Fan Assembly Flow Recirculation Circuit with Rotating Airfoils

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Solution Overview

Problem

The high slope of fan blades in turbofan gas turbine engines can compromise airflow downstream, leading to large circumferential wakes and thick end wall boundary layers, which impair the performance of downstream components due to minimized chord lengths or increased thickness for weight and structural reasons.

Innovation Solution

A flow recirculation circuit and recirculation rotor with airfoils are introduced to draw airflow from downstream of the fan stator, re-inject it upstream, and utilize a recirculation rotor to increase airflow speed, reducing boundary layer thickness and secondary flows, thereby improving downstream component performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If fan blade chord lengths are minimized to reduce overall weight, then weight is reduced, but the high slope compromises downstream flow quality

Engineering Contradiction:

Improvefan blade weightVSAvoiddownstream flow quality

Core Design Contradiction:

Weight of moving objectVSObject-generated harmful factors

Solution Approach 1:

A flow recirculation circuit is introduced as an intermediary system between the fan rotor and downstream components. This circuit extracts flow from the fan exit, passes it through a recirculation rotor, and re-injects it upstream of the fan stator. The recirculation rotor acts as a mediator that conditions the flow by reducing boundary layer thickness and circumferential wake, thereby improving downstream flow quality without requiring changes to the fan blade geometry or weight.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Strength

If fan blade thicknesses are increased for structural reasons, then structural strength is improved, but the resulting high slope impairs downstream component performance

Engineering Contradiction:

Improvefan blade structural strengthVSAvoiddownstream component performance

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The flow recirculation circuit serves as an intermediary flow conditioning system that compensates for the adverse effects of thick fan blades. By extracting flow downstream of the fan stator, processing it through the recirculation rotor to reduce boundary layer thickness and wake, and re-injecting it upstream, the system mitigates the harmful effects of high blade slope on downstream component performance while allowing the blades to maintain increased thickness for structural reasons.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If high slope fan blades are used, then certain aerodynamic advantages are achieved, but large circumferential wake and thick end wall boundary layers are generated

Engineering Contradiction:

Improveaerodynamic performanceVSAvoidcircumferential wake and boundary layers

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The flow recirculation circuit converts the harmful effects of high slope fan blades into beneficial outcomes. By extracting the flow containing thick boundary layers and large circumferential wake downstream of the fan stator, processing it through the recirculation rotor to thin the boundary layer and reduce wake, and re-injecting the conditioned flow upstream, the system transforms the originally harmful flow characteristics into improved flow quality that benefits downstream components.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 flow recirculation circuit and recirculation rotor enhance airflow momentum, reduce secondary flows, and improve the performance of downstream components by re-energizing the airflow and minimizing losses, even at higher incidence angles.

Implementation Method 1

a recirculation rotor with airfoils that rotate about the axis

Methodology Applied

Scientific EffectAerodynamic effect: Aerofoil

Implementation Method 2

the resulting high slope may compromise the flow downstream of the fan blades. Consequently, the flow downstream of the fan blades can sometimes carry large circumferential wake and thick end wall boundary layers

Methodology Applied

Scientific EffectBoundary layer: Boundary Layer

Data Source

PatentUS11499475B2Fan assembly having flow recirculation circuit with rotating airfoils

Publication Date: 2022.11.15 PRATT & WHITNEY CANADA CORP

AI summary

There is disclosed a fan assembly including a fan rotor including a hub and fan blades. The fan blades have a leading edge and a trailing edge. A fan stator downstream of the fan rotor relative to a direction of an airflow through the fan assembly. The fan stator includes vanes extending between radially inner ends and radially outer ends. A flow recirculation circuit has an inlet downstream of the vanes of the fan stator and an outlet upstream of the vanes. A recirculation rotor has a plurality of airfoils circumferentially distributed around the axis and located in the flow recirculation circuit. The recirculation rotor is rotatable about the axis within the recirculation circuit. A method of operating the fan assembly is also disclosed.