Flow over a cylinder
AIM : CFD on simulation of flow over pipe.
OBJECTIVES : The following objectives are carried on a cylinder.
- CFD analysis of a cylinder in which external flow takes place and running at different reynolds number.
- Calculating the Reynolds number and also the simulation end time. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
- Animations for pressure-velocity for all the three Reynolds number created.
INTRODUCTION :
Computational Fluid Dynamics : CFD has fascinated researchers, as it is a fast, accurate and reliable method of analyzing the variation of hydrodynamic properties of the flow over and within a body. Computational Fluid Dynamics (CFD) is a branch of fluid mechanics that uses numerical methods and algorithms to solve complex problems involving fluid flow.
Reynold's Number :
Where,
R = Reynolds Number
ρ = Fluid(Air) Density
v = Velocity of Fluid(Air)
D = Diameter of Cylinder
μ = Dynamic Viscosity of Fluid(Air)
GEOMETRY DIMENSIONS :
The design parameters are as follows:
- Diameter of the cylinder = 0.06 m
- Length of the cylinder = 0.1 m
CALCULATIONS :
BASELINE SIMULATION PARAMETERS :
Initially, We considered the baseline velocity of air to be 10m/s.
On the basis of initial velocity, Reynolds number is calculated.
By Substituting the above values in reynolds number formula we get,
the baseline case Reynolds number,Re = 40518.19
Similarly, Reynold's number and Velocity at 20%, 40% and 100% is calculated,
- At Baseline For V = 10 m/s , Re = 40518.19
- At 20% For V = 12 m/s , Re = 48621.83
- At 40% For V = 14 m/s , Re = 56725.46
- At 100% For V = 20 m/s , Re = 81036.38
INITIAL SETUP :
BASELINE SETUP :
- ANALYSIS TYPE : EXTERNAL FLOW (same in all cases)
- FLUID : AIR (same in all cases)
- GLOBAL MESH LEVEL : 5 (same in all cases)
- INLET VELOCITY : 10m/s
AT 20% INCREASED FACTOR :
- INLET VELOCITY : 12m/s
AT 40% INCREASED FACTOR :
- INLET VELOCITY : 14m/s
AT 100% INCREASED FACTOR :
- INLET VELOCITY : 20m/s
CALCULATING SIMULATION END TIME :
The length of the domain along the X axis is 0.540 m
Velocity = Distance / time
Flow Through Time = Distance / velocity
i.e. Flow Through Time = 0.54/10 = 0.054 sec
The end time should be 2 times the flow through time.........(GIVEN)
At Baseline For V = 10 m/s , Re = 40518.19 , Simulation end time = 0.108 sec
At 20% For V = 12 m/s , Re = 48621.83 , Simulation end time = 0.09 sec
At 40% For V = 14 m/s , Re = 56725.46 , Simulation end time = 0.08 sec
At 100% For V = 20 m/s , Re = 81036.38 , Simulation end time = 0.027 sec
RESULTS :
Flow over a cylinder at Baseline Velocity : 10m/s
Cut Plot of Velocity contour
Animation videos for velocity : 10 m/s and Re = 40518.19
Cut Plot for Pressure conture
Animation videos for Pressure at 10 m/s
Case 1: Flow over a cylinder at 20% of Reynolds Number i.e. VELOCITY :12m/s
Cut Plot of Velocity contour
Animation videos for velocity at 12 m/s and Re = 48621.83
Cut Plot of Pressure contour
Animation videos for Pressure at 12 m/s
Case 2: Flow over a cylinder at 40% of Reynolds Number i.e. VELOCITY : 14m/s
Cut Plot of Velocity contour
Animation videos for velocity : 14 m/s and Re = 56725.46
Cut Plot of Pressure contour
Animation videos for Pressure at 14 m/s
Case 3: Flow over a cylinder at 100% of Reynolds Number i.e. VELOCITY : 20m/s
Cut Plot of Velocity contour
Animation videos for velocity 20 m/s and Re = 81036.38
Cut Plot of Pressure contour
Animation videos for Pressure at 20 m/s
CONCLUSION :
- As Reynold's number increases the Velocity increases and the flow through time decreases.
- As the velocity or Renold's number increase the flow over the cylinder becomes steady and the velocity plot at 20% and 40% exhibit slight unsteady plot whereas at 100% the flow is steady and we can draw a clear understanding of the flow when velocity is increased.
- There is no significant change in the pressure plot .