In today's post, I would like to show you a classic tutorial with which beginners in CFD modeling should start. It is an analysis of the gas flow around the cylinder based on one laminar flow model.
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| Laminar flow over cylinder in Fluent |
At the beginning, I would like to introduce you the boundary conditions that will be defined for the geometric model. Classically, we will deal with Inlet and Outlet. The geometry will be constrained by the walls and the obstacle in the form of a cylinder. You can see the arrangement of all BC's in the picture below.
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| BC's for flow over cylinder in Ansys Fluent |
Our analysis is carried out in the transient mode, i.e. our parameters will change over time. Due to the low flow velocities (below Mach 0.3), we leave the Pressure-Based solver.
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| Solver and type of simulation definition in Ansys Fluent |
To make our problem as simple as possible (after all, this tutorial is dedicated to beginners), we set the flow as laminar (red frame). We also define our gas as linear, assuming a constant density independent of external factors (blue frame).
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| Viscosity model nad material properties definition |
We leave the definition of the boundary conditions in the default position for the cylinder and walls. So they will not be moving and there will be friction caused by the flowing gas (1, 4). For an inlet, we define an initial flow velocity of 80 m / s. Direction of gas movement perpendicular to the plane of the definition of this condition (2). We define an outlet using a pressure of 1 atm ABS. We might as well apply the outflow condition here for even more linearization of the problem (3).
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| BC's definition in Ansys Fluent |
In Solution Methods, we leave all simulation parameters unchanged. For such a simplified analysis, we do not need to use First Order for some solvers (1). As for the step size, due to the fact that we are dealing here with a fairly dynamic flow, we define the step size at 0.01 s. We set the number of iterations to 250, i.e. the total time of the analyzed flow phenomenon will be 2.5 s (2).
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| Simulation Settings in Ansys Fluent |
Below you can see the gas velocity distribution in the cylinder zone. As you can see, the "tail" behind the cylinder is quite straight. You can do a little experiment and do this analysis for the SST-k omega model, then your "tail" should start to ripple.
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| Velocity Distribution on Cylinder Zone - Ansys Fluent |
Below you can see the speed value at the reference point (it is marked in the second figure from the top). As you can see, the speed decreases with time. If we assume a sufficiently long simulation time, this value should start to stabilize for a small range of values.
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| Velocity Value at reference point (in function of time) - Chart in Fluent |
If U want to read about more CFD tips and tutorials go links below
https://howtooansys.blogspot.com/2021/11/investigation-of-influence-of_37.html
https://howtooansys.blogspot.com/2021/11/thermal-analysis-of-baffles-in-ansys.html
https://howtooansys.blogspot.com/2021/10/radiator-game-episode-3-modern-wall-cht.html
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