Anomalous intensification of a turbulent separated flow in inclined, single-row, oval-trench dimples on the wall of a narrow channel

In a long, plane-parallel channel with single-row, inclined, oval-trench dimples on the wall, a periodic section with a relative length of $8$ (the distance between centers of neighboring dimples), a width of $9$, a height of $1$, and a centrally located, inclined, oval-trench dimple with a length of $7.05$, a width of $1.05$, a depth of $0.25$, and with variation in the inclination angle from $1^{\circ}$ to $89^{\circ}$ is considered. An anomalous intensification of a separated turbulent air flow in an inclined dimple at the Reynolds number of $10^4$ is discovered. At an inclination angle of $60^{\circ}$, the maximum absolute value of negative friction in the middle longitudinal cross-section exceeds the friction in a plane-parallel channel by more than $2.5$ times. The cause of this phenomenon is related to the formation of a high pressure drop between the closely located zones of stagnation and low pressure in the semispherical inlet segment of the dimple.