In this paper a three-dimensional conjugate calculation has been performed for a passenger car turbo charger. The scope of this work is to investigate the heat fluxes in the radial compressor, which can be strongly influenced by the hot turbine. As a result of this, the compressor efficiency may deteriorate. Consequently, the heat fluxes have to be taken into account for the determination of the efficiency. To overcome this problem a complex three-dimensional model has been developed. It contains the compressor, the oil cooled center housing, and the turbine. Twelve operating points have been numerically simulated composed of three different turbine inlet temperatures and four different mass flows. The boundary conditions for the flow and for the outer casing were derived from experimental test data (Bohn et al.). Resulting from these conjugate calculations various one-dimensional calculation specifications have been developed. They describe the heat transfer phenomena inside the compressor with the help of a Nusselt number, which is a function of an artificial Reynolds number and the turbine inlet temperature.
Today an increasing need for gas turbines with extremely low flow rates can be noticed in many industrial sectors, e.g. power generation, aircraft or automotive turbo chargers. For any application it is essential for the turbine to operate at best possible efficiency. It is known that for turbines the specific optimum achievable power output decreases with smaller size. A major contribution for this reduction in efficiency comes from the relative increase of aerodynamic losses in smaller turbine stages. In the early turbine design stage, easy and fast to use two-dimensional calculation codes are widely used. In order to produce qualitatively good results, all of these codes contain a diversity of loss models that more or less exactly describe physical effects which generate losses. It emerges to be a real problem that most of these empirical models were derived for rather large scale turbo machines and that they are not necessarily suitable for application to small turbines. In this paper many of the commonly known and well established loss models used for the preliminary design of radial turbines were collected, reviewed, and validated with respect to their applicability to small-size turbines, i.e. turbines of inlet diameter smaller than 40 mm. Comprehensive numerical investigations were performed and the results were used to check and verify the outcome of loss models. Based on the results, loss models have been improved. Furthermore, new correlations were developed in order to raise the quality of loss prediction especially for the design of small-size turbines. After receiving an optimum set of loss prediction models, all of them were implemented into a two-dimensional solver program for the analytical iterative solution of a complete turbine stage. Hence a powerful tool for preliminary radial turbine design has been created. This program enables the user to analytically evaluate the effects of changing key design properties on performance. These are amongst others the optimum rotor inlet flow angle according to the slip-factor definition, the value of flow deviation, and hence the optimum blade outlet angle for a minimum adverse flow-swirl at turbine outlet. Complementarily the turbine key performance indicators, e.g. pressure ratio, power output, rotational turbine speed, and mass flow can be calculated for optimum efficiency of a given turbine geometry. The paper presents the most important loss models implemented in the new code and weights their relative importance to the performance of small size radial turbines. The data acquisition was done using the new code itself as well as accompanying full 3D CFD calculations.
In this paper a three-dimensional conjugate calculation has been performed for a passenger car turbo charger. The scope of this work is to investigate the heat fluxes in the radial compressor which can be strongly influenced by the hot turbine. As a result of this, the compressor efficiency may deteriorate. Consequently, the heat fluxes have to be taken into account for the determination of the efficiency. To overcome this problem a complex three-dimensional model has been developed. It contains the compressor, the oil cooled center housing, and the turbine. 12 operating points have been numerically simulated composed of three different turbine inlet temperatures and four different mass flows. The boundary conditions for the flow and for the outer casing were derived from experimental test data (part II of the paper). Resulting from these conjugate calculations various one-dimensional calculation specifications have been developed. They describe the heat transfer phenomena inside the compressor with the help of a Nusselt number which is a function of an artificial Reynolds number and the turbine inlet temperature.
To easily find an unoccupied parking space in a large car park is a problem for many drivers. Thus it is useful to have technical solutions which can provide information on parking space occupancy. A new monitor system is described in the following. It is based on passive magnetic field sensors. It provides occupancy information for car park users and helps them to place the car in a most efficient way.
One of the most challenging tasks in designing a turbocharger is to guarantee a sufficient lifetime. Turbine housings are critical parts due to their very complex geometry and consequently complicated temperature and stress distributions. Therefore, high thermal loads as well as thermo-mechanical fatigue have to be considered. Calculating the thermal stress distribution in the turbine housing, steady state and transient, can indicate the regions of crack initiation. From this information selective design improvements can be deduced to increase the component lifetime. But the quality of the stress analysis is strongly dependent on a reliable temperature distribution. Taking into account the interdependency of heat transfer between solid walls and fluid, conjugate heat transfer (CHT) calculations can provide temperature data of high accuracy. Since a transient CHT-calculation is still beyond state of the art, a new approach has been developed. Two steady state CHT-calculations serve to determine heat transfer coefficients at engine brake and full load. Beginning with the engine brake temperature distribution, it is assumed that the gas temperature and the mass flow change immediately. Therefore heat transfer coefficients at full load serve as a boundary condition for a subsequent transient solid body calculation simulating the acceleration process. For the deceleration process the full load temperature field is combined with the engine brake heat transfer coefficients. Monitor points give information about the steepest temperature gradients in the material. At discrete time points a steady state stress analysis has to be performed to detect the regions of highest loads. This subsequent step is essential because in a complex geometry like in a spiral housing with a divider and regionally different wall thicknesses, the stress maxima are not necessarily located at the same places as the temperature peaks. For the two steady state CHT-calculations the turbine wheel has been included in order to consider a realistic flow field. Compared to a transient calculation the degree of abstraction is as low as possible because the assumed frozen rotor boundary condition takes into account centrifugal and coriolis forces. This paper demonstrates the calculation procedure considering a twin-entry turbine housing with an integrated manifold designed for a truck application. The computational results are in excellent agreement with thermal shock test data. A second loop with an improved design proves the success of the method.
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