A combine harvester (10) comprises fan apparatus (26) for generating an air stream through cleaning apparatus (24) to separate chaff from grain is provided. The fan apparatus comprises a plurality of fan modules (35) for generating mutually spaced air sub-streams. The cleaning apparatus comprises an auxiliary air intake located between two adjacent air sub-streams, and means 52 to narrow the passage for each air sub-stream adjacent the auxiliary air intake 50. The narrowing serves to create a region of lower pressure (L) due to the venturi effect. The low pressure region draws air directly from the environment into the air stream through the auxiliary air intake thereby reducing the transverse component of the sub-streams and providing a more uniform air flow through the cleaning apparatus.
