This paper focuses on realistic ray-tracing rendering of scenes which integrate participating media. We work on the temperature sensitive index of refraction, in order to deflect the rays' path and thus visualize a scene through heat. We can also visualize three-dimensional convective motions, under the shape of fumes. In this respect, we suggest to solve the NS (Navier-Stokes) equations through a simple approach, which offers better steadiness than classical methods, and which is easy to implement. We are considering the three-dimensional and turbulent case of this system, combined with the energy equation, in order to obtain incompressible fluid or gaseous realistic participating media.