Unsteady Flow in a Turbocharger Compressor …...Unsteady Flow in a Turbocharger Compressor Simulation vs. Experiment Hans-Peter Dickmann, ABB Turbo Systems Ltd, Baden, Switzerland

Unsteady Flow in a Turbocharger CompressorSimulation vs. Experiment

Hans-Peter Dickmann, ABB Turbo Systems Ltd, Baden, Switzerland

Presented at the NUMECA German User Meeting, Lauf an der Pegnitz, Germany, October 21-22, 2014

Abstract

© ABB GroupNovember 14, 2014 | Slide 2

The here presented work can be regarded as a “prelude” of an extensive Fluid Structure Interaction (FSI) investigation

because it describes the computational fluid dynamics (CFD) part of a unidirectional FSI chain (consisting of fluid

mechanics and structural mechanics in series) only. The compressor is equipped with 5 circumferentially uneven

distributed struts upstream of the impeller. This configuration was chosen to excite a certain engine order of the impeller

main blades on purpose. As a means to evaluate the quality of the CFD data many steady and unsteady static pressure

measurements have been done along the casing contour above the rotating impeller. These measured data were

compared to time-averaged and unsteady results of the CFD simulations for 3 operating points (OPs). These 3 OPs

consist of 2 charged states with high and low inlet temperature and 1 atmospheric inlet state with high inlet temperature

for the high pressure component of a 2 stage turbocharger compressor. The agreement between measured and

simulated data is very good. Power generated by every single of 8 main blades during one revolution is compared for all

operating points with respect to size and shape. Videos per OP show the overall flow through the entire compressor,

state a non-reflecting inlet with respect to upstream traveling pressure waves generated by the impeller and document

the disturbed flow structure generated by the “excitation struts” in front of the impeller. The project team is still busy with

the 2nd part of the FSI chain (Forced Response Analyses). Improving the reliability of FSI simulations for compressor

blade vibrations will increase the comprehension of the FSI processes themselves (origins and impacts) and should

reduce the number of iterations on the path to a final compressor design.

Outline

1 Typical Applications of ABB Turbochargers

2 Compressor and Compressor Map

3 Flow Measurement Setup and CFD Simulation Setup

4 Results and Comparison «Simulation vs. Experiment»

5 Outlook

6 Conclusions


1 Typical Applications for ABB Turbochargers


2.1 Compressor and Compressor Map


Compressor Applicationq High pressure compressor of a 2 stage turbocharging system

q Run on 2 stage test facility with atmospheric and charged inlet conditions

Series Setupq Serial impeller with 8 pairs consisting of main blade and splitter blade

q Serial vaneless diffuser (à no influence of diffuser vanes)

q Serial volute

Non-Series Setup on Purposeq Axial inlet duct variant (to avoid secondary flows caused by radial inlet duct)

q 5 unevenly distributed struts in front of impeller for intentional excitation

q Inducer casing bleed system closed on purpose (to avoid its influence on flow)

2.2 Compressor and Compressor Map


Volume FlowT*=298K (Mass Flow)à

Tota

lPre

ssur

eR

atioà

ExperimentSimulation (time averaged)

charged, high T*IN

atmospheric, high T*IN

charged, low T*IN

LPC

HPC

Engine

LPT

HPTIdentical rpm,

but not

with respect to

T*IN=298K


Measured:

§ The usual thermodynamic data

§ Rotational speed

§ detailed pstatic (steady+unsteady)

§ Blade vibration (optically)

3.1 Experimental Setup and Simulation Setup


3.2 BCs & Interfaces / "Global Measurements "

Stator/Rotor-Interface:

«Inlet duct with struts ßà Impeller with diffuser»

Outlet BCs

Inlet BCs

Inlet pressure measurements

Outlet pressure measurements

Rotor-Stator-Interface

«Impeller+Diffuser ßà Volute»

«360° unsteady» simulation with 256 time steps per revolution

due to Nyquist criterion and later FFT analyses


3.3 "Local Measurements" along Impeller Casing Wall

(unsteady) Pressure

transducers (3)

LEMain Blade LESplitter Blade

Imp. Tip

(steady) Pressure

taps (11)+ extra taps in circumferential direction

Blade Vibration

optical sensors (2*8)

