Design Optimization and Experimental Verification of Centrifugal Compressors With Curvilinear Element Blades

Abstract

This paper describes the optimal design and experimental verification of centrifugal compressors with leaned curvilinear element blades. The design targets were a fully shrouded centrifugal impeller and a low-solidity vaned diffuser. First, a new method of defining the curvilinear element blade was developed for centrifugal turbomachinery using coordinate transformations between a revolutionary flow-surface coordinate system and a cylindrical coordinate system. All the blade sections in the transferred cylindrical coordinate system were moved and stacked spanwise to form a new leaned blade surface. The inverse transformation results in a curvilinear element blade in the original coordinate system. The direction of movement of the blade section could be any of the existing definitions such as sweep, dihedral, or tangential lean. For simplicity, we have defined a “lean profile” as a general expression for the spanwise distribution profile of movement of the blade sections. Model compressors with curvilinear element blades were then designed at a suction flow coefficient of 0.073. Optimal lean profiles for the impeller and vaned diffuser that maximized adiabatic efficiency and uniformity of outflow were explored using a multi-objective genetic algorithm, Kriging surrogate model, and steady Reynolds-averaged Navier Stokes simulations. We chose efficiency-weighted solutions since the efficiency and uniformity had a positive correlation. A sensitivity analysis showed that tangential leans near the endwalls are keys for improving the impeller’s efficiency. The chosen optimal impeller had a concave blade suction surface and a concave leading edge. Although clear patterns in geometrical features for optimal diffuser vanes could not be captured, we found that the dihedral profile had a predominant effect on efficiency. The model compressors was experimentally measured and compared with traditional compressors as to their aerodynamic performance. The experimental apparatus was composed of a suction nozzle, impeller, diffuser, and return channel. The results demonstrated that the models’ adiabatic efficiency was higher by 1.2–1.4% at the design point. Although the stall margins slightly decreased (by 0.7%) in the experiments, the surge margins expanded (by 3.7–6.7%).