MAE 4230-5230 Lecture 1 - Notes - Cornell UniversityMAE 4230-5230 Lecture 1 - Notes Monday, January...
Transcript of MAE 4230-5230 Lecture 1 - Notes - Cornell UniversityMAE 4230-5230 Lecture 1 - Notes Monday, January...
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MAE 4230-5230Lecture 1 - Notes
Monday, January 24th, 2011Presented by: Prof. Jane WangCompiled by: Acmae El Yacoubi
Cornell University, Spring 2011
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Flow patterns
left-right and top-bottom symmetries of the flowdifficult to determine flow directionupstream and downstream streamlines are parallel: uniform flowflow is warped close to the objectpotential flow: no vorticity (irrotational), seemingly no boundary layer (inviscid), and flow is independent of time.
Flow past a cylinder: potential flow limit
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top and bottom symmetry onlybreaking of the left-right symmetry and appearance of counter-rotating vorticity bubbles at the backflow is from left to right: deviation of streamlines at the front (over-pressure) and suction of the flow at the back (under-pressure)flow is warped further upstream
Flow patternsFlow past a cylinder: flow separation
Separation Bubbles
Re ~ 10
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same remarks as previous slide, with an increase in size and an elongation of vorticity bubblesflow remains steadyRe < Recr : the bubbles are still attached to the bodyflow at the front: laminarflow at the back is separated into two regions: the separation bubbles and outside the bubbles (laminar)
Flow patternsFlow past a cylinder as Re increases
Re = 24
Separation Bubbles
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all symmetries (up-down, left-right) are brokenthe flow is unsteadyRe > Recr : von Karman street - shedding of counter-rotating vorticesdiffusion of vorticity can be noticed from the growth in the size of vortices as they drift downstreampositive vorticity (ccw), negative vorticity (cw)
Flow patternsFlow past a cylinder: von Karman wake instability
++
+- - -
Re = 140
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airfoil inclined w.r.t incoming flow: non zero angle of attackfront stagnation point shifts to the bottom sideflow leaves the airfoil at the trailing edge (TE)onset of separation near (TE)
Flow patternsFlow past an airfoil
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Flow patternsFlow separation
attached (laminar) flow: flow is smooth, streamlines are parallel to the plate
flow separation: appearance of region of turbulencehigh mixing and stirring of the flowappearance of large eddies and smaller structures within them