It should be noted that region B may be expanded and combined as a secondary vortex in fans with specific types of rear wall entrance cavities (the rear wall feature in Fig. 15 lacks the appropriate geometry to set up a secondary vortex at the conditions analyzed). Region B may interact further at low flow coefficients as an entrance secondary vortex (or recirculation zone) with behavior strongly dependent upon casing design [8], [35] and [40].
As noted earlier, the overall flow pattern of the cross-flow fan is sustained by the circumferentially non-uniform loading in the impeller. The unsteady blade loading and casing wall interaction produce the eccentric vortex which is an unavoidable region of high loss and energy dissipation. Here, we assume that the flow power associated with the vortex is proportional to the product of the cascade work in region A, the vortex kinetic energy, and the vortex volume flow scale as follows: