Blocking effect of the orbiting scroll tip on the suction flow of a scroll expander, closely associated with the location of the suction port, has a vital role on the transient performances of the expander. In this study, CFD based 3D numerical simulations were performed on scroll expanders with different suction port locations to estimate transient features of the aerodynamic parameters including pulsating mass flow rate through the suction port, asymmetric distributions of the internal flow, gas forces and moments exerted on the orbiting scroll. The results illustrate the pulsating features of the suction mass flow rate, in response to both variations of the suction flow area and the suction chamber volume, change obviously for expanders with different suction port locations. A special aerodynamic separation of the suction chamber induces a sudden drop of the suction mass flow rate before the top profile meshing. Apart from the mass flow rate, both the fluctuating intensities and the magnitudes of the gas forces and moments change with different suction port locations as well. A proposed local analysis approach on the driving moment indicates the fluctuations of the driving moment in different time periods are induced by different factors, and transient moment features of all scroll segments are closely associated with the asymmetric pressure distribution which is an integrated result of the suction/discharging flows and the eccentric rotation of the orbiting scroll. (C) 2015 Elsevier Ltd. All rights reserved.