15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Authors
Abstract
Vaned diffusers coupled with centrifugal impellers are a well-established technology to enhance the pressure recovery and improve the overall stage efficiency. Ideally, fixed diffuser blades should not present any gap between the tip of the blade and the casing. However, due to manufacturability issued and assembly tolerances, it is known that the diffuser may have a clearance. This readily impacts the aerodynamic performance of the same, even though industrial experience and recent literature show that a precise, small gap on blades’ tip can even be beneficial for performance and stability of the diffuser. This study presents the results of a wide experimental campaign carried out using the innovative test rig of the University of Florence. A smart way of setting and verifying the gap on diffuser’s blades is first developed. An industrial mode stage provided by Baker Hughes is tested under various operating conditions, providing an experimental assessment of gap effect, and identifying the optimal value of the same. In addition to this, by using a calibrated digital-twin model of the test rig, an in-depth CFD study of the flow fields established at the blade tip gap was made to understand the occurred local phenomena. The study proves that a theoretical null gap is not strictly mandatory in real-life installations, thus paving the way for future design and verification strategies for industrial manufactures.
ETC2023-328