A reversible flat plate located inside a rectangular duct. The plate has one smooth and one artificially roughened face. The duct has removable profile plates that can establish an increasing or decreasing pressure gradient in the direction of flow.
To investigate the growth of the boundary layer profile in a variety of conditions along the plate a micro-pitot tube is provided.
This may be moved toward the plate in measured intervals using a micrometer adjustment. The growth of the boundary layer along the plate may be investigated.