Natural Convection in External Flows using Ansys CFD Tools
This model has a geometry that includes different name selections for the CFD analysis:
- Enclosure
- Inlet
- Outlet
- Surroundings
- Ground
Next, the name selections for the components include:
- Tanks
- Buildings
- Cooling Towers
Each cooling tower has two inlets and one outlet from the fluid domain perspective. The dimensions of the enclosure are based on the length of the building as the characteristic length. It has one upstream, two at both sides, and seven downstream.
Mesh Creation in ANSYS Meshing
We create a mesh for CFX using tetrahedral elements. The global controls include:
- Setup for capturing the curvature and proximity of the components
The local controls consist of:
- Method
- Inflation
We need elements close to the surfaces as this model involves capturing the fine details of small-scale components and the broader aspects of large-scale structures. The inflation includes all the surfaces of the buildings, the tanks, the cooling towers, and their inlets and outlets, distributing the elements in the boundary layer.
Analysis Setup in NCSIFExPRE
We define the analysis as a steady state. The domain setup includes:
- Selection of the fluid
- Buoyancy conditions such as the gravity vector
By selecting ideal gas, we are using the full buoyancy model, used for single-phase flows where the density is a function of the temperature or pressure. We also need to define the reference density. Here, the heat transfer is resolved using the total energy equation with all its terms. The turbulence model is the k-omega SST.
The velocity profile is defined using an expression. This profile is used in both the inlet and outlet boundary conditions. This is related to the upstream and downstream lengths of the fluid domain, mentioned before, to prevent backflow. The lateral surfaces are defined as free-slip walls and the ground as a non-slip wall. The top surface is an opening with the entrainment option for mass and momentum with zero relative pressure. The downstream floor is shaped.
Results and Observations
To compare the cross prospects of the fault zone, we see that the saturations are like the nostrils of the Ozen Engineering, Inc. We can also see that the flow pattern is shown in the graph. It follows a line two meters above the ground. The flow pattern is shown to be aligned with the height of the projection, dropping by one angle.
Another useful parameter is that the flow applies a local gravitational body force on the fluid that is related to the thermal expansivity and the local temperature difference with reference to an atom called the buoyancy reference temperature. Change to the thermal energy equation without the viscous term and it's done. Run the model.
The results show similar values for the temperature distribution. The maximum value of 90°C is the one that was included in the inlet boundary conditions. However, the maximum velocity for each model is different due to the assumption in the air density. Remember that in the ideal gas model, the density depends on pressure and temperature. In the Boussinesq model, the density is constant.
Let's check the exhaust flow of cooling tower 1 as a reference. We see that in both models, the value is the same. But if we calculate the air density at the same location, the ideal gas model shows one value, 0.99, and the Boussinesq model shows the constant value we saw in the setup.
Summary
After the mesh independence study, the results show similar temperature contours but different velocity values in the domain. For the cooling towers, for instance, we got a 20% difference between the two models. More information for the cooling towers is available in the description of this video. More info is available in the ANSYS Help. Log in to know more about the theory and applications.
Thank you for watching.
This model has a geometry that includes different name selections for the CFD analysis. First, those for the enclosure, the inlet, the outlet, the surroundings, and the ground. Next, the name selections for the components like the tanks, the buildings, and the cooling towers.
Each cooling tower has two inlets and one outlet from the fluid domain perspective. The dimensions of the enclosure are based on the length of the building as the characteristic length. Then, it has one upstream, two at both sides, and seven downstream.
In ANSYS Meshing, we create a mesh for CFX using tetrahedral elements. The global controls include a setup for capturing the curvature and proximity of the components. The local controls consist of the method and the inflation.
We need elements close to the surfaces as this model involves capturing the fine details of small-scale components, and the broader aspects of large-scale structures.
The inflation includes all the surfaces of the buildings, the tanks, the cooling towers, and also their inlets and outlets, with a distribution of elements in the boundary layer. In NCSIFExPRE, we define the analysis as a steady state.
The domain setup includes the selection of the fluid and the buoyancy conditions such as the gravity vector. By selecting ideal gas, we are using the full buoyancy model, used for single-phase flows where the density is a function of the temperature or pressure.
Then we need to define the reference density. Here, the heat transfer is resolved using the total energy equation with all its terms. And the turbulence model is the k-omega SST. Velocity profile is defined using an expression. This profile is used in both the inlet and outlet boundary conditions.
It is related to the upstream and downstream lengths of the fluid domain, mentioned before, and prevents backflow. The lateral surfaces are defined as free-slip walls and the ground as a non-slip wall.
The top surface is an opening with the entrainment option for mass and momentum with zero relative pressure. The downstream floor is shaped. To compare the cross prospects of the fault zone, we see that the saturations are like the nostrils of the aheim.
We can also see that the flow pattern is shown in the graph, following a line two meters above the ground. It is shown to be one at 90 degrees Celsius from an orientation. Sometimes, the flow is inflow and outflow or along because the flow is used over torrential OD.
Another useful parameter is that the flow is aligned with the relative height of the projection cor emails dropped by one angle Я, 2 meters above the ground.
However, it applies a local gravitational body force on the fluid that is related to the thermal expansivity and the local temperature difference with reference to an atom called the buoyancy reference temperature. Change to the thermal energy equation without the viscous term and it's done.
Run the model. The results show similar values for the temperature distribution. The maximum value of 90°C is the one that was included in the inlet boundary conditions. However, the maximum velocity for each model is different. That's because of the assumption in the air density.
Remember that in the ideal gas model, the density depends on pressure and temperature. And in the Boussinesq model, the density is constant. Let's check the exhaust flow of cooling tower 1 as a reference. Use the cooling tower 1 as a reference. We see that in both models, the value is the same.
But if we calculate the air density of the same location, the ideal gas model shows one value, 0. 99. And the Boussinesq model shows the constant value we saw in the setup. Finally, a brief summary.
After the mesh independence study, the results show similar temperature contours, but different velocity values in the domain. For the cooling towers, for instance, we got a 20% difference between the two models. More information for the cooling towers is available in the description of this video.
More info in the ANSYS Help. Log in to know more about the theory and applications. Thank you for watching.
