The aerodynamics of flapping flight for the smallest insects such as thrips is often characterized by a 'clap and fling' of the wings at the end of the upstroke and the beginning of the downstroke. These insects fly at Reynolds numbers (Re) of the order of 10 or less where viscous effects are significant. Although this wing motion is known to augment the lift generated during flight, the drag r...

Aerodynamic force generation and power requirements in forward flight in a fruit fly with modeled wing motion were studied using the method of computational fluid dynamics. The Navier-Stokes equations were solved numerically. The solution provided the flow velocity and pressure fields, from which the vorticity wake structure and the unsteady aerodynamic forces and torques were obtained (the ine...

The assessment of turbulence model performance in predicting ow elds that are directly relevant to industrial needs has become increasingly important. In aerodynamics, many problems exist for which the performance of some turbulence models is ambiguous at best and incorrect at worst. The application of many di erent turbulence models to a particular problem is a lengthy process that can lead to...

Simulations of the interaction between a vortex and a NACA0012 airfoil are performed with a stable, high-order accurate (in space and time), multi-block finite-difference solver for the compressible NavierStokes Equations. We begin by computing a benchmark test case to validate the code. Next, the flow with steady inflow conditions are computed on several different grids. The resolution of the ...

The morphology, kinematics and stiffness properties of lifting surfaces play a key role in the aerodynamic performance of vertebrate flight. These surfaces, as a result of their flexible nature, may move both actively, owing to muscle contraction, and passively, in reaction to fluid forces. However, the nature and implications of this fluid-structure interaction are not well understood. Here, w...

1 m⇥ 1 vectors of ones a Speed of sound A m⇥ 1 vector of homogeneous tangent solution weights B m⇥ 1 vector with projection of tangent onto homogeneous tangent solutions CD Drag coe cient CL Lift coe cient D Drag D Design variable of interest f , F Objective functions or instantaneous contribution to objective functions G Objective function sensitivities g n⇥ 1 linearization of instantaneous co...

The aerodynamic interference effects on tiltrotor performance in cruise are investigated using comprehensive calculations, to better understand the physics and to quantify the effects on the aircraft design. Performance calculations were conducted for 146,600-lb conventional and quad tiltrotors, which are to cruise at 300 knots at 4000 ft/95 deg F condition. A parametric study was conducted to ...

Tests have been made at a Mach number of 4.03 and Reynolds number of 3'4 million on two families of models, consisting of delta wings with underslung half-Cone bodies. The wing sweepback angles were 75 ° and 80 °, and the appropriate cone semi-vertex angles tested were 4 °, 10 ° and 13 ° for the larger wing and 4 °, 6"7 ° and 10 ° for the smaller wing. The surface distributions were measured at...

AtReynolds numbers approaching those ofmicro air vehicles (both engineered and natural), the Eppler 387 airfoil (in common with many other smooth profiles) can have multiple lift and drag states at a single wing-incidence angle. Prestall hysteresis and abrupt switching between stable states result from sudden flow reattachment and the appearance of a large separation bubble. It is shown that co...

Results are reported of an experimental investigation into the motion of a heavy cylinder free to move inside a water-filled drum rotating around its horizontal axis. The cylinder is observed to either co-rotate or, counter-intuitively, counter-rotate with respect to the rotating drum. The flow was measured with particle image velocimetry, and it was found that the inner cylinder significantly ...