## 3 Experimental Research Results, Analysis and Discussion  
Primary data on the change in instantaneous values of velocity \(w_{x}\) and local HTC \(\alpha_{x}\) over time during the movement of a pulsating air flow in round and triangular pipes without a turbulator are shown in Figures 4 and 5. The following conclusions were drawn based on a comparison of the data in Figures 4 and 5:  
* There are pronounced flow pulsations (with corresponding maxima and minima of \(w_{x}\) and \(\alpha_{x}\)), caused by the blocking of the pipe by the valve for both cases;
* The dependencies \(w_{x}=f\) (\(\tau\)) and \(\alpha_{x}=f\) (\(\tau\)) are practically smooth (with minimal fluctuations) when the flow moves in a round pipe, whereas noticeable fluctuations in the velocity \(w_{x}\) and the local HTC \(\alpha_{x}\) of the flow are observed when using a TrP; their formation can be associated with secondary vortex flows in the corners of the triangular profile;
* The maximum values of \(\alpha_{x}\) in a TrP are visually 10-15% less compared to a round pipe under these experimental conditions. Primary data on the change in instantaneous values of the velocity \(w_{x}\) and local HTC \(\alpha_{x}\) over time during the movement of a pulsating air flow in a round and TrP with a turbulator are shown in Figures 6 and 7. It can be seen from Figure 6 that an increase in the flow TI caused a significant deformation of the dependencies \(w_{x}=f\) (\(\tau\)) and \(\alpha_{x}=f\) (\(\tau\)) in the round tube. The amplitude of the air flow oscillation is comparable with the amplitude of the main pulsations. It is visually difficult to identify pulsations of the local HTC caused by a rotating damper on the function \(\alpha_{x}=f\) (\(\tau\)). Figure 4: Dependences of the local air flow velocity \(w_{x}\) (1) and the local HTC \(\alpha_{x}\) (2) on time \(\tau\) in a round pipe without a turbulator (TI \(\approx\) 0.03) under the following conditions: \(w=24.8\) m/s,\(f=10.6\) Hz. Figure 5: Dependences of the local air flow velocity \(w_{x}\) (1) and the local HTC \(\alpha_{x}\) (2) on time \(\tau\) in a triangular pipe without a turbulator (TI \(\approx\) 0.05) under the following conditions: \(w=23.8\) m/s, \(f=9.2\) Hz. Figure 6: Dependences of the local air flow velocity \(w_{x}\) (1) and the local HTC \(\alpha_{x}\) (2) on time \(\tau\) in a round pipe with a turbulator (TI \(\approx\) 0.12) under the following conditions: \(w=17.2\) m/s,\(f=16.6\) Hz. The pulsating air flow in a Trp is more resistant to an increase in TI (Figure 7). Fluctuations in the local flow velocity \(w_{x}\) have a significantly smaller amplitude in a Trp compared to a round one. The function \(\alpha_{x}=f(\tau)\) is more pronounced (clear); it is possible to easily identify the pulsations of the local HTC due to the damper rotation in the pipeline. Accordingly, it can be assumed that the secondary vortex structures in the Trp impart rigidity to the flow and prevent its deformation under the influence of external disturbances. The TI for round and triangular pipes in free flow (i.e., without using a turbulator) was calculated to quantitatively assess the magnitude of the pulsation component of the air flow velocity in the gas-dynamic system (Figures 8 and 9). Analysis of Figures 8 and 9 shows the influence of gas-dynamic non-stationarity and geometric shape of pipelines on the turbulence intensity in straight pipes. TI was defined as the ratio of the mean square pulsating component of velocity to the average velocity of the flow under study; the method for calculating TI for pulsating flows was described in detail in the article [35]. Figure 8 shows that there is a tendency for TI values to increase with a rise in the average air flow velocity in a circular pipe, which is typical for stationary and pulsating flows. At the same time, gas-dynamic non-stationarity (flow pulsations) causes a significant increase in the TI by almost double compared to stationary flow. These differences are typical for all the air flow velocities under study.