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Optimization of saw tooth for a better cavity control
Cavities generally exist in the form of landing gear wheel well and weapon bay in
aircrafts. The grazing flow over the cavity tends to produce high magnitudes of oscillation
at a frequency that depends on so many factors such as cavity dimensions, free stream
Mach number, boundary layer status at cavity leading edge.
The separated shear layer from the leading edge grows and the disturbances are amplified
due to Kelvin Helmholtz instability, and the shear layer is wrapped into vortices and the
unsteady impingement of the shear layer on the rear wall produces pressure waves
that travels inside the cavity toward leading edge. Upon reaching the leading edge,
the pressure wave energises the leading edge and completes the feedback loop which
leads to self sustained oscillations.
Without control this high amplitude self sustained oscillations (Upto 170 dB) can damage
the sensitive electronic equipments. The noise radiated from the cavity need to be
controlled.
Among passive, open and closed active control techniques, passive control has the
advantages over other control techniques in the form of simple, easy to install and
maintain. They dont need any external energy input. Saw tooth spoiler (Fig A) is one
such passive control technique which controls the cavity oscillation by introducing the
streamwise vorticity.
However the clockwise vorticity induced from one side of the saw tooth can be canceled
by the anticlockwise vorticity from the next next saw tooth (Fig B). Hence by displacing
the saw tooths the control can be enhanced. But by increasing the gap the control may
fail for larger width. Hence it is required to optimise the gap between the tooth and the
corresponding effect on the flow.
This study aims to optimise the saw tooth configuration by varying the distance between
the tooth and the height of the tooth with respect to the boundary layer thickness. The
optimised configurations will be tested at subsonic, transonic and supersonic Mach
numbers.
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Figure 1: Saw tooth spoiler
Relevant Papers
Note - Click on the link to go to the file location
• Cavity Oscillation Mechanisms in High-Speed Flows
URL: http://www.ae.utexas.edu/~clemens/AIAAJ-cavity2.pdf
• Review of active control of flow-induced cavity resonance
URL: http://www.marcodebiasi.net/MDresearch/references/AIAA2003-3567.pdf
• On self-sustained oscillations in two-dimensional compressible flow over rectangular
cavities
URL: http://authors.library.caltech.edu/1181/1/ROWjfm02.pdf
• Compressible cavity flow oscillation due to shear layer instabilities and pressure
feedback
URL: http://www.southampton.ac.uk/~mb4/xin_zhang/8.pdf
• Cavity Noise Contents
URL:
http://sin-web.paris.ensam.fr/squelettes/ref_biblio/Gloerfelt_VKI_
2009a.pdf
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• On the pressure oscillations inside a deep cavity excited by a grazing airflow
URL:
http://129.104.25.7/publications/documents/hemon2004rp-1pp.pdf
• Investigation of flow structures involved in sound generation by two-and three-dimensional
cavity flows
URL:
http://sin-web.paris.ensam.fr/squelettes/ref_biblio/Druault_CF_2011.
pdf
• Experimental Feedback Control of Flow Induced Cavity Tones
URL:
www.cs.odu.edu/~mln/ltrs-pdfs/NASA-aiaa-2002-2497.pdf
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