Ducted Fan Active Flow Control for Boundary Layer Separation
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Solution Overview
Problem
Ducted-fan and fan-in-wing aircraft face limitations in hover and forward flight due to boundary layer separation, longitudinal momentum drag, and nose-up pitching moments, which affect thrust generation, efficiency, and stability control.
Innovation Solution
An active flow control system is introduced, featuring suction outlets and injection inlets within the duct, where suction outlets are positioned beneath the fan blades to passively or actively remove air, and injection inlets provide air into the duct inlet section, optimizing aerodynamic flow by managing air circulation and momentum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If boundary layer separation is present on the blade surface, then thrust generation is reduced and efficiency is lost, but adding active flow control systems increases device complexity
Solution Approach 1:
The patent applies pneumatic principles by using air suction outlets and air injection inlets to control boundary layer separation. The suction outlets remove air from the diffuser section to prevent flow separation, while injection inlets add air to the inlet section to enhance flow attachment, both resolving the thrust-efficiency contradiction through fluid dynamic control.
Solution Approach 2:
The patent changes flow parameters by controlling pressure and velocity distributions through suction and injection. By adjusting the suction pressure in the diffuser section and injection pressure in the inlet section, the system optimizes boundary layer behavior to maintain high thrust generation while managing the complexity through parameter-based control.
2Loss of energy
If flow separation occurs in the duct diffuser section, then propulsive efficiency is reduced, but adding suction outlets increases manufacturing complexity
Solution Approach 1:
The patent extracts air from the duct diffuser section through suction outlets positioned at specific locations. By removing air at controlled rates, the system prevents flow separation and maintains propulsive efficiency. The suction outlets are integrated into the duct structure to minimize manufacturing complexity while achieving the desired flow control.
3Force
If longitudinal momentum drag increases in forward flight, then thrust generation is reduced, but adding flow control systems increases device complexity
Solution Approach 1:
The patent uses air injection as an intermediary to manage momentum drag. By injecting air into the inlet section, the system creates a protective layer that reduces the adverse effects of momentum drag during forward flight. This intermediary approach maintains thrust generation while avoiding more complex active control systems.
4Stability of the object's composition
If nose-up pitching moment occurs in forward flight, then stability control is compromised, but adding flow control systems increases device complexity
Solution Approach 1:
The patent implements a feedback-based flow control system where sensors detect flow conditions and control systems adjust suction and injection rates accordingly. This feedback mechanism maintains stability control by counteracting nose-up pitching moments while keeping device complexity manageable through automated regulation rather than mechanical adjustments.
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 active flow control system significantly enhances thrust and propulsive efficiency, reducing peak efficiency loss and improving stability, with up to 55% increase in maximum system thrust in hover and improved performance in forward flight.
Implementation Method 1
The at least one suction outlet is in the duct diffuser section and is configured to passively bleed or actively remove air from within the duct
Implementation Method 2
injection inlets provide air into the duct inlet section, optimizing aerodynamic flow by managing air circulation and momentum
Implementation Method 3
a fan, and at least one suction outlet. The duct has a duct wall defining a duct inlet section and a duct diffuser section. The fan is within the duct and has a center body and a plurality of blades configured to rotate around the center body
Data Source
AI summary
Systems, methods, lift fans, and aircraft involving active flow control of a ducted fan or fan-in-wing configuration are described.