Evaluation and Training Institute

Les onze territoires habités sur les trois océans qui constituent les outre-mers français, se caractérisent par une exposition à des aléas dont les effets peuvent être particulièrement dévastateurs. Les plus grandes catastrophes enregistrées à l’échelle nationale en termes de coût humain ou économique ont souvent eu pour cadre l’un de ces territoires. Les éruptions volcaniques, les séismes, les cyclones, les inondations ou les glissements de terrain ont été à l’origine d’événements catastrophiques qui ont causé, depuis le début du XXe siècle, la disparition de plusieurs dizaines de milliers de personnes et profondément modifié les trajectoires économiques et démographiques de nombreuses entités ultramarines.

This paper reports a traverse survey of the flow conditions at the exhaust pipe of two mixed-flow turbines. The experimental method is described and the results discussed. It shows that for both turbines, a shroud-hub flow migration might be generated within the blades at higher pressure ratios, which relieves the high blade loading at the shroud, and a flow separation from the suction side of the hub might occur at the lower pressure ratios. The turbine with ‘constant incidence angle’ rotor design suffered from greater swirl loss and a possible internal flow separation than the one with a constant blade inlet angle.

The performance of a high pressure ratio (P.R.=2.9) mixed flow turbine for an automotive turbocharger has been investigated and the results revealed its better performance relative to a radial-inflow geometry under both steady and pulsating flow conditions. The advantages offered by the constant blade angle rotor allow better turbocharger-engine matching and maximization of the energy extracted from the pulsating engine exhaust gases. In particular, the mixed inlet blade geometry resulted in high efficiency at high expansion ratios where the engine-exhaust pulse energy is maximum. The efficiency characteristics of the mixed flow turbine under steady conditions were found to be fairly uniform when plotted against the velocity ratio, with a peak efficiency at the design speed of 0.75. The unsteady performance as indicated by the mass-averaged total-to-static efficiency and the swallowing capacity exhibited a departure from the quasi-steady assumption which is analysed and discussed.