Unsteady Aerodynamics Over NACA0005 Airfoil for Ultra-Low Reynolds Numbers

In the present study, numerical simulation for a two-dimensional NACA0005 is performed for angles of attack ${\alpha } = {0^{\circ }-15^{\circ }}$ . The Reynolds numbers 1000, 2000 and 5000 are considered. Simulations show that the flow fields can be classified due to characteristics of vortex shedding based on Reynolds number and angle of attack. Furthermore, this study reveals that in the case of thinner airfoils, several modes (Mode I, Mode II, Mode III) are present at the same angle of attack for varying Reynolds number. Maximum lift to drag ratio is found at Reynolds number 5000 and angle of attack 6° as well as gradual stall is observed. Onset of oscillations to determine critical angles of attack is reported for NACA0005 with the dominant frequencies. A subcategory of mode III termed as mode IIIa/c, and recently reported mode 4i is also observed in present study. A new mode termed as k-mode is discovered for higher angles of attack at Re = 5000. In addition, numerical simulations of two-dimensional periodic flows around NACA0005 profile at Reynolds number Re = 5000 demonstrate that unsteady periodic flows reach different saturation states at angles of attack of $10^{\circ }-15^{\circ }$ . The coexisting periodic states and period-doubling (with higher and lower intensities) in this range indicate that the wake undergoes substantial changes from the Von-Kármán vortex street.