Counter rotating fans — An aircraft propulsion for the future?

Abstract

In the mid seventies a new propulsor for aircraft was designed and investigated -the so-called PROPFAN. With regard to the total pressure increase, it ranges between a conventional propeller and a turbofan with very high bypass ratio. This new propulsion system promised a reduction in fuel consumption of 15 to 25% compared to engines at that time. A lot of propfans (Hamilton Standard, USA) with different numbers of blades and blade shapes have been designed and tested in wind tunnels in order to find an optimum in efficiency, Fig. 1. Parallel to this development GE, USA, made a design of a counter rotating unducted propfan, the so-called UDE Fig.2. A prototype engine was manufactured and investigated on an in-flight test bed mounted at the MD82 and the B727. Since that time there has not been any further development of propfans (except AN 70 with NK 90-engine, Ukraine, which is more or less a propeller design) due to relatively low fuel prices and technical obstacles. Only technical programs in different countries are still going on in order to prepare a data base for designing counter rotating fans in terms of aeroacoustics, aerodynamics and aeroelasticities. In DLR, Germany, a lot of experimental and numerical work has been undertaken to understand the physical behaviour of the unsteady flow in a counter rotating fan.

A numerical study on the unsteady effect of axial spacing on the performance in a contra-rotating axial compressor

“…11,12 Several researchers have explored the effect of axial spacing between the two rotors in CRAC. The axial spacing study performed by Roy et al 13,14 indicates that the performance is improved with a smaller gap resulting in increased noise levels.…”

Robust Gas Turbine and Airframe System Design in Light of Uncertain Fuel and CO2 Prices

“…Of the ve system options, the open rotor presents the most technological and operational chal-lenges, however, including open rotor blade integration, control and reliability, engine installation and noise [32,46,47]. The two propeller rows can either be installed at the front or the rear of the engine, respectively known as the tractor and the pusher conguration [31].…”

Future Aero Engine Designs: An Evolving Vision

“…Potential year 2020 scenarios are explored by Birch (2000) while an overview of current aero engine technology and some insight on the future of aircraft propulsion is given by Ruffles (2000). Sieber (1991) and Schimming (2003) provide an excellent discussion on counter-rotating fan designs. Finally, for a review on the development of civil propulsion from the early 50's to recent years the interested reader is referred to Saravanamuttoo (2002).…”