Case Study: Compressor Impeller Inverse Design

Can You Draw Your Blade?:

When it comes to turbomachinery, the impeller is like the heart to the body. If the impeller fails it leads to secondary failures of other parts in the machine. Often, one wants to model the impeller for failure analysis. However, it may not be possible to obtain the impeller geometry, the geometry is key to the failure analysis. A powerful option in these scenarios is to recover the impeller geometry through reverse engineering.

Compressor Impeller Reverse Engineering

KHE was requested to analyze an open-faced centrifugal compressor impeller without detailed drawings of the equipment. Details of the impeller geometry is ruled by the performance and sizing of the machine. General sizing such as suction or discharge dimensions can be easily measured in the field. Performance data of the machine further defines the design constraints. Having a well-tested library of empirical relations is essential to cross check the unknown design parameters.

The inverse design procedure usually involves creating the hub and shroud curves as an early step to form the meridional flow path. Next, the blade profiles will be constructed based on the performance data such as the flow rate and pressure ratio. Advanced design of the blades have to meet flow variations from hub to shroud and leading to trailing edge, which often ends up in a complex 3D profile. Effects such as slip or inlet incidence angle should be incorporated into the blade design procedure for accurate prediction of final performance.

Upon competition of the hub and shroud geometry and the blade profiles, all parts are assembled together. Appropriate thickness distribution will be assigned to the blades and the leading and trailing edges are filleted or cut back. The CAD file is ready to input further FEA and CFD analysis to study the local effects. These analyses can be further backed by inverse design of upstream and downstream components such as suction pipe, diffuser and the volute which are more straightforward components compared to the impeller.