower won't solve the flow calculations.  DT on one of my best runs decrease by an order of magnitude every 2nd or 3rd iteration (started at e-005.)  Other runs had DT decreasing 3-5 orders of magnitude every iteration.  I think I have the .flw file (also attached) setup properly.  I have played with the mesh quite a bit, but honestly, I don't know what I am looking for i.e. what a good mesh looks like.  I suppose the other possibility is that this is a structure that can't be solved on a typical PC.

Thanks in advance for any guidance or suggestions that come in!
Brian

p.s. in the .geo:
cl is Characteristic length of the walls of the chamber
il is for the inlet
ol is for the outlet
I originally drew the chamber in inches and converted everything to metric, hence the small numbers

BEGIN GEO FILE

cl = 0.1;
il = 0.005;
ol = 0.01;

Point(1) = {0.5334, 0.5334, 0, cl};
Point(2) = {0, 0.5334, 0, cl};
Point(3) = {1.0668, 0.5334, 0, cl};
Point(5) = {0.5334, 1.0668, 0, cl};
Point(6) = {1.0668, 0.5334, 0.9144, cl};
Point(7) = {0.5334, 0.5334, 0.9144, cl};
Point(8) = {0.5334, 1.0668, 0.9144, cl};
Point(11) = {0, 0.5334, 0.9144, cl};
Point(15) = {0.4572, 0.5334, 0.9144, cl};
Point(16) = {0.6096, 0.5334, 0.9144, cl};
Point(17) = {0.5334, 0.4572, 0.9144, cl};
Point(18) = {0.5334, 0.6096, 0.9144, cl};

Point(19) = {0.5334, 0.6096, 1.3208, ol};
Point(20) = {0.5334, 0.5334, 1.3208, ol};
Point(21) = {0.4572, 0.5334, 1.3208, ol};
Point(22) = {0.6096, 0.5334, 1.3208, ol};
Point(23) = {0.5334, 0.4572, 1.3208, ol};

Point(29) = {0.5334, -0.3048, 0.4953, il};
Point(30) = {0.5334, -0.3048, 0.4572, il};
Point(31) = {0.5715, -0.3048, 0.4572, il};
Point(34) = {0.5334, -0.3048, 0.4191, il};
Point(37) = {0.4953, -0.3048, 0.4572, il};

