B. Zhang and C. Liang, "High-Order Numerical Simulation of Flapping Wing for Energy Harvesting", AIAA Paper, 2019-3338, June, 2019.
doi:10.2514/6.2019-3338

Flow field when heaving leads pitching with a phase angle $\phi=0^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=30^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=60^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=90^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=120^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=150^\circ$

Flow field when heaving leads pitching with a phase angle $\phi=180^\circ$