Bruno Demory

Space Infill Study of Kriging Meta-Model for Multi-Objective Optimization of an Engine Cooling Fan

The meta-model based optimization is widely used in the aerodynamical design process for rotating machines, and the main industrial cost of such techniques comes from physical evaluations of answers, either by experimental or numerical means. Design of experiment (DoE) with Latin Hypercube sampling has been studied for the design of an automotive fan system for engine cooling. Surrogate models constructed with Kriging and Co-Kriging methods are estimated with the help of a reference numerical model. The objective of the present work is to assess the necessary number of sampling points for the initial DoE for this kind of meta-model method and to study the influence brought by the sample dispersion. The objective being to execute future aerodynamic optimizations at a reduced cost in term of timeframe and CPU effort. Two parameters, camber and chord length were used to investigate geometrical changes and they are completed with a physical parameter which is the flow rate. The optimization should lead to a higher level of performances with given constraints of rotational speed, torque and packaging. A criterion was defined for the initial necessary number of evaluations and the variances for different DoE design were controlled for the sake of comparison. Starting from an initial meta-model, a variance based method was used for further training with additional points. Uncertainties due to lack of information outside the domain led the model to regularly propose new points on the borders, yielding to high sample variance. A genetic-algorithm was employed to explore the final meta-model and to conduct a multi-objective optimization. Results are presented in terms of Pareto Front and are analysed with SOM to understand the relations between factors and objectives. A final optimal design was selected, and proposed to demonstrate the relevancy of the method.Copyright

Test Rig Effect on Performance Measurement for Low Loaded Large Diameter Fan for Automotive Application

Large diameter fans with low solidity are widely used in automotive application for engine cooling. Their designs with small chord length help reducing the torque on the electrical motor and provide a good aerodynamic compromise between several operating conditions, some of these being at high flow rate. Their global performances are measured according to the ISO standard DP 5801, which allows comparison of results from different facilities. However, some variations in global performances are observed when considering results from two different test rigs. On a fan selected for the purpose of this study, up to 6 % of efficiency is lost on the worst case.As efficiency is more than ever a key factor to select a component, some experimental and numerical investigations were conducted to analyze the fan behavior on each facility. Two sets of measurement and simulation are performed and compared. Geometries considered for the domain of computation include the test rig plenum, the torquemeter, the ground and a large domain for the atmospheric conditions. The exact fan geometry with tip clearance and under-hub ribs is also considered. Numerical results show in both cases a good agreement with experiment when convergence is reached and for low flow rate when computations are switched to unsteady mode. Comparisons show that simulations are able to capture the different fan behaviors depending on the configuration and those efficiency losses previously observed are correctly predicted.These results are further analyzed to perform some post-processing. Blade loading remains identical for both cases but disparities appear in the wake and its interaction with the surrounding. Tiny details that are often neglected during experiment and/or simulation appear to be the cause of slight variations. Position of the torquemeter and shape of the plenum are among the parameters that varies and that have cumulative effects. Efficiency being a ration of pressure and torque, variations are rather important.Finally, these results are discussed in terms of rules for conception and a new geometry less sensible to loss of efficiency is proposed.© 2014 ASME