Аэродинамика плохообтекаемых тел на примере конвективного теплообменного аппарата

Abstract

Issues related to the research and study of regularities and features of external aerodynamics of various designs of thermal (including heat exchange) equipment, which are weakly streamlined bodies, remain uncovered and insufficiently studied. However, it is the control of the aerodynamic resistance of a design (aerodynamic imperfection) that can be a convenient criterion for both the thermal efficiency assessment and the optimisation of convective heat exchanger designs. The work is devoted to the study of the aerodynamics of poorly streamlined bodies using the example of a single section of a convective heat exchanger with a developed external surface. The single section is an assembly of two flat six-channel elements with non-standard external finning placed parallel to each other at a small distance, which leads to the formation of lattices in the inner space of the section. A numerical study of the influence of the structural parameters of the cross-section on the air flow regime and its local peculiarities has been carried out. The numerical solution is constructed in a quasi-stationary formulation based on the solution of the conservation equations of compressible continuous media by the control volume method. Due to the geometrically driven turbulence of the flow, the conservation equations were Favre and Reynolds averaged, followed by the closure of the averaged system of equations by the SST turbulence model. A counter-flow scheme of 2nd order accuracy is used to resolve non-viscous flows, and a central difference scheme of 2nd order accuracy is used for viscous flows. The conjugate gradient method is used to accelerate convergence. Significant non-uniformity of the flow both in the section channel and after the airflow exits to free space is shown, described and substantiated. The jet-like nature of the air flow after leaving the section is identified and shown. The essential non-uniformity and asymmetry of velocity and pressure profiles, and gradual pressure decrease along the length of the region are shown. At the same time, the peak values of the flow velocity maxima are 5 and more times higher than the velocity values in the middle section of the channel. It should also be noted that the formation of peripheral attached currents near symmetry planes with a local increase in the velocity modulus is observed. The analysis of the revealed peculiarities of the flow aerodynamics has allowed to designate constructive elements, the improvement of which will allow to optimise the design of the oil cooler in order to increase the efficiency of its operation. The possibility of the constructive optimisation of the external fin design is shown.