A LES investigation of off-design performance of a centrifugal pump with variable-geometry diffuser

•Influence on flow physics by the orientation of the diffuser blades is studied.•Geometry adjustment providing substantial benefits at off-design working conditions.•Setting angle of the diffuser blades affecting substantially separation phenomena.•Reduced incidence allowing higher pressure recovery and lower levels of turbulence.•Inlet and suction side of the impeller channels marginally affected.