Pipe flow simulation

Aim : - Run a pipe flow simulation with an inlet Reynolds number of 100,1000 and 10,000.

Objective : -

1. Place line probes at 95%, 90% and 85% of the pipe length.

2. Compare the normalized velocity profile at each of these locations

3. Normalize the velocity profile by the inlet velocity.

Theory: -

• The Reynolds number is the ratio of inertial forces to viscous forces and is a convenient parameter for predicting if a flow condition will be laminar or turbulent. It can be interpreted that when the viscous forces are dominant (slow flow, low Re) they are sufficient enough to keep all the fluid particles in line, then the flow is laminar. Even very low Re indicates viscous creeping motion, where inertia effects are negligible. When the inertial forces dominate over the viscous forces (when the fluid is flowing faster and Re is larger) then the flow is turbulent.
  • Laminar flow. For practical purposes, if the Reynolds number is less than 2000, the flow is laminar.
  • Transitional flow. At Reynolds numbers between about 2000 and 4000 the flow is unstable as a result of the onset of turbulence. These flows are sometimes referred to as transitional flows.
  • Turbulent flow. If the Reynolds number is greater than 4000, the flow is turbulent. Most fluid systems in nuclear facilities operate with turbulent flow.
• It is defined as:
  
  • `Re = (rhoVD)/mu`
  • Where
    • V is the flow velocity,
    • D is a characteristic liner dimension (whitch is equal to the diameter of pipe in pipe flow)
    • `rho` is fluid density
    • `mu`is dynamic viscosity
      

Procedure : -

1. Go to the part and model a pipe of inner diameter 38mm and outer diameter 40mm with the length of 1m
2. Make three sketch (line) at the distance of 50mm , 100mm and 150mm from one end and assume this end as exit.
3. Go the flow simulation and close the pipe using lids
4. Make a new project pipe_flow
5. Go to input data and select water as the fluid with default input data
6. Calculate the velocity corresponds to the reynolds number 100 , 1000 and 10000 using reynolds number formulae given in theory
   • `Re = (rhoVD)/mu`
   • Density of water at 20 degree celsius is 998.23 kg/m^3
   • Dynamic viscosity of water at 20 degree celsius is 0.001 Ns/m^2
   • D(Diamter) of pipe is 38mm which is 0.038m
     • Put the value of reynolds number we get velocity of water 0.0026m/s for 100 , 0.026 m/s for 1000 and 0.26m/s for 10000 reynolds number
7. Add boundary conditions to the pipe i.e static pressure at the outlet , real wall and inlet velocity and inlet
8. Edit the mesh size to 20 , 20 in x and y direction and 100 in z direction
9. Go to results and add a cut plot in xy plane at a distance of 0.95m from inlet and add three xy plot for sketchs
10. Go to new parametric study and add input as velocity in output variables all the plots and in scenario create 2 more degine points and change the velocity to 0.026m/s and 0.26m/s

Results

Cut plots

• For Reynolds number 100

• For Reynolds number 1000

• For Reynolds number 10000

Velocity profiles

• Velocity profile at 95% distance
  

• Velocity profile at 90% distance

• Velocity profile at 85% distance

Conclusion

For reynolds number 100 and 1000 the flow is laminar so the smooth circular contours are formed in cut plot and for reynolds number 10000 the flow is turbulent flow so there is a turbulance is low and different velocity can be find at same radius in different direction

From velocity profiles we can see that the velocity is very less near the surface of the pipe and increase as we go the the centre and max at the pipe central line . The velocity profile is becoming more parabolic as we increase the inlet velocity/reynolds number .