Session: 38-01 Radial & Mixed Flow Turbines

Paper Number: 101738

101738 - Investigating the Suitability of Multi-Scroll Volutes for Improving Spanwise Incidence of Mixed Flow Rotors With Varying Blade Cone Angles in Automotive Turbocharging Applications 

Targets to reduce fuel consumption and reduce CO2 emissions have been met using engine downsizing and turbocharging. In automotive applications, it is important that the turbocharger responds well to transient events and operates efficiently at both the Design and Off-Design conditions. The peak efficiency of a turbine can be shifted to a lower U/C by utilising a non-zero inlet blade angle. Due to structural limitations of a radial rotor, only minor deviations from the radial fibre can be made as additional stress is introduced. A Mixed Flow Turbine (MFT) is not constrained to a radial fibre, providing additional freedom to the designer. As the MFT leading edge varies in the radial direction, the spanwise incidence angle also varies, leading to additional separation on the suction surface of the blade near the hub because of increasingly positive incidence, most noticeable at off-design conditions. 

A multi-scroll volute was previously paired with a mixed flow rotor with a 45° blade cone angle (Ʌ). It was found that a multi-scroll volute could improve the off-design efficiency by shifting mass flow towards the hub and improving incidence, reducing the impact of the suction side separation.

This study considered the usefulness of a multi-scroll paired with two further mixed flow rotors of differing extremes of blade cone angle, which have previously been studied at QUB. One rotor had a low blade cone angle (Ʌ=30°) and therefore has a larger radial component. The second rotor had a large blade cone angle (Ʌ=60°) with a more substantial axial component.

The study aims to identify the range of blade cone angles that can be paired with a multi-scroll volute to reduce the hub region suction side separation. The multi-scroll design suffers from additional losses compared to a mono-scroll through the form of increased boundary layer due to additional wetted surface area and from the generation of a wake at the meridional divider tip. The multi-scroll system must therefore overcome these additional losses before achieving any additional benefit over a conventional mono-scroll volute. Although the flow was altered by the multi-scroll, the additional losses from the volute provided an overall performance reduction for the low blade cone angle MFT. An efficiency benefit at both Design and Off-Design conditions was observed for the large blade cone angle MFT, which also benefits from the largest inertia reduction compared to a radial rotor and therefore the best response to transient events, providing a desirable product for automotive applications.

Presenting Author: Peter Martin Trinity College Dublin, the University of Dublin

Presenting Author Biography: Peter completed his master’s degree in the summer of 2018 and then started studying for his PhD at Queen’s University Belfast. He is part of the Turbomachinery research group led by Professor Stephen Spence at Trinity College Dublin. Peter’s research is supported by IHI Charging Systems International GmbH. His project is investigating turbine housings to improve the spanwise incidence of mixed flow rotors for automotive applications.

Authors:

Peter Martin Trinity College Dublin
Stephen Spence Trinity College Ireland
Charles Stuart Trinity College Dublin
Andre Starke IHI Charging Systems International GmbH
Thomas Leonard IHI Charging Systems International GmbH
Marco Geron Queen's University Belfast