Flow conditioners for use with air inlets on computer cabinets are disclosed herein. In one embodiment, a large computer system includes a plurality of computer cabinets arranged in close proximity to each other. Each of the computer cabinets can include a fan, impellor, or other air mover positioned proximate to an inlet that receives cooling air from a plenum, such as a floor plenum. In this embodiment, a flow conditioner configured in accordance with the present invention can be positioned proximate to the air inlet. The flow conditioner can include a vortex diffuser and a flow-speed normalizer. The flow-speed normalizer can include a perforated screen that forms a cylinder around the inlet, and the vortex diffuser can include one or more vanes that extend across the cylinder adjacent to the inlet.