UNSTEADY FLOWFIELD AND NOISE-PROPAGATION DUE TO TRANSONIC AIRFOIL-AIRFOIL INTERACTION

As a two-dimensional approximation to the outer region of a coaxial ro tor, the flowfields induced by transonic airfoil-airfoil interaction a re numerically simulated to investigate the aerodynamic and acoustic c haracteristics. The processes of aerodynamic load fluctuation are moni tored with time for a transonic flowfield, It is observed that abrupt pressure disturbances around the leading edge of the upper airfoil ind uced by the shock wave of the lower airfoil and the ensuing oscillatio n of the shock wave cause the severe aerodynamic load fluctuation in t he upper airfoil, and a strong sound wave is radiated from the upper a irfoil in some cases. A series of parametric studies shows that both t he intensity and the slope of the load fluctuation are more sensitive to vertical miss distance than to angle of attack, but the hysteresis in lift is more dependent on angle of attack. A modified approach is s uggested to minimize the numerical compression wave generated when imp osing an initial condition for an asymmetric unsteady flowfield, and i t is shown to be very efficient for shortening the initial start dista nce, thereby saving computation time.