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Response Surface Mapping of Performance for Helical Groove Seals With Incompressible Flow

[+] Author Affiliations
Cori Watson, Houston G. Wood, Brian K. Weaver, Neal Morgan

University of Virginia, Charlottesville, VA

Alexandrina Untaroiu, Hanxiang Jin

Virginia Tech, Blacksburg, VA

Paper No. GT2016-57945, pp. V07BT31A036; 7 pages
doi:10.1115/GT2016-57945
From:
  • ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition
  • Volume 7B: Structures and Dynamics
  • Seoul, South Korea, June 13–17, 2016
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4984-2
  • Copyright © 2016 by ASME

abstract

Helical groove seals are commonly used in multistage pumps. These seals have continuously cut grooves, like a screw, into the surface of the stator. The effects of design parameters on the performance of these seals — both in terms of leakage and rotordynamic coefficients — are not well understood, therefore the goal of this study is to characterize that performance for a wide range of designs. The design variables of interest in this study are groove width, groove depth, groove helix angle, density of the fluid, and the number of continuously cut grooves around the seal. The spacing between the grooves is predetermined by the number of grooves and groove helix angle. The fluid is assumed to have a constant density. The helix angle is 0 degrees for circumferential grooves, between 0 and 90 degrees for grooves pumping towards the inlet, 90 degrees for axial grooves, and between 90 and 180 degrees for grooves pumping towards the outlet. A large number of levels of helix angles were selected to represent the variety of angles possible and the two pumping directions. Helical groove seals with grooves pumping towards the outlet have been shown to produce much higher leakage and decreased stability. For each seal design in the sample space, a bulk flow method was used to calculate the performance. The selection of designs in the sample space was derived using a design of experiments approach. Because of the computational efficiency of the bulk flow code, more than 360 designs were simulated. The response surfaces for leakage, effective damping and effective stiffness — measures of instability often called the instability coefficient — were plotted versus pairs of design parameters to show graphically the effect of changing design parameters on seal performance. Baseline designs for seals pumping towards the inlet and seals pumping towards the outlet were also analyzed in a full 360 degree model with ANSYS CFX. The agreement of the 3D computational fluid dynamics simulation in ANSYS with the bulk flow code verified the accuracy of the bulk flow response surfaces. Finally, a multifactor least-squares linear regression was used to derive a relationship between the design parameters selected and the leakage as well as effective damping and effective stiffness. These equations allow the user to predict the leakage and rotordynamic properties based on values of the design parameters. The results of this study are to be able to predict the leakage and rotordynamic system behavior of future designs and provide insight into the physical mechanisms of helical groove seals.

Copyright © 2016 by ASME

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