Numerical investigation of short takeoff and landing exhaust system using bypass dual throat nozzle

Abstract

Bypass dual throat nozzle (BDTN) is a new kind of fluidic thrust vectoring nozzle. Based on the excellent performance of BDTN, a short takeoff and landing (STOL) exhaust system as a substitute for the complex tilt rotor is investigated. The STOL exhaust system consists of a downward-bending transition part and a BDTN part. As the thrust vectoring angle reaches more than 35° in a separate BDTN, the transition part enables the actual thrust vectoring angle to reach a maximum of over 70° in STOL mode. In cruise mode, thrust vectoring effect of BDTN compensates the inherent deflection angle of the transition part, the thrust vectoring angle reaches nearly 0°. The transition part is designed with three area-laws and two centerline-laws. Results indicate that centerline-law II leads to less total pressure distortion than centreline-law I. Area-law B is the best area-law since it leads to the moderate change rate of cross-section, it makes the total pressure distribution at the outlet of the transition part more uniform. Then, the integrated STOL exhaust system is investigated, the performances are presented. The thrust direction can be changed by controlling two valves in BDTN, the redundant tilting mechanical structure of traditional tilt rotors is replaced by this way, the structural weight is reduced, and flight safety improves. Finally, the best configuration is selected according to the results of the numerical investigation, and the thrust coefficient is more than 0.920 in STOL and cruise mode. The thrust vectoring angle is -73.37° in STOL mode, and it's -1.81° in cruise mode. The design satisfies the basic requirements for STOL and cruising flight. Hence, the STOL exhaust system is worthy of further study.