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Stagnation points in 2D velocity field

Short answer

Yes, one stagnation point exists at x = -0.615 m, y = 0.538 m where u and v both vanish.

A steady, incompressible, two dimensional velocity field is given by V⃗=(1+2.5x+y)i^+(−0.5−3x−2.5y)j^\vec V = (1 + 2.5x + y)\hat i + (-0.5 - 3x - 2.5y)\hat j where x and y are in m and magnitude of velocity in m/s. Determine, if there are any stagnation points in this flow field and if so, where they are.

A stagnation point is a point where the velocity is zero, i.e. both u=0u = 0 and v=0v = 0 at the same time.

Given: u=1+2.5x+yu = 1 + 2.5x + y, v=−0.5−3x−2.5yv = -0.5 - 3x - 2.5y.

Set both components equal to zero:

1+2.5x+y=0(1)−0.5−3x−2.5y=0(2)\begin{aligned} 1 + 2.5x + y &= 0 \quad (1)\\ -0.5 - 3x - 2.5y &= 0 \quad (2) \end{aligned}

From (1): y=−1−2.5xy = -1 - 2.5x. Substituting in (2):

−0.5−3x−2.5(−1−2.5x)=0−0.5−3x+2.5+6.25x=02+3.25x=0x=−0.6154 m\begin{aligned} -0.5 - 3x - 2.5(-1 - 2.5x) &= 0\\ -0.5 - 3x + 2.5 + 6.25x &= 0\\ 2 + 3.25x &= 0\\ x &= -0.6154\ \text{m} \end{aligned} y=−1−2.5(−0.6154)=0.5385 my = -1 - 2.5(-0.6154) = 0.5385\ \text{m}

Check: u=1−1.5385+0.5385=0u = 1 - 1.5385 + 0.5385 = 0 and v=−0.5+1.8462−1.3462=0v = -0.5 + 1.8462 - 1.3462 = 0.

Answer: yes, there is one stagnation point, at (x,y)=(−0.615 m, 0.538 m)(x, y) = (-0.615\ \text{m},\ 0.538\ \text{m}).

✓ Answer checked by Claude Opus 5.5 (high effort)

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