Week 2 - Converging diverging nozzle

A nozzle is a relatively simple device, just a specially shaped tube through which hot gases flow. Ramjets and rockets typically use a fixed convergent section followed by a fixed divergent section for the design of the nozzle. This nozzle configuration is called a convergent-divergent, or CD, nozzle. In a CD nozzle, the hot exhaust leaves the combustion chamber and converges down to the minimum area, or throat, of the nozzle. The throat size is chosen to choke the flow and set the mass flow rate through the system. The flow in the throat is sonic which means the Mach number is equal to one in the throat.

The completed geometry in SpaceClaim:

Meshing:

The mesh contains 7263 nodes and 6991 elements.

Simulation Setup:

Boundries:

inlet: pressure-inlet with a gauge pressure and initial gauge pressure as 101325 Pa (1 atm), and a temperature of 300K.

outlet: pressure-outlet with a gauge pressure of 2735.775 Pa.

axis: symmetry boundary condition.

wall: wall boundary condition.

Results:

Temperature Contour:

Pressure Contour:

As air enters the converging part of the nozzle, the velocity increases rapidly and as a result, the pressure of the air around the throat reduces to the lowest in the entire domain. After expansion, pressure increases slightly but not as near the inlet.

Velocity Contour:

Mach Number:

The chart shows the variation of mach number throughout the axis of the nozzle (or symmetry axis), the mach number cross 1 around 0.25m from the inlet of the nozzle.