Control Of Separated Unsteady Flow

Abstract

NASA and the DLR, the German Aerospace Center are working together to create and operate the Stratospheric Observatory for Infrared Astronomy (SOFIA), a reflecting telescope located inside a Boeing 747SP aircraft. During observation in the stratosphere, a door in the fuselage will be opened to expose the infrared telescope to the atmosphere. In general, the flow over cavities such as the SOFIA telescope port is characterized by unsteady flow phenomena associated with prominent pressure fluctuations caused by amplified acoustic resonances. In the present case, this phenomenon causes unwanted vibrations of the telescope structure and reduces its pointing stability. Flow control in the case of SOFIA is performed by a slanted rear wall that stabilizes the shear layer’s impingement point and prevents it from oscillating violently.
The objective of the present numerical investigations is to estimate the potential to increase the performance of the system by active and passive flow control methods. These methods allow changing the shear layer’s characteristics and permit to shift the acoustic resonant frequencies away from resonance modes of the telescope structure.