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SESA2022/SESS2022 Aerodynamics/Hydrodynamics FINAL ASSESSMENT 2021-2022
发布时间:2024-01-25
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SESA2022/SESS2022
FINAL ASSESSMENT 2021-2022
TITLE: Aerodynamics/Hydrodynamics
DURATION: 8 hours
SUGGESTED DURATION: 4.5 hours
(including scanning and upload time).
There are three parts (Part A, B and C) to this as- sessment. Answer ALL questions in ALL parts.
Part A - 20%
Blackboard multiple choice conceptual or simple calcu- lation questions. You will have to answer a total of 10 questions on Blackboard Assignments across the differ- ent topics in the module. Please use the link for Part A to access the questions for this part.
Part B - 40%
This part contains 2 questions with each question con- tributing 20% to the total mark. Carry out the analytic work on paper (only hand-written solution is acceptable - this can be hand-written on a digital device). Numer- ical calculations can be carried out using calculators, spreadsheet or code with appropriate evidence. The fi- nal scanned (and/or exported) PDF should be uploaded as a Turnitin submission for Part B.
Part C - 40%
There are 2 questions with each question contributing 20% to the total mark. Start with the Jupyter notebook that is provided. Carry out the analytic work on pa- per and use the notebook to produce the required plots. Your submission should be PDF file that is a combina- tion of your hand-written solution and plots obtained from Jupyter Notebook (or other plotting software). The PDF should be uploaded as a Turnitin submission for Part C.
For both Part B and C, you can use equations from the lecture material as you require. Please clearly write down the equations that you used and provide citations to the appropriate topic notes (either the Jupyter note- book or the PPT slides). All steps leading up to the nu- merical evaluation should be clearly shown in the hand- written solution. If you used code/spreadsheet to carry out numerical calculations such as evaluating integrals or solving complex equations, then, you must include a screenshot of your code (or spreadsheet) in addition to the hand-written analytic work. If you use any other re- sources such as a textbook or the internet, then, these sources must be appropriately cited.
Part B
(All numerical answers in this Part should be rounded to 4 decimal places)
Q1. The shape of the camberline of a modified NACA aerofoil is defined by,
where z is the camberline, c is the chord length, x is the distance along the chordline with x = 0 is the leading-edge and x = c is the trailing edge.
(i) Sketch (or plot) the aerofoil, indicating the chordwise position and value of maximum camber (in terms of c) and the slope of the camberline at the leading and trailing edges. (4 marks)
For an angle of attack of 6。, calculate:
(ii) the zero-lift angle of attack (4 marks)
(iii) the moment coefficient about the leading-edge (4 marks)
(iv) the location of centre of pressure as a fraction of c (4 marks)
In real conditions, for this airfoil with thickness 10%,
(v) Sketch the typical lift curve indicating the stall region (if any) and its characteristics (2 marks)
(vi) Sketch the flow streamlines (or patterns) at angles of attack of 6。and 16。 (2 marks).
Q2. An aircraft is cruising at 100m/s with a non-elliptic wing of span b = 10m and an aspect ratio of 3. The
Γ = 2bV1 [0.0163sinθ - 0.0011sin3θ] (1)
The representative geometric angle-of-attack is 4。 and the representative zero lift angle-of-attack is -1。. The overall drag coefficient excluding the induced drag is 0.005. The induced drag factor and the induced lift slope factor are the same for this wing. Using density of the fluid as 1.255kg/m3 ,
(i) Calculate the induced drag coefficient for this wing (4 marks)
(ii) Calculate the power required to overcome this in- duced drag (4 marks)
(iii) What does the Oswald factor of this wing tell you about its planform? (2 marks)
(iv) If this aircraft is equipped with flaps, what is the im- pact of deploying it mid-air on the power consumption? (2 marks)
Now, a second aircraft with an aspect ratio of 6 is ob- served to be flying nearby. The second aircraft has the same airfoil section, cruising velocity, wing span, and the representative geometric AoA as the first one. The in- duced lift slope and induced drag factors for second air- craft are both equal to 0.2. The overall drag coefficient of second aircraft excluding the induced drag is 0.007. (v) Does this aircraft require more or less power than the first aircraft to overcome the generated drag? Calculate and give the values of power in kW. (8 marks)
Part C
Q1.
Velocity measurements are taken through a boundary layer on a flat plate in a wind tunnel at a distance x = 1.5m from the leading edge. The flow speed is U = 10m/s, the fluid density and viscosity are measured to be ρ = 1.225kg/m3 , μ = 1.8 根 10一5 k/(ms). The y posi- tion (in m) and measured average velocity u (in m/s) are given in the Jupyter notebook.
(i) Make a labeled plot of this velocity profile. How can you tell the boundary layer is turbulent? Estimate the boundary layer thickness δ and numerically calculate the displacement thickness δ and momentum thickness θ to 3 significant digits. (6 marks)
(ii) Briefly explain the concept of the virtual origin x0 and transition point xt of the turbulent boundary layer. In- clude a sketch. Based on the value of θ you numerically calculated above, calculate x0 and xt to 3 significant dig- its. Provide a check confirming these values are reason- able based on your sketch (14 marks)
Q2.
Consider the pressure coefficient on rounded wall which is taller than it is wide, as sketched in the notebook. We will model this with a vortex and the method of images. (i) Write the stream function and potential for this flow in terms of the flow speed U , vortex strength Γ and spac- ing a of the vortex relative to the x-axis. Discuss why each vortex has the sign it does, and why the group Ⅱ = Γ/(πU a) completely governs the shape and pres- sure distribution on the body. (6 marks)
(ii) Write the equation for the body streamline in polar co- ordinates. Can this equation be solved for r/a = f (Ⅱ, θ) explicitly? If not, how can you obtain a solution? (6 marks)
(iii) Plot the velocity field and streamlines of this flow for Ⅱ = 4/3. Also plot the body streamline using the equa- tion above. You can start from the code in the notebook. (8 marks)