Flow over a cylinder

                                                          Flow over Cylinder

 

AIM: To simulate Air flow over cylinder to obtain Pressure and Velocity profile and to increase the Reynold’s number by 20, 40 and 100 % to vary the velocity of Air.

Concept: This flow simulation over the cylinder is used to obtain the reaction of air flow over the cylindrical cross-sectional profile, the pressure and velocity behavior of air.

The Reynolds number is obtained for the velocity of air over the cylinder from the first instance and then the Reynolds number is increased by 20, 40, 100% and their corresponding velocity and pressure values are obtained.

Reynolds number are basically a unitless quantity that which is used to find the nature of flow of a substance. The output obtained from Reynolds number will define whether the flow of substance is Laminar or turbulent. If the flow is laminar then represent a smooth and frictionless flow of the substance over the boundary layer. In other case if the flow is turbulent then the flow is said to have friction contact at the boundary layers which is due to large amount of kinetic energy.

Formula used:

                                                             `Re = (ρ * U * D) / µ`

Where,

    Re- Reynolds number

    ρ – Density of substance (in our case air)

    U – inlet velocity of substance

    D – Diameter of the cross-sectional profile

    µ - Dynamic viscosity of substance

Objective of the project: -

• To run a base line simulation to investigate the Air flow over the cylinder
• To obtain the Reynolds number of the initial velocity value.
• To increment the Reynolds number by 20, 40, 100 % and then obtain their corresponding Air velocity values.
• To plot the velocity and pressure for each values of velocity.
• To make sure that the end time set for the simulation compensate with velocity with which the air travels to cover the profile to obtain the complete simulation.

Body of content: -

The substance is selected as AIR

Initial condition

Inlet velocity (U) = 10 m/s

Density of air (ρ) = 1.225 kg/m^3

Diameter of the profile (D) = 1 m

Dynamic viscosity (µ) = 1.81 * 10^ (-5) kg/(m-s)

From the above formula Re = 676795.6

Time = 0.1 sec in which the air will travel the 1 m in the profile completely

                                                                   Velocity

                                                                      Pressure

                             

Increment by 20%

Re = 676795.6 * 1.2 = 812154.7

Then U = 12 sec

Time is set to 0.12 sec in which the air will travel the 1 m in the profile completely

                                                                   Velocity

                           

                                                                 

                                                                              pressure

                                       

Increment by 40%

Re = 676795.6 * 1.4 = 947513.84

Then U = 14 sec

Time is set to 0.14 sec in which the air will travel the 1 m in the profile completely

                                                                  Velocity

                               

                                                         

                                                                                   Pressure

                                           

Increment by 100%

Re = 676795.6 * 2 = 1353591.2

Then U = 20 sec

Time is set to 0.2 sec in which the air will travel the 1 m in the profile completely

                                                                       Velocity

                                              

                                                                           Pressure

                                                

Velocity video : - https://youtu.be/LhDSjcROcnc

Pressure video : - https://youtu.be/HcFO4Lv7nL0

From the over profiles we can see that the boundary layer thickness for both pressure as well as velocity profile is very high as the velocity of the air keeps on increasing. Due to the increase in the Boundary layer thickness the flow can be more turbulent as we know that the flow becomes turbulent with increase in Reynolds number.

Conclusion: The flow over the cylinder is simulated and from the graph we can say that the flow becomes laminar or turbulent with respect to either change in velocity as well as Reynolds number.