f18_mud_0304 - the ow For an oblique shock, and positive...

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Lecture F18 Mud: Expansion Fans 1. Can you see expansion waves like you can see shocks? (1 student) Yes, but not as easily. Supersonic flow viz techniques sense frst or second gradients oF the air density. The gradients in a wave are much smaller in an expansion wave than in a shock. 2. Do you have any pictures of a supersonic razor blade? (1 student) No, but you can fnd pictures oF supersonic flows around various other shapes which show shocks and waves. The one I showed in class is one good example. A great book For showing all sorts oF flow viz photos is “An Album oF ±luid Motion”, by Milton Van Dyke, Parabolic Press, ISBN 0-915760-02-9 (paperback), ISBN 0-915760-03-7 (hardcover) 3. Does the change in zero moment location (center of pressure) affect the design of supersonic aircraft? (1 student) Yes, a great deal. The shiFt in center oF pressure must be trimmed out with substantial tail loads. This causes additional drag, among other problems. 4. Does the sign of matter when calculating the airfoil pressures? (1 student) By the convention used in our notes (and Anderson), ± is positive “into
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Unformatted text preview: the ow For an oblique shock, and positive away From the ow For a wave. So For the airFoil, = + on both sides. 5. Is an expansion fan a series of shock waves? (1 student) In eect, yes, but they are negative shock waves, with the pressure decreasing rather than increasing as the ow goes through them. Each one is also infnitesimally weak. 6. Does the expansion fan contribute to wave drag, or just the shock? (1 student) Only the shock causes disspation, so in that sense the wave does not contribute to the drag. However, its not possible to have only expansion waves on a body in a supersonic Freestream some shocks must be present as well. So theres always nonzero wave drag. 7. No mud (3 students)...
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This note was uploaded on 01/28/2012 for the course AERO 16.01 taught by Professor Markdrela during the Fall '05 term at MIT.

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