Fully Developed Turbulent Pipe Flow — Homework
Overview
When simulating internal fluid flows in complex geometries such a HVAC ducts, exhaust systems, water supply piping and many other systems, it is critical to provide the right set of boundary conditions to get the correct predictions. For example, in an automotive exhaust system like the one in the figure, by the time exhaust gases from the engine reach the catalytic converter, they exhibit a fully developed character. This is the situation where the boundary layers are fully formed and the fluid flow through the pipe/duct becomes independent of the length of the pipe. If you were to simulate the flow of these gases through the converter, the inlet conditions to the converter should consider this fully developed state of the gas flow to get accurate predictions of the flow physics. There are two ways of obtaining the fully developed conditions of the fluid flow:
- Simulate the entire flow path. Referring to the catalytic converter example, this method involves simulating the exhaust gases from the engine all the way to the converter. It is extremely resource-intensive to perform such a simulation.
- Use a precursor simulation. In this approach, a small section of the exhaust pipe is taken and simulated using periodic boundary conditions. By doing so, one can obtain the fully developed conditions of the fluid. These conditions can then be taken and imposed as inlet conditions in the simulation of the converter. This method is significantly less expensive.
Objectives
In this example, you will simulate a fully developed turbulent flow through a cylindrical pipe. You will learn how to set up a 2D axisymmetric simulation and impose translationally periodic boundary conditions with a pressure gradient.
Setup
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, then please use the corresponding initial and final Case and Data files.
Results and Discussion
Let’s now analyze the simulation and understand the fully developed turbulent flow in a circular pipe.