H. R. Hamdani - Aerospace Engineering Department, College of Aeronautical Engineering, National University of Sciences and Technology, Pakistan
A. Aizaz - Aerospace Engineering Department, College of Aeronautical Engineering, National University of Sciences and Technology, Pakistan
M. A. Naqvi - Aerospace Engineering Department, College of Aeronautical Engineering, National University of Sciences and Technology, Pakistan

An Unsteady force generation mechanisms (delayed stall, wake capture and rotational lift) during idealized hovering of insect flight at Reynolds number (Re) of ۱۳۶ 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 ۱۳۶ to ۴۰۰۰ to investigate persistence of delayed stall, wake capture and rotational lift phenomenon. Using the solution of ۳D 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=۴۰۰۰. After grid and Mach number sensitivity analysis, the results are compared with previous studies at Re=۱۳۶ for the code validation. The aerodynamic force and flow structure of a wing performing hovering motion at Re=۴۰۰۰ is calculated by solving Navier-Stokes equations. Re=۴۰۰۰ is selected on the premise that the length scale (mean aerodynamic chord) becomes closer to a Micro Air Vehicle (MAV); furthermore ۳۰ times increase in Re (from ۱۳۶ to ۴۰۰۰) 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 ۱ is initiated in still air, followed by flipping motion for reversing the direction and then stroke ۲ (similar to stroke ۱ 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.

Hovering, Delayed stall, Wake capture, Insect flight, Low Reynolds number, Unsteady mechanism, CFD, Flapping wing, Wing kinematics