Towards a Paradigm Shift in Centrifugal Compressor Architecture: Assessment of a Multistage Rotor Equipped With Forward and Back-Swept Impellers

A new generation of centrifugal compressors is required to meet the evolving demands of the industrial sector, which is increasingly seeking solutions that combine high performance, elevated pressure ratios, and compact design. The range of applications is broad, spanning from energy transition-related cases, with their specific requirements and constraints, to more conventional ones, including retrofitting and upgrading existing units. In these cases, preserving the original compressor casing, foundation, and loop piping is both cost-effective and environmentally sustainable.

Meeting these needs requires a paradigm shift and the adoption of advanced design methodologies, supported by a holistic and multidisciplinary approach. Traditionally, centrifugal compressor blades are back-swept to enhance efficiency and stability in the left region of the performance curve. In contrast, forward-swept blades are generally avoided due to their associated positively sloped characteristic curve, which can compromise compressor stability (i.e., a reduction in flow would lead to a reduction in pressure ratio). Nevertheless, forward-swept blades can offer significantly higher pressure ratios under equivalent conditions.

This paper presents conceptual studies of an innovative architecture for multistage centrifugal compressors, based on a strategic combination of forward-swept and back-swept impellers. This configuration is conceived and designed to enable a globally stable performance curve while achieving significantly increased pressure ratios. The concept could be applied to reduce the number of stages required for a given pressure ratio, to boost the pressure ratio within a fixed axial length, or conversely, to lower the rotational speed while maintaining the same number of stages and pressure ratio.

The study presents and discusses results from a series of analyses at increasing levels of complexity, culminating in unsteady computational fluid dynamics (CFD) simulations of various multistage compressor arrangements. These simulations aim to identify, understand, and evaluate the effects of this novel configuration not only on flange-to-flange performance but also on compressor dynamic behaviour and unsteady phenomena occurrence (e.g. rotating stall), providing fundamental insights towards its potential introduction into industrial applications.

This breakthrough concept could represent a true game changer in centrifugal compressor design, unlocking new frontiers in performance, efficiency, and adaptability across a wide range of industrial applications.