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External Aerodynamics

In flu­id me­chan­ics, an ex­ter­nal flow is such a flow that bound­ary lay­ers de­vel­op freely, with­out con­straints im­posed by ad­ja­cent sur­faces. Ac­cord­ing­ly, there will al­ways ex­ist a re­gion of the flow out­side the bound­ary lay­er in which ve­loc­i­ty, tem­per­a­ture, and/­or con­cen­tra­tion gra­di­ents are neg­li­gi­ble.It can be de­fined as the flow of a flu­id around a body that is com­plete­ly sub­merged in it.

Ex­ter­nal aero­dy­nam­ic flows can be fre­quent­ly en­coun­tered in the in­dus­try with ap­pli­ca­tions in­clud­ing the flu­id mo­tion over a flat plate (in­clined or par­al­lel to the free stream ve­loc­i­ty), the flow over curved sur­faces such as a sphere, cylin­der, air­foil, or tur­bine blade,air flow­ing around an air­plane, ground ve­hi­cles or wa­ter flow­ing around sub­marines.

 

 

In flu­id me­chan­ics, the bound­ary lay­er is the thin lay­er of flu­id in the im­me­di­ate vicin­i­ty of a sol­id bound­ary where the vis­cos­i­ty ef­fects are of great im­por­tance. The flow over a flat plate and the de­vel­op­ment of its bound­ary lay­er has been first stud­ied by Bla­sius in 1908 thus of­ten as­so­ci­at­ing this test case with the name "Bla­sius so­lu­tion" (Read more).

 The flow be­hind a cir­cu­lar cylin­der has al­ways been a ma­jor re­search and val­i­da­tion test case both for its sim­ple geom­e­try and for its great prac­ti­cal im­por­tance in en­gi­neer­ing ap­pli­ca­tions. This test case fo­cus­es on the steady lam­i­nar flow at low Reynolds num­bers as well as on the un­steady vor­tex shed­ding that ap­pears with in­creas­ing Reynolds num­ber (al­so called Von Kar­man Vor­tex Street) (Read more).
  This test case aims to val­i­date the re­al­iz­able k-Ep­silon tur­bu­lence mod­el by study­ing the re­cir­cu­la­tion zone that forms when a tur­bu­lent flow pas­es over a blunt flat plate (Read more).