i want to solve steady flow in vof model but by default it takes unsteady...then what should i do...please help thanks.

90% cases of multiphase model is unsteady. VOF model is run only in unsteady state--because it involves tracking of the interface with every timestep.

The methodology for VOF model is based on Density solver, which is by varying densities in the Voids of the pressure field.

The strategy is to solve the Transport equation with input volume fraction as variable.

Steady state solution should work in FLUENT, this infact consumes time triple the Non VOF model. Because the solution is obtained for every 20 iterations as default to reach convergence. And Re-constructs the geometry near surface of two phases.

Good luck.

thanks for help so what inputs i have to give while solving steady state problem..

that depend in what variables you want to predict and the type of your problem.I want to correct point mentioned in Ravi post the VOF model based on the pressure solver not density based and it depend mainly in the segregated solver cause the coupled solver not allowed with it (see the limitation of VOF model in the user guide).