An investigation was made in the Langley low-turbulence pressure tunnel to determine the effect of size and location of a sandpaper type for roughness on the Reynolds number for transition. Transition was observed by means of a hot-wire and mometer located at various chordwise stations for each position of the roughness. These observations indicated that when the roughness is sufficiently submerged in the boundary layer to provide a substantially linear variation of boundary-layer velocity with distance from the surface up to the top of the rough ness, turbulent "spots" begin to appear immediately behind the roughness when the Reynolds number based on the velocity at the top of the roughness and the roughness height exceeds a value of approximately 600.nAt Reynolds numbers even slightly below the critical value {value for transition), the sandpaper type of roughness introduced no measurable disturbances into the laminar layer downstream of the roughness. The extent of the roughened area does not appear to have an important effect on the critical value of the roughness Reynolds number.
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