Nacelle Plenum Design for Boundary Layer Ingestion
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Solution Overview
Problem
Current active laminar flow control systems for aircraft nacelles face challenges in maintaining consistent pressure gradients across suction holes due to varying external static pressure, leading to inefficiencies in drag reduction and increased weight and cost from complex rib structures.
Innovation Solution
The use of tunable plenums defined by circumferential and axial ribs creates regions of varying suction pressure to maintain a consistent pressure gradient across suction holes, allowing for controlled boundary layer ingestion and reduced drag, with options including hoop-shaped plenums and zones with perforations for air suction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional boundary layer suction systems are used with uniform rib structures, then suction holes can be provided across the nacelle surface, but the pressure gradient becomes inconsistent due to varying external static pressure, reducing drag reduction effectiveness
Solution Approach 1:
The nacelle skin is divided into multiple discrete suction zones separated by ribs, with each zone having independent suction holes. This segmentation allows each zone to independently manage its pressure gradient, compensating for variations in external static pressure across different locations on the nacelle surface.
Solution Approach 2:
Each suction zone is designed with specific local characteristics including varying hole densities, sizes, and orientations tailored to the local pressure distribution and flow conditions. This local optimization ensures consistent pressure gradients across the entire nacelle surface despite varying external conditions.
2Reliability
If complex rib structures are used to maintain consistent pressure gradients, then boundary layer ingestion can be controlled, but the weight and cost of the nacelle structure increases
Solution Approach 1:
The rib structure is segmented into minimal necessary elements that only divide the skin into functional suction zones. By using the fewest ribs required to create discrete zones, the structural weight is minimized while still achieving the necessary pressure gradient control for effective boundary layer ingestion.
3Shape
If natural laminar flow techniques are used alone, then the nacelle shape can be optimized for laminar flow, but the flow transitions to turbulent due to boundary layer energy loss over longer distances
Solution Approach 1:
The suction holes act as an intermediary mechanism between the natural laminar flow development and the boundary layer stability problem. By selectively removing boundary layer air through the holes, the system maintains the laminar flow characteristics over extended distances without requiring perfect natural laminar flow shaping.
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
This approach effectively maintains laminar flow over a larger surface area of the nacelle, reducing drag and minimizing weight and cost by simplifying the rib structure and ensuring consistent pressure gradients for efficient boundary layer ingestion.
Implementation Method 1
boundary layer ingestion or suction where the boundary layer next to the aircraft surface is pulled through small holes in the surface to remove the low energy boundary layer
Implementation Method 2
Active or hybrid laminar flow techniques may achieve and maintain laminar flow more consistently than natural means alone, and may be able to extend further aft the region on first section 23 of nacelle 22 which has laminar flow
Implementation Method 3
tunable plenums defined by circumferential and axial ribs creates regions of varying suction pressure to maintain a consistent pressure gradient across suction holes
Implementation Method 4
The nacelle may include a streamlined profile to delay flow separation and maintain attached flow over the nacelle surface
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
Aspects of the disclosure are directed to a nacelle of an aircraft, comprising a surface that is profiled such that during cruise flight operation lines of constant static pressure of a boundary layer around the nacelle (422; 522) in a given region are substantially contained within a plane that is normal to an engine axis.