UMHB ENGR 1310 - Lecture 12 - Fluid Mechanics Part 2

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Lecture 12 - Introduction to Fluid Mechanics - Part 2Slide 2© 2006 Baylor UniversityEGR 1301IntroductionDr. Carolyn SkurlaSpeakingSlide 3© 2006 Baylor UniversityEGR 1301Aerodynamics Forces On An Airplane• What causes drag and lift?ldaps.ivv.nasa.gov/physics/lift.htmlSlide 4© 2006 Baylor UniversityEGR 1301Drag• Drag is a function of ___________– F = drag force–CD= drag coefficient– ρ = density of the fluid– A = characteristic area• depends on body shape– v = free-stream velocity221AvCFDρ=Lecture 12 - Introduction to Fluid Mechanics - Part 2Slide 5© 2006 Baylor UniversityEGR 1301Characteristic Area• The shape of the _________ of the object– If you were a molecule of water flowing toward the object– And there was a light behind the object– What would the object look like to you?Slide 6© 2006 Baylor UniversityEGR 1301Characteristic Area• Cylinder with fluid flow perpendicular to length of cylinder?LdSlide 7© 2006 Baylor UniversityEGR 1301Characteristic Area• Cylinder with fluid flow parallel to length of cylinder?LdEGR1301 – Lecture 12 Fluid Mechanics Sample Problem: A semitubular cylinder of 15 cm radius with the concave side facing upstream is submerged in water flowing at 1 m/s. Calculate the drag for a cylinder that is 8 m long. CD is 2.3.Lecture 12 - Introduction to Fluid Mechanics - Part 2Slide 10© 2006 Baylor UniversityEGR 1301Drag On A Cylinder - Why?Slide 11© 2006 Baylor UniversityEGR 1301Drag On A Cylinder• Friction, that’s why!Slide 12© 2006 Baylor UniversityEGR 1301Which Has More Drag?Lecture 12 - Introduction to Fluid Mechanics - Part 2Slide 13© 2006 Baylor UniversityEGR 1301Why Do We Care About Drag?• Better streamlining of cars over the years– Lower drag force & better fuel efficiency!Slide 14© 2006 Baylor UniversityEGR 1301Example Of Frictionhttp://www.dfrc.nasa.gov/gallery/photo/SR-71/Slide 15© 2006 Baylor UniversityEGR 1301Example Of FrictionLecture 12 - Introduction to Fluid Mechanics - Part 2Slide 16© 2006 Baylor UniversityEGR 1301Fluid Exerts a Force• Drag -> Acts in the direction opposite to the motion of the object.• Lift -> Acts at right angles to the drag.(http://www.titleist.com/technology/aerodynamics.asp)Slide 17© 2006 Baylor UniversityEGR 1301Example of Liftldaps.ivv.nasa.gov/physics/lift.html• Lift caused by pressure differential between top and bottom of wing.Slide 18© 2006 Baylor UniversityEGR 1301How Does a Curveball Work?• A spinning ball curves in flight– Magnus effect• ________ are NOT required to make a baseball curvehttp://popularmechanics.com/science/sports/1997/4/breaking_pitch/print.phtmlLecture 12 - Introduction to Fluid Mechanics - Part 2Slide 19© 2006 Baylor UniversityEGR 1301Lift On A Golf Ball• How does a golf ball generate lift?(www.titleist.com/htm/tech/aero_main.asp)Slide 20© 2006 Baylor UniversityEGR 1301Why are Golf Balls Dimpled?DimplesNo Dimples(www.titleist.com/htm/tech/aero_main.asp)Slide 21© 2006 Baylor UniversityEGR 1301Drag Force on Dimpled vs. Smooth Golf Balls• Dimpled golf balls generate less drag!– Increases ________________ for transition to turbulence.(www.titleist.com/htm/tech/aero_main.asp)Lecture 12 - Introduction to Fluid Mechanics - Part 2Slide 22© 2006 Baylor UniversityEGR 1301Lift Force on Dimpled vs. Smooth Golf Balls• Backspin generates lift!– Dimpled golf balls have slightly improved


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