When can a flow net be drawn? Select the essential flow characteristics under which a valid flow net (equipotential lines and streamlines orthogonal) can be constructed for seepage or potential flow analysis.

Introduction / Context:
Flow nets (families of orthogonal streamlines and equipotential lines) are powerful graphical tools for groundwater seepage, sheet pile design, and potential flow around structures. They rely on the mathematics of Laplace’s equation.

Given Data / Assumptions:

• Steady conditions (time-invariant).
• Incompressible fluid (constant density).
• Two-dimensional domain (planar section).
• Irrotational flow (zero vorticity).

Concept / Approach:

Under these assumptions, the velocity potential φ and stream function ψ exist and satisfy Laplace’s equation. Their level sets are orthogonal, enabling the construction of a conformal mesh known as the flow net.

Step-by-Step Solution:

Verification / Alternative check:

Classic seepage under dams and around sheet piles is modeled with flow nets because porous media flow is well-approximated by 2D potential flow in many practical cases.

Why Other Options Are Wrong:

Turbulent, rotational, compressible with shocks, or massively unsteady separated flows violate the Laplacian assumptions; flow nets cease to be valid.

Common Pitfalls:

Forgetting to enforce boundary conditions on impervious and constant-head boundaries; drawing non-square curvilinear cells leads to inaccurate head loss estimates.

Final Answer:

Two-dimensional, incompressible, irrotational (potential) flow