Author Email: Aida_8691@Ramblerl.ru
This article presents the results of experimental studies of a fully developed turbulent air flow in a round pipe with superimposed flow pulsations. The time-averaged static pressure losses and instantaneous velocity values on the pipe axis were measured in a wide frequency range of superimposed harmonic pulsations of the air flow in three modes for the average flow rate. Data were obtained and analyzed on the dependence of the conditionally averaged values of the pulsation component of pressure and flow velocity in various sections of the pipe. It is revealed a complex spatio-temporal structure of the flow, which is influenced by both resonance phenomena and transfer of parameter fluctuations in the direction of average motion. It is revealed a complex spatio-temporal structure of the flow, which is influenced by both resonance phenomena and transfer of parameter fluctuations in the direction of average motion. It is also revealed a non-monotomic dependence of pressure losses on the frequency of flow pulsations. The nature of the change in pressure loss from the frequency of flow pulsations remains almost unchanged when the average flow rate is varied. However, the analysis of the results of these studies left the relationship between the flow parameters in each cross section of the pipe under conditions of periodic flow pulsations. The goal of this article is to carry out this analysis.
In various technical devices, the hydrodynamic processes in the channels are often unsteady. Currently, the most studied is the kinematic structure of unsteady turbulent boundary layers. The experimental studies of Bukreev and Shakhin, Grigoriev and Fafurin, Ramapryan and Tu, Achary and Reynolds, Cousteau, Carlson, Paris,
Simpson, Hartner, Mizushina, Shemer, Iguchi et al. are known. Given the complexity and diversity of effects of the unsteadiness impact on the kinematic flow structure, a number of attempts have been made to classify the unsteady flows. The most complete classifications are given by Ramporyan and Tu, Grigoryev and Fafurin. They distinguish five groups of unsteady flows in their works. The classification is based on the turbulence “transmission” mechanism, and the boundaries between groups are defined in the space with respect to the frequency and amplitude of superimposed pulsations. Known literature data do not give a complete picture of the influence of the factors of unsteady flow through the channel on the hydrodynamic parameters in general and on the hydraulic resistance of the channels under unsteady conditions relative to aperiodic processes of transition from one flow to another. It was established that the hydraulic resistance is higher with increasing and lower with decreasing flow velocity compared with the steady flow [1, 2]. Systematic
theoretical and experimental studies of the turbulent gas flow under conditions of hydrodynamic unsteadiness were carried out by G.A. Dreitser and V.M. Kraev [3, 4]. A significant impact of acceleration and deceleration of the flow on the averaged velocity profiles and the turbulent flow structure is established. A method for calculating the turbulent viscosity coefficient is proposed. The generalizing approximating dependences for unsteady flows are obtained, which can be used
in practical calculations.
To obtain more detailed information about the physical mechanisms of the impact of flow pulsations on the channel hydraulic resistance, additional studies are necessary, which shall include, in particular, simultaneous measurements of pressure pulsations, profiles of the averaged flow velocity and its pulsations at the boundaries of the measuring section.
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