ENH: snappyHexMesh: initial version of directional refinement

applications/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C

@@ -1082,7 +1082,29 @@ int main(int argc, char *argv[])
 
     if (!limitDict.empty())
     {
-        Info<< "Read refinement shells in = "
+        Info<< "Read limit shells in = "
+            << mesh.time().cpuTimeIncrement() << " s" << nl << endl;
+    }
+
+
+    // Optionally read directional refinement shells
+    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    const dictionary dirRefDict
+    (
+        refineDict.subOrEmptyDict("directionalRefinementRegions")
+    );
+
+    if (!dirRefDict.empty())
+    {
+        Info<< "Reading directional refinement shells." << endl;
+    }
+
+    shellSurfaces dirShells(allGeometry, dirRefDict);
+
+    if (!dirRefDict.empty())
+    {
+        Info<< "Read directional refinement shells in = "
             << mesh.time().cpuTimeIncrement() << " s" << nl << endl;
     }
 
@@ -1119,6 +1141,7 @@ int main(int argc, char *argv[])
         surfaces,           // for surface intersection refinement
         features,           // for feature edges/point based refinement
         shells,             // for volume (inside/outside) refinement
+        dirShells,          // vol volume directional refinement
         limitShells         // limit of volume refinement
     );
     Info<< "Calculated surface intersections in = "

applications/utilities/mesh/generation/snappyHexMesh/snappyHexMeshDict

@@ -49,6 +49,14 @@ geometry
         max (3.5 2 0.5);
     }
 
+    // Shell for directional refinement
+    refinementBox
+    {
+        type searchableBox;
+        min (1.5 1 -0.5);
+        max (3.5 2 0.5);
+    }
+
     sphere.stl
     {
         type triSurfaceMesh;
@@ -278,6 +286,21 @@ castellatedMeshControls
     }
 
 
+    directionalRefinementRegions
+    {
+        refinementBox       // Closed surface
+        {
+            mode inside;
+            levelIncrement  // Specification of additional refinement
+            (
+                (0 (1 0 0)) // For level 0 cells: add one level refinement in x
+                (1 (1 0 0)) // For level 1 cells: add one level refinement in x
+            );
+        }
+    }
+
+
+
     // Optionally limit refinement in geometric region. This limits all
     // refinement (from features, refinementSurfaces, refinementRegions)
     // in a given geometric region. The syntax is exactly the same as for the