Turbomachines such as air dynamometers are disclosed that include a radial outflow compressor and gas collector. In some examples, the gas collector is designed as a separate component that is coupled to the machine, such as coupled to a frame. In some examples, the collector and frame are intentionally spaced and coupled at discrete points to minimize the transfer of mechanical and thermal energy therebetween. Aspects of the present disclosure also include turbomachines that include at least one impeller bypass flow path for the direct transfer of air between ambient and a location in the collector downstream of the impeller blades. In some examples, such flowpath(s) may allow for the inflow of external ambient air into the collector.