From eb638254e458cc1dc37340b4153609f5664e0091 Mon Sep 17 00:00:00 2001
From: Ingmar Schoegl <ischoegl@lsu.edu>
Date: Wed, 26 Feb 2020 16:29:20 -0600
Subject: [PATCH] [1D] Deprecate component name 'u' in favor of 'velocity'

---
 .../examples/onedim/adiabatic_flame.py        |  4 +-
 .../examples/onedim/diffusion_flame_batch.py  | 10 ++--
 .../onedim/diffusion_flame_extinction.py      |  6 +--
 .../examples/onedim/flamespeed_sensitivity.py |  2 +-
 .../cantera/examples/onedim/ion_free_flame.py |  2 +-
 .../onedim/premixed_counterflow_twin_flame.py | 12 +++--
 interfaces/cython/cantera/onedim.py           | 49 ++++++++++++-------
 interfaces/cython/cantera/test/test_onedim.py | 45 +++++++++--------
 samples/cxx/flamespeed/flamespeed.cpp         | 20 +++++---
 src/oneD/StFlow.cpp                           |  7 ++-
 10 files changed, 93 insertions(+), 64 deletions(-)

diff --git a/interfaces/cython/cantera/examples/onedim/adiabatic_flame.py b/interfaces/cython/cantera/examples/onedim/adiabatic_flame.py
index 5c3b3f9f4..f3b0dbd05 100644
--- a/interfaces/cython/cantera/examples/onedim/adiabatic_flame.py
+++ b/interfaces/cython/cantera/examples/onedim/adiabatic_flame.py
@@ -31,13 +31,13 @@ f.solve(loglevel=loglevel, auto=True)
 # Solve with the energy equation enabled
 f.save('h2_adiabatic.xml', 'mix', 'solution with mixture-averaged transport')
 f.show_solution()
-print('mixture-averaged flamespeed = {0:7f} m/s'.format(f.u[0]))
+print('mixture-averaged flamespeed = {0:7f} m/s'.format(f.velocity[0]))
 
 # Solve with multi-component transport properties
 f.transport_model = 'Multi'
 f.solve(loglevel)  # don't use 'auto' on subsequent solves
 f.show_solution()
-print('multicomponent flamespeed = {0:7f} m/s'.format(f.u[0]))
+print('multicomponent flamespeed = {0:7f} m/s'.format(f.velocity[0]))
 f.save('h2_adiabatic.xml', 'multi', 'solution with multicomponent transport')
 
 # write the velocity, temperature, density, and mole fractions to a CSV file
diff --git a/interfaces/cython/cantera/examples/onedim/diffusion_flame_batch.py b/interfaces/cython/cantera/examples/onedim/diffusion_flame_batch.py
index 311b7dfb9..83a54c50c 100644
--- a/interfaces/cython/cantera/examples/onedim/diffusion_flame_batch.py
+++ b/interfaces/cython/cantera/examples/onedim/diffusion_flame_batch.py
@@ -111,8 +111,8 @@ for p in p_range:
     f.fuel_inlet.mdot *= rel_pressure_increase ** exp_mdot_p
     f.oxidizer_inlet.mdot *= rel_pressure_increase ** exp_mdot_p
     # Update velocities
-    f.set_profile('u', normalized_grid,
-                  f.u * rel_pressure_increase ** exp_u_p)
+    f.set_profile('velocity', normalized_grid,
+                  f.velocity * rel_pressure_increase ** exp_u_p)
     f.set_profile('V', normalized_grid,
                   f.V * rel_pressure_increase ** exp_V_p)
     # Update pressure curvature
@@ -167,7 +167,7 @@ while np.max(f.T) > temperature_limit_extinction:
     f.fuel_inlet.mdot *= strain_factor ** exp_mdot_a
     f.oxidizer_inlet.mdot *= strain_factor ** exp_mdot_a
     # Update velocities
-    f.set_profile('u', normalized_grid, f.u * strain_factor ** exp_u_a)
+    f.set_profile('velocity', normalized_grid, f.velocity * strain_factor ** exp_u_a)
     f.set_profile('V', normalized_grid, f.V * strain_factor ** exp_V_a)
     # Update pressure curvature
     f.set_profile('lambda', normalized_grid, f.L * strain_factor ** exp_lam_a)
@@ -203,7 +203,7 @@ for p in p_selected:
 
