Recent Question/Assignment

Final mark awarded:_____
Assessment Cover Sheet and Feedback Form 2014/15
Module Code: NG3S224 Module Title: Design & Analysis Module Lecturer: Dr James Jewkes
Assessment Title and Tasks:
Computational Fluid Dynamics (CFD) : Ahmed Body Assessment No.
1 of 3
No. of pages submitted in total including this page: Completed by student Word Count of submission
(if applicable): Completed by student
Date Set: 02/03/2015 Submission Date: 24/04/2015 Return Date:
Part A: Record of Submission (to be completed by Student)
Extenuating Circumstances
If there are any exceptional circumstances that may have affected your ability to undertake or submit this assignment, make sure you contact the Advice Centre on your campus prior to your submission deadline.
Fit to sit policy:
The University operates a fit to sit policy whereby you, in submitting or presenting yourself for an assessment, are declaring that you are fit to sit the assessment. You cannot subsequently claim that your performance in this assessment was affected by extenuating factors.
Plagiarism and Unfair Practice Declaration:
By submitting this assessment, you declare that it is your own work and that the sources of information and material you have used (including the internet) have been fully identified and properly acknowledged as required1. Additionally, the work presented has not been submitted for any other assessment. You also understand that the Faculty reserves the right to investigate allegations of plagiarism or unfair practice which, if proven, could result in a fail in this assessment and may affect your progress.
Details of Submission:
Note that all work handed in after the submission date and within 5 working days will be capped at 40%2. No marks will be awarded if the assessment is submitted after the late submission date unless extenuating circumstances are applied for and accepted (Advice Centre to be consulted).
Work should be submitted as detailed in your student handbook. You are responsible for checking the method of submission.
You are required to acknowledge that you have read the above statements by writing your student number (s) in the box:
Student Number(s):
1 University Academic Integrity Regulations
2 Information on exclusions to this rule is available from Campus Advice Shops
Part B: Marking and Assessment (to be completed by Module Lecturer)
This assignment will be marked out of
This assignment contributes to 35 module are unlearning outcomes of the module).
100 %
% of the total module marks. The assignments in this
bonded (i.e. you must pass each element of assessment to pass each of the
Assessment Task: CFD analysis of an Ahmed body
Figure 1 – Ahmed Body (units in mm)
The Ahmed body (Figure 1, flow from left to right) is a popular model used by aerodynamicists to learn more about the behaviour of automotive flows. It is a highly simplified analogue of an automotive flow field, and consists of a bluff body, mounted on four legs to a stationary ground plane.
It was first defined and its characteristics described in the experimental work of Ahmed [1]. Two configurations with slant angles of f=25°and f=35°are considered as a test case. For this configuration, detailed Experimental Measurements have been performed by Becker, Lienhart and Stoots [3] in a low-speed wind-tunnel with a cross-section of 1.87x1.4 m2 (width x height) with an average velocity of 40 m/s. The test-section of the wind-tunnel was 3/4 open (only ground plate present). The distance between the body and the plate representing the ground is 50 mm.
In this assignment, you will build a model of an Ahmed body, using the geometry shown above, and run a steady, external flow computational fluid dynamics (CFD) simulation of the flow past the body.
You will need to write a report of no more than 2000 words, which shows that you have done the following:
1. Validated and verified your simulation (mesh convergence, simulation convergence, and validation) against established experimental data.
2. Investigated a number modifications to the geometry, and assess their relative impact upon drag reduction.
1 – Validation and verification of the baseline model
i) Create the Ahmed body geometry shown in Figure 1.
ii) Set up a steady, turbulent, external flow simulation of the flow past the Ahmed body, as described above. (You may wish to begin by running the model in 2D, moving to a 3D model later on).
iii) To ensure the quality of your model, you will need to do the following things:
a. Demonstrate simulation convergence.
b. Demonstrate mesh, and domain independence.
c. Validate your model against established data qualitatively and/or quantitatively.
iv) Calculate the total drag of your Ahmed body, produce visualisations of the flowfield, using streamlines, contour plots etc.
2 – Drag reduction study
Investigate a number of means of reducing the drag of your Ahmed body, by modifying its form, running new simulations, and comparing your calculation to the baseline drag.
*You may not reduce the frontal area of the Ahmed body, or remove its legs!*
Submit a report of less than 2000 words, detailing your analysis, outlining ALL assumptions made in carrying out the analysis with a detailed review of the results obtained. Any introduction should focus on the problem and avoid any details about “What CFD is” or ”The history of CFD”. You should also avoid supplying details of SolidWorks commands and procedures.
[1] S.R. Ahmed, G. Ramm, Some Salient Features of the Time-Averaged Ground Vehicle Wake, SAEPaper 840300, 1984
[2] H. Lienhart, S. Becker, Flow and Turbulence Structure in the Wake of a Simplified Car Model, SAE
2003 World Congress, SAE Paper 2003-01-0656, Detroit, Michigan, USA, 2003
[3] H. Lienhart, C. Stoots, S. Becker, Flow and Turbulence Structures in the Wake of a Simplified Car
Model (Ahmed Model), DGLR Fach Symp. der AG STAB, Stuttgart University, 15-17 Nov., 2000
[4] C. Hinterberger, M. García-Villalba, W. Rodi, Large Eddy Simulation of flow around the Ahmed body. In -Lecture Notes in Applied and Computational Mechanics / The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains-, R. McCallen, F. Browand, J. Ross (Eds.), Springer Verlag, ISBN: 3-540-22088-7, 2004
[5] S. Krajnovic, L. Davidson, Large eddy simulation of the flow around a simplified car model, SAE
2004 World Congress, SAE Paper 2004-01-0227, Detroit, Michigan, USA, 2004
[6] M. Minguez, R. Pasquetti, E. Serre, High-order large-eddy simulation of flow over the “Ahmed body” car model, Phys. Fluids, 20, 9, 2008
Learning Outcomes to be assessed (as specified in the validated module descriptor
1. Carry out a computational fluid dynamics analysis of an engineering situation.
Grading Criteria:
Marking Scheme Marks Available Marks Awarded
1. CFD Model 20
2. Assumptions 10
3. Analysis 20
4. Results & Calculation 20
5. Discussion 20
6. Conclusions & References 10
Assessment Criteria
Performance Level Criteria
( 40%) Poor analysis with limited information provided in regards to the analysis and results.
3rd Class / PASS
(40% - 49%) Analysis completed with some detail of either the analysis or the results.
Lower 2nd Class / PASS (50% - 59%) Analysis completed with some detail on both the analysis and the results.
Upper 2nd Class / MERIT (60% - 69%) A good analysis with a good level of detail on either the results or analysis.
(70% +) A detailed analysis with a well-constructed argument to defend the results obtained.
Feedback/feed-forward (linked to assessment criteria):
• Areas where you have done well:
• Feedback from this assessment to help you to improve future assessments:
• Other comments
Marker’s Signature:
Provisional mark only: subject to change and/or confirmation by the Assessment
Part C: Reflections on Assessment (to be completed by student – optional)
Use of previous feedback:
In this assessment, I have taken/took note of the following points in feedback on previous work:
Please indicate which of the following you feel/felt applies/applied to your submitted work
• A reasonable attempt. I could have developed some of the sections further.
• A good attempt, displaying my understanding and learning, with analysis in some parts.
• A very good attempt. The work demonstrates my clear understanding of the learning supported by relevant literature and scholarly work with good analysis and evaluation.
• An excellent attempt, with clear application of literature and scholarly work, demonstrating significant analysis and evaluation.
What I found most difficult about this assessment:
The areas where I would value/would have valued feedback: