Editing Lift (force) (section)

===Bluff bodies===
{{Further|Vortex shedding|Vortex-induced vibration}}
The flow around [[bluff body|bluff bodies]] – i.e. without a [[:wikt:streamline|streamlined]] shape, or stalling airfoils – may also generate lift, in addition to a strong drag force. This lift may be steady, or it may [[oscillation|oscillate]] due to [[vortex shedding]]. Interaction of the object's flexibility with the vortex shedding may enhance the effects of fluctuating lift and cause [[vortex-induced vibration]]s.<ref name=Williamson>{{citation|journal=Annual Review of Fluid Mechanics|volume=36|pages=413–455|year=2004|doi=10.1146/annurev.fluid.36.050802.122128|title=Vortex-induced vibrations|first1=C. H. K.|last1=Williamson|first2=R.|last2=Govardhan|bibcode=2004AnRFM..36..413W|s2cid=58937745}}</ref> For instance, the flow around a circular cylinder generates a [[Kármán vortex street]]: [[vortex|vortices]] being shed in an alternating fashion from the cylinder's sides. The oscillatory nature of the flow produces a fluctuating lift force on the cylinder, even though the net (mean) force is negligible. The lift force [[frequency]] is characterised by the [[dimensionless]] [[Strouhal number]], which depends on the [[Reynolds number]] of the flow.<ref>{{citation|title=Hydrodynamics around cylindrical structures|first1=B. Mutlu|last1=Sumer|first2=Jørgen|last2=Fredsøe|edition=revised|publisher=World Scientific|year=2006|isbn=978-981-270-039-1|pages=6–13, 42–45 & 50–52}}</ref><ref>{{citation|title=Flow around circular cylinders|first=M.M.|last=Zdravkovich|publisher=Oxford University Press|year=2003|isbn=978-0-19-856561-1|volume=2|pages=850–855}}</ref>

For a flexible structure, this oscillatory lift force may induce vortex-induced vibrations. Under certain conditions – for instance [[resonance]] or strong spanwise [[correlation]] of the lift force – the resulting motion of the structure due to the lift fluctuations may be strongly enhanced. Such vibrations may pose problems and threaten collapse in tall man-made structures like industrial [[chimney]]s.<ref name=Williamson/>

In the [[Magnus effect]], a lift force is generated by a spinning cylinder in a freestream. Here the mechanical rotation acts on the boundary layer, causing it to separate at different locations on the two sides of the cylinder. The asymmetric separation changes the effective shape of the cylinder as far as the flow is concerned such that the cylinder acts like a lifting airfoil with circulation in the outer flow.<ref>Clancy, L. J., ''Aerodynamics'', Sections 4.5, 4.6</ref>