Correlation between the abnormal enhancement of the separated flow and extraordinary pressure drops in the groove on the plate when the angle of inclination changes from 0 to 90$^\circ$

A numerical and physical study of the air turbulent flow around a plate (with a long inclined groove of a moderate depth which has hemispherical ends) has been performed at the Reynolds number of 6.7 $\cdot$ 10$^4$ which is determined by the width of the groove. The groove inclination angle with respect to the oncoming flow varies from 0 to 90$^\circ$. The stationary near-wall flow of incompressible viscous medium was simulated by solving the Reynolds-averaged Navier–Stokes equations closed using the shear stress transport model. The static pressure distributions in single grooves were measured in a wind tunnel at the Institute of Mechanics of Moscow State University. There was determined a groove inclination angle at which the abnormal enhancement of the separated flow is observed. The resulting extraordinary pressure drops in the grooves were in a good agreement with ultrahigh absolute values of negative relative friction. Velocities of the return and secondary swirl flows turned out to be comparable with the oncoming flow velocity.