Research Papers: Gas Turbines: Turbomachinery

Accurate Radial Vaneless Diffuser One-Dimensional Model

[+] Author and Article Information
Fabio De Bellis

GE Oil & Gas,
Via F. Matteucci 2,
Florence 50127, Italy
e-mail: fabio.debellis@ge.com

Angelo Grimaldi

GE Oil & Gas,
Via F. Matteucci 2,
Florence 50127, Italy
e-mail: angelo.grimaldi@ge.com

Dante Tommaso Rubino

GE Oil & Gas,
Via F. Matteucci 2,
Florence 50127, Italy
e-mail: dantetommaso.rubino@ge.com

Riccardo Amirante

Department of Mechanic Mathematic
and Management,
Polytechnic University of Bari,
Via G. Re David,
Bari 70125, Italy
e-mail: amirante@poliba.it

Elia Distaso

Department of Mechanic Mathematic
and Management,
Polytechnic University of Bari,
Via G. Re David,
Bari 70125, Italy
e-mail: elia.distaso@gmail.com

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 4, 2014; final manuscript received December 18, 2014; published online February 3, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(8), 082603 (Aug 01, 2015) (7 pages) Paper No: GTP-14-1609; doi: 10.1115/1.4029482 History: Received November 04, 2014; Revised December 18, 2014; Online February 03, 2015

A simplified one-dimensional model for the performance estimation of vaneless radial diffusers is presented. The starting point of such a model is that angular momentum losses occurring in vaneless diffusers are usually neglected in the most common turbomachinery textbooks: It is assumed that the angular momentum is conserved inside a vaneless diffuser, although a nonisentropic pressure transformation is considered at the same time. This means that fluid-dynamic losses are taken into account only for what concerns pressure recovery, whereas the evaluation of the outlet tangential velocity incoherently follows an ideal behavior. Several attempts were presented in the past in order to consider the loss of angular momentum, mainly solving a full set of differential equations based on the various developments of the initial work by Stanitz (1952, “One-Dimensional Compressible Flow in Vaneless Diffusers of Radial or Mixed-Flow Centrifugal Compressors, Including Effects of Friction, Heat Transfer and Area Change,” Report No. NACA TN 2610). However, such formulations are significantly more complex and are based on two empirical or calibration coefficients (skin friction coefficient and dissipation or turbulent mixing loss coefficient) which need to be properly assessed. In the present paper, a 1D model for diffuser losses computation is derived considering a single loss coefficient, and without the need of solving a set of differential equations. The model has been validated against massive industrial experimental campaigns, in which several diffuser geometries and operating conditions have been considered. The obtained results confirm the reliability of the proposed approach, able to predict the diffuser performance with negligible drop of accuracy in comparison with more sophisticated techniques. Both preliminary industrial designs and experimental evaluations of the diffusers may benefit from the proposed model.

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Fig. 1

Test rig schematic drawing

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Fig. 2

Geometric characterization of the eight test campaigns

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Fig. 3

Mach ranges of the eight test campaigns

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Fig. 4

Reynolds number ranges of the eight test campaigns

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Fig. 5

Computations comparison with experiments for each test campaign: 2D H1, 2D H2, 3D E1, 3D E2, 3D E3, 3D H1, 3D H2, and 3D H3

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Fig. 6

Statistical distribution for cu4 (top) and α4 (bottom) of deviations from experimental data: angle error distributions are consistent with tangential velocity ones

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Fig. 7

Error on density introduced considering constant density in the diffuser, as a function of Mach number



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