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.
Designing and operating water supply systems is a multicriteria task: the energy efficiency shall be minimised while, at the same time, respecting technical requirements, such as balanced operation of available pumps. In this contribution, we present an optimisation and decision support methodology to improve the operation of pumps in the water sector of medium size cities (approximately 100000 inhabitants) in Germany. The emphasis is on the multicriteria nature of the problem. Besides the management of the waterworks system, we consider the goal to assist at the selection of a new pump. We discuss several examples to emphasise the benefits of obeying the rules of multicriteria decision-making and involving the user into the decision process.
This paper presents a study on the influence of the degree of reaction (DoR) on turbine performance under highly pulsating inflow. A reference test turbine wheel is designed and scaled to three different wheel diameters while an identical flow capacity of all three turbines is provided by adjusting the volute size. Hence, the three turbines differ by their DoR, inertia and efficiency characteristic. The investigation is done completely numerically using highly validated models. Naturally, the pulsating flow character of a 4-cylinder gasoline engine requires unsteady CFD. In addition steady-state turbine maps were calculated beforehand as a reference base. The results of the steady state calculation show that for the combination of the bigger turbine wheel with the smaller turbine volute the peak efficiency is smaller but is shifted towards higher pressure ratios respectively to lower blade speed ratios. This is fundamentally beneficial for turbines in automotive turbochargers for gasoline engines characterized by highly pulsating flow conditions, in particular at lower engine speeds. For the transient flow calculations with pulsating turbine inflow, the hysteresis loop and the turbine power generation was investigated. It is shown that the smallest volute compared to the biggest one causes a more contracted hysteresis loop combined with increased power output within one pulse cycle. In order to include the influence of moment of inertia, the turbines with varying DoR but same flow capacity were analytically compared with a 1D code simulating engine load step operation. Thus, the paper shows the effect of turbine DoR on both, steady-state turbine performance under pulsating inflow and the capability for optimum engine load step operation.
The design and operation of water supply systems is a multicriteria task: the energy efficiency should be minimized while, at the same time, respecting technical requirements, such as the balanced operation of available pumps. On one hand, the overall system can be improved by the use of variable speed pumps. They increase the number of operating options. On the other hand, they add more complexity to the operation problem. In this paper, we discuss the difficulties associated with speed control and propose a decision support process to overcome them.
A method for evaluating the transient performance of a turbocharger (TC) is so-called load step tests. In these tests, the load of the engine is increased at constant engine speed and the time measured from the start to the end of the load step is measured. Usually, these tests can be run relatively late in the development process, since hardware needs to be already available. In order to judge the transient TC performance at an earlier stage, engine process simulations are run using maps of compressor and turbine. For the turbine, these maps usually need to be extrapolated, since only a certain range of each speed line can be measured on a standard gas stand. Furthermore, because of the exhaust gas pulsation of the engine, it is known that the turbine performance differs from the steady-state case which the maps rely on. This has to be respected by additional models. Using computational fluid dynamics (CFD) simulations, the transient performance of the turbine can be analyzed independent from steady-state maps. So far, these investigations have been usually performed with a constant turbine speed. In this paper, a method is presented which includes the speed fluctuations of the TC caused by the exhaust pulsations as well as the change in mean speed during the load step by including compressor and engine in the CFD analysis with User-Fortran models. Results for a load step from 21,000 rpm to 196,400 rpm are discussed.
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