I am simulating slug flow in inclined pipe, so to avoid problems with geometry i have changed the gravitational vector into 2 components according to the angle of inclination. My question is, when i try to calculate the bubble velocity, i plot the y coordinate of the VOF with time and then i calculate the bubble velocity in the y direction. Now when i have placed the new components of the gravitational vector, is the y coordinate i plot the vertical y or the new inclined y coordinate?? I mean are the coordinates now inclined, or just the gravitational vector components that are used in the corresponding momentum equation???
Hello Enass,
I think that the enclosed sketch illustrates your problem rather well. In general we define the bubble velocity as the path length (L) per time step, right? In the case of the vertical pipe, the path length is identical to the y-coordinate because the bubble rises in parellel direction to the gravity vector. When you modify the inclined angle of the plate, the speed at which the bubble moves will change, but, irrespective of that "virtual" angle in your model, the y coordinate of your non-rotated mesh (i.e. the y coordinate that you plot) should always represent the bubble's path length for a given time. If you're interested in the projected coordinates (x' and y') you should correct the coordinates though, and I'm not sure how one would define a "rise velocity" in this case (whether this would be based on the absolute path length, or the distance in vertical direction). However, the "vertical y" should be correct for the calculation of the absolute bubble velocity.
Hope this helps.
Regards,
Stephan
thank you so much for your answer. plot the vertical distance with time and i calculate from them the rise velocity. For the inclined case that would be the vertical velocity in y direction so to get the inclined one i resolve it so it would be multiplied by cosine angle.
I just wanted to makesure that the coordinates x and y are rotated or not when i introduce the new gravitational vector in x and y directions????
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