Unsteady Flow Loss Mechanism and Aerodynamic Improvement of Two-Stage Turbine under Pulsating Conditions

The developments of two-stage turbocharging and turbocompounding promote the application of the two-stage turbine system in internal combustion engines. Since the turbine suffers from the pulsating exhaust, the performance deteriorates significantly from steady conditions. In the paper, the pulsating flow losses in the two-stage turbine are analyzed and a control method is proposed to improve the turbine performance. ANSYS CFX, which is a commercial software for computational fluid dynamic, is applied to resolve the three-dimensional unsteady flow problem. The accuracy of the simulation method is verified by the experimental data from each turbine. Firstly, the impacts of pulse amplitudes on transient loss of each component of the two-stage turbine are studied. Then flow field analysis is carried out to understand details of the unsteady flows. It is found that the variation of incidence angle at the low-pressure turbine (LPT) rotor tip is significantly larger than that at rotor hub, which causes severe flow loss near leading edge. As a result, the LPT performance drops down significantly. To improve the LPT performance, the blade shape at tip is modified. The aerodynamic performances of turbines with three different shapes under high- and low-load pulsating flow conditions are evaluated. It is found that increased inlet blade angle and medium thickness achieves good aerodynamic performance. The rotor averaged efficiency is improved by 2.27% under high-load pulsating condition.

[1]  Srithar Rajoo,et al.  Influence of pulsating flow frequencies towards the flow angle distributions of an automotive turbocharger mixed-flow turbine , 2015 .

[2]  Yangjun Zhang,et al.  Analysis on altitude adaptability of turbocharging systems for a heavy-duty diesel engine , 2018 .

[3]  Ricardo Martinez-Botas,et al.  Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions , 2000 .

[4]  Luis Miguel García-Cuevas,et al.  Characterization of a radial turbocharger turbine in pulsating flow by means of CFD and its application to engine modeling , 2013 .

[5]  I Hakeem,et al.  Modelling of a Turbocharger Turbine Under Pulsating Inlet Conditions , 1996 .

[6]  Ricardo Martinez-Botas,et al.  The Pulsating Flow Field in a Mixed Flow Turbocharger Turbine: An Experimental and Computational Study , 2005 .

[7]  Rongchao Zhao,et al.  Numerical study of a two-stage turbine characteristic under pulsating flow conditions , 2016 .

[8]  N. Baines.  Axial and Radial Turbines , 2003 .

[9]  Ricardo Martinez-Botas,et al.  The effect of unequal admission on the performance and loss generation in a double-entry turbocharger turbine , 2012 .

[10]  Apostolos Pesiridis.  The application of active control for turbocharger turbines , 2012 .

[11]  Srithar Rajoo,et al.  An investigation of volute cross-sectional shape on turbocharger turbine under pulsating conditions in internal combustion engine , 2015 .

[12]  Liping Xu,et al.  A LOW ORDER MODEL FOR PREDICTING TURBOCHARGER TURBINE UNSTEADY PERFORMANCE , 2014 .

[13]  Hans-Erik Ångström,et al.  A review of turbocompounding as a waste heat recovery system for internal combustion engines , 2015 .

[14]  Srithar Rajoo,et al.  Unsteady Effect in a Nozzled Turbocharger Turbine , 2010 .

[15]  Colin Copeland,et al.  The Effect of Unequal Admission on the Performance and Loss Generation in a Double-Entry Turbocharger Turbine , 2010 .

[16]  Silvia Marelli,et al.  Steady and pulsating flow efficiency of a waste-gated turbocharger radial flow turbine for automotiv , 2011 .

[17]  Mingyang Yang,et al.  Influence of altitude on two-stage turbocharging system in a heavy-duty diesel engine based on analysis of available flow energy , 2018 .

[18]  Srithar Rajoo,et al.  Unsteady performance analysis of a twin-entry variable geometry turbocharger turbine , 2012 .

[19]  Martinez-Botas Ricardo,et al.  Overview of boosting options for future downsized engines , 2011 .

[20]  R. Martinez-Botas,et al.  Comparison Between Steady and Unsteady Double-Entry Turbine Performance Using the Quasi-Steady Assumption , 2011 .

[22]  Silvia Marelli,et al.  Experimental analysis of unsteady flow performance in an automotive turbocharger turbine fitted with a waste-gate valve , 2011 .

[23]  Rongchao Zhao,et al.  Parametric study of a turbocompound diesel engine based on an analytical model , 2016 .

[24]  Weilin Zhuge,et al.  An investigation on unsteadiness of a mixed-flow turbine under pulsating conditions , 2016 .

[25]  Carl F. Fredriksson,et al.  The Mixed Flow Forward Swept Turbine for Next Generation Turbocharged Downsized Automotive Engines , 2010 .

[26]  Francisco José Arnau,et al.  A model of turbocharger radial turbines appropriate to be used in zero- and one-dimensional gas dynamics codes for internal combustion engines modelling , 2008 .

[27]  Srithar Rajoo,et al.  Influence of speed and frequency towards the automotive turbocharger turbine performance under pulsating flow conditions , 2014 .

[28]  N Karamanis,et al.  Mixed-flow turbines for automotive turbochargers: Steady and unsteady performance , 2002 .

[29]  Oscar Barambones,et al.  Computational Modelling of Rectangular Sub-Boundary Layer Vortex Generators , 2018 .

[30]  Miloud Abidat,et al.  Prediction of the steady and non-steady flow performance of a highly loaded mixed flow turbine , 1998 .

[31]  Srithar Rajoo,et al.  Novel method to improve engine exhaust energy extraction with active control turbocharger , 2014 .

[32]  Ricardo Martinez-Botas,et al.  A Three-Dimensional Computational Study of Pulsating Flow Inside a Double Entry Turbine , 2015 .

[33]  Srithar Rajoo,et al.  Waste heat recovery using a novel high performance low pressure turbine for electric turbocompounding in downsized gasoline engines: Experimental and computational analysis , 2015 .

[34]  Weilin Zhuge,et al.  Effects of pulse flow and leading edge sweep on mixed flow turbines for engine exhaust heat recovery , 2011 .