VMFL064

VMFL064
Low Reynolds Number Flow in a Channel with Sudden Asymmetric Expansion

Overview

Reference

B. Armaly, F. Durst, J. Pereira, B. Schönung. “Experimental and theoretical investigation of a backward-facing step”. Journal of Fluid Mechanics, Vol 127, pg. 473, 1983

C.J. Freitas. “Perspective: Selected Benchmarks from Commercial CFD Codes”. Journal of Fluids Engineering. Vol. 117, pg. 208, 1995

Solver Ansys Fluent

Physics/Models Laminar flow, Separation, and Reattachment

Input File

VMFL064_FLUENT.cas

Project Files Link to Project Files Download Page

Test Case

Laminar flow in a channel with a backward facing step expansion is modeled. The channel section upstream of the expansion is long enough to ensure fully developed laminar profile. The reattachment length predicted by the solvers is validated against experimental results. Reynolds number based on D (equal to twice the channel height at inlet) is 200. The domain extends to about 40 times the step-height upstream and over 20 times the step-height downstream.

Figure 154: Flow Domain

Material Properties	Geometry	Boundary Conditions
Density: 1 kg/m³ Viscosity: 1.5 X 10^-5 kg/m-s	Step height, s = 4.9 mm Channel height at inlet = 5.2 mm Length of inlet section = 200 mm Length downstream of the step = 100 mm	Velocity at inlet = 0.288462 m/s No-slip condition at the walls

Material Properties

Geometry

Boundary Conditions

Density: 1 kg/m³

Viscosity:

1.5 X 10^-5 kg/m-s

Step height, s = 4.9 mm

Channel height at inlet = 5.2 mm

Length of inlet section = 200 mm

Length downstream of the step =

100 mm

Velocity at inlet = 0.288462 m/s

No-slip condition at the walls

Analysis Assumptions and Modeling Notes

The flow is fully developed before the step. Reattachment length is measured from the reversal of the sign of the wall shear along the flow direction.

Results Comparison for Ansys Fluent

Table 38: Comparison of Reattachment Length

	Target	Ansys Fluent	Ratio
Non-dimensionalized Reattachment length (L_R/Step-height)	5.0	4.91	0.982