     # Plot the axial velocity profiles (normalized by the fuel inlet velocity)
     # for selected pressures
-    ax2.plot(f.grid / f.grid[-1], f.u / f.u[0],
+    ax2.plot(f.grid / f.grid[-1], f.velocity / f.velocity[0],
              label='{0:05.1f} bar'.format(p))
 
 ax1.legend(loc=0)
@@ -231,7 +231,7 @@ for n in n_selected:
 
     # Plot the axial velocity profiles (normalized by the fuel inlet velocity)
     # for the strain rate loop (selected)
-    ax4.plot(f.grid / f.grid[-1], f.u / f.u[0],
+    ax4.plot(f.grid / f.grid[-1], f.velocity / f.velocity[0],
              label=format(a_max, '.2e') + ' 1/s')
 
 ax3.legend(loc=0)
diff --git a/interfaces/cython/cantera/examples/onedim/diffusion_flame_extinction.py b/interfaces/cython/cantera/examples/onedim/diffusion_flame_extinction.py
index 1183f2a8c..5bd60abd1 100644
--- a/interfaces/cython/cantera/examples/onedim/diffusion_flame_extinction.py
+++ b/interfaces/cython/cantera/examples/onedim/diffusion_flame_extinction.py
@@ -88,7 +88,7 @@ n_last_burning = 0
 # List of peak temperatures
 T_max = [np.max(f.T)]
 # List of maximum axial velocity gradients
-a_max = [np.max(np.abs(np.gradient(f.u) / np.gradient(f.grid)))]
+a_max = [np.max(np.abs(np.gradient(f.velocity) / np.gradient(f.grid)))]
 
 # Simulate counterflow flames at increasing strain rates until the flame is
 # extinguished. To achieve a fast simulation, an initial coarse strain rate
@@ -109,7 +109,7 @@ while True:
     f.fuel_inlet.mdot *= strain_factor ** exp_mdot_a
     f.oxidizer_inlet.mdot *= strain_factor ** exp_mdot_a
     # Update velocities
-    f.set_profile('u', normalized_grid, f.u * strain_factor ** exp_u_a)
+    f.set_profile('velocity', normalized_grid, f.velocity * strain_factor ** exp_u_a)
     f.set_profile('V', normalized_grid, f.V * strain_factor ** exp_V_a)
     # Update pressure curvature
     f.set_profile('lambda', normalized_grid, f.L * strain_factor ** exp_lam_a)
@@ -125,7 +125,7 @@ while True:
                description='Cantera version ' + ct.__version__ +
                ', reaction mechanism ' + reaction_mechanism)
         T_max.append(np.max(f.T))
-        a_max.append(np.max(np.abs(np.gradient(f.u) / np.gradient(f.grid))))
+        a_max.append(np.max(np.abs(np.gradient(f.velocity) / np.gradient(f.grid))))
         # If the temperature difference is too small and the minimum relative
         # strain rate increase is reached, abort
         if ((T_max[-2] - T_max[-1] < delta_T_min) &
diff --git a/interfaces/cython/cantera/examples/onedim/flamespeed_sensitivity.py b/interfaces/cython/cantera/examples/onedim/flamespeed_sensitivity.py
index a4ee73601..b477f3e55 100644
--- a/interfaces/cython/cantera/examples/onedim/flamespeed_sensitivity.py
+++ b/interfaces/cython/cantera/examples/onedim/flamespeed_sensitivity.py
@@ -24,7 +24,7 @@ f = ct.FreeFlame(gas, width=width)
 f.set_refine_criteria(ratio=3, slope=0.07, curve=0.14)
 
 f.solve(loglevel=1, auto=True)
-print('\nmixture-averaged flamespeed = {:7f} m/s\n'.format(f.u[0]))
+print('\nmixture-averaged flamespeed = {:7f} m/s\n'.format(f.velocity[0]))
 
