Pipe Flow Simualtion for different inlet Reynolds number at different sections of pipe using Solidworks Flow Simualtion

OBJECTIVE:

To perform flow simulation in a straight pipe with inlet Reynolds number of 100, 1000 & 10,000 and generate outlet velocity profiles & plots at 95%, 90% & 85% of the total length of the pipe using Solidworks Flow Simulation and conclude the result.

ABSTRACT:

The purpose of this project was to perform flow motion analysis in a circular pipe having water as a fluid using SolidWorks Flow Simulaion. Here, the fluid has different values of Reynolds Number at inlet i.e. 100, 1000 & 10000. Outlet normalized velocity profile was generated at 95%, 90% & 85% of the total length of the pipe. Line probes were used to extract the output data at 95%, 90% & 85% of the total length of the pipe. Velocity plots were also generated using xy plot at the given locations. Further, for all Reynolds number value & all the positions, velocity profiles & plots were compared and a conclusion was made from the analysis results.

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CONTENTS:

1. Introduction

• Computational Fluid Dynamics (CFD)
• Boundary Layer Phenomenon
• Reynolds Number (Re)
• Velocity Profile
• Velocity Plot

2. Geometry Model

• Flow Motion Analysis
• Setup
• Boundary Condition
• Mesh Parameter
• Result (Setting cut plots & xy plots)

3. Parametric Study – What if Analysis

• Input Variables
• Output Parameters
• Scenario

4. Plot Results

5. Observation

6. Conclusion

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1. INTRODUCTION:

Computational Fluid Dynamics (CFD)

Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyse and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems.

CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering, fluid flows and heat transfer, and engine and combustion analysis.

Boundary Layer Phenomenon

A boundary layer is a thin layer of viscous fluid close to the solid surface of a wall in contact with a moving stream in which (within its thickness δ) the flow velocity varies from zero at the wall (where the flow “sticks” to the wall because of its viscosity) up to U_e at the boundary, which approximately (within 1% error) corresponds to the free stream velocity.

Fig: Boundary Layer Phenomenon

Reynolds Number (Re)

The Reynolds number (Re) is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents).

The Reynolds number is the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities. A region where these forces change behaviour is known as a boundary layer, such as the bounding surface in the interior of a pipe.

With respect to laminar and turbulent flow regimes:

• laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion;
• turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities.

The Reynolds number is defined as:

where:

ρ is the density of the fluid (SI units: kg/m3)

u is the flow speed (m/s)

D is the diameter of the tube (m)

μ is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/(m·s))

ν is the kinematic viscosity of the fluid (m2/s).

From the above formula, velocity at a particular Reynold Number can be calculated by putting the values as ρ = 1000kg/m³, D = 0.05 m, μ = 0.0017914 Ns/m² & ν = 1.7918 * 10^-6 m²/s

For Reynold Number (Re) = 100 Flow Speed (u) = 0.0035828 m/s

For Reynold Number (Re) = 1000 Flow Speed (u) = 0.035828 m/s

For Reynold Number (Re) = 10000 Flow Speed (u) = 0.35828 m/s

Velocity Profile

A pictorial graph of the speed of a fluid flow as a function of distance perpendicular to the direction of flow.

Velocity Plot

A graph of the speed of a fluid flow as a function of distance perpendicular to the direction of flow.

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2. GEOMETRY MODEL

Circular Pipe Diameter: 50 mm

Circular Pipe Length: 1000 mm

Circular Pipe Thickness: 5 mm

Distance of Line Probe from inlet: 850 mm, 900 mm & 950 mm

Material Assigned: AISI 1015 Steel, Cold Drawn (SS)

Fig: Geometry Model

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3. FLOW MOTION ANALYSIS

1. Setup

• Add the lids on both ends of the pipe to from a closed geometry.
• Setup of the new study
  • Project name: Flow_Through_Pipe
  • Type of fluid: Water (Liquid)
  • Type of flow: Laminar & Turbulent
  • Wall Condition: Adiabatic Wall with 0 micro-meter roughness
  • Initial Condition: Pressure (101325 Pa), Temperature (293.2K)
• Add transparency to view what’s happening inside the tube.

