Compressible Flow in a Convergent-Divergent Nozzle
In this project, the airflow will enter the convergent-divergent nozzle with a pressure of 70 bars and the Mach number of 0.2 with a temperature of 2735 K.
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Convergent-Divergent Nozzle Introduction
A de Laval nozzle (or convergent-divergent nozzle, CD nozzle, or con-di nozzle) is a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass shape. It is used to accelerate a hot, pressurized gas passing through it to a higher supersonic speed in the axial (thrust) direction, by converting the heat energy of the flow into kinetic energy. Because of this, the nozzle is widely used in some types of steam turbines and rocket engine nozzles.
Compressible Flow Project description
In this project, the airflow will enter the convergent-divergent nozzle with a pressure of 70 bars and the Mach number of 0.2 with a temperature of 2735 K. after passing the throat zone, the airflow will gain speed and lose its temperature as it passes through the diffuser. The standard k-epsilon model with standard wall function is used to solve fluid flow equations. The energy model is activated and the ideal gas equation is exploited to calculate the density changes in the computational domain.
geometry and mesh
The geometry of this model is designed in ANSYS design modeler and meshed in ANSYS meshing®. The mesh type used for this geometry is unstructured and has great accuracy in sensitive sections. Also, the element number is 898906.
Compressible Flow CFD Simulation Settings
The key assumptions considered in this project are:
- Simulation is done using Density-based solver.
- The present simulation and its results are steady.
- The effect of gravity is ignored.
The applied settings are summarized in the following table.
|Near wall treatment||Standard wall function|
|(Compressible Flow)||Boundary conditions|
|Gauge pressure||7000000 Pa|
|Gauge pressure||101325 Pa|
|Walls||wall motion||stationary wall|
|New wall||Heat flux||0 W/m2|
|(Compressible Flow)||Solution Methods|
|Spatial discretization||Flow||First order upwind|
|Turbulent kinetic energy||First order upwind|
|Turbulent Dissipation rate||First order upwind|
|Gauge pressure||7000000 Pa|
|Turbulent kinetic energy||7.265146 m2/s2|
|Turbulent Dissipation rate||5107.493 m2/s3|
The contours of pressure, temperature, velocity, Mach number, etc., are presented. As it is clear from the contours, the airflow loses its heat after passing through the nozzle opening. It increases its speed as the nozzle opening becomes more extensive than before ( in the divergent section), the volume of passing air increases. Due to the constant air mass, its density decreases, so according to the continuity law, the velocity increases along with the nozzle. As can be seen from the Mach contour, the Mach number in the nozzle throat according to the design mode is equal to one and then increases in the nozzle’s divergent part. The Mach number distribution is not uniform in this section due to the nozzle geometry lines’ fracture.
However, it has its maximum value at the nozzle output, i.e., where the pressure is precisely at its minimum. There is a border point separation point downstream of the throat. Normal shock also occurred in the throat.
There are a Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.