Using modern instrumentation such as PIV shown above, we carry out experiments in our wind-tunnels to attempt to identify underlying mechanisms producing the two different trends observed in previous literature. So far we have observed similar trends to the literature, and obtained detailed statistics of the dimensions of each recirculation regions. We also used modal decomposition to identify the various turbulent patterns present in the flow. Future plans aim to obtain refined information in carefully chosen regions around the obstacles to match surface pressure fluctuations with turbulent events in the flow above the surface of the obstacle.

Relevant literature

  • Arie, Mikio, Kiya, Masaru, Tamura, Hisataka & Kanayama, Yukio, 1975a. Flow over rectangular cylinders immersed in a turbulent boundary layer: Part 1, correlation between pressure drag and boundary-layer characteristics. Bulletin of JSME 18 (125), 1260-1268.

  • Bergeles, G & Athanassiadis, N, 1983. The flow past a surface-mounted obstacle. Journal of fluids engineering 105 (4), 461-463.

  • Antoniou, J & Bergeles, G, 1988. Development of the reattached ow behind surface-mounted two-dimensional prisms. ASME Transactions Journal of Fluids Engineering 110, 127-133.

Fig.1 Mean velocity distribution around ribs of varying length

​​We study various lengths of obstacles because it defines how the turbulent boundary layer will react to the obstacle. The picture above describes the two main responses seen. On top, if the rib is short, the flow will separate in front and on top much like a forward-facing step but the region on top will extend past the backward-facing corner of the obstacle. Below, if the rib is long, the flow may reattach on the top surface and separate again at the backward-facing corner. We investigate the differences between those two cases which were seen to produce widely different trends (Bergeles, 1983 and Antoniou, 1988) in mean and turbulent quantities.

Fig.2 Turbulent Kinetic Energy around ribs of varying length

Dynamics of separating and reattaching turbulent boundary layers


We study the dynamics of separated flows over two-dimensional wall-mounted obstacles embedded in a turbulent boundary layer. These obstacles are rectangular and vary in length from a thin fence to an elongated rib. This scenario simplifies many industrial applications where a turbulent boundary layer is unable to gently overcome the abrupt pressure gradient generated by the obstacle. As a result it separates producing several unsteady regions of separated flow. This separation has been observed in the past and has been identified as the source of strong fluctuations in velocity and pressure therefore producing noise, and stress on the underlying structures (Arie, 1975). 

Project leader : Jacques Van Der Kindere

Main supervisor(s): Prof. Ganapathisubramani