###### Abstract
Thermograms were obtained at a specific time for a stationary flow (output to the mode of about 10 min) in Figure 7 and all subsequent figures. Figure 7 confirms that the thermograms show the main elements of the flow structure in a vertical CD in comparison with the data of other authors. Accordingly, the method of thermal imaging is suitable and  
Figure 1:0 Photographs of the studied structures of a vertical diffuser with a nozzle air supply through tubes with different cross-sections: (**a**) circle; (**b**) square; (**c**) triangle. Figure 1:1 Comparison of the flow structure in a vertical diffuser for Re \(\approx\) 40,000: (**a**) data [37]; (**b**) the author’s thermogram. Note: I—stagnant zone; II—core of the flow. reliable for studying the patterns of changes in the gas dynamics of flows in the diffuser for different methods of air supply. At the same time, the use of half a vertical diffuser is acceptable for studying stationary flows. It has been established that the transverse profiling of the supply channel has significant effects on the flow structure in a CD (Figure 8). Figure 8 shows the flow structure in a vertical diffuser at an air flow rate of \(q\) = 0.018 m\({}^{3}\)/s for channels with different configurations. Figure 8a demonstrates that the use of a channel with a circular cross-sectional shape leads to the creation of a pronounced central flow (saturated colour on the thermogram) in the vertical diffuser. At the same time, in the corners of the diffuser there is virtually no air flow (white areas on the thermogram), that is, stagnant zones are created. It should be noted that in the upper part of the diffuser, air movement occurs throughout the entire volume. Figure 8b shows that the use of a channel with a square cross-section causes a significant change in the flow structure compared to a traditional round channel. When using a square channel, there are no stagnant zones in the corners of the diffuser. However, the presence of a pronounced central flow along the diffuser axis (dark orange area on the thermogram) should be noted. Figure 8c illustrates that the use of a triangular channel to supply air to the diffuser also leads to the formation of stagnant zones in the corners. At the same time, the flow along the height of the diffuser is more uniform (in fact, the colour of the thermogram is uniform) compared to round and square channels. Such significant changes in the flow structure in a vertical diffuser when using profiled supply channels can be explained by the influence of longitudinal vortex structures in the corners of square and triangular profiles. In this case, these structures contribute to a more uniform distribution of flow throughout the entire volume of the diffuser and prevent the formation of stagnant zones. The use of square and triangular pipelines also has a significant impact in the gas exchange systems of piston engines [38,39]. Figure 9 shows the flow structure in a vertical diffuser for holes with different sides when air flows through the system of \(q\) = 0.047 m\({}^{3}\)/s. Figure 9a demonstrates that an increase in flow rate (accordingly, the speed of flow) through the system causes a significant reduction in stagnant zones in the corners of the vertical diffuser in the case of air supply through a conventional round channel. At the same time, a pronounced central flow along the diffuser axis is maintained. Figure 9b illustrates that an increase in flow through the system has virtually no effect on the structure of the flow in the diffuser when air is supplied through a square channel; there are no stagnant  
Figure 1:2 Thermograms of the flow structure in a vertical diffuser when air is supplied through channels with different cross-sectional shapes (flow through the system \(q\) = 0.018 m\({}^{3}\)/s): (**a**) circle; (**b**) square; (**c**)—triangle. zones in the diffuser and a central flow can be recorded.