Dynamic Behavior and Reactive Control for Axi-symmetric Turbulent Separation

Overview

In the turbulent separation in an axi-symmetric pipe flow like a conical diffuser, even if boundary condition and infolow conditions are steady, it is not known at all　when and where backflow occurs.　Unlike especially the case of a rectangular cross section, the circumferential position is also free. There are large-scale backflow by generating, extinction, movement of separated region and small-scale backflow by passage of a turbulent eddies. In order to control separation of mean flow, "reactive control" which detected the former and performs suitable forcing is considered to be effective. So, in this research, the approach from both sides of an experiment and numerical computation is tried by making to perform reactive control into a end goal about the unsteady behavior of the backflow produced in a conical diffuser.

Experimental approach

The split film probe for backflow detection is arranged near the wall of a conical diffuser, from analysis of the signal, the information on the time sacale (a generating interval, temporal duration, etc.) of backflow are acquired, and discrimination of the large-scale backflow　which is the object of control is considered. Furthermore, it examines what kind of feature appears in wall mounted hot film sensor or static pressure signal at the time of large-scale backflow generating by acquiring simultaneously with a split film signal, wall mounted hot film sensor signal and static pressure signal, and comparing them supposing using in the case of reactive control.

Computational approach

By numerical computation, the flow field in a conical diffuser is analyzed by unsteady and three dimensional DNS and LES, and spatial change of separated region etc. acquires the information which is not acquired in experiment. The turbulent flow in a conical diffuser (diffuser part) using convective out flow condition is connected wtih fully developed turbulent upstream pipe flow part (driver part) simultaneously calculated.