Laminar air flow in a 2D channel - how to ensure that a flow is fully developed?

[Addeeellll]

Hello everyone,
I am studying laminar airflow in a channel (2D) and trying to simulate it with FLUENT software but I need to know about the entrance length, and I want to know how I can be sure that a flow is fully developed? is it just by looking at the velocity profile? or looking at the temperature contour?
I am tracking an article which has done numerical study for a smooth channel and a baffled channel. the Nu number for a smooth channel (100<Re<600) is around 7.54 and I am trying to reach this value but I should make sure about the Entrance Length first.

the formula for a laminar flow in a channel to obtain the entrance length is: l=0.05*Re_D*D_h
but this formula will not give me the desired results.
would anybody help me?
Thank You

 

[KataKoniK]

Thank you for sharing your research on laminar airflow in a channel and your questions about the entrance length and fully developed flow. As a scientist who has studied fluid dynamics extensively, I can offer some insights and suggestions to help you with your simulation.

Firstly, to determine the entrance length of your channel, the formula you are using is correct. However, it is important to note that this formula is an approximation and may not give you the exact results you are looking for. The entrance length of a channel can also be affected by various factors such as the geometry of the channel, the type of flow (laminar or turbulent), and the boundary conditions. Therefore, it is always a good practice to validate your results with experimental data or other numerical studies.

In terms of determining fully developed flow, there are a few methods you can use. One way is to look at the velocity profile in your channel. In fully developed flow, the velocity profile should be constant across the channel, and there should be no variations along the length of the channel. However, this method may not always be accurate, especially when dealing with complex geometries or turbulent flows.

Another way to determine fully developed flow is by looking at the Nusselt number (Nu). In laminar flow, the Nu number should be constant along the length of the channel once fully developed flow is achieved. If you are trying to reach a specific Nu number, you can adjust the boundary conditions or geometry of your channel to achieve it.

Additionally, it is important to ensure that your simulation setup is accurate and that you have a sufficient number of grid cells to capture the flow behavior accurately. This can also affect the results and the accuracy of your simulation.

I would also suggest looking into other resources, such as textbooks or research papers, to gain a better understanding of laminar flow and fully developed flow. You can also consult with other experts in the field or reach out to the FLUENT software support team for assistance.

I hope this helps and wish you the best of luck with your research.