INVESTIGATION OF NATURAL RAW MATERIALS TURBULENT FLOW STRUCTURE IN PIPELINES AT CONFUSER-DIFFUSER SECTION

• Main Authors: Sergey N. Kharlamov, Dmitry S. Fatyanov
• Format: Article
• Language: Russian
• Published: Tomsk Polytechnic University 2020-08-01
• Series: Известия Томского политехнического университета: Инжиниринг георесурсов
• Subjects: mathematical and numerical modeling; turbulence; hydrodynamics; near-wall flow; pipeline; confuser-diffuser connections
• Online Access: http://izvestiya.tpu.ru/archive/article/view/2768/2282

The relevance of the research is caused by the need to understand the mechanisms of restructuring hydrodynamic, thermal and diffusion processes accompanying the flow of hydrocarbon viscous media; to explain the nature of their interaction in limited internal areas under the action of complex effects accompanying the flow in complex pipelines; to develop effective solutions for optimal control of natural raw material transport and improvement of reliability of operation of pipelines energy-stressed nodes. The object of the research is the near-wall flows of drop and gaseous hydrocarbon media in structural elements of internal systems often encountered in engineering applications, in particular, oil and gas, chemical and thermal power industries. Such elements are sections of short or extended pipelines with curved wall surface in the form similar to connecting units or sections of confuser-diffuser type varying in length. Streams are complicated by effects of curvature of flow lines, spatial deformation, changes in dynamic structure and pressure. The aim of the work is to understand uncertainties, peculiarities and patterns of flows, as well as the possibility of applying modern models of turbulence to forecast the processes in pipelines at confuser-diffuser sections; to study in detail the changes in the «fine» structure of the complex shear flow; to give recommendations in calculating practice of near-wall flows in the specified hydrodynamic configuration and intensive operation modes of the equipment. Methods: theoretical and practical methods of mathematical modeling and numerical investigation of spatial turbulent flows, peculiarities of changes in their pulsation structure according to schemes (models) with a large number of equations – RANS-models of turbulence, including a dynamic two-parameter base. The choice of the latter depends on the representations: to reproduce statistical correlations or parameters of complex flows, local turbulent properties (integral scale, kinetic energy, dissipation, etc.) of the eddies; to take into account the non-uniform and anisotropic nature of changes in flow structure due to deformation effects excited by variable pressure and Reynolds stresses gradients. Results. The authors have analyzed the features of turbulent flows of hydrocarbon of viscous media in pipelines including connecting elements of confuser-diffuser type and studied the possibilities of complex shear flows of viscous media, popular in calculations of the pipelines at the curved wall boundary, multi-variable statistical models of second-order turbulence, implemented in high- and low-Reynolds versions. It has been found that a better description of the intensity and size of the recirculation zones of the pipelines is given by the k-klω/kL- and RSM-kL models as being more conservative and resistant to perturbations coming from the walls of the pipeline. Therefore, it is appropriate to include them as the basic base for the RSM-model. Calculations revealed the existence of a second separated flow zone. It is shown that the greatest changes of turbulent kinetic energy of turbulence, normal components of Reynolds stresses tensor are located in the zone of interaction of shear layer with return and straight-flow separated flow, and the generation is near the separated point. The compliance of calculations of the structure of similar flows with the data of other authors allows stating that understanding of processes, forecast of intensity of dynamic loads in local zones of flow connection to walls according to the presented models will not lead to emergency operation of equipment and will ensure optimal control of transportation of raw materials by pipelines.