Rotors and blades

Package @ferret/physics-rotor, capability rotors, phase field. It reads the medium of physics-media (density and the flow, which includes the flow field) at the rotor, so wind, a mill race and a whirlpool drive it without any wiring.

A rotor#

"physics": {
  "capabilities": ["media", "rotors"],
  "rotors": [
    { "name": "sails", "shaft": "MillShaft", "axis": [0, 0, 1], "at": [0, 10, 0], "radius": 2,
      "elements": { "kind": "blade", "count": 3, "area": 0.18, "pitch": "6deg" } },
    { "name": "wheel", "node": "WheelHub", "axis": [1, 0, 0], "radius": 2.4, "medium": "water",
      "elements": { "kind": "paddle", "count": 16, "area": 0.5, "depth": 0.5 } },
    { "name": "overshot", "shaft": "FlumeShaft", "axis": [1, 0, 0], "radius": 2.4,
      "elements": { "kind": "bucket", "count": 12, "capacity": 5, "fill": { "angle": 0.5, "width": 0.3, "rate": 2 }, "empty": { "from": 3.5 } } }
  ]
}

A rotor names a shaft (a shaft of the drivetrain: it becomes one more torque source of that shaft, so gears, clutches, the load and the housing reaction all follow) and/or a node (a body: the thrust, the weight of the water and the reaction go to it). With a node and no shaft the rotor spins by itself: spin: { J, friction } is a free rotor (a windmill on a boat), spin: { speed } holds a speed (a driven propeller). axis and at are in the body's frame with a node, in the world without one. Angle 0 of the elements points up (default world up); a positive turn goes from up towards axis × up.

Element	Force from
`blade`	blade-element and momentum theory at the 0.7 R station: the flow along the axis and the speed give the angle of attack, lift and drag from a `polar` (`clSlope`, `clMax`, `cd0`, `cdMax`, or your own `cl` / `cd` functions); the induced flow and the tip loss are iterated, so the power never passes the Betz limit. `pitch` is the angle of the chord from the plane of rotation. Windmill sails, wind turbine, fan; a propeller is a blade pitched past the inflow angle (negative torque and thrust). `induction: false` turns the induced flow off (a propeller at the bollard)
`paddle`	the drag `½ρ·Cd·A·(v − ω·r)²` of the immersed part of flat paddles, sampled at four points along each paddle's `depth`, in the local water: undershot wheel, paddle steamer
`bucket`	the weight of the water in each bucket: it fills at `fill.angle` (within `width`, `rate` kg/s, scaled by the rotor's `command`: a sluice) and pours from `empty.from` on: overshot wheel

model: "lumped" (blades only) is the cheap mode: the torque is windPower(Cp(λ)) / ω with lumped: { cpMax, peak, ct }, fitted to the elements (fitLumped) when you give none, or a propeller lumped: { kt, kq, diameter }.

Readouts and commands#

rotor.state { name? }: omega, theta, torque, power, thrust, force, tipSpeedRatio, flow (along the axis, against the rotor), cp, pitch, command, fill (kg per bucket). rotor.pitch { name, pitch } turns the blades (a windmill turned to the wind, a variable-pitch propeller), rotor.command { name, command } opens or shuts the sluice; editor: edit.physics.rotor.set | remove | list.

The blade actuator#

{ "name": "oar", "node": "Boat", "kind": "blade", "point": "Oarlock_L", "area": 0.12, "normal": [0, 0, 1], "stroke": { "dir": [0, 0, -1], "speed": 1 } }: a plate in the medium. The force comes from the plate's velocity against the local flow (plateForce: drag along the relative flow, lift across it); the profile drives the stroke (the plate moves relative to the body at speed × profile), not the force, so the same stroke gives less against the current. The kind is registered when @ferret/physics-rotor is loaded. How the stroke follows the oar's path and immersion comes with stage A7.

Not here#

Housing reactions of angle profiles (A10), the render of rotors (A9), the .ferret library build (M).