A vehicle including an operator cab having a frame defining an opening and a permeable material sheet mounted adjacent the frame to at least partially cover the opening. The permeable material sheet has a plurality of apertures. The operator cab further includes an air nozzle positioned proximal to the opening and positioned so that the air nozzle directs an airflow to contact at least a portion of the permeable material sheet to form a swirling air current proximal to at least one of the plurality of apertures.
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