The Pulsating Flow Field in a Mixed Flow Turbocharger Turbine: An Experimental and Computational Study

Abstract

The turbine stage of an automotive pulse system turbocharger is subjected to an unsteady pulsating flow field due to the rapid opening and closing of the reciprocating engine exhaust valves. This leads to a complex and highly disturbed flow field within the delivery volute and turbine passages, which results in an unusual ‘hysteresis’ type performance characteristic. The aim of this paper is to investigate the flow field within the turbine stage under these representative conditions, using a computational method validated against experimental data. This paper is separated into two sections. The first deals with the validation of the numerical code and modeling approach. A mesh dependency study is undertaken with cell discretization ranging 200,000, 850,000 and 1,750,000 cells, where the accuracy is assessed through comparison with experimental performance and flow field measurements. The second part presents an investigation of the flow field under pulse conditions. Time accurate spectra of turbine performance and flow properties at various locations in the turbine stage are presented, as well as contour plots of velocity within a turbine passage at two critical positions during the pulse period.

Effects of pulse flow and leading edge sweep on mixed flow turbines for engine exhaust heat recovery

“…The rotor rotating speed is varying in a real operation cycle under pulsating conditions, but the variation during the pulse cycle is not greater than ±1.0% [7], hence it would be considered as a constant in the analysis. From rotor inlet velocity triangle (Figure 2), the turbine is assumed running at a certain speed, and the blade speed U is constant.…”

“…Engine exhaust pulse flows can significantly affect the turbine performance of turbocharging and turbogenerating systems, and it is necessary to consider the pulse flow effects in turbine design and performance analysis. Until now, there have been some effective experimental and numerical studies of the performance of turbines under pulsating conditions [5][6][7][8][9]，which showed occurrence of significant deviation of quasi-steady and actual performance of the turbines, while the instantaneous efficiency formed a loop around the quasi-steady efficiency. Therefore, only using the steady or quasi-steady approach to evaluate the behaviors within a turbine may be simple and insufficient.…”

Flow and performance characteristics of twin-entry radial turbine under full and extreme partial admission conditions

“…Averaged equations are then discretized by evaluating them at the center of each side known as integration point, and fluxes are determined at the integration points. The Reynolds stress terms in the momentum transport equations are resolved using the (RNG) k-e turbulence model [17,29]. For determination of the near-wall velocities, a logarithmic wall function is used as considered in [10,30].…”

Numerical modelling of a supersonic axial turbine stator

“…Numerical studies on the performance of a radial or mixed flow turbine under a pulsatile inlet flow have been carried out e.g. by Lam et al [4] and Palfreyman et al [5]. They were both able to model the hysteresis-like behaviour of the turbine with CFD.…”