A new approach to understanding and modelling the influence of wall roughness on friction factors for pipe and channel flows

Abstract

In this study, it is shown how the equivalent sand roughness required in the Moody chart can be calculated for arbitrarily shaped wall roughnesses. After a discussion of how to define the wall location and roughness height in the most reasonable way, a numerical approach based on the determination of entropy production in rough pipes and channels is presented. As test cases, three different two-dimensional roughness types have been chosen which are representative of regular roughnesses on machined surfaces. In the turbulent range, skin friction results with these test roughnesses can be linked to Nikuradse's sand roughness results by a constant factor. For laminar flows, a significant effect of wall roughness is identified which in most other studies is neglected completely. The dissipation model of this study is validated with experimental data for laminar and turbulent flows.

How to Determine Losses in a Flow Field: A Paradigm Shift towards the Second Law Analysis

“…It can be seen that f for these roughness elements does not follow the general trend of the Moody chart with respect to the lines for increasing sand roughness height. This, however, is also predicted in our SLA results; for a detailed discussion, see [45]. With the same kind of analysis, we could show that, contrary to the common belief, there is also a definite roughness effect in laminar pipe and channel flows; see [47][48][49].…”

“…When roughness effects are included, a systematic analysis will always incorporate regular roughness elements, which follows the same idea as introducing (regular) sand roughness in experiments, which leads to the famous Moody chart; see [43] and [44]. In [45], we applied the SLA approach to the flow through a pipe with special roughness elements, called Loewenherz-roughness, [46]. Figure 7 shows both the experiments and our SLA results.…”

Heat Transfer and Its Assessment

“…This approach can for example be used to determine the friction factor of a pipe with a special roughness type, called Loewenherz-thread roughness, by integrating the entropy generation rate as shown in Fig. 2, see Herwig et al (2008) for details. The dark lines are numerical results based on (17)-(19).…”

Friction Factor Estimation for Turbulent Flows in Corrugated Pipes with Rough Walls

“…The pressure loss along a pipe is caused by the friction at the wall. In stationary flow, the friction is proportional to the pressure loss per unit distance [1]. Therefore, in this investigation, we are interested in estimating the friction factor for turbulent flow at Reynolds numbers around 10 6 in a flexible pipe with a specific configuration.…”