Control of separated turbulent stream by high-frequency rotary oscillations at Re=1,4x10[5]

Abstract

Relevance. Characteristics of separated turbulent streams are of great importance when designing effective hydro- and thermal power plants equipment. In such streams the flow regimes with harmful quasi-periodic high-amplitude oscillations of velocity and pressure behind the body are implemented. Thus, the knowledge on the ways of controlling turbulent streams can not only reduce the wear of working parts of equipment but prevent their destruction. Besides, to study the occurring optimization problems with the parameters, which change in a wide range, one needs the validated turbulence models which save significantly the computing time compared to Large-eddy simulations and direct numerical simulations. The aim of the research is to apply a promising method to control the flow using the rotary oscillations of cylinder around the axis of symmetry. The authors have carried out the investigations using high Reynolds numbers Re=1,4x10[5], and the validated numerical methods, to demonstrate the capabilities of the chosen control strategy to decrease the drag coefficient and fluctuating lift force effecting the cylinder. Methods. The authors used T-FlowS code which is based on finite-volume method and unstructured grids and solve unsteady Reynolds-averaged Navier-Stokes equations with second-moments closure. Results. The paper demonstrates the possibility to control the flow - decrease of trace width behind the cylinder, suppression of recirculating zone, increase of vortex shedding frequency, reduction of drag and lift forces. It is shown that at certain oscillating parameters of cylinder the resistance factor may be decreased by 78 % in comparison with non-rotating case.

Keywords

• turbulence
• flow around cylinder
• control
• URANS
• drag reduction