Session: 40-06 Centrifugal Compressors 4

Paper Number: 83269

83269 - Radial Compressors With Advanced Secondary Flow Paths for Extended Operating Range 

Adequate range is a critical criterion in determining the proper compressor for a given application.  In industries centering on turbochargers, range is often the dominant concern.  Many times, significant sacrifices in performance are made at the design point in order to obtain enough range of the machine for the duty required.  Active controls, the most common being inlet guide vanes (IGVs), can provide sufficient range extension while generating minimal degradation of performance at the design point.  Such devices, however, add significant cost and complexity to the machine as they require an active control mechanism.  Other devices, such as recirculating casing treatment (RCT), have the advantage of both cost and simplicity by virtue of their passive nature.  They’ve seen widespread adoption in the turbocharger industry though they are generally less effective than IGVs in extending range.

A novel approach to extend compressor range through a passive method is proposed here.  The method takes some inspiration from classical RCT applications in that it prompts recirculation at low flow rates and corresponding higher back pressures.  This recirculation then occupies a portion of the primary cross-sectional passage area and confines the rest of the non-recirculating flow to a smaller area.  This restriction forces a higher meridional velocity and a more favorable incidence angle at the impeller blade leading edge.  This recirculation is accomplished by laying out an expanded secondary flow path at the rear of the impeller leading back to the inlet hub region.  Vanes on the rear of the impeller disk provide just enough pressure rise to counter the induced pressure from the primary flow at the design point.  This yields very low mass flow in the secondary path, a condition known as “shutoff” in the pump industry.  At lower primary flow levels, and higher back pressures, the secondary flow is induced back to the impeller inlet setting up the recirculation region and pinching the primary flow.  Various vane configurations and layouts in the secondary region are explained and advantages and disadvantages of each are covered.  The range extensions made possible by this method and the corresponding impact on performance is discussed. 

Presenting Author: Mark Anderson Concepts NREC

Presenting Author Biography: Graduated from Northeastern University ME Class of 1985 with BS in ME . Graduated from MIT in 1987 with Masters in Mech. Engineering<br/>Mark Anderson has a B.S. in Mechanical Engineering from Northeastern University and a M.A. from the Massachusetts Institute of Technology. His experience includes research in the area of hypersonic propulsion for X-30 and NASA’s Atmospheric Effect of Aviation Programs. He was Vice President of Concepts NREC Software Development for 7 years leading a group developing advanced engineering software for turbomachinary design and analysis. Currently, he is Chief Technology Officer at Concepts NREC. He has authored or co-authored over 25 papers on turbomachinery, CFD, and environmental modeling.

Authors:

Mark Anderson Concepts NREC