An Experimental and Numerical Investigation on the Impact of Tip Gap on the Performance of Vaned Diffuser for Industrial Centrifugal Compressors

Ideally, vaned diffusers should not present any gap between the blade tip and the casing. However, manufacturability issues and assembly tolerances may create a clearance. This affects aerodynamic performance, although industrial experience and recent literature show that a small gap on blades’ tip can even be beneficial for performance and stability of the diffuser. To verify this hypothesis, this study presents the results of an experimental campaign carried out using the innovative test rig of the University of Florence. A smart way of setting and verifying the tip gap is first presented. An industrial model stage is then tested under various operating conditions, assessing gap effect. Moreover, an in-depth CFD study of the flow field at the blade tip region was made to understand local phenomena. The study proves that a null gap is not strictly mandatory in industrial installations, thus paving the way for new design and verification strategies.