Geometry scaling technique and application to aerodynamic redesign of multi-stage transonic axial-flow compressors

Abstract

Geometry scaling technique, as one of the essential steps in aerodynamic redesign of multi-stage compressor, directly determines whether the new scaled geometry meets the required performance or not. It is also one of the effective measures in unsteady flow simulation of multi-stage compressor to reduce greatly the computational cost by scaling the computational domain from full-annulus passages to partial-annulus passages. The common critical issue arisen from both practices is the geometry dissimilarity in which some certain difference exists between the original and scaled geometries due to a diversity of redesign requirements or model simplifications. However, the extent of how the geometry dissimilarity influences the aerodynamic performance of multi-stage transonic compressor is unclear up to now. Particularly, how to keep the aerodynamic performance similarity in the case of geometry dissimilarity has not been explored yet. Here we propose a geometry scaling technique in which 3D parametric geometry modeling and 1D mean-line analysis are combined to define a series of key redesign criteria in order to keep as minor as possible variations in the aerodynamic performance of multi-stage compressor. The proposed technique is applied to redesign a 3.5 stage transonic axial-flow compressor with two geometry scaling strategies, i.e., adjustable blade/vane numbers and inlet guide vane (IGV)-rotor-stator axial spacing. The key aerodynamic parameters determined by the key redesign criteria are then quantified to verify the feasibility and accuracy of the proposed technique by computational fluid dynamics (CFD) simulations. The results show that by keeping the similarity of key redesign criteria, that is, blade solidity, stagger angle, inlet blade angle, outlet blade angle and thickness to chord distribution, the similarity of key aerodynamic parameters (incidence angle, deviation angle, loss coefficient and aerodynamic blockage) and thus of overall aerodynamic performance (mass flow rate, pressure ratio and efficiency) can be generally guaranteed. The variations of aerodynamic performance in the case of geometry dissimilarity with different blade/vane numbers and IGV-rotor-stator axial spacing are generally within 1%. Compared against the similarity of the other key aerodynamic parameters, a certain dissimilarity of aerodynamic blockage is observed, impacting slightly on the mass flow rate and thus stall margin. The present work is of effective assistance to improve the redesign methodology for multi-stage axial-flow compressors.