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Cinimod
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[SOLVED] Rotating, submerged cylinder problem.
I need to develop the equations for describing a submerged cylinder which is rotating at an angular velocity of [tex] \omega [/tex], and there is a constant fluid flow of [itex] \overrightarrow{v} = v_0\overrightarrow{i} [/itex] acting on the cylinder (assume that the position of the cylinder is fixed, so that it doesn't get swept away, but that it rotates about its centre). I am to assume that the fluid is incompressible (at least for the first part. I'm suppose to drop that assumption later on).
The cylinder is considered to be solid, and so there is no fluid flow through the cylinder.
The cylinder is considered to be infinitely long in the z axis (cylindrical coordinates are used through out). Because of this, the z term in the laplacian can be dropped.
I need to solve:
[tex] \nabla^2 \phi = 0 [/tex]
Where [tex] \phi [/tex] is the velocity potential of the fluid, i.e. [tex] \overrightarrow{v} = \nabla \phi [/tex]
From what I can tell, these are the boundary Conditions of the problem:
1) For [tex] r >> a [/tex] (a being the radius of the cylinder), [tex] \overrightarrow{v} \rightarrow v_0\overrightarrow{i} [/tex].
2) [tex] \frac{\partial \phi}{\partial n} = 0 [/tex] for r = a, where n represents the vector normal to the surface of the cylinder (since the centre of the cylinder is at the coordinate system origin, this can be replaced with r).
3) at r = a, [tex] v = \omega a [/tex]. I am very unsure of this boundary condition.
At the moment, I have little clue how to do this, but I've tried two methods so far:
Method 1:
I took the case for a non-rotating cylinder, and assumed that there was another function of r, theta and omega which was added to it, and then substituted this into the laplacian equation, but I didn't get very far with that.
Method 2:
I started from the general solution for a non-rotating sphere, and then attempted to see how the new boundary conditions affected the constants given, but again, I was met with failure.
Any help at all would be appreciated.
Homework Statement
I need to develop the equations for describing a submerged cylinder which is rotating at an angular velocity of [tex] \omega [/tex], and there is a constant fluid flow of [itex] \overrightarrow{v} = v_0\overrightarrow{i} [/itex] acting on the cylinder (assume that the position of the cylinder is fixed, so that it doesn't get swept away, but that it rotates about its centre). I am to assume that the fluid is incompressible (at least for the first part. I'm suppose to drop that assumption later on).
The cylinder is considered to be solid, and so there is no fluid flow through the cylinder.
The cylinder is considered to be infinitely long in the z axis (cylindrical coordinates are used through out). Because of this, the z term in the laplacian can be dropped.
Homework Equations
I need to solve:
[tex] \nabla^2 \phi = 0 [/tex]
Where [tex] \phi [/tex] is the velocity potential of the fluid, i.e. [tex] \overrightarrow{v} = \nabla \phi [/tex]
From what I can tell, these are the boundary Conditions of the problem:
1) For [tex] r >> a [/tex] (a being the radius of the cylinder), [tex] \overrightarrow{v} \rightarrow v_0\overrightarrow{i} [/tex].
2) [tex] \frac{\partial \phi}{\partial n} = 0 [/tex] for r = a, where n represents the vector normal to the surface of the cylinder (since the centre of the cylinder is at the coordinate system origin, this can be replaced with r).
3) at r = a, [tex] v = \omega a [/tex]. I am very unsure of this boundary condition.
The Attempt at a Solution
At the moment, I have little clue how to do this, but I've tried two methods so far:
Method 1:
I took the case for a non-rotating cylinder, and assumed that there was another function of r, theta and omega which was added to it, and then substituted this into the laplacian equation, but I didn't get very far with that.
Method 2:
I started from the general solution for a non-rotating sphere, and then attempted to see how the new boundary conditions affected the constants given, but again, I was met with failure.
Any help at all would be appreciated.