International Journal for Numerical Methods in Fluids, Volume 71, Issue 9, pages 1073–1102, 2013.
N. A. Malamataris
Center for Computational Fluid Dynamics, Department of Computational and Data Siences, George Mason University, Fairfax, VA, USA and
TEI of W. Macedonia, Kila-Kozani, Greece.
The wall effects are investigated in the three-dimensional laminar flow over a backward-facing step. For this purpose, a numerical experiment is designed under actual laboratory conditions. The aspect ratio of the computational domain is 1:40 and the expansion ratio is 1:2. The Reynolds number ranges from 100 to 950. The governing equations are the steady state, isothermal and incompressible Navier–Stokes equations for Newtonian fluids. They are solved with a homemade Galerkin finite element code. The computations are validated with data from available laboratory and numerical experiments. The results focus on the variation of both velocity profiles and lengths of eddies along the lower and upper wall in the spanwise direction. Calculated streamlines in the streamwise and transverse direction show how the flow is distorted near the lateral wall and how it develops up to the plane of symmetry. The study of skin friction lines along the top and bottom wall of the domain reveals a flow that takes place in the spanwise direction. This spanwise component of the flow becomes more dominant with increasing Reynolds number and is impossible to be sustained at steady state for Reynolds numbers higher than 950 for this particular geometry. Copyright © 2012 John Wiley & Sons, Ltd.
Copyright © 2012 John Wiley & Sons, Ltd.
This computational work shows for the first time the flow that develops in the spanwise direction in an actual three dimensional separated flow. Although this phenomenon is well understood in laboratory experiments that have been performed at Onera (French Aerospave Lab) over the last five decades, a computational verification was missing so far. This result raises again the issue of the correct method of choice in the study of three dimensional flows in computational fluid mechanics as analogous studies with other methods seem unable to produce this transverse flow that clearly distinguishes between two and three dimensional flow separation.
Figure legend: Streamlines of the three dimensional flow at selected planes in the streamwise and spanwise direction at Re=950. The direction of the streamlines along the spanwise direction point both to the wall and to the plane of symmetry, which is a sign of destabilization of the flow. The streamlines in the streamwise direction show how the flow is completely disturbed close to the lateral wall and how it develops to its familiar two dimensional shape as it reaches the plane of symmetry.