[1D] Use a better default initial grid for FreeFlame

This initial grid is designed to work well with how the initial profile and
temperature fixed point are set. The only parameter that needs to be
user-specified is the width of the domain.

doc/sphinx/cython/onedim.rst

@@ -13,7 +13,7 @@ Composite Domains
 
 FreeFlame
 ^^^^^^^^^
-.. autoclass:: FreeFlame(gas, grid=None)
+.. autoclass:: FreeFlame(gas, grid=None, width=None)
 
 BurnerFlame
 ^^^^^^^^^^^

interfaces/cython/cantera/examples/onedim/adiabatic_flame.py

@@ -11,7 +11,7 @@
 Tin = 300.0  # unburned gas temperature [K]
 reactants = 'H2:1.1, O2:1, AR:5'  # premixed gas composition
 
-initial_grid = np.linspace(0.0, 0.03, 7)  # m
+width = 0.03  # m
 tol_ss = [1.0e-5, 1.0e-13]  # [rtol atol] for steady-state problem
 tol_ts = [1.0e-4, 1.0e-13]  # [rtol atol] for time stepping
 loglevel = 1  # amount of diagnostic output (0 to 8)
@@ -23,7 +23,7 @@
 gas.TPX = Tin, p, reactants
 
 # Flame object
-f = ct.FreeFlame(gas, initial_grid)
+f = ct.FreeFlame(gas, width=width)
 f.flame.set_steady_tolerances(default=tol_ss)
 f.flame.set_transient_tolerances(default=tol_ts)
 

interfaces/cython/cantera/examples/onedim/flamespeed_sensitivity.py

@@ -14,7 +14,7 @@
 Tin = 300.0  # unburned gas temperature [K]
 reactants = 'CH4:0.45, O2:1.0, N2:3.76'
 
-initial_grid = np.linspace(0, 0.03, 5)  # m
+width = 0.03  # m
 tol_ss = [1.0e-9, 1.0e-14]  # [rtol atol] for steady-state problem
 tol_ts = [1.0e-5, 1.0e-14]  # [rtol atol] for time stepping
 
@@ -23,7 +23,7 @@
 gas.TPX = Tin, p, reactants
 
 # Flame object
-f = ct.FreeFlame(gas, initial_grid)
+f = ct.FreeFlame(gas, width=width)
 f.flame.set_steady_tolerances(default=tol_ss)
 f.flame.set_transient_tolerances(default=tol_ts)
 

interfaces/cython/cantera/onedim.py

@@ -363,16 +363,27 @@ class FreeFlame(FlameBase):
     """A freely-propagating flat flame."""
     __slots__ = ('inlet', 'outlet', 'flame')
 
-    def __init__(self, gas, grid=None):
+    def __init__(self, gas, grid=None, width=None):
         """
         A domain of type FreeFlow named 'flame' will be created to represent
         the flame. The three domains comprising the stack are stored as
         ``self.inlet``, ``self.flame``, and ``self.outlet``.
+
+        :param grid:
+            A list of points to be used as the initial grid. Not recommended
+            unless solving only on a fixed grid; Use the `width` parameter
+            instead.
+        :param width:
+            Defines a grid on the interval [0, width] with internal points
+            determined automatically by the solver.
         """
         self.inlet = Inlet1D(name='reactants', phase=gas)
         self.outlet = Outlet1D(name='products', phase=gas)
         self.flame = FreeFlow(gas, name='flame')
 
+        if width is not None:
+            grid = np.array([0.0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0]) * width
+
         super(FreeFlame, self).__init__((self.inlet, self.flame, self.outlet),
                                         gas, grid)
 

interfaces/cython/cantera/test/test_onedim.py

@@ -92,15 +92,12 @@ class TestFreeFlame(utilities.CanteraTest):
     tol_ts = [1.0e-4, 1.0e-11]  # [rtol atol] for time stepping
 
     def create_sim(self, p, Tin, reactants, mech='h2o2.xml'):
-
-        initial_grid = [0.0, 0.001, 0.01, 0.02, 0.029, 0.03]  # m
-
         # IdealGasMix object used to compute mixture properties
         self.gas = ct.Solution(mech)
         self.gas.TPX = Tin, p, reactants
 
         # Flame object
-        self.sim = ct.FreeFlame(self.gas, initial_grid)
+        self.sim = ct.FreeFlame(self.gas, width=0.05)
         self.sim.flame.set_steady_tolerances(default=self.tol_ss)
         self.sim.flame.set_transient_tolerances(default=self.tol_ts)