AIRCRAFT WAKE VORTEX DETECTION IN LARGE TOWING TANK

The formation, motion and persistence of trailing vortices, shed by large commercial aircraft, is a relevant aspect to the safety and productivity of air traffic. An aircraft encountering a wake vortex formation on its path may experience severe control problem as uncontrollable rolling moment or loss of height. Air traffic control separation regulations determine the minimum distance between aircraft on the same path both in cruise condition, both approaching airports in high lift condition. The ICAO separation distance procedure foresees four nautical miles between two heavy (> 136 tons) aircraft. Reducing the trailing vortex hazardous allows increasing safety and capacity of the airports. During the designing phase of new commercial aircraft different philosophies can be adopted, as developing low vortex wing or developing active or passive systems generating counter rotating vortex or turbulence, leading the wake vortex collapse. In all cases an accurate wake vortex investigation is necessary. Nowadays aerodynamic wind tunnels provide accurate data of the wake vortex behavior up to near and extended near filed (8-10 wing spans) behind the aircraft model, using five hole probes arrays, Hot Wire probes, LDV or PIV techniques. A valuable facility is the catapult wind tunnel allowing investigation up to 80 wing spans (mid field) using smoke visualisation, PlV technique and LIDAR system. The mid/far field investigation is still obtained performing flight tests and measuring the released wake by ground station as LIDAR or ultrasound or density gradient technique. During the last two years in the framework of the European research project, named C-Wake, the wake vortex was also investigated in towing tank facilities, normally used for naval applications. These kind of facilities were used for wake vortex visualisation in the seventies but nowadays thanks to the availability of new measurement techniques, it is possible carrying out quantitative measurements. PlV measurements were performed at INSEAN large towing tank facility to investigate the wake vortex behavior up to 200-250 wing span behind the model corresponding to 6.2 - 7.5 nautical miles. I