fix: remove output fields subsumed by primitiveVars to prevent duplic…

flow360/component/simulation/outputs/output_fields.py

@@ -575,3 +575,33 @@ def append_component_to_output_fields(output_fields: List[str]) -> List[str]:
         if field == "vorticity" and "vorticityMagnitude" not in output_fields:
             output_fields_with_component.append("vorticityMagnitude")
     return output_fields_with_component
+
+
+# In the C++ solver, "primitiveVars" expands to DataArrays named "rho", "velocity", and "p".
+# "pressure" and "velocity" individually produce DataArrays with the same names ("p" and
+# "velocity"). Having both creates duplicate DataArray names in VTK output, which causes
+# ParaView to fail when loading a subset of fields.
+_FIELDS_SUBSUMED_BY_PRIMITIVE_VARS = {"pressure", "velocity"}
+
+
+def remove_fields_subsumed_by_primitive_vars(output_fields: List[str]) -> List[str]:
+    """
+    Remove output fields that are already included as sub-fields of ``primitiveVars``.
+
+    Must be called after :func:`append_component_to_output_fields` so that auto-appended
+    fields like ``velocity_magnitude`` are already in the list before ``velocity`` is removed.
+
+    Parameters:
+    -----------
+    output_fields : List[str]
+        The list of output fields to deduplicate.
+
+    Returns:
+    --------
+    List[str]
+        The deduplicated list with ``pressure`` and ``velocity`` removed when
+        ``primitiveVars`` is present.
+    """
+    if "primitiveVars" not in output_fields:
+        return output_fields
+    return [f for f in output_fields if f not in _FIELDS_SUBSUMED_BY_PRIMITIVE_VARS]

flow360/component/simulation/translator/solver_translator.py

@@ -67,6 +67,7 @@
     PREDEFINED_UDF_EXPRESSIONS,
     append_component_to_output_fields,
     generate_predefined_udf,
+    remove_fields_subsumed_by_primitive_vars,
 )
 from flow360.component.simulation.outputs.outputs import (
     AeroAcousticOutput,
@@ -304,6 +305,7 @@ def translate_output_fields(
             output_fields.append(output_field.name)
     # Filter out the UserVariable Dicts
     output_fields = [item for item in output_fields if isinstance(item, str)]
+    output_fields = remove_fields_subsumed_by_primitive_vars(output_fields)
     return {"outputFields": sorted(output_fields)}
 
 
@@ -532,6 +534,7 @@ def translate_volume_output(
             output_fields.append(output_field.name)
     # Filter out the UserVariable Dicts
     output_fields = [item for item in output_fields if isinstance(item, str)]
+    output_fields = remove_fields_subsumed_by_primitive_vars(output_fields)
     volume_output.update(
         {
             "outputFields": sorted(output_fields),

tests/simulation/outputs/test_output_fields.py

@@ -2,7 +2,10 @@
 
 import flow360 as fl
 from flow360 import SI_unit_system, u
-from flow360.component.simulation.outputs.output_fields import generate_predefined_udf
+from flow360.component.simulation.outputs.output_fields import (
+    generate_predefined_udf,
+    remove_fields_subsumed_by_primitive_vars,
+)
 
 
 @pytest.fixture
@@ -137,3 +140,47 @@ def test_generate_field_udf_no_match(simulation_params):
     """Test behavior when no matching predefined expression is found."""
     result = generate_predefined_udf("non_existent_field_for_udf", simulation_params)
     assert result is None
+
+
+class TestRemoveFieldsSubsumedByPrimitiveVars:
+    def test_removes_pressure_and_velocity_when_primitive_vars_present(self):
+        fields = ["Cp", "primitiveVars", "pressure", "velocity", "Mach"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert "primitiveVars" in result
+        assert "pressure" not in result
+        assert "velocity" not in result
+        assert "Cp" in result
+        assert "Mach" in result
+
+    def test_keeps_pressure_and_velocity_when_no_primitive_vars(self):
+        fields = ["pressure", "velocity", "Cp"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert result == ["pressure", "velocity", "Cp"]
+
+    def test_preserves_velocity_magnitude_when_velocity_removed(self):
+        fields = ["primitiveVars", "velocity", "velocity_magnitude", "pressure"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert "velocity" not in result
+        assert "pressure" not in result
+        assert "velocity_magnitude" in result
+        assert "primitiveVars" in result
+
+    def test_no_op_on_empty_list(self):
+        assert remove_fields_subsumed_by_primitive_vars([]) == []
+
+    def test_primitive_vars_only(self):
+        fields = ["primitiveVars"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert result == ["primitiveVars"]
+
+    def test_removes_pressure_only_when_velocity_absent(self):
+        fields = ["primitiveVars", "pressure", "Cp"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert "pressure" not in result
+        assert result == ["primitiveVars", "Cp"]
+
+    def test_removes_velocity_only_when_pressure_absent(self):
+        fields = ["primitiveVars", "velocity", "Mach"]
+        result = remove_fields_subsumed_by_primitive_vars(fields)
+        assert "velocity" not in result
+        assert result == ["primitiveVars", "Mach"]

tests/simulation/translator/test_output_translation.py

@@ -88,7 +88,6 @@ def volume_output_config(vel_in_km_per_hr):
                 "betMetrics",
                 "primitiveVars",
                 "qcriterion",
-                "velocity",
                 "velocity_in_km_per_hr",
                 "velocity_magnitude",
                 "vorticity",
@@ -125,7 +124,6 @@ def avg_volume_output_config(vel_in_km_per_hr):
                 "betMetrics",
                 "primitiveVars",
                 "qcriterion",
-                "velocity",
                 "velocity_in_km_per_hr",
                 "velocity_magnitude",
             ],
@@ -172,7 +170,6 @@ def test_volume_output(volume_output_config, avg_volume_output_config):
                 "betMetrics",
                 "primitiveVars",
                 "qcriterion",
-                "velocity",
                 "velocity_in_km_per_hr",
                 "velocity_magnitude",
                 "vorticity",
@@ -190,7 +187,6 @@ def test_volume_output(volume_output_config, avg_volume_output_config):
                 "betMetrics",
                 "primitiveVars",
                 "qcriterion",
-                "velocity",
                 "velocity_in_km_per_hr",
                 "velocity_magnitude",
             ],