Secondary flows in a flat diffuser and their significance for the formation of a turbulence field

Abstract

Turbulent flows in a flat diffuser are characterized by the presence of two local maxima in the profiles of longitudinal velocity pulsations. The mechanism of the formation of a turbulent flow structure in a flat diffuser was experimentally studied. For this purpose, the parameters of the flow kinematic structure in a diffuser with an opening angle of 2.5° were measured. The profiles of velocities and turbulent characteristics of the flow in typical cross sections of the channel were obtained using the optical measurement method; based on these profiles, the secondary flows in the diffuser were identified. A physical model of the formation of the turbulent flow structure is proposed. Within the framework of this model, a high degree of turbulent pulsations far from the wall is associated with the convection of turbulence from the near-wall region into the flow core by a secondary flow in the form of an averaged spiral motion of the medium in a flat diffuser.