Numerical Simulation of the Performance of a Twin Scroll Radial Turbine at Different Operating Conditions

Abstract

Twin scroll radial turbines are increasingly used for turbocharging applications, to take advantage of the pulsating exhaust gases. In spite of its relevance in turbocharging techniques, scientific literature about CFD applied to twin scroll turbines is limited, especially in case of partial admission. In the present paper a CFD complete model of a twin scroll radial turbine is developed in order to give a contribution to literature in understanding the capabilities of current industrial CFD approaches applied to these difficult cases and to develop performance index that can be used for turbine design optimization purposes. The flow solution is obtained by means of ANSYS CFX ® in a wide range of operating conditions in full and partial admission cases. The total-to-static efficiency and the mass flow parameter (MFP) have been calculated and compared with the experimental database in order to validate the numerical model. The purpose of the developed procedure is also to generate a database for twin scroll turbines useful for future applications. A comparison between performances obtained in different admission conditions was performed. In particular the analysis focused on the characterization of the flow at volute outlet/rotor inlet section. A flow distortion index at rotor inlet was introduced to correlate the turbine performance and the flow nonuniformities generated by the volute. Finally the influence of the backside cavity on the performance parameters is also discussed. The introduction of these new nonuniformity indices is proposed for volute design and optimization procedures.

Uncertainty Quantification Methodologies Applied to the Rotor Tip Clearance Effect in a Twin Scroll Radial Turbine

“…Geometrical and performance data are confidential then all quantities have been reported in the following in non-dimensional or reduced form. For volute and rotor geometrical details, the reader can refer to previous research works [5,10] which focus on a detailed study of the twin entry turbines fluid-dynamic behavior.…”

“…• high internal combustion engine exhaust gas temperature → thermal stress; • high peripheral speed values → centrifugal stress; • high flow momentum variation and flow leakage in the backside cavity [5] → maximum thrust on bearings.…”

“…This paper deals with the operational aleatory uncertainties to which the tip clearances (at leading and trailing edge) of a twin entry turbine impeller are subjected: centrifugal, thermal, assembly and wear effects can significantly affect tip clearance values. The turbine under investigation is for automotive turbocharging and the authors have previously developed a numerical model for the simulation of this turbine, validated with experimental data [5]. The uncertainties propagation through the CFD model of the turbine has been performed using an automated procedure developed within the Dakota ® environment, an open source toolset provided with a large number of optimization and uncertainty quantification utilities.…”

“…At first, based on experience gained on radial turbines [5,10], some key performance parameters have been selected as response functions for the UQ analysis. According to experimental/CFD data available on radial turbines for turbocharging applications, the input probability distribution functions assigned to the rotor tip clearance were selected considering physically suitable values for both the average values and the standard deviations.…”

Steady State Experimental Characterization of a Twin Entry Turbine under Different Admission Conditions

“…Wei et al [13] developed a reduced-order model of a twin entry turbine capable of capturing the influence of flow distortion, due to partial and unbalanced admission, on turbine rotor performance. Cravero et al [14] developed a complete CFD model of a twin scroll radial turbine and perform simulations in full and partial admission to contribute to the literature in the understanding of this turbomachinery; moreover, they proposed several performance indices for optimization purposes.…”