Roughness effects of commercial steel pipe in turbulent flow: universal scaling

2013 ◽  
Vol 40 (2) ◽  
pp. 188-193 ◽  
Author(s):  
Noor Afzal
Keyword(s):  
Surface Roughness ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Steel Pipe ◽  
Roughness Effects ◽  
Universal Scaling ◽  
Commercial Steel ◽  
The Mean ◽  
Grain Roughness

The mean turbulent flow over a transitional rough commercial steel pipe is considered in terms of alternate inner roughness variables. The matching of inner layer and outer layer in the overlap region leads to the universal log laws for velocity profile and friction factor, explicitly independent of surface roughness of all kinds. The roughness function, for commercial steel pipe differs from inflectional (sand grain) roughness. The traditional wall law and friction factor depends on type of surface roughness.

Alternate Scales for Turbulent Flow in Transitional Rough Pipes: Universal Log Laws

2006 ◽  
Vol 129 (1) ◽  
pp. 80-90 ◽  
Author(s):  
Noor Afzal ◽  
Abu Seena
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Friction Velocity ◽  
Strong Support ◽  
Reynolds Numbers ◽  
Momentum Theory ◽  
The Mean ◽  
Pipe Roughness

In transitional rough pipes, the present work deals with alternate four new scales, the inner wall transitional roughness variable ζ=Z+∕ϕ, associated with a particular roughness level, defined by roughness scale ϕ connected with roughness function ▵U+, the roughness friction Reynolds number Rϕ (based on roughness friction velocity), and roughness Reynolds number Reϕ (based on roughness average velocity) where the mean turbulent flow, little above the roughness sublayer, does not depend on pipes transitional roughness. In these alternate variables, a two layer mean momentum theory is analyzed by the method of matched asymptotic expansions for large Reynolds numbers. The matching of the velocity profile and friction factor by Izakson-Millikan-Kolmogorov hypothesis gives universal log laws that are explicitly independent of pipe roughness. The data of the velocity profile and friction factor on transitional rough pipes provide strong support to universal log laws, having the same constants as for smooth walls. There is no universality of scalings in traditional variables and different expressions are needed for various types of roughness, as suggested, for example, with inflectional-type roughness, monotonic Colebrook-Moody roughness, etc. In traditional variables, the roughness scale, velocity profile, and friction factor prediction for inflectional pipes roughness are supported very well by experimental data.

Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids

1982 ◽  
Vol 119 ◽  
pp. 423-441 ◽  
Author(s):  
M. A. Goldshtik ◽  
V. V. Zametalin ◽  
V. N. Shtern
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Outer Boundary ◽  
Viscous Sublayer ◽  
Viscous Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
The Mean ◽  
Near Wall

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.

The Effects of Surface Roughness on the Mean Velocity Profile in a Turbulent Boundary Layer

2002 ◽  
Vol 124 (3) ◽  
pp. 664-670 ◽  
Author(s):  
Donald J. Bergstrom ◽  
Nathan A. Kotey ◽  
Mark F. Tachie
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Friction Velocity ◽  
Outer Region ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Outer Flow ◽  
The Mean

Experimental measurements of the mean velocity profile in a canonical turbulent boundary layer are obtained for four different surface roughness conditions, as well as a smooth wall, at moderate Reynolds numbers in a wind tunnel. The mean streamwise velocity component is fitted to a correlation which allows both the strength of the wake, Π, and friction velocity, Uτ, to vary. The results show that the type of surface roughness affects the mean defect profile in the outer region of the turbulent boundary layer, as well as determining the value of the skin friction. The defect profiles normalized by the friction velocity were approximately independent of Reynolds number, while those normalized using the free stream velocity were not. The fact that the outer flow is significantly affected by the specific roughness characteristics at the wall implies that rough wall boundary layers are more complex than the wall similarity hypothesis would allow.

Measurement of Semi-Local Friction Factor of Gas Flow in Micro-Tube

2013 ◽  
Author(s):  
D. Kawashima ◽  
Y. Asako
Keyword(s):  
Surface Roughness ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Gas Flow ◽  
Flow Region ◽  
Nitrogen Gas ◽  
Gaseous Flow ◽  
Flow Through ◽  
Local Pressures ◽  
Measured Pressure

This paper presents experimental results on friction factor of gaseous flow in a PEEK micro-tube with relative surface roughness of 0.04 %. The experiments were performed for nitrogen gas flow through the micro-tube with 514.4 μm in diameter and 50 mm in length. Three pressure taps holes with 5 mm interval were drilled and the local pressures were measured. Friction factor is obtained from the measured pressure differences. The experiments were conducted for turbulent flow region. The friction factor obtained by the present study are compared with those in available literature and also numerical results. The friction factor obtained is slightly higher than the value of Blasius formula.

