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[Solution]

This example is taken from Cornell University’s ANSYS AIM Learning Modules

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Contents

1. Problem Specification
2. Pre-Analysis
3. Geometry Creation
4. Mesh
5. Physics Setup
6. Results Evaluation
7. Validation

Problem Specification

Consider the case of a fluid flowing past a cylinder, as illustrated above. Obtain the velocity and pressure distributions when the Reynolds number is chosen to be 20. In order to simplify the computation, the diameter of the cylinder is set to 1 m, the x component of the velocity is set to 1 m/s and the density of the fluid is set to 1 kg/m^3. Thus, the dynamic viscosity must be set to 0.05 kg/m*s in order to obtain the desired Reynolds number.

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Pre-Analysis

Solution Domain

For an external flow problem like this, one needs to determine where to place the outer boundary. A square domain will be used for this simulation. The effects that the cylinder has on the flow extend far downstream. Thus, the distance to the outlet end boundary will be much larger than the distance to the inlet boundary.

Boundary Conditions

First, we will specify a velocity inlet boundary condition. We will set the left side of the outer boundary as a velocity inlet with a velocity of 1 m/s in the x direction. Next, we will use a pressure outlet boundary condition for the right side of the outer boundary with a gauge pressure of 0 Pa. Lastly, we will apply a no slip boundary condition to the cylinder wall. The aforementioned boundary conditions are illustrated below.

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Geometry Creation

In this video, you will learn how to create a computational flow domain around the cylinder.

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Mesh

In this tutorial, we will be using Physics-Aware Meshing. Physics-aware meshing helps automate and simplify your problem setup. With physics-aware meshing, the computational mesh is generated automatically based on the solution fidelity setting and the physics inputs.

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Physics Setup

In this video, you will learn how to create a new material and assign fluid flow conditions to the model.

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Results Evaluation

In this video, you will learn how to check velocity vectors, pressure change in the fluid domain and total pressure on the cylinder walls.

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Validation

This tutorial will be compared to results found in the Fluent – SimCafe tutorial based on the same problem. Below is the pressure contour from the SimCafe tutorial.

This can be compared to the pressure contour calculated in the simulation. Select the pressure contour created in the results section, then change the Coloring to Banded to match the display style in the image above.

The AIM solution not only has similar maximum and minimum values for pressure, but the shapes of the pressure contours are virtually identical.

Reference

Singleton, John Matthew, Jr., and Sebastien Lachance-Barrett. “FLUENT – Steady Flow Past a Cylinder.” Dashboard. Cornell University, 8 Feb. 2014. Web. 19 July 2017.