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The aerodynamic optimization of an AUDI Q5 vehicle is presented using the continuous adjoint approach within the OpenFOAM framework. All calculations are performed on an unstructured automatically generated mesh. The primal flow, which serves as input for the adjoint method, is calculated using the standard CFD process at AUDI. It is based on DES calculations using a Spalart-Allmaras turbulence model. The transient results of the primal solution are time averaged and fed to a stationary adjoint solver using a frozen turbulence assumption. From the adjoint model, drag sensitivity maps are computed and measures for drag reduction are derived. The predicted measures are compared to CFD simulations and to wind tunnel experiments at 1:4 model scale. In this context, general challenges, such as convergence and accuracy of the adjoint method are discussed and best practice guidelines are demonstrated.

An investigation on reducing the set of modeling parameters for engine cycle simulation is presented. The investigation considers a detailed kinetic model for combustion and emissions predictions coupled to a complete cycle simulation tool applied to a modern Diesel engine. The analysis is based on a previously developed method that combines a 1-D gas dynamics model with a stochastic reactor model for direct injection engines (SRM-DI). Initially, the global and instantaneous performance parameters of a Diesel engine were simulated at different operating conditions. The model was validated and the simulated results were compared to experimental data to assess the quality of the model. Afterwards, the influence of the chosen modeling parameters on engine performance, such as in-cylinder pressure, emissions and global performances, were analyzed. The mixing time proved to be the most important modeling parameter for the stochastic reactor model.

In one-dimensional engine simulation programs the simulation of engine performance is mostly done by parameter fitting in order to match simulations with experimental data. The extensive fitting procedure is especially needed for emissions formation - CO, HC, NO, soot - simulations. An alternative to this approach is, to calculate the emissions based on detailed kinetic models. This however demands that the in-cylinder combustion-flow interaction can be modeled accurately, and that the CPU time needed for the model is still acceptable. PDF based stochastic reactor models offer one possible solution. They usually introduce only one (time dependent) parameter - the mixing time - to model the influence of flow on the chemistry. They offer the prediction of the heat release, together with all emission formation, if the optimum mixing time is given.

The CFD simulation of the turbulent flow induced by the intake port of a modern direct injection gasoline engine requires the application of advanced turbulence models taking into account the unsteady nature of the flow. The validation of such models necessitates the availability of high quality experimental data. The present paper describes a comparative analysis between Detached Eddy Simulation, a “standard” hybrid Large Eddy Simulation approach, and an innovative concept called Scale Adaptive Simulation. The flow field generated by the cylinder-head of a production four-valve gasoline engine in a configuration with fixed valve positions has been simulated. The same configuration has been investigated experimentally using a stereoscopic High-Speed Particle Image Velocimetry system. The main focus of the work has been put on the very high time-resolution of the measured data, as well as on the strong refinement of the numerical mesh employed.

A new optical-access steady-state test rig has been developed for the measurement of port generated swirl flow. A novel application of Particle Image Velocimetry allows non-intrusive / non-invasive flow visualization and full optical access of stationary in-cylinder flow. In the past, steady-state test rigs have provided Swirl numbers for the characterization of the flow. These traditional methods, however, do not provide any flow structure information. The new Swirl Optical Rig (SOR) provides instationary characterization of swirling motion including instantaneous and averaged flow images. A 2-valve swirl-port gasoline engine cylinder head was investigated to show the advantages of the new test rig. 3-D CFD simulations were also performed to better understand and validate the experimental results. Good correlation was obtained between the measured and simulated results for the case of well-established flow structures.

A 3-dimensional numerical study has been conducted investigating the combustion process in a VW 1.9l TDI Diesel engine. Simulations were performed modeling the spray injection of a 5-hole Diesel injector in a pressure chamber. A graphical methodology was utilized to match the spray resulting from the widely used Discrete Droplet Spray model to pressure chamber spray images. Satisfactory agreement has been obtained regarding the simulated and experimental spray penetration and cone angles. Thereafter, the combustion process in the engine was simulated. Using engine measurements to initialize the combustion chamber conditions, the compression stroke, the spray injection and the combustion simulation was performed. The novel RTZF two-zone flamelet combustion model was used for the combustion simulation and was tested for partial load operating conditions. An objective analysis of the model is presented including the results of a numerical parameter study.