Free Surface & Bi-Phasic flows

Home » Knowledge Base » ICFD / Incompressible CFD » Free Surface & Bi-Phasic flows

In physics, a free sur­face is the sur­face of a flu­id that is sub­ject to con­stant per­pen­dic­u­lar nor­mal stress and ze­ro par­al­lel shear stress, such as the bound­ary be­tween two ho­moge­nous flu­ids.

Ap­pli­ca­tions in­volv­ing free sur­face flows are nu­mer­ous in the naval in­dus­try in or­der to solve is­sues such as slosh­ing, wave im­pact or study­ing the im­pact of hulls against wa­ter. The free sur­face fea­ture al­so cov­ers a wide range of en­gi­neer­ing ap­pli­ca­tions such as the dam break­ing, the ero­sion of off­shore petrol sta­tion pil­lars or the mix­ing of two flu­ids of dif­fer­ent phys­i­cal prop­er­ties.

Two phase flow phe­nom­e­na oc­cur in var­i­ous in­dus­tri­al ap­pli­ca­tions with­in all flu­id me­chan­ics ap­pli­ca­tion fields. Aero­space, au­to­mo­tive, nu­clear ap­pli­ca­tions, etc. In all these do­mains, it is im­por­tant to pre­dict two phase be­hav­ior. Pre­dic­tion of liq­uid spray in an in­ter­nal com­bus­tion en­gine al­lows for bet­ter con­trol of the com­bus­tion process and helps to cur­tail pol­lu­tant emis­sions. An­oth­er im­por­tant ex­am­ples in­clude mix­ing of flu­ids, steam equi­lib­ri­um with­in a col­lar sys­tem etc.

The slosh­ing phe­nom­e­non is of great prac­ti­cal im­por­tance to the safe­ty of the liq­uid trans­port and is prob­a­bly one of the most clas­si­cal ex­am­ples of free sur­face analy­sis. It con­sists in a flu­id with a free sur­face in a par­tial­ly filled tank that is giv­en an ini­tial slope so as to trig­ger its pe­ri­od­ic os­cil­lat­ing un­der the in­flu­ence of grav­i­ty (Read more).

Dam break waves have been re­spon­si­ble for nu­mer­ous ac­ci­dents mak­ing them a chal­leng­ing field of re­search for nu­mer­i­cal sim­u­la­tions. The Dam break test case is a clas­sic val­i­da­tion prob­lem for sim­u­la­tions in­volv­ing free sur­faces and con­sists in re­pro­duc­ing the coll­pase of a col­umn of wa­ter un­der the in­flu­ence of grav­i­ty and to study its prop­a­ga­tion (Read more).

The slam­ming ef­fect oc­curs dur­ing im­pact be­tween a blunt body and the wa­ter thus gen­er­at­ing high pres­sure loads. It is there­fore of one the great is­sues that have to be ad­dressed by the re­search com­mu­ni­ty in Naval ship­build­ing. The bench­mark­ing test case con­sists in a wedge slow­ly en­ter­ing the wa­ter at a con­stant ve­loc­i­ty (Read more).

This val­i­da­tion test case is very sim­i­lar to the pre­vi­ous one and con­sists of a cylin­der im­pact­ing the wa­ter at a con­stant ve­loc­i­ty. How­ev­er, for this val­i­da­tion test case, the re­sults will be com­pared to ex­per­i­men­tal ones (Read more).
This val­i­da­tion test case al­so con­sists of a wedge en­ter­ing the wa­ter. How­ev­er, this time, the wedge will be con­sid­ered in free fall and the re­ac­tion of the wa­ter on the cylin­der’s ini­tial ve­loc­i­ty will be stud­ied thus re­sult­ing in a com­plex flu­id struc­ture in­ter­ac­tion prob­lem (Read more).
For this slam­ming val­i­da­tion test case, the en­ter­ing body will have a com­plex shape re­sult­ing in the ne­ces­si­ty to build a 3D mod­el. The wedge-cone spec­i­men will en­ter the wa­ter at a con­stant ve­loc­i­ty and re­sults of the im­pact force will be com­pared to the ex­per­i­ment (Read more).
This ver­i­fi­ca­tion test case will use the non-in­er­tial ref­er­ence frame fea­ture. It fea­tures a ro­tat­ing rigid cylin­der with in­side liq­uid and free sur­face. De­pend­ing on the flu­id’s an­gu­lar ve­loc­i­ty, the free sur­face will adopt a par­a­bol­ic shape of a cer­tain max­i­mum depth (Read more).

Table of Contents