Understanding of the asymmetric twin-stroll radial turbine under steady and pulsating inlet conditions

Abstract

Utilize asymmetrical twin-scroll turbines (ATSTs) to achieve high-pressure exhaust gas recirculation (EGR) with a single scroll while optimizing the other scroll’s design for engine scavenging optimization. ATST performance prediction relies heavily on understanding the turbine flow mechanism, which always faces the challenge posed by time-dependent non-uniform intake. This paper studied its performance and flow field under steady and unsteady intake conditions for a production ATST. Firstly, the steady performance of the ATST with different asymmetries (ASYs) under different scroll pressure ratios (SPRs) is investigated via the computational fluid dynamics (CFD) method. Results demonstrate that the distribution relationship between SPR and turbine flow parameter (MFP) has a certain symmetry based on SPR = 1. For efficiency, the imbalance of inlet conditions will lead to the reduction of turbine efficiency. Moreover, the ASY has little effect on the turbine’s efficiency under the condition of SPR = 1. Also, the unsteady CFD simulations are conducted under pulsating inlet conditions with different scroll averaged pressure ratios (SAPRs). The results show that the highest efficiency was achieved at an ASY of 0.5 under a SAPR of 1.2 conditions, and the maximum, minimum, and average efficiencies were 1.9%, 1.5%, and 0.9% higher than those at an ASY of 0.83. The turbine’s flow field at the optimal incidence angle point is analyzed. The secondary flow vortex in the volute of an ASY of 0.5 is more robust, and the volute outlet ‘s total pressure loss is more significant. However, a relatively good incidence angle is obtained at the rotor inlet, and the loss in the rotor flow field is more minor. Therefore, the turbine efficiency with an ASY of 0.5 is higher.