דניאלה רווה
Shock-buffet is a phenomenon of large, self-sustained shock oscillations that are observed for certain combinations of Mach number and steady mean angle of attack (without any structural motion!). Shock buffet has a characteristic frequency that is within the range of typical elastic structural and control frequencies of fighter and transport airplanes. A numerical study was initiated to study the shuck-buffet phenomenon, and examine the possible relationship of shock-buffet and undesirable nonlinear transonic aeroelastic phenomena such as limit-cycle oscillations (LCO), and control-surface buzz.
The on-going study has three parts – Numerical flow simulations of a NACA0012 airfoil in transonic buffeting flows. These simulations characterize the shock-buffet phenomenon and validate the computational methodology via comparison to wind tunnel experiments; Numerical simulations of flow responses to prescribed airfoil motion; and Numerical aeroelastic simulations of spring-suspended airfoils in transonic buffeting flows.
Prescribing airfoil motions revealed a frequency lock-in phenomenon – It was found that for prescribed airfoil motion of frequencies that are close to the shock-buffet frequency, and are beyond some threshold amplitude, the shockbuffet frequency synchronizes with the airfoil motion frequency. There is a broad analogy between this flow phenomenon and the flow field of the Von Karman vortex street found behind a cylinder with the cylinder undergoing a prescribed oscillation. It is speculated that the locked-in shock-buffet excites the elastic structure in a resonance mechanism, resulting in LCO or other nonlinear aeroelastic phenomena.
The seminar will present the phenomena of shock-buffet and shock-buffet lock-in, will present aeroelastic responses of single- and two-dof systems in buffeting flows, and suggest a physical mechanism that may contribute to LCO and control surface buzz observed in fighter planes.
ההרצאה תתקיים ביום שני י"ח טבת תש"ע (04.01.2010)
שעה 13:30
בנין אוירונוטיקה חדר 241
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