diff --git a/turek-hron-fsi3/fluid-openfoam/0/U b/turek-hron-fsi3/fluid-openfoam/0/U
index be5b1efd4..8bd25ec5f 100644
--- a/turek-hron-fsi3/fluid-openfoam/0/U
+++ b/turek-hron-fsi3/fluid-openfoam/0/U
@@ -46,23 +46,26 @@ boundaryField
             const vectorField& Cf = patch().Cf();
             vectorField& field = *this;
 
-            const scalar pi = 3.14159265358979;
+            const scalar pi = constant::mathematical::pi;
             const scalar Umean = 2.0;
+            const scalar H = 0.41;    // channel height
+            const scalar H_2 = H * H; // equals 0.1681
             const scalar t = this->db().time().value();
+            // ramp up below 2 seconds
             if (t < 2)
             {
                 forAll(Cf, faceI)
                 {
-                    const scalar y = Cf[faceI][1];
-                    field[faceI] = vector((1.5 * Umean * 4.0 / 0.1681) * y * (0.41 - y) * ((1 - cos(pi / 2 * t)) / 2), 0, 0);
+                    const scalar y = Cf[faceI].y();
+                    field[faceI] = vector((1.5 * Umean * 4.0 / H_2) * y * (H - y) * ((1 - cos((pi / 2) * t)) / 2), 0, 0);
                 }
             }
             else
             {
                 forAll(Cf, faceI)
                 {
-                    const scalar y = Cf[faceI][1];
-                    field[faceI] = vector((1.5 * Umean * 4.0 / 0.1681) * y * (0.41 - y), 0, 0);
+                    const scalar y = Cf[faceI].y();
+                    field[faceI] = vector((1.5 * Umean * 4.0 / H_2) * y * (H - y), 0, 0);
                 }
             }
         #};