At our laboratory extensive research has been conducted on the conversion of conventional Diesel cogeneration engines to operation on natural gas and biogas. In the framework of this research, a numerical simulation of a prechamber autoignition gas engine has been performed based on an experimental test case. With a simplified finiterate/eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with the simulation model. The influence of burnt gases inside the prechamber was assessed simulating the mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the combustion duration. The new cylindrical geometry envisaged did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is in fact not sufficient to properly ignite the main chamber according to the simulations. The model can be used to further guide design modifications of the prechamber engine to improve performance.
Purpose The paper deals with research activities to develop optimization workflows implying computational fluid dynamics (CFD) modelling. The purpose of this paper is to present an industrial and fully-automated optimal design tool, able to handle objectives, constraints, multi-parameters and multi-points optimization on a given CATIA CAD. The work is realized on Rapid And CostEffective Rotorcraft compound rotorcraft in the framework of the Fast RotorCraft Innovative Aircraft Demonstrator Platform (IADP) within the Clean Sky 2 programme. Design/methodology/approach The proposed solution relies on an automated CAD-CFD workflow called through the optimization process based on surrogate-based optimization (SBO) techniques. The SBO workflow has been specifically developed. Findings The methodology is validated on a simple configuration (bended pipe with two parameters). Then, the process is applied on a full compound rotorcraft to minimize the flow distortion at the engine entry. The design of the experiment and the optimization loop act on seven design parameters of the air inlet and for each individual the evaluation is performed on two operation points, namely, cruise flight and hover case. Finally, the best design is analyzed and aerodynamic performances are compared with the initial design. Originality/value The adding value of the developed process is to deal with geometric integration conflicts addressed through a specific CAD module and the implementation of a penalty function method to manage the unsuccessful evaluation of any individual.
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