From water sprinklers and vacuum systems to gas stoves and jacuzzies to carburetors and fuel spray systems, nozzles are common in many engineering applications. Nozzles are geometrical configurations of varying cross-sectional area whose intent is to control the characteristic properties of the fluid that is flowing through it. They are most often used to modify (increase) the velocity of the flowing fluid. At its core, nozzles work on the principles of conservation of mass and momentum. For incompressible flows where density is constant, mass conservation dictates that the velocity of the fluid is inversely proportional to the cross-sectional area of the nozzle. This means that as the cross-sectional area of the nozzle decreases, the velocity of the fluid increases. If we further assume that the viscosity of the fluid is negligible, i. e., the flow is inviscid, the conservation of linear momentum reduces to the famous Bernoulli’s equation. The aim of this example is to understand the role of conservation laws in determining the physics of incompressible air flow through a converging nozzle.
In this example, simulations are performed to compute the flow of air through a converging nozzle. You will learn how to set up 2D axisymmetric simulations in two situations: (1) with inviscid assumption, and (2) without inviscid assumption. Finally, you will understand how to interpret the results of the two simulations by comparing them with theory and with each other to identify differences and their causes.
Download the Mesh file needed for setting up the simulation and the associated Case & Data files here. Follow the instructions below to set up this simulation in Ansys Fluent starting with a Mesh file. In case you face any issues setting up or running the simulation, please refer to the corresponding initial and final Case and Data files.
Let us now analyze the simulations and understand the physics of incompressible air flow through a converging nozzle.