Aerothermodynamics and exergy analysis in turbocharger radial turbine

Opponent:

Professor Ricardo Martinez Botas (Imperial College London)

Grading committee: 

1. Professor Björn Laumert (KTH Heat and Power Technology)

2. Professor Simone Sebben (Chalmers tekniska högskolan)

3. Professor Lars Eriksson (Linköping University)

Click here  for to download the dissertation, and see below for the abstract.

Abstract:

Coupling of turbomachine to reciprocating automotive engine in turbocharging leads to complex fluid flow and thermal characteristics in the turbine. Some undesirable characteristics include heat transfer, flow pulsation and secondary flow due to the complex geometry of the upstream exhaust manifold. The performed literature review exposed that there is a need for an enhanced understanding of the thermo-fluid physics of a turbocharger turbine operating under realistic on-engine conditions, and on quantifying the impact on the performance. Often, simplified set-ups and geometries are employed, neglecting the heat transfer.

This dissertation aimed to improve the quality of heat transfer analysis in a turbocharger turbine, and to enhance the understanding of aerothermodynamic effects due to heat transfer on the performance under engine-like pulsatile flow scenarios. Firstly, a flow exergy based analysis was developed to be used with the input provided by three-dimensional flow field data predicted by Detached Eddy Simulation (DES). Its applicability to identify and to quantify the aerothermodynamic related losses due to heat transfer was thoroughly investigated with a set-up replicating a hot gas stand continuous flow scenario. Next, the developed methodology was applied to engine-like pulsatile flow scenarios, to investigate the effects of flow pulsation and the influences of upstream exhaust manifold on the heat transfer and turbine performance. For the investigated geometry and specified boundary conditions, this dissertation mainly concluded that 1) The most sensitive measures associated with heat loss are the flow exergy lost via heat transfer and the thermal irreversibilities. The influence of heat loss on turbine power reduction is small in a relative sense, and 2) Although the exhaust manifold characteristics govern the fundamental flow physics and heat transfer in the scroll, its impact on the turbine power seems to be small relatively.

The contributions with this dissertation were mainly twofold. Firstly, it contributes to a deeper understanding of the thermo-fluid physics of a turbocharger turbine operating under engine-like pulsating flow scenario. This knowledge might be useful for industrial product development in the future. Secondly, from academic perspective, the flow exergy budget analysis could potentially serve as a practical example to students in connecting the dots between classroom theory and real life engineering application.