 # Use the adjoint method to calculate sensitivities
 sens = f.get_flame_speed_reaction_sensitivities()
diff --git a/interfaces/cython/cantera/examples/onedim/ion_free_flame.py b/interfaces/cython/cantera/examples/onedim/ion_free_flame.py
index 0ab8fc12d..6dcf71573 100644
--- a/interfaces/cython/cantera/examples/onedim/ion_free_flame.py
+++ b/interfaces/cython/cantera/examples/onedim/ion_free_flame.py
@@ -31,7 +31,7 @@ f.solve(loglevel=loglevel, stage=2, enable_energy=True)
 
 f.save('CH4_adiabatic.xml', 'ion', 'solution with ionized gas transport')
 f.show_solution()
-print('mixture-averaged flamespeed = {0:7f} m/s'.format(f.u[0]))
+print('mixture-averaged flamespeed = {0:7f} m/s'.format(f.velocity[0]))
 
 # write the velocity, temperature, density, and mole fractions to a CSV file
 f.write_csv('CH4_adiabatic.csv', quiet=False)
diff --git a/interfaces/cython/cantera/examples/onedim/premixed_counterflow_twin_flame.py b/interfaces/cython/cantera/examples/onedim/premixed_counterflow_twin_flame.py
index 3bf8d05bf..72039209c 100644
--- a/interfaces/cython/cantera/examples/onedim/premixed_counterflow_twin_flame.py
+++ b/interfaces/cython/cantera/examples/onedim/premixed_counterflow_twin_flame.py
@@ -29,12 +29,12 @@ def derivative(x, y):
 
 def computeStrainRates(oppFlame):
     # Compute the derivative of axial velocity to obtain normal strain rate
-    strainRates = derivative(oppFlame.grid, oppFlame.u)
+    strainRates = derivative(oppFlame.grid, oppFlame.velocity)
 
     # Obtain the location of the max. strain rate upstream of the pre-heat zone.
     # This is the characteristic strain rate
     maxStrLocation = abs(strainRates).argmax()
-    minVelocityPoint = oppFlame.u[:maxStrLocation].argmin()
+    minVelocityPoint = oppFlame.velocity[:maxStrLocation].argmin()
 
     # Characteristic Strain Rate = K
     strainRatePoint = abs(strainRates[:minVelocityPoint]).argmax()
@@ -130,15 +130,17 @@ if '--plot' in sys.argv:
 
     # Axial Velocity Plot
     plt.subplot(1, 2, 1)
-    plt.plot(oppFlame.grid, oppFlame.u, 'r', lw=2)
+    plt.plot(oppFlame.grid, oppFlame.velocity, 'r', lw=2)
     plt.xlim(oppFlame.grid[0], oppFlame.grid[-1])
     plt.xlabel('Distance (m)')
     plt.ylabel('Axial Velocity (m/s)')
 
     # Identify the point where the strain rate is calculated
-    plt.plot(oppFlame.grid[strainRatePoint], oppFlame.u[strainRatePoint], 'gs')
+    plt.plot(oppFlame.grid[strainRatePoint],
+             oppFlame.velocity[strainRatePoint], 'gs')
     plt.annotate('Strain-Rate point',
-                 xy=(oppFlame.grid[strainRatePoint], oppFlame.u[strainRatePoint]),
+                 xy=(oppFlame.grid[strainRatePoint],
+                     oppFlame.velocity[strainRatePoint]),
                  xytext=(0.001, 0.1),
                  arrowprops={'arrowstyle': '->'})
 
