Force Generation Mechanisms by an Insect Wing in an Idealized Hovering Motion

An Unsteady force generation mechanisms (delayed stall, wake capture and rotational lift) during idealized hovering of insect flight at Reynolds number (Re) of 136 have been identified in this research. Dependence of flow physics on Re forms the basis of present study to observe the dependence of unsteady force generation mechanisms on Re. A systematic study has been carried out by increasing Re from 136 to 4000 to investigate persistence of delayed stall, wake capture and rotational lift phenomenon. Using the solution of 3D Navier-Stokes equations, the aerodynamic force and the detailed flow structure around the wing are obtained which can provide useful insights into mechanism of unsteady force generation during idealized hovering at Re=4000. After grid and Mach number sensitivity analysis, the results are compared with previous studies at Re=136 for the code validation. The aerodynamic force and flow structure of a wing performing hovering motion at Re=4000 is calculated by solving Navier-Stokes equations. Re=4000 is selected on the premise that the length scale (mean aerodynamic chord) becomes closer to a Micro Air Vehicle (MAV); furthermore 30 times increase in Re (from 136 to 4000) is considered sufficient to assess changes in flow physics while remaining in laminar flow regime. Calculations are conducted for idealized hovering motion during which stroke 1 is initiated in still air, followed by flipping motion for reversing the direction and then stroke 2 (similar to stroke 1 but in opposite direction). Results obtained from this research are helpful for future work where they can be compared with those obtained from actual wing kinematics to assess the impact of kinematics on unsteady mechanisms.