The wind tunnels branch of the Exterior Ballistics Laboratory (EBL), Ballistic Research Laboratories (BRL), Aberdeen Proving Ground, Maryland operates three supersonic wind tunnels and one hypersonic wind tunnel. The supersonic wind tunnels use flexible plate nozzles and may be operated up to a Mach Number of 5.5, whereas the hypersonic tunnel uses axisymmetric nozzles for operation at Mach Numbers 6, 7.5 and 9.2. Air is furnished to the tunnels by centrifugal compressors operating in a closed loop system. There are two compressor plants. (Author).

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