Secondary flows in a flat diffuser and their significance for the formation of a turbulence field
I.A. Davletshin, N.I. Mikheev, R.R. Shakirov
Institute of Power Engineering and Advanced Technologies FRC Kazan Scientific Center of RAS, Kazan, Russia
Keywords: gradient flow, flat diffuser, flow structure, turbulence, secondary flows
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 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 the 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 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.
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