In aeronautics, onboard axial fans, only used on the ground to cool heat exchangers, can be regarded as potential electrical generation devices when operating at freewindmill in flight. In this case, the appropriate windmilling configuration is the load-controlled one, from which energy recovery is possible. This paper presents a detailed experimental analysis, on a conventional axial compressor, of the continuous local topology evolution on both rotor and stator rows from compressor mode to highly loaded windmill. The objective is to deepen the understanding of windmilling flows and validate experimentally numerical results obtained on a previous paper from the present authors. In this latter, the innovative concept of a dualmachine, meant to reach good performances in both compressor and turbinemodes, was presented and numerically validated. The present paper experimentally confirms the relevance of the new design
