Week 2 - Converging diverging nozzle

Aim - To simulate the flow inside the CD or convergent divergent nozzle using the inlet and outlet pressure condition given.

Theory - The CD nozzle is a device that is used to accelerate the high pressure flows coming from the combustion chamber or reservoir to high velocity or supersonic flow if there is a favourable pressure gradient. 

Mainly it has three sections-

1) CONVERGENT SECTION-  IN this section the stationary high pressure fluid is accelarated to high subsonic mach number. In this section since the area is decreasing the velocty of the flowing gas will increase to high subsonic flow.

2) Throat region- This is the minimum area region of the cd nozzle here the flow reaches the sonic condition. So mach number equals 1. This condition is calledc as the critical condition or the nozzle is said to be choaked that means the mass flow rate3 through the nozzle will not increasen after this condition.

3) Divergent section- In this section since the area is also increasing the flow velocity increases to a high supersonic number. The static pressure drops as the flow is accelerated.

#) geometry creation-

The geometry was created in the design modeller using the lines and curves option and by giving the dimjensions of line and the curves.

Then the structure mesh is made in the fluent mesher- Face meshing option is used to create the structured mesh option.

In the fluent option we use the density based solver and steady based solver . Energy option is kept on and the viscous model is spalart Allmaras. 

iN THE MATERIAL OPtion the density if the air is changed from constant to ideal gas.

The boundary conditions are as follows-

In the inloet - The total gauge pressure is = 101325 pascals. The boundary condition is pressure inlet.

For outlet the gauge pressure is 2735.77 pascals.

The operating pressure is kept at 0 pascals.

Then hybrid initialization was done .

Thye solution method used is implicit formulation and for the flow and turbulent viscosity it is first order upwind.

Then iterations are carried out for 5000 iterations until convergence of the residuals of the variable are obtained-

tHE PRESSURE CONTOUR OBTAINED IS -

The temperature contour is -

The velocity contour is -

The mach number contour is -

The mach nnumber becomes 1 almost at the throat that is at 0.6 m from the inlet region.