Flow over a cylinder

Objective - Simulate the flow over a cylinder 

Theory

Reynolds number:-

1.  Ratio of internal force to viscous forces
2.  It is dimensionless number
3.  helps predict flow patterns in different fluid flow situations.
4.  At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be   turblent flow

The Reynolds number is defined as

• ρ is the density of the fluid (SI units: kg/m³)
• u is the flow speed (m/s)
• L is a characteristic linear dimension (m)
• μ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/(m·s))
• ν is the kinematic viscosity of the fluid (m²/s).

Laminar flow R < 2000

Transition flow 2000 < R > 4000

Turbulent flow R > 4000

Inputs

Cylinder Dia = 40mm = 0.04m

Air density = 1.2kg/m³

Dynamic viscousity = 1.825 x 10^(-5) N·s/m²

Reynolds number calculation

Re =(ρ x u x d)/μ

we have taken cylinder dia(d) instead of length L

As per given equation 

     ρ , d and μ are constant becouse we use Cylinder dia and air same for differnent simulation.

     so  

           (ρ x d)/μ = K (constant)

   now

       Reynolds number is directly proportion to Velocity of air.

    We have taken velocity is 10m/s

       Re = 10K=26300

   Now if Re increase Re by 20%

      Re = 12K = 31560

      velocity = 12m/s

 then 40%

     Re = 14K =36820

     velocity = 14m/s

  then 100%

     Re = 20K = 52600

     velocity = 20m/s

This show that if we increaes Re the velocity is also increase.

CYLINDER

Mesh 

Simulation

1. Velocity = 10 m/s

2. Velocity = 12 m/s

3. Velocity = 14m/s

4. Velocity = 20 m/s

Conlusion

As you see by increasing the Renolds number 

• Hardly change in pressure .
• vortices produce.