Title:Comparison of Pressure-based and Skin Friction-based Methods for the
Determination of Flow Separation of a Circular Cylinder with Roundness
Imperfection
Volume: 4
Issue: 3
Author(s): Ran Wang, Shaohong Cheng*David S.K. Ting
Affiliation:
- Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario, N9B 3P4, Canada
Keywords:
Circular cylinder, roundness imperfection, flow separation, delayed detached eddy simulation, skin friction, reynolds number.
Abstract:
Introduction: A delayed detached eddy simulation in Open FOAM was performed to
study flow separation of a circular cylinder with roundness imperfection up to 4% of its diameter
at Reynolds numbers of 100, 3900, and 104 in normal flow.
Methods: The flow was considered to be Newtonian and incompressible. The separation position
was determined independently based on surface pressure distribution and skin friction.
Results: Results show that the patterns of these distributions depend on both Reynolds number
and roundness imperfection level, and flow separation in an imperfectly round cylinder may be
induced by either an adverse pressure gradient or a Gentle Bend (GB) introduced by the roughness.
For the separation point determined by the pressure-based method, its accuracy can be affected
by the characteristic of pressure distribution near the separation point at low Reynolds
numbers, and, thus, its physical validity needs to be verified by flow visualization at high Reynolds
numbers.
Conclusion: The skin friction-based method can accurately predict separation point for both perfectly
and imperfectly round cylinders without additional information. When the roundness imperfection
ratio reaches 2% and the Reynolds number reaches 3900, both approaches indicate that the
flow separation point converges to the location of GB on the cylinder surface and the two sets of
predicted separation points agree well.