Numerical Investigation of Tip Clearance Effect on the Stage of a Tandem-Bladed Centrifugal Compressor for Turbocharger Application

摘要

To understand the effect of tip clearance on a tandem-bladed centrifugal impeller and diffuser, extensive 3D viscous, steady state, turbulent flow simulations have been conducted for the complete stage of a conventional and tandem-bladed centrifugal compressor, which was aimed for turbocharger application. The impeller and diffuser were connected through rotor stator boundary using frozen rotor approach. Conventional compressor was first modeled and simulated. Reasonably close agreement has been found between CFD and the experimental results. Conventional impeller was modified to tandem-bladed design and then thoroughly investigated. Overall performance and the flow configuration have been investigated for nine tip clearance levels from no gap to 1mm. It has been observed that at the mass flow rate of 0.4 kg/s, a loss of about 15 percent in the stage pressure ratio is observed as the tip clearance is increased from zero to 1mm whereas the peak efficiency has also been reduced by 12 percent. The impeller efficiency is found maximum at tip clearance of 0 mm however minimum diffuser effectiveness is observed at 0.4 mm clearance level. The mass average properties, entropy distributions, blade loading diagrams and relative velocity fields are presented showing the loss production within the impeller passage with tip clearance.