Fix in shear flow initialization (fluctuation now centered around 0)

lbmpy/geometry.py

@@ -185,7 +185,7 @@ def get_shear_flow_velocity_field(domain_size, u_max, random_y_factor=0.01):
     velocity[..., 0] = u_max
     velocity[..., height // 3: height // 3 * 2, 0] = -u_max
     for j in range(1, len(domain_size)):
-        velocity[..., j] = random_y_factor * u_max * np.random.rand(*domain_size)
+        velocity[..., j] = random_y_factor * u_max * (np.random.rand(*domain_size) - 0.5)
     return velocity