From af9afec75491bcaee21f187409739c763b62a2cc Mon Sep 17 00:00:00 2001
From: Chris Greenshields <https://cfd.direct>
Date: Fri, 18 Aug 2023 16:46:06 +0100
Subject: [PATCH] snappyHexMeshConfig: allow a cylindrical background mesh
 without a rotating zone

---
 .../blockMeshCylindricalConfiguration.C         | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/applications/utilities/preProcessing/snappyHexMeshConfig/blockMeshCylindricalConfiguration.C b/applications/utilities/preProcessing/snappyHexMeshConfig/blockMeshCylindricalConfiguration.C
index b22f620672..82559c14a6 100644
--- a/applications/utilities/preProcessing/snappyHexMeshConfig/blockMeshCylindricalConfiguration.C
+++ b/applications/utilities/preProcessing/snappyHexMeshConfig/blockMeshCylindricalConfiguration.C
@@ -136,7 +136,7 @@ void Foam::blockMeshCylindricalConfiguration::writeDefaultPatch()
     }
     else
     {
-        defaultPatch = {"sides", "patch"};
+        defaultPatch = {"background", "internal"};
     }
 
     beginDict(os_, "defaultPatch");
@@ -421,10 +421,17 @@ Foam::blockMeshCylindricalConfiguration::blockMeshCylindricalConfiguration
 
     if (rzbb_.volume() == 0)
     {
-        FatalErrorInFunction
-            << "Attempting to create a cylindrical background mesh"
-            << nl << "but the rotatingZone surface has zero volume."
-            << exit(FatalError);
+        WarningInFunction
+            << "Creating a cylindrical background mesh without a "
+            << "rotatingZone specified by the '-rotatingZones' option."
+            << nl <<endl;
+
+        // Create the intermediate interface at 40% of domain size if no
+        // rotating zone is specified
+        scalar factor = 0.4;
+
+        rzbb_.min() = factor*bb_.min();
+        rzbb_.max() = factor*bb_.max();
     }
 
     calcBlockMeshDict();