Implementation of a two-stream-fan in the CIRSTEL system
Files
Date
2006-12
Authors
Heise, R.
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
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.
Description
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006.
Keywords
Rotors (Helicopters)-- Aerodynamics, Axial flow, Dissertations -- Mechanical engineering, Theses -- Mechanical engineering