07 Innovative Centrifugal Compressor Design

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European Workshop on New Aero Engine ConceptsMunich, 30 June 1 July 2010

Innovative Centrifugal CompressorDesign

NEWAC is an Integrated Project Co-funded by the European Commission within the Sixth Framework Programme(2002-2006) under Thematic Priority 4 Aeronautics and Space.

L. TarnowskiTURBOMECA groupe SAFRAN


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INTRODUCTION

SP2 : IRA (Intercooled Recuperative Aero-engine) Task 2.2.5 HP Centrifugal Compressor Design


to improve significantly the efficiency of a 2D flanked milled blades of astate of the art centrifugal compressor with a high hub to tip radius ratio.

to maintain the initial stability range.


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OVERVIEW OF THE IRA CONCEPT

The new design approach is applied to the last stage of compression (HP) of theIRA engine concept


HP centrifugal compressor


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PARTNER INVOLVED in Task 2.2.5

PBS

PBS and Turbomeca advanced studies are complementary :

Centrifugal compressor with a low hub to tip radius ratio.


Main work :- Study of the rotor stator interactions.- Focusing on an optimisation of the geometrical definition of the radial

diffuser captation zone.


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TECHNICAL APPROACH

STEPS of DESIGN

Conventional 2D design of the centrifugal stage : rotor and stators Advanced 3D design of the rotor (unchanged stators) :- Identical meridional definition of the flow path- Identical throat area


- Identical leading edge and trailing edge radius- Modification of the rotor blade angle- Modification of the rotor blade thickness

Goals:- To increase the efficiency of the 2D design by 0.8 pts- To keep the stability of the 2D design- To comply with the mechanical criteria


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1D DEFINITION OF THE CONVENTIONAL DESIGN

Type of compressor:

HP compressor following an intercooler. High hub to tip radius ratio of 0.8 (leading edge hub radius / Leading edge tipradius).


Based upon the engine conditions: the mid-cruise flight.

HPC inlet pressureHPC inlet temperature

HPC PRHPC inlet mass flow

kPaK

-kg/s

129.8302

7.1327.72


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Designed at ambient inlet conditions

Aero-thermodynamic dataHPC inlet pressureHPC inlet temperature

kPaK

101.325288.15

Complementary data to estimate the efficiency

1D DEFINITION OF THE CONVENTIONAL DESIGN


Rotational speed rpm 12817Technological dataRadial and axial tip gapRoughness

Blade to hub radius

mmm

mm

0.40.8 (compressor cover)0.4 (rotor inducer)

0.8.(rotor exducer)2

Geometrical dataInlet hub radiusMaximum outer radius

Radial extension

mmmm

-

193.51416

1.4


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Efficiency and stability targets of the conventional design (1D estimate)

Isentropic efficiency pts 82.1

Surge margin (Kp (*)) pts 10

(*)Kp=( ////W)surge point /(//// W)aero design pointwith W the corrected mass flow and the total pressure ratio of the compressor stage.

DEFINITION OF THE CONVENTIONAL DESIGN


3D view of the 2Dflanked milled rotor andits associated diffuser


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3D DEFORMATIONS

The 2D blades geometry is modified step by step from hub to tip and alongthe blade to blade channel.

The level of deformation from hub to tip, controlled by Bezier curves, isdirectly applied to the blade surfaces.

This allows deformations as lean, bowed shapes, strong local curvatures,


.

Bowed Leading Edge

Strong curvatures at the Leading Edge

Types of Deformations


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ASSESMENTS : 3D CFD calculations

The performances and the surge margin are estimated with 3D CFDcalculations.

Numerical features: 3D NS CFD code called elsA developed by ONERA. Low Reynolds Number model for the boundary layer.


Code Name Elsa (ONERA)Grid Size 3*10 6 nodes

Kind of Grid Block structured

Turb Model K-l Smith (2-eq)


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CFD RESULTS

+1.6 pts

According to numerical predictions the final design is on target. With a factor ofachievement of 0.5, the efficiency is improved by 0.8 pts. This is achieved atcomparable surge margin.



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CFD RESULTS

State of the art impeller Advanced 3D impeller

Cross section views of the entropy distribution : about 50% down stream theleading edge of the splitters


These pictures show the reduction of loss generation between the state of the artdesign and the 3D improved version of the impeller by the reduction of secondary flows(see the red circles).


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TEST RIG

View of the fully instrumented test rigAir Exit


Air Intake


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TEST RIG

Manufacture of the test rig parts : Pictures of the instrumented diffuser


Diffuser of the centrifugalcompressor stage

Trailing edge of the 2D axialdiffuser


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TEST RESULTS

Main test results with 3D impeller : Increase of pressure ratio as predicted by CFD (+4% at given

mass flow) Increase of efficiency (+0.9 pt at nominal speed, +1.5 at part


,achievement varying between 0.6 to 1.0)

Slight deterioration of surge margin corresponding to the increaseof choke mass flow. Baseline surge line can be recovered withoutany penalty on peak efficiencies by matching the radial diffuser

Sensitivity to running clearances unchanged


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TEST RESULTS

2

2,5

i n (

p t s )

3D design vs State of the art design : measured improvement ofefficiency


0

0,5

1

1,5

60 65 70 75 80 85 90 95 100 105 110

N' (%)

I s e n

t r o p

i c e

f f i c i e n c y g a


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CONCLUSION & OUTLOOK

Changing the way of design with massive use of 3D CFD calculations hasallowed to generate 3D blades for the rotor which brought an improvementin efficiency better than the initial target (0.8 pt).

A tuning of the radial diffuser section has to be considered to get back to theinitial surge line.


Further investigation are necessary to understand the interaction betweenthe rotor and the stator to increase further more the overall efficiency of thecompressor stage.

Unsteady calculations will certainly be required to capture the flow featuresand allow a more efficient design of the rotor and the stator.

07 Innovative Centrifugal Compressor Design

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