Project on Flow Over Cylinder

Simulating flow over a cylinder for different reynolds numbers

To calculate the baseline case reynolds number. we have the following formula

Re = rho*U_inlet*D/mu

• D = cylinder diameter
• mu = dynamic viscosity
• rho = density
• U_inlet=Inlet velocity

Thus for Re = 20, 40 and 100 we are runing the transient flow simulation also called as time dependent flow simulation.

Air is the working fluid in our simulation hence for inlet velocity calculation we need density and dynamic viscocity of air.

• 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.

Thus calculating the inlet velocities by substituting the above values in the reynolds equation ,we get corresponding velocities as 0.00738 m/s ,0.0147 m/s and 0.0369 m/s. Here the inlet velocity is in the x direction.

The computational domain has a length of 360 mm in x direction thus for the above set of velocities the flow through time would be 50 sec for each domain.

Cylinder dimensions in mm

• Diameter of the cylinder is 40 mm.
• Length of the cylinder is 60 mm.
• Surface roughness is taken as zero.
• Gravity is not considered.

For the above conditions the velocity and the relative pressure plot results are as follows

For Reynolds number = 20

Relative Pressure cut-plot in top view

Click here for Animation

velocity cut-plot

click here for animation

For Reynolds number = 40

Relative Pressure cut-plot in top view

Click Here For Animation

Velocity cut_Plot

Click Here For Animation

For Reynolds number = 100

Relative Pressure cut-plot in top view

Click Here For Animation

Velocity cut-plot

Click Here for Animation

OBSERVATIONS

1. As the reynolds number increases the inlet velocity in x direction increases ,thus increasing the flow of air over the cylinder.
2. The Relative pressure variation in the above animation does not varry to a large extent for the reynolds number taken. It is observed that high pressure is created on the surface facing the inlet velocity.