Aerodynamic Assessment of Nozzle Area Variation by Core Fairing Modulation
- Aerodynamic assessment of nozzle area variation by core fairing modulation on the way towards the goals of ACARE 2020 and Flightpath 2050 [1], a next potential step in flight engine technology is to develop engines with by-pass ratios (BPR) far beyond the current levels of 10 to 12. These new engine concepts can have BPRs of up to 20 and require a significant step forward in low pressure system technologies.
The European Union supports within the 7th Framework the research activities for these new low pressure systems through the program ENOVAL [2]. Such a new low pressure technology can be achieved through an innovative fan design with a low fan pressure ratio and a radically increased fan diameter compared to the current conventional turbofan engine. The aerodynamic stability of such large fans is most likely very sensitive against backpressure variations. For this reason the backpressure regulation of such large fan, specially during take-off operation, can be achieved through the introduction of a Variable Area Fan Nozzle [VAFN].Aerodynamic assessment of nozzle area variation by core fairing modulation on the way towards the goals of ACARE 2020 and Flightpath 2050 [1], a next potential step in flight engine technology is to develop engines with by-pass ratios (BPR) far beyond the current levels of 10 to 12. These new engine concepts can have BPRs of up to 20 and require a significant step forward in low pressure system technologies.
The European Union supports within the 7th Framework the research activities for these new low pressure systems through the program ENOVAL [2]. Such a new low pressure technology can be achieved through an innovative fan design with a low fan pressure ratio and a radically increased fan diameter compared to the current conventional turbofan engine. The aerodynamic stability of such large fans is most likely very sensitive against backpressure variations. For this reason the backpressure regulation of such large fan, specially during take-off operation, can be achieved through the introduction of a Variable Area Fan Nozzle [VAFN].
This paper describes the aerodynamic study of a particular VAFN concept. This concept offers the variation in fan nozzle throat-area by the displacement of the inner fixed structure (IFS) (also known as core fairing structure). The aim of the assessment was to perform a comparative aerodynamic study at different design configurations.
These configurations were derived by varying the design parameters such as the location of section plane (divides the IFS into front and rear block) and the position of the rotational axis. The range of the area change for different flight cases was defined by the engine owner under the ENOVAL program. For each design configuration, the geometries for all the flight cases with their required variation in the nozzle throat area were developed. For the initial study phase the aero assessment a 2D axis-symmetric flow was considered and the airflow from the vent nozzle and core nozzle were included. At this stage, the flight cases with the maximum variation in throat area (e.g. max take-off and top of climb) and the nominal cruise case without area change were studied. Three major performance parameters, the thrust coefficient, nozzle drag coefficient and the after-body drag were calculated. The effects of the gaps and steps (resulting from the overlapping between the IFS segments) on the performance parameters were examined. A comparative result was produced in which the different design parameters of the VAFN were ranked. With the help of few iterations, the best possible design configuration was accessed. At the final stage, the detailed aerodynamic studies on the selected design configuration were performed for the whole range of area variation, including the cruise case with different power loops and the maximum area changes with the variations in the day temperature.
[1] Advisory Council for Aviation Research and Innovation in Europe (ACARE) with its targets for CO2 emission- and noise reduction by year 2020 for civil European aircraft industries to be more innovative, sustainable and highly competitive till year 2050 (Flightpath 2050) www.acare4europe.com/.
[2] European 7th Framework Program ENOVAL(ENgine mOdule VALidators) http://www.enoval.eu/.…
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