Question

Which of these terms in the pressure equation become zero?

(a) Viscous and pressure terms

(b) Viscous and transient terms

(c) Pressure and source terms

(d) Source and transient terms

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This interesting question is from Incompressible Flows topic in portion Incompressible Flows & Compressible Flows of Computational Fluid Dynamics

Answer 1

The correct answer is:

(d) Source and transient terms

In the context of incompressible flows, when solving for the pressure equation (typically in algorithms like SIMPLE), the source terms and transient terms often become zero under steady-state conditions.

Here’s why:

• Source terms typically represent external forces or volumetric sources (like heat sources or body forces), and in steady-state analysis or simplified cases, these terms can be neglected or assumed to be zero.

• Transient terms represent the time-dependent changes in flow properties. In steady-state problems, these terms also become zero because the solution no longer changes with time.

Explanation of other options:

• (a) Viscous and pressure terms: These terms don't generally become zero. The viscous terms (involving velocity gradients) are essential in momentum equations, and the pressure terms are crucial for the pressure-velocity coupling in incompressible flow.

• (b) Viscous and transient terms: While transient terms can become zero in steady-state analysis, the viscous terms usually do not. These terms are necessary for describing the viscous forces in the flow.

• (c) Pressure and source terms: The pressure terms generally do not become zero because pressure is a primary field in incompressible flow, and the source terms can be nonzero depending on the physical setup.

Correct Answer: (d) Source and transient terms