Analysis of Variation of Velocity Along the Radius for Fully Developed Turbulent Flow Through Pipe Using Cfd

Analysis of Variation of Velocity along the Radius for Fully Developed Turbulent Flow through Pipe Using CFD

Milap Kumar Sahu1, Brijesh Patel2

1M.Tech Scholar (Turbo machinery), MATS University, Raipur, (C.G.), India

2Asst. Prof., Department of Aeronautical Engineering, MATS University, Raipur, (C.G.), India

1sahumilap@gmail.com

2brijeshp@matsuniversity.ac.in

Keywords: Computational fluid dynamics, Reynolds Averaged Navier Stokes, Turbulent, Average Velocity, k- model.

Abstract-In this era fluid flow problems analysis is done by using Computational Fluid Dynamics. Simulation procedures used by Computational Fluid Dynamics are now considered as a crucial analysis and design tool worldwide having large range of applications including fluid flow. In the analysis of water transmission grid, the design parameters are the lengths, diameters, and the friction factor of a pipe. This paper demonstrates computational investigation of turbulent flow inside pipes for varying inlet velocity. Reynolds Averaged Navier Stokes Turbulent model; the k-ε model is used for the simulation. The Reynolds number varies based upon the inlet velocity. The material of pipe is not the concern. The fluid used for this purpose is water of density 1000 kg/m3.The results acquired are well in agreement with the results acquired experimentally.

Introduction

In recent decades, use of pipes for fluid transmission has great importance globally. Such applications range from the huge, man-made Alaskan pipeline that carries oil almost 1290 km across Alaska, to the more complex natural systems of “pipes” that carry blood through our veins and artery and air into and out of our lungs. The use of pipe transmission system without proper analysis of losses concerned to it has reduced the transmission efficiency. Consequently, demand and attention for efficient flow transmission has increased all over the world. Among new transmission systems, turbulent flow analysis has gained the spot of prime importance.

A pipe is hollow cylinder with dimension of length many times the diameter. Flow through pipes occurs due to pressure gradient, or from higher potential to lower potential. The inner surface of pipe can be smooth or rough, depending on the smoothness of inner surface there is boundary layer formation. The boundary layer formation starts at the solid boundary where variation of velocity occurs from zero to free stream velocity at the center of pipe. Initially the boundary layer formed is laminar boundary layer, as the length of pipe increases this layer increases and becomes unstable which leads to transition from laminar to turbulent flow. The term turbulent flow describes the flow pattern in which fluid flows in haphazard manner, i.e. flow across the layers.

Fig 1: Mechanism of internal flow. [3]

At the entry to a pipe, the fluid develops a boundary layer at the vicinity of pipe walls, while the center of the fluid may remain as an undisturbed uniform flow. Within the boundary layer, viscous stresses are very prominent, hindering the fluid movement due to its friction with the pipe walls. As fluid enters the pipe, layer at the vicinity of pipe walls sticks to pipe surface, reducing velocity at wall to zero. This layer then interacts with next layer and resists its motion, and so on until free stream velocity is reached. Downstream, the boundary layers therefore increases. Eventually, the velocity assumes some average profile across the pipe which is no longer influenced by any means arising from the pipe wall. At this point, the flow is not dependent on what was the effect of pipe wall at the pipe entrance, and we could solve for its properties (such as the velocity profile) without including an entrance region in the calculations.

Fig 2: boundary layer visualization. [5]

METHODOLOGY

We need to define a proper methodology to carry out the analysis thus shown below the methodology for carrying out the 3D simulation for the analysis of the variation of velocity along the radius for fully developed turbulent flow through pipe.

Flow chart of methodology for analysis.

For the first step various pipe dimension have been selected for various study done. Pipes are classified as smooth pipes or rough pipes based upon the coarseness of the internal surface of the pipe. Smooth pipes are those having very low or no coarseness whereas rough pipes are having high coarseness in internal surface. In this study we have considered smooth pipe. The analysis has been carried out for the variation of velocity along radius.

Table 1: Inlet parameters.

Parameters Values

Length 20 m

Diameter 1 m

Density 1000 kg/m3

Viscosity 0.001 kg/ms

Fig 3: Geometry of the Model.

For the analysis a hex mesh has been generated.Sweep method was followed in order to sweep the mesh elements from start to end. Velocity inlet was chosen. The dimensions of the hex mesh are as follows.

Table 2: hex mesh conditions.

Edge sizing 32 parts

Inflation 10 layers

Thickness of layer 5 mm

Elements 210120

Nodes 862458

Fig 4: hex mesh domain.