Three parameters are necessary for transient analysis: The correct choice of time step depends on the time scale of the analysis. For non-motion flow analyses, the time step size is a fraction of the mean flow velocity, and should be at least a tenth of the time needed to traverse the length of the device. In many cases a much smaller time step size will be required to adequately resolve the flow. For non-motion heat transfer analyses, the time scale is usually much larger, so a larger time step size can be used.
The time step should not exceed one tenth of the expected heat-up time. For solar heating analyses, a much larger time step can be used because the time scale is typically a day or more.
A time step for a typical solar heating analysis can be on the order of seconds or more. This time step size is usually quite small, and often a larger step size can be used effectively after disabling Intelligent Solution Control. For more about setting the time step size Rotating Analyses For Rotating analyses, a time step size ranging from individual blade passages to complete revolutions can be used effectively.
Smaller time step sizes are recommended for devices with many blades to resolve the interaction between the blades and surrounding, non-rotating geometry. To facilitate this, a time step calculator computes the time step size based on either a prescribed number of degrees per time step or the number of blades.
Open the dialog by clicking the pop-out button on the Time Step Size line. This is only available when a rotating region material exists in the model. The time step will be computed based on the rotational speed specified as part of the Rotating Region.
If the number of blades is specified, the time step size will be computed using a single time step per blade passage.
If the model contains multiple rotating objects, the fastest rotational speed is used as the basis for the time step size computed in this dialog. For more about Rotating Analyses Motion Analyses The time step size for moving solids analyses is computed based on the specified motion parameters and the mesh size. When the Solve dialog is first opened after assigning Motion parameters, the time step size is computed automatically.
If changes are made to the flow or motion velocities, click the button to recalculate the default time step. This will not conflict with the time step size determined by Intelligent Solution Control , but rather computes a reasonable starting time step size. Eliminate interferences. Examples include press-fits and improper mates.
Steps to help reduce the analysis time: Eliminate very small features that do not affect the analysis results. These include: Small fillets Very small parts Fill small gaps in the flow region that are not important.
Examples of models that benefit from removing components that do not affect simulation interferences, gaps, fasteners, small features Production Simulation Note: The interferences, fasteners, small gaps and the extremely small fillets were removed. In addition to removing the interferences, fasteners, small gaps and the extremely small fillets, several components that are not important to the analysis were removed.
Most CAD models do not include this by default, but there are three different ways that this model of the flow region can be created. Knowing which one best suits your analysis will influence how you prepare your CAD model: For internal flows such as pipes, valves, and electronic enclosures, this often means creating a volume for the flow: For external flows such as over a vehicle or around an exposed module, this usually means creating a box that encompasses the entire model: The flow geometry is part of the CAD model.
You control the size and position of the flow volumes. The flow geometry inside a complex model can be difficult to create. Need to eliminate any interferences between the flow volume and the other parts. These are included only in the design study, not in the CAD model. For internal flows such as pipes, valves, and electronic enclosures, create "caps" to cover the openings.
They ensure the void is "air tight" so Simulation CFD can create the flow volume. For external flows such as over a vehicle or around an exposed module, enclose the model with a box.
This method is generally simple to perform. The exact shape of the flow geometry is captured and interferences are not an issue. Cap volumes created in CAD are used as part of the flow region. You can vary the thickness of the caps to control the location of your boundary conditions. Create thicker caps to move the boundary condition further upstream from the object; use thinner caps to move the boundary condition closer.
For external flows, you can include the box as part of the flow or exclude it by suppressing it. If you suppress it, be sure to apply boundary conditions correctly to the generated flow region.
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The software provides computational fluid dynamics and thermal simulation tools to predict product performance, optimize designs, and validate product behavior before manufacturing. Through a hands-on, practice-intensive curriculum, students acquire the knowledge required to work in the Autodesk CFD environment to setup and conduct thermal and flow analyses on part and assembly models.
Exercises are provided that cover electronic cooling, flow control, and AEC type models. Topics Covered: Open and navigate the Autodesk CFD environment to conduct flow and thermal analyses on part and assembly models. Create internal and external fluid volumes.
Setup analyses by applying appropriate materials, boundary conditions and mesh settings. Refine mesh to obtain a proper solution. Apply appropriate solver settings to run your analyses and converge to an acceptable solution. Use the visualization tools to compare summary images, summary values, and summary plots of your analyses to compare design and scenario results of an Autodesk CFD analysis. Conduct a final validation of your solution by running through a validation checklist.
This student guide assumes that a student has some Flow and Thermal analysis knowledge and can interpret results. The main goal of this student guide is to teach a user that is new to the Autodesk CFD software how to navigate the interface to successfully analyze a model.
This student guide was written using the build of the Autodesk CFD software. The software user-interface and workflow may vary if newer versions of the software are being used. The exercises were completed using the advanced solver license. Instructions are provided to complete this class with a basic solver license.