Structure of turbulent flow in a semi-cylindrical groove located on the wall of a flat channel

This paper presents the results of an experimental study of the flow structure in a semi-cylindrical groove located on one of the walls of a rectangular channel with a height $H$ = 0.02 m and a length-to-width ratio of 7.5. A groove with a width $D$ = 0.0158 m and a length $L/D$ = 6.65 calibers could be located at different angles to the longitudinal axis of the channel ($\varphi$ = 0 $\div$ 90$^\circ$). In the experiments, we measured the pressure in median sections along and across the trench and the velocity components and their pulsations in the longitudinal and transverse directions. In the experiments, the Reynolds number calculated from the average flow rate velocity and the hydraulic diameter of the channel was constant and equal to Re$_{ch}$ = 3,88 $\cdot$ 10$^4$. The pressure distribution on the trench wall in both the transverse direction and along its length was found to depend significantly on the angle of its rotation relative to the channel axis. At the inlet section of the trench, where the flow enters, a zone of strong rarefaction is formed. The length of this zone along the trench does not exceed one caliber, and outside this zone, the pressure coefficient remains practically unchanged up to the outlet of the trench, where there is a sharp increase in pressure due to deceleration. The greatest rarefaction in the transverse direction relative to the trench is achieved at an inclination angle of $\varphi$ = 45$^\circ$. The flow structure in different sections along the trench length was studied. The maximum velocity of the circulation flow in the semi-cylindrical trench was obtained at its inlet. As the flow moves along the trench, the intensity of the vortex flow of the gas significantly reduces, and in the case of small trenches ($\Delta/D$ = 0,22), the flow becomes continuous.