Effects of pivot point and spacing on the aerodynamic characteristics of tilting biplane airfoils

The effects of pivot location ( x p / c ) and spacing ratio ( λ = d s / c ) on enhancing the lift generated by rigid biplane NACA 0012 airfoils at R e = 1.35 × 10 5 are studied through the numerical method. SST k − ω turbulence model is adopted to solve URANS equations with overset grids. Results reveal that C L hysteresis exist phase lag under five fixed pivot locations x p / c = 0 , 0.25, 0.5, 0.75 and 1 when biplane airfoils tilt just like pitching stroke. C M curves drop regularly as the pivot point moves towards the spacing direction. However, λ decreasing plays a important role in aerodynamics: C L , lower curve family significantly collapse and C L , upper hysteresis rise overall owing to intensified low-pressure distribution in the gap. Additionally, these performances can be explained from the view of vorticity evolution, particularly, high angles of attack around the stall induce violent turbulence structures. With rearward movement of the pivot point, resemble vortex details appear in the further upstream, indicating aerodynamic characteristics have high similarity under different x p / c regardless of λ. And thus a concept of effective angle of attack for biplane airfoils is proposed where a new factor λ must be introduced. Data assimilation results and vorticity contours are exhibited to prove the feasibility of α eff .