Supersonic Nozzle Plug Body for Sonic Boom Reduction
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Solution Overview
Problem
Conventional supersonic jet engine designs produce strong sonic booms due to spillage, cowl shock, and misalignment between the exhaust plume and free stream, which are difficult to attenuate using existing low sonic-boom design techniques.
Innovation Solution
The design includes a lengthened center body with an extended protruding portion to pre-spill excess air and a lengthened plug body with an isentropic compression surface to align the exhaust plume with the free stream, reducing spillage and shock formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional inlet design is used, then the propulsion system can operate at supersonic speeds, but spillage occurs through the terminal shock which strengthens the sonic boom
Solution Approach 1:
The inlet is designed with a streamlined shape that pre-spills excess flow before it reaches the terminal shock location. This preliminary action of flow redirection prevents the formation of a strong terminal shock, thereby reducing sonic boom strength while maintaining supersonic flight capability
Solution Approach 2:
The inlet geometry is optimized with specific angle parameters (such as 15-degree angles for the inlet lips) and streamlined contours that control the flow field characteristics. These parameter changes enable the inlet to manage spillage more effectively, reducing the strength of compression shocks and associated sonic booms
2Power
If the exhaust jet plume is misaligned with the nacelle cowling, then the propulsion system can generate thrust, but strong compression shock and expansion-reshock features are generated along the shear surface
Solution Approach 1:
The nozzle exit area is specifically designed with a rounded contour and optimized geometry to match the local flow conditions. This local quality enhancement at the nozzle exit ensures proper flow alignment with the nacelle cowling, eliminating misalignment-induced shocks and reducing acoustic disturbances while maintaining thrust generation
Solution Approach 2:
The nozzle exit features a rounded, curved contour rather than a sharp edge, which smooths the flow transition and eliminates flow-angle mismatch with the nacelle cowling. This curvature design prevents the formation of strong compression shocks and expansion-reshock features along the shear surface
3Ease of manufacture
If the cowling surface is angled in the stream-wise direction, then the nacelle can be fitted around engine protuberances, but blockage features are created that generate compression shocks
Solution Approach 1:
The cowling surface is designed with streamlined, curved contours rather than sharp angles. This curvature eliminates blockage features that would otherwise generate compression shocks, while still allowing the nacelle to be fitted around engine protuberances such as gearboxes
Solution Approach 2:
The cowling geometry is pre-shaped to accommodate engine protuberances without creating adverse flow features. The streamlined design anticipates and prevents the formation of compression shocks by smoothly guiding the supersonic flow around the nacelle and engine components
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 configuration significantly diminishes the strength of cowl shocks and eliminates misalignment-induced shocks, resulting in a reduced sonic boom and decreased drag for supersonic jet engines.
Implementation Method 1
a lengthened plug body with an isentropic compression surface to align the exhaust plume with the free stream
Implementation Method 2
Spillage is an inlet characteristic that contributes strongly to sonic boom strength. Spillage is excess flow that is unusable by the propulsion system and naturally diverted (spilled) around the sides of the intake through the inlet compression field
Implementation Method 3
Acoustic disturbances produced at supersonic flight speed by a propulsion system's nacelle cowling surface, along with those from the aerodynamic boundary surfaces of the inlet's captured stream tube and the jet plume exhaust from the nozzle, all influence the perceived loudness of an aircraft's sonic boom
Data Source
AI summary
A nozzle arrangement is disclosed herein for use with a supersonic jet engine that is configured to produce a plume of exhaust gases. The nozzle arrangement includes, but is not limited to, a nozzle having a trailing edge and a plug body partially positioned within the nozzle. The plug body has an expansion surface and a compression surface downstream of the expansion surface. A protruding portion of the plug body extends downstream of the trailing edge for a length greater than a conventional plug body length. The plug body is configured to shape the exhaust gases to flow substantially parallel to a free stream of air flowing off of the trailing edge of the nozzle and to cause the plume of exhaust gases to isentropically turn the free stream of air to move in a direction parallel to a longitudinal axis of the plug body.