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ESDU TN 08008

2008 Edition, December 1, 2009

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CFD studies for the validation of friction losses and flow characteristics in circular straight pipes with smooth walls

Includes all amendments and changes through AA, December 1, 2009


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Product Details:

  • Revision: 2008 Edition, December 1, 2009
  • Published Date: December 1, 2009
  • Status: Active, Most Current
  • Document Language: English
  • Published By: Engineering Sciences Data Unit (ESDU)
  • Page Count: 111
  • ANSI Approved: No
  • DoD Adopted: No

Description / Abstract:

INTRODUCTION

In this Technical Note, the ESDU CFD validation studies are presented for the prediction of friction losses and flow characteristics in straight circular pipes with smooth walls.

Understanding of pipe friction and associated flow characteristics in different flow regimes is fundamental to the understanding of boundary layer development and turbulence modelling in internal flow engineering applications such as viscous drag and heat-transfer processes.

Typical industrial CFD applications of pipe flow include systems where pipes are part of a more complex domain, such as aircraft ducts, pipe fittings, heat exchangers, various components of power generation plants, etc. In more general CFD applications, straight long pipes are often used to set inlet and outlet boundary conditions. At inlet boundaries, they are used as an artificial extension of the inlet to the investigated flow domain to allow the natural development of duct boundary layers. At outlet boundaries, straight pipes are used as an artificial extension to the outlet of the investigated flow domain to reduce the influence of the outlet local fluid dynamics on the CFD predictions. In all such applications, it is essential to reduce the sensitivity of CFD predictions of friction losses to mesh density and distribution, pipe length required for fully-developed flow, boundary conditions and turbulence modelling.

Accurate prediction of the friction losses and flow characteristics in straight pipes is one of the most challenging problems in CFD. Although direct numerical simulation (DNS) and large eddy simulation (LES) are used in research, in industry Reynolds-averaged Navier-Stokes (RANS) methods are largely used.

The purpose of this work is to provide guidance on the CFD modelling of friction losses and flow characteristics in:

• straight circular pipes with smooth walls,

• laminar, transitional and turbulent flow regimes,

• swirl-free, uniform inlet velocity conditions,

• fully-developed exit flow conditions,

• steady-state flow conditions,

• incompressible flow of single-phase, Newtonian liquids and gases.

• employing commercial CFD packages typically used in the industry, i.e. finite volume RANS code with low-Reynolds-number turbulence and transition correlation-based ‘bypass' modelling capabilities.

Extensions to rough pipes and to compressible flow will be considered in future work.

Three types of meshes were considered: 2D-axisymmetric hexahedral meshes, 3D purely tetrahedral meshes and 3D tetrahedral meshes with prismatic layers. Pipes with different lengths were tested in laminar, transitional and turbulent flow at Reynolds numbers ranging 1 less than Re less than 107.

Three different turbulence models were considered with different near-wall treatments: the k - ε with SCALABLE near-wall treatment, k - ω with AUTOMATIC near-wall treatment and SST with AUTOMATIC near-wall treatment. Three transition models were considered: the SST specific-γ, SST γ and SST γ-Reθ models. Detailed CFD validation studies on transitional flow are presented in ESDU TN 08009.

A brief description of the fundamental fluid mechanics in straight pipes is given in Section 3. In this section, correlations, measurements and DNS predictions in the literature for friction losses and flow characteristics in straight pipes are reviewed. The methodology used in the CFD predictions is described in Section 4.

The ESDU CFD predictions for the different meshes, pipe lengths, Reynolds number and turbulence models are discussed in Section 5 and compared to experimental data and correlations in Section 6. Best Practice Guidelines on mesh density and distribution, setting of boundary conditions and turbulence modelling are given in Section 7. Overviews on the CFD modelling of turbulent and transitional flows are given in Appendices A and B, respectively.