A methodology for loss and performance assessment of a variable geometry turbocharger turbine through a new meanline FORTRAN program

PurposeVariable geometry turbine (VGT), a key component of modern internal combustion engines (ICE) turbochargers, is increasingly used for better efficiency and reduced exhaust gas emissions. The aim of this study is the development of a new meanline FORTRAN code for accurate performance and loss assessment of VGTs under a wider operating range. This code is a useful alternative tool for engineers for fast design of VGT systems where higher efficiency and minimum loss are being required.Design/methodology/approachThe proposed meanline code was applied to a variable geometry mixed flow turbine at different nozzle vane angles and under a wide range of rotational speed and the expansion ratio. The numerical methodology was validated through a comparison of the predicted performance to test data. The maps of the mass flow rate as well as the efficiency of the VGT system are discussed for different nozzle vane angles under a wide range of rotational speed. Based on the developed model, a breakdown loss analysis was carried out showing a significant effect of the nozzle vane angle on the loss distribution.FindingsResults indicated that the nozzle angle of 70° has led to the maximum efficiency compared to the other investigated nozzle vane angles ranging from 30° up to 80°. The results showed that the passage loss was significantly reduced as the nozzle vane angle increases from 30° up to 70°.Originality/valueThis paper outlines a new meanline approach for variable geometry turbocharger turbines. The developed code presents the novelty of including the effect of the vane radii variation, due to the pivoting mechanism of the nozzle ring. The developed code can be generalized to either radial or mixed flow turbines with or without a VGT system.

Improving Vibration Response of Radial Turbine in Variable Geometry Turbochargers With CFD Analysis

Recent advancements in internal combustion engine for efficient fuel combustion, such as application of miller cycle, where the closing of engine intake valve is purposely delayed to provide more cooling of air-fuel mixture during compression stroke for better engine efficiency, has led to a requirement for turbochargers to function at a wider operating range and higher compression ratio. One of the methods which have been largely accepted is the use of variable geometry turbochargers. As compared to diesel engine, operating conditions for gasoline engine require the turbine to operate at higher exhaust temperature, which increases the risk of damaging the rotor. This paper discusses a detailed flow analysis of the effect of tip leakage and nozzle vane wake flow on surface pressure distribution of the turbine rotor, especially at the severe condition when vane trailing edge and rotor leading edge are in proximity. It was observed in steady and unsteady CFD simulations that the origination and propagation of tip leakage flow can be varied depending on the blade loading at the rotor leading edge, and the major interaction of nozzle wake can be switched from pressure surface to suction surface as rotor blade crossed a nozzle vane, which can drastically affect the alternating aerodynamic stresses. The sensitivity to this phenomenon has been evaluated by calculating the safety factor. The authors modified the rotor design to weaken the effect of tip leakage flow in order to suppress variations in rotor surface pressure as it crosses the nozzle vane. It significantly reduced the alternating stress and increased the safety factor at vibration mode 2 from 0.3 to 9.3 and mode 3 from 0.6 to 3.2 respectively.

Aerodynamic Design Optimization of a Variable Geometry Nozzle Vane For Automotive Turbochargers

An aerodynamic design optimization study of the nozzle vane of a variable geometry turbine (VGT) turbocharger for a diesel engine application was conducted using the commercial software, ANSYS CFX and DesignXplorer. The nozzle design was optimized at three critical engine operating points. The nozzle shape was parameterized using key design parameters including theta angle, thickness value and opening angle. For a good balance of computational time and accuracy, the optimization approach adopted meta-models and response surfaces to represent the training data and reduce the number of simulations required to reach an optimal design. Finally, more than 300 optimized designs were simulated to assess the performance and characteristics of each design. The final optimized nozzle design met all the design constraints and showed an improvement of up to 2% efficiency and reduced the maximum torque by 20% compared to the baseline nozzle.

The Study on Effect of the Number of Nozzle Vanes in a Radial Flow Turbine for the Turbocharger

The effect of number of nozzle vanes in the turbine stage of a turbocharger is studied using computational fluid dynamics. The nozzle vane unit having 8, 9 and 10 numbers of nozzle vanes configuration is proposed for the radial flow turbine with 30 mm wheel tip diameter. At maximum opening position of the nozzle vanes and for the typical turbine expansion ratio of 2.5, the reduction in mass flow parameter with 10 numbers of nozzle vanes is about 1% lower compared to the 8 numbers of nozzle vanes. The maximum turbine flow range is not affected with higher number of nozzle vanes. The improvement in flow guidance is observed in nozzle vane unit having 10 numbers of nozzle vanes. The improvement in pressure distribution is observed in both the nozzle vane and turbine wheel with increase in number of nozzle vanes. The entropy generation in a turbine stage is found to decrease with increase in the number of nozzle vanes.