diff --git a/interfaces/cython/cantera/onedim.py b/interfaces/cython/cantera/onedim.py
index 9594701b1..b0fb79c76 100644
--- a/interfaces/cython/cantera/onedim.py
+++ b/interfaces/cython/cantera/onedim.py
@@ -170,8 +170,23 @@ class FlameBase(Sim1D):
     def u(self):
         """
         Array containing the velocity [m/s] normal to the flame at each point.
+
+        .. deprecated:: 2.5
+
+             To be deprecated with version 2.5, and removed thereafter.
+             Replaced by property `velocity`.
         """
-        return self.profile(self.flame, 'u')
+        warnings.warn("To be removed after Cantera 2.5. "
+                      "Replaced by property 'velocity'",
+                      DeprecationWarning)
+        return self.profile(self.flame, 'velocity')
+
+    @property
+    def velocity(self):
+        """
+        Array containing the velocity [m/s] normal to the flame at each point.
+        """
+        return self.profile(self.flame, 'velocity')
 
     @property
     def V(self):
@@ -272,7 +287,7 @@ class FlameBase(Sim1D):
 
         z = self.grid
         T = self.T
-        u = self.u
+        u = self.velocity
         V = self.V
 
         with open(filename, 'w', newline='') as csvfile:
@@ -303,8 +318,6 @@ class FlameBase(Sim1D):
         for e in self._extra:
             if e == 'grid':
                 val = self.grid
-            elif e == 'velocity':
-                val = self.profile(self.flame, 'u')
             elif e == 'gradient':
                 val = self.profile(self.flame, 'V')
             else:
@@ -380,8 +393,6 @@ class FlameBase(Sim1D):
             val = getattr(arr, e)[idx]
             if e in ['grid', 'qdot']:
                 pass
-            elif e == 'velocity':
-                self.set_profile('u', xi, val)
             elif e == 'gradient':
                 self.set_profile('V', xi, val)
             else:
@@ -730,7 +741,7 @@ class FreeFlame(FlameBase):
         Yeq = self.gas.Y
         u1 = self.inlet.mdot/self.gas.density
 
-        self.set_profile('u', locs, [u0, u0, u1, u1])
+        self.set_profile('velocity', locs, [u0, u0, u1, u1])
         self.set_profile('T', locs, [T0, T0, Teq, Teq])
 
         # Pick the location of the fixed temperature point, using an existing
@@ -824,12 +835,12 @@ class FreeFlame(FlameBase):
         """
 
         def g(sim):
-            return sim.u[0]
+            return sim.velocity[0]
 
         Nvars = sum(D.n_components * D.n_points for D in self.domains)
 
         # Index of u[0] in the global solution vector
-        i_Su = self.inlet.n_components + self.flame.component_index('u')
+        i_Su = self.inlet.n_components + self.flame.component_index('velocity')
 
         dgdx = np.zeros(Nvars)
         dgdx[i_Su] = 1
@@ -856,13 +867,13 @@ class IonFlameBase(FlameBase):
         """
         z = self.grid
         T = self.T
-        u = self.u
+        u = self.velocity
         V = self.V
         E = self.E
 
         with open(filename, 'w', newline='') as csvfile:
             writer = _csv.writer(csvfile)
-            writer.writerow(['z (m)', 'u (m/s)', 'V (1/s)', 'T (K)',
+            writer.writerow(['z (m)', 'velocity (m/s)', 'V (1/s)', 'T (K)',
                             'E (V/m)', 'rho (kg/m3)'] + self.gas.species_names)
             for n in range(self.flame.n_points):
                 self.set_gas_state(n)
@@ -972,7 +983,7 @@ class BurnerFlame(FlameBase):
         u1 = self.burner.mdot/self.gas.density
 
         locs = [0.0, 0.2, 1.0]
-        self.set_profile('u', locs, [u0, u1, u1])
+        self.set_profile('velocity', locs, [u0, u1, u1])
         self.set_profile('T', locs, [T0, Teq, Teq])
         for n in range(self.gas.n_species):
             self.set_profile(self.gas.species_name(n),
@@ -1162,7 +1173,7 @@ class CounterflowDiffusionFlame(FlameBase):
         T[-1] = T0o
         zrel = (zz - zz[0])/dz
 
