The results of an experimental study of flow aerodynamics in a narrow channel with a rectangular cross-sectional height of = 20 mm and an aspect ratio of = 7.5 are presented. The channel surface contains a system of elongated trench dimples with a cylindrical cross-section. The dimples have a width of = 0.75, a relative depth of Δ/ = 0.22, and a length of = 7 calibers. They are positioned at a fixed angle of φ = 45°, to the longitudinal axis of the channel. The package contained a total of seven dimples, with a constant spacing of = 2. The Reynolds number, calculated from the hydraulic diameter, was constant at Re = 3.9 · 10 in the experiments measuring velocity components and velocity fluctuations. Hydraulic losses were measured over a wide range of Reynolds numbers, from Re = 1.9 · 10 to Re = 1.1 · 10. The experiments measured velocity components and their fluctuations in the longitudinal and transverse directions for a channel with dimples on one wall, and the hydraulic resistance of a channel with dimples on one and two opposite walls. It was found that the longitudinal velocity profiles U differ significantly depending on the position within the dimple for all the dimples studied. A boundary layer separation zone forms at the inlet of the dimple, where the flow enters. The extent of this zone along the dimple does not exceed one caliber, and further along the dimple, no negative values of the velocity U are observed. As one moves along the dimple, the intensity of the vortex motion of the gas inside significantly weakens. A similar flow structure was previously observed by the authors (Thermophysics and Aeromechanics. 2022. V. 29. No. 6. P. 935) in a single trench dimple with the same geometric parameters.
Terekhov et al. (Wed,) studied this question.