High Reynolds Number Turbulent Boundary Layer Flow over Small Forward Facing Steps

Measurements were made on three forward steps with step height to boundary layer ratio of approximately 3.8%, 15% and 60% and Reynolds number based on step height ranging from 6640 to 213,000. The measurements included mean wall pressure, single and 2 point wall pressure fluctuations, single and 2 point velocity fluctuations and, oil flow visualization. Pressure fluctuation measurements were made 5 boundary layer thicknesses upstream of step to 22 boundary layer thickness (or 600 step heights for smallest step size) downstream of the step. The results show that the steps remarkably enhance the wall pressure fluctuations that scale on the step height in the vicinity of the step and far downstream of the step. The decay of wall pressure fluctuations post reattachment is a slow process and elevated levels can be seen as far as 150 step heights downstream for the mid step size. The enhanced pressure fluctuations come from the unsteady reattachment region on top face of the step which was found to be a strong function of flow geometry and flow parameters such as Reynolds number. The 2 point pressure and velocity space-time correlations show a quasi-periodic structure which begins to develop close to the reattachment and grows in intensity and scale further downstream of reattachment and is responsible for the elevated pressure fluctuations downstream of the step. However, the velocity correlations lack in scale reflecting the fact that large scales reflected in pressure are masked by smaller scales that exist within them.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Aerospace and Ocean Engineering

Department dc:contributor.department

Aerospace and Ocean Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2012

Author dc:creator

• Awasthi, Manuj

Chair dc:contributor.committeechair

• Devenport, William J.

Committee members dc:contributor.committeemember

• Lowe, K. Todd
• Glegg, Stewart A. L.

• turbulent boundary layer
• forward facing steps
• wall pressure fluctuations
• separating-reattaching flow
• velocity fluctuation

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-06292012-120614

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/33820