###### Abstract
The use of this method made it possible to suppress massive flow separation in the diffuser's expansion section and in the downstream area, as well as to increase the efficiency of pressure recovery in a CD. There are also studies on the development of various structural elements in a diffuser to ensure a more uniform flow along the entire length of the CD [24; 25]. For example, [PERSON] installed a screw tape or spiral-screw insert on the inner surface of the conical diffuser to level the velocity field [24; 25]. A numerical study showed a significant effect in improving the uniformity of velocity distribution throughout the entire volume of the diffuser compared to CDs without such inserts. However, methods of the gas-dynamic improvement of processes in conical diffusers can cause an increase in hydraulic losses [1; 2]. Therefore, researchers and professionals are continuing to develop new ways to assess changes in the main flow parameters in CDs [26; 27]. For example, [PERSON] and colleagues proposed an original method for assessing the pressure drop coefficient in a conical diffuser [26]. [PERSON] and others have created a new method for calculating the loss coefficient in CDs of various designs [27]. There are comprehensive studies of the gas-dynamic features of complex flows (swirl flows, spiral vortices, vortex cores, etc.) in conical diffusers and their possible application in various fields [28; 29; 30; 31; 32; 33]. For example, [PERSON] and colleagues studied in detail the development and destruction of spiral vortices in conical diffusers with different cone expansion angles [28]. Similar studies were carried out by [PERSON] and colleagues in relation to vortex cores and their influence on flow characteristics in CDs. A large number of researchers are focused on studying swirl flows in conical diffusers of various configurations [30; 31; 32; 33]. This can be explained by the fact that swirl flows help intensify heat transfer, improve the mixing of various media, and distribute the flow throughout the entire volume of the diffuser. Therefore, swirl flows in CDs enhance the efficiency of various devices that use conical diffusers in their processes. Thus, [PERSON] and co-authors studied the specific problem of the influence of the expansion angle of the pressure vessel on the vortex core of a swirl flow with a PIV measuring system [30]. [PERSON] and colleagues studied the distribution of the average gas-dynamic behaviour of a swirl flow along a diffuser with different expansion angles [31]. Research has confirmed that introducing moderate inlet swirl reduces the likelihood of separation in wide-angle conical diffusers. Thus, the literature review showed that the following:  
* It remains an urgent task to study gas-dynamic behaviour in a CD for boundary conditions;
* It is also a critical task for improving technical devices to develop methods for forecasting and controlling the flow structure in a CD;
* CDs are widely exploited in almost all branches of science and technology. The key objectives of this study can be formulated as follows:
* To create a test bench and establish a methodology for conducting experiments to study flow structure in a vertical CD with different air supply methods;
* To evaluate the influence of conventional air supply through one channel and nozzle supply through four tubes into a vertical diffuser on the flow structure at different flow characteristics;
* To identify the influence of a cross-sectional shape of a supply channel and nozzle tubes on the gas-dynamic structure of the flow in a vertical diffuser. This research is part of a larger effort to create a highly efficient plant for producing synthesis gas from sawdust. Accordingly, it is necessary to obtain data on possible gas-dynamic structures in a vertical conical diffuser for different air supply configurations.