INVESTIGATING THE SUITABILITY OF MULTI-SCROLL VOLUTES FOR IMPROVING SPANWISE INCIDENCE OF MIXED FLOW TURBINE ROTORS WITH VARYING BLADE CONE ANGLES IN AUTOMOTIVE TURBOCHARGING APPLICATIONS

Abstract

Abstract A Mixed Flow Turbine (MFT) is not constrained to a radial inlet blade angle, providing additional design freedom. As the MFT leading edge varies in radius, the spanwise incidence angle varies, leading to additional separation on the blade suction surface (SS) near the hub because of increasingly positive incidence, most noticeable at off-design conditions. A multi-scroll volute was previously paired with a 45° blade cone angle (Λ) MFT which generated non-uniform spanwise flow that improved off-design efficiency at the cost of peak efficiency. The current study identified the range of blade cone angles that benefitted from a multi-scroll volute to reduce incidence at the hub region. A numerical investigation was conducted which determined the influence a multi-scroll volute can have on MFTs with different blade cone angles. When the MFT with large blade cone angle (Λ=60°) was paired with a multi-scroll volute, the efficiency improved by 2.2%pts at design and 0.5%pts at off-design conditions. The incidence improved and mass flow rate increased at the hub region. The MFT with smaller blade cone angle (Λ=30°) had an efficiency loss of 1.3%pts at design and 0.8%pts at off-design conditions when paired with a multi-scroll volute due to increased incidence within the hub region. The multi-scroll volute concept was shown to offer efficiency improvements for MFTs with larger blade cone angles through better management of the non-uniform spanwise velocity distribution at rotor inlet.