# Potential flow Potential flow is the idealisation in which a fluid has no [[Viscosity]] and no [[Vorticity]] anywhere. Under those assumptions the [[Velocity]] field is the gradient of a single scalar potential, and the whole problem collapses to Laplace's equation — linear, solvable, and superposable. It is wrong about real fluids in one specific and important way, and right enough elsewhere that it built classical [[Aerospace_engineering|aerodynamics]]. ## Building flows by addition Because the equation is linear, solutions add. A uniform stream plus a source plus a sink gives flow past an oval; a uniform stream plus a doublet gives flow past a cylinder; add a [[Vortex]] to that and you get lift, which is the [[Kutta–Joukowski_theorem]] in its natural setting. This construct-by-superposition habit is why panel methods and the vortex-lattice codes behind the [[Horseshoe_vortex]] model are still fast enough to sit inside an optimisation loop where full [[List_of_computational_fluid_dynamics_software|CFD]] cannot. [[Stream_function|Streamfunctions]] are the companion tool. ## The paradox that names the limit Solve potential flow around a sphere and you get zero [[Drag_(physics)|drag]] — d'Alembert's paradox, plainly false and enormously useful, because chasing it is what led Prandtl to the [[Boundary_layer]]. The resolution is that [[Viscosity]] matters only in a thin sheet at the wall, but what happens in that sheet — separation, [[Vortex_shedding]], a wake — is what produces the drag. So potential flow is accurate away from surfaces and useless at them, which is precisely the division of labour modern [[Fluid_dynamics]] is built on. **Microsim brief (next pass):** Palette of elementary flows — uniform, source, sink, doublet, vortex — that the viewer drops on a canvas and drags; streamlines recompute live, so a cylinder-with-lift can be built by hand. **On the spine:** [[Stream_function]] · [[Boundary_layer]] · [[Kutta–Joukowski_theorem]] · [[Vorticity]] · [[Fluid_dynamics]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Potential_flow) : [Wikitube](https://en.wikitube.io/wiki/Potential_flow) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Fluid seed wave · 2026-09-10 · seed register · microsim layer pending.*