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Fluids: Chapter 9
Question | Answer |
---|---|
external flows | flows where an object is completely surrounded by the fluid |
upstream velocity | U - velocity of a fluid flowing past a stationary body |
streamlined bodies | bodies that have little effect on the surrounding fluid |
blunt bodies | bodies that have a lot of effect on the surrounding fluid |
drag | the resultant force from pressure and shear stress in the direction of the upstream velocity |
lift | the resultant force from pressure and shear stress in the direction normal to the upstream velocity |
lift coefficient | Cl = lift/(.5*rho*U^2*A) |
drag coefficient | Cd = drag/(.5*rho*U^2*A) |
low Reynolds number flows | the viscous effects are felt far from the object in all directions (streamlines deflected considerably) |
large Reynolds number flows | flow is dominated by inertial effects and the viscous effects are negligible everywhere except in a region very close to the plate and in the relatively thin wake region behind the plate |
wage region | the region behind the object |
boundary layer | the region in which the fluid velocity changes from the upstream value to zero velocity |
flow separation | when nonstreamlined bodies are in flows with high Reynolds numbers- the flow separates from the body |
laminar boundary layer | near the leading edge of a flat plate with high Re, particles distort regularly |
turbulent boundary layer | some distance downstream from the leading edge, particles greatly distorted |
boundary layer thickness | that distance from the plate at which the fluid velocity is within some arbitrary value of the upstream velocity |
displacement thickness | represents the amount that the thickness of the body must be increased so that the fictitious uniform inviscid flow has the same mass flowrate properties as the actual viscous flow |
boundary layer momentum thickness | theta. often used when determining the drag on an object |
free-stream velocity | the fluid velocity at the edge of the boundary layer |
the cause of the pressure gradient in the boundary layer? | variation in the free-stream velocity |
friction drag | that part of the drag that is due directly to the shear stress on the object |
pressure drag | that part of the drag that is due directly to the pressure on the object |