The Influence of Design Parameters on the Compressor Smith Chart

The Smith Chart provides a mental framework through which compressor designers can understand the relationship between stage efficiency, flow coefficient and stage loading. Convention holds that maximum efficiency occurs at a loading of around 0.45 and a flow coefficient of around 0.6, irrespective of other design parameters. This paper challenges that convention. The effects of multiple design parameters on the shape of the Smith Chart are investigated: the way in which solidity is set, aero-mechanical parameters such as aspect ratio and blade thickness, and three-dimensional parameters such as lean and sweep. By varying these parameters in ways that occur in real engines, the maximum efficiency point can be shifted: the optimal loading can rise to 0.5, or the optimal flow coefficient can fall to 0.48. Of all parameters investigated, the method by which solidity is set has the largest impact. More importantly, a physical understanding of what governs the shape of the Smith Chart is established. This is shown to enable the design of efficient compressor stages with loadings as high as 0.65, around 50% higher than conventional designs, while maintaining the operating range and efficiency. This result is supported by experimental validation. Such an increase in stage loading could allow compressors to be designed with 30–40% fewer stages, offering significant benefits for applications where weight reduction, cost, and reliability are critical.