## 1 Introduction  
Working media in the form of pulsating flows of liquid and gas in pipes of various configurations are used in many branches of industry and technology (for example, pulsating heat pipes [1], solar energy [2] and piston engines [3]). In most cases, the efficiency of the final product (engine, heat exchanger, power plant, etc.) depends on the gas-dynamic and heat-exchange perfection of the working fluid processes in systems with pipes of various configurations. In such systems, the thermocapsdynamics of the flow are determined by a large number of factors: (1) the characteristics of the flow pulsations (frequency, amplitude, type); (2) the flow turbulence intensity, and (3) the geometric configuration of the pipeline. Therefore, obtaining data on gas dynamics and heat exchange of pulsating gas flows in straight pipes with different cross-section shapes for different turbulence conditions remains a relevant and important task for the development of fundamental and applied science, as well as for increasing the efficiency of energy technologies. A brief overview of modern research results on this topic is presented below. The impact of gas-dynamic non-stationarity (pulsations) of gas flow on the intensity of heat transfer in pipeline systems remains the focus of attention of many researchers [4; 5; 6; 7; 8]. [PERSON] and colleagues conducted a detailed study of the gas-dynamic features of pulsating flows in a pipe to clarify the physical mechanism of changes in the heat transfer level [4]. The authors identified several important factors that had a decisive influence on heat exchange: the Reynolds number, the length and diameter of the pipe, and the frequency and amplitude of the flow pulsation. It was found that high-frequency flow velocity pulsations increase the local Nusselt number in the pipe. [PERSON] et al. studied the effect of flow pulsations on the heat exchange level in a tube bundle of heat exchangers of various designs [5; 6]. It was established that, in this case, the intensification of heat exchange increases with the growth of the amplitude and frequency of flow pulsations and decreases with the growth of the Reynolds number. An increase in the heat transfer coefficient (HTC) by 1.25-1.6 times compared to a steady flow was recorded. [PERSON] et al. studied pulsating flows in a pipe with flow reversal [7]. It was shown that there was an increase in the HTC of up to 60% at the moments of flow reversal compared to the steady-state movement of the medium. At the same time, the increase in the average HTC for the full cycle of the pulsation under consideration was insignificant. [PERSON] and colleagues separately investigated the effect of air flow acceleration and deceleration on the heat transfer rate in a pipe [9]. There are also applied studies on the influence of gas flow pulsations on the heat exchange level in the exhaust systems of piston engines [10; 11]. For example, [PERSON] et al. studied the heat transfer of engine exhaust gases pulsating with frequencies from 10 to 95 Hz [10]. The authors found that flow pulsations improved heat transfer in the system across the entire frequency range. The key factor in increasing the HTC was the relative amplitude of the gas flow velocity. In turn, [PERSON] and colleagues found that the increased intensity of heat transfer of exhaust gases at frequencies of 25-35 Hz could be associated with increased flow turbulence caused by flow pulsations in the exhaust system [11]. A separate area of research into pulsating flows in various gas-dynamic systems consists of studying the effect of flow turbulence on the heat exchange intensity [12; 13; 14; 15; 16]. One of the most well-known and effective methods for improving heat exchange of air flow in channels is the creation of various types of dimples and/or grooves on the inner surface (spherical dimples, flat rectangle, square groove, rectangular groove, etc.).