[Mohamed Khaled]

Howdy;

I am simulating 2-phase flow "liquid and soli" in a 90 degree annuls between two horizontal pipe along z-axis. The inner pipe is rotating clockwise around z-axis while outer pipe is stationary

I set motion type to Moving reference frame, then i specify rotation axis. origin 0 to all x,y,z direction, then set x,y=0 and z=1 and i specify RPM=-50 (for clockwise direction)

I tried in two separate run RPM=50 & -50 to be sure that i did it correctly. But When i checked the velocity vector it did not show any clearly direction for both runs (attached)

Even Using RPM=-50, it gives me negative tangential velocity value in the results (which confused me more).

Kindly i am asking if anyone can advise should i put RPM=50 or -50? and why tangential velocity appears negative with -50 RPM

Appreciate your responses

[vinerm]

First of all, you do not need MRF. All you need is a moving wall. Give a rotation to the wall of the inner pipe. As far as negative and positive are concerned, it is governed by Right Hand Rule, i.e., if rotation about z-axis takes a point from x to y, then it is positive otherwise negative. This implies CCW rotation is positive and CW is negative when positive z-axis is pointing out of the screen. With CW rotation, i.e., -50 rpm, you are supposed to get negative circumferential velocity, so there should not be a confusion about it.

Secondly, you have to ensure that (0, 0, 0) is indeed the center of rotation. Since the pipes not concentric, only one of these would have center at origin.

[Mohamed Khaled]

Sir;

Thanks a lot for your reply and your comprehensive illustration.

Another question if you do not mind regrading pipe center rotation just to confirm with you that i set my boundary conditions probably.

My study case is a rotating inner pipe eccentric from the stationary outer pipe by 0.75 inch

So i put my rotation axis origin (0,0,0) and rotation axis direction (0,0,1) with -50 RPM (for Clockwise rotation).

Is that correct or i should apply eccentricity to the axis origin on y-direction?

From your point of view, why when i plot velocity vectors with 50 & -50 rpm in previous post it did not show clear direction of velocity?

Thanks Again and appreciate your response

Thanks;
MS

[vinerm]

Since you want only the inner pipe to rotate, you have to find out, from your CAD model, where does the center of the inner pipe lie. Is it at the origin or is it, say, moved downward? If it is moved, then change the rotation axis origin to (0, -0.75, 0), provided y is the vertical coordinate and unit is set to inch. Else, just provide appropriate numbers.

The difference in -50 and 50 will be clearly visible once the case is setup properly and the solution converged.

[Mohamed Khaled]

Thanks a lot sir.

My inner pipe is eccentric downward from center by 0.75 inch. so i will make my center axis of rotation (0,-0.75,0) and rotation axis direction (0,0,1) with -50 RPM (clockwise direction) for my annuls length 40 ft (total length between two pipes)

I will run the model again and check

Thanks;
MS