-        self.set_profile('u', [0.0, 1.0], [u0f, -u0o])
+        self.set_profile('velocity', [0.0, 1.0], [u0f, -u0o])
         self.set_profile('V', [0.0, x0/dz, 1.0], [0.0, a, 0.0])
         self.set_profile('T', zrel, T)
         for k,spec in enumerate(self.gas.species_names):
@@ -1273,10 +1284,10 @@ class CounterflowDiffusionFlame(FlameBase):
             .. math:: a_{o} = \sqrt{-\frac{\Lambda}{\rho_{o}}}
         """
         if definition == 'mean':
-            return - (self.u[-1] - self.u[0]) / self.grid[-1]
+            return - (self.velocity[-1] - self.velocity[0]) / self.grid[-1]
 
         elif definition == 'max':
-            return np.max(np.abs(np.gradient(self.u) / np.gradient(self.grid)))
+            return np.max(np.abs(np.gradient(self.velocity) / np.gradient(self.grid)))
 
         elif definition == 'stoichiometric':
             if fuel is None:
@@ -1292,7 +1303,7 @@ class CounterflowDiffusionFlame(FlameBase):
                 if 'C' in self.gas.element_names:
                     stoich += self.gas.n_atoms(fuel, 'C')
 
-            d_u_d_z = np.gradient(self.u) / np.gradient(self.grid)
+            d_u_d_z = np.gradient(self.velocity) / np.gradient(self.grid)
             phi = (self.X[self.gas.species_index(fuel)] * stoich /
                    np.maximum(self.X[self.gas.species_index(oxidizer)], 1e-20))
             z_stoich = np.interp(-1., -phi, self.grid)
@@ -1407,7 +1418,7 @@ class ImpingingJet(FlameBase):
                                  [Y0[k], Y0[k]])
 
         locs = np.array([0.0, 1.0])
-        self.set_profile('u', locs, [u0, 0.0])
+        self.set_profile('velocity', locs, [u0, 0.0])
         self.set_profile('V', locs, [0.0, 0.0])
 
 
@@ -1498,7 +1509,7 @@ class CounterflowPremixedFlame(FlameBase):
         # estimate stagnation point
         x0 = rhou*uu * dz / (rhou*uu + rhob*ub)
 
-        self.set_profile('u', [0.0, 1.0], [uu, -ub])
+        self.set_profile('velocity', [0.0, 1.0], [uu, -ub])
         self.set_profile('V', [0.0, x0/dz, 1.0], [0.0, a, 0.0])
 
 
@@ -1571,5 +1582,5 @@ class CounterflowTwinPremixedFlame(FlameBase):
         dz = zz[-1] - zz[0]
         a = 2 * uu / dz
 
-        self.set_profile('u', [0.0, 1.0], [uu, 0])
+        self.set_profile('velocity', [0.0, 1.0], [uu, 0])
         self.set_profile('V', [0.0, 1.0], [0.0, a])
diff --git a/interfaces/cython/cantera/test/test_onedim.py b/interfaces/cython/cantera/test/test_onedim.py
index 3fc4110d9..761be04b4 100644
--- a/interfaces/cython/cantera/test/test_onedim.py
+++ b/interfaces/cython/cantera/test/test_onedim.py
@@ -194,7 +194,7 @@ class TestFreeFlame(utilities.CanteraTest):
 
         self.sim.set_refine_criteria(ratio=4, slope=0.8, curve=0.8)
         self.sim.solve(refine_grid=True, auto=True, loglevel=0)
-        self.assertNear(self.sim.u[0], 17.02, 1e-1)
+        self.assertNear(self.sim.velocity[0], 17.02, 1e-1)
         self.assertLess(self.sim.grid[-1], 2.0) # grid should not be too wide
 
