Compressor Casing Bleed Holes for Tip Clearance Control

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Solution Overview

Problem

The clearance between the tips of moving blades and the casing in high pressure axial compressors of turbomachines leads to efficiency degradation and a 'pumping' phenomenon, which existing solutions attempt to address with complex shaping and air flow arrangements.

Innovation Solution

A turbomachine compressor design featuring bleed holes in the stationary casing, angled to direct air away from the blade tips, improving efficiency and reducing pumping margin, with bleed holes positioned 5% to 50% of the blade chord length and angled between 30° to 90°, and optionally accompanied by oblique tongues for enhanced air flow management.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If clearance exists between blade tips and casing, then manufacturing is easier and device complexity is reduced, but efficiency deteriorates and pumping phenomenon occurs

Engineering Contradiction:

Improveease of manufactureVSAvoidefficiency

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The invention extracts the harmful air flow from the clearance region by introducing bleed holes in the casing that capture and remove air leaking from the blade tip clearance, thereby preventing the harmful effects of clearance on efficiency while maintaining manufacturing simplicity

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The bleed holes act as an intermediary mechanism between the clearance region and the external environment, mediating the harmful air flow by capturing it through the angled holes and redirecting it away from the blade tips, thus eliminating the negative impact of clearance without modifying the blades or casing structure fundamentally

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If complex casing shaping and air flow arrangement are used, then pumping phenomenon is avoided, but device complexity increases

Engineering Contradiction:

Improvepumping marginVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of using complex overall casing shaping, the invention segments the problem by introducing discrete bleed holes at specific locations and angles, dividing the air flow control function into localized elements that collectively prevent pumping while maintaining simplicity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes key parameters of the bleed holes (position at 5-50% of blade chord, diameter less than 30% of blade chord, and angles θ and φ between 30° to 90°) to optimize performance, achieving reliable pumping prevention through parameter optimization rather than structural complexity

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If bleed holes are positioned at optimal locations and angled correctly, then efficiency is significantly improved and pumping margin is increased, but manufacturing precision requirements increase

Engineering Contradiction:

ImproveefficiencyVSAvoidmanufacturing precision

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The invention applies local quality by concentrating the air flow control function in specific localized regions (bleed holes at defined positions and angles) rather than requiring uniform precision throughout the entire casing, allowing manufacturing precision to be focused only on critical bleed hole parameters

Inventive Principle:

Principle #3Local quality

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

Significantly enhances compressor efficiency and operating safety by reducing turbulence and flow interference, with a bleed-off air rate of 0.1% to 5% improving compression ratio and stability, as shown in comparative efficiency and flow rate graphs.

Implementation Method 1

each of said bleed holes sloping at two angles relative to said longitudinal central axis

Methodology Applied

Scientific EffectFlow direction control through angled geometry:

Implementation Method 2

said stationary casing further includes oblique tongues disposed in register with said plurality of moving blades on either side of each bleed hole and oriented at said angle φ

Methodology Applied

Scientific EffectFlow redirection through oblique surfaces:

Data Source

PatentUS7549838B2Taking air away from the tips of the rotor wheels of a high pressure compressor in a turbojet

Publication Date: 2009.06.23 SAFRAN AIRCRAFT ENGINES SAS

AI summary

A turbomachine compressor comprises at least one plurality of moving blades and spaced apart therefrom in an axial direction relative to a central longitudinal axis of the turbomachine, a plurality of stationary vanes, and a stationary casing surrounding said plurality of moving blades and including a plurality of bleed holes centered in the range 5% to 50% of the blade chord length and having a diameter less than or equal to 30% of the blade chord length, each bleed hole sloping at two angles of inclination relative to the central longitudinal axis. Advantageously, each bleed hole has a first axis of inclination presenting an angle φ relative to the central longitudinal axis lying in the range 30° to 90°, and a second axis of inclination perpendicular to the first and presenting an angle θ relative to the central longitudinal axis lying in the range 30° to 90°.