1、ES 202 Fluid and Thermal Systems Lecture 30: Lift and Drag Wrap-Up (2/20/2003),Lecture 30,ES 202 Fluid & Thermal Systems,2,Assignments,Study for your finals,Lecture 30,ES 202 Fluid & Thermal Systems,3,Announcements,Problem session this evening at 7 pm lift and drag hydrostatics Bernoullis equation m
2、ajor and minor lossesTime and date for final review session (need your input)What can you bring to the exam textbook 3 sides of equation sheet computer (cannot use EES)My advice for you on final exam Study hard, see me if you have questions Keep calm! You should have more than enough time!,Lecture 3
3、0,ES 202 Fluid & Thermal Systems,4,Road Map of Lecture 30,High-light from John Adams talk on golf ball aerodynamics laminar-turbulent transition over curved surfaceReynolds number dependency of drag coefficient how it relates to terminal velocity calculationCommon feature between internal and extern
4、al flows formation of boundary layer inviscid core region merging of boundary layers (disappearance of inviscid core)Visual learning: variation of lift and drag with angle of attackAll about lift origin of lift definition of lift coefficient conditions at take-off and cruiseCourse evaluation,Lecture
5、 30,ES 202 Fluid & Thermal Systems,5,Drag on a Golf Ball,Taken from John Adams ASME talk,2/3 of range at max. height (very different from simple projectile),Lecture 30,ES 202 Fluid & Thermal Systems,6,Reynolds Number Dependency,taken from Figure 8.2 in Fluid Mechanics by Kundu,Lecture 30,ES 202 Flui
6、d & Thermal Systems,7,Connection with Internal Flow,Recall the drag analysis on a cross-flow cylinder in a wind tunnel The blockage effect of the cylinder causes the flow to accelerate. As a result, pressure drops.This pressure drop is totally different from the pressure drop in pipe flow analysis d
7、uring the 4th week of this class.The pressure drop in pipe flow is due to frictional effect, not flow acceleration.In fact, the average flow speed in a constant cross-sectional pipe is constant as a result of mass conservation.,Lecture 30,ES 202 Fluid & Thermal Systems,8,Boundary Layer in a Pipe,At
8、the pipe entrance, the development of boundary layer is similar to that on a flat plate.As a result of fluid deceleration in the boundary layer, the flow accelerates within the inviscid core.Beyond the merging point of boundary layers, the fully viscous region is termed the fully developed flow.With
9、in the fully developed flow, averaged flow speed stays constant; pressure drops as a response to fluid friction.,Lecture 30,ES 202 Fluid & Thermal Systems,9,Lift and Drag on an Airfoil,Visual learning: MMFM visualization of lift and drag variation as a function of angle of attack (serves as a motiva
10、tion to lift analysis) As the angle of attack is increased, the slender airfoil becomes more of a blunt body. Flow separation becomes more severe. The dominant drag component changes from frictional drag to pressure drag. Significant reduction in lift results. Notion of stall: large reduction in lif
11、t (highly unstable operating condition),Lecture 30,ES 202 Fluid & Thermal Systems,10,All about Lift,Generation of lift force high pressure on bottom surface, low pressure on top surface means of destroying flow symmetry non-zero angle of attack on symmetry airfoil asymmetric airfoil at zero angle of attack positive camber gives positive liftDesign criterion of airfoil design optimize the lift-to-drag ratioLift coefficient definition (similar to drag coefficient) take-off condition (L W) cruise condition (L = W),
