Direct Numerical Simulations (DNS) of pipe flow with and without swirl are carried out and compared. Swirling pipe flow due to pipe rotation has been reported numerous times in the past, e.g. by DNS in  or by experiments in . In the present case, a pressure gradient in the azimuthal direction is setting up a swirl in the near wall region. In comparison to the rotating pipe, the swirl is to a greater extent concentrated close to the pipe wall. However, while the rotating pipe has been investigated experimentally several times, e.g. in , the present case is not realizable in practice. A 25R long pipeline with diameter
is considered. The pipe is divided into about 6.3 million grid cells in a cylindrical coordinate system (129, 97, and 512 in
, r, and z, respectively). The Navier-Stokes equations are solved by a finite-difference code, developed by Orlandi , on a staggered grid, non-uniform in the radial direction. In addition, the flow is driven by an axial pressure gradient sufficient to keep a constant bulk Reynolds number
= 4900. Here,
is the bulk velocity and
is the kinematic viscosity.
( = 2
) is the centerline velocity in the laminar Poiseuille profile used as the initial start up profile. Cyclic boundary conditions are used in the axial- and the azimuthal direction.