Recessed Casing Treatment Effects on Fan Performance and Flow Field

Abstract

An experimental investigation to examine the influence of the vaned recess casing treatment on stall margin, operating efficiency and the flow field of a low speed axial flow fan with aerospace type blade loading is presented. Different geometrical designs of the vaned passages were examined. The best configuration resulted in a stall margin improvement of 67%, a significantly higher pressure rise in the stall region and insignificant change in peak efficiency. Detailed 3-D flow measurements in the endwall region and in the casing recess were carried out with a slanted hot-wire, providing some insight to the operation of the device. The results revealed that the stall margin improvement was largely due to the removal of flow from the blade tip to the recess, and the elimination of the growth of the stall region at the tip, which occurs at stall in the solid casing build.

A statistical model for the effect of casing treatment recesses on compressor rotor performance

“…In an untreated compressor, fluid associated with the stalling flow is first centrifuged towards the blade tip then recirculated axially and circumferentially [27]. When the treatment is applied, on the other hand, this tip flow first passes radially into the treatment recess and is then discharged into the primary flow.…”

Development of New Casing Treatment Configuration

“…The measurements indicate a strong radial flow from the rotor tip into the treatment recess. When the treatment is applied, this tip flow passes radially into the treatment recess, and then discharges out into the main flow (16) . And the more the recess volume, with stall margin improvement, the more efficiency penalty because of additional losses.…”

Application of casing treatment to an industrial axial-flow fan

“…4 6.2 kW motor located directly downstream of the impeller. Two rotors were used, both equipped with six blades whose setting angle could be adjusted.…”

“…Kang et al [4] obtained improvements in stall margin, of up to 67 per cent, for a rotor-only compressor.…”