CFD INTRODUCTION AND CONTINUITY

Question 1

What does CFD STAND FOR?

Answer 1

Computational Fluid Dynamics

Question 2

What are the ADVANTAGES OF CFD?

Answer 2

• Low cost (Compared to a physical experiment and testing)
• Quicker results than manual testing - easy to introduce and adapt designs (iterations)
• Can simulate real conditions (Assuming initial and bounding conditions are accurately set up!)
• Can take readings at any point in the system (Physical experiments can only take readings at sensors)

Question 3

What is the NAVIER STOKES EQUATION?

Answer 3

INERTIA FORCES = PRESSURE FORCES + ▲VISCOUS FORCES + EXTERNAL FORCES

Question 4

What is a STRUCTURED GRID?

Answer 4

• All cells have the same number of nodes
• All grid lines must pass through all of the domain
• Restricted to simple geometries

Question 5

What is an UNSTRUCTURED GRID?

Answer 5

• Cells can be arranged in an arbitrary fashion
• No grid index and therefore no constraints on cell layout
• Can be used on complex geometry

Question 6

What are some EXAMPLES OF CFD BOUNDARY CONDITIONS?

Answer 6

• Wall interactions
• Specified suction or blowing at interfaces
• Inflow/Outflow pressure
• Interface conditions
• Symmetry and Periodicity

Question 7

Do INITIAL CONDITIONS AFFECT THE FINAL RESULTS?

Answer 7

NO, they only affect the convergence path i.e number of iterations (steady flow) or time steps (unsteady flow) needed to reach convergence
They are used to minimise simulation time by speeding up convergence

Question 8

When is a CFD SIMULATION CONSIDERED CONVERGED?

Answer 8

• When changes in solution variables between adjacent iterations are negligible
• The solution no longer changes with additional iterations
• Mass, momentum, energy, and scalar balances are obtained

Question 9

What are RESIDUALS?

Answer 9

The measure of the imbalance (error) in the conservation equations

Question 10

What affects the ACCURACY OF A CONVERGED SOLUTION? (3)

Answer 10

• Appropriateness and accuracy of the physical models
• Grid resolution and independence
• Problem setup

Question 11

What are some EXAMPLES OF POST-PROCESSING IN CFD?

Answer 11

• Vector plots
• Contour Plots
• Particle Tracking (streamlines)

Question 12

How many CARTESIAN COORDINATES POSITIONS ARE THERE?

Answer 12

6 - North, East, South, West, Top, Bottom

Question 13

What does MASS GAIN EQUAL?

Answer 13

Inflow - Outflow

Question 14

What is a SIMPLE CFD CONTINUITY QUALITY CHECK?

Answer 14

If there is no mass accumulation mass flow out should equal mass flow in