Multidisciplinary Design Optimization of a Mixed Flow Turbine Wheel

Abstract

Designing turbine wheels for automotive turbochargers one is faced with a multidisciplinary design problem with many input and output parameters. Especially in the automotive industry short development cycles for high quality products in a competitive environment are daily routine. For meeting these requirements optimization algorithms can be a powerful tool in the design process. This paper presents the multidisciplinary optimization of an automotive mixed flow turbine wheel used in a 4 cylinder 1.6 l spark ignition engine. Before describing the optimization workflow in detail, the requirements for turbines operating in an automotive environment under pulsating flow conditions and during an engine load step are discussed. From there objectives for a multidisciplinary optimization are derived. The turbine wheel is optimized with respect to maximizing efficiency in two design points and minimizing its moment of inertia. For the optimization process, an algorithm based on evolution theory is used. As constraints, the operating points are fixed and the natural frequencies are limited to ensure the mechanical strength of the turbine. To speed up the optimization process meta models based on neural networks are applied. Three designs of the Pareto frontier are chosen and their characteristics are discussed. Using statistical methods, the interaction of the input variables and their impact on turbine performance are presented.

On the Design and Matching of Turbocharger Single Scroll Turbines for Pass Car Gasoline Engines

“…The basic blade geometry can be opti mized automatically using commercial software subjected to cer tain constraints and objectives as presented by Roclawski and Gugau [16] for instance. The basic blade geometry can be opti mized automatically using commercial software subjected to cer tain constraints and objectives as presented by Roclawski and Gugau [16] for instance.…”

Analysis of leading edge flow characteristics in a mixed flow turbine under pulsating flows

“…In this case, the radial stacked blade with zero-blade angle ( B Þ is shown in black and the equivalent mixed flow turbine blade, which is effectively swept back, is shown by the dashed red line, where the blade angle is defined as negative when opposite to the direction of wheel rotation. The resulting LE incidence is calculated from equation (2).…”

“…The maximum energy in the exhaust pulse is available at the peak pressure ratio running point which corresponds to the minimum velocity ratio (U=c s ) which is defined as the ratio of blade LE velocity to the velocity equivalent of an isentropic enthalpy drop over the turbine and the most positive flow relative angles. 2 Therefore, the non-zero blade angle introduced by the mixed flow effect can reduce loss associated with extreme flow angles and improve efficiency at low velocity ratio, high energy running points within the pulse.…”

The introduction of a tilted volute design for operation with a mixed flow turbine for turbocharger applications

“…This is of importance, as during the turbine inlet pulsations, the blade speed remains almost constant [7], but a significant variation in inlet pressure and velocity is experienced. The maximum energy in the exhaust pulse is available at higher pressure ratios that result in low values [8]. High efficiency at these points in the pulse can potentially improve energy extraction.…”

“…Furthermore, mixed flow turbines generally have lower inertia than radial turbines due to significant reduction in wheel mass and hence drastically improving transient response as shown by [8].…”