I use the boussinesq model for air and incompressible-idea-gas model for water to study the natural convection phenomenon duel to temperature change. I define the whole water area as a energy source term to simulate uniform heating. I use the interior boundary between air and water.
After 30min heating, I can clearly see the normal velocity at fluid-gas boundary, but the density figure without any change. I check the density figure of every timestep to prove it. The density result indicates the boundary do not change during the whole heating process, which is contradicted to the velocity vector result.
Thanks for any help.
I think you should try to use a model different from Boussinesq model. It could be limitations of its density assumptions.
Thanks, I have tried all models that can be used in natural convection for air, but with the same result.
The condition where the fluid-gas boundary has a normal velocity but without density change is known as a slip boundary condition or a no-slip boundary condition. It is a simplifying assumption often made in fluid dynamics and heat transfer simulations.
In reality, when a fluid (liquid or gas) flows over a solid surface, there is a thin layer near the surface called the boundary layer. Within this boundary layer, the fluid molecules experience frictional forces due to their interaction with the solid surface. This interaction causes the fluid molecules to stick to the surface and have zero relative velocity to the surface. This effect is known as the no-slip condition.
However, as you move away from the surface and go deeper into the fluid, the velocity profile starts to change, and the fluid molecules away from the surface have higher velocities. This velocity profile develops due to the momentum transfer between the fluid molecules through viscous effects.
When modeling fluid flow using computational methods or simulations, it is often challenging and computationally expensive to resolve the intricate details of the boundary layer and capture the no-slip condition accurately. Therefore, for simplicity, slip boundary conditions are commonly assumed, where the fluid-gas interface is considered to have a normal velocity but without density change. This means that the fluid near the surface moves with the same velocity as the surface but without affecting the density or changing the properties of the fluid.
This simplification allows for easier mathematical modeling and computational analysis, making it feasible to simulate larger-scale fluid flow problems. However, it's important to note that slip boundary conditions may not be appropriate for all situations, particularly when studying microscale or nanoscale flows, where the slip effects can become significant and need to be accounted for.
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