The Dow steam turbine illustrated by Hiscox uses two rotating disks on one shaft, opposed by two fixed disks. Concentric tongues and grooves on their faces interleave, and oblique cuts across the tongues form steam passages. Steam enters near the hub and crosses these passages toward the outer casing. This is a different construction from the single rim-bucket impulse wheel previously shown here.
Dow Steam Turbine Interactive Calculator
Inspect the interleaving fixed and rotating disks shown in the historical Dow turbine. Enter diameter and shaft rpm, then move the green inspection radius to compare local surface speed and acceleration.
Equation Used
- Rigid disks share a single angular speed.
- Input diameter refers to the outside rotating radius.
- Inspection radius is a fraction of that radius.
- No power, pressure, strength or steam-flow result is inferred.
Kinematics only. Entered rpm and dimensions are not operating limits. The model does not calculate steam flow, power, efficiency or rotor stress.
Two rotating disks and a fixed central pair
Hiscox’s figures 366–368 show two outer rotating disks connected to the shaft. Between them are fixed faces with concentric grooved tongues. The small detail shows the interleaving of the faces; cuts across the rotating tongues slope oppositely to those on the fixed tongues.
The animation’s face view separates the exposed ring rows by color. Blue rows rotate with the shaft and gold rows remain fixed. Representative slanted gaps show how each tongue is cut across. The axial section below shows the two blue rotor disks, the central fixed pair and inlet chamber, and their common rotating shaft.
Steam is supplied toward the hub and passes across the slotted rings. The flow arrows identify the outward direction; the cuts are distributed around the circumference and are not all visible in one axial section. The drawing does not depict a solved steam trajectory or pressure distribution. Ring count, slot count, slopes and clearances are representative, not manufacturing dimensions.
A historical disk-turbine construction
This page explains the Dow mechanism recorded in Hiscox’s collection. Its distinguishing feature is the pair of interleaving fixed and rotating grooved faces, rather than a single nozzle and rim-bucket wheel.
The calculator is useful for relating an entered disk diameter and shaft speed to peripheral speed and acceleration. It does not establish a historical unit’s rated power, normal rpm, nozzle specification or operating pressure. The earlier named ships, plants, performance ranges and restoration anecdotes lacked supporting sources and have been removed.
Disk-speed and centripetal-acceleration calculations
With rotor diameter D in metres, radius R=D/2 and shaft speed N in rpm, angular speed is ω=2πN/60. Outer-rim speed is u=ωR and centripetal acceleration is a=ω²R. Divide acceleration by standard gravity 9.80665 m/s² to express it in g.
The inspection slider chooses radius r=fR, where f is the entered percentage divided by 100. Local speed is ωr and local centripetal acceleration is ω²r. A green ring and rotating marker show that radius on the disk. Time per revolution is 60/N seconds; at zero rpm the disk stops and the period is reported as stopped.
These are rigid-body kinematics. They do not predict rotor stress, allowable speed, steam consumption, efficiency or power. Diameter and rpm are entered values, not a solved operating point. In particular, the earlier assumption that Dow’s optimum speed is one-half of a single nozzle’s jet speed is not supported by the illustrated construction and has been removed.
Example: a 200 mm disk at 3,000 rpm
For D=200 mm, R=0.1 m. At 3,000 rpm the angular speed is 314.16 rad/s, the outer-rim speed is 31.42 m/s and the rim’s centripetal acceleration is approximately 1,006.4 g. One revolution takes 20 ms.
At an inspection radius of 75%, r=75 mm. Local speed is 23.56 m/s and centripetal acceleration is approximately 754.8 g. Changing that slider moves the green inspection ring and updates both local values without changing the rim values.
Doubling rpm doubles surface speed and quadruples acceleration. Doubling diameter at the same rpm doubles surface speed and acceleration. These relationships are mathematical comparisons, not permission to operate a historical rotor at the entered speed.
What the reconstruction does and does not show
The face view exposes one representative fixed/rotating pair; the axial section shows both pairs on their common shaft. Opposite slot slopes and separated radial rows convey the interleaving construction. The color of a part identifies whether it rotates or is fixed.
Actual steam passages, ring dimensions, sealing and clearances require the machine’s drawings. The illustrated slot counts and proportions are schematic. Flow arrows indicate direction only, with no calculated steam velocity or transit time. The animation is slowed for inspection while its actual rpm and display slow-down are stated.
Rim acceleration is not rotor stress or a safety factor. Stress depends on disk shape, material, temperature, defects and attachments. This kinematic calculator deliberately does not claim a power rating, operating pressure or allowable rpm.
Dow turbine questions
What was wrong with the earlier animation?
It showed a generic single-stage rim-bucket impulse wheel. Hiscox’s Dow figures show two rotating disks with grooved faces opposed to two fixed faces.
Do the blue and gold rings touch?
They interleave with clearance. Blue rows rotate; gold rows stay attached to the fixed body. They are not gears rolling against each other.
Where does steam enter?
The historical section supplies steam to the central region near the hub. It then crosses the oblique openings in the tongues toward the outer casing.
Why is there an inspection-radius slider?
Speed and centripetal acceleration vary with radius even though every point on a rigid disk has the same angular speed. The green ring identifies the selected radius.
Does the calculator size a turbine?
No. It calculates kinematics from entered diameter and rpm. Steam properties, torque, power, stress and safe operating limits are not solved.
Why does the display turn slowly?
Real disk speeds are too high to inspect visually. The scene states the slow-down factor and the numerical results retain the entered rpm.
Primary construction reference
Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 99, figures 366–368. The text and section identify two rotating disks, the fixed grooved faces, opposite oblique cuts, and central steam supply. The kinematic formulas follow rigid circular motion and do not attribute undocumented performance to the historical machine.
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