Profile Macro: Pressure Profile

Profile Macro, UDF, Pressure Profile — ANSYS Fluent CFD Simulation

Description

This project implements the Profile macro through a User-Defined Function (UDF) to create a realistic pressure distribution in an urban CFD simulation using ANSYS Fluent. Rather than applying a single uniform inlet pressure, the DEFINE_PROFILE macro defines a height-dependent pressure profile that captures the natural variation of atmospheric pressure with altitude — a boundary condition the standard interface cannot express directly. The case is demonstrated on a simplified urban environment, where accurate inlet conditions matter for realistic airflow. Within the User-Defined Functions (UDF): Beginner CFD Training Package, this project introduces the DEFINE_PROFILE macro, teaching how to set a spatially varying boundary condition through code.

Methodology

The 3D urban geometry is modeled in Design Modeler and meshed in ANSYS Meshing with a structured grid of 118,400 cells. The core of the project is a custom implementation of atmospheric pressure variation: a pressure function based on height (the Y-coordinate) is written and applied at the inlet boundary through the DEFINE_PROFILE macro, integrating an atmospheric-pressure model into the urban flow simulation. The UDF process is covered step by step: writing the custom pressure-profile function, implementing the DEFINE_PROFILE macro, compiling and loading the UDF into ANSYS Fluent, and setting up the inlet boundary condition to use the custom profile.

Analysis

After running the simulation, the results are analyzed to evaluate how well the UDF creates a realistic pressure distribution. Post-processing includes pressure contours at the inlet boundary and on cross-sectional planes, vertical pressure-profile plots at the inlet and central domain locations, and a comparison of the UDF-generated profiles against theoretical atmospheric models to confirm the profile is correct. From these you can see how the height-dependent inlet pressure shapes the urban airflow more realistically than a uniform value would. This kind of custom profile improves the fidelity of urban airflow and tall-building aerodynamics, with applications from city planning to pollution-dispersion studies. By the end of this project, you'll be able to write a custom height-dependent profile function, implement the DEFINE_PROFILE macro, compile and load the UDF into ANSYS Fluent, and verify a UDF-generated boundary profile against a theoretical model.