TUT: use fast topological search for channel395DFSEM blockMesh

- same result, but approx 4x faster for this case

tutorials/incompressible/pimpleFoam/LES/channel395DFSEM/system/blockMeshDict

 /*--------------------------------*- C++ -*----------------------------------*\
 | =========                 |                                                 |
 | \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
-|  \\    /   O peration     | Version:  v1906                                 |
-|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
+|  \\    /   O peration     | Version:  v1912                                 |
+|   \\  /    A nd           | Website:  www.openfoam.com                      |
 |    \\/     M anipulation  |                                                 |
 \*---------------------------------------------------------------------------*/
 FoamFile
@@ -14,6 +14,8 @@ FoamFile
 }
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
+fastMerge   true;   // Use fast topological search
+
 scale   1;
 
 L   #eval{ 20*pi() };
@@ -21,7 +23,6 @@ H   1.0;
 H2  #eval{ 2*$H };
 W   #eval{ pi() };
 
-
 vertices
 (
     ( 0   0   0)
@@ -75,7 +76,6 @@ boundary
         faces           ((6 11 8 7)(11 10 9 8));
     }
 
-
     inlet
     {
         type            patch;