The detailed vortex flow structure behind a combination airfoil at a low Reynolds number region was measured by PIV. Moreover, the dynamic thrust acting on a combination airfoil was measured by a six-axes sensor in water tunnel. The combination airfoil can form clear thrust producing vortex street behind airfoil even at low non-dimensional trailing edge velocity and non-dimensional heaving velocity. Especially, it is possible to form the thrust producing vortex street with high vorticity at φ = π/2 and π. The jet velocity behind combination airfoil at φ = π/2 and π becomes over 2.0. The averaged dynamic thrust acting on a combination airfoil increases as the non-dimensional trailing edge velocity and non-dimensional heaving velocity increases, same as case in pitching and heaving airfoils. Moreover, the averaged dynamic thrust acting on combination airfoil at φ = π/2 and π is much larger than that on pitching and heaving airfoils. However, the maximum thrust efficiency of a combination airfoil at φ = π/2 was approximately 0.42 and was slightly higher than that on a pitching airfoil.

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