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2. Boundary Condition

• Inlet Velocity Boundary Condition: Inner face of lid 1

Fig: Boundary Condition 1

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• Outlet Static Pressure Boundary Condition: Inner face of lid 2

Fig: Boundary Condition 2

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• Wall Boundary Condition: Inner face of pipe/shell (Real Wall)

Fig: Boundary Condition 3

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3. Mesh Parameter

Automatic mesh with mesh level 6.

Fig: Mesh Parameter

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4. Result (Setting cut plots & xy plots)

Add the cut plots (total 3 cut plots) parallel to the circular cross-section of the pipe at or after each of the line probe sketches. Add xy plot (total 3) for each of the line probe sketch separately and another xy plot to compare the velocity at all line probes.

Fig: Result Setup

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3. PARAMETRIC STUDY – WHAT IF ANALYSIS

1. Input Variables

Add a parameter to vary: Inlet velocity boundary condition with all three discrete value of velocity corresponding to the Reynolds Number

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2. Output Parameters

Add all the cut plots and the xy plots (total 7)

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3. Scenario

Total 3 Design Points will be created which will evaluate the velocity profiles & plots for three different Inlet Velocity (0.0035828, 0.035828, 0.35828) corresponding to the Reynolds Number (100, 1000, 10000) respectively.

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4. PLOT RESULT:

Design Point 1 refer to Reynolds Number(Re) 100

Design Point 2 refer to Reynolds Number(Re) 1000

Design Point 3 refer to Reynolds Number(Re) 10000

• Cut Plot at 95% of total length of pipe

Re 100 Re 1000 Re 10000

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• Cut Plot at 90% of total length of pipe

Re 100 Re 1000 Re 10000

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• Cut Plot at 85% of total length of pipe

Re 100 Re 1000 Re 10000

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• XY Plot of outlet velocity at 95% of total length of pipe

Fig: XY Plot at 95% length

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• XY Plot of outlet velocity at 90% of total length of pipe

Fig: XY Plot at 90% length

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• XY Plot of outlet velocity at 85% of total length of pipe

Fig: XY Plot at 85% length

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• XY Plot comparing the outlet velocity at 95%, 90% & 85% of total length of pipe

Fig: XY Comparison Plot for all 3 length

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5. OBSERVATION:

From the above plots, an observation table was created.

From the above table, the following observation can be made-

1. Flow having low Reynolds number (100) has the output velocity approximately double at the centre of pipe and reduced by a factor of around 6.5 at the wall of pipe.

2. Flow having Reynolds number (1,000) has the output velocity increased by a factor of around 1.7 at the centre of pipe and reduced by a factor of around 6 at the wall of pipe.

3. Flow having high Reynolds number (10,000) has the output velocity increased by a factor of around 1.2 at the centre of pipe and reduced by a factor of around 1.7 at the wall of pipe.

Since, the pipe is horizontal, potential energy is unaltered, hence the increase in kinetic energy is at the cost of pressure energy. Therefore, as the fluid flows through a constricted passage its velocity increases whereas pressure drops. This causes the outlet velocity at the centre of pipe to increase.

The output velocity is reduced at the wall due to effects like viscosity and boundary layer formation.

For each Reynolds number, the outlet velocity at different sections i.e. 95%, 90% & 85% of total length of pipe is almost the same.

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6. CONCLUSION:

For flow having low Reynolds number, there is maximum increase at the centre and maximum reduction at the wall in outlet velocity in comparison with other two cases.

For flow having high Reynolds number, there is minimum increase at the centre and minimum reduction at the wall in outlet velocity in comparison with other two cases.

The maximum outlet velocity for each Reynolds number is observed at 95% of total length of the pipe.

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