The flow over ribs consists of a forward-facing step followed by a backward-facing step. The interaction between the aerodynamics of these two canonical obstacles leads to complex patterns in an oscillating flow which depend on rib length. In order to study the aerodynamics of ribs, four steps were taken which involve multiple forms of velocity and pressure measurements. To begin, a method to estimate pressure fields from particle image velocimetry is applied and validated against pressure measurements. This provides pressure information necessary for the rest of the study. Second, the characteristics of the flow over ribs of varying length are studied in a statistical sense. Trends identified in previous work were found and extended to new quantities. The effect of free-stream turbulence on the characteristics of the flow is studied. It highlights the sensitivity of separation over short obstacles to free-stream turbulence in contrast with the unchanging separation over longer obstacles. Finally, the relationship between pressure and velocity is described using modelling of velocity components from surface pressure information. It shows that individual patterns in velocity fluctuations such as vortex shedding and shear layer flapping are closely linked to surface pressure fluctuations.

Figure: Illustration of the flow captured by the low-speed PIV setup.

Bharath Ganapathisubramani's

Experimental Fluid Mechanics

Research Laboratory

The aerodynamics of surface-mounted ribs

Jacques Van der Kindere, Roeland de Kat, Bharath Ganapathisubramani