Implementation of a two-stream-fan in the CIRSTEL system
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006.
This thesis describes the design and incorporation of a twin-stream fan into the CIRSTEL tail boom. The Combined Infra-Red Suppression and Tail rotor Elimination (CIRSTEL) tail boom is a system designed to replace the tail rotor on a conventional helicopter. It relies on the Coanda effect to create circulation around the helicopter tail boom when exposed to the rotor downwash. This generates sideways-directed lift to counter the main rotor torque, and a tail thruster adds extra torque and directional control. A twin-stream fan supplies separate air streams to each of the Coanda and tail thruster sections. The first section of the study describes the experimental tests done on an 83% scale demonstrator of the twin-stream fan with the objective to verify the concept and determine the fan section efficiencies. Subsequent modifications done to the fan stator blades are also evaluated. The efficiencies of the design were shown to exceed the targets in both sections. The section concludes with design recommendations for a future fan, based on the findings of the experiments. A brief analysis of the CIRSTEL system is presented and by using optimisation techniques the predicted power demand of the system could be significantly reduced from a conventional tail rotor. The second section of the study details the conceptual design and CFD evaluation of air intakes for the fan that can be fitted to the helicopter. The objective here was to study the flow affecting helicopter intakes as well as to establish design considerations for a fan intake. A basic intake concept was developed for the Alouette III/CIRSTEL combination and modified according to results based on the CFD simulations. The intake design was evolved to the point were it was shown that the concept is feasible. These CFD simulations were an initial effort to design the fan intakes with the help of a simplified rotor flow field. The investigation was subsequently extended to investigate helicopter intake design considerations in the presence of a representative rotor, which was modelled as an actuator disk in the CFD simulations. In this investigation top and side mounted intake concepts were compared and analysed for suitability as a fan intake. Each intake concept showed its own advantages. Due to the proximity of the rotor hub to the intake, distortion and total pressure levels at the fan face are influenced negatively. The report is concluded with design recommendations for the intake as applied to the current Alouette III configuration, as well as for implementation on helicopters in general.