4 ms·

The core tenant of the paper is that roughness reduces drag IN the transition zone. A very small region of the total flow. Thats the region between laminar and

The core tenant of the paper is that roughness reduces drag IN the transition zone. A very small region of the total flow. Thats the region between laminar and turbulent flow. Laminar flow is typically 5x less drag than turbulent, and will be encountered about a Reynolds number of 500K-1M (ratio of inertial flow to viscous flow). Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A Cessna aircraft will have a Reynolds number of 1-5x10^6.

mike_hock 4mo ago
> core tenant And Lady Mondegreen.
deleted 4mo ago
[deleted]
bonsai_spool 4mo ago
Tenet is the word you mean
- nnevatie 4mo ago
  swoosh swoosh - that's the sound of things traversing backward in time.
  - taylorius 4mo ago
    I think you mean hsoows hsoows
- dsr_ 4mo ago
  And grit, not grid.
Maarten88 4mo ago
> Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A fin, foil or daggerboard below the board/boat is operating well within the range of Reynolds' numbers where laminar flow is relevant.
- otterdude 4mo ago
  The vertical stabilizing surface of these elements is really insignificant to the entire surface of a board. Combining drag coefficients is done with the wetted surface area. In truth there's some contamination from the upstream flow. Stabilizing elements are behind the center of pressure, so they will see the most "diry flow"
  - Maarten88 4mo ago
    You are thinking about a slow boat in displacement mode, or a wave-surf board with very small fins. But I can tell you that the wetted surface area of my wing-foil board is exactly zero after takeoff, and all wet surfaces of the foil are, for a significant percentage, in laminar flow. Same for a windsurf board planing: just the last 50cm of the board is touching the water and the fin is extremely significant for drag.
    - lymbo 4mo ago
      I have 2 foil drives for wake thieving and a SUP for downwinding and I’m just excited that someone on HN is talking about foiling. Such an underrated sport.

mike_hock 4mo ago

> core tenant And Lady Mondegreen.

deleted 4mo ago

[deleted]

bonsai_spool 4mo ago

Tenet is the word you mean

nnevatie 4mo ago
swoosh swoosh - that's the sound of things traversing backward in time.
- taylorius 4mo ago
  I think you mean hsoows hsoows
dsr_ 4mo ago
And grit, not grid.

Maarten88 4mo ago

> Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A fin, foil or daggerboard below the board/boat is operating well within the range of Reynolds' numbers where laminar flow is relevant.

otterdude 4mo ago
The vertical stabilizing surface of these elements is really insignificant to the entire surface of a board. Combining drag coefficients is done with the wetted surface area. In truth there's some contamination from the upstream flow. Stabilizing elements are behind the center of pressure, so they will see the most "diry flow"
- Maarten88 4mo ago
  You are thinking about a slow boat in displacement mode, or a wave-surf board with very small fins. But I can tell you that the wetted surface area of my wing-foil board is exactly zero after takeoff, and all wet surfaces of the foil are, for a significant percentage, in laminar flow. Same for a windsurf board planing: just the last 50cm of the board is touching the water and the fin is extremely significant for drag.
  - lymbo 4mo ago
    I have 2 foil drives for wake thieving and a SUP for downwinding and I’m just excited that someone on HN is talking about foiling. Such an underrated sport.