Flow over a backward facing step

OBJECTIVE:

  • To setup flow over a backward facing step for 3 different mesh size using preprocessor as Converge studio and paraview to simulate the data
  • Show pressure and velocity contours for the different mesh size.
  • Show the plots of velocity, pressure, mass flow rate and total cell count for all the 3 base mesh sizes.

PROFILE GEOMETRY:

INITIAL BOUNDARY CONDITIONS:

  1. The flow is general flow.
  2. Air contains a predefined mixture of oxygen and nitrogen.
  3. The pressure at inlet and outlet is 110325.0 Pa and 101325.0 Pa.
  4. The Prandtl number is 0.9 and the Schmidt number is 0.78.
  5. Total no of the cycle performed is 15000.

MESH SIZES:

  • dx = dy = dz =2e-3m
  • dx = dy = dz =1.5e-3m
  • dx = dy = dz =1.2e-3m

RESULTS:

The results after preprocessing and simulating the profile are given below.

BASE MESH SIZES:

Different base mesh grids are provided below using PARAVIEW

                                                        (dx = dy = dz =2e-3m)

                                                        (dx = dy = dz =1.5e-3m)

                                                       (dx = dy = dz =1.2e-3m)

VELOCITY CONTOURS:

Different velocity countours for different mesh grids are provided below using PARAVIEW

                                                       (dx = dy = dz =2e-3m)

                                                       (dx = dy = dz =1.5e-3 m)

  

                                                         (dx = dy = dz =1.2e-3m)

PRESSURE CONTOURS:

Different Pressure countours for different mesh grids are provided below using PARAVIEW

                                                   (dx = dy = dz =2e-3m)

                                                        (dx = dy = dz =1.5e-3m)

 

                                                         (dx = dy = dz =1.2e-3m)

TOTAL CELL COUNT PLOT:

                                                      (dx = dy = dz =2e-3m)

  • Above plot shows the total cells and the variation in cell region by  using 4 processors

                                                       (dx = dy = dz =1.5e-3m)

  • Above plot shows the total cells and the variation in cell region by  using 4 processors

                                                   (dx = dy = dz =1.2e-3m)

  • Above plot shows the total cells and the variation in cell region by  using 4 processors
  • Total cell count is 5000.

 

PRESSURE PLOT:

                                                    (dx = dy = dz =2e-3m)

  • The above graph shows the total pressure at boundary id 1 ie, the inlet is at steady condition throughout the cycle
  • The total pressure at boundary id 2 ie, the outlet attains the steady state after 1800 cycles.

                                                    (dx = dy = dz =1.5e-3m)

  • The above graph shows the total pressure at boundary id 1 ie, the inlet attains steady condition after 600 cycles.
  • The total pressure at boundary id 2 ie, the outlet attains the steady state after 3500 cycles.

 

                                                  (dx = dy = dz =1.2e-3m)

  • The above graph shows the total pressure at boundary id 1 ie, the inlet attains steady condition after 400 cycles.
  • The total pressure at boundary id 2 ie, the outlet attains the steady state after 2500 cycles.

TOTAL MASS PLOT:

                                                    (dx = dy = dz =2e-3m)

  • The above graph shows the total mass flow rate at boundary id 1 ie, the inlet attains steady condition after 3000 cycles.
  • The total mass flow rate at boundary id 2 ie, the outlet attains the steady state after 3000 cycles.
  • the graph shows the symmetry at inlet and outlet since in both cases the mass flow rate attains the steady state after similar cycles.

                                                   (dx = dy = dz =1.5e-3m)

  • The above graph shows the total mass flow rate at boundary id 1 ie, the inlet attains steady condition after 3000 cycles.
  • The total mass flow rate at boundary id 2 ie, the outlet attains the steady state after 3000 cycles.
  • the graph shows the symmetry at inlet and outlet since in both cases the mass flow rate attains the steady state after similar cycles.

 

                                                  (dx = dy = dz =1.2e-3m)

  • The above graph shows the total mass flow rate at boundary id 1 ie, the inlet attains steady condition after 2500 cycles.
  • The total mass flow rate at boundary id 2 ie, the outlet attains the steady state after 2500 cycles.
  • the graph shows the symmetry at inlet and outlet since in both cases the mass flow rate attains the steady state after similar cycles.

VELOCITY PLOTS:

                                                (dx = dy = dz =2e-3m)

  • The above graph shows the avg velocity flow rate at boundary id 1 ie, the inlet attains steady condition after 1500 cycles.
  • The velocity rate at boundary id 2 ie, the outlet attains the steady state after 1500 cycles.

                                                  (dx = dy = dz =1.5e-3m)

  • The above graph shows the avg velocity flow rate at boundary id 1 ie, the inlet attains steady condition after 4000 cycles.
  • The velocity rate at boundary id 2 ie, the outlet attains the steady state after 5000 cycles.

 

                                                        (dx = dy = dz =1.2e-3m)

  • The above graph shows the avg velocity flow rate at boundary id 1 ie, the inlet attains steady condition after 3000 cycles.
  • The velocity rate at boundary id 2 ie, the outlet attains the steady state after 4000 cycles.

CONCLUSIONS:

  • The separation in the geometry caused in the sudden increase in the area which results in the formation of recirculation region due to which the velocity of air decreases and since due to this phenomenon the pressure increases as the area increases. 
  • Pressure contour shows that the pressure up to the step decreases and after the step the pressure increases due to the recirculation of air.
  • The velocity of the air at the inlet is high compared to the outflow because the increase in the area of geometry, velocity decreases since fluid tries to fill the area and hence the flow of air gets distort which results in the reduction of the velocity.
  • The graph shows the symmetry in mass flow rate  at inlet and outlet 
  • The mass at inlet and outlet is conserved since the geometry doesn't contain any leaks. 

 

 

 


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The End