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ColdFusion85
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Homework Statement
The velocity components in a plane (i.e., 2-D) flow are measured at four points as indicated in the sketch at the bottom of this page (see attached doc. I wrote in the coords). The velocity components at the respective points are, in units of cm/sec:
[tex]u_a=5, v_a=2, u_b=7, v_b=3, u_c=6.5, v_c=3.5, u_d=5.5, v_d=1.5[/tex]
a) Estimate the percentage change in volume of a fluid parcel at the central point o.
b), c) no questions thus far on my part
Homework Equations
divergence of V = 0 for incompressible fluid (assumption made in problem since we haven't done compressible flow yet)
The Attempt at a Solution
So, I figured that since the divergence of V = partial(u)/partial(x) + partial (v)/partial(y), the partial(v)/partial(x) and partial(u)/partial(y) components don't need to be calculated (i.e., v_a, v_b, u_c, u_d are not relevant). Is this a correct assumption? If so, I took
(u_b-u_a)/2(dx)
= (7-5)/2(3) = (1/3)
and (v_d-v_c)/2(dy)
= (1.5-3.5)/2(2) = (1/2)
so div(V) = (1/3)-(1/2)
= -(1/6)
Thus, the total change in volume at the central point is (-1/6).
Does this make sense, or am I approaching the problem incorrectly?
Part b) asks whether this flow satisfies conservation of mass for an incompressible fluid. I would think that since there is a net change in volume, that it wouldn't satisfy it. Is this correct?