Flow over a cylinder
AIM :
To simulate the flow over a cylinder for the conditions :
- To calculate the baseline case Reynolds number.
- To run a baseline simulation and then calculate the Reynolds number. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
- To create animations for pressure-velocity for all the three Reynolds number.
- To explain and discuss observations
INTRODUCTION:
What is flow simulation ? : Flow simulation is a form of computational fluid dynamics which digitally replicates flows in surface water or collection systems. Performing flow simulation allows for the prediction and analysis of how a flow might be impacted by complex geometry in an operational environment.
Formula used :
Re = rho*U_inlet*D/mu
Re = Reynolds Number
D = cylinder diameter
mu = dynamic viscosity
rho = density
METHODOLOGY :
MODELLING :
Cylinder dimensions:
Diameter : 0.03 m
Length : 0.05 m
FLOW SIMULATION :
Calculation required :
Diameter : 0.03 m
Length : 0.05 m
Air is considered as fluid & Inlet velocity = 10 m/s
Re = rho*U_inlet*D/mu
Re = Reynolds Number
D = cylinder diameter = 0.03 m
mu = dynamic viscosity = 1.825 x 10-5 kg/m-s
rho = density = 1.204 Kg/m^3
Re = 1.204*10*0.03/ 1.825x10-5
Re = 19,792
Flow duration= Cylinder length / velocity
Flow duration = 0.05/10
Flow duration = 0.005 s
End time = Flow duration *2 = 0.005*2 = 0.01s
Case 1:
Reynolds number increased by 20%
Re 1 = 1.20 * 19792
Re 1 = 23,750.4
Flow velocity = 23,750.4 x 1.825 x 10-5 / 1.204 x 0.03
Flow velocity = 12 m/s
Flow duration = 0.05/12
Flow duration = 0.0042 s
End time = 0.0083 s
Case 2:
Reynolds number increased by 40%
Re 2 = 1.40 * 19792
Re 2 = 27,708.8
Flow velocity = 27,708.8 x 1.825 x 10-5 / 1.204 x 0.03
Flow velocity = 14 m/s
Flow duration = 0.05/14
Flow duration = 0.0036 s
End time = 0.0071 s
Case 3:
Reynolds number increased by 100%
Re 3 = 2 * 19792
Re 3 = 39,584
Flow velocity = 39,584 x 1.825 x 10-5 / 1.204 x 0.03
Flow velocity = 20 m/s
Flow duration = 0.05/20
Flow duration = 0.0025 s
End time = 0.005 s
| Properties | Baseline | case 1 | case 2 | case 3 |
| Reynolds Number | 19,792 | 23,750.4 | 27,708.8 | 39,584 |
| Velocity (m/s) | 10 | 12 | 14 | 20 |
| End time (s) | 0.01 | 0.0083 | 0.0071 | 0.005 |
Fluid : Air
Flow : External
Baseline simulation results :
Velocity : Pressure :
Case 1 simulation results :
Velocity : Pressure : 
Case 2 simulation results :
Velocity : Pressure : 
Case 3 simulation results :
Velocity : Pressure : 
Results and Observations :
From the velocity and pressure profile, it is observed that the velocity and pressure increases as Reynolds number increases. The velocity profile almost reamins the same in visual manner but each case has its own intensities range which varies a lot. But pressure profile various a bit from one another but the range remains almost the same for all the scenarios.