BY : CHAM Development Team - M R Malin VKI, Belgium - N P Waterson

FOR : Validation of Convection Discretisation Schemes

DATE : 1995 PHOENICS Version : 2.2

- 2d steady, incompressible, laminar, backward-facing-step flow at
Reynolds numbers of Re=150 and 450, where Re is based on 2h where
h is the flow inlet height.
- This test problem is widely used for assessing the accuracy of
numerical methods because of the dependence of the reattachment
lengths on Re.
- PHOENICS Library Case N103

- The flow has been studied experimentally by Armaly et al [1983],
and numerically by many workers, including Gartling [1990],
Gresho et al [1993] and Freitas [1995].
- Two cases are simulated by PHOENICS, namely Re=150 and Re=450.
- At Re=150, a primary recirculation zone develops immediately
downstream of the step with reattachment at X1/H=4.2, where H is
the step height.
- At Re=450, primary reattachment is at X1/H=9.5 and an additional
separation cell forms on the upper wall of the channel, with
separation at X2/H=7.6 and reattachment at X3/H=11.3.
- For Re>450, 3d effects become significant, and for Re >6,600 the flow is fully turbulent and 2d.

- PHOENICS calculations are performed on a 32 by 200 mesh with 3
different discretisation schemes for convection: HYBRID, CUBIC
UPWIND and VAN ALBADA.
- No grid refinement studies have been performed.
- The PHOENICS solutions are compared below with the data of Armaly
et al [1983] in terms of the reattachment lengths:
**Re=150 Data Hybrid Cubic-Upwind Van-Albada X1/H 4.2 4.17 4.24 4.25 Re=450 X1/H 9.5 8.79 9.13 9.06 X2/H 7.6 7.66 8.26 8.09 X3/H 11.3 11.14 11.39 11.52 DX/H 3.7 3.48 3.13 3.43**1. Laminar Backward Facing Step, Velocity Vectors & Streamlines; cubic upwind scheme

2. Laminar Backward Facing Step, Velocity Vectors & Streamlines; van Albada scheme

JJS