Experiments have been performed to examine the turbulence structure and development of a pair of counter-rotating wing-tip vortices. The vortices were generated by two rectangular NACA 0012 half wings placed tip to tip, separated by 0.25 chordlengths. Preliminary studies showed the vortices to be insensitive to the introduction of a probe and subject only to small wandering motions. Meaningful measurements could therefore be made using hot-wire probes. Three-component velocity measurements were made 10 and 30 chordlengths downstream of the wing leading edges for a chord Reynolds number of 260000.At 10 chordlengths the vortex cores are laminar. True turbulence levels within them are low and vary little with radius. The turbulence that surrounds the cores is formed by the roll-up of and interaction of the wing wakes that spiral around them. This turbulence is stretched and organized but apparently not produced by the circulating mean velocity fields of the vortices.At 30 chordlengths the vortex cores have become turbulent. True turbulence levels within them are larger and increase rapidly with radius. The turbulent region surrounding the cores has doubled in size and turbulence levels have not diminished, apparently being sustained by outward diffusion from the core regions. The distribution of the turbulence has also changed, the wake spirals having been replaced by a much more core-centred turbulence field.This change in flow structure contrasts sharply with what is seen in the equivalent isolated tip vortex, produced when one of the wings is removed. Here the vortex core remains laminar and the turbulence surrounding it decays rapidly with downstream distance. This implies that the transition to turbulence in the cores of the vortex pair is stimulated by interaction between the vortices. Spectral measurements at 10 chordlengths suggest that short-wave instability may be the cause.

Abstract-The Space Technology 8 (ST8) mission is the latest in NASA's New Millennium Program technology demonstration missions. ST8 includes a spacecraft bus built by industry, flying four new technology payloads in lowEarth orbit. This paper will describe each payload, along with a brief description of the mission and spacecraft. The payloads include a miniature loop heat pipe intended to save mass and power on future small satellites, designed and built by NASA's Goddard Space Flight Center; a lightweight, 35g/m linear mass, 40-m deployable boom intended as a future solar sail mast built by ATK Space Systems; a deployable, lightweight Ultraflex solar array producing 175W/kg, also built by ATK Space Systems; and a high-speed, parallel-processing computer system built of state-of-the-art COTS processors, demonstrating SEU tolerance without the need for radiation-hardened electronics, and 100M operations per second per Watt processing throughput density.