Study of Junctions in 1-D & 3-D Simulation for Steady and Unsteady Flow 2010-01-1050
In this work a comparative study between 1-D and 3-D
calculations has been performed on different junctions. The
geometries are a 90° T-junction with an area ratio of unity and a
45° junction with an area ratio of 1.78 between the main pipe and
the side branch. The latter case had an offset between the
centerlines of the main and the branched pipe. The 3-D modeling
framework uses the Reynolds Averaged Navier-Stokes (RANS) equations
with the k-ε model both for the steady and the unsteady flow cases.
The comparison is made both under steady and pulsating flow
conditions. The aim has been to assess the 1-D/3-D differences in
terms of measures for flow losses.
For the steady flow cases it is shown that there is a large
difference between the 1-D and 3-D computed losses for both
junction geometries. The differences are largest in the junction
and right downstream of it. For the 90° case the 1-D computed loss
in isentropic power is 10% higher as compared to the 3-D results
for the loss computed in the junction plus two pipe diameters into
the outlet pipe. The corresponding 1-D/3-D discrepancy for the 45°
junction is 115%. The 1-D/3-D comparison for the pulsating flow
case is a discrepancy of 30% for the 90° junction and as much as
365% for the 45° junction. The 1-D losses are the larger of the
two.
