University:
Massachusetts Institute of Technology
Course:
16.01 | Unified Engineering I, II, III, & IV
Academic year:

2019
Views:

46

Pages:

2
Author:

Beckett Gray

Lecture F23 Mud: Airfoil Polars, Quiz Review (34 respondents) 1. How is % camber deﬁned? (2 students) Example: 8% camber means that the maximum camber line height is 0.08c high, where c is the airfoil’s chord. 2. On a NACA 4-digit airfoil, what if the camber is a fraction of a percent? (1 student) There’s no standard notation for this. One lame attempt I’ve seen: An airfoil with a 2.5% camber was given as a NACA (2.5)415, which is midway between a 2415 and 3415. Such fractional specs on 4-digit airfoils are rarely used. 3. Typo in notes handed out: Vmax /Vmin = CLmax /CLmin ? (2 students) Yep, it’s a typo. It should be � Vmax CLmax = Vmin CLmin The posted notes have been ﬁxed. 4. How would we calculate �∂/�n? (2 students) The relation �∂ = 0 �n φ ·n or V ˆ = 0 is a boundary condition imposed at a wall. How exactly this is done depends on the method used to solve the governing Laplace’s equation �2 ∂ = 0. In a panel method, we determine both u and v at the surface as a superposition of the freestream u� and v� , plus the velocity contributions from all the panels with their strengths ξj . Then we require φ ·n V ˆ � unx + vny = 0 which becomes one of the equation rows in the big matrix system to be solved. 5. What is the Helmholtz Equation D�/Dt = 0? (1 student) See F16. 6. Still don’t understand circulation. (1 student) Try reviewing F11, F18, F20. Also Anderson 2.13 . 7. How did you get � = ξ ρ? (1 student) The vortex sheet strength ξ is deﬁned as “circulation per length”. See F20. 8. What do we need to know about lifting cylinders? (1 student) Here’s a list of relevant things which I can think of: Superposition, surface velocity and pressure, circulation, d’Alembert Paradox, Kutta-Joukowsky Theorem, ideal versus real ﬂow. There may be a few others in the notes which I missed here. 9. Will we need to do any numerical analysis of c� , cd graphs? (1 student) I expect to you be able to pick numbers oﬀ a graphs and to apply equations involving c� and cd , such as L = 21 �V�2 c c� , etc. 10. Can you give us a table for all the sources, vortices, etc.? (1 student) Anderson Table 3.1, page 232. 11. What are the objectives in Uniﬁed Fluids? (1 student) See “Learning Objectives” link in Fluids section of UE website. 12. How do you keep all these concepts straight? Experience? (1 student) Yeah, pretty much. Eventually even new and complex things become familiar and natural if you work with them long enough. 13. Will you be around this week for questions? (2 students) Yep, but my schedule is ﬂaky at this point. Try knocking on my door. 14. No mud (19 students)