April 2009

Multi Object Design Optimization in connection with computerized fluid dynamics allows fine tuning of the shape of SmartFish to achieve supercritical flow up to Mach 0.88. This quite new possibility permits SmartFish to develop its full possibilities during cruise at high subsonic speeds.

Supercritical Flow at cruise with Mach 0.88

The colors on the surface show the pressure distribution. The surface streamlines are white. The travelling yellow feature (only visible with Flash Player installed) shows iso-Mach lines in the locally supersonic region.

Supercritical flow means that flow, which is accelerated locally to a supersonic speed, is decelerated downstream smoothly and without any shockwave to a subsonic speed. The isobars are well separated everywhere, hence no abrupt pressure rise. There is no loss of dynamic pressure and no danger of boundary layer separation. This means no drag rise and no buffet, despite a thick wing profile and a high Mach number.

Conventional moderately swept wing with shockwave at Mach 0.82 for comparison

The colors and the black lines on the surface show the pressure distribution. The broken red line marks the position of the shockwave. At a certain position on the wing chord, the isobars are very dense. This means a sharp pressure rise in flow direction caused by a shockwave. Any shockwave leads to a loss of dynamic pressure in the flow downstream, generating drag. The first occurrence of such a shock wave is associated with the transonic drag-rise Mach number. Furthermore the shockwave may generate a local separation of the boundary layer, with more drag and the possibility of buffeting, if the separated region extends to the trailing edge.

The absence of shockwaves in the operating domain of SmartFish despite a big internal volume is a great advantage of the concept.