The wing of a butterfly consists of partially overlapping forewing and hindwing, and forewing sweeping can dynamically change the shape of the whole wing. In this work, the effect of forewing sweeping on aerodynamic performance of a butterfly like model is studied using a solver based on immersed boundary method and adaptive mesh. For aerodynamic performance, adding a “forward-backward-forward” sweeping motion to the forewing makes it more suitable for fast cruising flight, and compared to the situation without forewing sweeping, the drag is reduced by 46% and the lift to drag ratio is increased by 45%. On the contrary, adding a “backward-forward-backward” sweeping motion to the forewing increases lift and makes it more suitable for climb flight. For downstroke and middle to late upstroke, the forewing sweeping affects the Leading-Edge Vortex (LEV) through two factors: sweeping velocity and forward sweeping angle, and their effects are coupled. A large forward sweeping velocity can enhance the strength of LEV, while a large forward sweeping angle can weaken it. For early upstroke, the forewing sweeping can affect the wake capture mechanism, sweeping backward can enhance it while sweeping forward can weaken it. The findings in this work provide insight into the design of butterfly like Micro Air Vehicles (MAVs).

The precision of numerical simulations for hypersonic flows is significantly influenced by the uncertainties in the closure coefficients of the Menter SST turbulence model. This study conducts a quantitative assessment of these uncertainties across three canonical hypersonic models: the two-dimensional compression corner, the two-dimensional cylinder, and the three-dimensional double ellipsoid. Firstly, the non-intrusive polynomial chaos method is used to quantify the uncertainty in the numerical simulations of aerodynamic forces and heating caused by the uncertain closure coefficients of the Menter SST turbulence model. The sensitivities of the closure coefficients are then ranked based on the Sobol sensitivity index to identify the key factors contributing to the uncertainty. The results show that uncertainties in aerodynamic heating generally exceed those in aerodynamic forces. Among all the nine closure coefficients examined in this paper, ${\sigma }_{\omega 1}$、 ${\beta }^{\ast }$、 $\kappa$、 $a_1$ are the key model parameters that contribute significantly to the uncertainty of the simulation results. And the sensitivities of which are related to local flow characteristics. In most flow areas, the coefficients of production term ${\sigma }_{\omega 1}$ and $\kappa$ are the main factors contributing to the uncertainty of the numerical simulation results. While in regions of flow separation or behind shock waves, the simulation results are more significantly influenced the dissipation term coefficient ${\beta }^{\ast }$ and the shear stress limiter $a_1$.