Design and experimental investigations of a new type of casing treatment for an axial flow compressor

Abstract

A new type of bend skewed groove casing treatment was designed on the basis of the test results of the axial skewed groove casing treatment. The influences of utilizing it on an isolated axial-flow rotor, as well as comparisons between it and the axial skewed groove, have been investigated experimentally. The effects on overall performance of the axial chord of the rotor exposed to the treated area have been examined, and the ideal axial position of the casing treatment relative to the rotor leading edge was found. For the tested rotor with the new casing treatment, experimental results showed that significant improvements in stall margin were observed without efficiency penalty (in some axial locations) at two different speeds. Compared with the axial skewed groove casing treatment, the new treated casing at the axial exposure does not increase the secondary circulation in the radial—circumferential plane based on x-wire, hot-wire measurements under the operating conditions near peak efficiency. This can be considered to be one of many factors that keep the rotor efficiency identical.

Eliminating the head instability of an axial-flow pump using axial grooves

“…These grooves are located in the casing wall over the rotor blades and are reported to have two main impacts: (a) removal of fluid from the pressure side of the blade and re-injection of this fluid in front of the rotor, thereby energizing the fluid in the casing boundary layer and (b) reduction of blade tip load due to positive swirl introduced by the skewed grooves. 3,4 Furthermore, the axial position of the grooves relative to the rotor inlet was found to have a major impact on the peak efficiency. 4 The configuration with the smallest overlap of axial grooves and rotor blades showed the best efficiency curves.…”

“…Several investigations suggest that the more effective a type of treatment is in improving the stall margin the larger the adverse effect on the efficiency becomes. [1][2][3] Due to this negative implication of casing treatment, the so-called active control has been chosen in many cases as a possible alternative for delaying stall inception. However, with respect to energy input and costs, the comparably simple method of casing treatment still seems to be an attractive concept.…”