A study for trade-offs of a centrifugal compressor by comparing parameters of 1D model and results of a 3D CFD simulations

Abstract

In modern centrifugal compressor design, engineers must compare trade-offs to meet increasingly demanding design needs. The centrifugal compressor must operate for long periods under high load, have low manufacturing costs, a high flow coefficient, be compact, aerodynamically efficient, structurally feasible, and so on. Understanding trade-offs in the design process can be useful. These trade-offs interest the turbocharging team at Wärtsilä because they could be beneficial in many ways. This thesis studies trade-offs related to the aerodynamical design side.

In this thesis four new compressors are designed from scratch using AxSTREAM software, and aerodynamical and structural analyses are performed. Three trade-offs are studied with these compressors. The first trade-off is related to increased losses due to a higher inlet relative Mach number, which is affected by the inlet blade metal angle. The second trade-off is related to how a higher pressure ratio affects the flow coefficient and inlet relative Mach number. A third trade-off is related to increased losses of too-high inlet relative Mach number, with too-high flow coefficient and tip-speed Mach number.

The 1D parameters were compared between each other and 3D CFD results to identify possible trade-offs. Only one trade-off, involving the relation between the higher pressure ratio, inlet relative Mach number, and flow coefficient was confirmed. Due to the limited amount of design rounds, other trade-offs could not be confirmed.