Abstract: This invention concerns a flow seal (42) for location between opposing components of a fluid flow machine, such as rotor (44) and stator (46) components of a turbomachine (10). The seal (42) has an upstream fin (24) depending from one of components (44) towards an opposing surface (28) of the other (46) of the components and a wall (26) downstream of the fin (24) defining a flow cavity between the fin (24) and wall (26). The fin (24) terminates at a fin tip (24A) so as to define a gap between the fin tip (24A) and the opposing surface (28), through which a leakage flow enters the flow cavity in use. The seal (42) also has a flow guide member (30A) located in the cavity, the flow guide member (30A) being arranged to define a flow path that promotes a vortical flow regime in the cavity. The flow cavity geometry is altered to promote a desired vortical flow regime, such as by way of a projection (39) in an intermediate wall portion of the flow cavity. The vortical flow regime may hinder flow leakage.