[cratermons]

Hi everyone,

Fairly new to the world of turbulence CFD and I am hoping to bug y'all with a question.

Let's assume liquid water is flowing within a perfectly straight 1 km long pipe with a diameter of 1 m at 10s of m/s velocity. The Reynolds number in this case will be extremely large (more or less 10^5-10^9). The primary goal is to look at how turbulent flow affects the temperature distribution of the water as it flows in the pipe. The temperature external of the pipe can increase or decrease as a function of the length. (just imagine a 1 km long pipe drilled into Earth's crust for geothermal energy). So I am coupling turbulent flow with heat transfer on COMSOL. I hope this image gives a clearer sense of what I am describing here:

https://imgur.com/a/JHP3r1m

Based on what I have read so far, one should strive for a y+ value of unity to resolve the viscous layer. To achieve y+ value of 1 or something close to 1, one would have to create an extremely, extremely fine mesh. I just used the cfd calculator to compute the mesh requirements:

https://www.cadence.com/en_US/home/t...cs/y-plus.html

My first element will have to be at ~1E-7 m. Given the extreme aspect ratio in this scenario, I am facing quite a lot of difficulty trying to get a y+ value of 1. My current mesh is a custom build one, where I don't use a boundary layer but divide my domain into a thick x=0.99 m region and a smaller domain with a width of 0.01 m. It looks something like the following.


I have spent a lot of time tweaking my mesh but I am getting nowhere close to y+ of 1. I am just wondering if I am going about this completely wrong. Any advice would be much appreciated.