Abstract:
Self sustained shock wave oscillation on airfoils at transonic flow conditions are associated with the
phenomenon of buffeting, high speed impulsive noise, non synchronous vibration, high cycle fatigue
failure and so on. Though experiments demonstrate the presence of periodic shock oscillation in flow
over airfoil in some transonic speeds, the physical mechanism of periodic shock motion is not fully
understood yet. The present numerical study investigates the intricate flow phenomenon associated
with self sustained shock oscillation and the passive control of shock oscillation using cavity over a
symmetrical circular arc airfoil at zero incidence. The effect of incorporating both open and perforated
cavity on the airfoil surfaces are demonstrated systematically considering pressure rise across the
shock as an indicator of shock strength. Three different cases of open cavity control and nine different
cases of perforated cavity control is studied along with the clean (base airfoil) airfoil. Results for base
airfoil and airfoil with cavities (open and perforated) are compared to understand the effects of cavity
installation. Shock strength, total pressure loss and surface pressure fluctuation are investigated by
interpreting various shock characteristics like shock location, shock Mach number, boundary layer
thickness and shock boundary layer interaction zone for all the cases. Results show that both open and
perforated cavity can reduce the shock strength, surface pressure fluctuation near the airfoil and total
pressure loss. The change in both flow characteristics and shock wave characteristics is studied and
their dependency on the configuration of cavity and percentage of perforation are observed and proper
suggestions are made.
The results suggest that open cavity can be a better choice to control shock oscillation for external
high speed flow over a single airfoil or internal flows through a series of airfoils separated by
sufficient distance. But open cavities have a major difficulty for internal high speed flow application
through a series of airfoils placed close to one another. On the other hand perforated cavities can also
reduce surface pressure fluctuation for both internal and external high speed flows though their
performance is not as good as open cavities. A comparative assessment is performed to ensure the
economic feasibility of both open and perforated cavity control by calculating the integrated total
pressure loss (ITPL).
