Abstract: A method of extracting cross-sections for performing vortex detection in a flow volume is provided. The method includes the steps of: (i) providing a simulated flow field for a meshed volume, the flow field providing discrete values of a selected flow parameter at respective positions distributed throughout the volume as determined by the meshing of the volume, the selected flow parameter being one of Q-criterion, vorticity magnitude, velocity magnitude and lambda2; (ii) calculating, for each position, a direction of slowest change of the selected flow parameter; (iii) identifying one or more of the positions for 2D cross-section extraction; and (iv) extracting for the, or each, identified position a respective 2D cross-section from the volume, the extracted cross-section containing the respective identified position and being perpendicular to the calculated direction of slowest change at the respective identified position.