Offset Fan Propulsion Assembly with Inter-Fan Fairing
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Solution Overview
Problem
Existing propulsion assembly architectures with offset fans and a gas generator suffer from high aerodynamic drag due to sonic or supersonic flows in the air inlet space between the fans, and are prone to ingesting foreign particles.
Innovation Solution
A propulsion assembly design featuring a single gas generator with two offset fans, a faired air inlet fairing upstream of the nacelle connecting the fans, and an air supply device that provides cooling airflow to reduce drag and protect the gas generator from foreign bodies, while maintaining efficient airflow distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gas generator casing is disposed to straddle the fan casings with offset fans, then the propulsion efficiency is optimized by achieving high bypass ratio while maintaining acceptable ground clearance, but the air inlet space between the fans generates sonic or supersonic flow causing strong aerodynamic drag
Solution Approach 1:
A fairing is introduced as an intermediary component between the fans and the gas generator casing. This fairing fills the inter-fan space and guides the airflow smoothly, acting as a mediator that reduces the sonic/supersonic flow effects while maintaining the offset fan configuration for high bypass ratio efficiency.
Solution Approach 2:
The fairing modifies the airflow parameters by changing the flow velocity distribution and pressure gradients in the inter-fan region. By reshaping the airflow path, the fairing reduces the Mach number in the critical zones, thereby decreasing aerodynamic drag while preserving the propulsion efficiency benefits of the offset fan arrangement.
2Device complexity
If the air inlet is disposed in the small space between the two fan casings, then the propulsion assembly achieves compact configuration, but the air inlet is liable to take in foreign bodies such as sand, hail, or birds
Solution Approach 1:
The fairing serves as a protective intermediary structure that shields the gas generator air inlet from direct exposure to foreign objects. By positioning the fairing between the external environment and the inlet, it acts as a first line of defense against sand, hail, birds, and other foreign bodies while maintaining the compact inter-fan inlet configuration.
Solution Approach 2:
The fairing provides beforehand protection by creating a controlled airflow path that prevents foreign objects from reaching the gas generator inlet. The fairing's geometry is designed to deflect or filter potential foreign objects before they can enter the critical ingestion zone, thereby cushioning the system against reliability risks in advance.
3Temperature
If cooling airflow is taken from the air inlet opening, then the gas generator and adjacent elements are cooled directly without passing through the fans, but the cooling airflow must be separated from the main airflow supply
Solution Approach 1:
The air inlet opening and airflow path are segmented into two distinct streams: one for cooling the gas generator and adjacent elements, and another for supplying the gas generator combustion air. This segmentation allows independent control and optimization of each airflow path, achieving effective cooling while maintaining proper air supply to the engine.
Solution Approach 2:
Different regions of the air inlet opening are assigned different functions: one region directs cooling airflow to the gas generator casing and adjacent equipment, while another region supplies air to the gas generator combustion process. This local differentiation of airflow quality and destination enables simultaneous cooling and combustion supply from a single inlet structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design minimizes aerodynamic drag and protects the gas generator from foreign particles by using a faired air inlet and cooling airflow, enhancing propulsion efficiency and reliability.
Implementation Method 1
an air supply device configured so as to supply the gas generator with a part of the air entering through the air inlet opening and to take off, from the remaining part of the air entering through the air inlet opening, a cooling airflow intended to cool elements of the propulsion assembly
Data Source
AI summary
The invention relates to an aircraft propulsion assembly (10), comprising a single gas generator (11) and two fans (12) drive in rotation by the gas generator (11) and offset on either side of a vertical plane passing through a longitudinal axis (X) of the gas generator, the rotational axes of the fans lying substantially in the same fan plane.According to the invention, the propulsion assembly (10) comprises an air inlet fairing formed upstream of a nacelle (25) connecting the fans, said fairing (15) having, between the fans (12), an air inlet opening (17, 17′) lying substantially perpendicular to the fan plane and on either side of this plane, the propulsion assembly further comprising an air supply device configured so as to supply the gas generator (11) with a part of the incoming air and to take off, from the remaining part of the incoming air, a cooling airflow intended to cool elements of the propulsion assembly and/or a wing supporting the propulsion assembly.