Master Degree presentation by Omar Elias – “Project of fabrication and performance test of an apparatus to the experimental study of laminar separation bubbles”

The present work involves design, construction and performance test of an
apparatus for investigation of laminar separation bubbles in a flat plate boundary
layer. Laminar separation bubbles are relevant for many engineering applications
and the dynamic of such bubbles has a strong impact on the performance of aircrafts
and turbines. The separated boundary layer reattaches to the surface due to the
laminar-turbulent transition in the bubble region. This dynamic process is highly
challenging for flow simulation tools used for engineering purposes. Thus, there is
a demand for experimental studies that can be used for calibration of models present
in those simulation tools. To this end, an apparatus was designed and built for the
water channel of the Laboratory of Fluid Engineering at PUC-Rio. The boundary
layer separation on the flat plate was induced by imposing a constant adverse
pressure gradient to the flow. To this end a false wall was built, in order to form a
converging-diverging channel with the flat plate. Flow separation on the false wall
was avoided using a suction mechanism that was designed to reduce locally the
boundary layer thickness. Location of suction and suction flow rates were
determined with aid of numerical simulations. In addition, it was designed and built
a disturbance source to generate Tollmien-Schlichting waves in the boundary layer
of the flat plate. This device was used to trigger the boundary layer transition in a
controlled manner. All equipments were tested and their designs were validated
against experimental measurements. Laser Doppler anemometry and Particle Image
Velocimetry techniques were adopted for assessment of each equipment. Results
validate the design and show that separation bubbles can be investigated in detail
using this apparatus.