Fluid Mechanics
A fluid is defined by what it cannot do: resist shear without moving. Everything after that — pressure distributions, Bernoulli, boundary layers, losses — follows from that one inability, and these topics trace the consequence.
Start from the beginning →10 topics you can watch now, 14 still to come.
Fluid properties
What makes a fluid a fluid, and the properties that follow.
- What Makes a Fluid a FluidStart here. Apply the same small shear to a solid and to water, and watch only one of them stop deforming.
- Viscosity and the Properties That MatterWhy dividing viscosity by density reverses the ranking of air and water — and why heating thins a liquid but thickens a gas.
- Newtonian and non-Newtonian fluids in depth
- Rheology of suspensions and slurries
Fluid statics
A fluid that is not moving still pushes, and it pushes everywhere.
- Pressure, Pascal's Law and ManometryA one-centimetre tube pushes on its base as hard as a swimming pool of the same depth. Then two rules that read any manometer.
- Hydrostatic Force on a Submerged SurfaceThe magnitude is one multiplication. The line of action is not at the centroid — and assuming it is under-predicts a dam's overturning moment by a third.
- Buoyancy and Floating StabilityWhether it floats is a density question. Whether it stays upright is a geometry question, and a body can pass one and fail the other.
- Pressure measurement instruments in practice
- Fluids in rigid-body rotation and acceleration
Fluid kinematics
Describing the motion before asking what caused it.
- Lagrangian and Eulerian descriptions
- Streamlines, streaklines and pathlines
- Stream function and velocity potential
- Rotational and irrotational flow
Fluid dynamics
Energy along a streamline, and what it is worth.
- Venturimeter, orifice meter and pitot tube in detail
- Momentum equation and force on a bend
- Navier-Stokes overview
Flow through pipes and boundary layers
Where the idealisation stops and the losses start.
- Reynolds Number: Laminar to TurbulentReynolds' dye experiment, run frame by frame — a straight thread that starts to wobble and then vanishes into the flow.
- Boundary Layers, Separation and DragWhy a golf ball has dimples, why a wing stalls at an angle rather than a speed, and why streamlining increases friction and still wins.
- Head Loss in PipesWhere the subject stops being elegant and starts sizing pumps: Darcy-Weisbach, the Moody chart, and the two ways to get pipe diameter expensively wrong.
- Pipes in series and parallel, and network solutions
- Drag and lift coefficients in depth
- Dimensional analysis and model similitude
About Fluid Mechanics
Fluid mechanics studies matter that cannot resist being sheared. That single property is the definition of a fluid and the source of everything that follows: fluids flow, they transmit pressure in all directions, and they will not hold a shape.
The subject divides by whether the fluid is moving. Statics is the easier half and still useful — manometry, buoyancy, forces on submerged surfaces. Dynamics is harder because a moving fluid trades pressure, velocity and height against one another, which is what Bernoulli's equation states and what its assumptions restrict.
The Reynolds number deserves particular attention, because it is the subject's great simplification: one dimensionless ratio that predicts whether flow will be orderly or chaotic, and lets a small model stand in for a full-size design.
What to know first
- Mechanics — forces, momentum, equilibrium
- Basic calculus for the flow relations
Where it gets used
- Sizing a pipe and pump for a required flow rate
- Understanding why aircraft and vehicle testing uses scale models
- Estimating pressure losses along a real pipe run