 
@@ -241,7 +241,7 @@ class TestFreeFlame(utilities.CanteraTest):
         rhou = self.sim.inlet.mdot
 
         # Check continuity
-        for rhou_j in self.sim.density * self.sim.u:
+        for rhou_j in self.sim.density * self.sim.velocity:
             self.assertNear(rhou_j, rhou, 1e-4)
 
     def test_solution_array_output(self):
@@ -272,7 +272,7 @@ class TestFreeFlame(utilities.CanteraTest):
 
         # Check continuity
         rhou = self.sim.inlet.mdot
-        for rhou_j in self.sim.density * self.sim.u:
+        for rhou_j in self.sim.density * self.sim.velocity:
             self.assertNear(rhou_j, rhou, 1e-4)
 
     def test_mixture_averaged_case1(self):
@@ -309,15 +309,15 @@ class TestFreeFlame(utilities.CanteraTest):
 
         # Forward sensitivities
         dk = 1e-4
-        Su0 = self.sim.u[0]
+        Su0 = self.sim.velocity[0]
         for m in range(self.gas.n_reactions):
             self.gas.set_multiplier(1.0) # reset all multipliers
             self.gas.set_multiplier(1+dk, m) # perturb reaction m
             self.sim.solve(loglevel=0, refine_grid=False)
-            Suplus = self.sim.u[0]
+            Suplus = self.sim.velocity[0]
             self.gas.set_multiplier(1-dk, m) # perturb reaction m
             self.sim.solve(loglevel=0, refine_grid=False)
-            Suminus = self.sim.u[0]
+            Suminus = self.sim.velocity[0]
             fwd = (Suplus-Suminus)/(2*Su0*dk)
             self.assertNear(fwd, dSdk_adj[m], 5e-3)
 
@@ -330,12 +330,12 @@ class TestFreeFlame(utilities.CanteraTest):
         self.create_sim(p, Tin, reactants)
         self.solve_fixed_T()
         self.solve_mix(ratio=5, slope=0.5, curve=0.3)
-        Su_mix = self.sim.u[0]
+        Su_mix = self.sim.velocity[0]
 
         # Multicomponent flame speed should be similar but not identical to
         # the mixture-averaged flame speed.
         self.solve_multi()
-        Su_multi = self.sim.u[0]
+        Su_multi = self.sim.velocity[0]
         self.assertFalse(self.sim.soret_enabled)
 
         self.assertNear(Su_mix, Su_multi, 5e-2)
@@ -346,7 +346,7 @@ class TestFreeFlame(utilities.CanteraTest):
         self.sim.soret_enabled = True
         self.sim.solve(loglevel=0, refine_grid=True)
         self.assertTrue(self.sim.soret_enabled)
-        Su_soret = self.sim.u[0]
+        Su_soret = self.sim.velocity[0]
 
         self.assertNear(Su_multi, Su_soret, 2e-1)
         self.assertNotEqual(Su_multi, Su_soret)
@@ -429,7 +429,7 @@ class TestFreeFlame(utilities.CanteraTest):
             os.remove(filename)
 
         Y1 = self.sim.Y
-        u1 = self.sim.u
+        u1 = self.sim.velocity
         V1 = self.sim.V
         P1 = self.sim.P
 
@@ -455,7 +455,7 @@ class TestFreeFlame(utilities.CanteraTest):
         self.assertNear(P1, P2a)
 
         Y2 = self.sim.Y
-        u2 = self.sim.u
+        u2 = self.sim.velocity
         V2 = self.sim.V
 
         self.assertArrayNear(Y1, Y2)
@@ -464,7 +464,7 @@ class TestFreeFlame(utilities.CanteraTest):
 
         self.solve_fixed_T()
         Y3 = self.sim.Y
-        u3 = self.sim.u
+        u3 = self.sim.velocity
         V3 = self.sim.V
 
