assignment 1

ASSIGNMENT 1

Computational Fluid Dynamic (CFD) MKAA8

10/30/2014MUHAMMAD AZHAR BIN MAT MARZUKI164369

OBJECTIVE

To investigate the flow past a circular cylinder and study the turbulent wake flow field

using Computational Fluid Dynamic (CFD) animation with PHOENICS software.

INTRODUCTION

External flows past objects have been studied extensively because of their many practical

applications. For example, airfoils are made into streamline shapes in order to increase the

lifts, and at the same time, reducing the aerodynamic drags exerted on the wings. On the

other hand, flow past a blunt body, such as a circular cylinder, usually experiences boundary

layer separation and very strong flow oscillations in the wake region behind the body. In

certain Reynolds number range, a periodic flow motion will develop in the wake as a result of

boundary layer vortice being shed alternatively from either side of the cylinder. This regular

pattern of vortices in the wake is called a Karman vortex street. It creates an oscillating flow

at a discrete frequency that is correlated to the Reynolds number of the flow. The periodic

nature of the vortex shedding phenomenon can sometimes lead to unwanted structural

vibrations, especially when the shedding frequency matches one of the resonant frequencies

of the structure. In this assignment were going to simulate this flow using fluid dynamic via

phoenics software.

Figure 1: Flow over cylinder for difference reynold number

METHODOLOGY

Phoenics software:

1. Start new case and set the model of the simulation into laminar flow and turn on the solution for velocities and pressure.

2. The domain is set at default 1x1x1 m.3. The inlet and outlet are created in the domain with both place at the X (0.0) and (1.0)

position. Set the attribute for the inlet 0.0031 m/s for reynold numbers, Re = 4.4. Create the cylinder with diameter 0.02m and 1m length. Place it at 0.5m for X and Z

position. And rotate it until rotate object face = 6. 5. Next for the mesh 1st, 2nd & 3rd region, edit mesh for X direction to 30, 12, 30, Z

direction 30, 18, 30 and Y direction let it in auto setting. For Z direction change it power ratio to -1.1, 1.0, 1.1 for 1st, 2nd & 3rd region.

6. Change the time dependence from steady to transient. In the time step settings change “time at end of the last step” to 10s with frist number 1 and last number 100. Everything else at default.

7. At numeric change the total number of iterations to 2 and global convergence criterion to 0.001%.

8. At output, for field dumping setting set the step frequency to 2 and “start letter for PHI to M.

9. Run the simulation “solver” first and then “post processor” for VR viewer. 10. Save the case data and the animation of the flow in avi. format.11. Change the attributes of the inlet with different velocities to get the required Re.

Matlab

This matlab coding is for calculating the velocities for satisfied Re for each cases.

clear all; close all; clc;

% reynolds number calculator

%T=275; M=0.8;

%u=M*sqrt(1.4*287*T)

%u=1; % velocity in m/s

v=1.544E-5; %kinematic viscosity in m^2/s

L=0.02; %cylinder diameter in m

RE=4;

%RE=u*L/v

u=RE*v/L

%v=u*L/RE

RESULT

Case 1: Re<5

Reynold number, Re = 4

Velocity = 0.0031 m/s

Case 2: 5 < Re < 40



Case 3: 40 < Re < 200



DISCUSSION

Case 1:

Base on the figure for case 1, we can observe that the flow that passes through the cylinder was a very smooth flow. From the velocity lines, we can observe the streamline direction of the flow move in ethical manner without creating any vortices behind the cylinder. This is due the low value of the velocity in this case.

Case 2:

In this case, the flow experienced vortices behind the cylinder. From the velocity line for case 2, we can observe that the direction of the line swirl behind the cylinder. This due to the fact we increase the velocity higher than case 1 in order to get Reynolds number 30.

Case 3:

Based on the velocity line figure for this case, the vortices behind the cylinder more vigorously compare to case 2. In this case the velocity is much higher than case 2 resulting higher Reynolds number. The vortex also became larger compare to case 2, but unlike case 2 the velocity of the vortex in case 3 have 3 different layer with high velocity inside the vortex compare to case 2 which only had 2 layer.

CONCLUSION

The flow of the fluid has been identified. The usage of phoenics software for CFD purposes has been achieved. Able to study the behaviour of flow over cylinder with different Reynolds number.

REFERENCE

https://www.eng.fsu.edu/~shih/succeed/cylinder/cylinder.htm

assignment 1

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