Оцінка впливу канавок у дифузорі на втрати повного тиску

Abstract

The subject of the study is the total pressure in the diffuser channel with passive control of the boundary layer. The object of this research is a diffuser channel with riblets. The mechanism of total pressure reduction due to the presence of longitudinal grooves on the streamlined surface is related to the strengthening of viscous forces acting in the transverse direction caused by them. These forces generate a relatively calm flow inside the riblets, which pushes out the turbulent flow, which causes surface friction, pushing it away from the surface. Thus, the process of generation and growth of elongated wall turbulent formations. In addition, in the presence of riblets, a change in the pressure field in the transverse direction is possible, as well as the creation of a quasi-two-dimensional flow in the immediate vicinity of the wall. In this work, the aim of research to investigate the influence of riblets on total pressure loss in the diffuser channel with the purpose of evaluating the influence of riblets on the change in the nature of the flow and the change in pressure, using numerical modeling. To study the nature of the flow in the diffuser channel, we resolved the following tasks: a diffuser channel was modeled with the following dimensions: length L=50 mm, hydraulic diameter at the inlet X=25 mm, hydraulic diameter at the outlet Y=40 mm, riblets diameter d=4 mm, number of riblets n =4 and n=8. The study was compared with a diffuser with the following dimensions: length L=50 mm, diameter at the inlet X=25 mm, diameter at the outlet Y=40 mm. To research the flow in the diffuser, the method of numerical experiment was chosen. An unstructured calculation grid was used in the diffuser for the research. The calculation of the turbulent gas flow was performed by numerically solving the averaged Navier-Stokes equations. During the numerical simulation of the flow, the Reynolds stress turbulent viscosity model will be used. As a result, using a diffuser with riblets increases the coefficient of hydraulic resistance compared to a smooth diffuser. The resistance reduction mechanism does not work due to the relatively short length of the diffuser and small longitudinal vortices of the riblets scale do not have time to form. There are pressure increasing instead of laminization of the flow and pressure decreasing. Scientific novelty - received new data on the effect of riblets in the diffuser channel on the total pressure loss coefficient. Practical significance - the obtained results can be used to control the boundary layer in diffuser channels (in diffuser compressor grates) to improve their characteristics.