CFD Modelling Strategies for the Simulation of Roughness Effects on Friction and Heat Transfer in Additive Manufactured Components

2020 ◽  
Author(s):  
Lorenzo Mazzei ◽  
Riccardo Da Soghe ◽  
Cosimo Bianchini
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Thermal Performance ◽  
Accurate Estimation ◽  
Real Surface ◽  
Cfd Modelling ◽  
Roughness Effects ◽  
Modelling Strategies ◽  
The Impact ◽  
Grain Roughness

Abstract It is well-known from the literature that surface roughness affects significantly friction and heat transfer. This is even more evident for additive manufactured (AM) components, which are taking an increasingly important role in the gas turbine field. However, the exploitation of numerical approaches to improve their design is hindered by the lack of dedicated correlations and CFD model developed for such high roughness conditions. Usually the additive manufactured components are simulated considering the surfaces as smooth or applying an equivalent sand-grain roughness (ks) that results in a velocity shift in the boundary layer. However, determining a priori the most appropriate value of ks is challenging, as dozens of correlations are available, returning scattered and uncertain results. The aim of this work is to benchmark some existing modelling strategies (among which the equivalent sand grain roughness) and test a numerical approach capable of narrowing the existing gap between simulated and tested thermal performance of additive manufactured devices. The technology enabler is represented by higher-fidelity CFD simulations accounting for the impact of real surface roughness on pressure drop and heat transfer. At this purpose, an existing literature model for rough walls has been implemented in ANSYS Fluent and tested on a variety of AM mini-channels so as to determine the best-fitting values of ks and corrected wetted surface ratio Scorr that match the experimental data in terms of friction factor and Nusselt number. Knowing also the measured roughness descriptors of each component, it has been possible to derive valuable guidelines for an effective exploitation of CFD on additive manufactured components, thus allowing a more accurate estimation of the thermal performance in additive manufactured components.

scholarly journals Surface-roughness effects on the mean flow past circular cylinders

1980 ◽  
Vol 98 (4) ◽  
pp. 673-701 ◽  
Author(s):  
O. Güven ◽  
C. Farell ◽  
V. C. Patel
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Roughness Effects ◽  
Number Range ◽  
Mean Pressure ◽  
The Mean

Measurements of mean-pressure distributions and boundary-layer development on rough-walled circular cylinders in a uniform stream are described. Five sizes of distributed sandpaper roughness have been tested over the Reynolds-number range 7 × 104to 5·5 × 105. The results are examined together with those of previous investigators, and the observed roughness effects are discussed in the light of boundary-layer theory. It is found that there is a significant influence of surface roughness on the mean-pressure distribution even at very large Reynolds numbers. This observation is supported by an extension of the Stratford–Townsend theory of turbulent boundary-layer separation to the case of circular cylinders with distributed roughness. The pressure rise to separation is shown to be closely related, as expected, to the characteristics of the boundary layer, smaller pressure rises being associated with thicker boundary layers with greater momentum deficits. Larger roughness gives rise to a thicker and more retarded boundary layer which separates earlier and with a smaller pressure recovery.

Another look at unidirectional turbulent flow

1995 ◽  
Vol 287 ◽  
pp. 75-92 ◽  
Author(s):  
A. J. Reynolds ◽  
K. Wieghardt
Keyword(s):  
Variational Principle ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Core Region ◽  
Flat Channel ◽  
Mean Velocity ◽  
Channel One ◽  
The Core ◽  
The Mean

Here we consider the mean velocity profile in the core region of a unidirectional turbulent flow, that is, a flow in which the turbulent motion is superposed upon parallel time-averaged streamlines. A kinematical variational principle, originally developed for three-dimensional free-turbulent motions, is shown to be applicable to significant parts of the velocity profiles for flows of both Couette and Poiseuille types. In addition to pure plane Couette and pure plane Poiseuille flows, the motions considered include a variety of admixtures produced by blowing through a wide flat channel one of whose walls comprises a belt which moves either in the direction of the blowing or counter to it.

Surface Roughness of Graphite and Its Effect on Friction Factor

1974 ◽  
Vol 188 (1) ◽  
pp. 457-460 ◽  
Author(s):  
C. Warburton
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Friction Factor ◽  
Surface Finish ◽  
Graphite Surface ◽  
Experimental Results ◽  
Stanton Number ◽  
Surface Finishes ◽  
Similarity Law ◽  
Grain Roughness

Experimental results are presented for friction factor and surface finish measurements on eight graphite tubes machined to give a range of surface finishes from smooth up to the maximum roughness likely to occur in a reactor. Correlations are given which allow estimation of friction factor from graphite surface finish measurements. The results are compared with those obtained by Nikuradse in his sand-grain roughness tests. Except at low values of es+, agreement is good, enabling the heat transfer similarity law of Dipprey and Sabersky to be used to predict any increases in Stanton number due to surface roughness.

The Importance of the Mean Elevation in Predicting Skin Friction for Flow Over Closely Packed Surface Roughness

2005 ◽  
Vol 128 (3) ◽  
pp. 579-586 ◽  
Author(s):  
Stephen T. McClain ◽  
S. Patrick Collins ◽  
B. Keith Hodge ◽  
Jeffrey P. Bons
Keyword(s):  
Surface Roughness ◽  
Skin Friction ◽  
Element Model ◽  
Discrete Element ◽  
Discrete Element Model ◽  
Roughness Model ◽  
The Mean ◽  
Insight Into ◽  
Single Relation ◽  
Grain Roughness

The discrete-element surface roughness model is used to provide insight into the importance of the mean elevation of surface roughness in predicting skin friction over rough surfaces. Comparison of experimental data and extensive computational results using the discrete-element model confirm that the appropriate surface for the imposition of the no-slip condition is the mean elevation of the surface roughness. Additionally, the use of the mean elevation in the Sigal-Danberg approach relating their parameter to the equivalent sand-grain roughness height results in replacing three different piecewise expressions with a single relation. The appropriate mean elevation for closely-packed spherical roughness is also examined.

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