The VAROC Air Dynamometer from Concepts NREC is used worldwide by both military and commercial organizations for testing  a broad range of gas turbines. (The term  VAROC stands for Variable-geometry Radial Outflow Compressor.)

The new dynamometer can withstand an d operate in any climate, reports Concepts NREC. It is reliable, simple, easy to maintain, compact, and lightweight. Accordingly, it is said to be preferred by defense agencies of many countries. Since iIt uses ambient air for power absorption, there is no need for the water systems required by conventional dynamometer designs.

An air dynamometer eliminates any need for fixed plumbing installations, heat exchangers, cooling towers, and electrical load banks commonly required of other designs. Using air as the working fluid also eliminates environmental pollution caused by oil contamination of the water system.

The VAROC design uses a two-sided impeller to create a balanced double air-entry arrangement. Power absorption is precisely controlled by a moving shroud which exposes a portion of the rotating impeller blades to the flow path.

This variable-length blade system is regulated by a high-speed servo motor. The inertia of the impeller provides stable control and eliminates the need for a separate flywheel. Moving parts are limited to the impeller, bearings, and the shroud-actuating mechanism.

Recently, this Concepts NREC tool has been re-engineered to have a smaller footprint, a better price-point, and testing on angle. The VAROC Air Dynamometer V85 is an updated version of the variable-geometry radial outflow compressor used by the U.S. military for testing turboshaft engines. It offers speeds up to 26,500 rpm and power levels of up to 5,500 hp.