         # TODO: These tolereances seem too loose, but the tests fail on some
@@ -478,7 +478,12 @@ class TestFreeFlame(utilities.CanteraTest):
 
         for attr in ct.FlameBase.__dict__:
             if isinstance(ct.FlameBase.__dict__[attr], property):
-                getattr(self.sim, attr)
+                if attr == 'u':
+                    msg = "Replaced by property 'velocity'"
+                    with self.assertWarnsRegex(DeprecationWarning, msg):
+                        getattr(self.sim, attr)
+                else:
+                    getattr(self.sim, attr)
 
     def test_save_restore_add_species(self):
         reactants = 'H2:1.1, O2:1, AR:5'
@@ -571,7 +576,7 @@ class TestFreeFlame(utilities.CanteraTest):
     def test_replace_grid(self):
         self.create_sim(ct.one_atm, 300.0, 'H2:1.1, O2:1, AR:5')
         self.solve_fixed_T()
-        ub = self.sim.u[-1]
+        ub = self.sim.velocity[-1]
 
         # add some points to the grid
         grid = list(self.sim.grid)
@@ -581,7 +586,7 @@ class TestFreeFlame(utilities.CanteraTest):
         self.sim.set_initial_guess()
 
         self.solve_fixed_T()
-        self.assertNear(self.sim.u[-1], ub, 1e-2)
+        self.assertNear(self.sim.velocity[-1], ub, 1e-2)
 
     def test_exceed_max_grid_points(self):
         self.create_sim(ct.one_atm, 400.0, 'H2:1.1, O2:1, AR:5')
@@ -657,7 +662,7 @@ class TestDiffusionFlame(utilities.CanteraTest):
         self.solve_mix()
         data = np.empty((self.sim.flame.n_points, self.gas.n_species + 4))
         data[:,0] = self.sim.grid
-        data[:,1] = self.sim.u
+        data[:,1] = self.sim.velocity
         data[:,2] = self.sim.V
         data[:,3] = self.sim.T
         data[:,4:] = self.sim.Y.T
@@ -696,7 +701,7 @@ class TestDiffusionFlame(utilities.CanteraTest):
 
         data = np.empty((self.sim.flame.n_points, self.gas.n_species + 4))
         data[:,0] = self.sim.grid
-        data[:,1] = self.sim.u
+        data[:,1] = self.sim.velocity
         data[:,2] = self.sim.V
         data[:,3] = self.sim.T
         data[:,4:] = self.sim.Y.T
@@ -752,7 +757,7 @@ class TestDiffusionFlame(utilities.CanteraTest):
         self.solve_mix()
         data = np.empty((self.sim.flame.n_points, self.gas.n_species + 4))
         data[:,0] = self.sim.grid
-        data[:,1] = self.sim.u
+        data[:,1] = self.sim.velocity
         data[:,2] = self.sim.V
         data[:,3] = self.sim.T
         data[:,4:] = self.sim.Y.T
@@ -838,7 +843,7 @@ class TestCounterflowPremixedFlame(utilities.CanteraTest):
 
         data = np.empty((sim.flame.n_points, gas.n_species + 4))
         data[:,0] = sim.grid
-        data[:,1] = sim.u
+        data[:,1] = sim.velocity
         data[:,2] = sim.V
         data[:,3] = sim.T
         data[:,4:] = sim.Y.T
@@ -927,7 +932,7 @@ class TestBurnerFlame(utilities.CanteraTest):
         sim.solve(loglevel=0, auto=True)
         # nonreacting solution
         self.assertNear(sim.T[-1], sim.T[0], 1e-6)
-        self.assertNear(sim.u[-1], sim.u[0], 1e-6)
+        self.assertNear(sim.velocity[-1], sim.velocity[0], 1e-6)
         self.assertArrayNear(sim.Y[:,0], sim.Y[:,-1], 1e-6, atol=1e-6)
 
 
diff --git a/samples/cxx/flamespeed/flamespeed.cpp b/samples/cxx/flamespeed/flamespeed.cpp
index d687671d7..c6a219a10 100644
--- a/samples/cxx/flamespeed/flamespeed.cpp
+++ b/samples/cxx/flamespeed/flamespeed.cpp
@@ -101,7 +101,7 @@ int flamespeed(double phi)
 
         double uout = inlet.mdot()/rho_out;
         value = {uin, uin, uout, uout};
-        flame.setInitialGuess("u",locs,value);
+        flame.setInitialGuess("velocity",locs,value);
         value = {temp, temp, Tad, Tad};
         flame.setInitialGuess("T",locs,value);
 
