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research-article

EFFECT OF FREE-STREAM VELOCITY DEFINITION ON BOUNDARY LAYER THICKNESS AND LOSSES IN CENTRIFUGAL COMPRESSORS

[+] Author and Article Information
Jonna Tiainen

Laboratory of Fluid Dynamics, LUT School of Energy Systems, Lappeenranta University of Technology, 53851 Lappeenranta, Finland
jonna.tiainen@lut.fi

Ahti Jaatinen-Värri

Laboratory of Fluid Dynamics, LUT School of Energy Systems, Lappeenranta University of Technology, 53851 Lappeenranta, Finland
ahti.jaatinen-varri@lut.fi

Aki Grönman

Laboratory of Fluid Dynamics, LUT School of Energy Systems, Lappeenranta University of Technology, 53851 Lappeenranta, Finland
aki.gronman@lut.fi

Teemu Turunen-Saaresti

Laboratory of Fluid Dynamics, LUT School of Energy Systems, Lappeenranta University of Technology, 53851 Lappeenranta, Finland
teemu.turunen-saaresti@lut.fi

Jari Backman

Laboratory of Fluid Dynamics, LUT School of Energy Systems, Lappeenranta University of Technology, 53851 Lappeenranta, Finland
jari.backman@lut.fi

1Corresponding author.

ASME doi:10.1115/1.4038872 History: Received October 21, 2017; Revised November 07, 2017

Abstract

The estimation of boundary layer losses requires the accurate specification of the free-stream velocity, which is not straightforward in centrifugal compressor blade passages. This challenge stems from the jet-wake flow structure, where the free-stream velocity between the blades cannot be clearly specified. In addition, the relative velocity decreases due to adverse pressure gradient. Therefore, the common assumption of a single free-stream velocity over the blade surface might not be valid in centrifugal compressors.

Generally in turbomachinery, the losses in the blade cascade boundary layers are estimated e.g. with different loss coefficients, but they often rely on the assumption of a uniform flow field between the blades. To give guidelines for the estimation of the mentioned losses in highly distorted centrifugal compressor flow fields, this paper discusses the difficulties in the calculation of the boundary layer thickness in the compressor blade passages, compares different free-stream velocity definitions, and demonstrates their effect on estimated boundary layer losses. Additionally, a hybrid method is proposed to overcome the challenges of defining a boundary layer in centrifugal compressors.

Copyright (c) 2017 by ASME
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