State whether the following flow field is physically possible? u = 3x...
Checking for incompressible continuity equation i.e
⇒∂u / ∂x + ∂v / ∂y = 3y2 + 2 − 2 − 3y2 = 0 The flow satisfies incompressible continuity equation, so it is incompressible.
Since u and v are not functions of time, flow is steady. Also
∂v / ∂x − ∂u / ∂y = 2x − 6xy − 2y
i.e vorticity is non-zero.
Thus, flow is rotational.
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State whether the following flow field is physically possible? u = 3x...
Given flow field: u = 3xy^2 + 2x - y^2 and v = x^2 - 2y - y^3
To determine whether the flow field is physically possible, we need to consider certain properties of the flow field such as continuity equation, irrotational flow, and compressibility.
1. Continuity Equation:
The continuity equation for an incompressible flow is given by ∇ · V = 0, where V is the velocity vector field. Let's calculate ∇ · V for the given flow field:
∇ · V = ∂u/∂x + ∂v/∂y
= (3y^2 + 2) + (2x - 2y - 3y^2)
= 2x - 2y
From the continuity equation, it can be observed that the flow field is incompressible only if ∇ · V = 0. In this case, the flow field is incompressible as the equation evaluates to 2x - 2y.
2. Irrotational Flow:
An irrotational flow field has zero vorticity, which means the curl of the velocity vector field (∇ × V) should be zero. Let's calculate ∇ × V for the given flow field:
∇ × V = (∂v/∂x - ∂u/∂y) i + (∂u/∂x + ∂v/∂y) j
= (-2 + 2x - 6y^2) i + (3y^2 + 2 - 2x) j
From the expression for ∇ × V, it can be observed that the flow field is rotational as it has non-zero vorticity.
3. Compressibility:
To determine compressibility, we need to check if the flow field satisfies the compressible flow equations, which are not given in the question. As the equations are not provided, we cannot determine the compressibility of the flow field.
Conclusion:
Based on the analysis above, we can conclude that the given flow field is possible for steady incompressible rotational flow.
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