Meteorites

The atmospheric erosion of meteors is a splendid example of the reshaping of a solid object due to its motion through a fluid. Motivated by meteorite samples collected on Earth that suggest fixed orientation during flight–most notably the strikingly conical shape of so-called oriented meteorites–here the hypothesis that such forms result from an aerodynamic stabilization of posture that may be achieved only by specific shapes, is explored. The laboratory scale experiment is conducted for exploring systematic static stability tests on cones of varying apex angles in fast flows, and the resulting map of the orientational equilibria and their stability shows how oriented flight emerges through blue-sky and pitchfork bifurcations. A 2D mathematical model has been developed, and is being compared with the experimental results. Armed with the simplified 2D model of oriented meteorites (with a conical shape), an isosceles triangle is considered in order to calculate its flow wake structure using free streamline theory. Preliminary comparisons with experiment appear very promising.

Recent experiments have shown that cones of intermediate apex angles display orientational stability with apex leading in flight. Here we show in experiments and simulations that analogous results hold in the two-dimensional setting of solid wedges or triangular shapes in planar flows at Reynolds numbers Re~100-1000. Slender wedges are statically unstable with apex leading and tend to flip over or tumble, and broad wedges oscillate or flutter due to dynamical instabilities, but those of apex half-angles between about 40 and 55 maintain stable posture during flight. The existence of these ``Goldilocks" shapes that possess the ``just right" angularity for flight stability is thus robust across dimensions. The stability is also robust to moderate changes in shape and Reynolds number.