To contrast the solution for no inertia, we write down the average velocity for the inviscid (meaning viscous terms are not considered) flow case from a standard reference
![[Graphics:../Images/creeping_sphere_gr_182.gif]](../Images/creeping_sphere_gr_182.gif)
![[Graphics:../Images/creeping_sphere_gr_183.gif]](../Images/creeping_sphere_gr_183.gif)
![[Graphics:../Images/creeping_sphere_gr_184.gif]](../Images/creeping_sphere_gr_184.gif)
![[Graphics:../Images/creeping_sphere_gr_185.gif]](../Images/creeping_sphere_gr_185.gif)
![[Graphics:../Images/creeping_sphere_gr_186.gif]](../Images/creeping_sphere_gr_186.gif)
The code is as the shading gets darker, the velocity is slower. We see that coming in the y=0 axis from x=-Infinity, the velocity is decreasing to agree with the: no flow through the surface boundary condition. Looking at the x=0 axis, coming in from y=∞, the velocity is increasing reflecting the deflection of fluid around the sphere. This results in a Bernoulli effect with local fluid acceleration. Below we check some numbers to verify these statements.
![[Graphics:../Images/creeping_sphere_gr_187.gif]](../Images/creeping_sphere_gr_187.gif)
![[Graphics:../Images/creeping_sphere_gr_189.gif]](../Images/creeping_sphere_gr_189.gif)
![[Graphics:../Images/creeping_sphere_gr_191.gif]](../Images/creeping_sphere_gr_191.gif)
The same question can be asked about the pressure field. We will find that the pressure is always at or below the far away value for Re=0. Substitute for the pressure field equation,
In contrast, if a high velocity fluid is impinging on a surface, there will be a pressure increase. For an inviscid flow, from Bernoulli's equation, we find that dp ~ (U0^2-u^2)/2, where we have already plotted u^2
![[Graphics:../Images/creeping_sphere_gr_193.gif]](../Images/creeping_sphere_gr_193.gif)
![[Graphics:../Images/creeping_sphere_gr_195.gif]](../Images/creeping_sphere_gr_195.gif)
![[Graphics:../Images/creeping_sphere_gr_196.gif]](../Images/creeping_sphere_gr_196.gif)
![[Graphics:../Images/creeping_sphere_gr_197.gif]](../Images/creeping_sphere_gr_197.gif)
![[Graphics:../Images/creeping_sphere_gr_198.gif]](../Images/creeping_sphere_gr_198.gif)
So that the pressure is highest at y=0, x=1,-1 (i.e. the stagnation point) and decreases out to infinity. The pressure is lowest, consistent with the Bernoulli effect, at y=1,-1,x=0, and increases out to y=infinity.
A stream function, which is a function that is always tangent to the velocity field, is another way to view the solution of this problem. The Re = 0 solution can be used to write the stream function which is, -1/2f[r]
.
![[Graphics:../Images/creeping_sphere_gr_201.gif]](../Images/creeping_sphere_gr_201.gif)
We can make a plot of this if we transform from polar to Cartesian coordinates
![[Graphics:../Images/creeping_sphere_gr_203.gif]](../Images/creeping_sphere_gr_203.gif)
![[Graphics:../Images/creeping_sphere_gr_205.gif]](../Images/creeping_sphere_gr_205.gif)
![[Graphics:../Images/creeping_sphere_gr_206.gif]](../Images/creeping_sphere_gr_206.gif)
![[Graphics:../Images/creeping_sphere_gr_207.gif]](../Images/creeping_sphere_gr_207.gif)
Note that at y=4, the contours are still deformed, the effect of the sphere is felt very far away!
Now compare the inviscid flow case:
![[Graphics:../Images/creeping_sphere_gr_208.gif]](../Images/creeping_sphere_gr_208.gif)
![[Graphics:../Images/creeping_sphere_gr_209.gif]](../Images/creeping_sphere_gr_209.gif)
![[Graphics:../Images/creeping_sphere_gr_210.gif]](../Images/creeping_sphere_gr_210.gif)
![[Graphics:../Images/creeping_sphere_gr_211.gif]](../Images/creeping_sphere_gr_211.gif)
This last plot is a bit messy but shows that inviscid flow is disturbed much less a few diameters from the sphere than Stokes flow.