Flow over a cylinder
Simulation of the flow over a cylinder with different reynolds number.
A cylinder with followig dimensions are created in solidworks.
- Diameter = 40mm
- Length = 50mm
- Surface roughness is taken as zero.
- Gravity is not considered.
Formula to calculate the baseline case Reynolds number.
Re = rho*U_inlet*D/mu
where
D= cylinder diameter in m
mu = dynamic viscosity in kg/ms
rho = density in kg/m^3
U_inlet= inlet velocity in m/s
Air is the working fluid in our simulation.
- Density of air approx 1.225 Kg/m^3[according to ISA (International Standard Atmosphere)].
- Dynamic viscosity of air is 1.81x10^(-3) Kg/ms at temperature 300 k pressure 1 atmosphere.
The velocity of the air is calculated by using the formula for reynolds number.
The computational domain has a length of 300mm. Thus the flow through time is given as the time taken for the velocity to reach the end of computational domain. The end time is taken as twice that of flow throught time.
The calculations are as follows for Re=20,40and 100
As er the calculations the For Re=20,40,100
- velocity=0.0074, 0.0148, 0.0369 m/s in x direction.
- Flow through time=40.54, 20.27, 8.13 s
- End time= 81, 40.54, 16.26 s respectively.
While conducting the analysis in the simulation wizard the total analysis time is equal to the end time obtained.
The variable pressure and velocity for the respective Reynolds number is shown below.
For Re=20
Variable pressure plot
Click the below link for animation
Velocity plot
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For Re=40
Variable pressure plot
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Velocity plot
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For Re=100
Variable pressure plot
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Velocity plot
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Observations
- Inlet velocity in x direction increaseswith the increase in reynolds number, thus increasing the flow of air over the cylinder.
- The Relative pressure variation does not varry to a large extent for the reynolds numbers taken.
- It is observed that the high pressure is created on the surface facing the inlet velocity.
- The velocity variation in the above animations has different velocity profiles, when the velocity is larger the velocity profile is longer behind the cylinder surface and it is approximately zero nearer to the cylinder surface [The surface which is not in contact with inlet velocity].For higher values of the velocity waves are created behind the cylinder.