Revert "Merge branch 'main' into mixed_fs_supg"

This reverts commit ac03896, reversing
changes made to 62d1d49.

examples/compressible_euler/mountain_hydrostatic.py

@@ -18,7 +18,7 @@
     TrapeziumRule, SUPGOptions, ZComponent, Perturbation,
     CompressibleParameters, HydrostaticCompressibleEulerEquations,
     CompressibleSolver, compressible_hydrostatic_balance, HydrostaticImbalance,
-    SpongeLayerParameters, MinKernel, MaxKernel, logger
+    SpongeLayerParameters, MinKernel, MaxKernel, remove_initial_w, logger
 )
 
 mountain_hydrostatic_defaults = {
@@ -243,7 +243,8 @@ def mountain_hydrostatic(
 
     theta0.assign(theta_b)
     rho0.assign(rho_b)
-    u0.project(as_vector([initial_wind, 0.0]), bcs=eqns.bcs['u'])
+    u0.project(as_vector([initial_wind, 0.0]))
+    remove_initial_w(u0)
 
     stepper.set_reference_profiles([('rho', rho_b), ('theta', theta_b)])
 

gusto/initialisation/hydrostatic_initialisation.py

@@ -12,10 +12,9 @@
 from gusto.recovery import Recoverer, BoundaryMethod
 
 
-__all__ = [
-    "boussinesq_hydrostatic_balance", "compressible_hydrostatic_balance",
-    "saturated_hydrostatic_balance", "unsaturated_hydrostatic_balance"
-]
+__all__ = ["boussinesq_hydrostatic_balance",
+           "compressible_hydrostatic_balance", "remove_initial_w",
+           "saturated_hydrostatic_balance", "unsaturated_hydrostatic_balance"]
 
 
 def boussinesq_hydrostatic_balance(equation, b0, p0, top=False, params=None):
@@ -220,6 +219,23 @@ def compressible_hydrostatic_balance(equation, theta0, rho0, exner0=None,
         rho0.interpolate(thermodynamics.rho(parameters, theta0, exner))
 
 
+def remove_initial_w(u):
+    """
+    Removes the vertical component of a velocity field.
+
+    Args:
+        u (:class:`Function`): the velocity field to be altered.
+    """
+    Vu = u.function_space()
+    Vv = FunctionSpace(Vu._ufl_domain, Vu.ufl_element()._elements[-1])
+    bc = DirichletBC(Vu[0], 0.0, "bottom")
+    bc.apply(u)
+    uv = Function(Vv).project(u)
+    ustar = Function(u.function_space()).project(uv)
+    uin = Function(u.function_space()).assign(u - ustar)
+    u.assign(uin)
+
+
 def saturated_hydrostatic_balance(equation, state_fields, theta_e, mr_t,
                                   exner0=None, top=False,
                                   exner_boundary=Constant(1.0),