In ANSYS AIM 18.2, several improvements have been introduced to the capabilities for simulating fluids. In this blog, I’ll highlight two of what I think are the most significant.
First: time-dependent fluid flow (including solid-fluid heat transfer). Time-dependent fluid flow enables the modelling of both applied physics conditions that change over time, and unsteady flow phenomena, for example varying inlet velocity and/or temperature in an internal pipe flow simulation; or vortex shedding from external flow around a cylinder, such as a chimney.
Second: particle injection (also known as discrete phase modelling, or DPM for short), where the injected particle could be a droplet, for example, a fire sprinkler system spraying water into air, or raindrops, but it could also be a bubble of gas into a fluid.
Time-dependent fluid flow
With the introduction of time-dependent fluid flow, design engineers can now model and see the result of transient effects within unsteady flow, with either constant or time-varying physics conditions.
Animation of unsteady flow
AIM 18.2 ensures that you can perform what would typically be a challenging simulation with ease, by optimizing the workflow and ensuring that appropriate defaults are intelligently chosen to achieve solution convergence.
Templates have also been enhanced, to enable the specification of time-dependent flow, which sets up the base of your simulation. Importantly, for fluid-solid heat transfer (CHT) and fluid-solid force transfer (FSI), the templates now streamline the setup by allowing the definition of the solid and fluid regions.
After a template has been run, typically, all you need to do is specify the duration and the fluid flow conditions (and any heat flow conditions for solid regions, if needed) and then update to obtain a solution and results. Once the results are updated, you can use the time selection control to view results from any time point, or animate over the duration of the simulation.
Flow over cylinder
When defining the applied conditions, expressions can be used to define how the condition behaves. For example, the rate or temperature of an inflow may be defined with respect to time, or an outlet may only allow flow for a limited period.
The power of expressions also enable one condition to be dependent on variables other than time, for example the velocity of an inlet may be dependent on the temperature at a sensor location, enabling the design engineer to model system behavior.
Animation of manifold
These temperature dependent fluid conditions are easily integrated in a multi-physics, fluid-solid simulation. After the template has created the tasks for your simulation, you just need to add the conditions, the transfer of heat between the fluid and the solid is done automatically. In ANSYS AIM 18.2 you can now also define the thermal conductivity to enable the representation of a thin film or other coating applied to the surface of the solid. Any stress due to the heat at the final duration can also be simulated.
Battery bank airflow cooling
Charts of inlet velocity and outlet temperature against time:
Using an expression, as the temperature rises (left chart) the fan velocity switches to a faster rate. At first it is able to cope with the temperature rise, but after a period of time, the generated heat means that it constantly runs at the faster rate.
Separately from the new time-dependent capabilities, the ability to inject particles has been released with 18.2. This allows for a particle of another material (technically, of a different material phase) to be injected into the fluid domain. As they are different material phases, the particles remain as discrete entities and their path can be tracked within the fluid.
Sprinkler positioning for irrigation or fire suppression example
Sand injection example
The designer can control how the particles interact with walls or other conditions, to define if they stick or reflect away, as well as erosion options. The particle residual time, density, and erosion along with other particle track results can be visualized.