Simulation Example - Falling Sphere Viscometer

Overview

A falling-sphere viscometer is a device used to measure the viscosity of a fluid by measuring the time required for a spherical ball to fall a certain distance under gravity through a tube filled with the fluid whose viscosity is to be determined. When the sphere is dropped, the sphere experiences three forces: its weight, the buoyancy force and the drag force. Of these three forces, we will be analyzing the drag force as it is directly related to the fluid viscosity. To simplify the problem, we will simulate laminar flow over a sphere and analyze the drag force experienced by it for different fluids. The setup consists of a solid sphere, fixed in space, and the fluid flowing over the sphere. The moving fluid exerts a pressure force and a viscous force on the surface of the sphere. The pressure force acts in a direction normal to the surface of the sphere, while the viscous force acts tangential to the surface of the sphere. The sum of the pressure and viscous forces is the resultant drag force acting on the surface of the sphere. The aim of this simulation is to analyze the pressure forces and the wall shear stresses acting on the sphere's surface for fluids with different viscosities.

Objectives

In this simulation example, you will learn:

• How to simulate the flow over a sphere in Ansys Fluent and compute the resulting drag forces
• How to create and analyze pressure and wall shear stress contours
• How to change and assign different fluid materials

Setup

Download the mesh file needed for setting up the simulation and the associated Case and 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 use the corresponding initial and final Case and Data files.

Alternate video link.

Results and Discussion

Let’s now analyze the simulation results and understand the physics of a sphere moving through a fluid.