scholarly journals An Accurate and Computationally Efficient Explicit Friction Factor Model

2016 ◽  
Vol 06 (03) ◽  
pp. 237-245 ◽  
Author(s):  
Uchechukwu Herbert Offor ◽  
Sunday Boladale Alabi
Keyword(s):  
Friction Factor ◽  
Factor Model ◽  
Computationally Efficient

A Comparison of Rotordynamic-Coefficient Predictions for Annular Honeycomb Gas Seals Using Three Different Friction-Factor Models

2002 ◽  
Vol 124 (3) ◽  
pp. 524-529 ◽  
Author(s):  
Rohan J. D’Souza ◽  
Dara W. Childs
Keyword(s):  
Friction Factor ◽  
Flow Model ◽  
Factor Model ◽  
Control Volume ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Steam Turbines ◽  
Frequency Range ◽  
Rotordynamic Coefficients ◽  
Rotordynamic Coefficient

A two-control-volume bulk-flow model is used to predict rotordynamic coefficients for an annular, honeycomb-stator/smooth-rotor gas seal. The bulk-flow model uses Hirs’ turbulent-lubrication model, which requires a friction factor model to define the shear stresses at the rotor and stator wall. Rotordynamic coefficients predictions are compared for the following three variations of the Blasius pipe-friction model: (i) a basic model where the Reynolds number is a linear function of the local clearance, fs=ns Rems (ii) a model where the coefficient is a function of the local clearance, and (iii) a model where both the coefficient and exponent are functions of the local clearance. The latter models are based on data that shows the friction factor increasing with increasing clearances. Rotordynamic-coefficient predictions shows that the friction-factor-model choice is important in predicting the effective-damping coefficients at a lower frequency range (60∼70 Hz) where industrial centrifugal compressors and steam turbines tend to become unstable. At a higher frequency range, irrespective of the friction-factor model, the rotordynamic-coefficient predictions tend to coincide. Blasius-based Models which directly account for the observed increase in stator friction factors with increasing clearance predict significantly lower values for the destabilizing cross-coupled stiffness coefficients.

An Entrance Region Friction Factor Model Applied to Annular Seal Analysis: Theory Versus Experiment for Smooth and Honeycomb Seals

1989 ◽  
Vol 111 (2) ◽  
pp. 337-343 ◽  
Author(s):  
D. Elrod ◽  
C. Nelson ◽  
D. Childs
Keyword(s):  
Friction Factor ◽  
Factor Model ◽  
Experimental Results ◽  
Entrance Region ◽  
Analysis Theory ◽  
Annular Seal ◽  
Theory Versus ◽  
Direct Stiffness ◽  
Honeycomb Seals

A friction factor model is developed for the entrance-region of a duct. The model is used in an annular gas seal analysis similar to Nelson’s (1984). Predictions of the analysis are compared to experimental results for a smooth-stator/smooth-rotor seal and three honeycomb-stator/smooth-rotor seals. The model predicts leakage and direct damping well. The model overpredicts the dependence of cross-coupled stiffness on fluid prerotation. The model predicts direct stiffness poorly.

scholarly journals Friction-Factor Data for Flat-Plate Tests of Smooth and Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 722-729 ◽  
Author(s):  
T. W. Ha ◽  
Dara W. Childs
Keyword(s):  
Flat Plate ◽  
Friction Factor ◽  
Smooth Surface ◽  
Factor Model ◽  
Test Apparatus ◽  
Cell Width ◽  
Plate Test ◽  
Friction Factors ◽  
Line Flow ◽  
Factor Data

Friction-factors for honeycomb surfaces are measured with a flat plate tester. The flat plate test apparatus is described and a method is discussed for determining the friction-factor experimentally. The friction-factor model is developed for the flat plate test based on the Fanno Line Flow. The comparisons of the friction-factor are plotted for smooth surface and twelve-honeycomb surfaces with three-clearances, 6.9 bar to 17.9 bar range of inlet pressure, and 5,000 to 130,000 range of the Reynolds number. The optimum geometries for the maximum friction-factor are found as a function of cell width to cell depth and clearance to cell width ratios.

scholarly journals A study of friction factor model for directional wells

2017 ◽  
Vol 26 (2) ◽  
pp. 489-504 ◽  
Author(s):  
Ahmed A. Elgibaly ◽  
Mohammed Shehata Farhat ◽  
Eric W. Trant ◽  
Mohammed Kelany
Keyword(s):  
Friction Factor ◽  
Factor Model

Improved method of determining friction factor in pipes

2015 ◽  
Vol 25 (4) ◽  
pp. 941-949 ◽  
Author(s):  
Herbert Keith Winning ◽  
Tim Coole
Keyword(s):  
Friction Factor ◽  
Computational Efficiency ◽  
Design Methodology ◽  
Computational Method ◽  
Computationally Efficient ◽  
Explicit Equation ◽  
Content Type ◽  
Pipe Roughness ◽  
Similar Accuracy ◽  
Practical Implications

Purpose – The purpose of this paper is to present an improved computational method for determining the friction factor for turbulent flow in pipes. Design/methodology/approach – Given that the absolute pipe roughness is generally constant in most systems, and that there are few changes to the pipe diameter, the proposed method uses a simplified equation for systems with a specific relative pipe roughness. The accuracy of the estimation of the friction factor using the proposed method is compared to the values obtained using the implicit Colebrook-White equation while the computational efficiency is determined by comparing the time taken to perform 300 million calculations. Findings – The proposed method offers a significant improvement in computational efficiency for its accuracy and is compared 28 of the explicit equations currently in use. Practical implications – This method enables a simplified equation to offer a significant improvement in computational efficiency for its accuracy and is easier to code, enabling engineers to more efficiently calculate frictional pressure loss for flow in pipes. Originality/value – Due to the complexities in flow regime and pipe roughness, there is a limit to the scope for further computational efficiency through simplification of the explicit equation. This paper presents a new method and simplified equation which combined are able to deliver results with similar accuracy to less computationally efficient explicit equations.

scholarly journals Accurate and Efficient Explicit Approximations of the Colebrook Flow Friction Equation Based on Wright-Omega Function

2018 ◽  
Author(s):  
Dejan Brkić ◽  
Pavel Praks
Keyword(s):  
Friction Factor ◽  
Relative Error ◽  
Efficient Solution ◽  
Friction Loss ◽  
Series Expansions ◽  
Wright Function ◽  
Lambert Function ◽  
Computationally Efficient ◽  
Flow Friction ◽  
Loss Coefficients

The Colebrook equation is a popular model for estimating friction loss coefficients in water and gas pipes. The model is implicit in the unknown flow friction factor . To date, the captured flow friction factor  can be extracted from the logarithmic form analytically only in the term of the Lambert -function. The purpose of this study is to find an accurate and computationally efficient solution based on the shifted Lambert -function also known as the Wright -function. The Wright -function is more suitable because it overcomes the problem with the overflow error by switching the fast growing term  of the Lambert -function to the series expansions that further can be easily evaluated in computers without causing overflow run-time errors. Although the Colebrook equation transformed through the Lambert -function is identical to the original expression in term of accuracy, a further evaluation of the Lambert -function can be only approximate. Very accurate explicit approximations of the Colebrook equation that contains only one or two logarithms are shown. The final result is an accurate explicit approximation of the Colebrook equation with the relative error of no more than 0.0096%. The presented approximations are in the form suitable for everyday engineering use, they are both accurate and computationally efficient.

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