Unsteady aerodynamics of blade-blade interactions

A time domain method has been developed for treatments of unsteady aerodynamics and vortex dynamics for all classes of blade-blade interaction (BBI) problems. Extensive studies have been conducted on the airfoil-wake interaction (AWI) problem, the vortex-airfoil interaction (VAI) problem, the wake-airfoil interaction (WAI) problem and the blade-blade interaction (BBI) problem. A newly introduced wake-airfoil interaction (WAI) problem is found instrumental in bridging the studies of the AWI problem through the VAI problem leading to the successful treatment of the BBI problem. A new "vortex impingement" condition is introduced to improve the robustness of the discrete vortex tracking scheme and was found most effective in handling the interactions between vortex and airfoil for the VAI, WAI and BBI problems.;From the present BBI study, it is concluded that any front blade movement will induce a strong interaction between the wake of the front blade and the rear blade (the front wake-rear blade interaction); hence, it alters drastically the system response and the wake structure. Any rear blade movement induces only weak interaction; hence, it remains nearly ineffective to the response. Comparative study of WAI and BBI results indicates that the effect of the blade-blade interference effect is relatively insignificant in contrast to that of the shed front wake-rear blade interaction As a result of the latter, a coplanar stationary blade placed in the rear of another blade in harmonic oscillation could generate considerable thrust. Consequently, the overall propulsive efficiency of this blade system increases. The present study verified this earlier finding and further concludes that the thrust and propulsive efficiency decrease with increasing blade thickness.;Various computed examples are presented for different classes of problems ranging from single to airfoils-in-tandem performing indicial or oscillatory motions. For verification, present computed results are found in excellent agreement with all classical solutions. Also, good agreements are found between the present computed results and those of the existing methods.