The presence of tip clearance between rotating blades and casing produces unfavorable influences upon compressor stage performances. Application of abradable linings (inserts) in the casing above rotating blades reduces this tip clearance to practically zero. And the variant is spread enough when rotor blade tips make an entire annular recess (EAR) of approximately rectangular configuration (RC) in the meridional section of casing (of lining).
Some researches proved that the presence of entire annular recess in abradable lining may compensate somewhat the influence of tip clearance between blade tips and casing baseline. Therefore it is possible to substitute abradable linings for entire annular recess of rectangular configuration specially manufactured in the casing.
Special aerodynamic investigations and generalization of their results have permitted to develop the procedure of estimation of entire annular recess of rectangular configuration influence upon compressor stage efficiency. These investigations were fulfilled for six test stages with the relative tip clearance in the range from 0 to 1.6%. The pattern above rotor blades in the presence of entire annular recess of rectangular configuration was featured by three radial and three axial relative geometric parameters.
The analysis of effects of these geometric parameters allowed determining of the primary geometric parameter as to influence of entire annular recess of rectangular configuration upon efficiency change. The relative effective tip clearance (?) is considered as such one. The criterion of comparison and selection was root-square mean (RSM) error for approximating relationships.
For taking into account the influence of all six parameters jointly the Group Method of Data Handling (GMDH) was used. The generalizing geometric parameter (P
1
) was obtained as a result. However the kinematic peculiarities of stages must influence upon efficiency besides the entire annular recess geometric parameters. Lieblein rotor D
t
-factor for blade tip was chosen as effecting kinematic parameter.
Application of the Group Method of Data Handling for seven arguments (six geometric and one kinematic ones) simultaneously was especially effective one. The generalizing complex parameter (P
2
) was obtained as a concluding result.
The fulfilled generalization allows to explain previously obtained results of entire annular recess of rectangular configuration use and to outline the spheres of their effective applying.
In the special test study it was succeeded to increase test compressor rotor efficiency with the help of entire annular recess of rectangular configuration and proposed procedure by 1.8%.
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