Research Papers: Gas Turbines: Turbomachinery

Lumped Capacitance and Three-Dimensional Computational Fluid Dynamics Conjugate Heat Transfer Modeling of an Automotive Turbocharger

[+] Author and Article Information
R. D. Burke

Powertrain and Vehicle Research Centre,
University of Bath,
Bath BA2 7AY, UK
e-mail: R.D.Burke@bath.ac.uk

C. D. Copeland, T. Duda, M. A. Rayes-Belmote

Powertrain and Vehicle Research Centre,
University of Bath,
Bath BA2 7AY, UK

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 23, 2015; final manuscript received January 5, 2016; published online March 22, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(9), 092602 (Mar 22, 2016) (9 pages) Paper No: GTP-15-1489; doi: 10.1115/1.4032663 History: Received July 23, 2015; Revised January 05, 2016

One-dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions, and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools, and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process. Initially, a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre- and postcompression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency, whereas at high speed αA had a similar influence to TIT. However, modeling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%. Three-dimensional computational fluid dynamics (CFD) analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA = 0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the precompression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.

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Fig. 1

Diabatic processes in a turbocharger: (a) compressor process and (b) turbine expansion process

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Fig. 2

Heat transfer processes in a turbocharger

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Fig. 3

Two-node thermal network used in the model

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Fig. 4

Heat transfer from the compressor casing to the environment (50 krpm and 150 krpm)

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Fig. 5

Heat transfer from the central housing to the compressor casing (50 krpm and 150 krpm)

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Fig. 6

Heat transfer between compressor housing and intake air before compression at (a) 50 and 150 krpm and (b) 50 krpm

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Fig. 7

Heat transfer between compressor housing and air post compression at (a) 50 and 150 krpm and (b) 50 krpm

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Fig. 8

Diagram of the two-node compressor thermal network

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Fig. 9

Heat transfer to the precompressed air for the assumption of two compressor nodes

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Fig. 10

Heat transfer to the postcompressed air for the assumption of two compressor nodes (50 krpm and 150 krpm)

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Fig. 11

Compressor wall boundary conditions: (a) case 1, (b) case 2 (bearing housing indication), and (c) measuring planes

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Fig. 12

Compressor housing temperature profiles from conjugate heat transfer calculations for (a) case 1—externally insulated housing, (b) case 2—externally insulated without precompression heat transfer, and (c) case 3—fully diabatic housing

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Fig. 13

Single line flow path across compressor model

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Fig. 14

(a) Pressure and (b) temperature distribution along single flow path inside the compressor case

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Fig. 15

(a) Effect of αa and TIT on compressor efficiency determination (50 krpm), (b) effect of αa for a given temperature (150 krpm − 500 °C), and (c) effect of TIT for a given αa (150 krpm − αa = 0.2)




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