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Transport of concentrated species with Level-Set and laminar-flow

Posted 18 sept. 2025, 11:27 UTC−4 0 Replies

Pieter Heijne

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Dear COMSOL users,

I am simulating 2 phase laminar flow of immiscible fluids flow in a 3D microchannel. I am using the level-set (ls) module to to model the interface between the fluids. My system has three components in total, of which one diffuses via the transport of concentrated species (tcs) module. Attached are images of the face of the outlet at t=0s, and at t= 100s. The image with the perfectly straight red part is my initial case at t=0s. The red part indicates the dimensions of the inlet of fluid 1 and this is where it is located initially. On the top and bottom is fluid 2. The black lines are my initial interface positions through the channel, matching the dimensions of the inlet of fluid 1.

The initial case shows a color plot of the concentration of one of my components. This component is only present in the middle fluid 1. In this fluid 1 there is also another component flowing in that has a nonzero diffusion coefficient, which diffuses towards the blue fluid 2. In the second image you see that the interface has formed a circle after running for 100s (black line), to minimize the surface tension. The problem I am experiencing is that here my concentrated non-diffusing red component is not fully captured in this interface anymore, there seems to be a discrepancy in the way the interface is advected and the way my tcs species are advected. I checked the velocity profiles of the tcs and ls module, and they exactly match.

I want my interface to be perfectly coupled to my species movement; this red non-diffusing species needs to remain within the bounds of the interface at all times. Does anyone know why this happens, or a solution to this problem? Any help would be greatly appreciated.

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