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research-article

On the Influence of the Entrance Section on the Rotordynamic Performance of a Pump Seal with Uniform clearance: a Sharp Edge VS. a Round Inlet

[+] Author and Article Information
Jing Yang

Research Associate, Mechanical Engineering Dept. Texas A&M University, College Station, TX 77843, USA
yangjing@tamu.edu

Luis San Andres

Mast-Childs Chair Professor, Fellow ASME, Mechanical Engineering Dept. Texas A&M University, College Station, TX 77843, USA
lsanandres@tamu.edu

1Corresponding author.

ASME doi:10.1115/1.4040742 History: Received June 25, 2018; Revised June 28, 2018

Abstract

Most seal designs regard the inlet as a sharp edge. In actuality, a customary manufacturing process could produce a rounded inlet corner. Furthermore, after a period of operation, a sharp corner may wear out into a round section. To this date, bulk flow model (BFM) analyses rely on an unknown entrance pressure coefficient to deliver predictions for seals. This paper quantifies the influence of an inlet corner on the performance of a water lubricated smooth seal. Computational fluid dynamics (CFD) simulations apply to a seal with either a sharp edge or an inlet section with curvature radius rc varying from ¼Cr to 5Cr. Going from a sharp inlet to one with a small curvature rc = ¼Cr produces a ~20% decrease on the entrance pressure loss coefficient. Further CFD simulations show that rotor speed and pressure drop do not affect the entrance loss coefficient, while the inlet circumferential velocity does. In addition, CFD results for a shorter (half) length seal produce a very similar entrance loss coefficient. For the seal with a rounded edge (rc = 5Cr), both direct stiffness K and direct damping C decrease about 10% compared against the coefficients for the seal with a sharp edge. A BFM incorporates the CFD derived entrance loss coefficients and produces rotordynamic coefficients for the same operating conditions. The CFD and BFM predictions are in good agreement. In the end, the CFD analysis quantifies the entrance loss coefficient as a function of the inlet geometry for ready use in engineering BFM tools.

Copyright (c) 2018 by ASME
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