CFD Assignment Brief

Assignment Details

Assessment

Answer ALL the following questions:

1. Mathematical models

a. Please list the governing equations of fire simulation and explain the physical meaning of each equation. To solve the equations, do we need to consider boundary conditions? Give three typical boundary condition examples.
(12 marks).

b. Explain the reasons why CFD codes are written in low speed solver and high speed solvers. A student is simulating an object flying at a velocity of 290m/s in the air using FDS6. Can this student obtain acceptable results and why? (7 marks)

c. What is background pressure used in FDS? Can different rooms have different background pressures? Please explain using a formula and define two pressure zones using FDS input instructions. (6 marks)

2. Turbulence

a. Explain the reasons why turbulence models are required in CFD. (5 marks). What are Large Eddy Simulation (LES), Reynolds-Averaged Navier-Stokes (RANS), and Direct Numerical Simulation (DNS)?(6 marks).List and explain the parameters of the LES model used in the FDS software. (4 marks).

b. Based on Kolmogorov’s turbulence theory, explain the mesh resolution required by DNS and LES (4 marks). Critically compare their pros and cons (6 marks).

3. Combustion

a. Why a combustion model is required in fire simulations (6 marks)? Using the parameters given in the FDS theoretical manual, explain what are the major assumptions in the mixture fraction approach to simulate a diffusion flame (6 marks)? Can FDS simulate pre-mixed combustion and explosion (3 marks)?

b. Mixture fraction Z is defined as

Where

– mass fraction of fuel
– mass fraction of oxygen
– fuel mass fraction in the fuel stream
– mass fraction of oxygen at infinity
– ratio of oxygen and fuel molecular weight in stoichiometric mixture

It is known that =0.94, =0.23 and s = 0.64. Calculate Z on the flame front (5 marks). If at some position = 0.78, calculate Z at this position (5 marks). When use a value that is not given, please explain the reason for taking that value.

4. Numerical techniques

a. Write procedures to numerically solve the 1D unsteady heat conduction equation using explicit scheme (8 marks) and implicit scheme (7 marks).

b. Consider a thin insulated rod 0.11 m long with k = 0.835×10-4 m2/s. Let Δx = 0.022 m and Δ t = 0.1 seconds. At t=0 the temperature of the rod is zero. If one of the two ends is maintained at a temperature of zero and the other end is raised to a constant temperature 24°C immediately after 0s. Calculate the temperature distribution at t = 1 sec (10 marks).

Total maximum mark for this assignment 100

• Submit all drawings and calculations with your answers.
• Reasonable data of student’s own choice should be used in cases where assignment does not provide sufficient information. The choice should be explained.

The word limit is 3,000 per assessment – indicative only (+/-10%). This excludes footnotes but includes quotations. The word count must be printed on the top right hand corner of your work.

Remember:

•   You must answer the questions set
•   You must demonstrate that you have met the learning outcomes
•   As you construct and present your answers, consider the assessment criteria

Presentation Instructions

It is your responsibility to ensure that your work is neatly and accurately presented.

The work must be:
•   Word-processed
•   Single sided
•   1.5 or double line spaced
•   Ariel 12 point font
•   Justified
•   Page numbered
•   On A4 paper
•   Margins left and right 3cm
•   Attached to a cover sheet.

Marks may be deducted for failure to follow these instructions. Please look at the Student Guide to Assessment for more information.

Referencing

All academic writing must be referenced. If you use other people’s ideas without referencing them you are plagiarising their work.

Either:

Use the Harvard system of referencing within your text. This will take the form: surname, year of publication, page number, and is enclosed within brackets, for example (Bradley 1998, 277). At the end of your essay you should provide an alphabetical list of all the works you cite

Or:

Use the Numeric System of referencing within your text. At every point in the text where a reference is made, insert a number (in brackets or superscript) and then list the references numerically at the end of your work.

Plagiarism

The use of work produced for another purpose by you, working alone or with others, must be acknowledged.

Copying from the works of another person (including Internet sources) constitutes plagiarism, which is an offence within the University’s regulations. Brief quotations from the published or unpublished works of another person, suitably attributed, are acceptable. You must always use your own words except when using properly referenced quotations.

You are advised when taking notes from books or other sources to make notes in your own words, in a selective and critical way.

Submission

Your work must be submitted with:
• a front cover sheet (detailing the module code and title, coursework title, module name and student name, word count, date submitted).

Learning outcomes
This assessment will test your ability to meet the learning outcomes as described in your module booklet, specifically:

1.   Effectively use CFD software associated with the module
2.   Carry out post processing of calculated data and understand procedures of validation and verification of numerical solutions
3.   Critically review specialist CFD literature
4.   Model fires in a realistic built environment using CFD
5.   Explain of the limitations of CFD software

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