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Aero Engineering 315

Aero Engineering 315. Lesson 7 Viscous Flow – Part I. Viscous Flow Outcomes. Know how temp effects viscosity for liquid & gas Understand importance of boundary layers Describe laminar flow, transition & turbulent BLs List factors effecting BL transition

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Aero Engineering 315

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  1. Aero Engineering 315 Lesson 7Viscous Flow – Part I

  2. Viscous Flow Outcomes • Know how temp effects viscosity for liquid & gas • Understand importance of boundary layers • Describe laminar flow, transition & turbulent BLs • List factors effecting BL transition • Describe design techniques to delay transition • Distinguish between transition and separation • Explain effect of BL separation on drag & lift • Describe components of viscous drag • Describe how to minimize skin friction and pressure drag for slender and blunt bodies • Calculate Reynolds number and explain its significance • Calculate transition point and critical Reynolds number Lsn 7/8 #2

  3. Introduction to Viscous Flow – Part I Pressure Shear Stress increases decreases inviscid viscous Lsn 7/8 #3

  4. Introduction to Viscous Flow – Part I Chapter 4 Very little Skin Friction Drag Pressure Drag Lsn 7/8 #4

  5. V=VLfs* * Lfs = local free stream (predicted by Bernoulli’s eq. at that point) d = 99% of the way to “local velocity” outside the boundary layer d Lfs Lfs Lfs Introduction to Viscous Flow – Part I V=0 Lsn 7/8 #5

  6. Introduction to Viscous Flow – Part I resist velocity discontinuities temperature resistance to flow “viscosity decreases with temperature for liquids” forces “viscosity increases with temperature for gases” collisions Lsn 7/8 #6

  7. lfs Introduction to Viscous Flow – Part I higher higher Lsn 7/8 #7

  8. Introduction to Viscous Flow – Part I V < VLfs Static Dynamic Lsn 7/8 #8

  9. Introduction to Viscous Flow – Part I decreases decreases increases increases increases Lsn 7/8 #9

  10. Introduction to Viscous Flow – Part I Laminar Turbulent Lsn 7/8 #10

  11. Boundary Layer Transition

  12. Introduction to Viscous Flow – Part I thicker velocity more more < <?> < <?> < <?> Lsn 7/8 #12

  13. Introduction to Viscous Flow – Part I xcrit ReXcrit 500,000 Lsn 7/8 #13

  14. Reynolds number example • A B-2 is flying at 43,000 ft in standard • day conditions at 400KTAS. If the mean • chord length is 39.6 ft, find: • Overall Reynolds number for the aircraft (Rec) • Percentage of the wing chord where laminar flow is present Lsn 7/8 #14

  15. Next Lesson (T8)… • Prior to Class • Work homework problems (14 and 15) • Review/reread section 3.4 • In Class • Viscous Flow – Part II Lsn 7/8 #15

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