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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.

This paper investigates the formation control of multiple heterogeneous quadrotor unmanned aerial vehicles (UAVs). The research focuses on developing a distributed robust formation control strategy to effectively manage the translational and attitude motions of the UAVs utilizing an active virtual leader. The communication of each agent in a connected environment is represented by a directed graph. To align with real applications, only a minimum of one agent is required to connect with the leader. The challenge associated with controlling systems is more complicated by the inherent heterogeneity of UAVs, characterized by variations in their model parameters and the presence of external disturbances in the system dynamics. A robust term is proposed to handle time-varying disturbances added to the closed-loop systems. A comprehensive mathematical proof and numerical illustrations are provided to validate the efficacy of the proposed formation control strategy.

In this article, direct numerical simulations of flow around NACA0012 hydrofoil with superhydrophobic surface (SHS) is presented. Surface heterogeneity takes into account by periodic no-slip and shear-free grates on the surface. The study is conducted for a range of 0 o − 25 o degree angles of attack and at fixed Reynolds number ( Re ) 1000. SHS leads to effective Navier slip on the hydrofoil surface and corresponding changes in velocity profile. Bubble separation delays for higher gas-fraction ( G.F ), and minimizes the vortex shedding effects. As a result, flow remains two-dimensional (2D) for higher angles of attack as compared to flow over three-dimensional (3D) hydrofoil with no-slip boundary. Both the drag reduction and enhancement of lift force are observed. Maximum lift are observed at α = 13 o , while the drag force continues to decrease with the gradual increase in angle of attack and patterned micro-grates fraction. Mode C with smaller wavelength is observed at α = 15 o . Furthermore, increase in gas-fraction leads to increase in slip length which thickens the boundary layer and mimics the vorticity implies drag reduction. Thus, replacement of the no-slip surfaces by superhydrophobic surfaces can be treated as a promising drag reduction technology.