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Introduction to Fluid Analysis

10.1 Introduction
Flow simulations are widely used in engineering applications ranging from flow around
airplane wings and hydraulic turbines to flow in blood vessels and other circulatory sys-
tems (see Figure 10.1). We may gain a better understanding of the motion of fluid around
objects as well as the fluid behavior in complex circulatory systems by conducting fluid
analysis. Computational fluid dynamics (CFD) simulation complements experimental test-
ing, helps reduce cost and turnaround time for design iterations, and has become an indis-
pensable tool whenever practical design involving fluids is required. In this chapter, we
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will discuss fluid analysis using ANSYS Workbench.

10.2 Review of Basic Equations

We begin by briefly reviewing the fundamentals of fluid mechanics.

10.2.1 Describing Fluid Motion

In fluid dynamics, the motion of a fluid is mathematically described using physical quanti-
ties such as the flow velocity u, flow pressure p, fluid density ρ, and fluid viscosity ν. The
flow velocity or flow pressure is different at a different point in a fluid volume. The objec-
tive of fluid simulation is to track the fluid velocity and pressure variations at different
points in the fluid domain.

10.2.2 Types of Fluid Flow

There are many different types of fluid flow. A flow can be compressible (ρ ≠ constant)
or incompressible (ρ = constant), viscous (ν ≠ 0) or inviscid (ν = 0), steady (∂u/ ∂t = ) 0 or
unsteady (∂u/ ∂t ≠ ) 0 and laminar (streamline) or turbulent (chaotic). Furthermore, a fluid
can be Newtonian (if the viscosity depends only on temperature and pressure, not on
forces acting upon it; in other words, shear stress is a linear function of the fluid strain rate)
or non-Newtonian (if the viscosity depends on forces acting upon it, i.e., shear stress is a
nonlinear function of the fluid strain rate).

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