Task1_Hemant_Bansal

8/6/2019 Task1_Hemant_Bansal

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Task 1 : Flow of a Pipe through an

Orifice

Simulation-report

Bansal, Hemant

Esslingen 27.06.2011

Computation Fluid Dynamics

Prof. Dr.-Ing. Muris Torlak

Hemant Bansal

73953


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Introduction

1. Introduction

Computational Fluid Dynamics, CFD has gained a very wide popularity in

the recent times owing to its numerous applications and advantages.

In addition to knowing the fundamentals of CFD it is very important to

have the know-how of the commercial softwares code for CFD, as for

indsutrial applications these commercial codes are widely used.

The scope of the task here is to work with one of the CFD softwares

STAR CCM+ was used in this case for simulations. A pipe with an orifice

was considered, and internal fow thorugh the pipe was considered.

The Scope of the task was to get familirized with various aspects of CFD

commercial softwares, experiment with different setting conditions for

models and analyse the simulation results.


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Definition of problem

2. Problem Description

Internal Flow through a pipe with orifice has to be analyzed.

2.1. Production of raw material

A fluid passing though an orifice constriction will experience a drop in

pressure across the orifice. This change can be used to measure the

flowrate of the fluid.Orifice plates are most commonly used for continuous

measurement of fluid flow in pipes.

The Present task involved setting up a CFD model for the given problem

with different CFD parameters, Inlet and outlet conditions were already

provided, flow was to be simulated at two different inlet conditions.

For familirizing with the software it was stated to test different meshes

and med refinement techniques.

The following results should be analyzed

Pressure, velocity and temperature contours in the pipe Streamlines at the mid section of pipe 2-D plots for axial velocity and static pressure along the pipe axis.


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Definition of problem

Measuring the Reattachment length o In a sudden expansion an inlet pipe with small diameter, flow

is unable to follow the sudden enlargement and will detach at

the sudden expansion. After some length downstream, called

the reattachment length, the flow attaches to the outlet pipe.

This reattachment length is highly dependent on the inlet

conditions of the flow and the expansion ratio.


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3. CFD Modelling - Pre Processing

Pre processing of the model was using STAR CCM+

The CAD model of the pipe was available in STL format orifice.x_t. The

model represented only quarter of the pipe as flow is symmetric inside the

pipe. Hence the initial settings were made on the pipe to make detachg al

its surfaces in order to assign them different properties and boundary

conditions.

Periodic Boundary Conditions: As discussed, because only quarter of pipe

is analyzed here periodic boundary conditions should be assigned to theopposite walls so as to indicate the flow across them takes place with

similar conditions.

General Settings and Boundary conditions:

Fluid : Air

Density: 1,205 kg/m3

Dynamic Viscosity: 1,845 E-05 Pa-s

3D simulation, Steady-state

Incompressible, with segregated flow.

Turbulent (k-epsilon) and heat transfer included.

Periodic Boundary Conditions


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Boundary Conditions

Inlet temperature: 20 C Orifice wall Temperature: 300 C Static- Pressure outlet at down stream boundary: 0 Pa

3.1. Meshing models and Simulations Matrix

It was decided to conduct the Simualtions under various conditions listed

in the table below, to familirize with the software and also to be able to

analyze consequences of various paremeters of simulation.

SimulationNo.

Mesh TypeBase MeshSize

Prism LayerVolumetricBlock aroundOrifice

Inlet Velocitym/s

1Trimmed

Mesh6 mm Yes, 3

10% of Base

size3

2Trimmed

Mesh

6 mm Yes, 340% of Base

size

15

3Trimmed

Mesh6 mm Yes, 3

20% of Basesize

15

4 Tetrahedral 6 mm Yes, 310% of Base

size3


size6

.


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4. Simulation and Post Processing

On the above mentioned conditions, simulation was carried out and the

results are enclosed in this section.

Simulation 1

1Trimmed

Mesh6 mm Yes, 3

10% of Basesize

3 m/s

Fig 4.1 Meshed Model of pipe

Fig 4.2 Velocity contour along the pipe


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Fig 4.3 Static Pressure contours along the pipe

Fig 4.4 Temperature contour along the pipe


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Reattacment Length measured from contour - 0,07m

Fig 4.6 Reattachment length using Wall shear stress

Fig 4.5 Stream Lines on the mid-section


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Fig 4.8 2D plot of Axial Velocity along the axis

Fig 4.7 2D plot of Static pressure along the axis


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Simulation 2

2Trimmed

Mesh6 mm Yes, 3

40% of Base

size15 m/s

Same simulation and post processing was done under the higher velocity

of 15m/s. Here the volumetric Block was not meshed to a very fine , it

was also kept coarse.

Fig 4.9 Mesh (trimmed) with different block

Fig: Contours of velocity and Pressure


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Reattacment Length measured from contour - 0,115 m

Fig: 2D plot for axial velociy and Static Pressure

Fig: Contours of temperature and streamlines at mid section


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Simulation 3

3Trimmed

Mesh6 mm Yes, 3

20% of Base

size15 m/s


of 15m/s. The volumetric Block was meshed to a very fine value of 20%,

i.e. a mesh size of 1.2 mm.



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Reattacment Length measured from contour - 0,08m




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Simulation 4


of 15m/s. The volumetric Block was meshed to a very fine value of 20%,

i.e. a mesh size of 1.2 mm.


size3 m/s



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Simulation 5


size6 m/s


of 15m/s. Here the vaolumetric Block was not meshed to a very fine , it

was also kept coarse.



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Reattachment Length: 0,082m



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5. Conclusions & Discussions

Different Mesh types were compared, and their influence onsimulation accuracy and simulation time was studied.

Pre processing was made to test different block mesh sizes to seetheir effect on the solution and how can the gradients be captured at

critical sections. We can see from the contours as well as 2D plot

their due to mesh refinement at the critical section, the velocity

fluctuations were captured at fine spacing as well.

Stream lines on the mid plane compare very well to the physicalbehaviour of the flow through an orifice.

Effect of including heat transfer in the model also yielded interestifresults as we can see from the temperature contours that temp

effect should not be neglected. But further analysis is recommended

here to include for thermal expansion as well as simulation correct

convection behaviours.

Working with different meshes in this case we cannot see majordifferences as the problem is not complex, and computing memory

and space were not critical.

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