Point(38) = {0.5334, 0.00127, 0.4191, cl};
Point(39) = {0.5334, 0.00127, 0.4953, cl};
Point(40) = {0.5715, 0.00127, 0.4572, cl};
Point(41) = {0.4953, 0.00127, 0.4572, cl};
Point(42) = {0.5334, 0.00127, 0.4572, cl};
Point(43) = {0.4953, 0.00127, 0.9144, cl};
Point(44) = {0.5715, 0.00127, 0.9144, cl};
Point(45) = {0.5715, 0.00127, 0, cl};
Point(46) = {0.4953, 0.00127, 0, cl};
Circle (3) = {3, 1, 5};
Circle (4) = {5, 1, 2};
Circle (5) = {6, 7, 8};
Line (6) = {3, 6};
Line (7) = {5, 8};
Circle (9) = {8, 7, 11};
Line (11) = {2, 11};
Circle (21) = {18, 7, 15};
Circle (22) = {15, 7, 17};
Circle (23) = {17, 7, 16};
Circle (24) = {16, 7, 18};
Circle (25) = {19, 20, 21};
Line (26) = {18, 19};
Line (27) = {15, 21};
Circle (29) = {22, 20, 19};
Line (30) = {16, 22};
Circle (33) = {23, 20, 22};
Line (34) = {17, 23};
Circle (37) = {21, 20, 23};
Circle (45) = {29, 30, 31};
Circle (49) = {31, 30, 34};
Circle (53) = {34, 30, 37};
Circle (57) = {37, 30, 29};
Circle (72) = {38, 42, 40};
Circle (73) = {40, 42, 39};
Circle (74) = {39, 42, 41};
Circle (75) = {41, 42, 38};
Line (76) = {46, 43};
Line (77) = {45, 44};
Circle (78) = {3, 1, 45};
Circle (79) = {2, 1, 46};
Circle (80) = {6, 7, 44};
Circle (81) = {11, 7, 43};
Line (92) = {37, 41};
Line (93) = {29, 39};
Line (94) = {31, 40};
Line (95) = {34, 38};
Line (127) = {46, 45};
Line (128) = {43, 44};
Line Loop (1000008) = {3, 7, -5, -6};
Ruled Surface (8) = {1000008};
Line Loop (1000012) = {4, 11, -9, -7};
Ruled Surface (12) = {1000012};
Line Loop (1000028) = {21, 27, -25, -26};
Ruled Surface (28) = {1000028};
Line Loop (1000032) = {24, 26, -29, -30};
Ruled Surface (32) = {1000032};
Line Loop (1000036) = {23, 30, -33, -34};
Ruled Surface (36) = {1000036};
Line Loop (1000040) = {22, 34, -37, -27};
Ruled Surface (40) = {1000040};
Line Loop (1000067) = {33, 29, 25, 37};
Plane Surface (67) = {1000067};
Line Loop (1000069) = {-49, -45, -57, -53};
Plane Surface (69) = {1000069};
Line Loop (1000083) = {80, -77, -78, 6};
Ruled Surface (83) = {1000083};
Line Loop (1000085) = {-81, -11, 79, 76};
Ruled Surface (85) = {1000085};
Line Loop (1000097) = {75, -95, 53, 92};
Ruled Surface (97) = {1000097};
Line Loop (1000099) = {95, 72, -94, 49};
Ruled Surface (99) = {1000099};
Line Loop (1000101) = {94, 73, -93, 45};
Ruled Surface (101) = {1000101};
Line Loop (1000103) = {-92, 57, 93, 74};
Ruled Surface (103) = {1000103};
Line Loop (1000131) = {127, 77, -128, -76, -73, -72, -75, -74};
Plane Surface (131) = {1000131};
Line Loop (1000133) = {9, 81, 128, -80, 5, -23, -22, -21, -24};
Plane Surface (133) = {1000133};
Line Loop (1000135) = {-3, -4, -79, -127, 78};
Plane Surface (135) = {1000135};
Surface Loop (1000137) = {8, 135, 12, 85, 133, 131, 83, 101, 99, 97, 69, 103, 36, 32, 28, 40, 67};
Volume (137) = {1000137};
// outlet
Physical Surface (138) = {67};
// inlet
Physical Surface (139) = {69};
// walls
Physical Surface (140) = {83, 101, 99, 103, 97, 36, 131, 32, 40, 133, 28, 8, 85, 135, 12};
Physical Volume (141) = {137};
Translate {0.001,0,0} {
  Point{45,44};
}
Translate {-0.001,0,0} {
  Point{46,43};
}

END GEO FILE
BEGIN FLW FILE

// INPUT DATA FILE for testing OpenFlower.
// Created on 09/12/2004.
// This is how you comment your code.
// There is a space before your text

// Here is the time block
TimeBegin 0.
TimeEnd 5.
MaxTimeSteps 500
// CFL has to be equal or less than 1
CFL 0.5

// Declare your medium name
// This block is compulsory
Medium nitrogen
{
rho 1.16
mu 0.000017632
}

// Declare algorithm name
// Exactly this written below for Nav Stokes
Algorithm AlgoNavierStokes { eqn1 }

// Declare the mesh file and the physical surfaces
// notice the names inlet_1 .. walls
// walls equals physical surface 128 for example
Mesh gmsh
{
file metricconsolidated.msh
frontiers
  {
  surface 139 inlet
  surface 138 outlet
  surface 140 walls
  }
}

// Equation block
// Notice the the BC's names inlet_1 .. walls again
// This is the declaration of a boundary .. boundary_condition velocity ..
Equation navier_stokes_incompressible eqn1
{
Medium nitrogen

// boundary conditions block
boundary_condition wall walls 0. 0. 0
boundary_condition velocity inlet 0. 86. 0.
boundary_condition pressure_outlet outlet 0.0

// list the operators and solver
// It is required : they must be declared in this order. Some improvement must be done concerning
// declaration of operators (in the end, users should not matter for declaring which operators are used
// in an equation).
operator diffusion
operator convection

solver GMRES

// Here we have to specify initial conditions for the main unknown (here velocity field)
// Users can either recover from a previously saved field (“File”) from OpenFlower :
// Initial_Condition File eqn1.save

// Or specify an expression (“Expr”) for all components of the variable (here velocity has 3
// components : u=0, v=0, w=0)
Initial_Condition Expr 0. 0. 0.
}

// This will create output files .pos for you to visualize results in Gmsh

// Post_Processing block
post_processing
   {
   global gmsh eqn1.Velocity 0. 1000.0 0.005
// global gmsh eqn1.Pressure 0. 1000.0 0.25
// probe eqn1.Velocity 0. 1000. 0.001 position 0.5 0.1 0.1
   }

end

END FLW FILE