Movable Duct Section for Axial Flow Fan Stability

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Solution Overview

Problem

Axial flow ducted fans face fluid flow separation issues during high angle of attack, leading to problems such as violent pitching moments, vibrations, instability, and increased power requirements when transitioning from vertical takeoff and landing (VTOL) to level flight.

Innovation Solution

A movable duct section is designed to be selectively extended and retracted using an actuator and linkage system, adjusting its position and orientation to control fluid flow, preventing separation by positioning the leading edge of the movable duct section ahead of the cutout, thereby creating a pressure differential that ensures uniform fluid flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the ducted fan operates at high angle of attack during mode transition, then the thrust vector can be redirected for level flight, but fluid flow separation occurs causing violent pitching moments, vibrations, and instability

Engineering Contradiction:

Improvemode transition capabilityVSAvoidflight stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies the Dynamics principle by making the duct section movable rather than fixed. The duct can dynamically adjust its position and orientation in response to changing flight conditions, specifically extending or retracting to control flow attachment during mode transitions. This dynamic adjustment allows the system to maintain stable operation across different angle of attack ranges, resolving the contradiction between adaptability and stability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements Preliminary action by positioning the movable duct section in advance to prevent flow separation before it occurs. During mode transition, the duct is extended or retracted proactively to maintain attached flow conditions, preventing the occurrence of violent pitching moments and vibrations rather than correcting them after they arise.

Inventive Principle:

Principle #10Preliminary action

2Adaptability or versatility

If the ducted fan operates at high angle of attack, then mode transition is enabled, but power requirements increase due to flow separation

Engineering Contradiction:

Improvemode transition capabilityVSAvoidpower requirement

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The movable duct section dynamically adjusts its configuration during mode transition to maintain efficient attached flow conditions. By actively controlling the duct position, the system avoids the energy penalty of flow separation, allowing mode transition to occur without excessive power requirements.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If a fixed duct design is used, then the structure is simple, but flow separation causes violent pitching moments and vibrations

Engineering Contradiction:

Improveduct structureVSAvoidpitching moments and vibrations

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent transforms the fixed duct structure into a dynamic, movable duct section that can adjust its position and orientation. This added complexity in the mechanical structure is traded for the elimination of harmful flow separation effects, allowing the duct to maintain attached flow during mode transitions and thereby eliminating violent pitching moments and vibrations.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the geometric parameters of the duct by making it movable. The duct can alter its effective length, position, and orientation relative to the fan, thereby changing the flow parameters and preventing flow separation. This parameter adjustment resolves the contradiction between structural simplicity and elimination of harmful flow effects.

Inventive Principle:

Principle #35Parameter changes

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 solution improves fluid flow control during high angle of attack, reducing flow separation and associated issues like vibrations and power imbalances, enhancing the stability and efficiency of axial flow ducted fans during mode transitions.

Implementation Method 1

creating a pressure differential that ensures uniform fluid flow

Methodology Applied

Scientific EffectPressure differential: Pressure Gradient

Implementation Method 2

Axial flow ducted fans face fluid flow separation issues during high angle of attack

Methodology Applied

Scientific EffectFluid flow separation: Flow Separation

Data Source

PatentUS11891163B2Axial flow ducted fan with a movable section

Publication Date: 2024.02.06 SUPRA LUMINA TECH INC

AI summary

A ducted fan propulsion comprises a duct with a cutout and a movable duct section that is moved between a retracted position within the cutout and am extended position relative to the duct. An actuator is disposed within the duct wall and is connected to the movable duct section with actuating linkage. A control linkage connects the movable duct section to the cutout edges. The movable duct section is extended when the ducted fan propulsion transitions from vertical takeoff to a level flight or transitions from level flight to a vertical landing. The movable duct section is retracted into cutout an becomes integrated with the duct during level flight.