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RESEARCH PAPERS

Comparison of Hirs’ Equation With Moody’s Equation for Determining Rotordynamic Coefficients of Annular Pressure Seals

[+] Author and Article Information
C. C. Nelson, D. T. Nguyen

Mechanical Engineering Department, Turbomachinery Laboratories, Texas A&M University, College Station, Texas 77843

J. Tribol 109(1), 144-148 (Jan 01, 1987) (5 pages) doi:10.1115/1.3261306 History: Received April 01, 1986; Online October 29, 2009

Abstract

The rotordynamic coefficients of an incompressible-flow annular pressure seal were determined using a bulk-flow model in conjunction with two different friction factor relationships. The first, Hirs’ equation, assumes the friction factor is a function of Reynolds number only. The second, Moody’s equation, approximates Moody’s diagram and assumes the friction factor is a function of both Reynolds number and relative roughness. For each value of relative roughness, Hirs’ constants were determined so that both equations gave the same magnitude and slope of the friction factor. For smooth seals, both relationships give the same results. For rough seals (e/2H0 = 0.05) Moody’s equation predicts 44 percent greater direct stiffness, 35 percent greater cross-coupled stiffness, 19 percent smaller cross-coupled damping, 59 percent smaller cross-coupled inertia, and nominally the same direct damping and direct inertia.

Copyright © 1987 by ASME
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