Address Peter's review:

- stop defining cpT and rho cp T functors
- add a transient test
+ add an exception test

modules/navier_stokes/src/functormaterials/INSFVEnthalpyFunctorMaterial.C

@@ -94,28 +94,21 @@ INSFVEnthalpyFunctorMaterial::INSFVEnthalpyFunctorMaterial(const InputParameters
   }
   else if (_h)
   {
-    const auto & rho_h = addFunctorProperty<ADReal>(NS::enthalpy_density,
+    addFunctorProperty<ADReal>(NS::enthalpy_density,
                                                     [this](const auto & r, const auto & t)
                                                     { return _rho(r, t) * (*_h)(r, t); });
 
     addFunctorProperty<ADReal>(NS::time_deriv(getParam<MooseFunctorName>(NS::specific_enthalpy)),
                                [this](const auto & r, const auto & t) { return _h->dot(r, t); });
-
-    addFunctorProperty<ADReal>(
-        "rho_cp_temp", [&rho_h](const auto & r, const auto & t) -> ADReal { return rho_h(r, t); });
-
-    addFunctorProperty<ADReal>(
-        "cp_temp", [this](const auto & r, const auto & t) -> ADReal { return (*_h)(r, t); });
   }
   else
   {
-    const auto & rho_h = addFunctorProperty<ADReal>(
+    addFunctorProperty<ADReal>(
         NS::enthalpy_density,
         [this](const auto & r, const auto & t)
         { return _rho(r, t) * _fp->h_from_p_T((*_pressure)(r, t), _temperature(r, t)); });
 
-    const auto & h =
-        addFunctorProperty<ADReal>(NS::specific_enthalpy,
+    addFunctorProperty<ADReal>(NS::specific_enthalpy,
                                    [this](const auto & r, const auto & t) {
                                      return _fp->h_from_p_T((*_pressure)(r, t), _temperature(r, t));
                                    });
@@ -128,11 +121,5 @@ INSFVEnthalpyFunctorMaterial::INSFVEnthalpyFunctorMaterial(const InputParameters
           _fp->h_from_p_T((*_pressure)(r, t).value(), _temperature(r, t).value(), h, dh_dp, dh_dT);
           return dh_dT * _temperature.dot(r, t) + dh_dp * _pressure->dot(r, t);
         });
-
-    addFunctorProperty<ADReal>(
-        "rho_cp_temp", [&rho_h](const auto & r, const auto & t) -> ADReal { return rho_h(r, t); });
-
-    addFunctorProperty<ADReal>("cp_temp",
-                               [&h](const auto & r, const auto & t) -> ADReal { return h(r, t); });
   }
 }

modules/navier_stokes/test/tests/finite_volume/wcns/materials/tests

@@ -1,11 +1,24 @@
 [Tests]
   issues = '#16809'
   design = 'navier_stokes/wcnsfv.md'
-  [transient]
+  [transient_constant_cp_approx]
     type = 'Exodiff'
     input = 2d-transient.i
     exodiff = 2d-transient_out.e
     method = "!dbg"
+    requirement = 'The system shall be able to use realistic fluid properties in a weakly compressible flow simulation, while approximating enthalpy as the product of specific heat and temperature'
+    rel_err = 7e-5
+    # The non-linear tolerance is actually fairly tight, but the variable values
+    # are small at the no-slip boundary conditions, and this leads to absolute diffs of around 1e-15,
+    # triggering the default relative tolerance error criterion
+    valgrind = HEAVY
+  []
+  [transient_using_h]
+    type = 'Exodiff'
+    input = 2d-transient.i
+    cli_args = 'FunctorMaterials/ins_fv/assume_constant_cp=false FunctorMaterials/ins_fv/fp=fp FunctorMaterials/ins_fv/pressure=pressure'
+    exodiff = 2d-transient_out.e
+    method = "!dbg"
     requirement = 'The system shall be able to use realistic fluid properties in a weakly compressible flow simulation'
     rel_err = 7e-5
     # The non-linear tolerance is actually fairly tight, but the variable values
@@ -81,5 +94,12 @@
       expect_err = "'reference_pressure_point' and 'reference_pressure' should not be set unless solving for the dynamic pressure"
       detail = "the reference pressure is set when not solving for the dynamic pressure"
     []
+    [missing_fp]
+      type = RunException
+      input = '2d-transient.i'
+      cli_args = "FunctorMaterials/ins_fv/assume_constant_cp=false"
+      expect_err = "Must specify both fluid properties and pressure or an enthalpy functor "
+      detail = "not enough parameters are specified when defining the enthalpy functor."
+    []
   []
 []