07 Innovative Centrifugal Compressor Design … Centrifugal Compressor Design ... (compressor cover) 0.4 (rotor inducer) 0.8.(rotor exducer) 2 ... • The thickness of the blade is

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

Innovative Centrifugal Compressor Design

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


INTRODUCTION

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

The challenge is :


The challenge is :

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

• to maintain the initial stability range.


OVERVIEW OF THE IRA CONCEPT

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


HP centrifugal compressor


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.


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


- 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


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 tip

radius).

Aerodynamic design point:


Aerodynamic design point:• Based upon the engine conditions: the mid-cruise flight.

HPC inlet pressureHPC inlet temperatureHPC PRHPC inlet mass flow

kPaK-kg/s

129.83027.1327.72


• 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 12817

“ Technological” dataRadial and axial tip gapRoughness

Blade to hub radius

mmµµµµm

mm

0.40.8 (compressor cover)0.4 (rotor inducer)0.8.(rotor exducer)2

Geometrical dataInlet hub radiusMaximum outer radiusRadial extension

mmmm-

193.514161.4


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

Isentropic efficiency pts 82.1

Surge margin (Kp(*)) pts 10

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

DEFINITION OF THE CONVENTIONAL DESIGN


3D view of the 2D flanked milled rotor and its associated diffuser


3D DEFORMATIONS

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

• The level of deformation from hub to tip, controlled by “Bezier” curves, is directly applied to the blade surfaces.

• This allows deformations as lean, bowed shapes, strong local curvatures, …• The thickness of the blade is controlled under the same principles.


• The thickness of the blade is controlled under the same principles.

Bowed Leading Edge

Strong curvatures at the Leading Edge

Types of Deformations


ASSESMENTS : 3D CFD calculations

• The performances and the surge margin are estimated with 3D CFD calculations.

• 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*106 nodes

Kind of Grid Block structured

Turb Model K-l Smith (2-eq)


CFD RESULTS

+1.6 pts

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



CFD RESULTS

« State of the art » impeller « Advanced 3D » impeller

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


These pictures show the reduction of loss generatio n between the “state of the art” design and the 3D improved version of the impeller by the reduction of secondary flows (see the red circles).


TEST RIG

• View of the fully instrumented test rigAir Exit


Air Intake


TEST RIG

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


Diffuser of the centrifugal compressor stage

Trailing edge of the 2D axial diffuser


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

speed), pretty consistent with CFD prediction (factor of


speed), pretty consistent with CFD prediction (factor of achievement varying between 0.6 to 1.0)

• Slight deterioration of surge margin corresponding to the increase of choke mass flow. Baseline surge line can be recovered without any penalty on peak efficiencies by matching the radial diffuser

• Sensitivity to running clearances unchanged


TEST RESULTS

2

2,5

Isen

trop

ic e

ffici

ency

gai

n (p

ts)

« 3D design » vs « State of the art design » : meas ured improvement of efficiency


0

0,5

1

1,5

60 65 70 75 80 85 90 95 100 105 110

N' (%)

Isen

trop

ic e

ffici

ency

gai

n (p

ts)


CONCLUSION & OUTLOOK

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

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


• Further investigation are necessary to understand the interaction between the rotor and the stator to increase further more the overall efficiency of the compressor stage.

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

Documents

07 Innovative Centrifugal Compressor Design … Centrifugal Compressor Design ... (compressor cover) 0.4 (rotor inducer) 0.8.(rotor exducer) 2 ... • The thickness of the blade is