High-dimensional multi-fidelity optimisation of a 2.5 stage low pressure compressor

Abstract

The low pressure compressor in modern jet engines has to meet high demands in performance and needs to operate in various conditions. Moreover, the low pressure compressor of an embedded engine has to deal with a distorted inflow, which makes it necessary to take a sufficient surge margin into account during design phase. These requirements become even more challenging, when weight restrictions lead to a narrow installation space. In this paper the multi-disciplinary design optimisation of a highly loaded 2.5 stage low pressure compressor with 264 free parameters under challenging constraints is presented. The automated optimiser AutoOpti, developed at DLR’s Institute of Propulsion Technology, is used to carry out the multi-fidelity optimisation. The aim of the optimisation is the improvement of isentropic efficiency and surge margin with the simultaneous fulfilment of geometric, aerodynamic and mechanical constraints. More than 25 constraints were active at the same time, which leads to great challenges for the optimisation procedure. The final design fulfils all aerodynamic and mechanical constraints. The main part of the optimisation had to be spent on the fulfilment of these constraints, because the initial geometry did not fulfil most of them. The isentropic efficiencies of the optimised final geometry is slightly improved at design speed compared to the initial geometry (about 1%), while at part speed the increase is about 3%. The drawback is that the surge margin could not be conserved with a drop of 2.5 and 2.9 percentage points respectively at the two considered rotational speeds.