Update comments and allow mesh not to be redownloaded if present for shell tube test

Author: mattfalcone1997

.gitignore

@@ -151,6 +151,9 @@ moose/include/base/Precompiled.h.gch
 # OpenFOAM mesh object files
 test/**/*.obj
 
+# downloaded mesh tarballs
+test/tests/**/*.tar.gz
+
 framework/contrib/exodiff/exodiff
 
 # Mac garbage

test/tests/multiapps/shell_tube_heat_exchanger/prep.sh

@@ -1,14 +1,19 @@
 #!/bin/bash
 
+set -e -u -o pipefail
+
 # Downloads mesh file and check the hash against known reference
 downloadMesh()
 {
     DIRECTORY=$1
     URL=$2
     HASH=$3
-    FILE=$(basename ${URL})
+    FILE=${DIRECTORY}_mesh.tar.gz
+
+    if [ ! -f $FILE ]; then
+        wget -O $FILE -nv ${URL}
+    fi
 
-    wget -O $FILE -nv ${URL}
     if [ $? -ne 0 ]; then
         echo "Download failed"
         exit 1
@@ -21,9 +26,7 @@ downloadMesh()
 
     tar -xvf $FILE
     mv polyMesh.org $DIRECTORY/constant/polyMesh
-    rm -f $FILE
     gzip -d -q $DIRECTORY/constant/polyMesh/*
-    return 0
 }
 
 foamCleanCase -case fluid_inner

test/tests/multiapps/shell_tube_heat_exchanger/solid.i

@@ -87,13 +87,7 @@
     []
 []
 [Materials]
-    # The example specifies that the thermal diffusivity of the solid should
-    # be α = 1 m2/s, and the thermal conductivity should be k = 100 W/(m.K).
-    #
-    # We know α = k/(Cp.ρ), where k is thermal conductivity, Cp is specific
-    # heat capacity, and ρ is density.
-    #
-    # Hence we require that Cp.ρ = k = 100.
+    # Solid material properties for copper
     [thermal-conduction]
         type = ADGenericConstantMaterial
         prop_names = 'thermal_conductivity density'