8 8

Charged - high T*IN

Pow

erN

orm

[-]

256 time steps = 1 revolution

Charged - low T*IN

Pow

erN

orm

[-]


Atmospheric - high T*IN

Pow

erN

orm

[-]



4.1 Main Blade Powers per Operating Point … in series

PowerNorm = single main blade power / average power of «Charged –low T*IN»

after 21 revs

after 21 revs

after 17 revs

atmospheric

charged

chargedP

ower

Nor

m[-]



4.2 Main Blade Powers per OP … synchronized

PowerNorm = single main blade power / average power of «Charged –low T*IN»

Pow

erN

orm

[-]

after 17 revs

1 non-dimensional revolution

Charged - high T*IN


after 21 revs

Charged - low T*IN


after 21 revs


43

51 2

T


4.3 Static Pressures along Impeller Casing Contour


Rel. D = 0.2 – 7.0 %

Average Error = 1.9%

Charged - low T*IN

Rel. D = 0.5 – 7.6 %


psN = static pressure / static pressure EXP-Tap 11

1 2 34

56

7

8

91011

Charged - high T*IN

Rel. D = 0.2 – 4.4 %



4.4 Unsteady pstatic @ close to LEMain Blade

Experiment: average over 14 (15) revolutionsSimulation: just last revolutionDp = around time averaged value

Charged - high T*IN

Charged - low T*IN



4.5 Unsteady pstatic @ close to LESplitter Blade

Experiment: average over 14 (15) revolutionsSimulation: just last revolutionDp = around time averaged value

Charged - high T*IN

Charged - low T*IN



4.6 Unsteady pstatic @ close to ImpellerTip

Experiment: average over 14 (15) revolutionsSimulation: just last revolutionDp around time averaged value

Charged - high T*IN

Charged - low T*IN



4.7 Unsteady Flow «Mach Number @ ½ Diffuser Width Cut»

Charged - low T*IN

Atmospheric - high T*IN Charged - high T*IN


4.8 Unsteady Flow «pstatic-fluctuations on 2 crossing planes»

Charged - low T*IN


psNorm = Static Pressure / Inlet Total Pressure

Charged - high T*IN


4.9 Unsteady Flow «Streaklines @ 5 struts in front of impeller»

Charged - low T*IN

Atmospheric - high T*IN Charged - high T*IN

5 Outlook


q Comparison of computed Fluid Structure Interaction (FSI) data to experimental data:

Ø FFT (Fast Fourier Transformation) & forced response analysis of pstatic of main blade 1

Ø agreement of absolute maximum displacements Dsmax per OP? (a very ambitious goal)

Ø agreement of displacement ratios «Dsmax-OP / Dsmax-OP»? (would already be a great success)

q In case of good agreement only:

Ø rerun of operating points with the NLH module instead of «unsteady 360°»

Ø comparison of experimental vs. «unsteady 360°» vs. NLH (Nonlinear Harmonics Method)

q In case of good agreement only:

Ø increase the degree of complexity (+bypass, +diffuser vanes, +suction elbow)

Ø again comparison to unsteady pressure and blade vibration measurements

6 Conclusions


à Successful quality assessment of flow simulations prior to forced response analyses

q Static pressure rise along casing confirmed by experiment

q Unsteady pressure fluctuations confirmed by experiment

q No disturbance by reflections at compressor inlet

Acknowledgments


I appreciate the support of and a lot of fruitful interesting discussions on this project …

… and thank

q ABB Turbo Systems Ltd to publish this presentation,

q Raphael Brechbühler (student at ETH Zürich) for almost the entire preprocessing, many

runs, a lot of postprocessing and many valuable ideas concerning the project.

q … at the test facility for all those numerous and detailed measurements.

q … of the CFD Team and Compressor Design Team for all kinds of support.

q NUMECA Ingenieurbüro Altdorf for the support concerning NUMECA software.

q … of the application team for the installation of a very high number of probes.

q … of the Structural Mechanics Team for the FSI analyses preparation discussions.

My colleagues at ABB Turbo Systems Ltd …

Documents

Unsteady Flow in a Turbocharger Compressor …...Unsteady Flow in a Turbocharger Compressor Simulation vs. Experiment Hans-Peter Dickmann, ABB Turbo Systems Ltd, Baden, Switzerland