Experimental and theoretical investigation of backward-facing step flow

Abstract

Laser-Doppler measurements of velocity distribution and reattachment length are reported downstream of a single backward-facing step mounted in a two-dimensional channel. Results are presented for laminar, transitional and turbulent flow of air in a Reynolds-number range of 70 < Re < 8000. The experimental results show that the various flow regimes are characterized by typical variations of the separation length with Reynolds number. The reported laser-Doppler measurements do not only yield the expected primary zone of recirculating flow attached to the backward-facing step but also show additional regions of flow separation downstream of the step and on both sides of the channel test section. These additional separation regions have not been previously reported in the literature.Although the high aspect ratio of the test section (1:36) ensured that the oncoming flow was fully developed and two-dimensional, the experiments showed that the flow downstream of the step only remained two-dimensional at low and high Reynolds numbers.The present study also included numerical predictions of backward-facing step flow. The two-dimensional steady differential equations for conservation of mass and momentum were solved. Results are reported and are compared with experiments for those Reynolds numbers for which the flow maintained its two-dimensionality in the experiments. Under these circumstances, good agreement between experimental and numerical results is obtained.

A simple and efficient outflow boundary condition for the incompressible Navier–Stokes equations

“…To obtain a more accurate result, we numerically compute the reattachment length X h r by using the quadratic polynomial α = aβ 2 + bβ + c with three given points, (x m , y 3 ), (x p , y 2 ), and (x q , y 1 ) (see Figure 8 them together. From these results, we observe that the results obtained by using our proposed method are in good agreement with those from the previous numerical methods (Barton, 1997;Kim & Moin, 1985) and experiment (Armaly, Durst, & Pereira, 1983). The agreement in our computational results obtained from a larger domain and a smaller domain suggests that our proposed outflow boundary condition is efficient.…”

“…We then compare our results with the previous experimental (Armaly, Durst, & Pereira, 1983) and numerical (Barton, 1997;Kim & Moin, 1985) results.…”

Reduction of Numerical Diffusion in FFD Model

“…There are many experimental data (Armaly et al, 1983;Driver and Seegmiller, 1985;Durst and Schmitt, 1985) and numerical simulations (Barton, 1994 Fig. 8 gives the schematic view of the experiment.…”

“…Four different meshes (25 × 25, 50 × 50, 100 × 100 and 200 × 200) are used to achieve a mesh independent solution. Table 1 compares the calculated reattachment length from the step with the experimental data (Armaly, et al, 1983). The grids are 100 × 100 for the flow at Re = 100 and 200 × 200 for Re = 389.…”

Laminar CuO–water nano-fluid flow and heat transfer in a backward-facing step with and without obstacle

“…In their study, LES was used where good agreement noted between 2D and 3D numerical data with experimental data in profile of both velocity and temperature. Laminar, transition, and turbulent fluid flow over backward-facing step were experimentally and numerically studied by Armaly et al (1983). The results revealed the increase in separation length with increase of Reynolds number for Re \ 1200 but decrease at Re between 1200 and 5550.…”