Investigation on the Degree of Reaction in Twin Scroll Radial Turbines at Different Operating Conditions for Turbocharging Applications

Abstract

Frequently in turbocharging radial turbine studies, some assumptions have to be done in order to make 1D matching calculations as easy as possible and to develop simulation approaches that can be useful for different purposes, like axial thrust prediction. One of these assumptions concerns the degree of reaction, which is often considered constant and equal to the value 0.5. In standard radial turbines design the velocity triangles are set by the target to keep a mean degree of reaction of 50%, in order to obtain low rotor losses and to minimize the exit swirl to get lower losses in the exhaust diffuser. From the experience gained on radial turbines operating in a wide range of conditions, it is evident that: the degree of reaction presents large variations along a given isospeed (especially at low rotational speed) and the mean value is far from 0.5 (particularly true in high performance applications). In the present work a method for the representation of the degree of reaction for radial turbine is suggested. The approach has been developed onto a twin scroll radial turbine for turbocharging, considering a large dataset of operating conditions (at both equal and partial admission). The discussion and the method suggested are based on a rich database from experimental data and numerical simulations developed by the authors on the 3D configuration of the turbines under investigation.

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

“…It emerged that values of MFP from CFD are in good agreement with the reference experimental data and that the total-to-static isentropic efficiency calculated with the numerical model does not take into account the mechanical losses, leading to an overestimation of the experimental thermomechanical efficiency. The systematic application of the present can generate performance database useful for investigation on turbine performance or operating parameters [17].…”

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

“…The set of boundary conditions used for the different domains is reported in Table 1. Simulations were performed with steady-state flow condition and in full admission (for more details on twin entry admission conditions see [11,12]). The choice to simulate a fixed operating point is due to the necessity to isolate the effects of tip clearance uncertainties on selected turbine performance parameters.…”