@@ -135,21 +135,24 @@ int flamespeed(double phi)
         bool refine_grid = true;
 
         flame.solve(loglevel,refine_grid);
-        double flameSpeed_mix = flame.value(flowdomain,flow.componentIndex("u"),0);
+        double flameSpeed_mix = flame.value(flowdomain,
+                                            flow.componentIndex("velocity"),0);
         print("Flame speed with mixture-averaged transport: {} m/s\n",
               flameSpeed_mix);
 
         // now switch to multicomponent transport
         flow.setTransport(*trmulti);
         flame.solve(loglevel, refine_grid);
-        double flameSpeed_multi = flame.value(flowdomain,flow.componentIndex("u"),0);
+        double flameSpeed_multi = flame.value(flowdomain,
+                                              flow.componentIndex("velocity"),0);
         print("Flame speed with multicomponent transport: {} m/s\n",
               flameSpeed_multi);
 
         // now enable Soret diffusion
         flow.enableSoret(true);
         flame.solve(loglevel, refine_grid);
-        double flameSpeed_full = flame.value(flowdomain,flow.componentIndex("u"),0);
+        double flameSpeed_full = flame.value(flowdomain,
+                                             flow.componentIndex("velocity"),0);
         print("Flame speed with multicomponent transport + Soret: {} m/s\n",
               flameSpeed_full);
 
@@ -159,9 +162,12 @@ int flamespeed(double phi)
               "z (m)", "T (K)", "U (m/s)", "Y(CO)");
         for (size_t n = 0; n < flow.nPoints(); n++) {
             Tvec.push_back(flame.value(flowdomain,flow.componentIndex("T"),n));
-            COvec.push_back(flame.value(flowdomain,flow.componentIndex("CO"),n));
-            CO2vec.push_back(flame.value(flowdomain,flow.componentIndex("CO2"),n));
-            Uvec.push_back(flame.value(flowdomain,flow.componentIndex("u"),n));
+            COvec.push_back(flame.value(flowdomain,
+                                        flow.componentIndex("CO"),n));
+            CO2vec.push_back(flame.value(flowdomain,
+                                         flow.componentIndex("CO2"),n));
+            Uvec.push_back(flame.value(flowdomain,
+                                       flow.componentIndex("velocity"),n));
             zvec.push_back(flow.grid(n));
             print("{:9.6f}\t{:8.3f}\t{:5.3f}\t{:7.5f}\n",
                   flow.grid(n), Tvec[n], Uvec[n], COvec[n]);
diff --git a/src/oneD/StFlow.cpp b/src/oneD/StFlow.cpp
index e8faee316..925934030 100644
--- a/src/oneD/StFlow.cpp
+++ b/src/oneD/StFlow.cpp
@@ -574,7 +574,7 @@ string StFlow::componentName(size_t n) const
 {
     switch (n) {
     case 0:
-        return "u";
+        return "velocity";
     case 1:
         return "V";
     case 2:
@@ -595,6 +595,11 @@ string StFlow::componentName(size_t n) const
 size_t StFlow::componentIndex(const std::string& name) const
 {
     if (name=="u") {
+        warn_deprecated("StFlow::componentIndex",
+                        "To be changed after Cantera 2.5. "
+                        "Solution component 'u' renamed to 'velocity'");
+        return 0;
+    } else if (name=="velocity") {
         return 0;
     } else if (name=="V") {
         return 1;