ARL Penn State COMPUTATIONAL MECHANICS 1 Computational Evaluation of the Cavitating Flow through Automotive Torque Converters Acknowledgement: This work

ARLPenn StateCOMPUTATIONAL MECHANICS

1

Computational Evaluation of the Cavitating Flow through

Automotive Torque Converters

Acknowledgement: This work is supported by the General Motors Corporation

15 August 2012

J.W. Lindau F.J. Zajaczkowski M.F. Shanks R.F. Kunz


CONTENTS

• Introduction

• Computational Methods

• Results

• Summary

2


CAVITATION IN A TORQUE CONVERTER:•Working fluid is ATF, heat, extreme pressures•Torque converters have historically not suffered negative effects from cavitation •However, the trend is to smaller, lighter, etc•Minimum pressure/stator region may cavitate at high torque, low turbine speed•Concerns are performance, vibration, noise

Introduction: Automotive Torque Converter

Torque Converter from Wikipedia

3


Methodology• First principals model of…

– Mixture of gases and liquids– Gas-liquid interfaces– Large scale gas cavities– Incompressible to compressible: disparate sound speeds– Shocks– Significant inherent unsteadiness (even in steady, planing configuration)– Energetic propulsion

• Chemistry and phase change– Liquid/vapor mass transfer (stiff)– Chemical reactions (stiff)

• Control Surfaces--6DOF: fully coupled to flow• Preconditioning (addresses stiff physical eigensystem)• Turbulence modeled and (where feasible, required) simulated• Numerical model: fully-conservative, unsteady, implicit, multiphase, preconditioned

finite volume form• Unsteady simulations with many millions of degrees of freedom are feasible/required

4


DIFFERENTIAL MODEL

• Computational tool—• n-liquid+n-gas• preconditioned• all-Mach number• compressible• total energy conservation• any 2-variable eos/species• body forces/propulsors• mass-transfer=phase change and chemistry• shock-capturing• level-set—free-surface or cavity interface• multibody-control surfaces-6DOF• overset • 2-eq RANS/DES/transition

HFFQ

t

Q vjjjj

pc

,,

Numerical solution of mixture: mass, momentum, energy, additional phases,

species, and turbulence models on moving or static, overset computational

meshes.

5


VALIDATION HIGHLIGHTS

Cavitator Lift and Drag


Lift and drag values and comparison of experimental

and computational geometries and computed cavities (with

gas streamlines) from experiments of Waid and

Kermeen (1957).



0

0.2

0.4

0.6

0 0.1 0.2 0.3Cavitation Number, s

Air

En

tra

inm

en

t R

ate

, C

Q

Exp. Fr=26.7DESDES:w/strutURANSURANS:w/strutRANSSpurk Eq. 33

Cavity Size vs. Ventilation Rate



Mesh showing flowpath, rotor, and stator in NSWC-CD Tunnel

0.5 1 1.5 2 2.5 3 3.5 40.8

0.85

0.9

0.95

1

1.05

CFDEFD

Normalized inlet total pressure

0.5 1 1.5 2 2.5 3 3.5 40.8

0.9

1

1.1

CFDEFD

Normalized Head Rise

Normalized Power

9



10

pump turbine

stator

pumpturbine

stator

Torque Converters: Computational Mesh

Round Torus: Research Converter

Thin Torus: Converter Approximating Current Designs Trends

BOTH A MIXING PLANE AND A BODY FORCE BASED COUPLING APPROACH ARE APPLIED

COMPUTATIONAL GEOMETRY REPEATED OVER FULL 360deg


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Cavitating CFD current effort

Single Phase CFD current effort

a)

1700 1800 1900 2000 2100 2200 2300 2400 25002.15

2.16

2.17

2.18

Tor

que

Rat

io

1700 1800 1900 2000 2100 2200 2300 2400 2500-4

-3.5

-3%

Err

or v

s. E

xper

imen

ts

RPM

b)

CFD and test results on research converter. K-factor (RPM/[torque]1/2) and torque ratio.

Round Torus CFD Results

MPa

0.8

0.0


12

Through-flow Pump

Turbine

Stator

Grids for body force based method. Computational meshes, thin-torus torque converter (coarse). Solid surfaces are illustrated with black mesh. Periodic boundaries are illustrated with green mesh.

Thin Torus CFD Mesh


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Speed Ratio

CFD results (red)diamond: cavitating

square: 1-phase

Dyno-135 N-m

Dyno-250 N-mK-factor/100

Torque Ratio

• Computation and testing of Thin Torus TC. • Single-phase and cavitating.

Plot of K-factor/100 and torque ratio versus speed ratio. • Dynomometer: black marks with black lines. • CFD: red diamonds and dashed==single-phase, and • CFD: red squares and dashed ==cavitating

Thin Torus CFD Results


MPa

1.1

0.0

suction side pump and stator

pressure-side pump and stator

MPa

0.5

0.0

Single-phase solution, pump at 3000RPM, turbine stationary, thin-torus torque converter.

Cavitating CFD solution, thin-torus unit. Elements repeated periodically for visual effect. Surfaces made translucent to better visualize stator and cavity. All surfaces colored by pressure. Isosurface of vapor volume fraction at 0.5. Pump at 3000RPM, stall condition

Thin Torus CFD Results


SUMMARY

• CFD methodology validated for ventilated and natural cavitation, supercavitation, and turbomachinery

• Torque converters modeled using single blade passage, multi-blade row (steady, periodic assumption) CFD

• Mixing plane and body force coupling• Both approaches are problematic• Cavitation effects on pump torque captured• For high torque/large cavities and impact on

noise/vibration, a full 360deg unsteady analysis may be needed

15


1

1pp Q

Q

k

i

Y

T

u

p

Q1

Preconditioner

Derivation simplified working in terms of mass fraction

l

ll

l

l

YkklTkpk

YYTTkpp

YiTiijpi

YTp

p

YYY

hhhhuhh

uuu

0

)1(

0

000

1

k

i

T

u

p

Q


Preconditioner

• We choose: c’=min[ max( Vcut-off , |V|ijk ), cijk ] (c’=cijk yields the unconditioned result)

• Introduces artificial sound speeds yielding good convergence/accuracy regardless of Mach number/density ratio

Documents

ARL Penn State COMPUTATIONAL MECHANICS 1 Computational Evaluation of the Cavitating Flow through Automotive Torque Converters Acknowledgement: This work